Photonic crystals in biology

Poster Session, Tuesday, June 15
Theme A1 - B702
The effect of transition metals on electronical properties of nanocrystalline indium oxide films by
experimental and theoretical approaches
Hossein Asghar Rahnamaye Aliabad, 1* Seyed Mohammad Hosseini 2 and Mohammad-Mehdi Bagheri-Mohagheghi 3
1 Department of Physics, Sabzevar Tarbiat Moallem University, Sabzevar, Iran
2 Department of Physics, Ferdowsi University of Mashhad, Mashhad, Iran
3 Department of Physics, Damghan University of Basic Sciences, Damghan, Iran
Abstract— Electronical properties of pure nanocrystalline indium oxide films and its alloys with Y and La have been investigated
using experimental and theoretical methods. The Full Potential Linearized Augmented Plane Wave (FP-LAPW)approach was used
with the Local Density Approximation plus Hubbard potential (LDA+U). Theoretical calculations have indicated that there are two
band gaps for pure Indium Oxide. The band gap is increased with Y dopant while decreases with La dopant. These impurities
increase the value of the electron effective mass in the bottom of the conduction band. We have also prepared samples by spray
pyrolysis method at 500 degree centigrade as thin films. The obtained optical band gap for pure indium oxide sample is 4.1 eV. It
was found that adding Y and La impurities increases and decreases the band gap, respectively. Increasing and decreasing
procedure of the band gap is conformed to both theoretical and experimental methods and also is in good agreement with others.
Over the last two decades there has been an attracted
increasing attention in both fundamental research and
industrial applications of transparent conducting oxides
(TCOs). These materials have many applications in numerous
devices such as flat panel displays, solar cells, gas sensors and
low-emissive windows [1, 2]. Among various transparent
oxides the indium tin oxide (ITO), indium oxide (In 2 O 3 ), tin
oxide (SnO 2 ), and zinc oxide (ZnO) are the dominant TCOs.
Tin-doped indium oxide (ITO), with a typical electrical
conductivity and transparency in the visible region is usually
used in thin coating form. Also the developments of
polycrystalline and amorphous transparent conducting oxide
semiconductors, used for practical thin-film transparent
electrode applications, have been under discussion in the
literature during the last few years [3, 4].
In this work, We have studied, the effect of Y and La on
electronical properties of In 2 O 3 nanostructure by using two
methods spray pyrolysis metod and Local density
approximation (LDA+U) based on the density functional
theory (DFT). Indium oxide can exist in three different phases
[5] characterized by space group symmetries I2 1 3, Ia 3 and
R 3 . In 2 O 3 with space group Ia 3 and the band gap of
Eg =3.7 eV is similar to many trivalent rare-earth oxides, such
as Yb 2 O 3 and Dy 2 O 3 . This phase of indium oxide has two nonequivalent
six-fold coordinated cation sites. The two cation
sites are referred to as equipoints “b” and “d”. The sites of the
cations are coordinated to six oxygen anions at three different
distances, which lie near the corners of a distorted cube with
two empty ions along one face diagonal. The unit cell contains
80 atoms and crystallized in cubic bixbyite structure. We
substituted the impurities in b positions, since at low
temperatures the impurities prefer to sit at b positions [6].
The Y an La -doped In 2 O 3 thin films have been deposited on
glass substrates at 500 °C with 250 nm thickness. For
deposition of In 2 O 3 films, we used the technique of spray
pyrolysis. The carrier gas used in all the experiments was N 2 .
These films have been prepared by sol–gel technique that is a
suitable chemical method for the preparation of
nanostructures. Initial solution composed of
In(NO 3 ).4H 2 O(0.08 wt%), H 2 O(0.44 wt%), HNO 3 (0.04 wt%)
and CH 3 CH 2 OH(0.44 wt%). For doping of Y and La, we have
used an aqueous ethanol solution consisting of Y(NO 3 ).5H 2 O
and N 3 O 9 La.6H 2 O with various doping levels from 0 to 25
and 33 wt% in solution.
The optical absorption and transmission spectra of films were
recorded using a UV visible Spectrophotometer and X-ray
diffraction was used to characterize the crystal structure of the
films.
The optical absorption edge for undoped In 2 O 3 film by spray
pyrolysis lies at 4.1 eV. This result is good agreement with
others [7].The effect of Y(In 1.85 Y 0.15 O 3 ) and La (In 1.85 Y 0.15 O 3 )
with 15 wt% increases and decreses optical band gap to 4.3 eV
and 4.05 eV respetively.
Obtained band gap for In 2 O 3 by density functional theory
(DFT) is 1.43 eV. This result is good agreement with others
[5]. The effect of Y (In 1.5 Y 0.5 O 3 ) and La (In 1.5 La 0.5 O 3 )
increases and decreses band gap to 1.88 eV and 1.24 eV
respetively. The experimental and theoretical results are good
agreement with each other.
*Corresponding author: h_rahnamay@yahoo.com
[1] T. J. Coutts, J. D. Perkins, D. S. Ginley and T. O. Mason,, Presented at the
195th Meeting of the Electrochemical Society, Seattle, Washington May 2-6,
(1999).
[2] D. S. Ginley and C. Bright (Guest Editors), "Transparent Conducting
Oxides" MRS Bulletin, 15-18, August (2000).
[3] T. Minami, , Semicond. Sci. Technol., 20 ,S35-S44 (2005)
[4] N. G. Lewis and D. C. Paine, , MRS Bulletin- Materials Research Society,
Vol. 25; Part 8,22-27 (2000).
[5]S. Zh. Karazhanov, P. Ravindran, P. Vajeeston, A. Ulyashin, T. G. Finstad
and H. Fjellvåg, , Phys. Rev. B 76, 075129(1-13) (2007).
[6]J. E. Medvedeva, Phys. Rev. Lett. 97, 086401(1-4) (2006).
[7] Prathap, P., Subbaiah ,Y.P.V., Devika ,M.and Ramakrishna Reddy, K.T.,
Materials Chemistry and Physics 100, pp. 375–379(2006).
Figure: Non-equivalent cation sites and anion vacancies in In 2 O 3 .
6th Nanoscience and Nanotechnology Conference, zmir, 2010 390