Рeculiarities of interaction of low-energy protons with tungsten surface
The results of investigations of the interaction of protons with energy of 250…260 eV with the surface of tungsten foil are presented. Sputtering of tungsten occurs at a rate of ~ 0.5 μm/h at a temperature of 300°C and an ion current density of 1.5 mA/cm² . The surface of tungsten significantly ch...
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| Zitieren: | Рeculiarities of interaction of low-energy protons with tungsten surface / O.A. Fedorovich, V.V. Hladkovskyi, B.P. Polozov, L.M. Voitenko, E.G. Kostin, V.А. Petriakov, А.A. Rokitskyi, А.S. Oberemok, V.V. Burdin // Вопросы атомной науки и техники. — 2018. — № 4. — С. 302-306. — Бібліогр.: 16 назв. — англ. |
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irk-123456789-1476642019-02-16T01:25:08Z Рeculiarities of interaction of low-energy protons with tungsten surface Fedorovich, O.A. Hladkovskyi, V.V. Polozov, B.P. Voitenko, L.M. Kostin, E.G. Petriakov, V.А. Rokitskyi, А.A. Oberemok, А.S. Burdin, V.V. Приложения и технологии The results of investigations of the interaction of protons with energy of 250…260 eV with the surface of tungsten foil are presented. Sputtering of tungsten occurs at a rate of ~ 0.5 μm/h at a temperature of 300°C and an ion current density of 1.5 mA/cm² . The surface of tungsten significantly changes after the irradiation process. The substantial surface cleaning occurs from oxides due to surface sputtering, and also because of their reduction in hydrogen plasma. The hydrogen content increases near the surface of the tungsten sample after irradiation with protons. The hydrogen content decreases in depth in tungsten. Наведено результати досліджень взаємодії протонів з енергією 250…260 еВ з поверхнею вольфрамової фольги. Відбувається розпорошення вольфраму зі швидкістю ~ 0,5 мкм/год при температурі 300°С і щільності іонного струму ~ 1,5 мА/см² . Поверхня вольфраму значно змінюється після процесу опромінення. Відбувається істотне очищення поверхні від оксидів через розпорошення поверхні, а також із-за їх відновлення у водневій плазмі. Після опромінення вольфраму протонами істотно збільшується вміст водню поблизу поверхні зразка. Вміст водню у вольфрамі повільно зменшується по глибині. Приведены результаты исследований взаимодействия протонов с энергией 250…260 эВ с поверхностью вольфрамовой фольги. Происходит распыление вольфрама со скоростью ~ 0,5 мкм/ч при температуре 300°С и плотности ионного тока ~ 1,5 мА/см² . Поверхность вольфрама значительно изменяется после процесса облучения. Происходит существенная очистка поверхности от оксидов из-за распыления поверхности, а также из-за их восстановления в водородной плазме. После облучения вольфрама протонами существенно увеличивается содержание водорода вблизи поверхности образца. Содержание водорода в вольфраме плавно уменьшается по глубине. 2018 Article Рeculiarities of interaction of low-energy protons with tungsten surface / O.A. Fedorovich, V.V. Hladkovskyi, B.P. Polozov, L.M. Voitenko, E.G. Kostin, V.А. Petriakov, А.A. Rokitskyi, А.S. Oberemok, V.V. Burdin // Вопросы атомной науки и техники. — 2018. — № 4. — С. 302-306. — Бібліогр.: 16 назв. — англ. 1562-6016 PACS: 52.40.Hf http://dspace.nbuv.gov.ua/handle/123456789/147664 en Вопросы атомной науки и техники Національний науковий центр «Харківський фізико-технічний інститут» НАН України |
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Digital Library of Periodicals of National Academy of Sciences of Ukraine |
| collection |
DSpace DC |
| language |
English |
| topic |
Приложения и технологии Приложения и технологии |
| spellingShingle |
Приложения и технологии Приложения и технологии Fedorovich, O.A. Hladkovskyi, V.V. Polozov, B.P. Voitenko, L.M. Kostin, E.G. Petriakov, V.А. Rokitskyi, А.A. Oberemok, А.S. Burdin, V.V. Рeculiarities of interaction of low-energy protons with tungsten surface Вопросы атомной науки и техники |
| description |
The results of investigations of the interaction of protons with energy of 250…260 eV with the surface of tungsten foil are presented. Sputtering of tungsten occurs at a rate of ~ 0.5 μm/h at a temperature of 300°C and an ion
current density of 1.5 mA/cm²
. The surface of tungsten significantly changes after the irradiation process. The substantial surface cleaning occurs from oxides due to surface sputtering, and also because of their reduction in hydrogen plasma. The hydrogen content increases near the surface of the tungsten sample after irradiation with protons.
