Radiation/annealing-induced structural changes in GexAs₄₀-xS₆₀ glasses as revealed from high-energy synchrotron X-ray diffraction measurements
Local atomic structure of GexAs₄₀-xS₆₀ glasses (x = 16, 24, 32, and 36) has been investigated in the -irradiated (2.41 MGy dose) and annealed after irradiation states by using the high-energy synchrotron X-ray diffraction technique. The accumulated dose of 2.41 MGy is chosen to be close to th...
Gespeichert in:
| Veröffentlicht in: | Semiconductor Physics Quantum Electronics & Optoelectronics |
|---|---|
| Datum: | 2012 |
| Hauptverfasser: | , , |
| Format: | Artikel |
| Sprache: | English |
| Veröffentlicht: |
Інститут фізики напівпровідників імені В.Є. Лашкарьова НАН України
2012
|
| Online Zugang: | https://nasplib.isofts.kiev.ua/handle/123456789/118720 |
| Tags: |
Tag hinzufügen
Keine Tags, Fügen Sie den ersten Tag hinzu!
|
| Назва журналу: | Digital Library of Periodicals of National Academy of Sciences of Ukraine |
| Zitieren: | Radiation/annealing-induced structural changes in GexAs₄₀-xS₆₀ glasses as revealed from high-energy synchrotron X-ray diffraction measurements / T.S. Kavetskyy, V.M. Tsmots, A.L. Stepanov // Semiconductor Physics Quantum Electronics & Optoelectronics. — 2012. — Т. 15, № 4. — С. 310-320. — Бібліогр.: 43 назв. — англ. |
Institution
Digital Library of Periodicals of National Academy of Sciences of Ukraine| id |
nasplib_isofts_kiev_ua-123456789-118720 |
|---|---|
| record_format |
dspace |
| spelling |
Kavetskyy, T.S. Tsmots, V.M. Stepanov, A.L. 2017-05-31T05:15:55Z 2017-05-31T05:15:55Z 2012 Radiation/annealing-induced structural changes in GexAs₄₀-xS₆₀ glasses as revealed from high-energy synchrotron X-ray diffraction measurements / T.S. Kavetskyy, V.M. Tsmots, A.L. Stepanov // Semiconductor Physics Quantum Electronics & Optoelectronics. — 2012. — Т. 15, № 4. — С. 310-320. — Бібліогр.: 43 назв. — англ. 1560-8034 PACS 61.05.cp, 61.43.Fs, 61.80.Ed https://nasplib.isofts.kiev.ua/handle/123456789/118720 Local atomic structure of GexAs₄₀-xS₆₀ glasses (x = 16, 24, 32, and 36) has been investigated in the -irradiated (2.41 MGy dose) and annealed after irradiation states by using the high-energy synchrotron X-ray diffraction technique. The accumulated dose of 2.41 MGy is chosen to be close to the known in literature focal point (~2.0 MGy) for the system tested, at which the y-irradiation-induced optical (darkening) effect does not depend on the composition. It is established that the first sharp diffraction peak (FSDP) is located at around 1.1 Е - in the structure factors S(Q) of all the alloys studied. The FSDP position is found to be constant on radiation/annealing treatment, but the intensity of the FSDP reveals changes under irradiation/annealing only for the compositions with x = 16 and 24. The radiation/annealing-induced changes are also observed on the pair distribution functions in the first and second coordination shells for these compounds. Practically invisible effects on the FSDP and pair distribution functions are found for the alloys with x = 32 and 36. The radiation/annealing-induced structural changes detected mainly in the As - S sub-system of the glasses examined are well explainable within the Tanaka approach for interpretation of the photo-induced structural changes and related phenomena in As₂S₃ chalcogenide glass and similar materials The authors would like to thank Dr. Ivan Kaban (IFW Dresden, Germany) for his help with high-energy synchrotron XRD measurements, Dr. Pal Jóvári (Research Institute for Solid State Physics and Optics, Budapest, Hungary) for his help with experimental data treatment, Prof. Walter Hoyer (Institute of Physics, TU Chemnitz, Germany) and Prof. Guorong Chen (East China University of Science and Technology, Shanghai, China) for stimulating discussions. The investigated samples used for measurements were prepared within joint research projects (#0106U007386 and #0109U007446c) between Ivan Franko Drohobych State Pedagogical University (Drohobych, Ukraine) and Scientific Research Company “Carat” (Lviv, Ukraine) supported by the Ministry of Education and Science of Ukraine (#0106U007385 and #0109U007445). T.S.K. acknowledges DAAD for support of his research work at TU Chemnitz (Germany) and Deutsches ElektronenSynchrotron DESY for support of the experiments performed at HASYLAB (Hamburg, Germany). T.S.K. and V.M.T. acknowledge national project (#0111U001021) supported by the Ministry of Education and Science, Youth and Sport of Ukraine. A.L.S. grateful to the Alexander von Humboldt Foundation, DFG and DAAD (Germany). Support from the Ukrainian-Russian projects funded by the State Fund for Fundamental Researches of Ukraine (#F40.2/019) and the Ministry of Education and Science of the Russian Federation (#02.740.11.0797) and the Russian Foundation for Basic Research (#11-02-90420-Ukraine, #11-02-91341-Germany and #12-02-00528-a) is also gratefully acknowledged. en Інститут фізики напівпровідників імені В.Є. Лашкарьова НАН України Semiconductor Physics Quantum Electronics & Optoelectronics Radiation/annealing-induced structural changes in GexAs₄₀-xS₆₀ glasses as revealed from high-energy synchrotron X-ray diffraction measurements Article published earlier |
| institution |
Digital Library of Periodicals of National Academy of Sciences of Ukraine |
| collection |
DSpace DC |
| title |
Radiation/annealing-induced structural changes in GexAs₄₀-xS₆₀ glasses as revealed from high-energy synchrotron X-ray diffraction measurements |
| spellingShingle |
Radiation/annealing-induced structural changes in GexAs₄₀-xS₆₀ glasses as revealed from high-energy synchrotron X-ray diffraction measurements Kavetskyy, T.S. Tsmots, V.M. Stepanov, A.L. |
| title_short |
Radiation/annealing-induced structural changes in GexAs₄₀-xS₆₀ glasses as revealed from high-energy synchrotron X-ray diffraction measurements |
| title_full |
Radiation/annealing-induced structural changes in GexAs₄₀-xS₆₀ glasses as revealed from high-energy synchrotron X-ray diffraction measurements |
| title_fullStr |
Radiation/annealing-induced structural changes in GexAs₄₀-xS₆₀ glasses as revealed from high-energy synchrotron X-ray diffraction measurements |
| title_full_unstemmed |
Radiation/annealing-induced structural changes in GexAs₄₀-xS₆₀ glasses as revealed from high-energy synchrotron X-ray diffraction measurements |
| title_sort |
radiation/annealing-induced structural changes in gexas₄₀-xs₆₀ glasses as revealed from high-energy synchrotron x-ray diffraction measurements |
| author |
Kavetskyy, T.S. Tsmots, V.M. Stepanov, A.L. |
| author_facet |
Kavetskyy, T.S. Tsmots, V.M. Stepanov, A.L. |
| publishDate |
2012 |
| language |
English |
| container_title |
Semiconductor Physics Quantum Electronics & Optoelectronics |
| publisher |
Інститут фізики напівпровідників імені В.Є. Лашкарьова НАН України |
| format |
Article |
| description |
Local atomic structure of GexAs₄₀-xS₆₀ glasses (x = 16, 24, 32, and 36) has
been investigated in the -irradiated (2.41 MGy dose) and annealed after irradiation
states by using the high-energy synchrotron X-ray diffraction technique. The
accumulated dose of 2.41 MGy is chosen to be close to the known in literature focal
point (~2.0 MGy) for the system tested, at which the y-irradiation-induced optical
(darkening) effect does not depend on the composition. It is established that the first
sharp diffraction peak (FSDP) is located at around 1.1 Е - in the structure factors S(Q) of
all the alloys studied. The FSDP position is found to be constant on radiation/annealing
treatment, but the intensity of the FSDP reveals changes under irradiation/annealing only
for the compositions with x = 16 and 24. The radiation/annealing-induced changes are
also observed on the pair distribution functions in the first and second coordination shells
for these compounds. Practically invisible effects on the FSDP and pair distribution
functions are found for the alloys with x = 32 and 36. The radiation/annealing-induced
structural changes detected mainly in the As - S sub-system of the glasses examined are
well explainable within the Tanaka approach for interpretation of the photo-induced
structural changes and related phenomena in As₂S₃ chalcogenide glass and similar
materials
|
| issn |
1560-8034 |
| url |
https://nasplib.isofts.kiev.ua/handle/123456789/118720 |
| citation_txt |
Radiation/annealing-induced structural changes in GexAs₄₀-xS₆₀ glasses as revealed from high-energy synchrotron X-ray diffraction measurements / T.S. Kavetskyy, V.M. Tsmots, A.L. Stepanov // Semiconductor Physics Quantum Electronics & Optoelectronics. — 2012. — Т. 15, № 4. — С. 310-320. — Бібліогр.: 43 назв. — англ. |
| work_keys_str_mv |
AT kavetskyyts radiationannealinginducedstructuralchangesingexas40xs60glassesasrevealedfromhighenergysynchrotronxraydiffractionmeasurements AT tsmotsvm radiationannealinginducedstructuralchangesingexas40xs60glassesasrevealedfromhighenergysynchrotronxraydiffractionmeasurements AT stepanoval radiationannealinginducedstructuralchangesingexas40xs60glassesasrevealedfromhighenergysynchrotronxraydiffractionmeasurements |
| first_indexed |
2025-11-25T22:20:35Z |
| last_indexed |
2025-11-25T22:20:35Z |
| _version_ |
1850563110050463744 |
| fulltext |
Semiconductor Physics, Quantum Electronics & Optoelectronics, 2012. V. 15, N 4. P. 310-320.
© 2012, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
310
PACS 61.05.cp, 61.43.Fs, 61.80.Ed
Radiation/annealing-induced structural changes
in GexAs40xS60 glasses as revealed from high-energy synchrotron
X-ray diffraction measurements
T.S. Kavetskyy1, V.M. Tsmots1, A.L. Stepanov2,3
1Ivan Franko Drohobych State Pedagogical University,
Solid-State Microelectronics Laboratory,
24, I. Franko str., 82100 Drohobych, Ukraine
2Kazan Physical-Technical Institute, Russian Academy of Sciences,
10/7 Sibirskiy trakt, 420029 Kazan, Russian Federation
3Kazan Federal University, 18, Kremlyovskaya str., 420008 Kazan, Russian Federation
Abstract. Local atomic structure of GexAs40xS60 glasses (x = 16, 24, 32, and 36) has
been investigated in the -irradiated (2.41 MGy dose) and annealed after -irradiation
states by using the high-energy synchrotron X-ray diffraction technique. The
accumulated dose of 2.41 MGy is chosen to be close to the known in literature focal
point (2.0 MGy) for the system tested, at which the -irradiation-induced optical
(darkening) effect does not depend on the composition. It is established that the first
sharp diffraction peak (FSDP) is located at around 1Е1.1 in the structure factors S(Q) of
all the alloys studied. The FSDP position is found to be constant on radiation/annealing
treatment, but the intensity of the FSDP reveals changes under irradiation/annealing only
for the compositions with x = 16 and 24. The radiation/annealing-induced changes are
also observed on the pair distribution functions in the first and second coordination shells
for these compounds. Practically invisible effects on the FSDP and pair distribution
functions are found for the alloys with x = 32 and 36. The radiation/annealing-induced
structural changes detected mainly in the SAs sub-system of the glasses examined are
well explainable within the Tanaka approach for interpretation of the photo-induced
structural changes and related phenomena in As2S3 chalcogenide glass and similar
materials.
Keywords: chalcogenide glasses, structure, X-ray diffraction, radiation modification.
Manuscript received 20.06.12; revised version received 15.08.12; accepted for
publication 17.10.12; published online 12.12.12.
1. Introduction
The concept of coordination defects or valence
alternation pairs (VAPs) in chalcogenide glasses is a
fundamental and topical problem for understanding the
structure and properties of these materials. Nevertheless,
there are a lot of contradictions between researches in
application of the VAP concept for explanation of
different processes and phenomena in chalcogenide
glasses. For instance, Dembovskii et al. [1] showed that
the generally accepted concept of VAPs must be
reexamined, since formation of pairs of separated
charged point defects of the type
3C and
1C requires
too much energy. On the other hand, the authors have
shown by analogy with a-Se that centers connected by a
strong bond can coexist in the form of rigid VAP
dipoles. It was also found in [1] that nonrigid,
metastable, hypervalent configurations (HVCs) exist in
the form of HVC dipoles, which are neutral and
diamagnetic in the ground state and lie below 0
1C on the
energy scale.
Semiconductor Physics, Quantum Electronics & Optoelectronics, 2012. V. 15, N 4. P. 310-320.
