Transparent and Conducting TiO2 : Nb Thin Films Prepared by Spray Pyrolysis Technique

American Research Journal of Physics Original Article
ISSN 2380-5714 Volume 1, Issue 2, 2015
www.arjonline.org 57
Transparent and Conducting Nb:TiO2 Thin Films Prepared by
Spray Pyrolysis Technique
Maxwell J. Mageto1,4 .,
C.M. Maghanga2
., M. Mwamburi3
, Hassan Jafri4
1
Department of Physics, Masinde Muliro University of Science and Technology, P.O. Box 190, 50100, Kakamega,
Kenya.
2
Department of Physics, Kabarak University, P.o. Private Bag, Nakuru, Kenya.
3
Department of Physics, University of Eldoret, P.o. Box 1125, Eldoret, Kenya.
4
Ångström Laboratory, Uppsala University, P.O. Box 524, SE.75120 Uppsala, Sweden.
Abstract: To date, only sputtering and pulsed laser deposition (PLD) techniques have been employed
successfully to fabricate highly conducting and transparent TiO2:Nb (TNO) films. In this article, we demonstrate
that transparent and conducting Nb:TiO2
films can be made by the spray pyrolysis technique. The films were
deposited on Corning 7059 glass substrates at 500  15˚C using an alcoholic precursor solution consisting of
titanium (iv) isopropoxide and 5NbCl . The influence of increasing Nbconcentration on the electrical, optical
and structural properties was investigated. The minimum resistivity, 3.36 -3
10 Ω cm, for 2xx-1 ONbTi film (x
= 0.15) was obtained after 1 hour post deposition annealing in hydrogen atmosphere at 500˚C. The x-ray
diffraction of hydrogen annealed films showed a polycrystalline anatase (004)-oriented phase without any second
phases. The optical band gap for undoped and doped films lay in the range 3.38 – 3.47 eV. Using dispersion
analysis, optical constants were determined from spectro-photometric measurements for films on glass.
Keywords: Spray Pyrolysis; Titanium dioxide; Transparent conductor; Doping.
I. INTRODUCTION
Titanium dioxide ( 2TiO ) thin films have been investigated extensively in recent years owing to their potential
applications in areas such as photo-catalysis [1], electro-chromism [2], solar cells [3], self cleaning windows[2], gas
sensors[2], optical wave-guides[3] etc. Transparent conducting oxides (TCOs) [2] such as fluorine doped tin oxide
(FTO), tin doped indium oxide (ITO), aluminum doped zinc oxide (AZO) have attracted much attention both in
fundamental research and device applications such as flat panel displays (FPDs), touch panels, light emitting diodes
(LEDs), and Si-based solar cells [4]. Since 2005, niobium doped titanium oxide (TNO) has joined the conventional
class of TCOs mentioned above [2].
Anatase undoped 2TiO films have been deposited by various techniques [4,5] including sputtering, pulsed laser
deposition (PLD), chemical vapour deposition (CVD)[6], sol-gel[ 7,8] and spray pyrolysis[ 9]. To date, only
sputtering [10,11 ,12 ,13 ,14] and pulsed laser deposition (PLD) [15,16 ,17 ,18 ,19] techniques have been employed
successfully to fabricate highly conducting and transparent TiO2:Nb (TNO) films [4]. TNO films with resistivity 2 -
310-4
Ω cm at do pant concentrations of 3 - 6 at. % have been achieved by PLD [4,18] although unexpectedly,
resistivity remained on the order of 10-4
Ω cm for do pant concentrations as high as 20 at. % [18]. These highly
conductive TNO films are typically degenerate semiconductors: the do pant Nb atoms exist as Nb5+
ions, and release
conduction electrons with high efficiency [4]. The ionic radius of
5
Nb is 0.64 Å. This is close to that of
4
Ti
radius (0.60 Å). Thus, Nb is supposed to be substituted for Ti, in the lattice making the doped 2TiO a n-type
semiconductor.
In this paper, we report for the first time, the fabrication of low resistivity and transparent TNO films made by the
low cost, vacuum-free spray pyrolysis combined with post deposition annealing. The influence of increasing Nb
concentration on the electrical, optical and structural properties was investigated. This paper is organized as follows:
Section 2 describes the experimental setup for the preparation of the films including sample preparation, post
1
Corresponding Author: jmmageto@yahoo.com

