Exciton-induced lattice defect formation
The lattice defect formation in solid Ne induced by electronic excitation was studied using the selective vacuum ultraviolet spectroscopy method. The samples were excited with synchrotron radiation in the range of excitonic absorption n = 2Г(3/2). The dose dependence of the intensity distribution in...
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Фізико-технічний інститут низьких температур ім. Б.І. Вєркіна НАН України
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Savchenko, E.V. Ogurtsov, A.N. Zimmerer, G. 2018-01-14T09:17:33Z 2018-01-14T09:17:33Z 2003 Exciton-induced lattice defect formation / E.V. Savchenko, A.N. Ogurtsov, G. Zimmerer // Физика низких температур. — 2003. — Т. 29, № 3. — С. 356-360. — Бібліогр.: 26 назв. — англ. 0132-6414 PACS: 61.82.Ms, 71.35.-y, 78.55.Hx https://nasplib.isofts.kiev.ua/handle/123456789/128823 The lattice defect formation in solid Ne induced by electronic excitation was studied using the selective vacuum ultraviolet spectroscopy method. The samples were excited with synchrotron radiation in the range of excitonic absorption n = 2Г(3/2). The dose dependence of the intensity distribution in the band of atomic type self-trapped exciton luminescence was analyzed. A direct evidence of the formation and accumulation of point lattice defects in solid Ne via the excitonic mechanism was obtained for the first time. The model of the permanent lattice defect formation is discussed. It is a pleasure to thank Prof. A.K. Song for fruitful discussions. The authors (E.S. and A.O.) gratefully acknowledge the support by DFG. en Фізико-технічний інститут низьких температур ім. Б.І. Вєркіна НАН України Физика низких температур Electronically Induced Phenomena: Low Temperature Aspects Exciton-induced lattice defect formation Article published earlier |
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Exciton-induced lattice defect formation |
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Exciton-induced lattice defect formation Savchenko, E.V. Ogurtsov, A.N. Zimmerer, G. Electronically Induced Phenomena: Low Temperature Aspects |
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Exciton-induced lattice defect formation |
| title_full |
Exciton-induced lattice defect formation |
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Exciton-induced lattice defect formation |
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Exciton-induced lattice defect formation |
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exciton-induced lattice defect formation |
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Savchenko, E.V. Ogurtsov, A.N. Zimmerer, G. |
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Savchenko, E.V. Ogurtsov, A.N. Zimmerer, G. |
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Electronically Induced Phenomena: Low Temperature Aspects |
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Electronically Induced Phenomena: Low Temperature Aspects |
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2003 |
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English |
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Физика низких температур |
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Фізико-технічний інститут низьких температур ім. Б.І. Вєркіна НАН України |
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Article |
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The lattice defect formation in solid Ne induced by electronic excitation was studied using the selective vacuum ultraviolet spectroscopy method. The samples were excited with synchrotron radiation in the range of excitonic absorption n = 2Г(3/2). The dose dependence of the intensity distribution in the band of atomic type self-trapped exciton luminescence was analyzed. A direct evidence of the formation and accumulation of point lattice defects in solid Ne via the excitonic mechanism was obtained for the first time. The model of the permanent lattice defect formation is discussed.
|
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0132-6414 |
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https://nasplib.isofts.kiev.ua/handle/123456789/128823 |
| citation_txt |
Exciton-induced lattice defect formation / E.V. Savchenko, A.N. Ogurtsov, G. Zimmerer // Физика низких температур. — 2003. — Т. 29, № 3. — С. 356-360. — Бібліогр.: 26 назв. — англ. |
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2025-11-27T07:13:11Z |
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2025-11-27T07:13:11Z |
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1850803091818938368 |
| fulltext |
Fizika Nizkikh Temperatur, 2003, v. 29, No. 3, p. 356–360
Exciton-induced lattice defect formation
E.V. Savchenko and A.N. Ogurtsov
B. Verkin Institute for Low Temperature Physics and Engineering
of the National Academy of Science of Ukraine, 47 Lenin Ave., Kharkov 61103, Ukraine
E-mail: savchenko@ilt.kharkov.ua
G. Zimmerer
Institut für Experimentalphysik der Universität Hamburg, Hamburg 22761, Germany
Received December 25, 2002
The lattice defect formation in solid Ne induced by electronic excitation was studied using the
selective vacuum ultraviolet spectroscopy method. The samples were excited with synchrotron ra-
diation in the range of excitonic absorption n = 2�(3/2). The dose dependence of the intensity dis-
tribution in the band of atomic type self-trapped exciton luminescence was analyzed. A direct evi-
dence of the formation and accumulation of point lattice defects in solid Ne via the excitonic
mechanism was obtained for the first time. The model of the permanent lattice defect formation is
discussed.
