U. Strom

Photo-induced changes in the infrared vibrational spectrum of evaporated As2S3

Abstract Photo-induced changes in the infrared spectrum of amorphous, evaporated As 2 S 3 films are described. The results are interpreted in terms of the photopolymerization of As 4 S 4 molecular units and sulfur chains into an As 2 S 3 glassy network. The role of photo-induced charged states in the polymerization process is discussed.

Photostructural effects in glassy As2Se3 and As2S3

Abstract Photostructural effects are investigated in 300K substrate evaporated films of As2S3 and As2Se3 using nuclear quadrupole resonance (NQR) techniques. NQR results confirm the existence of As2S4 (or As4Se4) molecular units in the films and suggest the presence of AsS3 (or AsSe3) pyramidal units which lack the longer range (two-dimensional) correlations present in the bulk. Structural differences between film and bulk are greater (and photostructural changes are easier to induce) in As2S3 than in As2Se3.

Optically induced localized paramagnetic states in amorphous As

Abstract Photoluminescence and optically induced ESR and absorption due to localized states in the forbidden gap have been observed in amorphous As below 77 K. Analysis of the ESR spectru, indicates that these centers are highly localized and in orbitals which are predominantly p-like.

Raman scattering of the mixed chalcogenide glass system As2SxSe3-x

Abstract Polarized room temperature Raman spectra of glassy As 2 S x Se 3-x for 0≦×≦3 have been measured. Spectra for crystalline As 2 S 1 Se 2 are reported. The polarization and intensity dependence upon composition are consistent with mixed pyramids of composition As 2 S n Se 3-n and preclude phase separation in the glassy system.

Use of granular NbN as a superconducting bolometer

An ultrathin film of granular NbN is used as a superconducting bolometer. The bolometer has a high operating temperature (∼12 K), is very sensitive (∼5000 Ω/deg), and exhibits a fast thermal response time, which is estimated to be less than 10−10 sec.

The effects of impurities upon photoluminescence and optically induced paramagnetic states in chalcogenide glasses

Abstract Photoluminescence (PL) and optically induced electron spin resonance (ESR) have been studied in As2Se3 glasses doped with Cu, Tl, I, Ag, In, and K and in B-doped As2S3 glass. In all cases there is no significant change in PL efficiency or intensity of induced ESR until dopant concentrations exceed ∼1 at.%. These results are in marked contrast the strong dependence of transient hole transport upon dopant concentration in the same glasses. These parallel but contrasting observations are discussed in terms of the predicted effects of dopants on defects in chalcogenide glasses postulated by Mott on the basis of the charged defect model of Mott, Davis and Street (MDS). PL and ESR studies of the Asue5f8Se glass system have revealed that oxygen contamination can severely quench PL efficiency and ESR intensity for As concentrations

Nature of the linear frequency-dependent ac conductivity in glassy ionic conductors☆

Abstract A very common observation for glassy ionic conductors is an ac conductivity which depends linearly on frequency. Another common feature of these glasses in an NMR spin-relaxation rate 1/ T 1 which has an approximately linear Larmour frequency and a slightly stronger than linear temperature dependence. It is proposed that these two properties are related and stem from a common physical mechanism. Information about the nature of this mechanism and the type of excitations involved in these processes can be gained from similar observations in non-glassy, but disordered ionic conductors, such as Naβ-Alumina.

Direct electromegnetic generation of high frequency acoustic waves in semiconductor superlattices

Abstract The periodic space charge layers formed in semiconducting superlattice structures can be used for direct electromagnetic generation of high frequency acoustic waves. The mechanism for and resonant nature of the acoustic generation are discussed.

Temperature dependence of the density of optically-induced localized paramagnetic states in glassy As2Se3

Abstract Optically-induced localized paramagnetic gap states in glassy As2Se3 have been studied as a function of temperature from 4–2 K to ∼ 150 K using E.S.R. and optical absorption techniques. The number of paramagnetic states stable at ∼ 150 K is an order of magnitude less than the number stable at low temperatures. Densities of thermal release energies for the metastable states are estimated from the data.

Low frequency Raman spectra of chalcogenide glasses

Abstract Low frequency ( -1 ) Raman scattering lineshapes for the chalcogenide glasses As 2 S 3 and As 2 Se 3 have been interpreted in terms of a model which explicitly includes acoustic (∼ ω2 density-of-states) and optic (rigid-layer like) vibrational modes.