Thermally stimulated exoelectron emission from solid Xe
Thermally-stimulated emission of exoelectrons and photons from solid Xe pre-irradiated by low-energy electrons were studied. A high sensitivity of thermally-stimulated luminescence (TSL) and thermally-stimulated exoelectron emission (TSEE) to sample prehistory was demonstrated. It was shown that e...
Gespeichert in:
| Datum: | 2007 |
|---|---|
| Hauptverfasser: | , , , , |
| Format: | Artikel |
| Sprache: | English |
| Veröffentlicht: |
Фізико-технічний інститут низьких температур ім. Б.І. Вєркіна НАН України
2007
|
| Schriftenreihe: | Физика низких температур |
| Schlagworte: | |
| Online Zugang: | http://dspace.nbuv.gov.ua/handle/123456789/121792 |
| 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: | Thermally stimulated exoelectron emission from solid Xe / I.V. Khyzhniy, O.N. Grigorashchenko, A.N. Ponomaryov, E.V. Savchenko, V.E. Bondybey // Физика низких температур. — 2007. — Т. 33, № 6-7. — С. 701-704. — Бібліогр.: 11 назв. — рос. |
Institution
Digital Library of Periodicals of National Academy of Sciences of Ukraine| id |
irk-123456789-121792 |
|---|---|
| record_format |
dspace |
| spelling |
irk-123456789-1217922017-06-17T03:02:59Z Thermally stimulated exoelectron emission from solid Xe Khyzhniy, I.V. Grigorashchenko, O.N. Ponomaryov, A.N. Savchenko, E.V. Bondybey, V.E. Electronic Processes in Cryocrystals Thermally-stimulated emission of exoelectrons and photons from solid Xe pre-irradiated by low-energy electrons were studied. A high sensitivity of thermally-stimulated luminescence (TSL) and thermally-stimulated exoelectron emission (TSEE) to sample prehistory was demonstrated. It was shown that electron traps in unannealed samples are characterized by a much broader distribution of trap levels in comparison with annealed samples and their concentration exceeds in number that in annealed samples. Both phenomena, TSL and TSEE, were found to be triggered by release of electrons from the same kind of traps. The data obtained suggest a competition between two relaxation channels: charge recombination and electron transport terminated by TSL and TSEE. It was found that TSEE predominates at low temperatures while at higher temperatures TSL prevails. An additional relaxation channel, a photon-stimulated exoelectron emission from pre-irradiated solid Xe, was revealed. 2007 Article Thermally stimulated exoelectron emission from solid Xe / I.V. Khyzhniy, O.N. Grigorashchenko, A.N. Ponomaryov, E.V. Savchenko, V.E. Bondybey // Физика низких температур. — 2007. — Т. 33, № 6-7. — С. 701-704. — Бібліогр.: 11 назв. — рос. 0132-6414 PACS: 78.60.Kn; 79.75.+g http://dspace.nbuv.gov.ua/handle/123456789/121792 en Физика низких температур Фізико-технічний інститут низьких температур ім. Б.І. Вєркіна НАН України |
| institution |
Digital Library of Periodicals of National Academy of Sciences of Ukraine |
| collection |
DSpace DC |
| language |
English |
| topic |
Electronic Processes in Cryocrystals Electronic Processes in Cryocrystals |
| spellingShingle |
Electronic Processes in Cryocrystals Electronic Processes in Cryocrystals Khyzhniy, I.V. Grigorashchenko, O.N. Ponomaryov, A.N. Savchenko, E.V. Bondybey, V.E. Thermally stimulated exoelectron emission from solid Xe Физика низких температур |
| description |
Thermally-stimulated emission of exoelectrons and photons from solid Xe pre-irradiated by low-energy
electrons were studied. A high sensitivity of thermally-stimulated luminescence (TSL) and thermally-stimulated
exoelectron emission (TSEE) to sample prehistory was demonstrated. It was shown that electron traps
in unannealed samples are characterized by a much broader distribution of trap levels in comparison with annealed
samples and their concentration exceeds in number that in annealed samples. Both phenomena, TSL
and TSEE, were found to be triggered by release of electrons from the same kind of traps. The data obtained