American Research Journal of Physics, Volume 1, Issue 2, 2015
ISSN 2380-5714
deposition annealing and characterization techniques. Section 3 is devoted to experimental results including
chemical composition, structural, optical and electrical properties. An analysis of the optical data is given; results are
reported for optical constants and band gaps. This Section also covers film characterization with x-ray diffraction
and scanning electron microscopy. Section 4, summarizes the main results.
II. EXPERIMENTAL
2.1. Sample Preparation
Substrates were cleaned in an ultrasonic bath containing soap detergent for 15 minutes and the procedure was
repeated using pure ethanol instead of detergent. Undoped and niobium-doped titanium oxide films were deposited
onto pre-cleaned 0.5 mm thick
2
cm52.5 Corning 7059 glass and silicon substrates by spray pyrolysis at a
substrate temperature of 500  15˚C. The detailed description of the spray pyrolysis reactor is given elsewhere [20].
The deposition apparatus consists of a spray chamber, hot plate (substrate heater), temperature controller, atomizer
(spray nozzle) of diameter ~1mm, input gas valve, gas compressor, gas flow meter, conduit tube, pressure gauge.
Fig1. Spray Pyrolysis experimental setup.
The schematic view of the in-house-made spray pyrolysis system is depicted in
Fig1. The setup works inside a fume chamber whose air venting velocity is 0.51 m/s.The undoped 2TiO films were
produced from a precursor solution consisting of titanium (iv) isopropoxide (TPT) (97% Alfa Aesar) prepared by
mixing 34.7g of TPT with 54ml of 2,4-pentanedione (99% Alfa Aesar). They react to form Titanium diisopropoxide
bis(acetylacetonate) and isopropanol [21]. This reaction is exothermic meaning that the flask gets hot. After cooling,
the resulting solution was diluted with 810 ml pure ethanol and 10ml of 35% HCl under standard atmospheric
conditions and then stirred at 60rpm for 5 hours at room temperature. During this stirring step, plastic wrap was used
to cover the top of the beaker to prevent reaction with humidity. The resulting solution (labeled T) was divided into
several portions each of 200 ml per beaker. Nb - doped 2TiO films were prepared from solutions (labeled N) of
(28.4g, 0.11 mol) Niobium (V) Chloride, 5NbCl ,(99% Alfa Aesar) dissolved in 500 ml pure ethanol as well as
10ml of acetic acid, stirred as above and certain different amounts of this solution N added to each of the 200 ml of
solution T. Since solution N was responsible for the introduction of do pant, the amount of 5NbCl in the solution
mixture of T and N was based on the required doping level. The mixture was also stirred as stated above for 30
minutes.
The spraying parameters were as follows: substrate temperature of 500  15˚C was monitored with a thermocouple
fixed 1 mm deep in the interior of the substrate holder, directly under the substrate position. Carrier-gas: Nitrogen,
Carrier-gas pressure: 2.1 bar, flow rate of solution 7ml/min, nozzle-to-substrate distance: 65 cm horizontally and 40
cm vertically. To prevent rapid cooling of the hot plate temperature, spraying was done in short bursts.
2.2. Postdepositionannealing
After recording their transmittance, reflectance and x-ray diffraction (XRD) spectra, the sprayed samples were
annealed in hydrogen ambient at a pressure of 1atm at heating ramp speed of 4°/min with a dwell time of 1 hour at a
temperature of 500°C and thereafter cooling at a ramp speed of 4.4°/min, translating to a total of 4.8 hours.