© 2012, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
311
Recently, Munzar and Tichy [2] have reported that
kinetics of photo-darkening of amorphous As2S3 and a-
As2Se3 thin films follows a single exponential, but the
magnitude and the rate of the process is higher in the
case of As2S3. The authors found out explanation for
these facts estimating the probability of breaking of
SAs and SeAs bonds on illumination. They
showed that in the case of a-As2S3 around two bonds can
be broken from each 2000 SAs bonds, whereas in the
case of a-As2Se3 around two bonds can be broken only
for each 108 SeAs bonds. It means the probability of
photo-induced bond breaking in a-As2S3 film is much
higher than that for a-As2Se3 film. As a result, it has
been concluded in [2] that photo-darkening in a-As2S3 is
accompanied by changes in short-range order
interactions, while photo-darkening in a-As2Se3 is
accompanied rather by changes in Coulomb interactions
in an agreement with “slip motion of the layers” model
introduced by Shimakawa et al. [3]. The estimated
probability for a-As2S3 corresponds to the existence of
concentration of defects at the level less than 1% of all
atomic sites. Is this level of concentration of defects
enough to be identified using a experimental technique
like X-ray diffraction (XRD), which can provide direct
structural information?
Tanaka [4] mentioned that reversible photo-
induced phenomena, involving structural changes at
atomic sites of 31817 cm10-10 (approximately ppm
order [5]), exist in tetrahedral and chalcogenide
systems. The density is comparable to that of point
defects in crystals, and it is far below a detection limit
of the XRD technique. Thus, mechanisms of these
phenomena are largely speculative, especially, when
related sites are ESR-inactive. However, there are
several photo-induced phenomena involving atomic
sites of 1% [5] and these kinds of phenomena have
only been detected for chalcogenide glasses. If
considering all the photo-induced phenomena (see
Table 1 in [4]) involving atomic sites less and more
than 320 cm10 or 1% of the total atom density, these
phenomena can be both irreversible and reversible. The
irreversible phenomena can involve greater atom
numbers, since the changes occur towards more stable
atomic structures (see Table 1 in [4]); then, why should
the atomic sites be less than 1% in the reversible
changes according to the Tanaka model? This fact is
considered [4] as follows: “The density of 1% reads
one photo-induced atomic site per cube with a side
length of 5-6 atoms, which is 1-3 nm, depending on the
atomic bonds involved, i.e. covalent and/or van der
Waals bonds. The atomic density of defects 1% is the
limit arising from the structures that can localize
photo-induced strains. The critical length of 1-3 nm is
comparable to the medium-range structural length in
chalcogenide glasses”. According to the Tanaka model,
the photo-structural changes on the medium-range
order scale may be considered as a signature of photo-
induced defect formation with the density less than 1%
per cube with a side length of 5-6 atoms (1-3 nm). This
is indeed observed [4] in the case of bulk glass As2S3
using the XRD method (the medium-range order is
exemplified by the first sharp diffraction peak (FSDP)).
The photo-structural changes may be explained in
terms of defect models, presuming creation of some
kinds of defects, and a non-defect or distortion model,
postulating randomness increase in normal bonding
configurations; although structural changes interpreted
within the distortion model appear to be consistent with
experimental observation of the FSDP weakening and
broadening on illumination [4].
In contrast to the intensive study of photo-structural
changes in chalcogenide glasses using the XRD method,
less information and lack of our knowledge to
understand -irradiation-induced structural changes in
these materials are available, although, there are some
methodological advantages to XRD study of -
irradiation-induced effects as compared to the photo-
induced ones. First, in the case of photo-induced
phenomena [4], illumination and diffraction
measurements should be performed in-situ, which is
important to exclude thermal expansion effects and to
detect minute changes. While for radiation-induced
phenomena, -irradiation produces changes inside the
whole glass matrix, but not in the spot as for laser
illumination, and, thus, an in-situ experiment is not
required and it is not possible to be performed
experimentally in the case of -irradiation. Second, the
investigation of radiation-modified structure of a glass is
important within ex-situ measurements in order to find
how structure is changed after a long period of time
following radiation treatment of a sample (static
radiation-induced effects [ 86 ]). Third, in contrast to
photo-induced phenomena (irreversible or reversible), -
irradiation-induced phenomena are mainly always
reversible with annealing at the temperature 40-50 K
below the glass transition temperature Tg [9, 10], which
allows to investigate the radiation/annealing-induced
structural changes for the same sample measured first as
-irradiated and than as annealed after -irradiation under
the same experimental conditions.
The purpose of this work is to study the
radiation/annealing-induced structural changes in
GexAs40–xS60 (x = 16, 24, 32, and 36) glasses using the
high-energy synchrotron XRD technique. Among a
number of chalcogenides, as far as we know, only this
system demonstrates the focal point (2.0 MGy), at
which the -irradiation-induced optical (darkening)
effect does not depend on the composition [11]. We
believe that the glasses examined should also exhibit this
effect at the accumulated dose close to 2.0 MGy. The
origin of the focal point is not clear, and we suggest that
the precise high-energy synchrotron XRD study of the
GexAs40–xS60 glasses in the -irradiated and annealed
after -irradiation states under the same experimental
conditions will help us to obtain more information and to
cast light on this issue.
Semiconductor Physics, Quantum Electronics & Optoelectronics, 2012. V. 15, N 4. P. 310-320.
© 2012, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
312
2. Experimental
The bulk glasses of GexAs40xS60 system at x = 16, 24,
32, and 36 were prepared from elements of 99.9999%
purity in evacuated silica ampoules by standard melt
quenching procedure as described elsewhere [12]. As-
prepared glasses were cut to the disk-like specimens and
polished to a high optical quality. Then, in order to
remove possible mechanical stresses formed after
synthesis, the samples were annealed at about 20-30 K
below the glass transition temperature [12] (Tg = 530 K
for Ge16As24S60, 620 K for Ge24As16S60, 670-675 K for
Ge32As8S60, and 682 K for Ge36As4S60).
Radiation treatment of the glasses was performed
by -quanta (average energy E = 1.25 MeV) with the
accumulated dose 2.41 MGy (close to the focal point
[11] near 2.0 MGy) at normal conditions of stationary
radiation field created in a closed cylindrical cavity by a
number of circularly established 60Co radioisotope
capsules. No special measures were taken to prevent
uncontrolled thermal annealing of the samples, but
maximum temperature in the irradiating camera did not
exceed 320-330 K during prolonged -irradiation (about
30 days), providing the absorbed dose power P < 5 Gy/s.
The -irradiated samples were measured for more than 2
months after -irradiation (static component of radiation-
induced effects [6-8]). The -irradiated samples were
annealed at the temperature 40-50 K below Tg following
the previous results on the reversible -irradiation-
induced optical (darkening) effects in the 6040 SAsGe xx
glasses with thermal annealing [9, 10].
High-energy synchrotron X-ray diffraction
experiments were carried out at the BW5 experimental
station at HASYLAB, DESY in Hamburg, Germany. All
the samples were examined in transmission geometry.
The energy of synchrotron radiation was 98.9 keV.
Scattered intensity was measured between 0.5 and
1Е19 . Raw data were corrected for detector dead-time,
polarization, absorption and variation in detector solid
angle [13]. The scattering intensity was converted into
the coherent scattering intensity per atom in electronic
units by using the Krogh-Moe-Norman method [14, 15].
Compton scattering was corrected using the values given
by Balyuzi [16]. Faber-Ziman [17] total structure factor
S(Q) was calculated from the scattering intensity as
2
22
..
Qf
QfQfQI
QS
coh
ue
(1)
with
QfcQf i
i
i
22 , QfcQf i
i
i , (2)
where ci is the molar fraction and fi(Q) is the total atomic
scattering factor of the i-th component of the glass.
The total pair distribution function g(r) was
obtained via transformation
QdQrQSQ
rρπ
rg )sin(1)(
2
1
1)(
00
2
, (3)
where 0 is the average number density.
It is known that the impact of chalcogenide glasses
induced by external influence (i.e. -irradiation,
hydrostatic pressure or illumination) on the experimental
structure factors is rather small [4, 2118 ]. Therefore,
the experimental error should be minimized for correct
investigation of such phenomena. In the present study,
like in the case of 6040 SSbGe xx glasses [18], all XRD
experiments were carried out within a couple of hours;
the specimens were of the same thickness; they were
fixed in a holder moving horizontally, providing
practically identical sample adjustment during
measurements. The samples were positioned in the
holder at the same position to be measured first as -
irradiated and than as annealed after -irradiation. All
this helped to reduce the random error to a minimum.
3. Results
Experimental structure factors S(Q) for the investigated
6040 SAsGe xx glasses in -irradiated and annealed after
-irradiation states are shown in Fig. 1a. Oscillations in
S(Q) persist up to high Q values for all the samples. The
first sharp diffraction peak (FSDP) exists on the S(Q) for
all the alloys studied (Fig. 1b). The intensity of the
FSDP, measured as a relation of the intensities at the
maximum and at the tail of peak (IFSDP =
S(Q)max/S(Q)min), for the annealed samples demonstrates
non-monotonic trend from 4.38 at x = 16 to 4.06 at
x = 36 reaching a maximum value of 4.56 at x = 32.
Position of the FSDP shifts continuously from 1Е13.1
(x = 16) to 1Å01.1 (x = 36). It should be noted that the
values of QFSDP = 1Å08.1 and 1Å01.1 for x = 24 and
36 of the 6040 SSbGe xx glasses agree with the values of
QFSDP = 1Е08.1 and 1Е02.1 for x = 25 and 35 of
6040 SSbGe xx glasses [18]. This non-monotonic trend in
the FSDP intensity and monotonic one in the FSDP
position detected for the annealed 6040 SAsGe xx glasses
have also been observed in other non-stoichiometric
xxx 2100SAsGe and yxyx 100SAsGe glasses in the
course of neutron and X-ray diffraction studies [22, 23].
For all the compositions studied, positions of
maxima and minima of the structure factors of -
irradiated and annealed glasses coincide with those of
radiation-modified Ge25Sb15S60 and Ge35Sb5S60 glasses.
Main difference between -irradiated and annealed
glasses is observed only in the intensity of the FSDP for
As-enriched composition Ge16As24S60 for which the pre-
peak becomes weaker and broader under irradiation
(Fig. 1b) similarly to the binary As2S3 glass [19]. This
Semiconductor Physics, Quantum Electronics & Optoelectronics, 2012. V. 15, N 4. P. 310-320.
© 2012, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
313
(a)
(b)
Fig. 1. (a) The total structure factors S(Q) for the samples of the investigated GexAs40–xS60 system in -irradiated (the curves
for -irradiated state is shifted (+1) for clarity) and annealed after -irradiation states; and (b) the first sharp diffraction peak
(FSDP) in -irradiated and annealed after -irradiation states.
difference is notably larger than the total experimental
error of the structure factor, which is estimated to be
below 1% in the low Q-part of S(Q) as shown in [18].
Fig. 2a shows the pair distribution functions g(r)
for the investigated 6040 SAsGe xx glasses, both in the -
irradiated and annealed after -irradiation states. For a
better comparison, parts of the pair distribution functions
g(r) corresponding to the first and second (insertion)
coordination shells are plotted in Fig. 2b. For all the
alloys studied, a peak on g(r) at r = 2.26-2.27 Å can be
attributed to the nearest neighbor correlations. On the
pair distribution functions of 6040 SAsGe xx , there is
either a small peak (for x = 16 and 24) or a shoulder (for
x = 32 and 36) at r 2.60-2.65 Å. As this distance does
Semiconductor Physics, Quantum Electronics & Optoelectronics, 2012. V. 15, N 4. P. 310-320.
© 2012, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
314
(a)
(b)
Fig. 2. (a) The pair distribution functions g(r) for the samples of the investigated GexAs40–xS60 system in -irradiated (the
curves for -irradiated state is shifted (+1) for clarity) and annealed after -irradiation states; and (b) the part of g(r) in the first
and second (insertion) coordination shells in -irradiated and annealed after -irradiation states.
not correlate with any possible interatomic distance of
any two glass constituents, most probably this feature
(peak, shoulder) is caused by the termination of the
experimental data at a final value of the diffraction
vector. It is known that false oscillations appear on the
pair distribution function near the main peak due to the
termination effect [24]. A maximum at r = 3.55-3.60 Å
reflects the second coordination sphere. Also, a hump at
r = 2.99 Å is observed on g(r) of all the investigated
samples in the second coordination shell like to the
samples of GexSb40–xS60 with x = 25 and 35 [18]. But due
to the risk that this hump may come from the termination
effect, we will not analyze this hump in further
consideration.
Semiconductor Physics, Quantum Electronics & Optoelectronics, 2012. V. 15, N 4. P. 310-320.
© 2012, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
315
Fig. 3 shows the observed peaks on g(r) located in
the first and second coordination shells for the annealed
samples of 6040 SAsGe xx system. One may clearly see
that the first peak at r = 2.26-2.27 Å becomes weaker
and broader with increasing x. The second peak r = 3.55-
3.60 Å becomes weaker and broader with increasing x
similar to the first peak. The shape of the second peak is
different for the As-rich sample (xGe = 16) as compared
to the Ge-rich samples (xGe = 24, 32 and 36), which have
slightly narrower maximum.
The structural parameters such as intensity and
position of the FSDP, as well as intensities and positions
of the peaks g(r1) and g(r2) for 6040 SAsGe xx glasses are
given in Table. The intensities of these structural
parameters are also plotted in Fig. 4 as a function of x
for better observation of their compositional
dependence. The plots of the IFSDP, g(r1) and g(r2) as a
function of x for both irradiated and annealed samples
show non-monotonic trend with an extremum at x = 32.
