Photonic crystals in biology

Poster Session, Tuesday, June 15
Theme A1 - B702
Formation of Thermoelectric Nanos tructures by2T Electroche mical Atom-by-atom Codeposition
Ümit Demir 1 *
1 Department of Chemistry, Atatürk University, Erzurum 25240, Turkey
Abstract-Nanostructures of Bi 2 Te 3 , Sb 2 Te 3 and PbS were electrodeposited using a novel and p ractical electrochemical method, based on
simultaneous underpotential deposition of precursors of target compound from the same solution at a constant potential. These nanostructures
are characterized by X-ray diffraction (XRD), atomic force microscopy (AFM), energy dispersive spectroscopy (EDS) and reflection
absorption-FTIR (RA-FTIR) to determine structure, morphology, composition and optic properties.
Synthesis of nanomaterials with controlled size, shape and
crystalographic orientation has become an important issue in
material science research. Since the properties of
semiconductor nanocrystals, which possess many novel
properties that differ considerably from those of the bulk [1,2],
depend both on dimension and superlattice structure.
Therefore, the development of synthetic methods that enable
their precise control is expected to have a significant impact
on progress. Bi2Te 3 and Sb 2 Te 3 with a narrow band gap and
other V-VI group semiconductors are best-known materials
for TE applications at room temperature and are widely used
for thermoelectric (TE), biomedical and optoelectronic
applications as heat pumps, power generations, solid state
refrigeration, cooling IC chips, biochips, infrared sensors,
optoelectronic sensors, photo detectors, and so on. Recently,
we have developed a new electrochemical process, based on
co-deposition from the same solution at the upd of the
precursors of the target compound, which have been used for
the electrochemical deposition of PbS, PbTe, ZnS, and CdS in
the single crystal form [3-6]. The appropriate
electrodeposition potentials based on the underpotential
deposition potentials (upd) of precursors have been
determined by the cyclic voltammetric measurements. In the
present study, we illustrated the detailed growth process of
Bi 2 Te 3 and Sb 2 Te 3 [7] nano films and Bi 2 Te 3 nanorodstructured
films on single crystalline Au(111) electrodes by
using Atomic Force Microscopy (AFM), X-ray Diffraction
(XRD), Electron Dispersive Spectroscopy (EDS), and UV-v is-
NIR Spectroscopy techniques. We found out that that the
growth direction (orientation) and thickness of nanostructured
Bi 2 TeR 3 can be readily controlled by pH, composition of the
solution, and the time of the electrodeposition.
The morphological investigation of Bi2Te 3 nanostructures
revealed that the film growth follows 3D and 2D nucleation
and growth mechanism in acidic and basic solutions, resulting
in nanofilms and nanowires, respectively. XRD results show
that single crystalline nanostructures of Bi2Te 3 are highly
preferentially orientated along the (015) for nanofilms and
(110) for nanowires. The growth of Sb 2 Te 3 nanofilms follows
the nucleation and three-dimensional (3D) growth mechanism
resulting in high crystalline films of Sb 2 Te 3 (110) in
hexagonal structure, which were grown at a kinetically
preferred orientation at (110) on Au (111). Highly strong
quantum confinement effect, for both Sb 2 Te 3 and Bi 2 Te 3
nanostructures, was observed.
Figure 1. Bi 2 Te 3 nanostructures; (a) nanofilm, (b) nanowires
Figure 2. Nanostructures of Sb 2 Te 3 (a) and PbS (b)
Moreover, we applied a new modified electrochemical
method [8] to deposit nanostructure of PbS on a thiol modified
Au(111) surfaces. Electrochemical deposition was carried out
after the stripping of thiol from the surface at different
potential pulses. We showed that the size of the PbS
nanostructures could be controlled by the electrochemical
deposition time and pulse width.
In summary, structural and morphological studies indicate
that growth of these nanostructures follows atom by atom
growth mechanism resulting in highly crystalline
nanostructures grown at a kinetically preferred orientation.
Absorption measurements as a function of thicknesses
indicated that the band gap of the nanostructures increase as
the thickness decreases.
This study was supported by Atatürk University
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[6] T. Öznülüer, F. Bülbül, Ü. Demir, Thin Solid Films
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6th Nanoscience and Nanotechnology Conference, zmir, 2010 367