ISSN 2380-5714
2.3. Sample characterization
The crystal structure and phase characterization were determined using a Siemens D5000 X-ray diffract meter
(XRD). The glazing incident angle was
0
1 in parallel beam geometry with the diffraction angle, 2θ , between
0
20
and
0
70 . The wavelength, λ , of the αCuK radiation was 1.540598 Å..A high resolution LEO 1550 Scanning
Electron Microscope (SEM) with a field emission gun was used to examine grain size, surface and cross-sectional
morphologies for different concentrations of Nb in the doped samples on silicon substrates. The elemental chemical
compositions of the TiO2: Nb films deposited on Si substrates were determined by Energy Dispersive X-ray
Spectroscopy (EDS).
The transmittance and reflectance measurements were done at near normal angle of incidence in the solar
wavelength range from 0.3 to 2.5 µm on a Perkin-Elmer Lamda 900 UV/VIS/NIR double beam spectrophotometer
equipped with an integrating sphere. A barium sulphate film served as reflectance standard.
Thickness d, of the as-deposited and hydrogen annealed samples prepared with different Nb doping concentrations
were estimated using the number of interference fringes, from the equation [[21]].
 1221
21
nλnλ2
λλ
d


(1)
Where 1n and 2n are refractive indices at two adjacent maxima (or minima) at 1λ and 2λ respectively and the
refractive index, n was determined as described by Swanepoel [22].
22
SNNn  (2)
Where
2
1S
TT
TT
2SN
2
mM
mM 



(3)
Here S denotes the refractive index of the substrate, MT and mT represents the maximum and minimum
transmittance envelopes at the fringes.
The estimated thickness was verified by fitting the experimental spectral data to theoretical spectral data based on
dispersion analysis using the SCOUT software [23] in the wavelength range 0.3 - 2.5 µm and also from SEM cross
sections. The thicknesses obtained from the three different methods agree within a discrepancy of not more than 5%
and are indicated below XRD spectra.
Dispersion analysis using a model for dielectric susceptibility of the film consisting of two parts: Drude [24] and
Kim terms [25] was used to simulate the measured reflectance and transmittance. Drude free electron model
accounts for intraband transitions of the conduction electrons which contribute to the optical properties. This model
has two adjustable parameters: plasma frequency, pΩ and damping constant, γ . The plasma frequency is
proportional to the square root of the carrier density; the damping constant is proportional to the inverse of the
mobility. The Drude dielectric susceptibility Drudeχ , expressed as a function of frequency ω, is given as [24]
 
iω
Ω
ωχ 2
2
p
Drude


(4)
The one oscillator contribution developed by Kim contains four adjustable parameters: TOΩ resonance frequency,
pΩ oscillator strength, τΩ damping constant, and the so called Gauss–Lorentz-switch constant σ .σ may vary
between zero and infinity. For σ = 0, a Gaussian line shape is achieved. A large value of σ (larger than 5) leads to a
Lorentzian line shape. The Kim oscillator models the weak broad interbank absorption in the measured wavelength
range. The interbank dielectric susceptibility described by Kim is given by [25];
 ωτωiωΩ
Ω
χ 22
TO
2
p
OscillatorKim,

 (5)
Model parameters were determined from best fits between computed and experimental data using Scout software
[23]. The best fit directly gave the optical constants of the film being studied as well as film thickness.

ISSN 2380-5714
Where
 













 


2
τ
TO
2τ
Ω
Ωω
σ1
1
expΩωτ
(5)
The sheet resistance of the thin films was determined by a two-point square probe with 8 point electrodes, having
Au tips in a linear arrangement and touching the coated surface. Since the two-point probe had equal length and
width, resistance per unit square was obtained. By measuring the sheet resistance, sR and the average thickness, t ,
of the films, the electrical resistivity, ρ or conductivity, σ of the samples was calculated using the following
relation.
tR
σ
1
ρ s (6)
Temperature dependent electrical resistivity measurements were done in the temperature range 10K to 300K in a
physical property measurement system (PPMS-6000, quantum design) using the standard four-probe method.
III. RESULTS AND DISCUSSION
3.1. Composition
0
5
10
15
0 10 20 30 40 50 60 70
Nb atomic % in solution
Nbatomic%inthefilm
Fig2. Nb at. % in solution (calculated) versus Nb at. % as determined from EDS
Energy dispersive spectroscopy (EDS) was used to measure the percentage of niobium in the films. Fig shows the
niobium concentration in the film as a function of chemical solution concentration for films deposited under similar
conditions. The composition of the as deposited Nb:TiO2 films were determined using Silicon substrates. The
experimentally determined composition was proportional to the Nb content in the solution, as shown in Fig. This
difference is attributed to low efficiency and a high consumption of chemical [26] due to the large separation
between the nozzle and substrate to allow vaporization of the solution.
3.2. Structural Studies
Fig3. XRD pattern of undoped and Nb-doped 2TiO films on Corning 7059 glass substrates before and after post
deposition annealing in hydrogen at 500°C Thickness of each film was 600 ± 10 nm.