PACS: 61.82.Ms, 71.35.–y, 78.55.Hx
Introduction
The mechanisms of material modification via elec-
tronic subsystem are of considerable interest from the
point of view of the fundamental solid-state physics,
and their understanding is an important prerequisite
for many novel technological applications in material
and surface sciences, micro- and nanoelectronics,
photochemistry. The basis for the physics of electroni-
cally induced lattice rearrangement is a concentration
of the excitation energy in the relaxation process
within a volume about that of a unit cell followed by
the energy transfer to the crystal surrounding. A vari-
ety of inelastic processes induced by excitation of the
electronic subsystem were studied in wide-gap insula-
tors [1–6] and was found more recently even in nar-
row-gap materials [7]. The main phenomena under in-
vestigation are atomic processes such as lattice defect
formation or annealing of the existing defects, mass
diffusion, desorption of atoms, ions and molecules
from surfaces.
Considerable progress was made towards an insight
into their mechanisms. However, many details of the
electronically induced processes underlying these phe-
nomena are still not understood in deep. Rare gas so-
lids (RGS) with their simple lattice and well-defined
electronic structure are excellent objects for investiga-
tion of the electronically induced phenomena. Small
binding energies in conjunction with a strong
exciton-phonon interaction result in a high quantum
yield of electronically induced defect formation and
desorption that makes RGS especially suitable for ex-
perimental study. Moreover, study of electronically
induced atomic processes in the above solids offers
unique possibility to elucidate the role of acoustic
phonons in these processes. The pronounced effects of
exciton self-trapping observed in RGS are essential for
efficient energy localization and transfer to induce a
lattice modification. It is well known [1–3,8–10] that
in solid Ne the excitons are self-trapped predomi-
nantly into atomic type states (A-STE). A rich struc-
ture of the atomic transitions has been already found
in the early high-resolution studies of lumines-
cence from solid Ne [11–13]. It has been shown [11]
that the emissions observed stem from the transitions
1P1 �
1S0,
3P1 �
1S0, and 3P2 �
1S0. The spectral
features related to the surface and to the bulk were
distinguished by their dependence on sample thickness
and exciting electron energy [13]. The narrow emis-
sion lines were supposed [14] to stem from the
desorbing atoms in the states 1P1 and 3P1. The wider
bulk emissions matched to the transitions 3P1 �
1S0,
1P1 �
1S0 were found to be of a doublet structure
[13]. The similar features observed in [14] were inter-
© E.V. Savchenko, A.N. Ogurtsov, and G. Zimmerer, 2003
preted in the frame of the coexistence of exciton
self-trapping in a regular lattice and trapping in the
vicinity of initial nonequilibrium defects of structure,
e.g., trapping near a vacancy. Note that the transfor-
mation of defects involving A-STE and mobile ther-
mal vacancies at a «high» temperature of 19 K close to
the melting point was considered in [15].
In order to elucidate the internal structure of
A-STE emission bands, special experiments on low
temperature irradiation by high- and low-energy elec-
tron beams were performed [16,17]. In the first case
the electrons of superthreshold energy Ee > Ethr
(Ethr = 1 keV) produced point defects (Frenkel pairs)
during excitation via the knock-on mechanism. Based
on the dose dependence, the defect related spectral
features were clearly identified. For comparison pur-
pose the same luminescence spectra and their dose be-
havior were studied under irradiation by an electron
beam of subthreshold energy Ee < Ethr, i.e., by elec-
trons of energy deficient to move a lattice atom from
the substitutional site to an interstitional one via the
knock-on mechanism. A striking resemblance found in
the dose behavior — the increase in the intensity of
the defect related components, has given conclusive
evidence of the electronically induced point defect for-
mation and their accumulation in the lattice of Ne
[16,17]. It has been suggested that the self-trapping of
excitons into A-STE states is a stimulating factor.