The hydrogen content decreases in depth in tungsten. |
| format |
Article |
| author |
Fedorovich, O.A. Hladkovskyi, V.V. Polozov, B.P. Voitenko, L.M. Kostin, E.G. Petriakov, V.А. Rokitskyi, А.A. Oberemok, А.S. Burdin, V.V. |
| author_facet |
Fedorovich, O.A. Hladkovskyi, V.V. Polozov, B.P. Voitenko, L.M. Kostin, E.G. Petriakov, V.А. Rokitskyi, А.A. Oberemok, А.S. Burdin, V.V. |
| author_sort |
Fedorovich, O.A. |
| title |
Рeculiarities of interaction of low-energy protons with tungsten surface |
| title_short |
Рeculiarities of interaction of low-energy protons with tungsten surface |
| title_full |
Рeculiarities of interaction of low-energy protons with tungsten surface |
| title_fullStr |
Рeculiarities of interaction of low-energy protons with tungsten surface |
| title_full_unstemmed |
Рeculiarities of interaction of low-energy protons with tungsten surface |
| title_sort |
рeculiarities of interaction of low-energy protons with tungsten surface |
| publisher |
Національний науковий центр «Харківський фізико-технічний інститут» НАН України |
| publishDate |
2018 |
| topic_facet |
Приложения и технологии |
| url |
http://dspace.nbuv.gov.ua/handle/123456789/147664 |
| citation_txt |
Рeculiarities of interaction of low-energy protons with tungsten surface / O.A. Fedorovich, V.V. Hladkovskyi, B.P. Polozov, L.M. Voitenko, E.G. Kostin, V.А. Petriakov, А.A. Rokitskyi, А.S. Oberemok, V.V. Burdin // Вопросы атомной науки и техники. — 2018. — № 4. — С. 302-306. — Бібліогр.: 16 назв. — англ. |
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Вопросы атомной науки и техники |
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| fulltext |
ISSN 1562-6016. ВАНТ. 2018. №4(116) 302
PECULIARITIES OF INTERACTION OF LOW-ENERGY PROTONS
WITH TUNGSTEN SURFACE
O.A. Fedorovich1, V.V. Hladkovskyi1, B.P. Polozov1, L.M. Voitenko1, E.G. Kostin1,
V.А. Petriakov1, А.A. Rokitskyi1, А.S. Oberemok2, V.V. Burdin3
1Institute for Nuclear Research NASU, Kiev, Ukraine;
2Institute of Semiconductor Physics NASU, Kiev, Ukraine;
3Institute for Problems of Material Sciences NASU, Kiev, Ukraine
E-mail: oafedorovich@kinr.kiev.ua
The results of investigations of the interaction of protons with energy of 250…260 eV with the surface of tung-
sten foil are presented. Sputtering of tungsten occurs at a rate of ~ 0.5 μm/h at a temperature of 300°C and an ion
current density of 1.5 mA/cm2. The surface of tungsten significantly changes after the irradiation process. The sub-
stantial surface cleaning occurs from oxides due to surface sputtering, and also because of their reduction in hydro-
gen plasma. The hydrogen content increases near the surface of the tungsten sample after irradiation with protons.
The hydrogen content decreases in depth in tungsten.
PACS: 52.40.Hf
INTRODUCTION
The aim of this work is a comprehensive research of
the results of the hydrogen ions interaction with the
constructural materials used in nuclear reactors and in
the future fusion devices. In comparison with traditional
power plants, materials in nuclear and especially in
thermonuclear plants operate in much more difficult
conditions [1, 2]. When neutrons and protons irradiate
the first wall of a thermonuclear reactor, their transfor-
mation into hydrogen atoms takes place. As a result of
interaction with the material of investigation sample, the
protons are converted to atomic hydrogen, which leads
to gas sputtering and the appearance of hydrogen brit-
tleness of materials. At elevated temperatures (up to
150°C), high (~ 800°C), and especially ultrahigh tem-
peratures (more than 800°C), there is an increased diffu-
sion of hydrogen atoms into the depth of the material.
