Volume 11, Issue 8, 15 October 1967
Index of content:
11(1967); http://dx.doi.org/10.1063/1.1755118View Description Hide Description
The spontaneous reorientation of the weak ferromagnetic moment (``temperature‐induced spin flop'') in the rare earth orthoferrites is found to take place over a well‐defined temperature range. In TmFeO3, this range is 12°K wide and centered at 88°K. Susceptibility peaks have been observed at the ends of this temperature interval where the magnetic easy axis just begins to rotate away from the a or c axis.
11(1967); http://dx.doi.org/10.1063/1.1755120View Description Hide Description
11(1967); http://dx.doi.org/10.1063/1.1755121View Description Hide Description
A pulsed laser source has been developed, which is continuously tunable from 4820 Å to 5790 Å, with power in the kilowatt range, and spectral width ≈14 cm−1. The technique used frequency addition in KDP. One frequency was that of a Nd‐glass laser, while the other frequency was selected by phase matching, from the continuum produced by self‐focusing and small‐scale trapping of the laser beam in CS2. Methods are outlined of extending the wavelength range to ≈50% of the 0.25 μ to 1.0 μ spectrum available with KDP and KD*P.
11(1967); http://dx.doi.org/10.1063/1.1755122View Description Hide Description
Measurements have been made on n‐type Ge at 77°K and 27°K, which show the existence of a bulk negative differential conductivity at electric fields above about 3 kV cm−1. This effect is believed to be the cause of previously observed current oscillations, and of traveling domains of high electric field which we have now observed at 27°K.
11(1967); http://dx.doi.org/10.1063/1.1755124View Description Hide Description
The thickness of films (<900 Å) of silicon dioxide on silicon can be determined by observation near Brewster's angle for silicon with the light polarized in the plane of incidence. Since the intensity of the reflected light increases with thickness for these films, the measurement is made by direct comparison of the light reflected by a sample with a calibrated SiO2 on silicon ``thickness gauge.'' Film thicknesses can be estimated to an accuracy of about±30 Å for thicknesses less than 150 Å and±50 Å for thicknesses between 150 Å and 900 Å.
11(1967); http://dx.doi.org/10.1063/1.1755125View Description Hide Description
Voids were produced by the precipitation of excess quenched‐in vacancies in aluminum. The annealing of these voids in thin foil specimens by a self‐diffusion mechanism was studied using transmission electron microscopy. The annealing rates of both isolated voids and voids which were connected to the foil surfaces by dislocations were observed. The voids which were hooked up to the surfaces by dislocations annealed out at appreciably higher rates than the isolated voids. The results indicate that the dislocations acted as rapid self‐diffusion pipes for the transport of atoms into the voids from the surfaces.
11(1967); http://dx.doi.org/10.1063/1.1755127View Description Hide Description
Electrotransport in thin Al strips was directly observed by transmission electron microscopy. As expected, hole formation was seen in regions where the electron flow was in the direction of increasing temperature. Hillocks and whiskers were seen to form where the electron flow was in the direction of decreasing temperature. Ciné films taken of the process show the holes to grow predominantly by a transverse movement of narrow fingers which ultimately coalesce and lead to a catastrophic strip burn‐out.
11(1967); http://dx.doi.org/10.1063/1.1755128View Description Hide Description
Acoustic holographic experiments of the Leith‐Upatnieks type in which the inclined planar reference is simulated electrically by a simple technique are described. The results graphically illustrate that finite ``film'' resolution introduces ambiguities into acoustic and optical holograms. The experiments were performed at 1 MHz, a frequency suitable for long‐range underwater imaging and detection.