Influence of Various Alcoholic Solvents on Structural, Morphological and Compositional Properties of Sprayed TiO2 Films

Titanium oxide thin films were prepared using solutions of titanium (IV) isopropoxide, acetyl acetonate dissolved in various alcoholic solvents such as methanol, absolute ethanol, 1-butanol, 2-butanol, 1-propanol, 2-propanol and tbutanol in the volumetric ratio’s of 1:1.5:22.5 by spray pyrolysis technique at substrate temperature of 350ºC under optimum conditions. The films have uniform thickness varying from 0.8–0.9 µm and good adherence to the substrate. XRD studies show poly crystalline nature of films. The Crystallite size (D), microstrain (e) and dislocation density (d) values varied from 96–289 nm, 1.25–3.75 10-4 lin-2m-4 and 1.2–10.76 1013lin m-2 respectively. Increase of microstrain, dislocation density and anatase to anatse-rutile mixed phase change may be attributed to increase in the concentration of lattice imperfections, crystallization of amorphous TiO2 films and long carbon chains in alcohol solvents. Present investigation reveals that alcohols play an important role in the crystallization of TiO2 layers. SEM micrographs exhibit spherical, square, needle shaped grains and grain boundary formation. Comparative study of SEM micrographs indicates variation of grain size from 0.1–0.7 µm. EDAX analysis shows the formation of stoichiometric TiO2 films, with an O-to-Ti atomic ratio of near 2 and variation of ratio as a function of various

Studies on optical and dielectric properties of Al2O 3 thin films prepared by electron beam evaporation and spray pyrolysis method

Al2O3 thin films find a number of applications in optoelectronics, sensors and tribology. In this paper, we report the preparation and characterization of alumina films prepared by both electron beam evaporation and spray pyrolysis method. The electrical properties of alumina films were determined by measuring (C-V) and (I-V) characteristics in a metal oxide semiconductor (MOS) structure. A relative dielectric constant (εr) of 9.6 for spray pyrolysed films and 8.3 for evaporated films was obtained. The breakdown electric field was found to be around 5 and 1MV/cm, respectively for spray pyrolysed and evaporated films. The refractive index of alumina films by evaporation was found to be 1.71 and 1.61 at 275 and 500 nm, respectively. The optical band gap of spray pyrolysed films deposited at 300 °C was found to be in the range of 5.40-5.55 eV. Structural, elemental analysis and stoichiometry of the films was studied by scanning electron microscope (SEM), energy dispersive X-ray analysis (EDAX), Auger electron spectroscopy (AES) and Rutherford back scattering (RBS) spectra. © 2003 Elsevier B.V. All rights reserved

Characterization of Al2O3 thin films prepared by spray pyrolysis method for humidity sensor

Al2O3 thin films were deposited on silicon, steel and nickel substrates to fabricate MOS and MIM devices. The films were prepared by spray pyrolysis method using a spray solution of Aluminium acetyl acetonate dissolved in dimethyl formamide and this solution was sprayed on to the hot substrates at temperatures of 300 and 350 °C. The films were amorphous in nature as detected by XRD. Capacitance versus voltage (C-V), current versus voltage (I-V) and capacitance versus frequency (C-f) measurements were taken for these films. MOS capacitor was used as a humidity sensor using the home made humidity sensor setup. ac capacitance and parallel resistance of the capacitor as a function of humidity were studied. It was found that the capacitance value increases from 0.537 to 2.073 nf with the increase in relative humidity (RH) from 0 to 90 and the resistance decreases from 153 to 93 kΩ with the increase in relative humidity from 20 to 87. Relative dielectric constant versus temperature measurements were done for the MOS device to check its ferroelectric behavior and its critical temperature was found to be around 66 °C. MIM device was also used as a humidity sensor by measuring capacitance as a function of time by keeping the sensor in a dessicator. The 555 timer circuits were used to check the sensor behavior of the MOS device. Volume resistivity and breakdown electric field of the film deposited on steel were measured and found to be 5 à 1011 Ω cm and 5 MV/cm, respectively. © 2006 Elsevier B.V. All rights reserved

Thickness dependent electrical properties of CdO thin films prepared by spray pyrolysis method

A large number of thin films of cadmium oxide have been prepared on glass substrates by spray pyrolysis method. The prepared films have uniform thickness varying from 200-600 nm and good adherence to the glass substrate. A systematic study has been made on the influence of thickness on resistivity, sheet resistance, carrier concentration and mobility of the films. The resistivity, sheet resistance, carrier concentration and mobility values varied from 1.56-5.72 à 10-3 Ω-cm, 128-189 Ω/â¡, 1.6-3.9 à 1021 cm-3 and 0.3-3 cm2/Vs, respectively for varying film thicknesses. A systematic increase in mobility with grain size clearly indicates the reduction of overall scattering of charge carriers at the grain boundaries. The large concentration of charge carriers and low mobility values have been attributed to the presence of Cd as an impurity in CdO microcrystallites. Using the optical transmission data, the band gap was estimated and found to vary from 2.20-2.42 eV. These films have transmittance around 77 and average reflectance is below 2.6 in the spectral range 350-850 nm. The films are n-type and polycrystalline in nature. SEM micrographs of the CdO films were taken and the films exhibit clear grains and grain boundary formation at a substrate temperature as low as 523 K

Effect of antimony and fluorine doping on electrical, optical and structural properties of tin oxide films prepared by spray pyrolysis method