This reduces corrosion resistance. At present, many
reviews have been published on the effect of proton
irradiation of the reactor wall, especially the first wall of
a thermonuclear reactor (TNR), where deuterium and
tritium will be used. According to some calculations [3],
the hydrogen concentration that occurs in the first wall
of the reactor can become critical for the material, with
respect to its resistance to hydrogen brittleness [4].
The constructural materials for the first wall of fu-
sion reactor change all the time. In the 1980s titanium,
niobium and tantalum carbides were used as the first
wall [2], nowadays, for example, ITER ELMs use Ti-
Zn-Ni (Ti 41.5, Zn 41.5, Ni 17) alloys [5], beryllium
lining [7]. For mirrors and diverters are used tungsten
coatings and tungsten [6].
The tungsten (W) is considered as the promising ma-
terial of elements in contact with the plasma in future
fusion reactors such as ITER [9] and DEMO [10], due
to its physical properties such as low coefficient of
physical sputtering and high melting point. In addition,
W is considered as a promising material for the internal
mirrors of optical diagnostics of plasma and construc-
tion material for the diverter in ITER [11].
The numerous studies in Ukraine and abroad are car-
ried out by scientists and materials scientists who are
engaged in the construction of tokamaks, stellarators,
and also investigate possible terms for prolonging the
operation of functioning reactors.
But until now, a complex investigation of the effects
of the interaction of hydrogen ions and its isotopes with
various materials by using the methods of secondary ion
mass spectrometry (SIMS), X-ray luminescence analy-
sis; scanning electron microscopy; optical microscopy;
X-ray diffraction analysis, has not been carried out. The
SIMS method makes it possible to determine the isotop-
ic composition of various materials (metals and alloys)
before and after irradiation, as well as by layer-by-layer
removal of surface films in order to determine the depth
of penetration and hydrogen concentrations in the mate-
rials under study, depending on the interaction time,
proton energy, dose, and sample temperature.
1. EXPERIMENTAL SETUP
The researches were conducted on the modernized
experimental source of hydrogen (protons) that was
described in [8]. The planar plasma chemical reactor
(PCR) was used to produce hydrogen ions. It consisted
of two electrodes of various sizes, one of which was
active (with an electrode diameter of 150 mm) and the
HF potential was applied to it. The second electrode,
110 mm in diameter, is grounded, but it serves as a sub-
strate holder.
The heater made of molybdenum wire have been
manufactured and calibrated for heating substrate holder
up to 1000°C [8]. But not all processed materials were
kept at such high temperature. Therefore, researches
were first carried out to the temperature of 400°C. The
heater was screened by with three screens which made
of molybdenum foil to reduce the heating of additional
floating electrodes and the grounded pats of the plasma
ion source. The ion source housing and power inputs of
the heater were cooled with water. The scheme of the
upgraded experimental setup is shown in Fig. 1.
The floating duralumin electrodes were mounted on
ceramic insulators. The floating electrodes have a sig-
nificant capacitance, so the RF discharge began to burn
on them. This led to the appearance of a plus potential
on the substrate holder. In this regard, positively
charged hydrogen ions were not attracted to the sub-
strate holder. The deposition of atomized neutral atoms
ISSN 1562-6016. ВАНТ. 2018. №4(116) 303
of the upper electrode on the surface of the samples was
the result of this. Therefore, floating electrodes were
completely isolated by fluoroplastic plates placed on top
of the electrodes from the possibility of burning an RF
discharge on them. The part of the substrate holder was
covered with high-temperature ceramics from corundum
to reduce its area. But it was not enough to obtain a
negative self-bias voltage 250…300 eV. Therefore, it is
necessary to produce an additional regulated source
with a voltage of 1 kV and a current of up to 1 A. The
power source was connected to a hydrogen ion genera-
tor through special filters. The negative pole is connect-
ed to the substrate holder, and positive to the active
electrode.