ISSN 2380-5714
Fig4. XRD pattern of undoped and Nb-doped 2TiO films on Corning 7059 glass substrates at before and after post
deposition annealing in hydrogen at 500°C Thickness of each film 336 ± 6 nm
Fig shows the XRD patterns of the undoped and Nb doped (low Nb concentrations) polycrystalline titanium oxide
films on Corning 7059 glass substrates before and after post annealing. The peaks in the spectra are identified as
originating from reflections from the (101), (103), (004), (200), (105) planes of polycrystalline anatase titanium
oxide. No peaks from starting materials or any residual species were found in the spectra, confirming the proper
phase formation of the materials. Before annealing, the (101) peak increases with increasing Nb-doping, but after
post annealing the peak is suppressed.
Fig shows the XRD patterns of Nb doped (high Nb concentrations) amorphous and polycrystalline titanium oxide
films on Corning 7059 glass substrates before and after post annealing respectively. Note that as Nb concentration
was increased to 9.3 at. % Nb, the films turned from crystalline to amorphous structure before annealing. After post
annealing in hydrogen, the films crystallized. The intensity of the (004) peak increased remarkably as the Nb
concentration was increased to 15 at. % Nb, as shown in Fig
Fig5.Variation of grain size for Nb:TiO2
films annealed at 500 C
0
in hydrogen as a function of doping
concentration
Fig6.SEM image of films on silicon substrates as deposited (a) Undoped film (b) 5.7% Nb doped (c) 9.3% Nb
doped 2TiO

ISSN 2380-5714
The effective grain size was determined from the full-width at half-maximum (FWHM) of the x-ray peak of the
(004) plane using the well known Debye-Scherer formula, i.e.
 θcosL
λ0.9
D 
(7)
Where L is the diameter of the crystallites forming the film, λ is the wavelength of the x-ray line, and D is the
FWHM of the XRD peak. As displayed in Fig, for samples post annealed in hydrogen atmosphere at 500 C0
for 1
hour, the estimated crystallite size increased with increasing Nb content up to 15 at. %.
Fig7.Elemental chemical mapping for 9.3 at % Nb doped 2TiO
From the SEM observations in Error! Reference source not found., it can be concluded that the average particle
size of undoped titanium oxide is 70-150 nm. For Nb-doped titanium oxide, the particle size is larger in Nb-
containing samples and the homogeneity is good as evidenced from the elemental chemical mapping Figure 7.
3.3. Optical studies
Fig8. Experimental Spectral Transmittance and Reflectance of undoped and Nb-doped titanium oxide films
prepared at 500  15°C before and after post-annealing in Hydrogen atmosphere at 500°C for 1 hour (low Nb
concentrations). Thickness of films was 609  10 nm.
In order to compare the transparency of hydrogen annealed Nb:TiO2
thin films with various Nb-doping levels, their
optical spectra in the UV-VIS–NIR region were measured. The optical transparency of Nb:TiO2 thin films for