suggest a competition between two relaxation channels: charge recombination and electron transport terminated
by TSL and TSEE. It was found that TSEE predominates at low temperatures while at higher temperatures
TSL prevails. An additional relaxation channel, a photon-stimulated exoelectron emission from pre-irradiated
solid Xe, was revealed. |
| format |
Article |
| author |
Khyzhniy, I.V. Grigorashchenko, O.N. Ponomaryov, A.N. Savchenko, E.V. Bondybey, V.E. |
| author_facet |
Khyzhniy, I.V. Grigorashchenko, O.N. Ponomaryov, A.N. Savchenko, E.V. Bondybey, V.E. |
| author_sort |
Khyzhniy, I.V. |
| title |
Thermally stimulated exoelectron emission from solid Xe |
| title_short |
Thermally stimulated exoelectron emission from solid Xe |
| title_full |
Thermally stimulated exoelectron emission from solid Xe |
| title_fullStr |
Thermally stimulated exoelectron emission from solid Xe |
| title_full_unstemmed |
Thermally stimulated exoelectron emission from solid Xe |
| title_sort |
thermally stimulated exoelectron emission from solid xe |
| publisher |
Фізико-технічний інститут низьких температур ім. Б.І. Вєркіна НАН України |
| publishDate |
2007 |
| topic_facet |
Electronic Processes in Cryocrystals |
| url |
http://dspace.nbuv.gov.ua/handle/123456789/121792 |
| citation_txt |
Thermally stimulated exoelectron emission from solid Xe / I.V. Khyzhniy, O.N. Grigorashchenko, A.N. Ponomaryov, E.V. Savchenko, V.E. Bondybey // Физика низких температур. — 2007. — Т. 33, № 6-7. — С. 701-704. — Бібліогр.: 11 назв. — рос. |
| series |
Физика низких температур |
| work_keys_str_mv |
AT khyzhniyiv thermallystimulatedexoelectronemissionfromsolidxe AT grigorashchenkoon thermallystimulatedexoelectronemissionfromsolidxe AT ponomaryovan thermallystimulatedexoelectronemissionfromsolidxe AT savchenkoev thermallystimulatedexoelectronemissionfromsolidxe AT bondybeyve thermallystimulatedexoelectronemissionfromsolidxe |
| first_indexed |
2025-07-08T20:31:48Z |
| last_indexed |
2025-07-08T20:31:48Z |
| _version_ |
1837112188388507648 |
| fulltext |
Fizika Nizkikh Temperatur, 2007, v. 33, Nos. 6/7, p. 701–704
Thermally stimulated exoelectron emission from solid Xe
I.V. Khyzhniy1, O.N. Grigorashchenko1, A.N. Ponomaryov2, E.V. Savchenko1,
and V.E. Bondybey2
1
B. Verkin Institute for Low Temperature Physics and Engineering of the National Academy of Sciences of Ukraine
47 Lenin Ave., Kharkov 61103, Ukraine
2
Lehrstuhl für Physikalische Chemie II TU München, 4 Lichtenbergstraße, Garching 85747, Germany
Received November 20, 2006
Thermally-stimulated emission of exoelectrons and photons from solid Xe pre-irradiated by low-energy
electrons were studied. A high sensitivity of thermally-stimulated luminescence (TSL) and thermally-stimu-
lated exoelectron emission (TSEE) to sample prehistory was demonstrated. It was shown that electron traps
in unannealed samples are characterized by a much broader distribution of trap levels in comparison with an-
nealed samples and their concentration exceeds in number that in annealed samples. Both phenomena, TSL
and TSEE, were found to be triggered by release of electrons from the same kind of traps. The data obtained
suggest a competition between two relaxation channels: charge recombination and electron transport termi-
nated by TSL and TSEE. It was found that TSEE predominates at low temperatures while at higher tempera-
tures TSL prevails. An additional relaxation channel, a photon-stimulated exoelectron emission from pre-ir-
radiated solid Xe, was revealed.
PACS: 78.60.Kn Thermoluminescence;
79.75.+g Exoelectron emission.
Keywords: rare gas solids, thermally stimulated luminescence, exoelectron emission, relaxation processes.
Introduction
Relaxation processes in cryocrystals are of consider-
able interest from the standpoint of fundamental con-
densed-matter physics, and for various important app-
lications especially for solid-state photochemistry.