Fig. 1. The scheme of the experimental setup:
1 − chamber; 2 − substrate; 3 − substrate holder
(grounded electrode); 4 − plasma quencher; 5 − heater;
6 − gas inlet system; 7 − magnetic coils; 8 isolated
floating electrodes; 9 − active electrode; 10 − pumping
system; 11 − vacuummeter; 12 − thermocouple
The RF discharge modes were chosen so that there
were no breakdowns between the active electrode and
the substrate holder to avoid radiation damage Proton
irradiation was carried out at currents of RF discharges
in hydrogen of 5.5 A, the negative bias voltage (without
breakdown) 250…260 V. Exposure was 11.0 hours, the
temperature of heating 150…400°C. Working pressure
in the PCR of 0.13 Torr at an intensity of magnetic field
300 E. Average proton energy was 250…260 eV.
2. EXPERIMENTAL RESULTS
AND DISCUSSION
2.1. RESEARCH OF THE SURFACE CHEMICAL
COMPOSITION OF THE IRRADIATED
SAMPLES
The chemical composition of the surface of the sam-
ples was investigated by the method of secondary ion
mass spectrometry (SIMS) after their treatment with
hydrogen ions. The investigations of treated and un-
treated samples were carried out in the range from 1 to
250 atomic mass units (amu), as well as individual
masses in the depth of penetration into the samples dur-
ing their sputtering with an argon ion beam up to
1200 s. The sputtering of the samples was carried out by
argon ions with energy of 500 eV with a primary ion
current of 4 mA.
SIMS is based on measuring the ratio m/z of the ions
emitted by the surface and measuring the currents
formed by them under the action of a primary ion beam
(where m is the ion mass and z is its electric charge).
SIMS is one of the most powerful and informative
methods for analyzing the surface of solids. It allows
determining the elemental and molecular composition of
the samples, conduct isotope and analysis of impurities
in depth, and the likes. The main advantages of the
method are the high elemental sensitivity, which in
modern instruments reaches 1012…1014 cm-3 (Fig. 2),
large dynamic range and depth resolution.
Fig. 2. The boundaries of the detection of atoms
in various techniques
The schematic diagram of the method is shown in
Fig. 3. The knocked secondary ions are collected by a
system of electrostatic lenses and focused into a narrow
beam with the same energy and are separated in the
mass separator, the ratio of the ion mass m to its electric
charge q. The separated secondary ion currents carry
information about the type of atoms and the type of
molecules on the surface of the samples, and the magni-
tude of the currents − about their concentration. SIMS is
divided into static and dynamic depending on the densi-
ty of the primary current.
Fig. 3. The schematic diagram of the mass spectrometer
operation
In a static SIMS, the ion current density is less than
1013 at/cm3, which allows an elemental and molecular
analysis of surface and adsorbed layers. The interaction
of ions with the sample surface is considered as a static
event at such current densities. In this case, the proba-
bility of formation of the secondary ion will be affected
by the energy distribution over the surface of the mono-
ISSN 1562-6016. ВАНТ. 2018. №4(116) 304
layer. The number of ion-surface interaction events in-
creases with increasing primary current density to 1017
at/cm3, and the sputtering regime changes from static to
dynamic. This means that it is impossible to consider
the interaction of the ion as a static event, and the need
to consider the interaction of the whole flow of ions
with the surface, i.e. the dynamics of the system. In this
case, the energy distribution over the surface loses its
meaning, since such a large flow gives each atom the
surface energy sufficient to break all the molecular
bonds. The conducting molecular analysis becomes im-
possible.
Most of the samples were foils from various pure
metals and metal alloys. Part of the sample was closed
by mask during processing in the plasma. Mass spec-
trometric analysis of both (treated and untreated) parts
was carried out. The holders were placed in the lock
chamber of the device, which was pumped to a vacuum
level no worse than 7.5×10-7 Torr.