ISSN 2380-5714
various Nb-doping levels is shown in Fig. The transparency at 540 nm decreased with increasing Nb doping
concentration. Near the infrared wavelength range, the transparency decrease with increasing Nb doping became
much more pronounced for the hydrogen annealed films only.
Fig9. Experimental Spectral Transmittance and Reflectance of undoped and Nb-doped titanium oxide films
prepared at 500  15°C before and after post-annealing in Hydrogen atmosphere at 500°C for 1 hour (higher Nb
concentrations). Thickness of films was 336  6 nm
Transmittance and reflectance spectra for the TNO films before and after post annealing for low (Fig) and high Nb
concentrations (Fig) demonstrate the high transparency of TNO. The Thickness of films displayed in Fig is almost
twice those shown in Fig for the purpose of amplifying their optical behaviour in the NIR for ease of comparison.
Doping transforms the optical properties of the films to a significant degree only after post annealing in hydrogen.
Transmittance is approximately 65 - 83% throughout the visible wavelength region. With increasing
5
Nb concentration, the transmittance decreased in the wavelength region over 1000 nm. The film with the lowest
resistivity had the lowest transmission, especially in the near infrared. According to [[12]], the above can be
expected for plasma oscillations of the conduction band electrons in a partially filled d band.
Fig10. Spectral refractive index and extinction coefficient for 2TiO and Nb:TiO2
films after annealing in 1 atm
2H atmosphere at 500˚C for 1 hour
The optical constants are reported in Fig showing spectral refractive index n (λ) and extinction coefficient k (λ) for
undoped and doped films. The undoped film and the 22 at. % Nb doped film exhibit a dielectric behaviour with
n≈2.1 irrespective of wavelength for λ>500 nm. For the Nb doped films, the optical constants are qualitatively
different. In this case k(λ) increases for increasing λ, as expected for a metallic material, while n(λ) drops gently
towards larger λ. These effects increase in magnitude with increasing doping level of Nb.
The optical band gap, gE , was determined using the standard formula [[26]].
 n
gEhνααhν  (8)
Where α=2πk/λ is the absorption coefficient, hν, the photon energy, and n = 2 accounts for the fact that the indirectly

ISSN 2380-5714
allowed transitions across the band gap are expected to dominate. Fig shows plots of  2
1
αhν versus photon energy,
hν , in the high absorption region. Extrapolation of the curve to hν = 0 gave the indirect band gap of Nb:TiO2
films in the range 3.38 eV – 3.47 eV for the undoped and heavily doped films; which is comparable with the values
already reported [10,14 ,28]. The indirect band gap slightly widens due to the increase in the number of charge
carriers with increase in Nb-doping. The direct band gap (n = 1/2) was determined to be 3.75 eV which compares
well with 3.8 eV as reported [29].
Fig11.  2
αhv and  1/2
αhv versus hv plots for determining the optical direct and indirect band gaps of 9.3% Nb-
doped titanium oxide films indicated in the figure
3.4. Electrical Studies
Fig12.Resistivity variation as a function of temperature for 2 films
To determine whether the TNO films exhibited metallic behaviour, we measured the resistivity variation with
temperature from 10 to 300 K for 9.3%Nb and 2%Nb films and the results are presented in Fig. Surprisingly, the
polycrystalline TNO film with room temperature ρ ~10-3
Ω cm did not exhibit metallic ρ – T behaviour. Instead, the
ρ – T curve exhibited semiconducting behaviour. The semiconducting carrier transport with dρ/dT< 0 is a result of
the formation of shallow Nb impurity states [4].
Fig.13.Variation in electrical resistivity with increasing Nb doping concentration in TiO2 for Hydrogen annealed
films

ISSN 2380-5714
The literature values of resistivity variation with temperature from 10 to 300 K of 8 at % Nb doped [10] and 15 at %
Nb doped TiO2 [30] increases with increasing temperature depicting a metallic behavior
Undoped anatase TiO2 exhibited no measurable conductivity. Nb-doping caused a marked decrease in resistivity,
with a minimum values being 3.36 ×10-3
Ωcm at 300 K for 15 at. % Nb as shown in Fig.. Xiao Wan Zheng [Ref 30]
has documented a room temperature resistivity of ~1.3×10-3
Ωcm for 420 nm thick 15 at% Nb doped TiO2 thin films
deposited on (100) LaAlO3 substrates by rf sputtering method.
Fig14. ln σ versus 1/T plots for Nb-doped TiO2 films.
The Arrhenius plots of natural logarithm of electrical conductivity, Inσ (T), versus reciprocal temperature, 1/T, for
films having Nb/Ti = 2 and 9.3 in the temperature range from 10 to 300 K is depicted in figure 14. The films clearly
do not follow Arrhenius behavior.
Three non distinct regions of σ (T) corresponding to the low, intermediate and high temperature ranges are observed.
In the high temperature region (190 – 300 K) for 9.3% Nb and (227 - 300 K) for 2% Nb the abrupt increase in σ
means that the conduction is thermally activated and assumed to arise from the contribution of the conduction
between the extended states. This behaviour of σ (T) is well described by the simple Arrhenius law,
σ(T)= σ0 exp.∆E/KBT, (9)
Where ∆E is the corresponding activation energy and σ0 the pre-exponential factor. From the slope, the activation
energy for 2TiO was calculated to be ~ 1.0 eV which compares favorably with the value of 0.78 eV as already
reported for sprayed undoped 2TiO films [31]. The calculated values of both ∆E and σ0 are given in Table 1. It is
seen that uncertainties in the values of both parameters are high.
Fig15.Plots of ln( σT1/2
) versus (1/T)1/4
for Nb-doped TiO2 films.
The intrinsic electrical conductivity in n-type anatase 2TiO films has been measured. The value for the band gap Eg
was calculated from the experimental data, assuming intrinsic conductivity of the form
 T/2kEExp.constantσ Bg (10)
We used the intrinsic region in the figure to calculate the band gap of 2TiO samples. The intrinsic region is the
straight line extrapolated with a dashed line.