Finally, for all the glasses studied, it is found that
radiation impact results in weakening and broadening of
the FSDP with the first peak at r = 2.26-2.27 Å and the
second peak at r = 3.55-3.60 Å; the effect is the largest
one for Ge16As24S60 (x = 16), smaller for Ge24As16S60
(x = 24), and practically invisible for Ge32As8S60 (x = 32)
and Ge36As4S60 (x = 36) alloys.
Fig. 3. The observed peaks on g(r) located in the first and
second coordination shells for the annealed samples of
GexAs40–xS60 system. See the text for details.
Fig. 4. The intensities of the peaks (a) FSDP, measured as a
ratio of the intensities at the maximum and at the tail of peak
(IFSDP = S(Q)max/S(Q)min), (b) g(r1), and (c) g(r2) for the
investigated GexAs40–xS60 glasses in -irradiated (open cycles)
and annealed after -irradiation (closed cycles) states as a
function of the composition x.
4. Discussion
Investigating the physical properties, in particular,
optical bang gap Eg and structural compactness in the
bulk glasses and thin films from 6040 SAsGe xx family in
dependence on x or average coordination number Z (i.e.,
Z = (4x + 3(40x) +260)/100, where 4, 3 and 2 stand for
the coordination numbers of Ge, As, and S,
respectively), Skordeva and Arsova [25] concluded that
the peculiarities of the properties (e.g., a maximum on Eg
for annealed films and a minimum on for bulk glasses)
are caused by the topological structural 2D-3D phase
transition according to the Tanaka model [26] from a
two-dimensional (2D) layer-like structure to a three-
dimensional (3D) cross-linked network at the average
coordination number Z of about 2.67. Later Tichy and
Ticha [27] reported on the possibility of chemical
threshold at Z 2.7.
Stronski et al. [28] reported that the compactness
is well sensitive to the structure of glass network and its
compositional dependence is supposed to be connected
with atomic rearrangements in the glass backbone. On
the other hand, in the first approximation, the
compactness is also a measure of free volume of glass
[29]. It is interesting to note that the compactness for
Semiconductor Physics, Quantum Electronics & Optoelectronics, 2012. V. 15, N 4. P. 310-320.
© 2012, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
316
the GexAs40–xS60 glasses has attained a minimum value
at Z = 2.72 (see Fig. 3 in [13]). Thus, the maximum free
volume in the investigated 6040 SAsGe xx glasses is
attained for alloy with x = 32 (Z = 2.72). Hence, it is
reasonable to relate the features (plateau, extremum)
observed in the composition trends of the FSDP intensity
and those of the peaks g(r1) and g(r2) for alloy with
x = 32 (Z = 2.72) with the maximum free volume and
atomic rearrangements resulting in the topological or
chemical threshold attained at Z 2.7 (Fig. 4). These
findings may be considered as an evidence of the
anomalous structural features on the short-range order
(exemplified by the first and second neighbor
correlations) and medium-range order (exemplified by
the FSDP) scale in the vicinity of the topological or
chemical threshold at Z 2.7.
Let us consider the radiation/annealing-induced
structural changes detected on the FSDP and the pair
distribution functions g(r) for the investigated glasses
(Figs. 1, 2, 4 and Table).
The well observable weakening and broadening of
the FSDP with the unchanged position under irradiation
for the As-enriched glass Ge16As24S60 (x = 16) is similar
to the radiation-induced changes [20] and photo-induced
changes [4] in the FSDP intensity and position for the
binary As2S3 glass. Thus, the mechanism of the
radiation- and photo-induced structural changes on the
medium-range order scale exemplified by the FSDP
would be the same.
As it was mentioned in Introduction, according to
the Tanaka model [4], the photo-structural changes on
the medium-range order scale may be considered as a
signature of photo-induced defect formation with the
density less than 1% (i.e., one photo-induced atomic site
per cube with a side length of 5-6 atoms). Thus, the
radiation-induced changes observed on the medium-
range order scale (FSDP) indicate formation of one
radiation-induced atomic site per cube with a side length
of 5-6 atoms (1-3 nm). According to the Tanaka model
[4], with account of the term for the single radiation-
induced atomic site (defect), we consider a strain
produced by -irradiation and confined in the cube
leading finally to a radiation-induced metastable
structural configuration, which can then relax into a
stable structure with thermal relaxation induced by
annealing (reversible changes). Producing the strain in
chalcogenide glass matrix under -irradiation is
confirmed by the recent study of microindentation
cracks in bismuth-doped arsenic selenide glasses [30]. In
particular, it has been found that radial cracks around
indentations are produced on the surfaces of the
chalcogenide glass samples at loads exceeding the
specific applied load Pc
app that somewhat increases under
-irradiation of samples even at the relatively low
0.76 MGy accumulated dose. Besides, the well known
increase in microhardness of chalcogenide glass under -
irradiation may also be an additional confirmation for
this ([31] and references therein).
The mechanism providing formation of radiation-
induced strain can be considered using both defect
models and non-defect or distortion model reported by
Tanaka [4] to explain the photo-structural changes in
As2S3 chalcogenide glass and similar materials.
Although different known structural models could be
applied to interpret the observed weakening and
broadening of the FSDP under -irradiation (Fig. 1b), we
prefer more Tanaka’s explanation of the weakening and
broadening of the FSDP on illumination within the
distortion model ([4] and references therein). In this
approach, there are two kinds of the structural changes
Table. Structural parameters of GexAs40xS60 glasses (x = 16 (Z = 2.56), x = 24 (Z = 2.64), x = 32 (Z = 2.72), and x = 36
(Z = 2.76)) in -irradiated (irrad.) and annealed after -irradiation (ann.) states. QFSDP – position of the FSDP and IFSDP –
intensity of the FSDP, measured as a relation of the intensities at the maximum and at the tail of peak (IFSDP =
S(Q)max/S(Q)min); ri – position and g(ri) – intensity of peaks on the pair distribution functions. The errors of QFSDP and ri
are estimated from the Gaussian fits of the peaks. The error bars for the IFSDP and g(ri) are 2% of the reported values.
x State QFSDP (Å
-1) IFSDP (a.u.) r1 (Å) g(r1) r2 (Å) g(r2)
irrad. 1.130.01 3.650.07 2.270.01 4.220.08 3.550.02 1.970.04
16
ann. 1.130.01 4.380.09 2.270.01 4.850.10 3.550.02 2.050.04
irrad. 1.080.01 4.250.09 2.260.01 4.490.09 3.600.02 1.920.04
24
ann. 1.080.01 4.450.09 2.260.01 4.720.09 3.600.02 1.940.04
irrad. 1.030.01 4.530.09 2.260.01 4.750.10 3.610.02 1.910.04
32
ann. 1.030.01 4.560.09 2.260.01 4.810.10 3.610.02 1.970.04
irrad. 1.010.01 3.880.08 2.260.01 4.560.09 3.590.02 1.900.04
36
ann. 1.010.01 4.060.08 2.260.01 4.630.09 3.590.02 1.950.04
Semiconductor Physics, Quantum Electronics & Optoelectronics, 2012. V. 15, N 4. P. 310-320.
© 2012, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
317
involved in this model. On the one hand, plausible
structural changes can be sought in the distortions in
bond angles, dihedral angles, and van der Waals
distances resulting in: (i) changes in the short-range
order, (ii) the increase in the conduction band width and,
consequently, decrease in the optical band gap
(darkening effect), and (iii) the enhancement of the
randomness in the medium-range structural order. On
the other hand, the intermolecular distortion through
bond-twisting motion of chalcogen atom is the second
kind of the structural changes within the distortion
model. Finally, according to the Tanaka model [4], these
two kinds of structural changes are interrelated (thus, if
an intermolecular bond is distorted on illumination,
structural relaxation will necessarily occur, leading to
appreciable angular distortions) and appear to be
consistent with the weakening and broadening of the
FSDP on illumination.
With account of the above mentioned, we suggest
that the observed radiation-induced structural changes on
the medium-range order scale (FSDP) in Ge16As24S60
(x = 16) glass are caused by distortion in bond angles,
dihedral angles, van der Waals distances and
intermolecular distortion through bond-twisting motion
of chalcogen atom leading together to formation of
radiation-induced defects with the density 1%
( 320 cm10 ), which annihilate with annealing through
thermal relaxation of the radiation-induced metastable
structural configuration (strain) to a more stable
structure. As the changes in the FSDP are very small for
Ge24As16S60 (x = 24) and invisible for Ge32As8S60
(x = 32) and Ge36As4S60 (x = 36), one may assume that
the radiation-induced defects with the density 1% are
probably not formed for the Ge-enriched glasses studied
with dominant SGe correlations. In other words, we
may conclude that the radiation/annealing-induced
structural changes on the medium-range order scale for
the 6040 SAsGe xx system occur mainly in the SAs
sub-system.
The distortion model seems to be applicable for the
interpretation of the radiation/annealing-induced
structural changes on the short-range order scale
exemplified by the first and second coordination shells
on the pair distribution functions g(r) as well. Let us
consider this in detail.
The first peaks on g(r) at 2.26 and 2.27 Å for the
6040 SAsGe xx glasses can be attributed to the SGe
and SAs correlations. The value 2.26 Å for Ge-
enriched samples (x = 24, 32, and 36) is consistent with
2.21-2.24 Å distances corresponding to SGe first
neighbors in the germanium sulphide glasses [32] and
with 2.24-2.27 Å distances corresponding to SGe first
neighbors in the mixed germanium-arsenic sulphide
glasses [23, 24], as well as the value 2.27 Å for As-
enriched sample (x = 16) is consistent with 2.27-2.30 Å
distances corresponding to SAs first neighbors in the
arsenic trisulphide glass [20, 33-35] and with 2.17-
2.27 Å distances corresponding to SAs first neighbors
in the mixed AsGe sulphide glasses [23, 24].
AsAs (2.43-2.53 Å [23, 24, 32]), GeGe
(2.46 Å [36]) and SS (2.0-2.04 Å [23, 32]) neighbor
correlations (if exist) cannot be resolved on the pair
distribution functions as they can simply be covered by
the peak from SGe or SAs contributions. Besides,
like for 6040 SSbGe xx [19], we suppose that SS bonds
are very improbable in the 6040 SAsGe xx glasses.
It is difficult to resolve the peak located at 3.55-
3.6 Å on the pair distribution functions g(r). In
6040 SSbGe xx family, Kakinuma et al. [37] attributed the
peak at 3.61 Å to the secondary partial correlations
GeGe , SbGe , SbSb , and SS . The structural
study of SGe glasses [32] shows that the broad peak
at ~3.6 Å corresponds to the second SS and GeGe
correlations in the corner-shared GeS4 tetrahedra
( 4GeSCS ). The structural study of As2S3 glass [20,
3633 ] indicates that the broad peak at ~3.5 Å
corresponds to the second neighbor distances SS and
AsAs in the corner-shared AsS3 pyramids. Brabec
[33] reported that in As2S3 glass the AsAs second-
neighbor distance is 3.52± 0.01 Å and the SS second-
neighbor distance is 3.5 ±0.1 Å. Soyer-Uzun et al.
[23, 24] showed that for the xxx 2100SAsGe glasses a
peak centered at 3.4 Å can be readily correlated to the
metal-metal next-nearest neighbors that are connected
through S atom, namely GeSGe , AsSGe , and
AsSAs linkages, as well as a peak centered at
3.5 Å for the yxyx 100SAsGe glasses corresponds
primarily to AsAs and Ge/AsGe next-nearest
neighbors in the AsSAs and Ge/AsSGe
linkages. In principle, all secondary partial correlations
GeGe , AsGe , AsAs and SS may exist in
6040 SAsGe xx family within the range of 3.5-3.6 Å
distances. Taking into account different shapes of the
second peak on g(r) at r = 3.55 Å (for x = 16) and r =
3.6 Å (for x = 24, 32, 36) in Fig. 3, it is reasonable to
separate secondary partial correlations SS and
AsAs for As-enriched sample (x = 16) and SS and
GeGe for Ge-enriched samples (x = 24, 32, 36).
Similar to the GexSb40xS60 glasses [19, 37], the
intensity of the second peak g(r2) for Ge-enriched
samples increases, and its position r2 shifts to lower r
values with increasing the Ge concentration with
maximum for Ge32As8S60 glass (Table). The ratio of the
peak positions at 3.6 Å (second neighbor correlations)
and 2.26 Å (first neighbor correlations) is 1.59. This is
somewhat lower than the value of 38 = 1.63 for
perfect tetrahedra, what can be a result of GeS4/2 unit
deformation, probably, due to the existance of GeGe
bonding in the ethane-like units 3/23/2 GeSGeS
(Ge2S6/2) in non-stoichiometric alloys of 6040 SAsGe xx
Semiconductor Physics, Quantum Electronics & Optoelectronics, 2012. V. 15, N 4. P. 310-320.
© 2012, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
318
or 3232 SGeSAs family [38]. Recently, the existence of
the ethane-like units 3/23/2 GeSGeS has also been
confirmed for the technologically important
multicomponent AgISInGeS 322 chalcohalide
glasses [39] by using combination of XRD, EXAFS,
reverse Monte Carlo modelling, Raman scattering and
density functional theoretical calculations [40].
