Structural Phase Transition and Electronic Properties of AISb Nanocrystal Neha Tyagi , Anurag Srivastava Advance Material Research Laboratory ABV- Indian Institute of Information Technology and Management Gwalior (M.P), India
[email protected],
[email protected]
Abstract-
ab-initio
model. Recently our group has also performed the first
approach has been used to investigate the structural stability of
principle calculation to investigate the effect of shape on the
Density
functional
theory
(DFT)
based
-lnm sized AlSb nanocrystal in its zinc blende (B3), rocksalt (Bl)
structural and electronic properties of Pb and Si nanowires
and CsCl (B2) type phases under high compression. The self
[[0,1[]. The review of literature shows that probably no
consistent total energy calculations have been performed for
experimental
analyzing the stability of the material and found that B3 type phase is most stable amongst the other considered phases. It is revealed that under compression, the original B3 type phase of AlSb nanocrystal transforms to Bl type phase at a pressure of about 8.9 GPa, which is larger than that of bulk crystal. The
as
well
stable
(B3)
phase
is
comparatively
lower
than
its
bulk
counterpart.
research
has
been
the material, we thought it pertinent to perform the present analysis. II.
and pressure derivative have been calculated for all the three analysis finds that the band gap of AlSb nanocrystal in its most
theoretical
nanocrystal. Inspiring this and the technological importance of
ground state properties such as lattice parameter, bulk modulus stable phases of AlSb nanocrystal. The electronic band structure
as
performed on the pressure induced phase transition in A1Sb
COMPUTATIONAL DETAILS
Ab-initio pseudopotential approach as implemented in the Atomistix Toolkit Virtual Nano Lab (ATK-VNL) [[2] has been used for the present study. The computation has been made
in
self
consistent
manner
using
steepest
descent
geometric optimization technique with Pulay algorithm for
Keywords-phase transition; nanocrystal; AISb; first -principle I.
iteration mixing. A mesh cut-off of [00 Rydberg has been used throughout the study. The Brilloun-zone (BZ) integration is
[NTRODUCTION
performed with a Monkhorst-Pack scheme using lxlxSO k
Semiconductor nanocrystals of III-V compounds are of
points. The cutoff energy and the number of k points are varied
great significance due to their applications in various electronic
to test the convergence and are found to converge within the
and optical devices [1]. Rapid advances that have occurred in
force tolerance of O.OSeV/A for the reported value. The
the preparation and characterization of nanocrystals, finally
exchange correlation functional described within the local
enables the studies of transformations between stable states of
density approximation (LDA-PZ) proposed by Perdew and
fmite systems. Aluminum antimony (A1Sb) seems to be a
Zunger [13] and with generalized gradient approximation
promising candidate for transistors and p-n junction diodes due
revised-PBE (rev-PBE) as proposed by Zhang and Yang
to large band gap [2]. A1Sb nanoclusters have also been
[14,15], are used for the computation of total energies of A1Sb
synthesized
nanocrystal in its zinc blende (B3), rocksalt (B[) and CsCI
by
nanoscale
electrodeposition
[3,4].
Experimentally, the size dependent solid-solid transition have
(B2) type phases. The total energy for B3 type phase of A1Sb
been firstly reported by Tolbert and Alivisatos[S] in 1994,
nanocrystal with GGA rev-PBE potential is -299.07eV and
where they observed a wurtzite to rocksalt phase transition in
with LDA-PZ potential is -293.24eV, which indicates that
CdSe nanocrystal. A pressure induced first-order structural
GGA rev-PBE potential is quite good for the computation of
phase transition from wurtzite to rocksalt type structure has
total energy. The nanocrystals have been assumed to be
been observed in GaN nanocrystals at around 48.8 GPa using
roughly spherical and their diameter can be calculated by using
x-ray diffraction technique [6]. Similarly Lei et al.[7] have
the relationship of lattice parameter and number of atoms
investigated the wurtzite to rocksalt phase transfonnation in
present in the nanocrystal, given elsewhere [9]. Bulk modulus
AIN nanocrystal with an average size of lOmn and 4Smn at
and pressure derivaties have been analyzed using Murnaghan's
around 14.SGPa and 21.SGPa respectively. Zhang et al. [8]
equation of state[16].
used the pseudopotential total-energy approach to analyzed the
III. RESULTS AND DISCUSSIONS
stability of two high pressure structures, the AS (�-Sn) and rocksalt
structures, for
zinc blende
III-V
semiconductors
andfound that the bulk AISb shows zinc blende to rocksalt transformation
at
S.6GPa.
