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Materiak Chemistry and Physics, 16 (1987) 189-195 189
PRELIMINARY NOTE
GROWTH OF Sb13 SINGLE CRYSTALS FROM VAPOUR BY THE TEMPERATURE
OSCILLATION METHOD
D. ARIVUOLI, F'.D. GNANAM and P. RAMASAMY
Crystal Growth Centre, Anna University, Madras-25 (India)
Received April 22, 1986; accepted June 5, 1986
ABSTRACT
Platelets of Sb13 were grown from vapour by the temperature oscillation
method. The surface features of the as grown crystals were found to depend
upon temperature gradients. The grown crystals were confirmed by chemical
and X-ray analysis.
INTRODUCTrON
The triiodides of antimony, arsenic and bismuth have semiconducting
properties which are retained even in the Liquid state [ll. They are
interesting due to the specific character of the chemical bond and the
associated crystal structure characteristics. These layered compounds SbI3
and Bi13 exist in several modifications or polytypes [21. These crystals
can be divided into two main types according to the type of spectrum of
the thermally stimulated depolarisation current (TSDCJ in photoelectret
state conditions. The first type crystals are obtained from the melt by
the Bridgman method or from the gas phase with high supersaturation. The
TSDC maxima for the first type crystals of BiI3 lie in the range 180 - 200 K
and for As1 3
and SbI 3
in the range 230 - 270 K 131. The second type of crystals
is obtained from gas phase with lower supersaturation. This type of
crystal does not show clear maxima.
Crystals of SbI3 were grown from the gas phase by the Bridgman method
[41 and from the vapour phase by Gasinets et al. [Sl. The present paper
describes the growth of SbI3 from vapour by the temperature oscillation
method and the surface features of the as grown platelets grown for different
temperature gradients.
0 Else~ierSequoia/Printed in The ~etheriands
190
EXPERIMENTAL
The polycrystalline sample was prepared from organic solvents using
antimony (99.999%) and analar grade (99.9%) resublimed iodine. The prepared
compound was confirmed by wide angle X-ray analysis [61. Experiments were
carried out in a sealed point tipped glass ampoule of length 15 cm and
diameter 12 mm, vacuum sealed at a pressure of 10 -4
torr. Crystals were
grown from vapour for different growth zone temperatures by oscillating the
source zone temperature. The source zone was oscillated between 170°C and
190°c. The experiments were carried out for the growth zone temperature
160, 140 and 130°C. The time-temperature profile for the source zone
temperature is as shown in Fig. 1.
190
182
174
166 I I I I I .- _
0 120 240 360 480 600
TIME ( seconds 1
Fig. 1. The time-temperature profile for the source zone.
RESULTS AND DISCUSSION
When the growth period is about 3 to 4 days platelets of SbI3 of dimensions
8 mm x 4 mm x 0.2 mm were obtained. Surface studies were done on the as
grown crystals using a Leitz polarising microscope. Figure 2 shows the surface
of the SbI 3 platelet depicting the hexagonal morphology. In some of the
crystals grown for the growth temperature of 160°C, growth layers far separated
from each other as they reach the edge of the crystal were obtained.
191
Fig. 2. surface of the as grown SbI3 single crystal.
Fig. 3. Instability pattern obtained for the growth zone temperatures of 160'~.
Figure 3 shows the instability pattern obtained on the smooth face. The
lnstablllty appears through the roughening of the macrosteps which seem to
indicate a lateral layer spreading mechanism of growth, typlcal of atomically
smooth interfaces. In some of the platelets the ripple morphology with the
elevated part as shown in Fig. 3 is suppressed. Figure 4 is the bunch of
growth steps formed due to the bidimensional nucleation. Figure 5 shows
the special type of macrolayers obtained when the growth temperature is
150°c. The spreading of the layers is due to bidimensional nucleation and
the spreading occurs layer by layer over a perfect crystal surface and steps
Fig. 4. Bunch of growth steps formed on the surface of the as grown crystal.
Fig. 5. Peculiar type of layers obtained for the growth zone temperature
of 140°c.
when the bunches of macrosteps cease to progress. The higher magnification
of Fig. 5 clearly showed that each macrostep or layer is a collection of
interlaced layers and diminishes in size and step height as it spreads over
another due to two dimensional nucleation. Figure 6 shows the assembly of
many spiral steps originating from dislocations distributed along a straight
line.
193
Fig. 6. Assembly of many spiral steps.
Fig. I. FormatIon of the flat topped steps.
When the growth zone temperature was 13O'C interesting features were
obtained. Flat topped hexagonal pyramidal patterns as shown in the Fig. 7
were obtained after 1 or 2 days. When the experiment was carried out for
5 to 10 hours deposition of pyramidal hexagonal platelets (Fig. 8) was
Fig. 8. Pyramidal platelets deposited after 5 to 10 hours.
obtained. This c!an be explained as follows. Let there be a homogeneous
flat surface on which deposits a solution of iodine and Sb13. The Sb13 vapour
dissolves in the liquid saturating the solution. So SbI 3 condenses, due
to heat loss along the temperature gradient created by the substrate, in
the form of flat topped hexagonal pyramids and platelets confirming that
the growth takes place by a vapour-liquid-solid mechanism. At high tempe-
ratures, the overgrowth formed in the initial process evaporates, resulting
in layers. So in a vapour-liquid-solid mechanism, large pyramids and spirals
are formed in the initial process. At high temperatures well developed wave-
like central regions and rarely well formed edges were obtained. At tempe-
ratures 150 to 160°C flat topped layers with spirals appear. So a vapour-
liquid-solid mechanism plays an important role in the initial phase of the
process in the present case and its effect decreases in the process of layer
growth when the temperature rises.
The grown crystals were confirmed as single crystals by the Laue technique
and the lattice parameters were found to be a = 7.49 i and c = 20.87 i.
ACKNOWLEDGEMENT
One of the authors (D.A) is grateful to UGC for awarding the research
fellowship.
195
REFERENCES
1 G. Fisher, Helv. Phys. Acta., 34 (1961) 827.
2 R.F. Rolsten, Iodide metals and metal iodides, Wiley, New York, (1961).
3 A.A. Kikunesh, I.P. Mikhalko, D.G. Semak and I.D. Turyanitsa, Izv. Akad.
Nauk. SSSR. Neorg. Mater., 10 (1974) 559.
4 T.N. Melnichenko, I.P. Mikhalko, A.A. Kikunesh, D.G. Semak and I.D. Turyanlsta, Izv. Akad. Nauk. SSSR. Neorq. Mater., 7 (1971) 2071.
5 S.M. Gasinets, G.M. Shpyrko, M.I. Golovei and T.N. Melnichenko, Inv. Akad.
Nauk. SSSR. Neorg. Mater., 13 (1977) 912.
6 Backer, Structure Reports, 11 (1947) 272.
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