It is noteworthy that the radiation/annealing-
induced changes in the main peak g(r1) correlate well
with those for the FSDP (see Figs 1b, 2b and 4), i.e., the
first peak g(r1) reveals the largest changes (weakening
and broadening) under -irradiation mainly for As-
enriched Ge16As24S60 (x = 16) alloy, smaller changes for
Ge24As16S60 (x = 24) and practically no changes for
Ge32As8S60 (x = 32) and Ge36As4S60 (x = 36) compounds.
The second peak g(r2) exhibits the largest effect
(weakening and broadening) under -irradiation for As-
enriched Ge16As24S60 (x = 16) glass as well. Thus, we
assume like to the medium-range order (FSDP) that the
radiation/annealing-induced structural changes on the
short-range order scale (first and second coordination
shells) are plausibly connected with the structural
transformations in the SAs sub-system. Tanaka’s
approach within the distortion model explains also
weakening and broadening of the first and second peaks
on g(r) under irradiation due to intermolecular distortion
through bond-twisting motion of chalcogen atom, which
is also interrelated with the distortion in bond angles,
dihedral angles, and van der Waals distances.
It should be noted that the recent [41] Doppler
broadening spectroscopy study of xx 1232 GeSSAs
glasses (As2S3 (x = 1.0), Ge9.5As28.6S61.9 (x = 0.6),
Ge15.8As21S63.2 (x = 0.4), and Ge23.5As11.8S64.7 (x = 0.2))
in the unirradiated (annealed) and -irradiated states
showed that the defect structure of Ge15.8As21S63.2 glass
is significantly different as compared to other alloys
(obviously, as a result of different mechanisms (defect or
non-defect ones) of radiation-structural changes).
Kavetskyy et al. [42] reported that the charged
coordination topological defects are quite responsible for
the defect mechanism of radiation-structural changes in
the case of Ge15.8As21S63.2 glass. While, likely to photo-
structural changes, the non-defect mechanism within the
Tanaka distortion model is supposed to be responsible
for the radiation-structural changes in the As2S3 alloy
and similar materials. The void-species nanostructure
(nanovoids) of the As2S3-based glasses studied with
positron annihilation lifetime spectroscopy [43] should
be taken into account for further consideration of
validity of Tanaka’s distortion model in explanation of
radiation-structural changes in chalcogenides.
In summary, with account of the results obtained,
we speculate that the existance of the focal point
(2.0 MGy) for the investigated 6040 SAsGe xx glasses,
at which the -irradiation-induced optical (darkening)
effect does not depend on the composition [11], can
simply be related with the dominant radiation-structural
changes in the SAs sub-system, and embedding the
Ge atoms into SAs glass matrix does not affect their
mechanism, since the radiation-structural changes in the
SGe sub-system are invisible on both short- and
medium-range order scales. Finally, we would like to
state that the alternative interpretation of the
radiation/annealing-induced structural changes reported
here may be also proposed.
5. Conclusions
Impact of -irradiation (2.41 MGy dose) and subsequent
annealing on the atomic structure of 6040 SAsGe xx
glasses (x = 16, 24, 32, 36) is studied using high-energy
XRD measurements. Analysis of the experimental
structure factors and pair distribution functions has
revealed the differences related to the structural changes
at the short-range order scale (exemplified by the first
and second nearest neighbor correlations) and medium-
range order scale (exemplified by the FSDP). Nonlinear
compositional trends in the IFSDP, g(r1) and g(r2) values
with features (plateau, extremum) nearby the topological
structural phase transition [26] or chemical threshold
[27] at the average coordination number Z 2.7 (x = 32)
are detected for the both -irradiated and annealed
alloys.
The FSDP position is found to be constant on
radiation/annealing treatment, but the intensity of the
FSDP reveals changes under irradiation/annealing only
for the compositions with x = 16 and 24. The
radiation/annealing-induced changes are also observed
on the pair distribution functions in the first and second
coordination shells for these compounds. Practically
invisible effects on the FSDP and pair distribution
functions are found for the alloys with x = 32 and 36.
The radiation/annealing-induced structural changes
detected mainly in the SAs sub-system of the glasses
examined can be well explained within the Tanaka
approach [4] for interpretation of the photo-induced
structural changes and related phenomena in the As2S3
chalcogenide glass and similar materials.
Existence of the focal point (2.0 MGy) for the
6040 SAsGe xx glasses, at which the -irradiation-induced
optical (darkening) effect does not depend on the
composition [11], can simply be related with the
dominant radiation-structural changes in the SAs sub-
system and embedding the Ge atoms into the SAs
glass matrix does not affect their mechanism, since the
radiation-structural changes in the SGe sub-system
are invisible on both short- and medium-range order
scales.
Acknowledgements
The authors would like to thank Dr. Ivan Kaban (IFW
Dresden, Germany) for his help with high-energy
synchrotron XRD measurements, Dr. Pal Jóvári
Semiconductor Physics, Quantum Electronics & Optoelectronics, 2012. V. 15, N 4. P. 310-320.
© 2012, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
319
(Research Institute for Solid State Physics and Optics,
Budapest, Hungary) for his help with experimental data
treatment, Prof. Walter Hoyer (Institute of Physics, TU
Chemnitz, Germany) and Prof. Guorong Chen (East
China University of Science and Technology, Shanghai,
China) for stimulating discussions. The investigated
samples used for measurements were prepared within
joint research projects (#0106U007386 and
#0109U007446c) between Ivan Franko Drohobych State
Pedagogical University (Drohobych, Ukraine) and
Scientific Research Company “Carat” (Lviv, Ukraine)
supported by the Ministry of Education and Science of
Ukraine (#0106U007385 and #0109U007445). T.S.K.
acknowledges DAAD for support of his research work at
TU Chemnitz (Germany) and Deutsches Elektronen-
Synchrotron DESY for support of the experiments
performed at HASYLAB (Hamburg, Germany). T.S.K.
and V.M.T. acknowledge national project
(#0111U001021) supported by the Ministry of Education
and Science, Youth and Sport of Ukraine. A.L.S.
grateful to the Alexander von Humboldt Foundation,
DFG and DAAD (Germany). Support from the
Ukrainian-Russian projects funded by the State Fund for
Fundamental Researches of Ukraine (#F40.2/019) and
the Ministry of Education and Science of the Russian
Federation (#02.740.11.0797) and the Russian
Foundation for Basic Research (#11-02-90420-Ukraine,
#11-02-91341-Germany and #12-02-00528-a) is also
gratefully acknowledged.
References
1. S.A. Dembovsky, A.S. Zyubin, F.V. Grigor’ev,
Modeling of hypervalent configurations, valence
alternation pairs, deformed structure, and properties
of a-S and a-As2S3 // Semiconductors, 32(8),
p. 843-849 (1998).
2. M. Munzar, L. Tichy, Kinetics of photo-darkening
abd self-bleaching in amorphous As2S3 and As2Se3
thin films // Phys. Stat. Sol. (RRL), 1(2), p. R74-
R76 (2007).
3. K. Shimakawa, N. Yoshida, A. Ganjo,
Y. Kuzukawa, J. Singh, A model for the
photostructural changes in amorphous
chalcogenides // Philos. Mag. Lett., 77(3), p. 153-
158 (1998).
4. K. Tanaka, Photoinduced structural changes in
amorphous semiconductors // Semiconductors,
32(8), p. 861-866 (1998).
5. K. Shimakawa, A. Kolobov, S.R. Elliott,
Photoinduced effects and metastability in
amorphous semiconductors and insulators // Adv.
Phys., 44(6), p. 475-588 (1995).
6. T.S. Kavetskyy, Impact of the sample thickness and
-irradiation dose on the occurrence of radiation-
induced optical effects in chalcogenide vitreous
semiconductors of the Ge-Sb-S system //
Semiconductors, 45(4), p. 499-502 (2011).
7. O.I. Shpotyuk, R.Ya. Golovchak, A.P. Kovalskiy,
T.S. Kavetskyy, Time and temperature stability of
radiation-induced changes of optical properties in
ternary systems of chalcogenide vitreous
semiconductors // Functional Materials, 10(2),
p. 317-321 (2003).
8. O.I. Shpotyuk, T.S. Kavetskyy, A.P. Kovalskiy,
V. Pamukchieva, Gamma-irradiation effect on the
optical properties of 6040 SSbGe xx chalcogenide
glasses // Proc. SPIE, 4415, p. 278-283 (2001).
9. O. Shpotyuk, A. Kovalskiy, T. Kavetskyy,
R. Golovchak, Post-irradiation thermally stimulated
recovering effects in some ternary chalcogenide
glasses // J. Optoelectron. Adv. Mater., 5(5),
p. 1169-1179 (2003).
10. O.I. Shpotyuk, A.P. Kovalskiy, T.S. Kavetskyy,
R.Ya. Golovchak, Threshold restoration effects in
-irradiated chalcogenide glasses // J. Non-Cryst.
Solids, 351, p. 993-997 (2005).
11. V. Balitska, R. Golovchak, A. Kovalskiy,
E. Skordeva, O.I. Shpotyuk, Effect of Co60 -
irradiation on the optical properties of As-Ge-S
glasses // J. Non-Cryst. Solids, 326&327, p. 130-
134 (2003).
12. A. Feltz, Amorphous and Vitreous Inorganic
Solids. Moscow, Mir, 1986 (in Russian).
13. H.F. Poulsen, J. Neuefeind, H.-B. Neumann,
J.R. Schneider, M.D. Zeidler, Amorphous silica
studied by high energy X-ray diffraction // J. Non-
Cryst. Solids, 188, p. 63-74 (1995).
14. J. Krogh-Moe, A method for converting
experimental X-ray intensities to an absolute scale
// Acta Cryst., 9, p. 951-953 (1956).
15. N. Norman, The Fourier transform method for
normalizing intensities // Acta Cryst., 10, p. 370-
373 (1957).
16. H.H.M. Balyuzi, Analytic approximation to
incoherently scattered X-ray intensities // Acta
Cryst. A, 31, p. 600-602 (1975).
17. T.E. Faber, J.M. Ziman, A theory of the electrical
properties of liquid metals // Philos. Mag., 11(109),
p. 153-173 (1965).
18. T. Kavetskyy, O. Shpotyuk, I. Kaban, W. Hoyer,
Radiation-modified structure of Ge25Sb15S60 and
Ge35Sb5S60 glasses // J. Сhem. Phys., 128(24),
244514(1-8) (2008).
19. T. Kavetskyy, O. Shpotyuk, I. Kaban, W. Hoyer,
Atomic- and void-species nanostructures in
chalcogenide glasses modified by high energy
gamma-irradiation // J. Optoelectron. Adv. Mater.,
9(10), p. 3247-3252 (2007).
20. H. Hamanaka, S. Minomura, K. Tsuji, Comparative
studies of pressure and photo induced structural
changes in As2S3 glass // J. Non-Cryst. Solids,
137&138, p. 977-980 (1991).
21. S.R. Elliott, Scattering studies of photostructural
changes in chalcogenide glasses // J. Non-Cryst.
Solids, 59&60, p. 899-908 (1983).
Semiconductor Physics, Quantum Electronics & Optoelectronics, 2012. V. 15, N 4. P. 310-320.
© 2012, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
320
22. S. Soyer-Uzun, S. Sen, C.J. Benmore, B.G. Aitken,
Compositional variation of short- and intermediate-
range structure and chemical order in Ge-As sulfide
glasses: A neutron diffraction study // J. Phys.
Chem. C, 112, p. 7263-7269 (2008).
23. S. Soyer-Uzun, S. Sen, B.G. Aitken, Newtork vs
molecular structural characteristics of Ge-doped
arsenic sulfide glasses: A combined neutron/X-ray
diffraction, extended X-ray absorption fine
structure, and Raman spectroscopic study // J.
Phys. Chem. C, 113, p. 6231-6242 (2009).
24. R. Kaplow, S.L. Strong, B.L. Averbach, Radial
density functions for liquid mercury and lead //
Phys. Rev., 138, p. A1336-A1345 (1965).
25. E.R. Skordeva, D.D. Arsova, A topological phase
transition in ternary chalcogenide films // J. Non-
Cryst. Solids, 192&193, p. 665-668 (1995).
26. K. Tanaka, Structural phase transitions in
chalcogenide glasses // Phys. Rev. B, 39(2),
p. 1270-1279 (1989).
27. L. Tichy, H. Ticha, Is the chemical threshold in
certain chalcogenide glasses responsible for the
threshold at the mean coordination number of
approximately 2.7? // Phil. Mag. B, 79(2), p. 373-
380 (1999).
28. A.V. Stronski, M. Vlček, P.F. Oleksenko, Fourier
Raman spectroscopy studies of the As40S60–xSex
glasses // Semiconductor Physics, Quantum
Electronics & Optoelectronics, 4(3), p. 210-213
(2001).
29. I.P. Kotsalas, D. Papadimitriou, C. Raptis,
M. Vlcek, M. Frumar, Raman study of photo-
structural changes in amorphous 6.04.0 SSbGe xx // J.
Non-Cryst. Solids, 226, p. 85-91 (1998).
30. K. Sangwal, J. Borc, T. Kavetskyy, Study of
microindentation cracks in bismuth-doped arsenic
selenide glasses // J. Non-Cryst. Solids, 357,
p. 3117-3122 (2011).
31. O.I. Shpotyuk, Radiation-induced effects in
chalcogenide vitreous semiconductors //
Semiconducting Chalcogenide Glass I: Glass
Formation, Structure, and Stimulated
Transformations in Chalcogenide Glasses,
Semiconductors and Semimetals, edited by R.
