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

Abstract. 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 undoped evaporated films varied from 2.65× $10^{-2}$ $\Omega-cm$ to 3.57× $10^{-3}$ $\Omega-cm$ 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 × $10^{-2}$ $\Omega-cm$ 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×$10^{-4}$ \Omega-cm, which was deposited at 350°C with 0.26 g of $SbCl_3$ and 4 g of $SnCl_4$ $(SbCl_3/SnCl_4 = 0.065)$ .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

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 $(SnCl_4)$. Dopants used were antimony tri chloride $(SbCl_3)$ for antimony doped tin oxide (ATO) films, and ammonium fluoride $(NH_4F)$ for fluorine doped tin oxide (FTO) films. Among undoped tin oxide films, the least resistivity was found to be $3.1\times 10^{-3} \Omega-cm$ for a molar concentration of 0.75 M. In case of antimony doped films minimum resistivity value was found to be $7.7\times 10^{-4} \Omega-cm$ for a film with (Sb/Sn) = 0.065, deposited at 370°C and in case of fluorine doped films it was found to be $1.67\times 10^{-3}\Omega-cm$ 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 $1.8\times 10^{20}/cm^3$ and $9.98\times 10^{20}/cm^3$, 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

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 oil glass substrates by spray pyrolysis and electron beam evaporation techniques. The Substrate temperature was varied between 300 and 370 degrees C in case of spray pyrolysis and 200 degrees 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 degrees 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 all operating temperature of 375 degrees C oil 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

Characterization of Al2O3Al_2O_3 thin films prepared by spray pyrolysis method for humidity sensor

$Al_2O_3$ 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 $350^oC$. 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 $k\Omega$ 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 $66^oC$. 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 $5\times10^{11} \Omega \hspace{2mm} cm \hspace{2mm} and\hspace{2mm} 5\hspace{2mm} MV/cm$, respectively

Effect of ethanol concentration on the porosity of spray pyrolyzed TiO2 films and their utility as humidity sensor

Titanium oxide films were prepared on ITO coated glass substrates at 350 degrees C using titanium (IV) isopropoxide, acetylacetonate and absolute ethanol as precursors by spray pyrolysis technique. The prepared films were characterized by X-ray diffraction, Scanning electron microscope, Fourier transform infrared spectroscopy and Energy dispersive analysis of X-rays. Estimated optical and electrical parameters such as refractive index, porosity, dielectric constant, energy band gap, carrier concentration, mobility by UV-Vis spectrophotometer, Hall effect and Van der pauw techniques were found to vary with ethanol volumetric concentration of 22.5-23. The observed increase in porosity from 45-59% facilitates the adsorption of water molecules inside films. The capacitance and resistance of metal-insulator-semiconductor structure were found to vary between 1.08-3.48 nF and 436-15 k Omega with increase in relative humidity. The fabricated humidity sensor found to posses 4s criterion such as sensitivity, stability and response-recovery times as 180%, +/- 10% and 58-106 s, respectively

Plant products with antifungal activity. From field to biotechnology strategies

In this chapter, informations on the recent advances regarding antifungal activity of natural products obtained from plants collected directly from their natural habitat or from plant cell and organ, cultures have been reported. The biotechnological approaches could increase uniformity and predictability of the extracts and overcome problems associated with geographical, seasonal, and environmental variations. Human fungal pathogens are the cause of severe diseases associated with high morbidity and mortality. The major human fungal pathogens are Candida species, dermatophytes, Aspergillus species, and Cryptococcus neoformans. Side effects and resistance are frequently attributed to the current antifungal agents. Moreover, the treatments often require long-term therapy and are not resolving. Plants represent a source of antifungal agents, but up to date, the number of new phytochemicals reaching the market is very low. This review attempts to summarize the current status of botanical screening efforts, as well as in vitro and in vivo studies on antifungal activity of plant products. Despite the currently non-uniform regulatory framework in all the states, the plant-derived products are increasingly in demand for their effectiveness. The basic conclusion from these studies is that rigorous, well-designed clinical trials are needed to validate the effectiveness and safety of plant extracts for their use as antifungals