Hiroji Mitsuhashi

The effects of substrate bias on the structural and electrical properties of TiN films prepared by reactive r.f. sputtering

TiN films of the f.c.c. phase were grown by reactive r.f. sputtering on negatively biased substrates. The effects of the bias voltages on electrical properties such as the resistivity ϱ, the differential change in resistivity with respect to temperature dϱ/dT, the Hall coefficients and the superconductivity were studied in terms of the structural features of the films prepared. At sufficient substrate bias voltage (≈ 100 V) it was found that films with stable electrical properties could be produced.

Structure and Electrical Properties of Titanium Nitride Films

Metallic titanium, in nitrogen atmosphere with specified pressures (pN) ranging from 10-6 to 10-4 Torr, was evaporated on glass substrates heated at temperatures (Ts) between 300 to 500°C. X-ray analysis revealed that the films were composed of α-titanium, distorted titanium phase, amorphous phase, and TiN. The distorted titanium phase was found to extend to a high concentration of nitrogen (x=0.5). In particular, the specimens evaporated at pN=2.0×10-5 Torr and Ts=500°C had maximum resistivity of 270 µΩ-cm and a very small negative value of the temperature coefficient of resistance (0 to -20 ppm/°C) for an extended range of temperatures (-190 to 200°C). The excess resistivity of the distorted titanium phase can be mainly interpreted in terms of two kinds of carrier scattering, one due to nitrogen atoms randomly distributed at vacant interstitials, another attributable to grain boundaries involved.

Crystal structures and electrical properties of titanium films evaporated in high vacuum

Abstract Thin titanium films were deposited on glass substrates maintained at various elevated temperatures. X-ray studies showed that higher substrate temperatures caused growth of the {10 1 1} orientation in preference to the {0002} orientation and also increased the grain size in the films. The dependences of the electrical resistivity and the Hall coefficient on the substrate temperature were investigated: the variation of the resistivity with substrate temperature can be explained qualitatively in terms of the grain sizes of the films, but the main feature of the Hall coefficient was found to be closely related to the differences in preferred orientation of the crystals.

X-Ray Diffraction Data on Evaporated Organic Films of Fatty Acids

It was found by X-ray analysis and mass-spectrography that organic films of margaric and palmitic acids, belonging to a group of long chain saturated fatty acids, were obtained by thermal evaporation in vacuum. The present paper deals with their structural analysis by the powder diffraction X-ray technique: They are characterised by the fact that they posess a preferred orientation of the monoclinic structure with the basal plane which is parallel to the substrate plane, and that they show no thermal decomposition of the powders. In addition, the X-ray diffraction data on powder margaric acid is presented which exhibit several more peaks, not reported in an earlier work. The Miller indices are also assigned to the initial several peaks in the case of margaric acid. Alternation in physical properties expected between odd and even members of the fatty acids could not be found between margaric and palmitic acids as far as the crystal structure of the films is concerned.

Origin of negative temperature coefficient of resistivity in polycrystalline Ti‐N films

A negative temperature coefficient of electrical resistivity (TCR) has been observed in Ti‐N films prepared by reactive evaporation or sputtering. Some samples measured had a resistivity minimum and the minimum temperature changing with varying nitrogen contents. To study the origin of this anomalous temperature dependence of resistivity, the crystallographic structures of Ti‐N films were measured by x‐ray diffraction. The resistivity data could be analyzed in terms of the existing theory based on the structural Kondo effect. The results demonstrated that the negative TCR originated from higher concentration of interstitial nitrogen atoms in the Ti‐Nx solid‐solution phase, and nitrogen vacancies and/or intrinsic stacking faults in the fcc TiNx compounds.

Preparation and electrical properties of ε‐Ti2N thin films

An e‐Ti2N film nearly free from any other phase of the Ti‐N compound was deposited and the temperature dependencies of the resistivity and the Hall coefficient of the film were measured. The resistivity data were analyzed in terms of the Bloch–Gruneisen equation. The characteristic temperature θ of the film was 410.8 K, independent of the temperature ranging from 4.2 to 300 K. From a Hall measurement it was determined that the conduction carriers in the e‐Ti2N were holelike over the temperature range from 77 to 300 K.

D.C. conduction studies in evaporated films of stearic acid using an unconventional electrode geometry

Experimental studies of d.c. conduction in evaporated films of stearic acid are reported for the first time. An unconventional electrode geometry consisting of two lateral electrodes placed on the film symmetrically with a gap between of either 0.01 or 0.02 cm was used. The experimental results are found to favour the Poole-Frenkel type of electronic conduction mechanism, yielding values of the coefficient βPF that are relatively larger than the expected theoretical value. Some of the proposals suggested by other workers to explain the observed discrepancy in the βPF values are discussed, but in the present work it is mainly attributed to the different geometry of the electrodes in our test samples, and it is shown analytically that the fringe field region has an influence on the conduction characteristics that increases with increasing gap.

Structure of Ti–Fe Alloy Films Prepared by Composite-Cathode Sputtering

Films of the binary alloy TixFe1-x (0<x<1) of uniform composition, from 500 A to 1 µm thick, were prepared by d.c. sputtering with a composite cathode containing a Ti plate and Fe wires, or an Fe plate and Ti wires. Analyses of the films by EPMA and Auger electron spectroscopy showed that the composition was uniform over an area of about 20×20 mm2. X-ray and electron diffraction analyses of the the films showed the existence of amorphous phases at 0.05<x<0.30, 0.35<x<0.50 and 0.55<x<0.83 and a β-Ti (b.c.c.) phase at 0.80<x<0.94, in addition to an α-Fe (b.c.c.) phase at 0<x<0.30, a TiFe2 (hexagonal) Laves phase at 0.25<x<0.35, a TiFe (CsCl type) phase at 0.45<x<0.55 and an α-Ti (h.c.p.) phase at 0.83<x<1.

LUMINESCENCE FROM PLASTICALLY BENT CRYSTALS OF CADMIUM SULFIDE

Plastically bent crystals of CdS exhibit different luminescent spectra at 77°K depending on the type of edge dislocations. The bending of the crystals around an axis in a [0110] direction permits selective introduction of either Cd or S dislocations after completion of polygonization in conformity to the sense of the bending. The crystals with S dislocations showed two emission bands at about 6350 A and 7400 A of much more brightness than those with Cd dislocations.

Structures of Photoconductivity Spectra near the Fundamental Absorption Edge of Cadmium Sulfide

The photoconductivity structures of CdS single crystals near the adsorption edge were investigated using polarized light at about 81°K. Field dependence of wavelengths of peaks and spectral dependence of decay time of the response were measured as well. From these experimental results, the structures are classified into two groups, one is attributed to the photoconductivity due to excitons which occurs in the shorter wavelength range (λ<4870A) and the other to that from some imperfections involved in the crystal, which appears on the longer wavelength side.