Fairman and B. Ushkov, Amsterdam-Boston-
London-New York-Oxford-Paris-San Diego-San
Francisco-Singapore-Sydney-Tokyo, Elsevier
Academic Press, 78, p. 215-260 (2004).
32. E. Bychkov, M. Miloshova, D.L. Price,
C.J. Benmore, A. Lorriaux, Short, intermediate and
mesoscopic range order in sulfur-rich binary
glasses // J. Non-Cryst. Solids, 352, p. 63-70
(2006).
33. C.J. Brabec, Structural model of amorphous arsenic
sulfide // Phys. Rev. B, 44(24), p. 13332-13342
(1991).
34. T.G. Fowler, S.R. Elliott, Continuos random
network models for a-As2S3 // J. Non-Cryst. Solids,
92, p. 31-50 (1987).
35. F. Shimojo, K. Hoshino, Y. Zempo, Intermediate-
range order in liquid and amorphous As2S3 by ab
initio molecular-dynamics simulations // J. Non-
Cryst. Solids, 312-314, p. 388-391 (2002).
36. W. Zhou, M. Pasesler, D.E. Sayers, Structure of
germanium-selenium glasses: An X-ray-absorption
fine-structure study // Phys. Rev. B, 43(3), p. 2315-
2321 (1991).
37. F. Kakinuma, T. Fukunaga, K. Suzuki, Structural
study of GexSb40–xS60 (x = 10, 20 and 30) glasses //
J. Non-Cryst. Solids, 353, p. 3045-3048 (2007).
38. D. Arsova, E. Skordeva, D. Nesheva, E. Vateva, A.
Perakis, C. Raptis, A comparative Raman study of
the local structure in (Ge2S3)(As2S3)1–x and
(GeS2)(As2S3)1–x glasses // Glass Phys. Chem.,
26(3), p. 247-251 (2000).
39. T. Kavetskyy, N. Pavlyukh, V. Tsmots, W. Wang,
J. Ren, G. Chen, A.L. Stepanov, IR impurity
absorption in GeS2-In2S3-AgI chalcohalide glasses //
In book: NATO Science for Peace and Security
Series B: Physics and Biophysics. Chapter 25
“Nanotechnological basis for advanced sensors” ed.
by J.P. Riethmaier, P. Paunović, W. Kulisch,
C. Popov, P. Petkov, Berlin, Springer, p. 231-234
(2011).
40. A. Chrissanthopoulos, P. Jóvári, I. Kaban,
S. Gruner, T. Kavetskyy, J. Borc, W. Wang, J. Ren,
G. Chen, S.N. Yannopoulos, Structure of AgI-
doped Ge-In-S glasses: Experiment, reverse Monte
Carlo modelling, and density functional
calculations // J. Solid State Chem. (2012);
http://dx.doi.org/10.1016/j.jssc.2012.03.046
41. T.S. Kavetskyy, O. Šauša, V.F. Valeev, V.I. Nuzhdin,
N.M. Lyadov, A.L. Stepanov, Raman, positron
annihilation and Doppler broadening spectroscopy of
gamma-irradiated and Cu-ion implanted
Ge15.8As21S63.2 glass // In book: Coherent optics and
optical spectroscopy: XV Intern. junior sci. school,
24-26 October 2011. Ed. by M.Kh. Salakhov. Kazan,
Kazan Univ., 15, p. 86-89 (2011).
42. T. Kavetskyy, M. Vakiv, O. Shpotyuk, Charged
defects in chalcogenide vitreous semiconductors
studied with combined Raman scattering and PALS
methods // Radiation Measurements, 42, p. 712-
714 (2007).
43. T. Kavetskyy, K. Kolev, V. Boev, P. Petkov,
T. Petkova, A.L. Stepanov, Nanovoids in glasses
and polymers probed by positron annihilation
lifetime spectroscopy // In book: NATO Science for
Peace and Security Series B: Physics and
Biophysics. Chapter 11 “Nanotechnological basis
for advanced sensors”, ed. by J.P. Riethmaier,
P. Paunović, W. Kulisch, C. Popov, P. Petkov.
Berlin, Springer, p. 103-110 (2011).
Semiconductor Physics, Quantum Electronics & Optoelectronics, 2012. V. 15, N 4. P. 310-320.
PACS 61.05.cp, 61.43.Fs, 61.80.Ed
Radiation/annealing-induced structural changes
in GexAs40(xS60 glasses as revealed from high-energy synchrotron
X-ray diffraction measurements
T.S. Kavetskyy1, V.M. Tsmots1, A.L. Stepanov2,3
1Ivan Franko Drohobych State Pedagogical University,
Solid-State Microelectronics Laboratory,
24, I. Franko str., 82100 Drohobych, Ukraine
2Kazan Physical-Technical Institute, Russian Academy of Sciences,
10/7 Sibirskiy trakt, 420029 Kazan, Russian Federation
3Kazan Federal University, 18, Kremlyovskaya str., 420008 Kazan, Russian Federation
Abstract. Local atomic structure of GexAs40(xS60 glasses (x = 16, 24, 32, and 36) has been investigated in the (-irradiated (2.41 MGy dose) and annealed after (-irradiation states by using the high-energy synchrotron X-ray diffraction technique. The accumulated dose of 2.41 MGy is chosen to be close to the known in literature focal point ((2.0 MGy) for the system tested, at which the (-irradiation-induced optical (darkening) effect does not depend on the composition. It is established that the first sharp diffraction peak (FSDP) is located at around
1
Å
1
.
1
-
in the structure factors S(Q) of all the alloys studied. The FSDP position is found to be constant on radiation/annealing treatment, but the intensity of the FSDP reveals changes under irradiation/annealing only for the compositions with x = 16 and 24. The radiation/annealing-induced changes are also observed on the pair distribution functions in the first and second coordination shells for these compounds. Practically invisible effects on the FSDP and pair distribution functions are found for the alloys with x = 32 and 36. The radiation/annealing-induced structural changes detected mainly in the
S
As
-
sub-system of the glasses examined are well explainable within the Tanaka approach for interpretation of the photo-induced structural changes and related phenomena in As2S3 chalcogenide glass and similar materials.
Keywords: chalcogenide glasses, structure, X-ray diffraction, radiation modification.
Manuscript received 20.06.12; revised version received 15.08.12; accepted for publication 17.10.12; published online 12.12.12.
1. Introduction
The concept of coordination defects or valence alternation pairs (VAPs) in chalcogenide glasses is a fundamental and topical problem for understanding the structure and properties of these materials. Nevertheless, there are a lot of contradictions between researches in application of the VAP concept for explanation of different processes and phenomena in chalcogenide glasses. For instance, Dembovskii et al. [1] showed that the generally accepted concept of VAPs must be reexamined, since formation of pairs of separated charged point defects of the type
+
3
C
and
-
1
C
requires too much energy. On the other hand, the authors have shown by analogy with a-Se that centers connected by a strong bond can coexist in the form of rigid VAP dipoles. It was also found in [1] that nonrigid, metastable, hypervalent configurations (HVCs) exist in the form of HVC dipoles, which are neutral and diamagnetic in the ground state and lie below
0
1
C
on the energy scale.
Recently, Munzar and Tichy [2] have reported that kinetics of photo-darkening of amorphous As2S3 and a-As2Se3 thin films follows a single exponential, but the magnitude and the rate of the process is higher in the case of As2S3. The authors found out explanation for these facts estimating the probability of breaking of
S
As
-
and
Se
As
-
bonds on illumination. They showed that in the case of a-As2S3 around two bonds can be broken from each 2000
S
As
-
bonds, whereas in the case of a-As2Se3 around two bonds can be broken only for each 108
Se
As
-
bonds. It means the probability of photo-induced bond breaking in a-As2S3 film is much higher than that for a-As2Se3 film. As a result, it has been concluded in [2] that photo-darkening in a-As2S3 is accompanied by changes in short-range order interactions, while photo-darkening in a-As2Se3 is accompanied rather by changes in Coulomb interactions in an agreement with “slip motion of the layers” model introduced by Shimakawa et al. [3]. The estimated probability for a-As2S3 corresponds to the existence of concentration of defects at the level less than 1% of all atomic sites. Is this level of concentration of defects enough to be identified using a experimental technique like X-ray diffraction (XRD), which can provide direct structural information?
Tanaka [4] mentioned that reversible photo-induced phenomena, involving structural changes at atomic sites of
3
18
17
cm
10
-
10
-
(approximately ppm order [5]), exist in tetrahedral and chalcogenide systems. The density is comparable to that of point defects in crystals, and it is far below a detection limit of the XRD technique. Thus, mechanisms of these phenomena are largely speculative, especially, when related sites are ESR-inactive. However, there are several photo-induced phenomena involving atomic sites of (1% [5] and these kinds of phenomena have only been detected for chalcogenide glasses. If considering all the photo-induced phenomena (see Table 1 in [4]) involving atomic sites less and more than (
3
20
cm
10
-
or (1% of the total atom density, these phenomena can be both irreversible and reversible. The irreversible phenomena can involve greater atom numbers, since the changes occur towards more stable atomic structures (see Table 1 in [4]); then, why should the atomic sites be less than 1% in the reversible changes according to the Tanaka model? This fact is considered [4] as follows: “The density of 1% reads one photo-induced atomic site per cube with a side length of 5-6 atoms, which is 1-3 nm, depending on the atomic bonds involved, i.e. covalent and/or van der Waals bonds. The atomic density of defects 1% is the limit arising from the structures that can localize photo-induced strains. The critical length of 1-3 nm is comparable to the medium-range structural length in chalcogenide glasses”. According to the Tanaka model, the photo-structural changes on the medium-range order scale may be considered as a signature of photo-induced defect formation with the density less than 1% per cube with a side length of 5-6 atoms (1-3 nm). This is indeed observed [4] in the case of bulk glass As2S3 using the XRD method (the medium-range order is exemplified by the first sharp diffraction peak (FSDP)). The photo-structural changes may be explained in terms of defect models, presuming creation of some kinds of defects, and a non-defect or distortion model, postulating randomness increase in normal bonding configurations; although structural changes interpreted within the distortion model appear to be consistent with experimental observation of the FSDP weakening and broadening on illumination [4].
In contrast to the intensive study of photo-structural changes in chalcogenide glasses using the XRD method, less information and lack of our knowledge to understand (-irradiation-induced structural changes in these materials are available, although, there are some methodological advantages to XRD study of (-irradiation-induced effects as compared to the photo-induced ones. First, in the case of photo-induced phenomena [4], illumination and diffraction measurements should be performed in-situ, which is important to exclude thermal expansion effects and to detect minute changes. While for radiation-induced phenomena, (-irradiation produces changes inside the whole glass matrix, but not in the spot as for laser illumination, and, thus, an in-situ experiment is not required and it is not possible to be performed experimentally in the case of (-irradiation. Second, the investigation of radiation-modified structure of a glass is important within ex-situ measurements in order to find how structure is changed after a long period of time following radiation treatment of a sample (static radiation-induced effects [
8
6
-
]). Third, in contrast to photo-induced phenomena (irreversible or reversible), (-irradiation-induced phenomena are mainly always reversible with annealing at the temperature 40-50 K below the glass transition temperature Tg [9, 10], which allows to investigate the radiation/annealing-induced structural changes for the same sample measured first as (-irradiated and than as annealed after (-irradiation under the same experimental conditions.
The purpose of this work is to study the radiation/annealing-induced structural changes in GexAs40–xS60 (x = 16, 24, 32, and 36) glasses using the high-energy synchrotron XRD technique. Among a number of chalcogenides, as far as we know, only this system demonstrates the focal point ((2.0 MGy), at which the (-irradiation-induced optical (darkening) effect does not depend on the composition [11]. We believe that the glasses examined should also exhibit this effect at the accumulated dose close to 2.0 MGy. The origin of the focal point is not clear, and we suggest that the precise high-energy synchrotron XRD study of the GexAs40–xS60 glasses in the (-irradiated and annealed after (-irradiation states under the same experimental conditions will help us to obtain more information and to cast light on this issue.
2. Experimental
The bulk glasses of GexAs40(xS60 system at x = 16, 24, 32, and 36 were prepared from elements of 99.9999% purity in evacuated silica ampoules by standard melt quenching procedure as described elsewhere [12]. As-prepared glasses were cut to the disk-like specimens and polished to a high optical quality. Then, in order to remove possible mechanical stresses formed after synthesis, the samples were annealed at about 20-30 K below the glass transition temperature [12] (Tg = 530 K for Ge16As24S60, 620 K for Ge24As16S60, 670-675 K for Ge32As8S60, and 682 K for Ge36As4S60).
Radiation treatment of the glasses was performed by (-quanta (average energy E = 1.25 MeV) with the accumulated dose 2.41 MGy (close to the focal point [11] near 2.0 MGy) at normal conditions of stationary radiation field created in a closed cylindrical cavity by a number of circularly established 60Co radioisotope capsules. No special measures were taken to prevent uncontrolled thermal annealing of the samples, but maximum temperature in the irradiating camera did not exceed 320-330 K during prolonged (-irradiation (about 30 days), providing the absorbed dose power P < 5 Gy/s. The (-irradiated samples were measured for more than 2 months after (-irradiation (static component of radiation-induced effects [6-8]). The (-irradiated samples were annealed at the temperature 40-50 K below Tg following the previous results on the reversible (-irradiation-induced optical (darkening) effects in the
60
40
S
As
Ge
x
x
-
glasses with thermal annealing [9, 10].