Undoped, antimony doped and fluorine doped tin oxide films have been prepared by spray pyrolysis technique. The films were deposited on glass substrates at temperatures ranging between 300°C and 370° C by spraying an alcoholic solution of tin tetra chloride (SnCl4). Dopants used were antimony tri chloride (SbCl3) for antimony doped tin oxide (ATO) films, and ammonium fluoride (NH4F) for fluorine doped tin oxide (FTO) films. Among undoped tin oxide films, the least resistivity was found to be 3.1 à 10-3 Ω-cm for a molar concentration of 0.75M. In case of antimony doped films minimum resistivity value was found to be 7.7 Ã10 -4 Ω-cm for a film with (Sb/Sn) = 0.065, deposited at 370°C and in case of fluorine doped films it was found to be 1.67 à 10-3-cm for a doping percentage of 3 at of fluorine in 0.1 M solution. The corresponding values of the carrier concentrations were found to be 1.8 à 1020/cm3 and 9.98 à 10 20/cm3, respectively. The electrical and optical properties of these films were studied as a function of both doping concentration and substrate temperature. Doping percentage of antimony and fluorine in the spray solution has been optimized for achieving a minimum electrical resistivity. The dependence of electrical properties such as resistivity, carrier concentration and mobility of doped films were analyzed. Influence of antimony dopant on the optical band gap of the films has been reported on the basis of electron conduction mechanism. Air and argon annealing effects on the electrical properties of antimony doped tin oxide films were also studied. © World Scientific Publishing Company

Studies on tin oxide films prepared by electron beam evaporation and spray pyrolysis methods

Transparent conducting tin oxide thin films have been prepared by electron beam evaporation and spray pyrolysis methods. Structural, optical and electrical properties were studied under different preparation conditions like substrate temperature, solution flow rate and rate of deposition. Resistivity of un-doped evaporated films varied from 2·65 × 10-2 Ω-cm to 3·57 × 10-3 Ω-cm in the temperature range 150-200°C. For undoped spray pyrolyzed films, the resistivity was observed to be in the range 1·2 × 10-1 to 1·69 × 10-2 Ω-cm in the temperature range 250-370°C. Hall effect measurements indicated that the mobility as well as carrier concentration of evaporated films were greater than that of spray deposited films. The lowest resistivity for antimony doped tin oxide film was found to be 7·74 × 10-4 Ω-cm, which was deposited at 350°C with 0·26 g of SbCl3 and 4 g of SnCl4 (SbCl 3/SnCl4 = 0·065). Evaporated films were found to be amorphous in the temperature range up to 200°C, whereas spray pyrolyzed films prepared at substrate temperature of 300-370°C were polycrystalline. The morphology of tin oxide films was studied using SEM

Gas sensing properties of undoped and antimony doped tin oxide films prepared by spray pyrolysis and electron beam evaporation method

The thin films of undoped and antimony doped tin oxide films were prepared on glass substrates by spray pyrolysis and electron beam evaporation techniques. The substrate temperature was varied between 300 and 370°C in case of spray pyrolysis and 200°C in case of electron beam evaporation. The films were tested as gas sensors in the presence of liquid petroleum gas (LPG) and compressed natural gas (CNG). Undoped and antimony doped tin oxide films prepared by spray pyrolysis were more sensitive to LPG. Sensitivity of spray deposited ATO film in the presence of 1000 PPM of LPG was found to be 0.86 at an operating temperature of 400°C and it was 0.23 for undoped film. Undoped tin oxide films prepared by electron beam evaporation showed a maximum sensitivity of 0.79 at an operating temperature of 375°C on its exposure to 1000 PPM of LPG. The performance of the sensor has been explained on the basis of the structure and conduction mechanism of the tin oxide film

Electrical and optical properties of Al2O3 thin films prepared by electron beam evaporation and spray pyrolysis method

Al2O3 thin films find a no. of applications in optoelectronic sensors and tribol. In this paper, the authors report the prepn. and characterization of alumina films prepd. by both electron beam evapn. and spray pyrolysis. The elec. properties of alumina films were detd. by measuring the C-​V and I-​V characteristics in MOS structures. A relative dielec. const. (er)​ of 9.6 for spray pyrolyzed films and 8.3 for evapd. films was found. The breakdown elec. field was found to be 5 MV​/cm and 1 MV​/cm, resp., for spray pyrolyzed and evapd. films. The refractive index of alumina films by evapn. was found to be 1.71 and 1.61 at 300 nm and 500 nm resp. The optical band gap of spray pyrolyzed films deposited at 300° was found to be in the range of 5.4 eV to 5.55 eV

Influence of spray deposited TiO2 film thickness on the performance of n-TiO2/p-Si low cost hetero-junction solar cell and its utility as a carrier blocking layer

Titanium dioxide (TiO2) thin films with different thicknesses (55–95nm) were deposited in a multi-cycle on Si (100) substrates at a temperature of 350°C by spray pyrolysis technique under optimum conditions, for the application as a window layer for hetero-junction solar cells. The dark-light I-V characteristics of Au/TiO2/p-Si/Al hetero-junction solar cells have shown excellent rectifying behavior. The increase in film thickness can improve the short-circuit photocurrent (Isc) and open-circuit voltage (Voc), respectively. The estimated lower Isc and Voc confirm that the photo generated charge carriers being blocked or trapped at pin-holes which are rich in sprayed films, as carriers pass through the multi-cycle deposited TiO2 layers. The observed variation in the photovoltaic properties of cells could be due to oxidation on the Si substrate. Power conversion efficiency (η) of 0.00021% was obtained in a cell with the TiO2 film thickness of 55 nm. Decrease in dark current as a function of thickness indicates, the hole blocking behavior of hetero-junction solar cells