A. Subrahmanyam

Electrical and optical properties of reactive DC magnetron sputtered silver oxide thin films: role of oxygen

Abstract Silver oxide thin films have been prepared on soda lime glass substrates at room temperature (300 K) by reactive DC Magnetron sputtering technique using pure silver metal target; the oxygen flow rates have been varied in the range 0.00–2.01 sccm. The X-ray diffraction data on these films show a systematic change from metallic silver to silver (sub) oxides. The electrical resistivity increases with increasing oxygen flow. The films show a p-type behavior (by both Hall and Seebeck measurements) for the oxygen flow rates of 0.54, 1.09 and 1.43 sccm. The refractive index of the films (at 632.8 nm) decreases with increasing oxygen content and is in the range 1.167–1.145, whereas the p-type films show a higher refractive index (1.186–1.204). The work function of these silver oxide films has been measured by Kelvin Probe technique. The results, in specific, the p-type conductivity in the silver oxide films, have been explained on the basis of the theory of partial ionic charge proposed by Sanderson.

Electrical and optical properties of reactively evaporated indium tin oxide (ITO) films-dependence on substrate temperature and tin concentration

The dependence of the electrical and optical properties of reactively evaporated indium tin oxide films on substrate temperature and tin concentration has been studied. Films of resistivity as low as 3*10-4 Omega cm and high visible transparency of about 91% have been obtained at higher deposition temperatures ( approximately 300 degrees C) for tin concentrations of 10-15 wt.% in the source alloy. Hall mobility in the films has been found to decrease with the addition of tin and increase with deposition temperature. An observed increase in carrier density with substrate temperature has been viewed as being due to the possibility that higher deposition temperature favours the incorporation of tin as Sn4+ in the films. In the optical band-gap calculation the effect of collision broadening, which is typical for a degenerate semiconductor, has been included and found to be significant.

Reaction kinetics of the formation of indium tin oxide films grown by spray pyrolysis

Abstract The electrical and optical properties of sprayed indium tin oxide (ITO) films have been reported as a function of tin concentration, substrate temperature Ts and the substrate-nozzle distance Dsn· Dsn and Ts seem to be interrelated for the optimization of good quality ITO films. Highly conduction (3 × 105 ohm−1m−1) and transparent (90% in visible region) ITO films were obtained when Dsn = 0.3 m, Ts = 693 K with 5% by weight of SnCl4 in the starting material. These data are discussed in the light of reaction kinetics.

Physical properties of silver oxide thin films by pulsed laser deposition: effect of oxygen pressure during growth

Silver oxide thin films have potential applications in ultra-high density optical non-volatile memories and in fluorescence imaging. In this paper, the physical properties of silver oxide thin films prepared at room temperature by the pulsed laser deposition (PLD) technique with varying oxygen pressure during growth are reported. The oxygen pressure in the growth chamber is varied between 9 and 50 Pa. The x-ray diffraction (XRD) analysis showed that all the films were polycrystalline. With increasing oxygen pressure in the growth chamber, it is observed that (i) the hexagonal Ag2O transforms to monoclinic AgO, (ii) the grain size in the film increases from 59 to 200 nm, (iii) the surface roughness of the film increases from 9 to 42 nm, (iv) the resistivity of the films increases from 1 to 4 × 104 Ω m, (v) the surface work function of the films increases from 5.47 to 5.61 eV and (vi) the optical band gap of AgO thin films decreases from 1.01 to 0.93 eV. Raman spectroscopy on AgO thin films shows low wave number peaks corresponding to the stretching vibration of Ag–O bonds. This study shows that single phase AgO thin films, a requirement for plasmonic devices, can be prepared at room temperature by the PLD technique with an oxygen pressure of 20 Pa.

Nano-vanadium oxide thin films in mixed phase for microbolometer applications

Among the several phases of vanadium oxide, mixed phases of VO2 and V2O5 are preferred for uncooled micro-bolometers with low noise. The aim of this investigation is to achieve mixed phase VO2 and V2O5 thin films with nanometre grain sizes and high temperature coefficient of resistance (TCR). Since the phase depends upon the oxygen reactivity, these vanadium oxide thin films are prepared by reactive electron beam evaporation at different oxygen flow rates and substrate temperatures. The mixed phases have been evaluated through x-ray diffraction and x-ray photo emission studies. The temperature dependence of resistance has shown that the films grown at 473 K with 2.8 × 10−5 mbar chamber pressure of oxygen (VO2 : V2O5 ratio of 36 : 64) have the highest TCR of −3.2 K−1 with a reasonable low resistance (120 Ω/square).