However, direct proof of the excitonic mechanism re-
quires state-selective experiments. Synchrotron radia-
tion providing intense vacuum ultraviolet (VUV)
light tunable through the exciton absorption range is
best suited to this kind of experiments.
The paper reports the results on synchrotron radia-
tion study of permanent lattice defect formation in
solid Ne via the excitonic mechanism. The experimen-
tal findings are compared with the results of recent
molecular dynamics studies of the evolution of the
self-trapped excitons into the permanent lattice de-
fects [18,19].
Experimental
The selective excitation experiments were carried
out at the SUPERLUMI station at the Hamburger
Synchrotronstrahlungslabor HASYLAB. Since we are
interested in a control of the lattice permanent defect
creation induced by excitation of electronic subsystem
a quality of the samples under study (concentration of
initial defects and impurities) is of critical impor-
tance. The samples were grown in a special closed cell
mounted on a He-flow cryostat holder in ultrahigh
vacuum (UHV) environment (10–10 mbar). The high
purity Ne gas (99,998 %) was used, and the gas han-
dling system was operated under UHV conditions.
The samples were condensed from the vapor phase at
elevated temperatures under isobaric conditions (P =
= 10 Pa). The initial temperature of 18 K was fixed,
whereupon the sample was cooled down to 5 K with a
constant rate of 0.1 K/s. On the sample preparation
the cell was removed and the free-standing crystal was
studied. The high quality optically transparent poly-
crystalline sample of 1 mm thickness was subjected
then to a long-duration exposure to the VUV light.
Selective photon excitation was performed with a
band pass of �� = 0.25 nm. The excitation energy of
20 eV was chosen in the range of n = 2 term of the
excitonic series. The luminescence analysis was carried
out using a 1 m near-normal incidence monochromator
equipped with a position-sensitive detector. The spec-
tra were recorded with spectral resolution (� �/� ) of
750 and 1500. The resonance lines of gaseous Ne were
used for the energy calibration. The dose dependence
of the luminescence intensity spectral distribution was
measured, and the influence of the annealing at 11.5 K
on the spectral features was examined.
Results and discussion
The typical photoemission spectra of self-trapped
excitons in solid Ne taken with different resolution are
presented in Fig. 1. Spectrum 2 recorded with the
spectral resolution of 1500 shows a number of overlap-
ping spectral peaks. Weak wide band W at the low en-
ergy side is known as a vibrationally hot luminescence
Exciton-induced lattice defect formation
Fizika Nizkikh Temperatur, 2003, v. 29, No. 3 357
16,0 16,5 17,0
0
1
a
b
2
b
1
b
0
c
W
2
1
L
u
m
in
e
sc
e
n
ce
in
te
n
si
ty
,
a
.u
.
Photon energy, eV
Fig. 1. STE luminescence of solid Ne excited with 20 eV
(curve 1) and with 22 eV (curve 2) photons. Curve 2 was
recorded with a higher resolution (���� = 1500). The spec-
tra were measured at T = 5 K.
of M-STE in solid Ne (see, e.g., [11,14]). The contri-
butions to the W band from M-STE in the bulk and
those at the surface were discriminated in [20]. It is
very likely that the desorption of Ne2
* observed in
[21,22] contributes the W band too. However, this
presumption needs a special check. The most intense
structured composite of bands is the A-STE emission
in the range 16.6–17 eV. The experiments with highly
effective excitation of solid Ne by an electron beam
[11,13,14,16,17] made it possible to observe the lumi-
nescence from three atomic states 1P1,
3P1, and 3P2 –
a, b and c bands by the notations given in [16]. All
bands have an internal structure with the components
of different origin. The narrow «0» peaks coinciding
with the transitions 1P1 �
1S0 and 3P1 �
1S0 in the
gas phase in energy were identified as emissions from
the desorbing atoms in the excited states [14]. The
components labeled «1» and «2» which fall into pairs
with a splitting close to the spin-orbit splitting, stem
from the A-STE centers in the bulk. The «1» compo-
nents were found to be related to the lattice defects,
whereas the «2»-components were associated with the
A-STE in the regular lattice [14,16,17]. Several fea-
tures were assigned to the A-STE at the surface. In the
experiments [23] performed with tunable synchrotron
radiation the authors were able to isolate some of the
peaks by choosing the appropriate excitation energy
and time gating. The relevant peak positions and their
assignments are listed in the Table.