High-energy synchrotron X-ray diffraction experiments were carried out at the BW5 experimental station at HASYLAB, DESY in Hamburg, Germany. All the samples were examined in transmission geometry. The energy of synchrotron radiation was 98.9 keV. Scattered intensity was measured between 0.5 and
1
Å
19
-
. Raw data were corrected for detector dead-time, polarization, absorption and variation in detector solid angle [13]. The scattering intensity was converted into the coherent scattering intensity per atom in electronic units by using the Krogh-Moe-Norman method [14, 15]. Compton scattering was corrected using the values given by Balyuzi [16]. Faber-Ziman [17] total structure factor S(Q) was calculated from the scattering intensity as
(
)
(
)
(
)
(
)
{
}
(
)
2
2
2
.
.
Q
f
Q
f
Q
f
Q
I
Q
S
coh
u
e
-
-
=
(1)
with
(
)
(
)
Q
f
c
Q
f
i
i
i
2
2
å
=
,
(
)
(
)
Q
f
c
Q
f
i
i
i
å
=
,
(2)
where ci is the molar fraction and fi(Q) is the total atomic scattering factor of the i-th component of the glass.
The total pair distribution function g(r) was obtained via transformation
[
]
Q
d
Qr
Q
S
Q
r
ρ
π
r
g
)
sin(
1
)
(
2
1
1
)
(
0
0
2
ò
¥
-
+
=
,
(3)
where (0 is the average number density.
It is known that the impact of chalcogenide glasses induced by external influence (i.e. (-irradiation, hydrostatic pressure or illumination) on the experimental structure factors is rather small [4,
21
18
-
]. Therefore, the experimental error should be minimized for correct investigation of such phenomena. In the present study, like in the case of
60
40
S
Sb
Ge
x
x
-
glasses [18], all XRD experiments were carried out within a couple of hours; the specimens were of the same thickness; they were fixed in a holder moving horizontally, providing practically identical sample adjustment during measurements. The samples were positioned in the holder at the same position to be measured first as (-irradiated and than as annealed after (-irradiation. All this helped to reduce the random error to a minimum.
3. Results
Experimental structure factors S(Q) for the investigated
60
40
S
As
Ge
x
x
-
glasses in (-irradiated and annealed after (-irradiation states are shown in Fig. 1a. Oscillations in S(Q) persist up to high Q values for all the samples. The first sharp diffraction peak (FSDP) exists on the S(Q) for all the alloys studied (Fig. 1b). The intensity of the FSDP, measured as a relation of the intensities at the maximum and at the tail of peak (IFSDP = S(Q)max/S(Q)min), for the annealed samples demonstrates non-monotonic trend from 4.38 at x = 16 to 4.06 at x = 36 reaching a maximum value of 4.56 at x = 32. Position of the FSDP shifts continuously from
1
Å
13
.
1
-
(x = 16) to
1
Å
01
.
1
-
(x = 36). It should be noted that the values of QFSDP =
1
Å
08
.
1
-
and
1
Å
01
.
1
-
for x = 24 and 36 of the
60
40
S
Sb
Ge
x
x
-
glasses agree with the values of QFSDP =
1
Å
08
.
1
-
and
1
Å
02
.
1
-
for x = 25 and 35 of
60
40
S
Sb
Ge
x
x
-
glasses [18]. This non-monotonic trend in the FSDP intensity and monotonic one in the FSDP position detected for the annealed
60
40
S
As
Ge
x
x
-
glasses have also been observed in other non-stoichiometric
x
x
x
2
100
S
As
Ge
-
and
y
x
y
x
-
-
100
S
As
Ge
glasses in the course of neutron and X-ray diffraction studies [22, 23].
For all the compositions studied, positions of maxima and minima of the structure factors of (-irradiated and annealed glasses coincide with those of radiation-modified Ge25Sb15S60 and Ge35Sb5S60 glasses. Main difference between (-irradiated and annealed glasses is observed only in the intensity of the FSDP for As-enriched composition Ge16As24S60 for which the pre-peak becomes weaker and broader under irradiation (Fig. 1b) similarly to the binary As2S3 glass [19]. This difference is notably larger than the total experimental error of the structure factor, which is estimated to be below 1% in the low Q-part of S(Q) as shown in [18].
Fig. 2a shows the pair distribution functions g(r) for the investigated
60
40
S
As
Ge
x
x
-
glasses, both in the (-irradiated and annealed after (-irradiation states. For a better comparison, parts of the pair distribution functions g(r) corresponding to the first and second (insertion) coordination shells are plotted in Fig. 2b. For all the alloys studied, a peak on g(r) at r = 2.26-2.27 Å can be attributed to the nearest neighbor correlations. On the pair distribution functions of
60
40
S
As
Ge
x
x
-
, there is either a small peak (for x = 16 and 24) or a shoulder (for x = 32 and 36) at r ( 2.60-2.65 Å. As this distance does not correlate with any possible interatomic distance of any two glass constituents, most probably this feature (peak, shoulder) is caused by the termination of the experimental data at a final value of the diffraction vector. It is known that false oscillations appear on the pair distribution function near the main peak due to the termination effect [24]. A maximum at r = 3.55-3.60 Å reflects the second coordination sphere. Also, a hump at r = 2.99 Å is observed on g(r) of all the investigated samples in the second coordination shell like to the samples of GexSb40–xS60 with x = 25 and 35 [18]. But due to the risk that this hump may come from the termination effect, we will not analyze this hump in further consideration.
Fig. 3 shows the observed peaks on g(r) located in the first and second coordination shells for the annealed samples of
60
40
S
As
Ge
x
x
-
system. One may clearly see that the first peak at r = 2.26-2.27 Å becomes weaker and broader with increasing x. The second peak r = 3.55-3.60 Å becomes weaker and broader with increasing x similar to the first peak. The shape of the second peak is different for the As-rich sample (xGe = 16) as compared to the Ge-rich samples (xGe = 24, 32 and 36), which have slightly narrower maximum.
The structural parameters such as intensity and position of the FSDP, as well as intensities and positions of the peaks g(r1) and g(r2) for
60
40
S
As
Ge
x
x
-
glasses are given in Table. The intensities of these structural parameters are also plotted in Fig. 4 as a function of x for better observation of their compositional dependence. The plots of the IFSDP, g(r1) and g(r2) as a function of x for both irradiated and annealed samples show non-monotonic trend with an extremum at x = 32.
Finally, for all the glasses studied, it is found that radiation impact results in weakening and broadening of the FSDP with the first peak at r = 2.26-2.27 Å and the second peak at r = 3.55-3.60 Å; the effect is the largest one for Ge16As24S60 (x = 16), smaller for Ge24As16S60 (x = 24), and practically invisible for Ge32As8S60 (x = 32) and Ge36As4S60 (x = 36) alloys.
Fig. 3. The observed peaks on g(r) located in the first and second coordination shells for the annealed samples of GexAs40–xS60 system. See the text for details.
Fig. 4. The intensities of the peaks (a) FSDP, measured as a ratio of the intensities at the maximum and at the tail of peak (IFSDP = S(Q)max/S(Q)min), (b) g(r1), and (c) g(r2) for the investigated GexAs40–xS60 glasses in (-irradiated (open cycles) and annealed after (-irradiation (closed cycles) states as a function of the composition x.
4. Discussion
Investigating the physical properties, in particular, optical bang gap Eg and structural compactness ( in the bulk glasses and thin films from
60
40
S
As
Ge
x
x
-
family in dependence on x or average coordination number Z (i.e., Z = (4x + 3(40(x) +2(60)/100, where 4, 3 and 2 stand for the coordination numbers of Ge, As, and S, respectively), Skordeva and Arsova [25] concluded that the peculiarities of the properties (e.g., a maximum on Eg for annealed films and a minimum on ( for bulk glasses) are caused by the topological structural 2D-3D phase transition according to the Tanaka model [26] from a two-dimensional (2D) layer-like structure to a three-dimensional (3D) cross-linked network at the average coordination number Z of about 2.67. Later Tichy and Ticha [27] reported on the possibility of chemical threshold at Z ( 2.7.
Stronski et al. [28] reported that the compactness ( is well sensitive to the structure of glass network and its compositional dependence is supposed to be connected with atomic rearrangements in the glass backbone. On the other hand, in the first approximation, the compactness ( is also a measure of free volume of glass [29]. It is interesting to note that the compactness ( for the GexAs40–xS60 glasses has attained a minimum value at Z = 2.72 (see Fig. 3 in [13]). Thus, the maximum free volume in the investigated
60
40
S
As
Ge
x
x
-
glasses is attained for alloy with x = 32 (Z = 2.72). Hence, it is reasonable to relate the features (plateau, extremum) observed in the composition trends of the FSDP intensity and those of the peaks g(r1) and g(r2) for alloy with x = 32 (Z = 2.72) with the maximum free volume and atomic rearrangements resulting in the topological or chemical threshold attained at Z ( 2.7 (Fig. 4). These findings may be considered as an evidence of the anomalous structural features on the short-range order (exemplified by the first and second neighbor correlations) and medium-range order (exemplified by the FSDP) scale in the vicinity of the topological or chemical threshold at Z ( 2.7.
Let us consider the radiation/annealing-induced structural changes detected on the FSDP and the pair distribution functions g(r) for the investigated glasses (Figs. 1, 2, 4 and Table).
The well observable weakening and broadening of the FSDP with the unchanged position under irradiation for the As-enriched glass Ge16As24S60 (x = 16) is similar to the radiation-induced changes [20] and photo-induced changes [4] in the FSDP intensity and position for the binary As2S3 glass. Thus, the mechanism of the radiation- and photo-induced structural changes on the medium-range order scale exemplified by the FSDP would be the same.
As it was mentioned in Introduction, according to the Tanaka model [4], the photo-structural changes on the medium-range order scale may be considered as a signature of photo-induced defect formation with the density less than 1% (i.e., one photo-induced atomic site per cube with a side length of 5-6 atoms). Thus, the radiation-induced changes observed on the medium-range order scale (FSDP) indicate formation of one radiation-induced atomic site per cube with a side length of 5-6 atoms (1-3 nm). According to the Tanaka model [4], with account of the term for the single radiation-induced atomic site (defect), we consider a strain produced by (-irradiation and confined in the cube leading finally to a radiation-induced metastable structural configuration, which can then relax into a stable structure with thermal relaxation induced by annealing (reversible changes). Producing the strain in chalcogenide glass matrix under (-irradiation is confirmed by the recent study of microindentation cracks in bismuth-doped arsenic selenide glasses [30]. In particular, it has been found that radial cracks around indentations are produced on the surfaces of the chalcogenide glass samples at loads exceeding the specific applied load Pcapp that somewhat increases under (-irradiation of samples even at the relatively low 0.76 MGy accumulated dose. Besides, the well known increase in microhardness of chalcogenide glass under (-irradiation may also be an additional confirmation for this ([31] and references therein).
The mechanism providing formation of radiation-induced strain can be considered using both defect models and non-defect or distortion model reported by Tanaka [4] to explain the photo-structural changes in As2S3 chalcogenide glass and similar materials. Although different known structural models could be applied to interpret the observed weakening and broadening of the FSDP under (-irradiation (Fig. 1b), we prefer more Tanaka’s explanation of the weakening and broadening of the FSDP on illumination within the distortion model ([4] and references therein). In this approach, there are two kinds of the structural changes involved in this model. On the one hand, plausible structural changes can be sought in the distortions in bond angles, dihedral angles, and van der Waals distances resulting in: (i) changes in the short-range order, (ii) the increase in the conduction band width and, consequently, decrease in the optical band gap (darkening effect), and (iii) the enhancement of the randomness in the medium-range structural order. On the other hand, the intermolecular distortion through bond-twisting motion of chalcogen atom is the second kind of the structural changes within the distortion model. Finally, according to the Tanaka model [4], these two kinds of structural changes are interrelated (thus, if an intermolecular bond is distorted on illumination, structural relaxation will necessarily occur, leading to appreciable angular distortions) and appear to be consistent with the weakening and broadening of the FSDP on illumination.
With account of the above mentioned, we suggest that the observed radiation-induced structural changes on the medium-range order scale (FSDP) in Ge16As24S60 (x = 16) glass are caused by distortion in bond angles, dihedral angles, van der Waals distances and intermolecular distortion through bond-twisting motion of chalcogen atom leading together to formation of radiation-induced defects with the density (1% ((
3
20
cm
10
-
), which annihilate with annealing through thermal relaxation of the radiation-induced metastable structural configuration (strain) to a more stable structure. As the changes in the FSDP are very small for Ge24As16S60 (x = 24) and invisible for Ge32As8S60 (x = 32) and Ge36As4S60 (x = 36), one may assume that the radiation-induced defects with the density (1% are probably not formed for the Ge-enriched glasses studied with dominant
S
Ge
-
correlations. In other words, we may conclude that the radiation/annealing-induced structural changes on the medium-range order scale for the
60
40
S
As
Ge
x
x
-
system occur mainly in the
S
As
-
sub-system.