Elucidation of elementary relaxation stages in pre-irradi-
ated solids can make a significant contribution to a con-
trolled material modification via the electronic subsystem
of the crystal. Exposure of solid insulating materials to
ionizing radiation results in the modification of their phy-
sical properties. A number of structural defects, metas-
table species, ionic centers, trapped electrons, etc. are
formed due to the interaction between the crystal and the
radiation. Radiation-induced reactions produce guest at-
oms, molecules and radicals. Energy in different forms is
stored by the crystal after the irradiation and can be re-
leased by heating or by irradiation with light initiating re-
laxation cascades. Electron traps play an important role in
these processes. For a detailed understanding of the radia-
tion effects it is necessary to follow the sequence of relax-
ation processes in solids after irradiation. Different
classes of materials were investigated in view of this
problem [1–3]. Rare gas solids (RGS) are effectively used
as very convenient model systems for elucidating the ele-
mentary stages of charge transfer and energy relaxation in
solid wide-gap insulators. These cryocrystals, composed
of closed-shell atoms, possess comparatively simple elec-
tronic and crystal structure and weak interatomic forces
in combination with a strong electron–lattice interaction.
The specific properties of RGS give a possibility to un-
derstand electronically-induced processes on the atomic
level (because of their high quantum yield) and to explain
similar ones in more complex solids.
Activation spectroscopy methods are usually em-
ployed as powerful instruments for the analysis of the fi-
nal stage of relaxation, e.g., processes occurring after the
irradiation is completed. The method used most frequent-
ly is based on thermally stimulated luminescence (TSL)
measurements. TSL of halogen- and oxygen-doped solid
Xe was measured in [4] and [5] respectively. Kink at. al.
[6] measured TSL of nominally pure solid Xe pre-irradi-
ated by x-rays. In [7], the TSL was combined with vac-
uum ultraviolet spectroscopy methods to study creation
of lattice defects via exciton self-trapping in solid Xe.
© I.V. Khyzhniy, O.N. Grigorashchenko, A.N. Ponomaryov, E.V. Savchenko, and V.E. Bondybey, 2007
Recombination of both charged and neutral centers
contributes to the yield of TSL. As the temperature is
increased neutral impurity atoms become mobile enough
to move through the crystal and recombine, forming mo-
lecules in excited states. Radiative transitions of such
molecules contribute to the TSL yield. It is difficult to dis-
tinguish this process, called chemiluminescence, from ra-
diative recombination of charged particles using only the
TSL method. That is why it is reasonable to perform si-
multaneous measurements of TSL and, for instance, ther-
mally stimulated exoelectron emission (TSEE), e.g.,
apply TSL in combination with some kind of current acti-
vation spectroscopy methods. For this purpose we devel-
oped a low temperature modification of correlation spec-
troscopy, i.e., simultaneous measurements of TSL, TSEE
and desorption of neutral atoms [8] from pre-irradiated
RGS. In our previous experiments, TSEE was detected
from solid Ar [9] and Ne [10,11]. In this article we present
our results of an activation spectroscopy study in solid Xe
pre-irradiated with an electron beam.
Experiment
Xe cryocrystals were grown using a high purity gas
(99.9996%) were used. Before experiment the gas inlet
system was pumped and degassed by heating under
pumping. The samples were condensed from the gas
phase under isobaric conditions (P = 10
–7
bar) on a metal
substrate cooled by a closed-cycle 2-stage Leybold RGD
580 cryostat. The structure of the samples and therefore
the distribution of the defect energy levels within the
energy gap could be varied by changing the deposition
temperature and the gas flux. The deposition rate was
about 10
–2
�m/s. A typical sample thickness was 100 �m.
The samples were irradiated with electrons of 500 eV
at a current density of 30 �Acm
–2
. The irradiation and re-
cording of cathodoluminescence spectra were performed
at low temperature (6 K) in order to exclude the conven-
tional thermal mechanism of defect creation and to avoid
the annealing of radiation-induced defects. The irradia-
tion over TSL and TSEE yield spectra were recorded us-
ing different heating regimes. The total yield of TSL was
measured with a PMT sensitized to VUV light.
In TSEE experiments the emission of electrons from
pre-irradiated samples was detected with an Au-coated
Faraday plate kept at a small positive potential +9 V. The
current from the Faraday plate was amplified by a
FEMTO DLPCA 100 current amplifier. The signal was
reversed in polarity by an inverter and digitized in a PC.
For experiments on photon stimulated exoelectron
emission we used a Coherent 899-05 dye laser pumped
with Ar-ion laser. The power of laser beam was 35 mW.
The sample heating under laser light did not exceed 0.5 K.