Viswanatha
et
al.
[9]
have
investigated the electronic structure of group III-V and II-VI semiconducting nanocrystals using full potential linearized augmented plane wave (FP-LAPW) method and tight-binding
978-1-4673-0074-2/11/$26.00 @2011IEEE
A.
Stability analysis andphase transition The stability of A1Sb nanocrystal of -1 mn size has been
analyzed in zinc blende (B3), rocksalt (B[) and CsCI (B2) type phases using density functional theory (DFT) approach. The computated lattice parameter (6.235 A) for bulk AISb in B3
421
type phase is in close match with its experimental as well as
semiconducting behavior of the AISb nanocrystal is very
theoretical Counterparts[17,S]. The calculated total energies
useful for various technological applications. In Fig.3 the DOS
for 83, 82 and 8I type phases of AISb nanocrystals are found
has been presented for 83 type phase of AISb nanocrystal,
to be -299.07eV, -29S.94eV and -29S.5IeV. In view of the
where the absence of electronic states near the Fermi level
total energies and binding energies of AISb nanocrystal in its
clearly supports the semiconducting behavior as predicted
different stable phases, B3 type phase is the most stable one
through band structure analysis. The calculated band gap for
with lowest total energy and highest binding energy. The
bulk AISb in original 83 type phase is around 1.40eV. The
stability trend for AISb nanocrystal is noticed as B3--->B2--->Bl.
comparative analysis shows that the calculated band gap of
The variation of calculated total energy of the system as a
AISb nanocrystal is 27.14% lower than its bulk counterpart.
function of volume has been plotted in Fig.l. The ground state properties such as lattice parameter, bulk modulus and pressure derivatives have been calculated for all the three stable phases
�
of AISb nanocrystal and summarized in table-I. The calculated bulk modulus for bulk AISb in its original B3 type phase is
4
-
.,
:::2::::
�
--
u
&i
the most stable 83 type phase of AISb nanocrystal is lower
-;:;>
0 ,..---------
§
66.ISGPa. On comparison, we found that the bulk modulus of
--=
-2
--=
">
than its bulk counterpart, which shows softening of material at
z
reduced dimension. On the other hand the 82 type phase of AISb nanocrystal attains the highest bulk modulus than the other two phases, which reveals that this phase is mechanically
Figure 2. Electronic band structure of AISb nanocrystal in B3 phase. The dashed line at 0 represents the Fermi level.
much stronger. However, due to the absence of any other reported data on AISb nanocrystals, the present computed values
could
not
get
compared.
AISb nanocrystal under
ambient conditions of temperature and pressure is found to
.2
crystallize in rocksalt type phase. The study also observes the
.s
'" "-' 0
83 to 8I structural transformation in AISb nanocrystal at around S.9GPa and in bulk around 7.I2GPa.
II
Il
.c 'V;
(I
I=: ,�
'�94 ,------,
I
I
�
-4 -+-tI:! ___ w
�
r
\"-
V \,
'\
'- I
-'2
�
I
0
:2
En!1'�y �e'1)
·1
Figure 3. The DOS profile for AISb nanocrystal in B3 phase. IV. ,�OII
The
-/-T---r-.-,--r----r-.-,-T"T"""i !U
�
�o
5U
6J
-,0
III
�u
,lil IN
present
CONCLUSIONS
paper
discusses
the
stability
of
AISb
nanocrystal in its zinc blende (83), rocksalt (8I) and CsCI
\'0,.,.(.8I phase transition in AISb nanocrystal at comparatively larger pressure than its bulk counterpart. The electronic band structure of AISb nanocrystal confirms its semiconducting behavior. ACKNOWLEDGMENT
Authors gratefully acknowledge the A8V-lndian Institute of Information Technology and Management, Gwalior for providing the infrastructural support and also thankful to Prof.
Electronic properties
Rajeev Ahuja, Uppsala
The electronic band structure and density of states (DOS)
University,
Sweden
for
valuable
discussions.
for AISb nanocrystals in its most stable zinc blende (B3) type
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