Optical absorption in sputtered amorphous phosphorus

Optical absorption measurements are reported on r.f. sputtered films of a-P prepared at variable substrate temperatures. With decreasing substrate temperature the absorption spectra shift to lower frequencies and the energy gap decreases. The form of the spectra are, however, similar both in the band edge and Urbach tail regions. The Urbach slope is found to differ substantially from that of a-As, indicating that factors other than coordination number may influence this parameter. The changes in the absorption spectra are suggestive of a possible role of intermediate range order on the electronic states in a-P.     

Vibrational spectra of crystalline Bi1−xSbx alloys

Second order Raman scattering is reported at 300 K in crystalline Bi_1?x Sb_x alloys. The spectra, which are interpreted in terms of dominant overtone processes, indicate variations in the phonon density of states for the optical bands with composition. The form of the spectra, which include contributions from Bi-Bi, Bi-Sb and Sb-Sb bonds, implies microscopic statistical clustering effects analogous to those in Ge_1?xSi_x alloys. A comparison of the spectra with inelastic tunneling results in superconducting amorphous Bi_1?xSb_x indicates covalent bonding contributions in the latter.     

Raman scattering and infrared absorption in bulk amorphous red phosphorous

Raman scattering and infrared absorption measurements in bulk amorphous red P indicate considerable spectral detail for an elemental amorphous solid, including a distinct separation of acoustic and lower lying optic-like bands. The results suggest appreciable structural correlations and weak interlayer-like bonding. Increased covalency of amorphous red P relative to amorphous As is indicated.     

Integral equation formulation for buoyancy-driven convection problems

An integral equation formulation for buoyancy-driven convection problems is developed and illustrated. Buoyancy-driven convection in a bounded cylindrical geometry with a free surface is studied for a range of aspect ratios and Nusselt numbers. The critical Rayleigh number, the nature of the cellular motion, and the heat transfer enhancement are computed using linear theory. Green's functions are used to convert the linear problem into linear Fredholm integral equations. Theorems are proved which establish the properties of the eigenvalues and eigenfunctions of the linear integral operator which appears in these equations.