Topographical Defects Research Articles

A new X-ray topographic defect contrast on swept quartz crystals

X-ray topographic studies are made on vacuum-swept α-quartz crystals. A strong defect contrast is observed on X-ray topographs near the anode side of the crystal. This contrast disappears when the crystals are subjected to prolonged X-ray irradiation. The presence of this unusual contrast is attributed to lattice strains due to the collection of space charges near the anode side during vacuum sweeping. The negative space charge so formed is compensated by forming Al-OH and Al-hole centres during irradiation.

Determination of the effective contact radius between a conducting sphere and a thin metallic film

A method for studying the contact surface between a sphere and a plane is presented. The contact consists of a conducting sphere pressed against a metallised insulating strip. A model presented in the appendix allows one to calculate either the effective radius of contact or the electric resistance of an eventual interface layer. A set of experiments involving loading-unloading cycles (from 6 gf to 350 gf) of the sphere is described. Experimental values of the electric resistance are in good agreement with those obtained for the ideal case of a Hertz contact. The discrepancy with the Hertz law is found to be due to topographical defects.

On the origin and elimination of macroscopic defects in MBE films

Spitting of group III metal droplets from Knudsen type effusion cells has been found culpable for a genre of problematical macroscopic surface topographical defects observed in the growth of semiconductor films by molecular beam epitaxy. Successful precautions are described which virtually eliminate the problem.

The topographical structure of grain boundaries in tungsten

SUMMARYThis paper discusses the observation of a variety of topographical defects in grain boundaries in tungsten as a function of thermomechanical treatment. It is shown that, for both cold worked and crept specimen material, the boundary topography is highly complex, whereas for secondary recrystallized specimen materials the boundaries approximate to that expected for an ‘equilibrium’ configuration. However, no evidence for any period step structure was observed in this specimen material although, in this and all specimen states, grain boundary dislocations were frequently observed.

Model Experiments on the Site of Rongotai Aerodrome, Wellington, New Zealand

Wellington, the capital city of New Zealand, is situated in the south of the North Island, among the mountainous masses 2,000ft., high which form the northern shore of Cook Strait. The winds in this latitude are strong and persistent, and this, combined with the venturi effect of the Straits, gives-Wellington a very boisterous climate. The average run of wind per 24 hours is 310 miles and the average number of gales of force 8 or over is in excess of 60 per annum. There is little open ground near the city, and there is no aerodrome site within 30 miles which is free from atmospheric disturbances or topographical defects.