Crystal growth and orientations in vacuum-condensed silver films and their systematic dependance on the residual air pressure, film thickness, rate of deposition and substrate temperature

Abstract

Grazing-incidence electron diffraction is used to show the surface structure and mode of growth of silver films condensed in vacuum, in relation to film thickness H, rate of deposition, substrate temperature and, especially, the residual gas nature and pressure p. In air at 7 × 10−6 to 7 × 10−3 torr, on glass at room temperature, silver deposited at 30-35 Å s−1 showed random polycrystalline initial structure up to a certain thickness, then {111} orientation, then additional {111} twinning, followed by {110} and later {110}+{211} orientation, at all these pressures. Additionally some hexagonal silver was present in films at 10−3 to 10−2 torr of air or nitrogen, but not oxygen. The thickness at which these orientations were first observed is approximately H=Kprime ln (p0/p), where Kprime and p0 are constants, p0 being approximately 2 × 10−2 torr.The {111} orientation results from {111} crystal faces being formed, and more rapid lateral growth and predominance of crystals with this face normal to the vapour stream. The {110} and {211} orientations appear to be due to secondary twinning combined with presence of {110} or {211} faces on the twins.A theory is developed which accounts well for the (H, ln p) rectilinear locus in terms of a Temkin isotherm for adsorption of the oxygen, and indicates a stepped nature of the {111} faces. The coverage fraction θ of the oxygen adsorption is estimated.At 60-160 Å s−1, the {111} orientation develops slightly earlier, but little or no twinning occurs at up to 12 000 Å film thickness.