Arun K. Pal

Morphology of thin silver film grown by dc sputtering on Si(001)

The morphology and growth mechanism of silver films approximately 150 A in thickness on Si(001) substrates have been studied by atomic force microscopy and x-ray reflectivity. The thin films prepared by dc sputtering at room temperature are composed of islands of silver. The shape and size distribution of these islands are studied using these two complementary measurement techniques.

In situ measurement of Hall effect, magnetoresistance, resistivity, and TCR of bismuth films

In situ measurements of Hall effect, magnetoresistance, resistivity, and temperature coefficient of resistivity of bismuth films (700–2600 A) were carried out in a specially designed evacuation chamber. The films were deposited on a glass substrate at 150°C and at a pressure of ∼10−6 Torr. The values of the mean free path and specular scattering parameter obtained were 14100 A and 0.5, respectively. The effect of the grain boundary on the electrical resistivity was also accounted for in the light of the Mayadas‐Shatzkes theory.

Effect of grain-boundary scattering on the electrical resistivity of indium films

Electrical resistivity and temperature coefficient of resistivity of polycrystalline indium films have been studied in the temperature range 30 to 90‡ C. It has been observed that the grain-boundary scattering theory of Mayadas and Shatzkes reproduces the experimental observations more faithfully than the size-effect theory given by Fuchs.

The effect of grain boundary scattering on the electron transport of aluminium films

The electrical resistivity and temperature coefficient of the resistivity of polycrystalline aluminium films (500-1700 AA) deposited on to a glass substrate were measured in situ at temperatures of 50, 100 and 140 degrees C. The effect of grain boundary scattering was analysed using the Mayadas-Shatzkes theory (1970). It is observed that the Mayadas-Shatzkes equation reproduces the experimental observation quite faithfully with R=0.28 and p=0, which indicates that the contribution from grain boundary scattering should be quite appreciable.

Resistivity and temperature coefficient of resistivity of tin films

The electrical resistivity and the temperature coefficient of resistivity of tin films (490 to 5000 Å) deposited onto glass substrates at room temperature (30° C) were measured in situ in the temperature range 30 to 150° C. It is concluded that Mayadas-Shatzkes theory reproduces the experimental observations more faithfully than Fuchs-Sondheimers theory.

Viscosity of Hydrogen—Nitrogen and Hydrogen—Ammonia Gas Mixtures

The viscosity of the binary gas mixtures H2–N2 and H2–NH3 has been measured in the temperature range 33°—200°C and at pressure below 10 cm Hg, by using a precise oscillating‐disk method. The data have been utilized to calculate interdiffusion coefficients for these systems.

Size-dependent magnetic properties of VO2 nanocrystals dispersed in a silica matrix

Magnetic nanocrystalline VO2 particles have been successfully synthesized in a silica glass matrix by the sol–gel method at calcination temperatures of 700 °C and above. The presence of small quantities of diamagnetic V2O5 nanocrystals in glass samples calcined at ≥800 °C has been confirmed. The thermal behavior of magnetization (zero-field-cooled and field-cooled) and magnetic hysteresis of VO2 nanocrystals in the 10–300 K temperature interval have demonstrated that the VO2 nanocrystals present in these glasses display superparamagnetic–ferromagnetic transition at low temperatures. X-band electron paramagnetic resonance (EPR) spectra of VO2 nanoparticles have depicted broad symmetric lines [ΔHpp~104 mT at room temperature (RT) and 250 mT at liquid nitrogen temperature (LNT)]. The increase in EPR line intensity on going from RT to LNT suggests that VO2 nanocrystals have undergone ferromagnetic-like ordering in the temperature interval RT–77 K. The presence of small numbers of isolated VO2+ ions in the SiO2 matrix has also been confirmed from EPR studies. From EPR and optical spectral studies it has been shown that the VO2+ ion has square pyramidal conformation with tetragonal compression having C4v symmetry. It is established that the in-plane σ bonding and out-of-plane π bonding are predominantly ionic in nature.

Electron paramagnetic resonance and other allied studies of sol?gel derived nanocrystalline chromium oxides in a silica glass matrix

Monolithic silica gels doped with various concentrations (1, 5, 10 mol%) of chromium oxide are prepared by a sol–gel process and are subjected to calcination at different temperatures up to 1200 °C. This has principally led to the formation of Cr2O3 nanocrystals and also of CrO3 nanocrystals at the higher calcination temperatures. The sizes of the Cr2O3 nanocrystals have been determined by x-ray diffraction (XRD) and transmission electron microscopy (TEM) studies and have been found to lie in the range 5–30 nm depending upon the dopant concentration as well as the calcination temperature. The formation of nonmagnetic CrO3 crystals in 10 mol% chromium oxide doped silica glass calcined at 1200 °C as a result of oxidation of Cr5+ ions to Cr6+ ions has been confirmed from XRD studies. Optical, infrared and X-band electron paramagnetic resonance (EPR) spectra of these nanocrystals have also been studied. EPR behaviours such as the g-factor and linewidth of Cr2O3 nanocrystals investigated at room and liquid nitrogen temperatures have been found to be quite distinct from those of antiferromagnetic (AF) bulk Cr2O3 crystals and may be manifestations of superparamagnetism/ferromagnetism in these nanocrystals. A narrow anisotropic EPR line () has been detected for chromium oxide doped silica gel calcined at 800 °C and has been assigned to isolated Cr5+ ions in a tetragonally distorted tetrahedral environment. Studies of the thermal dependence of zero-field-cooled (ZFC) and field-cooled (FC) magnetization (σ) 10 mol% chromium oxide doped silica glasses calcined at 800 °C by a SQUID magnetometer in the 5–300 K temperature range have revealed the occurrence of the blocking temperature TB at about 250 K, which is a characteristic feature of superparamagnetism in Cr2O3 nanocrystals. The superparamagnetic effects are almost quenched in the samples calcined at 1000 and 1200 °C because of the presence of larger nanocrystals in these samples. Magnetic hysteresis effects in these calcined samples at 300 K as well as at 5 K in the ± 6 T magnetic field range have also been investigated. The existence of ferromagnetic order at low temperature (5 K) as well as at room temperature (300 K) (for samples calcined at higher temperatures) has been confirmed.

Viscosity of Binary Polar‐Gas Mixtures

Viscosity of the binary polar‐gas mixtures ammonia–diethyl ether and hydrogen sulfide–diethyl ether has been measured as a function of composition and temperature by a precision oscillating‐disk method. The experimental results have been interpreted in terms of the Chapman–Enskog theory by using the 12–6–3 potential with a set of combination rules for polar–polar interaction. The viscosity data have been used to obtain the interdiffusion coefficients for these systems.

Size Effect Study on the Electrical Properties of Bismuth Films

Dependence of resistivity of bismuth films deposited onto microscopic glass slides at room temperature was studied at temperatures between –60°C to 110°C. The study revealed an interesting phenomenon that the negative TCR in the thinner films changes with thickness becoming positive at higher thickness. It was also observed that films deposited at a low rate onto a heated substrate at 160°C produces reversible films. The values of the mean free path and the specular scattering parameter obtained were 10300 A and 0.9 respectively.