Photonic crystals in biology

Poster Session, Tuesday, June 15
Theme A1 - B702
Fabrication and Band Gap Engineering of Te rnary Nanofilms by Electroche mical Co-depos ition
1 *and Ümit Demir 2
1 Bingöl University, Sciences and Arts Faculty, Department of Chemistry, 12000, Bingöl-Turkey
2 Atatürk University, Sciences Faculty, Department of Chemistry, 25240, Erzurum-Turkey
Abstract-We report on the preparation of ternary compound (Bi x Sb 1-x ) 2 Te 3 nanofilms on single crystal Au (1 1 1) using a practical
electrochemical method, based on the simultaneous underpotential deposition (UPD) of Bi, Sb and Te from the same. Nanofilms are
characterized by X-ray diffraction (XRD), atomic force microscopy (AFM), energy dispersive spectroscopy (EDS) and reflection absorption-
FTIR (RA-FTIR). Nanofilms of bismuth-antimony-telluride with various compositions are highly crystalline and have a kinetically preferred
orientation at (0 1 5) for hexagonal crystal structure. AFM studies show uniform morphology with hexagonal-shaped crystals deposited over the
entire gold substrate. The compositional and structural analyses reveal that the films are pure phase with corresponding atomic ratios. The
absorbance studies show that the band gap of nanofilms could be tuned as a function of composition.
The binary and ternary compound semiconductors such as
Bi2Te 3 , Sb 2 Te 3 and (Bi x Sb 1-x ) 2 Te 3 have also attracted
considerable interest due to the requirements of environment
protection and military applications [1]. Particularly for
optoelectronic applications, it is important to be able to tune
the band gap of the material [2].
In recent years, extensive attention has been devoted to tune
the band gap of the binary compound semiconductors through
the quantum confinement effect [3]. However, progress in this
field has so far only allowed generating films with thickness
of a limited range, in which the quantum confinement effect is
prominent. The superior success of compound semiconductors
in optoelectronics, integrated circuits and thermoelectric
applications is largely attributed to the capability of energyband
gap engineering through composition modulation of
ternary compound semiconductors [4]. Most of the difficulties
experienced in research on alloy films lie in devising a
synthetic scheme to produce the desired ternary homogeneous
structure. To achieve homogeneous ternary compounds, the
growth rates of the two constituent materials (Bi2Te 3 and
Sb 2 Te 3 ) must be equal and the conditions necessary for the
growth of one constituent cannot impede the growth of the
other. Furthermore, the structure and bonding of the two
materials must be sufficiently similar to allow their facile
mixing; otherwise, the formation of segregated structures such
as two different binary compounds may occur [5].
Various methods have been used to synthesize ternary
(BixSb 1-x ) 2 Te 3 films. In these studies, ternary compounds
with only several x values were prepared. No comprehensive
study has yet been conducted on (Bi x Sb 1-x ) 2 Te 3 compound in
which x displays a broad variation. Here, we report on the
electrochemical synthesis of homogeneous ternary films in all
proportions.
Recently, we have developed a simple and convenient way
for electrochemical deposition of compound semiconductor
materials on the basis of a combination of co-deposition and
the UPD [6]. We have shown that this method could be used
to grow highly crystalline binary thin films [7,8].
In this study, we report on the synthesis of homogeneous
ternary nanofilms with various compositions. Nanofilms of
bismuth-antimony-telluride with various compositions are
highly crystalline preferred orientation at (0 1 5) for hexagonal
crystal structure. Studies show uniform morphology with
hexagonal-shaped nanocrystals. The films are pure phase with
corresponding atomic ratios. The band gap of nanofilms could
be tuned as a function of composition.
(a)
Figure 1. (a) Absorbance of (Bi x Sb 1-x ) 2 Te 3 nanofilms for different
compositions, (b) Plot of shifting of XRD peak positions for
nanofilms, with different compositions.
In summary, bismuth-antimony-telluride nanofilms could
be deposited underpotentially by an electrochemical codeposition
method at room temperature. The prepared
nanofilms with various compositions were homogeneous and
in highly crystalline structure. The dependence of the band
gap on the alloy composition is found to be linear and the
band gap could be tuned from 0.17 eV to 0.29 eV by changing
the concentration ratio of (Bi+Sb) solutions during
electrochemical deposition. These results indicate that ternary
compound semiconductor thin films could be successfully
prepared by UPD-based electrochemical co-deposition
technique. Atatürk University is gratefully acknowledged for
the financial support of this work.
*Corresponding author : 2Tiern@mynet.com
[1] J. Yang, W. Zhu, X. Gao, S. Bao, X. Fan, X. Duan, J. Hou, J.
Phys. Chem. B 110, 4599 (2006).
[2] J.B. Chaudhari, N.G. Deshpande, Y.G. Gudage, A. Ghosh, V.B.
Huse, R. Sharma, Appl. Surf. Sci. 254, 6810 (2008).
[3] Langmuir, 22, 4415 (2006).
[4] Y. Liang, L. Zhai, X. Zhao, D. Xu, J. Phys. Chem. B 109, 7120
(2005).
[5] R.E. Bailey, S.M. Nie, J. Am. Chem. Soc. 125, 7100 (2003).
[6] Chem Mater, 17,
935 (2005).
[7
517, 5419 (2009).
(b)
6th Nanoscience and Nanotechnology Conference, zmir, 2010 362