Resistivities of evaporated or sputtered polycrystalline and epitaxially grown single-crystal gold films of thickness 100–1000 Å have been measured in situ during deposition. Single-crystal gold films have been grown epitaxially on cleaved mica by sputtering and, as indicated by electron diffraction studies, are atomically smooth over large areas. The resistivities of such films are very close to the bulk value for all thicknesses greater than a limiting thickness at which the film becomes continuous. Since the limiting thickness is appreciably lower than the mean free path for conduction electrons, this result is considered to be a consequence of the existence of specular (elastic) reflection of electrons from the film surface. Resistivities of polycrystalline films of thicknesses comparable to the electron mean free path are higher than the bulk value; and, for films grown on cold substrates, their dependence on thickness is in qualitative agreement with the theory of diffuse (inelastic) scattering of conduction electrons from the surface. For polycrystalline films deposited on heated substrates, the measured resistivity appears to be dominated chiefly by structural changes occurring during growth.

Biconically tapered single-mode fibers are fabricated and their characteristics are studied experimentally. The optical throughput is measured as the fiber is being pulled to produce the required radial profile. The tapered single-mode fiber is then bent in a simple fixture and the optical throughput is measured as a function of the bending angle. It is seen that the bending results in very strong oscillations of the optical power as the bend angle is varied; the optical throughput goes nearly to zero at about 3.5" before increasing afterward. At the point when the light in the core is minimum, the cladding 9-

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Gallium arsenide has been grown on germanium using arsenic trichloride and gallium. With optimum growth conditions the epitaxial layers have properties close to those of good-quality bulk crystals. Comparison between epitaxial and bulk crystals is made in terms of the widths of the x-ray rocking curves and of the properties of p-n junctions formed within the epitaxial layer.