The distortion model seems to be applicable for the interpretation of the radiation/annealing-induced structural changes on the short-range order scale exemplified by the first and second coordination shells on the pair distribution functions g(r) as well. Let us consider this in detail.
The first peaks on g(r) at 2.26 and 2.27 Å for the
60
40
S
As
Ge
x
x
-
glasses can be attributed to the
S
Ge
-
and
S
As
-
correlations. The value 2.26 Å for Ge-enriched samples (x = 24, 32, and 36) is consistent with 2.21-2.24 Å distances corresponding to
S
Ge
-
first neighbors in the germanium sulphide glasses [32] and with 2.24-2.27 Å distances corresponding to
S
Ge
-
first neighbors in the mixed germanium-arsenic sulphide glasses [23, 24], as well as the value 2.27 Å for As-enriched sample (x = 16) is consistent with 2.27-2.30 Å distances corresponding to
S
As
-
first neighbors in the arsenic trisulphide glass [20, 33-35] and with 2.17-2.27 Å distances corresponding to
S
As
-
first neighbors in the mixed
As
Ge
-
sulphide glasses [23, 24].
As(As (2.43-2.53 Å [23, 24, 32]),
Ge
Ge
-
(2.46 Å [36]) and
S
S
-
(2.0-2.04 Å [23, 32]) neighbor correlations (if exist) cannot be resolved on the pair distribution functions as they can simply be covered by the peak from
S
Ge
-
or
S
As
-
contributions. Besides, like for
60
40
S
Sb
Ge
x
x
-
[19], we suppose that
S
S
-
bonds are very improbable in the
60
40
S
As
Ge
x
x
-
glasses.
It is difficult to resolve the peak located at 3.55-3.6 Å on the pair distribution functions g(r). In
60
40
S
Sb
Ge
x
x
-
family, Kakinuma et al. [37] attributed the peak at 3.61 Å to the secondary partial correlations
Ge
Ge
-
,
Sb
Ge
-
,
Sb
Sb
-
, and
S
S
-
. The structural study of
S
Ge
-
glasses [32] shows that the broad peak at ~3.6 Å corresponds to the second
S
S
-
and
Ge
Ge
-
correlations in the corner-shared GeS4 tetrahedra (
4
GeS
CS
-
). The structural study of As2S3 glass [20,
36
33
-
] indicates that the broad peak at ~3.5 Å corresponds to the second neighbor distances
S
S
-
and
As
As
-
in the corner-shared AsS3 pyramids. Brabec [33] reported that in As2S3 glass the
As
As
-
second-neighbor distance is 3.52±0.01 Å and the
S
S
-
second-neighbor distance is 3.5±0.1 Å. Soyer-Uzun et al. [23, 24] showed that for the
x
x
x
2
100
S
As
Ge
-
glasses a peak centered at (3.4 Å can be readily correlated to the metal-metal next-nearest neighbors that are connected through S atom, namely
Ge
S
Ge
-
-
,
As
S
Ge
-
-
, and
As
S
As
-
-
linkages, as well as a peak centered at (3.5 Å for the
y
x
y
x
-
-
100
S
As
Ge
glasses corresponds primarily to
As
As
-
and
Ge/As
Ge
-
next-nearest neighbors in the
As
S
As
-
-
and
Ge/As
S
Ge
-
-
linkages. In principle, all secondary partial correlations
Ge
Ge
-
,
As
Ge
-
,
As
As
-
and
S
S
-
may exist in
60
40
S
As
Ge
x
x
-
family within the range of 3.5-3.6 Å distances. Taking into account different shapes of the second peak on g(r) at r = 3.55 Å (for x = 16) and r = 3.6 Å (for x = 24, 32, 36) in Fig. 3, it is reasonable to separate secondary partial correlations
S
S
-
and
As
As
-
for As-enriched sample (x = 16) and
S
S
-
and
Ge
Ge
-
for Ge-enriched samples (x = 24, 32, 36).
Similar to the GexSb40(xS60 glasses [19, 37], the intensity of the second peak g(r2) for Ge-enriched samples increases, and its position r2 shifts to lower r values with increasing the Ge concentration with maximum for Ge32As8S60 glass (Table). The ratio of the peak positions at 3.6 Å (second neighbor correlations) and 2.26 Å (first neighbor correlations) is 1.59. This is somewhat lower than the value of
3
8
= 1.63 for perfect tetrahedra, what can be a result of GeS4/2 unit deformation, probably, due to the existance of
Ge
Ge
-
bonding in the ethane-like units
3/2
3/2
GeS
Ge
S
-
(Ge2S6/2) in non-stoichiometric alloys of
60
40
S
As
Ge
x
x
-
or
3
2
3
2
S
Ge
S
As
-
family [38]. Recently, the existence of the ethane-like units
3/2
3/2
GeS
Ge
S
-
has also been confirmed for the technologically important multicomponent
AgI
S
In
GeS
3
2
2
-
-
chalcohalide glasses [39] by using combination of XRD, EXAFS, reverse Monte Carlo modelling, Raman scattering and density functional theoretical calculations [40].
It is noteworthy that the radiation/annealing-induced changes in the main peak g(r1) correlate well with those for the FSDP (see Figs 1b, 2b and 4), i.e., the first peak g(r1) reveals the largest changes (weakening and broadening) under (-irradiation mainly for As-enriched Ge16As24S60 (x = 16) alloy, smaller changes for Ge24As16S60 (x = 24) and practically no changes for Ge32As8S60 (x = 32) and Ge36As4S60 (x = 36) compounds. The second peak g(r2) exhibits the largest effect (weakening and broadening) under (-irradiation for As-enriched Ge16As24S60 (x = 16) glass as well. Thus, we assume like to the medium-range order (FSDP) that the radiation/annealing-induced structural changes on the short-range order scale (first and second coordination shells) are plausibly connected with the structural transformations in the
S
As
-
sub-system. Tanaka’s approach within the distortion model explains also weakening and broadening of the first and second peaks on g(r) under irradiation due to intermolecular distortion through bond-twisting motion of chalcogen atom, which is also interrelated with the distortion in bond angles, dihedral angles, and van der Waals distances.
It should be noted that the recent [41] Doppler broadening spectroscopy study of
(
)
(
)
x
x
-
1
2
3
2
GeS
S
As
glasses (As2S3 (x = 1.0), Ge9.5As28.6S61.9 (x = 0.6), Ge15.8As21S63.2 (x = 0.4), and Ge23.5As11.8S64.7 (x = 0.2)) in the unirradiated (annealed) and (-irradiated states showed that the defect structure of Ge15.8As21S63.2 glass is significantly different as compared to other alloys (obviously, as a result of different mechanisms (defect or non-defect ones) of radiation-structural changes). Kavetskyy et al. [42] reported that the charged coordination topological defects are quite responsible for the defect mechanism of radiation-structural changes in the case of Ge15.8As21S63.2 glass. While, likely to photo-structural changes, the non-defect mechanism within the Tanaka distortion model is supposed to be responsible for the radiation-structural changes in the As2S3 alloy and similar materials. The void-species nanostructure (nanovoids) of the As2S3-based glasses studied with positron annihilation lifetime spectroscopy [43] should be taken into account for further consideration of validity of Tanaka’s distortion model in explanation of radiation-structural changes in chalcogenides.
In summary, with account of the results obtained, we speculate that the existance of the focal point ((2.0 MGy) for the investigated
60
40
S
As
Ge
x
x
-
glasses, at which the (-irradiation-induced optical (darkening) effect does not depend on the composition [11], can simply be related with the dominant radiation-structural changes in the
S
As
-
sub-system, and embedding the Ge atoms into
S
As
-
glass matrix does not affect their mechanism, since the radiation-structural changes in the
S
Ge
-
sub-system are invisible on both short- and medium-range order scales. Finally, we would like to state that the alternative interpretation of the radiation/annealing-induced structural changes reported here may be also proposed.
5. Conclusions
Impact of (-irradiation (2.41 MGy dose) and subsequent annealing on the atomic structure of
60
40
S
As
Ge
x
x
-
glasses (x = 16, 24, 32, 36) is studied using high-energy XRD measurements. Analysis of the experimental structure factors and pair distribution functions has revealed the differences related to the structural changes at the short-range order scale (exemplified by the first and second nearest neighbor correlations) and medium-range order scale (exemplified by the FSDP). Nonlinear compositional trends in the IFSDP, g(r1) and g(r2) values with features (plateau, extremum) nearby the topological structural phase transition [26] or chemical threshold [27] at the average coordination number Z ( 2.7 (x = 32) are detected for the both (-irradiated and annealed alloys.
The FSDP position is found to be constant on radiation/annealing treatment, but the intensity of the FSDP reveals changes under irradiation/annealing only for the compositions with x = 16 and 24. The radiation/annealing-induced changes are also observed on the pair distribution functions in the first and second coordination shells for these compounds. Practically invisible effects on the FSDP and pair distribution functions are found for the alloys with x = 32 and 36. The radiation/annealing-induced structural changes detected mainly in the
S
As
-
sub-system of the glasses examined can be well explained within the Tanaka approach [4] for interpretation of the photo-induced structural changes and related phenomena in the As2S3 chalcogenide glass and similar materials.
Existence of the focal point ((2.0 MGy) for the
60
40
S
As
Ge
x
x
-
glasses, at which the (-irradiation-induced optical (darkening) effect does not depend on the composition [11], can simply be related with the dominant radiation-structural changes in the
S
As
-
sub-system and embedding the Ge atoms into the
S
As
-
glass matrix does not affect their mechanism, since the radiation-structural changes in the
S
Ge
-
sub-system are invisible on both short- and medium-range order scales.
Acknowledgements
The authors would like to thank Dr. Ivan Kaban (IFW Dresden, Germany) for his help with high-energy synchrotron XRD measurements, Dr. Pal Jóvári (Research Institute for Solid State Physics and Optics, Budapest, Hungary) for his help with experimental data treatment, Prof. Walter Hoyer (Institute of Physics, TU Chemnitz, Germany) and Prof. Guorong Chen (East China University of Science and Technology, Shanghai, China) for stimulating discussions. The investigated samples used for measurements were prepared within joint research projects (#0106U007386 and #0109U007446c) between Ivan Franko Drohobych State Pedagogical University (Drohobych, Ukraine) and Scientific Research Company “Carat” (Lviv, Ukraine) supported by the Ministry of Education and Science of Ukraine (#0106U007385 and #0109U007445). T.S.K. acknowledges DAAD for support of his research work at TU Chemnitz (Germany) and Deutsches Elektronen-Synchrotron DESY for support of the experiments performed at HASYLAB (Hamburg, Germany). T.S.K. and V.M.T. acknowledge national project (#0111U001021) supported by the Ministry of Education and Science, Youth and Sport of Ukraine. A.L.S. grateful to the Alexander von Humboldt Foundation, DFG and DAAD (Germany). Support from the Ukrainian-Russian projects funded by the State Fund for Fundamental Researches of Ukraine (#F40.2/019) and the Ministry of Education and Science of the Russian Federation (#02.740.11.0797) and the Russian Foundation for Basic Research (#11-02-90420-Ukraine, #11-02-91341-Germany and #12-02-00528-a) is also gratefully acknowledged.
References
1. S.A. Dembovsky, A.S. Zyubin, F.V. Grigor’ev, Modeling of hypervalent configurations, valence alternation pairs, deformed structure, and properties of a-S and a-As2S3 // Semiconductors, 32(8), p. 843-849 (1998).
2. M. Munzar, L. Tichy, Kinetics of photo-darkening abd self-bleaching in amorphous As2S3 and As2Se3 thin films // Phys. Stat. Sol. (RRL), 1(2), p. R74-R76 (2007).
3. K. Shimakawa, N. Yoshida, A. Ganjo, Y. Kuzukawa, J. Singh, A model for the photostructural changes in amorphous chalcogenides // Philos. Mag. Lett., 77(3), p. 153-158 (1998).
4. K. Tanaka, Photoinduced structural changes in amorphous semiconductors // Semiconductors, 32(8), p. 861-866 (1998).
5. K. Shimakawa, A. Kolobov, S.R. Elliott, Photoinduced effects and metastability in amorphous semiconductors and insulators // Adv. Phys., 44(6), p. 475-588 (1995).
6. T.S. Kavetskyy, Impact of the sample thickness and (-irradiation dose on the occurrence of radiation-induced optical effects in chalcogenide vitreous semiconductors of the Ge-Sb-S system // Semiconductors, 45(4), p. 499-502 (2011).
7. O.I. Shpotyuk, R.Ya. Golovchak, A.P. Kovalskiy, T.S. Kavetskyy, Time and temperature stability of radiation-induced changes of optical properties in ternary systems of chalcogenide vitreous semiconductors // Functional Materials, 10(2), p. 317-321 (2003).
8. O.I. Shpotyuk, T.S. Kavetskyy, A.P. Kovalskiy, V. Pamukchieva, Gamma-irradiation effect on the optical properties of
60
40
S
Sb
Ge
x
x
-
chalcogenide glasses // Proc. SPIE, 4415, p. 278-283 (2001).
9. O. Shpotyuk, A. Kovalskiy, T. Kavetskyy, R. Golovchak, Post-irradiation thermally stimulated recovering effects in some ternary chalcogenide glasses // J. Optoelectron. Adv. Mater., 5(5), p. 1169-1179 (2003).
