Joy George

X-ray diffraction studies of Bi2O3 films prepared by reactive and activated reactive evaporation

Abstract Bi2O3 films were prepared by reactive evaporation and by activated reactive evaporation. The various phases obtained were studied using X-ray diffraction. Reactive evaporation always produced β-Bi2O3 films. For a given substrate temperature, low rates of deposition (less than 20 A s-1) always produced β-Bi2O3 films, whereas high rates of deposition (greater than 35 A s-1) produced α-Bi2O3 films when the oxygen partial pressure inside the chamber was kept constant. Films prepared by both reactive evaporation and activated reactive evaporation at substrate temperatures below 400 K were amorphous in nature and at higher substrate temperatures polycrystalline films were produced. The results obtained on annealing these films in high vacuum and in air are also reported.

Oxidation of bismuth films in air and superheated steam

Abstract Thin films of Bi 2 O 3 were prepared by oxidizing bismuth films (thickness about 2500 A) in air and superheated steam in the temperature interval 500–640 K. X-ray diffraction was used to identify the phases present. Single-phase films of α-Bi 2 O 3 , β-Bi 2 O 3 and γ-Bi 2 O 3 were prepared for the first time. It was found that oxidation and annealing of bismuth films in an oxygen-rich atmosphere always produced pure β-Bi 2 O 3 films, whereas oxidation and annealing in an oxygen-deficient atmosphere gave pure α-Bi 2 O 3 . α-Bi 2 O 3 films were converted to α-Bi 2 O 3 by heating in an oxygen-rich atmosphere, and β-Bi 2 O 3 was converted to α-Bi 2 O 3 by heating in an oxygen-deficient atmosphere.

Dendritic growth of phthalic anhydride crystals

Dendritic crystals of phthalic anhydride [C6H4(CO)2O] have been grown from solution and melt. The growth and morphology of these dendrites growing in the (001) plane are described. The , and directions are found to be the most active directions of growth in these dendrites. Some features of these dendrites hitherto unreported, have been observed which may account for the growth of platelet crystals.

Growth and morphology of phthalic anhydride crystals

Abstract Hollow crystals of phthalic anhydride have been grown from vapour in an open tube system. The whisker crystals are found to have incomplete prismatic walls leaving an opening in it. The different stages of growth are described.

The effect of the annealing of electrode films on the electrical resistivity of thin aluminium films

Abstract The resistance of aluminium films, coated on glass substrates with annealed and unannealed thick films of gold, silver, copper and aluminium as electrodes, was measured. The percentage variation in resistance of the aluminium films differs with the use of annealed and unannealed electrodes. This variation was found to be greater for gold, silver and copper electrodes and not very marked for aluminium electrodes. The respective roles of factors such as oxide formation and alloying at the film-electrode junction are discussed by considering the observed variation in the resistance of the films. An attempt is also made to correlate this variation with the microscopic features seen at particular electrode-film junctions.

Method for the preparation of dielectric films by activated reactive evaporation using resistively heated sources

A simple method is reported for the deposition of dielectric films using activated reactive evaporation (ARE). This method uses heated tungsten wire as an electron emitter and does not require a magnetic field for stabilizing the plasma, as required in an earlier reported method. The reactive gas pressure during coating is 5×10−4 Torr. An x‐ray diffractogram and optical transmission spectra of Bi2O3 films deposited at a rate ≊50 A/s using this apparatus are also presented.

The effect of the annealing of indium electrode films on the electrical resistivity of thin metal films

Abstract The resistances of thin films of gold, silver, copper and aluminium deposited onto glass substrates were measured using annealed and unannealed films of indium as electrodes. The percentage variation in resistance for the different metal films differs with annealed and unannealed electrodes. The effect of factors such as oxide formation, bubble formation and alloying at the electrode-film junction are discussed in the light of the observed variations in resistance of the films. An attempt is also made to correlate this variation with the microscopic features observed at particular electrode-film junctions.

Growth of phthalic anhydride spherulites

Abstract Spherulites of phthalic anhydride have been grown from melt, and the growth morphology described. It has been shown that the presence of impurities is not a necessary condition for spherulitic growth in the system. The surfaces of the melt grown spherulities have been characterised by chemical etching and quenching. The slip systems operating on these spherulites are identifed.

Amorphous films of PbS

Abstract The optical and electrical properties of amorphous PbS films prepared by reactive evaporation have been studied. Optical measurements indicate a band gap of 1·66 eV at room temperature. Optical studies and dielectric measurements suggest that amorphous PbS comprises a covalent network, in contrast to the rock-salt structure of crystalline PbS.

The variation in electrical resistance with temperature for Bi/Ag bilayer films

Abstract The variation in the electrical resistance of vacuum-evaporated Bi/Ag bilayers with different layer thicknesses was studied as a function of temperature. A silver overlayer 50 A thick increased the variation in R T /R with temperature of the bismuth film ( R T is the resistance of the film at temperature T and R the resistance at room temperature). It increased the resistance of the film and made the temperature coefficient of resistance at room temperature more negative. In addition, the resistance minimum was shifted to higher temperatures. The variation in resistance with temperature is explained on the basis of the Kaidanov and Regal model. When the total thickness of the bilayer film was kept constant (approximately 1000 A), the variation in resistance on annealing was dependent on the thickness of the silver layer. The rapid rise in resistance above 100 °C observed in films with silver layers between 100 and 600 A thick is explained on the basis of diffusion at the interface and aggregation of the silver film on the surface. By controlling the thickness of the layers it is possible to keep the variation in resistance with temperature of the film to a minimum.