No abstract

No abstract

No abstract

We report a hydrogen-related defect that establishes the direct role of hydrogen in stabilizing the silicon dangling bonds created in the Staebler-Wronski effect in hydrogenated amorphous silicon. A specific NMR signal due to paired hydrogen atoms occurs only after optical excitation, exists at an intensity that is consistent with the density of optically induced silicon dangling bonds, and anneals at temperatures that are consistent with the annealing of the optically induced silicon dangling bonds. At this defect the hydrogen atoms are 2.3+/-0.2 A apart.

No abstract

No abstract

Microwave absorption in the superconducting and normal phases of Y-Ba- Cu-O" (1987). Stephen Ducharme Publications. 25.

Four different metastable paramagnetic centers have been identified in the low-temperature, light-induced electron-spin resonance (ESR) spectrum of glassy As&S3. Two of the centers anneal at significantly lower temperatures than the other two, allowing the line shapes to be partially separated with isochronal annealing experiments. The two centers which anneal at lower temperatures, labeled type-I centers, constitute approximately 15% of the induced spins after long-time irradiation at high intensities ( 100 mW/crn~). These centers consist of a hole on a nonbonding 3p orbital of a sulfur atom (Si) and an electron on an s-p hybridized orbital of an arsenic atom (As&). Similar kinetic behavior suggests that the origin of these two centers is a single event, which may be the breaking of an arsenic-sulfur bond. The type-II centers, which are thermally more stable, represent -85%%uo of the induced spins and are concluded to be due to an electron in a nonbonding 4p wave function on a twofold-coordinated arsenic atom (As») and a hole on a nonbonding 3p orbital of a sulfur atom (Si&).The origin of these centers is suggested to be the breaking of As -As and S -S bonds. The densities of the different spins vary rapidly with the stoichiometry. Interpretation of the kinetic behavior of the type-I and type-II ESR signals suggests the existence of a third intermediate metastable state in addition to the ground state and the excited paramagnetic state. High-intensity () 100 mWcm ) light with energy above the band gap (A,~514.5 nm) creates new structural defects in the glass at densities which exceed 10' cm '. At high temperatures (T)250 K) the shift of the opticalabsorption edge to lower energies, which is known as the photodarkening effect, exhibits different kinetics from the electron-spin resonance. This fact suggests that there exists no one-to-one correlation between these two effects. There is, however, a close parallel at all temperatures between absorption well below the gap (midgap absorption) and the type-I ESR centers.