10. O.I. Shpotyuk, A.P. Kovalskiy, T.S. Kavetskyy, R.Ya. Golovchak, Threshold restoration effects in (-irradiated chalcogenide glasses // J. Non-Cryst. Solids, 351, p. 993-997 (2005).
11. V. Balitska, R. Golovchak, A. Kovalskiy, E. Skordeva, O.I. Shpotyuk, Effect of Co60 (-irradiation on the optical properties of As-Ge-S glasses // J. Non-Cryst. Solids, 326&327, p. 130-134 (2003).
12. A. Feltz, Amorphous and Vitreous Inorganic Solids. Moscow, Mir, 1986 (in Russian).
13. H.F. Poulsen, J. Neuefeind, H.-B. Neumann, J.R. Schneider, M.D. Zeidler, Amorphous silica studied by high energy X-ray diffraction // J. Non-Cryst. Solids, 188, p. 63-74 (1995).
14. J. Krogh-Moe, A method for converting experimental X-ray intensities to an absolute scale // Acta Cryst., 9, p. 951-953 (1956).
15. N. Norman, The Fourier transform method for normalizing intensities // Acta Cryst., 10, p. 370-373 (1957).
16. H.H.M. Balyuzi, Analytic approximation to incoherently scattered X-ray intensities // Acta Cryst. A, 31, p. 600-602 (1975).
17. T.E. Faber, J.M. Ziman, A theory of the electrical properties of liquid metals // Philos. Mag., 11(109), p. 153-173 (1965).
18. T. Kavetskyy, O. Shpotyuk, I. Kaban, W. Hoyer, Radiation-modified structure of Ge25Sb15S60 and Ge35Sb5S60 glasses // J. Сhem. Phys., 128(24), 244514(1-8) (2008).
19. T. Kavetskyy, O. Shpotyuk, I. Kaban, W. Hoyer, Atomic- and void-species nanostructures in chalcogenide glasses modified by high energy gamma-irradiation // J. Optoelectron. Adv. Mater., 9(10), p. 3247-3252 (2007).
20. H. Hamanaka, S. Minomura, K. Tsuji, Comparative studies of pressure and photo induced structural changes in As2S3 glass // J. Non-Cryst. Solids, 137&138, p. 977-980 (1991).
21. S.R. Elliott, Scattering studies of photostructural changes in chalcogenide glasses // J. Non-Cryst. Solids, 59&60, p. 899-908 (1983).
22. S. Soyer-Uzun, S. Sen, C.J. Benmore, B.G. Aitken, Compositional variation of short- and intermediate-range structure and chemical order in Ge-As sulfide glasses: A neutron diffraction study // J. Phys. Chem. C, 112, p. 7263-7269 (2008).
23. S. Soyer-Uzun, S. Sen, B.G. Aitken, Newtork vs molecular structural characteristics of Ge-doped arsenic sulfide glasses: A combined neutron/X-ray diffraction, extended X-ray absorption fine structure, and Raman spectroscopic study // J. Phys. Chem. C, 113, p. 6231-6242 (2009).
24. R. Kaplow, S.L. Strong, B.L. Averbach, Radial density functions for liquid mercury and lead // Phys. Rev., 138, p. A1336-A1345 (1965).
25. E.R. Skordeva, D.D. Arsova, A topological phase transition in ternary chalcogenide films // J. Non-Cryst. Solids, 192&193, p. 665-668 (1995).
26. K. Tanaka, Structural phase transitions in chalcogenide glasses // Phys. Rev. B, 39(2), p. 1270-1279 (1989).
27. L. Tichy, H. Ticha, Is the chemical threshold in certain chalcogenide glasses responsible for the threshold at the mean coordination number of approximately 2.7? // Phil. Mag. B, 79(2), p. 373-380 (1999).
28. A.V. Stronski, M. Vlček, P.F. Oleksenko, Fourier Raman spectroscopy studies of the As40S60–xSex glasses // Semiconductor Physics, Quantum Electronics & Optoelectronics, 4(3), p. 210-213 (2001).
29. I.P. Kotsalas, D. Papadimitriou, C. Raptis, M. Vlcek, M. Frumar, Raman study of photostructural changes in amorphous
6
.
0
4
.
0
S
Sb
Ge
x
x
-
// J. Non-Cryst. Solids, 226, p. 85-91 (1998).
30. K. Sangwal, J. Borc, T. Kavetskyy, Study of microindentation cracks in bismuth-doped arsenic selenide glasses // J. Non-Cryst. Solids, 357, p. 3117-3122 (2011).
31. O.I. Shpotyuk, Radiation-induced effects in chalcogenide vitreous semiconductors // Semiconducting Chalcogenide Glass I: Glass Formation, Structure, and Stimulated Transformations in Chalcogenide Glasses, Semiconductors and Semimetals, edited by R. Fairman and B. Ushkov, Amsterdam-Boston-London-New York-Oxford-Paris-San Diego-San Francisco-Singapore-Sydney-Tokyo, Elsevier Academic Press, 78, p. 215-260 (2004).
32. E. Bychkov, M. Miloshova, D.L. Price, C.J. Benmore, A. Lorriaux, Short, intermediate and mesoscopic range order in sulfur-rich binary glasses // J. Non-Cryst. Solids, 352, p. 63-70 (2006).
33. C.J. Brabec, Structural model of amorphous arsenic sulfide // Phys. Rev. B, 44(24), p. 13332-13342 (1991).
34. T.G. Fowler, S.R. Elliott, Continuos random network models for a-As2S3 // J. Non-Cryst. Solids, 92, p. 31-50 (1987).
35. F. Shimojo, K. Hoshino, Y. Zempo, Intermediate-range order in liquid and amorphous As2S3 by ab initio molecular-dynamics simulations // J. Non-Cryst. Solids, 312-314, p. 388-391 (2002).
36. W. Zhou, M. Pasesler, D.E. Sayers, Structure of germanium-selenium glasses: An X-ray-absorption fine-structure study // Phys. Rev. B, 43(3), p. 2315-2321 (1991).
37. F. Kakinuma, T. Fukunaga, K. Suzuki, Structural study of GexSb40–xS60 (x = 10, 20 and 30) glasses // J. Non-Cryst. Solids, 353, p. 3045-3048 (2007).
38. D. Arsova, E. Skordeva, D. Nesheva, E. Vateva, A. Perakis, C. Raptis, A comparative Raman study of the local structure in (Ge2S3)(As2S3)1–x and (GeS2)(As2S3)1–x glasses // Glass Phys. Chem., 26(3), p. 247-251 (2000).
39. T. Kavetskyy, N. Pavlyukh, V. Tsmots, W. Wang, J. Ren, G. Chen, A.L. Stepanov, IR impurity absorption in GeS2-In2S3-AgI chalcohalide glasses // In book: NATO Science for Peace and Security Series B: Physics and Biophysics. Chapter 25 “Nanotechnological basis for advanced sensors” ed. by J.P. Riethmaier, P. Paunović, W. Kulisch, C. Popov, P. Petkov, Berlin, Springer, p. 231-234 (2011).
40. A. Chrissanthopoulos, P. Jóvári, I. Kaban, S. Gruner, T. Kavetskyy, J. Borc, W. Wang, J. Ren, G. Chen, S.N. Yannopoulos, Structure of AgI-doped Ge-In-S glasses: Experiment, reverse Monte Carlo modelling, and density functional calculations // J. Solid State Chem. (2012); http://dx.doi.org/10.1016/j.jssc.2012.03.046
41. T.S. Kavetskyy, O. Šauša, V.F. Valeev, V.I. Nuzhdin, N.M. Lyadov, A.L. Stepanov, Raman, positron annihilation and Doppler broadening spectroscopy of gamma-irradiated and Cu-ion implanted Ge15.8As21S63.2 glass // In book: Coherent optics and optical spectroscopy: XV Intern. junior sci. school, 24-26 October 2011. Ed. by M.Kh. Salakhov. Kazan, Kazan Univ., 15, p. 86-89 (2011).
42. T. Kavetskyy, M. Vakiv, O. Shpotyuk, Charged defects in chalcogenide vitreous semiconductors studied with combined Raman scattering and PALS methods // Radiation Measurements, 42, p. 712-714 (2007).
43. T. Kavetskyy, K. Kolev, V. Boev, P. Petkov, T. Petkova, A.L. Stepanov, Nanovoids in glasses and polymers probed by positron annihilation lifetime spectroscopy // In book: NATO Science for Peace and Security Series B: Physics and Biophysics. Chapter 11 “Nanotechnological basis for advanced sensors”, ed. by J.P. Riethmaier, P. Paunović, W. Kulisch, C. Popov, P. Petkov. Berlin, Springer, p. 103-110 (2011).
(a)
� �
� �
(b)
� �
� �
Fig. 1. (a) The total structure factors S(Q) for the samples of the investigated GexAs40–xS60 system in (-irradiated (the curves for (-irradiated state is shifted (+1) for clarity) and annealed after (-irradiation states; and (b) the first sharp diffraction peak (FSDP) in (-irradiated and annealed after (-irradiation states.
(a)
� �
� �
(b)
� �
� �
Fig. 2. (a) The pair distribution functions g(r) for the samples of the investigated GexAs40–xS60 system in (-irradiated (the curves for (-irradiated state is shifted (+1) for clarity) and annealed after (-irradiation states; and (b) the part of g(r) in the first and second (insertion) coordination shells in (-irradiated and annealed after (-irradiation states.
Table. Structural parameters of GexAs40(xS60 glasses (x = 16 (Z = 2.56), x = 24 (Z = 2.64), x = 32 (Z = 2.72), and x = 36 (Z = 2.76)) in (-irradiated (irrad.) and annealed after (-irradiation (ann.) states. QFSDP – position of the FSDP and IFSDP – intensity of the FSDP, measured as a relation of the intensities at the maximum and at the tail of peak (IFSDP = S(Q)max/S(Q)min); ri – position and g(ri) – intensity of peaks on the pair distribution functions. The errors of QFSDP and ri are estimated from the Gaussian fits of the peaks. The error bars for the IFSDP and g(ri) are (2% of the reported values.
x�
State�
QFSDP (Å-1) �
IFSDP (a.u.)�
r1 (Å) �
g(r1)�
r2 (Å) �
g(r2)�
�
16�
irrad.�
1.13(0.01�
3.65(0.07�
2.27(0.01�
4.22(0.08�
3.55(0.02�
1.97(0.04�
�
�
ann.�
1.13(0.01�
4.38(0.09�
2.27(0.01�
4.85(0.10�
3.55(0.02�
2.05(0.04�
�
�
�
�
�
�
�
�
�
�
24�
irrad.�
1.08(0.01�
4.25(0.09�
2.26(0.01�
4.49(0.09�
3.60(0.02�
1.92(0.04�
�
�
ann.�
1.08(0.01�
4.45(0.09�
2.26(0.01�
4.72(0.09�
3.60(0.02�
1.94(0.04�
�
�
�
�
�
�
�
�
�
�
32�
irrad.�
1.03(0.01�
4.53(0.09�
2.26(0.01�
4.75(0.10�
3.61(0.02�
1.91(0.04�
�
�
ann.�
1.03(0.01�
4.56(0.09�
2.26(0.01�
4.81(0.10�
3.61(0.02�
1.97(0.04�
�
�
�
�
�
�
�
�
�
�
36�
irrad.�
1.01(0.01�
3.88(0.08�
2.26(0.01�
4.56(0.09�
3.59(0.02�
1.90(0.04�
�
�
ann.�
1.01(0.01�
4.06(0.08�
2.26(0.01�
4.63(0.09�
3.59(0.02�
1.95(0.04�
�
© 2012, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
310
_1406887895.unknown
_1410878818.unknown
_1413708971.unknown
_1413708981.unknown
_1413708994.unknown
_1413708997.unknown
_1413708992.unknown
_1413708973.unknown
_1411298009.unknown
_1411298062.unknown
_1413708965.unknown
_1411298153.unknown
_1411298055.unknown
_1411226977.unknown
_1411228835.unknown
_1411228848.unknown
_1411226234.unknown
_1406888325.unknown
_1406889203.unknown
_1406889480.unknown
_1406890794.unknown
_1406891279.unknown
_1406889579.unknown
_1406889373.unknown
_1406889407.unknown
_1406889449.unknown
_1406889250.unknown
_1406888968.unknown
_1406889108.unknown
_1406889168.unknown
_1406889087.unknown
_1406888934.unknown
_1406888738.unknown
_1406888752.unknown
_1406888458.unknown
_1406888707.unknown
_1406888136.unknown
_1406888211.unknown
_1406887936.unknown
_1406714971.unknown
_1406723340.unknown
_1406723977.unknown
_1406724593.unknown
_1406724827.unknown
_1406724862.unknown
_1406724684.unknown
_1406724721.unknown
_1406724699.unknown
_1406724662.unknown
_1406724058.unknown
_1406724455.unknown
_1406723900.unknown
_1406723953.unknown
_1406723877.unknown
_1406723363.unknown
_1406723282.unknown
_1406715849.unknown
_1406716123.unknown
_1406717183.unknown
_1406722957.unknown
_1406716867.unknown
_1406716069.unknown
_1406715830.unknown
_1406714879.unknown
_1406714916.unknown
_1406714929.unknown
_1406714897.unknown
_1406714818.unknown
_1406714852.unknown
_1406714791.unknown
_1272701459.unknown
|