ISSN 2380-5714
constant
T
1
2K
E
σn
B
g

(11)
The slope,
B
g
2K
E

, directly gave the band gap of intrinsic 2TiO as 2eV which was somewhat narrower than the
empirical value of 3.2 eV. This under estimation of the band gap is similar to the one reported for GGA calculations.
We plotted  Tσn versus  1/41/T for the low temperature (9.7 - 38.9 K ) regime shown in figure 15. The
curves are well fitted with straight lines, satisfying Mott’s formula for variable range hopping [32]
    1/4
0
/
0 /TTexpT/σTσ  (12)
Where  fB
3
0 EN/K16αT 
Rearranging the above equation
   constant
T
1
TTTσn 1/4
1/4
0  (13)
Gradient = 1/4
0T =   1/4
fB
3
EN/K16α
0 is the pre-exponential factor,  fEN is the density of localized states at the Fermi level, α describes the spatial
extent of the localized wave function and is assumed to be 0.124 Å-1
and KB is the Boltzmann constant. In
accordance to Mott’s theory, the room temperature hopping distance, R, and hopping energy, W, is given by the
following expressions
  1/4
fB ENTKαπ9/8R  (14)
  f
3
ENRπ43/W (15)
Necessary conditions for Mott’s variable-range hopping process TKW B and 1Rα  are satisfied.
Table1.Calculated values of ∆E and associated parameters.
Nb/Ti ∆E(eV)
0σ 1
cm)(Ω  2
10
 0T (K) /
0σ 1/21
Kcm)(Ω 
 fEN
31
cmeV  25
10
 R(cm)
9
10
W(MeV)
4
10

2 1.2 1.77 731.16 3007.005 1.9 2.2 1.2
9.3 1.0 0.19 530.84 17.68117 2.6 2.2 1.2
IV. CONCLUSION
Conducting and transparent thin films of Nb doped 2TiO on Corning 7059 glass substrates were successfully
synthesized at C15500 o
 by the low cost, vacuum-free spray pyrolysis technique for the first time. Prior to this,
only sputtering and PLD had been used successfully to fabricate highly conducting and transparent TNO films. The
Nb-doped 2TiO films were deposited with do pant concentrations ranging from 0 to 22 at% in the film. The XRD of
annealed films showed a polycrystalline anatase (004)-oriented phase without any second phases. ED’s studies of
chemical composition of the films showed that the exact amounts of Nb in the films are less than that taken in the
solution. SEM studies showed that the particle sizes lie in the range 70–300 nm. In the 2TiO thin films,
5
Nb acts
as a donor so that, with increasing Nb doping up to 15 at%, the resistivity of the films decreases systematically.
However, increase in Nb doping beyond 15 at%, the resistivity increases sharply. The as deposited films were non-
conductive but after annealing in 2H at 1 atm. for 1 hour, doped films turned conductive. Films doped with 15 at.%
Nb, 336 nm thick, exhibited a lowest room temperature resistivity of 3.36  -3
10 Ω cm and visible transmittance of