The intention of the present study was to measure
the dose dependence of the intensity distribution in
the luminescence spectra of solid Ne under the selec-
tive excitation in the range of free excitons. We tuned
the excitation energy to the band of exciton absorp-
tion n = 2�(3/2). Due to the low absorption coeffi-
cient the exciting light penetrated deep inside the
sample and the A-STE centers were efficiently formed
in the bulk. The temporal behavior of the lumines-
cence was monitored at 5 K to rule out thermally stim-
ulated processes. The sequence of spectra was mea-
sured during the exposure to VUV light. The most
intense b band was analyzed. The initial intensity distri-
bution is shown in Fig. 2,a, the final one — in Fig. 2,c.
The positions and the widths of the components were
obtained from the numerical fit of the band contour
assuming the Gaussian shape of the components. The
fitting was made taking into account the overlapping
of the A-STE emission with a high-energy tail of the
358 Fizika Nizkikh Temperatur, 2003, v. 29, No. 3
E.V. Savchenko, A.N. Ogurtsov, and G. Zimmerer
16,6 16,8
0
500
1000
1500 a)
d
b
0
b
2
b
1
Energy, eV
In
te
n
si
ty
,
a
.u
.
0 100 200
b)
Time, min
b
1
b
2
16,6 16,8
d
b
1
b
0
c)
Energy, eV
16,6 16,8
db
2
b
0
b
1
b
2
Ne
Energy, eV
d)
Fig. 2. Photoluminescence of solid Ne in the range of 3P1 �
1S0 transition (b band): (a) and (c) — the evolution of the
b band upon irradiation with 20 eV photons, (b) — the dose dependence of the b1 and b2 components, (d) — the spec-
trum recorded after the sample annealing at T = 11.5 K. The spectra were recorded at T = 5 K.
ba c d
Table
Positions at T = 5 K, FWHM, and assignments of the
A-STE luminescence components in the range of resonance
transitions
Band Position, eV
FWHM,
meV
Assignment
b
0 16.671 —
3P
1
(desorbing atom)
b
1
*
16.746 ± 0.002 48 ± 5
3P
1
(defect related A-STE)
b
2
* 16.807 ± 0.002 48 ± 6 3P
1
(A-STE in the bulk)
a
0
16.848 — 1P
1
(desorbing atom)
a
1
** 16.931 ± 0.005 50 ± 5 1P
1
(defect related A-STE)
a
2
**
16.992 ± 0.01 45 ± 5
1P
1
(A-STE in the bulk)
C o m m e n t. Position and in full width at half maximum
(FWHM) are given by the data in [23] (*) and [14] (**).
M-STE luminescence shown in Fig. 2. The result of
this treatment for the b1 and b2 components is shown
in Fig. 2,b as the corresponding points of the curves.
Despite the fact that the n = 2�(3/2) excitons are
formed predominantly deep in the bulk, they reach the
surface and then are trapped into the A-STE configu-
ration with a subsequent desorption of the excited
atom. The appearance of the b0 component in the
A-STE emission is in line with the results on the par-
tial yield of the Ne atoms in the 3P1 state [24]. The
desorption is due to the microcavity (bubble) forma-
tion around the A-STE as a result of the prevailing re-
pulsive interaction between the excited electron and
surrounding atoms because of the negative electron af-
finity of solid Ne [1]. This so-called «cavity ejection»
mechanism was studied in detail (see [2] and refer-
ences therein). The width of the b0 component related
to the desorbing atoms is resolution limited. The posi-
tions and the widths of the b1 and b2 components are
in perfect agreement with the data given in [23].
These bulk components have analogs in the matrix-iso-
lated Ar center spectra [17]. The d component may be
tentatively assigned to the transition from the me-
tastable 3P2 state at defect sites or near the surface.
Note, the transition from this state is strictly forbid-
den in a regular lattice. To the best of our knowledge
the geometrical configuration of the centers emitting
peaks in the range of 3P2 �
1S0 transition has not been
fully ascertained. Because of the long lifetime of this
state and negative electron affinity the chance for the
atom to desorb prior the radiation is very high [25].
