ISSN 0036-0244, Russian Journal of Physical Chemistry A, 2007, Vol. 81, No. 9, pp. 1532–1536. © Pleiades Publishing, Ltd., 2007.
Original Russian Text © I.A. Kirovskaya, L.V. Novgorodtseva, M.V. Vasina, 2007, published in Zhurnal Fizicheskoi Khimii, 2007, Vol. 81, No. 9, pp. 1719–1723.
PHYSICAL CHEMISTRY
OF SURFACE PHENOMENA
The Adsorption of Gases on the Surface of Solid Solutions
and Binary Compounds of the GaSb–ZnTe System
I. A. Kirovskaya, L. V. Novgorodtseva, and M. V. Vasina
Omsk State Technical University, Omsk, Russia
e-mail: phiscem@omgtu.ru
Received July 13, 2006
Abstract—The adsorption of ammonia, carbon monoxide, and oxygen on solid solution and binary compound
films of the GaSb–ZnTe system was studied. The mechanism of adsorption and rules governing adsorption pro-
cesses depending on adsorption conditions and system composition were determined by analyzing adsorption
isobars, equilibrium and kinetic isotherms, the thermodynamic and kinetic characteristics of adsorption, and the
electronic nature of adsorbate molecules. The behavior of (GaSb)x(ZnTe)1 – x solid solutions was similar to that
of binary compounds (GaSb and ZnTe) and had special features characteristic of multicomponent systems. The
latter manifested themselves by the presence of extrema in adsorption characteristic–composition diagrams.
The use of such diagrams allowed us to identify system components most active with respect to NH3, CO, and
O2 and use them to create high-sensitivity and selectivity sensors.
DOI: 10.1134/S0036024407090361
INTRODUCTION
in initial material vapors under the corresponding con-
ditions [2, 4]. The same samples were used to study
changes in conductivity and, accordingly, surface
charge under the influence of adsorbed gases. Solid
solution powders were prepared by isothermal diffu-
sion of binary components in evacuated sealed quartz
ampules at temperatures above the temperature of
fusion of the low-melting component (GaSb) [1]. Their
composition was determined by the GaSb and ZnTe
mutual solubility limits.
The GaSb–ZnTe system had not been obtained by
the time when this study was initiated. Its volume and,
all the more, surface properties had therefore
remained unstudied. Like other complex systems
based on diamond-like semiconductors endowed with
unexpected properties [1–3], the GaSb–ZnTe system
is of interest for seeking new adsorbents, catalysts,
and new materials such as are used in sensor electron-
ics, including ecological sensors [2]. The creation of
sensors of this kind based on the necessary data on the
adsorption and other physicochemical properties of
the surface of semiconductors is an especially urgent
problem at present in view of the ecological crisis that
we face. Accordingly, the adsorbates selected (CO,
NH3, and é2) are of interest not only because they dif-
fer in their chemical nature but also as components of
the environment, including technological environ-
ment.
The solid solutions were characterized by recording
their X-ray diffraction patterns, electrical conductivity
measurements (by the van der Pauw four-probe
method), and the determination of the pH isoelectric
state of the surface (by the hydrolytic adsorption
method). The adsorbates were prepared following stan-
dard procedures [5]. Carbon monoxide was synthesized
by the decomposition of formic acid in the presence of
hot concentrated sulfuric acid, ammonia, by the decom-
position of ammonium salts (ammonium chloride or
sulfate) with calcium oxide, and oxygen, by the decom-
position of potassium permanganate. The products
were analyzed by chromatography. The reproducibility
of the results was checked by repeating experiments.
Calculations and statistical data processing were per-
formed on a computer.
EXPERIMENTAL
Adsorption was studied by piezoquartz micro-
weighing [2] (sensitivity 1.23 × 10–11 g/(cm2 Hz)) over
the temperature and pressure ranges 252–393 K and
1.1–10.7 Pa, respectively. The adsorbents were films (d =
0.18–0.22 µm) of GaSb, ZnTe, and (GaSb)x(ZnTe)1 – x
solid solutions (x = 5, 10, 15, 90, and 95 mol % GaSb)
prepared by discrete thermal deposition in a vacuum
(Tcond = 298 K, p = 1.33 × 10–3 Pa) onto electrode sur-
RESULTS AND DISCUSSION
The adsorption values α for the gases studied
on GaSb–ZnTe system components were of 10−4–
faces of piezoquartz resonators (AT cut, eigenfre- 10–3 mol/m2. The experimental adsorption depen-
quency of vibrations 4.5 MHz) followed by annealing dences αp = f(T), αT = f(p), and αT = f(t) (typical depen-
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