ISSN 2380-5714
over 65% after post deposition annealing in 2H . The electrical conductivity increases with the (004) peak intensity
which is strongly correlated with the anatase crystallinity. The ρ - T curve for Nb:TiO2
exhibited semiconducting
behavior. The optical band gap for undoped and doped films lay in the range 3.38 – 3.47 eV.
V. ACKNOWLEDGEMENTS
The authors would like to thank the International Program in the Physical Sciences (IPPS), Uppsala University for
the financial and material support to the Department of Physics, Moi University. Financial support from the Swedish
Research Council for this research is greatly appreciated.
REFERENCES
[1] Fujishima A. and Honda K., Nature, 238 (1972) 37
[2] C.G. Granqvist, Transparent conductors as solar energy materials: A panoramic review, Solar Energy Materials & Solar
Cells 91 (2007) 1529–1598
[3] Siefering K.L. and Griffin G.L., J. Electrochem. Soc. 137 (1990) 1206.
[4] T. Hitosugi, N. Yamada, S. Nakao and T. Hesegawa, Properties of 2TiO -based transparent conducting oxides, Phys. Status
Solidi A 207, No. 7 (2010) 1529-1537.
[5] D. P. Norton, Synthesis and properties of epitaxial electronic oxide thin-film materials, Mater. Sci. and Eng. R 43 (2004)
139–247
[6] Kurtz S. R. and Gordon R. G., Chemical vapor deposition of doped TiO2, thin films, Thin Solid Films, 147 (1987) 167-176
[7] Mattsson A., Leideborg M., Larsson K., Westin G., and Osterlund L., Adsorption and Solar Light Decomposition of
Acetone on Anatase TiO2 and Niobium Doped TiO2 thin Films, J. Phys. Chem. B, 110, No. 3 (2006) 1212-1220
A. Tsuzuki, H. Murakami, K. Kani, S. Kawakami, Y. Torii, Preparation of Nb-doped TiO2 films by Sol-gel method, J. Mater.
Sci. Lett. 9 (1990) 624 - 626
[8] Conde-Gallardo A., Guerreroa M., Castillo N., Soto A.B., Fragoso R., Cabanas-Moreno J.G., TiO2 anatase thin films
deposited by spray pyrolysis of an aerosol
[9] of titanium diisopropoxide, Thin Solid Films 473 (2005) 68– 73
[10] Y. Sato, Y. Sanno, C. Tasaki, N. Oka, T. Kamiyama, Y. Shigesato, Electrical and optical properties of Nb-doped 2TiO
films deposited by dc magnetron sputtering using slightly reduced Nb-doped x-2TiO ceramic targets, J. Vac. Sci. Technol.
A 28(4), (2010) 851–855.
[11] N. Yamada, T. Hitosugi, J. Kasai, N. L. H. Hoang, S. Nakao, Y. Hirose, T. Shimada, T. Hesegawa, Transparent conducting
Nb-doped 2TiO (TNO) thin films sputtered from various targets, Thin Solid Films 518 (2010) 3101–3104
[12] M. A. Gillispie, M. F. A. M. van Hest, M. S. Dabney, J. D. Perkins, and D. S. Ginley, rf magnetron sputter deposition of
transparent conducting Nb-doped 2TiO films on 3SrTiO , J. Appl. Phys. 101, (2007) 033125
[13] N. L. H. Hoang, N. Yamada, T. Hitosugi, J. Kasai, S. Nakao, T. Shimada, and T. Hasegawa, Low-temperature Fabrication
of Transparent Conducting Anatase Nb-doped 2TiO Films by Sputtering, Appl. Phys. Express 1 (2008) 115001
[14] C.M. Maghanga, J. Jensen, G.A. Niklasson, C.G. Granqvist and M. Mwamburi, Transparent and conducting Nb:TiO2
films made by sputter deposition: Application to spectrally selective solar reflectors, Solar Energy Materials & Solar Cells
94 (2010) 75–79
[15] T. Hitosugi, A. Ueda, S. Nakao, N. Yamada, Y. Furubayashi, Y. Hirose, S. Konuma, T. Shimada, T. Hasegawa,
Transparent conducting properties of anatase 20.060.94 ONbTi polycrystalline films on glass substrate, Thin Solid Films 516
(2008) 5750–5753.
[16] T. Hitosugia, A. Ueda, S. Nakao, N. Yamada, Y. Furubayashi, Y. Hirose, T. Shimada and T. Hasegawa, Fabrication of
highly conductive 2xx-1 ONbTi polycrystalline films on glass substrates via crystallization of amorphous phase grown by
pulsed laser deposition, Appl. Phys. Lett 90, (2007) 212106–3.
[17] T. Hitosugi, A. Ueda, Y. Furubayashi, Y. Hirose, S. Konuma, T. Shimada, and T. Hasegawa, Fabrication of 2TiO -Based
Transparent Conducting Oxide Films on Glass by Pulsed Laser Deposition, Jpn. J. Appl. Phys. Vol. 46, No. 3, (2007), pp.
L86–L88.
[18] Y. Furubayashi, T. Hitosugi, Y. Yamamoto, K. Inaba, G. Kinoda, Y. Hirose, T. Shimada and T. Hasegawa, A transparent
metal: Nb-doped anatase 2TiO , Appl. Phys. Lett. 86, (2005) 252101–3 Y. Furubayashi, T. Hitosugi, Y. Yamamoto, Y.

