Kazutoshi Ohashi

Thermal Expansion Coefficient of Synthetic Diamond Single Crystal at Low Temperatures

The lattice parameter of synthetic diamond single crystals has been measured in the range 4.2-320 K by the X-ray diffraction method. The lattice parameter is found to be nearly constant between 4.2 and 90 K. The thermal expansion coefficient α calculated from the experimental results is very small (of the order of 10-7 or less) and no definite evidence of the negative thermal expansion is found within our relative experimental accuracy of the order of ±1×10-6.

The thermal expansion coefficient and Gruneisen parameter of InP crystal at low temperatures

The thermal expansion of the lattice constant of InP crystal has been measured in the range 4.2-300 K by the Bond method and the results are shown graphically. The thermal expansion coefficient alpha calculated from the experimental results is negative between 15 and 80 K and positive below 15 K. The corresponding Gruneisen parameter gamma closely follows the behaviour of alpha and the values of alpha and gamma are tabulated and shown graphically. The results do not agree with the phenomenological theory in which only a negative alpha is predicted for InP at low temperatures.

Sputter-induced defects in Zn-doped GaAs Schottky diodes

Schottky barrier diodes are made by ac magnetron deposition of Au on p-type GaAs substrates. Sputtering causes donor-like defects in the surface region of semiconductors, and these donor-like states compensate mostly the Zn shallow acceptor states over distances of 200 nm below the surface. These defects are attributed to the As Frenkel pairs VAs?Asi with an energy level at 0.27 eV below the conduction band. The As Frenkel pairs are responsible for the Fermi level pinning at metal?semiconductor interfaces and also for the observed change in barrier height in sputtered GaAs material.

Thermal expansion of a boron-doped diamond single crystal at low temperatures

The lattice parameter of a single-crystal boron-doped synthetic diamond has been measured in the range 4.2-300 K by x-ray diffraction (Bond method), with precision . Over the whole range the results are consistent with A, where T is the absolute temperature. The dilation due to doping indicates a boron concentration of about 100 ppm. The increase of thermal expansion over that of an undoped synthetic diamond is found to be unexpectedly large (10-15%), giving an apparent dilation on doping that is markedly temperature dependent.

The negative thermal expansion coefficient of GaP crystal at low temperatures

The thermal expansion of the lattice constant of a GaP crystal was measured in the range 4.2-300K using the Bond method. The authors found a negative thermal expansion coefficient for GaP at low temperatures. They also calculated the Gruneisen parameter and this was negative below 50K. These experimental results do not agree with the phenomenological theory in which a positive thermal expansion coefficient for GaP is predicted at low temperatures.

Thermal properties of vibrating dislocations

Abstract Using the elastic theory and Green function method, the changes in the vibrational properties of a solid containing vibrating dislocations are studied. Particular, the enhanced specific heat due to dislocations is discussed in detail. Furthermore, the influence of the localized mode created by dislocations is considered.

Phonon scattering by dislocations in LiF crystals

Abstract A theory is presented of the interaction between thermal phonons and a vibrating dislocation. An expression for the relaxation time of the phonon is obtained which is valid in an anisotropic medium. The relaxation time depends on the strength of the imaginary part of the effective mass of the vibrating dislocation. We have calculated numerically this factor for LiF and have found the mode dependence to be very strong. The slow transverse-mode component is about ten times larger than the other mode components. Hence, the slow transverse mode is scattered more strongly than other modes by vibrating dislocations in LiF. Agreement with experimental data is obtained.

Breakdown properties of random systems with distributed conductances

The breakdown problem in a random system is investigated by numerical simulation for a network of distributed conductance The breakdown voltages are studied in the different conductance configurations. The mean breakdown strength shows anomalous size dependence given by ∝1/((ln L )) y for L (the linear dimension of the network). The exponent y depends upon a degree of non-uniformity of the system and gives an information on the critical event of the breakdown. For the case of a comparatively homogeneous network the micro-crack nucleation is the critical event of a breakdown. In such a random resistor network funnel defects act as the appropriate critical defects. On the other hand, in the case of strongly disordered system the critical event in a breakdown is attributed to growth of cracks.

Dynamics of an impurity hydrogen in magnesium

The dynamics of an impurity hydrogen in magnesium is investigated by using the pair potential technique. We have calculated the pair potential between hydrogen and magnesium, taking account of the non-linear screening effects of an impurity hydrogen. By use of it, we have calculated the energy profile for interstitial hydrogen and the force constants between hydrogen and magnesium. As the results of them, it is found that the minimum point of energy is too shallow to localize the interstitial hydrogen, and that the coupling between substitutional hydrogen and the nearest neighbor magnesium ion is very weak.

Mass and Line Tension of a Vibrating Dislocation

We have calculated the mass and line tension of a vibrating dislocation in LiF crystal. The results of our analysis were somewhat smaller than that predicted by the string model. They indicate that localized mode exists due to vibrating dislocation in LiF crystal.