Discussion
After the irradiation with electrons the samples of
RGS contain self-trapped holes, trapped electrons,
metastable dopant states and other stable radiation-in-
duced defects. To switch on the relaxation processes it is
necessary to release electrons from their traps to the con-
duction band of the crystal. Because of the high mobility
of free electrons in RGS they can move through the crys-
tal and recombine with positive centers (intrinsic or ex-
trinsic) giving rise to recombination luminescence. Note
that holes are self-trapped in solid Xe as well as in other
RGS. In Fig. 1 a correlation of the TSL and TSEE from
the crystalline Xe is shown. The sample was deposited at
20 K to suppress the TSL and TSEE maxima in the tem-
perature range lower then 20 K.
The main maximum on the TSEE curve correlates with
the first maximum in TSL while the main TSL maximum
correlates with the high-temperature shoulder of the main
TSEE peak. This means that TSL and TSEE are due to
release of electrons from the traps characterized by the
same activation energy. There is a competition between
these thermally stimulated processes because electrons
released from the traps have two possibilities — to re-
combine with positively charged centers or to escape
from the surface of the crystal. It was found that at low
temperatures TSEE predominates. As the temperature is
increased, the probability of recombination reactions in-
creases as evidenced by a rise of the the intensities of in-
trinsic and extrinsic recombination emission peaks in
comparison with the TSEE yield.
Figure 2 represents a comparison of TSL and TSEE
yields from the sample of solid Xe which was first an-
nealed at 60 K and than irradiated with electrons. The
main peak of TSEE appears at the same temperature as the
high-temperature shoulder of the main TSL peak.
Taking into account the positive electron affinity of
solid Xe (0.5 eV) [3], the peak of TSEE should be shifted
702 Fizika Nizkikh Temperatur, 2007, v. 33, Nos. 6/7
I.V. Khyzhniy, O.N. Grigorashchenko, A.N. Ponomaryov, E.V. Savchenko, and V.E. Bondybey
10 20 30 40 50 60
51
52
53
54
55
T, K
TSL
TSEE
T
S
E
E
cu
rr
en
t,
p
A
T
S
L
in
te
n
si
ty
,
ar
b
.
u
n
it
s
Fig. 1. A correlation of TSEE and TSL total yield from solid
Xe. The sample was deposited at 20 K.
to higher temperatures in comparison with the corre-
sponding TSL peak. We did not observe any shift. This
could be caused by the negative space charge of accumu-
lated in the sample during irradiation. However, this as-
sumption needs further experimental verification.
Figure 3 demonstrates the effect of sample quality on
TSL and TSEE. The samples annealed at temperatures
close to the characteristic sublimation temperature con-
tain fewer structural defects than the samples deposited at
low temperatures without further annealing. Lattice de-
fects serve as shallow traps for electrons. The more de-
fects in the crystal, the lower concentration of electrons
escaping from traps at low temperatures and vice versa.
That is the reason why the low-temperature peak predom-
inates in TSEE from unannealed samples. The TSL spec-
trum in this case is a broad band of a few overlapping
peaks. In the crystal grown at 20 K the maxima below this
temperature are not observed either in TSL or TSEE be-
cause of a depopulation of traps with the corresponding
activation energies formed during sample preparation.
The structure of the TSL and TSEE curves in this case re-
solves.
Note that the values of TSEE current for the sample
deposited at 20 K and for the one annealed at 60 K (Fig. 3)
are multiplied by 50 and 100, respectively, because they
are much lower than those from the unannealed sample.
The only pronounced feature in TSEE from the sample of
solid Xe annealed at 60 K is the peak at about 45 K. The
low-temperature maxima are strongly suppressed.
Taking into account that RGS have comparatively
wide conduction bands (about several eV), one can ex-
pect effective release of electrons under the beam of visi-
ble light both from deep and shallow traps with a sub-
sequent cascade of relaxation processes. The photon-
stimulated exoelectron emission (PSEE) from pre-irradi-
ated solid Xe is shown in Fig. 4. The initial decrease of
the exoelectron emission current recorded just after
switching off the electron beam (range 0–100 s) is the
so-called afteremission caused by the presence of metast-
able guest atoms in the Xe matrix, i.e., nitrogen (from
residual gases in the vacuum chamber). These centers,
which are formed during the irradiation of the sample by
electrons, exhibit a long afterglow after switching off the
irradiating beam. This internal source of photons in the
visible range causes the phenomenon of afteremission.
Figure 4 demonstrates the influence of visible range
photons on the exoelectron emission from pre-irradiated
solid Xe.