ISSN 2380-5714
Hirose, G. Kinoda, K. Inaba, T. Shimada, T. Hasegawa, Novel transparent conducting oxide: Anabas 2xx-1 ONbTi , Thin
Solid Films 496 (2006) 157 – 159.
[19] Karl son T., Roes A. and Ribbing C. G., Influence of spray conditions and do pants on highly conducting tin oxide films,
Solar Energy Materials 11 (1985) 469 – 478
[20] L. Kavan and M. Gratzel, Highly efficient semiconducting tio2, photo electrodes prepared by aerosol pyrolysis,
Electrochemical Acta, 40 No. 5 (1995) 643-652
[21] Swinepoxes R. Determination of the thickness and optical constants of amorphous silicon. Phys. E, Sci. In strum. 16, 1214
(1983)
[22] W. Thesis, in: W. Teiss (Ed.), Scout Thin Film Analysis Software Handbook, Hard- and Software, Aachen, Germany, 2001
<www.mtheiss.com>, pp. 54–57.
[23] N. W. Ashcroft, N. D. Mermin, Solid State Physics,, CBS Publishing, Philadelphia, USA, 1976, p. 18.
[24] C.C. Kim, J.W. Garland, H. Abad, P.M. Raccah, Modeling the optical dielectric function of semiconductors: extension of
the critical-point parabolic-band approximation, Phys. Rev. B 45 (1992) 11749
[25] J. C. Manifacier, Thin metallic oxides as transparent conductors, Thin Solid Films, 90 (1982) 297 – 308
[26] C.G. Granqvist, Handbook of Inorganic Electrochromic Materials, Elsevier, Amsterdam, the Netherlands, 1995, pp. 265–
275.
[27] R. Ayouchi, C. Casteleiro, R. Schwarz, J. R. Barrado, and F. Martín, Optical properties of TiO2 thin films prepared by
chemical spray pyrolysis from aqueous solutions, Phys. Status Solidi C 7, No. 3–4, (2010) 933– 936.
[28] Nickolay Golego, Thin-film polycrystalline titanium-oxygen semiconductors prepared by spray spray pyrolysis, PhD
thesis, The University of Guelph, Canada, August 1998.
[29] Xiao Wan Zheng, Zhi Qing Li, (2010) Low-Temperature magnetoresistance of Nb – doped TiO2 transparent conducting
films, Solid State Communications, Vol. 150 PP 1625 – 1628.
[30] Ayouchi R. (2010), C. Casteleiro, R. Schwarz, J.R. Barrado, and F. Martín, Optical properties of TiO2 thin films prepared
by chemical spray pyrolysis from aqueous solutions, Phys. Status Solidi C, volume 7, No. 3–4, pp. 933– 936.
[31] Mott, N.F., Conduction in non-crystalline materials, III. Localized states in a pseudo gap and near extremities of
conduction and valence bands Phil. Mag. 19: (1969) 835.

Transparent and Conducting TiO2 : Nb Thin Films Prepared by Spray Pyrolysis Technique

More Related Content

What's hot

Viewers also liked

Similar to Transparent and Conducting TiO2 : Nb Thin Films Prepared by Spray Pyrolysis Technique

Recently uploaded

Transparent and Conducting TiO2 : Nb Thin Films Prepared by Spray Pyrolysis Technique