For this reason the assignment of some emission lines
as emissions from the surface centers in the 3P2 state
seems to be very unlikely. The efficient excitation of
this emission in the range below the lowest bulk
exciton band may also be due to excitation of some
centers at defect sites because the defect levels could
be expected to occur quite close to the surface exciton
band. Note that the d component has an analog in the
matrix-isolated center spectra in the range of the low
concentrations [17]. The width narrowing and the de-
crease in intensity observed for the d component upon
annealing (see Fig. 2,d) seems to support the assign-
ment of the d component as being related to the defect
sites.
In order to get a direct proof of the permanent lat-
tice defect formation in the initially perfect lattice via
the excitonic mechanism, let us consider the features
in the range of resonance transition 3P1 �
1S0. It is
just a transformation of the most intense b band on ex-
posure to VUV photons in the range of the second
term of the excitonic series well below the band gap
energy. The shape of the b band after the cycle of irra-
diation is shown in Fig. 2,c. The pronounced enhance-
ment of the defect related components b1 and d was
found. As for the b2 component associated with the
A-STE centers in the regular lattice, it remained un-
changed. Figure 2,b depicts the dose dependence of
the b1 and b2 component intensity. The exposure time
not corrected for the synchrotron radiation pulse dura-
tion is in fact a real time of the measurements. The radi-
ation-induced enhancement of the defect components
clearly indicates the formation and accumulation of
the permanent lattice defects in solid Ne generated by
the self-trapping of excitons into the A-STE states.
The 30 min annealing of the samples at T = 11.5 K
caused a decrease in the intensity of the defect related
components. The intensities of the b1 and b2 compo-
nents were restored. The results obtained in the pre-
sent experiments with selective excitation accord well
with the results of the experiments performed with
electron beams [17]. Note, that in these experiments
the similar dose dependence was observed for the com-
ponents of the transitions 1P1 �
1S0 and 3P1 �
1S0
(see Table) dipole allowed in a cubic lattice. The simi-
lar dose dependences of the A-STE luminescence com-
ponents found in the cases of superthreshold and
subthreshold excitation by electron beams as well as
selective excitation into excitonic states provide a con-
vincing proof of the excitonic mechanism of the point
lattice defect formation.
The recent excited state molecular dynamics stud-
ies [18,19] of a possible evolution of the A-STE states
into stable lattice defects suggest a microscopic model
of conversion from the A-STE to Frenkel pairs. The
elastic deformation followed by the primary bubble
formation because of the prevailing repulsive forces
between the excited atomic center and surrounding
atoms takes place within a very short time. It is inte-
resting that an ultrafast expansion of the bubble was
observed upon excitation of the Rydberg orbital of the
NO impurity center in solid Ne [26]. Such primary
bubbles with elastic deformation collapse once the
electronic subsystem returns to the ground state. High
local elastic stresses in the lattice can induce some
plastic deformation during the lifetime of the excited
state. Several cases of possible plastic deformation
were examined. It was calculated that the energy le-
vels of some of the bubbles accompanied with a plastic
deformation are at energies lower than that of the pri-
mary bubble. The lowest energies were found for a
bubble with two vacancies in the first atomic shell. It
was revealed that the second-nearest neighboring va-
cancy-interstitial pairs are formed and remain stable
in the lattice after exciton annihilation. The estimated
differences in energies of radiative transitions of the
atomic centers in the primary bubble and in the bub-
ble with plastic deformation 54–66 meV are in perfect
Exciton-induced lattice defect formation
Fizika Nizkikh Temperatur, 2003, v. 29, No. 3 359
agreement with the experimental value 60 meV ob-
tained in the present study and with the results given
in [14,23] for the 3P1 �
1S0 and 1P1 �
1S0 transitions
(see the Table). A quite similar process of electroni-
cally induced defect formation upon excitation of the
Ar atoms in the Neon matrix was observed experimen-
tally [4] and considered theoretically [18]. To some
extent the considered mechanism of lattice defect for-
mation resembles that in alkali halides, where the
Frenkel pair formation is induced by the repulsive in-
teraction between the excited electron of the STE and
core electrons of the molecular ion pairs [1].
Acknowledgment
It is a pleasure to thank Prof. A.K. Song for fruit-
ful discussions. The authors (E.S. and A.O.) grate-
fully acknowledge the support by DFG.
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