Thermally stimulated exoelectron emission from solid Xe
Fizika Nizkikh Temperatur, 2007, v. 33, Nos. 6/7 703
10
10
20
20
50
100
150
200
250
30
30
40
40
50
50
60
60
70
70
20 30 40
40
50
60
TSEE current*50
sample deposited at 20 K
unannealed
Sample deposited
at 20 K
Sample annealed at 60 K
Unannealed
sample
T, K
T, K
T
S
L
in
te
n
si
ty
,
ar
b
.
u
n
it
s
T
S
E
E
cu
rr
en
t,
p
A
Fig. 3. Comparison of TSL and TSEE yields from the solid Xe
samples of different quality.
0 20 40 60 80 100 120
2
6
10
14
18
22
T, K
TSL
TSEE
T
S
E
E
cu
rr
en
t,
p
A
T
S
L
in
te
n
si
ty
,
ar
b
.
u
n
it
s
Fig. 2. Total yield of TSL and TSEE current from solid Xe an-
nealed at 60 K.
0 100 200 300 400 500 600 700
0
1
2
3
Time, s
P
S
E
E
cu
rr
en
t,
p
A
Fig. 4. Photo-stimulated exoelectron emission current from so-
lid Xe.
The laser light of 510 nm wavelength was directed on
the sample surface when the afteremission was on the
background level. We detected a strong increase of the
exoelectron emission current. Then the current decayed
exponentially in time because the electron traps were de-
populating under the influence of the laser light. The ini-
tial part of the decay curve can be fitted by a first-order
exponential function with the characteristic decay time
� = (15 ± 4) s.
Summary
Relaxation processes in solid Xe pre-irradiated with an
electron beam were studied by activation spectroscopy
methods – thermally stimulated luminescence in combi-
n a t i o n w i th th e r ma l ly - an d p h o to n - s t imu la t e d
exoelectron emission measurements. Correlated in time
measurements of TSL and TSEE from electron beam
pre-irradiated solid Xe were performed for the first time.
The main role of electron traps in the charge and energy
transfer processes has been demonstrated. The channel
relaxation related with the depopulation of traps induced
by visible light has been revealed.
1. N. Itoh and A.M. Stoneham, Material Modification by
Electronic Excitations, University Press, Cambridge
(2000).
2. Ch.B. Lushchik and A.Ch. Lushchik, Decay of Electronic
Excitations With Defect Formation in Solids, Nauka, Mos-
cow (1989).
3. K.S. Song and R.T. Williams, Self-Trapped Excitons.
Springer Series in Solid-State Science, Springer Verlag,
Berlin (1996), v. 105.
4. M.E. Fajardo and V.A. Apkarian, J. Chem. Phys. 89, 4124
(1988).
5. A.V. Danilychev and V.A. Apkarian, J. Chem. Phys. 99,
8617 (1993).
6. M. Kink, R. Kink, V. Kisand, J. Maksimov, and M. Selg,
Nucl. Instr. Meth. Phys. Res. B122, 668 (1997).
7. E.V. Savchenko, A.N Ogurtsov, I.V. Khyzhniy, G. Stry-
ganyuk, and G. Zimmerer, Phys. Chem. Chem. Phys. 7, 785
(2005).
8. E.V. Savchenko and V.E. Bondybey, Phys. Status Solidi
A202, 221 (2005).
9. E.V. Savchenko, O.N. Grigorashchenko, A.N. Ogurtsov,
V.V. Rudenkov, G.B. Gumenchuk, M. Lorenz, A. Lam-
mers, and V.E. Bondybey, J. Low Temp. Phys. 122, 379
(2001).
10. O.N. Grigorashchenko, V.V. Rudenkov, I.V. Khyzhniy,
E.V. Savchenko, M. Frankowski, A.M. Smith-Gicklhorn,
M.K. Beyer, and V.E. Bondybey, Fiz. Nizk. Temp. 29,
1147 (2003) [Low Temp. Phys. 29, 876 (2003)].
11. M. Frankowski, E.V. Savchenko, A.M. Smith-Gicklhorn,
O.N. Grigorashchenko, G.B. Gumenchuk, and V.E. Bondy-
bey, J. Chem. Phys. 121, 1474 (2004).
704 Fizika Nizkikh Temperatur, 2007, v. 33, Nos. 6/7
I.V. Khyzhniy, O.N. Grigorashchenko, A.N. Ponomaryov, E.V. Savchenko, and V.E. Bondybey
|