The registration of the SIMS spectra occurred under
the following conditions: ion type Ar+; primary ion en-
ergy of 500 eV; the primary ion current 4 mA; type of
spraying HFM; the frequency of sputtering of 50 kHz;
duty cycle voltage 0.6; the area of analysis 5 mm; the
chamber pressure of 7.5×10-7 Torr; the gas pressure in
the cell plasma of 2.3×10-3 Torr; plasma power of
220 W.
2.2. INFLUENCE OF HYDROGEN PLASMA
TREATMENT ON SURFACE OF TUNGSTEN
SAMPLES
The effects of irradiation of low-energy hydrogen
and helium ions on the W surface were investigated in
[14]. One of the factors that affect the surface properties
of W is swelling (blistering), which occurs when the
implanted gas concentration is high. Blistering appears
on the surface of W when irradiated with ions of hydro-
gen plasma, even with energies much less than the
threshold of the displacement of W atoms [15, 16].
In Fig. 4, it can be seen that after treatment of the W
samples in the hydrogen plasma during 11 hours at a
temperature T = 300°C and an ion energy E = 260 eV,
an increase of hydrogen ion H+ occurs approximately 5
times. Molecular hydrogen ion H2
+ on mass spectra is
practically not observed (only about 0.02%).
Fig. 4. Increase of hydrogen ion H+ in mass spectra
of secondary ion emission in W samples after treatment
in hydrogen plasma
The hydrogen concentration an increase not only at
the surface but also in the depth of the sample occurred,
after treatment of the W samples in a hydrogen plasma
for 11 hours at temperature T = 300°C and ion energy
E = 260 eV (Fig. 5). The increase in hydrogen concen-
tration over the depth of sample W is approximately
14%. It can be assumed that the penetration of hydrogen
into the deeper layers of W occurs due to diffusion, in-
cluding radiation-induced diffusion. It should be noted
that in the near-surface layer of tungsten, peak intensity
greater than twice the intensity of the hydrogen ion in
the deeper layers is observed. But it falls very quickly.
Fig. 5. The changes in secondary emission of hydrogen
ions H+ in W sample in the process of etching
with 500 eV argon ions (Upper curve − after treatment,
lower curve- before treatment).
W, t=11 hours, T = 300°C
Fig. 6 shows the changes in the mass spectra of sec-
ondary ion emission in the mass range m/z = 175…220
in W samples after proton treatment. Before treatment
in a hydrogen plasma, the peak values of the isotopes of
the oxides WO+ and WO2
+ with respect to the isotope
peaks of pure W+ are not the same as after the treatment.
If the magnitude of the W+ peak is taken as unity, then
before the treatment in the hydrogen plasma, the propor-
tion of the oxides ions WO+ and WO2
+ with respect to
tungsten ion W+ is equal to 0.86 and 0.06, respectively.
Fig. 6. Changes in the mass spectra of secondary ion
emission in the mass range m/z = 175…220 in samples
W after proton treatment (circles - sample before pro-
cessing, triangles − sample after treatment)
ISSN 1562-6016. ВАНТ. 2018. №4(116) 305
After treatment in plasma, the ratio of the intensities
of the WO+ isotope peaks to the W+ isotopes in the mass
spectrum is 0.2 and the intensities of the WO2
+ isotope
peaks to the W+ isotopes are equal to ≈ 0.009. The peak
of WO+ decreased by 4.3 times, and the peak of WО2
+
in 6.7 times.
Thus, one can speak of a decrease in oxides in the
tungsten sample after treatment. The cleaning of the
surface of tungsten occurs under the influence of two
processes. The first is the sputtering of the oxidized
tungsten foil. During the processing (11 hours) of tung-
sten foil, a thickness reduction of ~ 5…6 μm
(~ 0.5 μm/h) occurs. The second is the possible reduc-
tion of oxides in hydrogen plasma. To justify this as-
sumption, we present the results of a number of papers.
Thus, in work [15] arguments are discussed regarding
the activity of hydrogen plasma during the reduction of
metal oxides and semiconductors. It is known that the
plasma changes hydrogen molecules to atomic, ionic,
vibrationally - activated and other excited particles. Hy-
drogen in the atomic, ionic and excited states can restore
almost every metal oxide even at lower temperatures. In
Ref. [16], the reduction temperature of MoO3, WO3,
Fe2O3 oxides, when using atomic hydrogen as compared
with molecular hydrogen, decreased from 610 to 43°C,
from 535 to 25oC, from 310 to 40°C, respectively.
