Mihaela Girtan

Structural and optical properties of indium oxide thin films prepared by an ultrasonic spray CVD process

Polycrystalline In2O3 thin films have been synthesized by a modified chemical vapor deposition process using the pyrolysis of an aerosol generated by ultrahigh frequency spraying of a volatile precursor solution. The deposition has been carried out on glass substrates (350–550 °C). X-Ray diffraction has shown that deposited films are polycrystalline without second phases. The morphology of the surface as function of the substrate temperature has been studied using scanning electron microscopy (LEO Stereoscan 440). Transmission and reflection spectra of the sprayed films were examined in the 260–2600 nm spectral range and, for investigated films, the transmission coefficient in the visible and infrared regions exceed 85% and is weakly affected by deposition temperature. The optical band gap values, Eg, ranged between 3.57 and 3.68 eV. The Urbach tail parameter E0, was calculated for films deposited at different temperatures.

Influence of oxidation conditions on the properties of indium oxide thin films

Abstract Indium oxide (In 2 O 3 ) thin films have been prepared by thermal evaporation of indium in vacuum on a glass substrate at room temperature, followed by thermal oxidation in air. It was experimentally established that the heating velocity during the oxidation process has a strong influence on the electrical and optical properties of films as prepared. The temperature was increased from room temperature to 450°C, with velocities ranging between 0.1°C/s and 0.5°C/s. In 2 O 3 thin films as obtained have been examined for optical transparency function on wavelength. The calculated values of optical band gap range between 2.99 and 3.31 eV. Electrical conductivity measurements have also been carried out on the above oxide thin films as a function of temperature. Both the electrical and optical studies showed that In 2 O 3 thin films with higher transparency and electrical conductivity are obtained at higher oxidation velocities. Also, the experimental results show linear dependences of transmission coefficient on the oxidation velocity.

On the physical properties of indium oxide thin films deposited by pyrosol in comparison with films deposited by pneumatic spray pyrolysis

Abstract This paper presents the structural, electrical and optical properties of indium oxide thin films deposited by (1) pyrosol technique in comparison with the results that were obtained by spraying the same solution using (2) a pneumatic spray system. Films were deposited at temperatures ranged between 623 and 863 K onto glass substrates and investigated by scanning electron microscopy and X-ray diffraction. The transmission and reflectance spectra were determined in the 260–2600 nm spectral range. Resistivity as low as 6×10−3 Ωxa0cm with high optical transmission (>90%) have been obtained in In2O3 thin films deposited, when the ultrasonic atomizer system was used. The figures of merit ΦTC=T10/Rsh of films deposited using the two methods were calculated at different wavelengths. The advantages of the pyrosol method were obvious. The atomization of solution using the ultrasonic system leads to an improvement of the structural and electrical properties of films and allows the deposition of films with high transparency and electrical conductivity at lower substrate temperatures (∼673 K) compared to that needed in the case of pneumatic spray method (⩾773 K).

The influence of preparation conditions on the electrical and optical properties of oxidized indium thin films

Highly conductive indium oxide thin films (ρ=5×10−3 Ω cm) have been prepared by thermal oxidation in an open atmosphere of indium films deposited in vacuum by evaporation. The rate of indium film deposition was high (5 A s−1), and the oxidation has been carried out by exposing the samples to the atmosphere directly at high temperature (500°C) for different times. Structural, optical and electrical properties of these samples were investigated. Films exhibit a (111) preferred orientation, The value of the transmittance coefficient in the visible region of the spectrum was low (50%) but, concerning the electrical properties, an interesting behaviour was observed: at temperatures above room temperature the electrical resistance depends on the sense of the electrical current flow.

Surface wettability of titania thin films with increasing Nb content

TiO2 and TiO2/Nb amorphous thin films were grown on glass substrates by a sol-gel technique (spin coating). Films surface composition, structure, and morphology were derived from x-ray photoelectron spectroscopy, x-ray diffraction, and atomic force microscopy data. The investigated films showed a smooth surface (roughness values below 5u2009nm). A separate surface wettability investigation showed that by increasing the Nb amount in pristine titania films results in a decrease of contact angle (CA) values from 40° to nearly 0°, thus, indicating a super-hydrophilic conversion under UV illumination. This conversion rate is greatly enhanced by increasing the Nb content, the surface super-hydrophilic behavior occurring after a couple of minutes in the TiO2/Nb samples, but after 4u2009h in the pristine titania specimen. The current results are discussed in terms of the optical band gap shift towards higher energies, by increasing the Nb content in the films, a process explained based on small polaron hopping model.

Gas sensing materials based on TiO2 thin films

TiO2 thin films were prepared by spray pyrolysis using a solution of titanium tetrachloride and ethyl alcohol. The deposition was performed onto different substrates (silicon, quartz, glass) maintained at the same temperature, 270°C. After annealing, a predominant rutile structure is obtained for films deposited onto silicon and quartz substrates, as revealed by x-ray diffraction patterns. The TiO2 films were exposed to different gases, at different temperatures, in order to evaluate their gas sensitivity. The optimum operating temperatures, showing the highest gas sensitivity, were determined for some gases (acetone, ethanol, methane, and liquefied petroleum gas).

Nb-doped TiO2 thin films as photocatalytic materials

Amorphous undoped and Nb-doped films were obtained by the spin coating method. The films have a compact structure, as revealed by scanning electron microscopy, and are very thin, with thickness values under 100 nm. The photocatalytic activity of the films was evaluated by observing the decomposition of an oleic acid solution under UV irradiation, and by studying the change in the optical transmittance of an aqueous solution containing methylene blue, in the presence of the UV-irradiated films. More than 30 h, depending on doping, are needed to recover their initial contact angles before applying oleic acid. The increase of the optical transmittance of the methylene blue solution confirms the photocatalytic degradation of methylene blue on the Nb-doped TiO2 films. X-ray photoelectron spectroscopy studies, performed to detect the presence of the carbon on the irradiated surface of the films, drive to the conclusion that at the surface of the films, even for contact angles close to 0 ∘, the presence of carbon still can be detected, which demonstrates that hydrophilicity is ruled by a different mechanism than photocatalysis.