Electrical and optical properties of pyrolytically sprayed SnO2 film : dependence on substrate temperature and substrate-nozzle distance

Abstract The dependence of electrical and optical properties of SnO2 films, prepared using the spray pyrolysis technique, on the substrate temperature and substrate-nozzle distance was studied. A 0.05 cm diameter spray nozzle was employed ( 1 4 JAU, Spraying Systems Inc., U.S.A.). Films of about 10−3 Ω cm resistivity and high visible transparency of about 90% were obtained at a substrate temperature of 400°C and a substrate-nozzle distance of 30 cm. It has been observed that substrate-nozzle distance plays an important role in the reaction kinetics of SnO2 films. At a substrate-nozzle distance greater than 30 cm, the homogeneous reaction enhances and hence impedes the growth rate, resulting in inferior electrical and optical properties of the films.

Studies on the room temperature growth of nanoanatase phase TiO2 thin films by pulsed dc magnetron with oxygen as sputter gas

The anatase phase titanium dioxide (TiO2) thin films were deposited at room temperature by pulsed dc magnetron sputtering using pure oxygen as sputter gas. The structural, optical, electrical, and electrochromic properties of the films have been studied as a function of oxygen pressure in the chamber. The x-ray diffraction results indicate that the films grown above 4.5×10−2mbar are nanocrystalline (grain size of 28–43nm) with anatase phase. The films deposited at the chamber pressure of 7.2×10−2mbar are found to be highly crystalline with a direct optical band gap of 3.40eV, refractive index of 2.54 (at λ=400nm), and work function of 4.77eV (determined by the Kelvin probe measurements). From the optical emission spectra of the plasma and transport of ions in matter calculations, we find that the crystallization of TiO2 at room temperature is due to the impingement of electrons and ions on the growing films. Particularly, the negative oxygen ions reflected from the target by “negative ion effects” and the...

Giant magnetostriction in Sm1−xNdxFe1.93 compounds

The polycrystalline Sm1−xNdxFe1.93 (x=0, 0.08, 0.12, 0.16, 0.2, 0.24, 0.32, and 0.36) compounds are found to stabilize in MgCu2-type C15 cubic Laves phase structure. The compound x=0.12 is found to exhibit giant magnetostriction value of −1572×10−6 due to the anisotropy compensation between Sm3+ and Nd3+ ions. The easy direction of magnetization (EMD) is observed towards ⟨111⟩ for the 0⩽x⩽0.20 compounds, accompanied by a rhombohedral distortion. For the x=0.32 compound, an orthorhombic distortion, with a support that the EMD is towards ⟨110⟩, is observed.

Studies on the electrical and optical properties of reactive electron beam evaporated indium tin oxide films

Highly conducting ( rho =2.5*10-4 Omega cm) and transparent (92%) tin-doped indium oxide (ITO) films have been prepared by a reactive electron beam evaporation technique; the dependence of these properties on the substrate temperature (150-275 degrees C) and tin doping (0-15% by weight) has been studied. Hall mobility in the films has been found to increase with substrate temperature and decrease with the addition of tin. An attempt has been made to distinguish the different scattering mechanisms responsible for electrical conduction; it is found that the grain boundary scattering is negligibly small in these films. An analysis of the optical data has been made to evaluate the broadening parameter and the Burstein-Moss shift in optical band gaps.

Synthesis of Cu2O from CuO thin films: Optical and electrical properties

Hole conducting, optically transparent Cu2O thin films on glass substrates have been synthesized by vacuum annealing (5×10−6 mbar at 700 K for 1 hour) of magnetron sputtered (at 300 K) CuO thin films. The Cu2O thin films are p-type and show enhanced properties: grain size (54.7 nm), optical transmission 72% (at 600 nm) and Hall mobility 51 cm2/Vs. The bulk and surface Valence band spectra of Cu2O and CuO thin films are studied by temperature dependent Hall effect and Ultra violet photo electron Spectroscopy (UPS). CuO thin films show a significant band bending downwards (due to higher hole concentration) than Cu2O thin films.