2.3. INVESTIGATION OF SURFACE CHANGES
AFTER IRRADIATION BY METHOD
OF RASTER ELECTRONIC MICROSCOPY
The investigation was made of surface changes after
proton irradiation of tungsten samples using scanning
electron microscopy. The significant surfaces of chang-
es were observed after proton irradiation at the tempera-
ture of 300°C.
In Fig. 7 electron images the surface of tungsten be-
fore (see Fig. 7,a) and after processing (see Fig. 7,b) are
given. Significant decreases in the surface irregularities
after surface treatment by protons and the appearance of
a finer structure on the surface of the metal are ob-
served. The blistering of the tungsten surface was not
detected in these investigations.
The separate cavities are observed in the photographs of
the end face of a tungsten sample (see Fig. 7,c). They
can appear with a relatively deep penetration of hydro-
gen in the depth.
Fig. 7. The structure of the surface of the tungsten foil
before treatment (a) and after treatment with protons
(b, c) (main HF discharge current 5.5 A, proton energy
250 eV, exposure 11 hours, heating temperature 300°C,
operating pressure 1.2·10-1 Torr)
CONCLUSIONS
There is an accumulation of hydrogen not only on
the surface, but also (in a lesser degree) in the depth of
the tungsten sample. Molecular hydrogen is observed at
the level of noise.
The investigation of the surface of irradiated and ir-
radiated samples showed significant differences. After
treatment in hydrogen plasma, a decrease in the amount
of oxides on the surface of tungsten samples is ob-
served. The substantial surface cleaning occurs from
oxides due to surface sputtering, and also because of
their reduction in hydrogen plasma.
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Article received 09.06.2018
ОСОБЕННОСТИ ВЗАИМОДЕЙСТВИЯ НИЗКОЭНЕРГЕТИЧНЫХ ПРОТОНОВ
С ПОВЕРХНОСТЬЮ ВОЛЬФРАМА
О.А. Федорович, В.В. Гладковский, Б.П. Полозов, Л.М. Войтенко, Е.Г. Костин, В.А. Петряков,
А.А. Рокицкий, А.С. Оберемок, В.В. Бурдин
Приведены результаты исследований взаимодействия протонов с энергией 250…260 эВ с поверхностью
вольфрамовой фольги. Происходит распыление вольфрама со скоростью ~ 0,5 мкм/ч при температуре 300°С
и плотности ионного тока ~ 1,5 мА/см2. Поверхность вольфрама значительно изменяется после процесса
облучения. Происходит существенная очистка поверхности от оксидов из-за распыления поверхности, а
также из-за их восстановления в водородной плазме. После облучения вольфрама протонами существенно
увеличивается содержание водорода вблизи поверхности образца. Содержание водорода в вольфраме плав-
но уменьшается по глубине.
ОСОБЛИВОСТІ ВЗАЄМОДІЇ НИЗЬКОЕНЕРГЕТИЧНИХ ПРОТОНІВ
З ПОВЕРХНЕЮ ВОЛЬФРАМУ
О.А. Федорович, В.В. Гладковський, Б.П. Полозов, Л.М. Войтенко, Є.Г. Костін, В.О. Петряков,
О.А. Рокицький, О.С. Оберемок, В.В. Бурдін
Наведено результати досліджень взаємодії протонів з енергією 250…260 еВ з поверхнею вольфрамової
фольги. Відбувається розпорошення вольфраму зі швидкістю ~ 0,5 мкм/год при температурі 300°С і щільно-
сті іонного струму ~ 1,5 мА/см2. Поверхня вольфраму значно змінюється після процесу опромінення. Відбу-
вається істотне очищення поверхні від оксидів через розпорошення поверхні, а також із-за їх відновлення у
водневій плазмі. Після опромінення вольфраму протонами істотно збільшується вміст водню поблизу пове-
рхні зразка. Вміст водню у вольфрамі повільно зменшується по глибині.
introduction
1. EXPERIMENTAL setup
2. Experimental Results and Discussion
2.1. RESEARCH OF THE SURFACE CHEMICAL COMPOSITION OF THE IRRADIATED SAMPLES
2.2. INFLUENCE OF HYDROGEN PLASMA treatment ON surface OF TUNGSTEN SAMPLES
2.3. investigation OF SURFACE CHANGES AFTER IRRADIATION BY METHOD OF RASTER ELECTRONIC MICROSCOPY
CONCLUSIONS
references
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