Volume 9, Issue 7, 01 October 1966
Index of content:
9(1966); http://dx.doi.org/10.1063/1.1754738View Description Hide Description
Excitation can move from Tb to Eu at 4.2°K by processes involving exchange even though the electronic transitions concerned are not matched in energy. At 295°K, thermal effects cause an overlap permitting dipole‐dipole transfer to occur. Transfer to Eu may be enhanced by excitation migration from more remote Tb ions to those closer to Eu at 295°K. This migration is not effective at 4.2°K, and hence appears to require thermal activation.
9(1966); http://dx.doi.org/10.1063/1.1754739View Description Hide Description
The selection of a single mode‐locked pulse from a Q‐switched Nd+3‐doped glass laser is described. Mode‐locking is achieved by self‐mode‐locking the laser using a bleachable dye Q switch. Selection of a single pulse is achieved by means of a modification of the pulse transmission mode described by Vuylsteke.
9(1966); http://dx.doi.org/10.1063/1.1754740View Description Hide Description
InAsthin films have been prepared by coevaporation. Hall mobilities up to 8000 cm2/V‐sec have been obtained in films 3000‐Å thick, and 3000 cm2/V‐sec in 1000‐Å films. Field‐effect transistors have been fabriacted of such films, exhibiting good saturation in both enhancement and depletion modes of operation. Field‐effect mobilities of 1800 cm2/V‐sec, transconductances of 10,000 μ‐mhos and gain‐bandwidth products of 8 MHz were obtained in devices with a 100‐μ source‐drain spacing. Performance in the GHz region is predicted for devices of suitable geometry.
9(1966); http://dx.doi.org/10.1063/1.1754741View Description Hide Description
LEED observations between 200–1000 V on the clean (111) face of silicon indicate a set of diffuse rings which, contrary to normal behavior of diffraction features, move outward from the normal with decreasing electron wave‐length. The origin of these rings is determined to be multiple scattering from nearest‐neighbor pairs. Estimates of the electron mean free path average about a value larger than the nearest‐neighbor distance but smaller than the separation of nearest‐neighbor pairs in the (111) direction. The rings appear to be associated with Kikuchi patterns which are observed down to 400 V.
9(1966); http://dx.doi.org/10.1063/1.1754742View Description Hide Description
Whisker crystals and related filamentary and spherical shapes grow at the solder terminations of thin‐film resistors when the circuits carry excessive direct current. The growths have been observed in most instances near the positive termination. With tin‐lead solder the growths at the positive termination are predominantly tin.Whisker crystals are often single. Studies show that electrotransport plays a role in the growth.
9(1966); http://dx.doi.org/10.1063/1.1754743View Description Hide Description
Work functionmeasurements have been carried out on the densely packed (110) plane of tungsten. Field‐ion microscope techniques have been used to obtain atomically perfect single‐crystal (110) planes. Field‐electron emission energy distributions have been combined with Fowler‐Nordheim measurements to give work function values at 77°K. The electrostatic patch fields which exist at the measured surface result in corrections which tend to increase the work function value. The measurements reported here are not corrected for patch fields and range in value from 7.1 eV to 8.7 eV for the (110) plane. Future measurements will employ a newly developed technique involving a family of energy distribution plots which eliminates the correction for patch fields.
9(1966); http://dx.doi.org/10.1063/1.1754744View Description Hide Description
9(1966); http://dx.doi.org/10.1063/1.1754745View Description Hide Description
A peak in the critical current vs magnetic fieldcharacteristic of Nb−25% Zr has been produced during a low‐temperature (∼30°K), 15‐MeV deuteron irradiation (1017 deuterons/cm2). The peak occurs at fields near the upper critical field,H c2; essentially no changes were observed at lower fields. Annealing at 77°K produced almost no change in the peak whereas it nearly disappeared after annealing at 300°K. It is concluded that this peak is a bulk effect associated with radiation‐induced defects of intermediate size and complexity which are effective pinning centers near H c2, but are too ``weak'' to affect the critical current at lower fields. A number of possible mechanisms are briefly discussed.
9(1966); http://dx.doi.org/10.1063/1.1754746View Description Hide Description
Single high‐power output pulses from a Q‐switched ruby laser are focused onto thin copper crystals. Diffraction‐contrasttransmission electron microscopy reveals that so‐called black spot defects are introduced in the samples, within the laser‐produced crater areas. These defects are similar to those observed, for example, in neutron‐irradiated copper samples. They cause a marked increase in hardness at and near the crystal surface.
9(1966); http://dx.doi.org/10.1063/1.1754747View Description Hide Description
The parallel‐pumped spin‐elastic wave instability and ferromagnetic resonance were used to measure the dispersion and losses of π/2 spin waves in high‐purity, single‐crystal GdIG at low temperatures. The spin wavedispersion constant varies more rapidly with temperature than predicted by molecular field theory and the resonance losses are only a factor of three greater than those for YIG.