R. Braunstein

Identification of tungstate complexes in lithium-tungstate-borate glasses by Raman spectroscopy☆

Changes in the Raman spectra of (Li2B4O7)0.5(WO3)0.5 glasses, when prepared under slightly different conditions, are interpreted as arising from tungstate complexes in the glass matrix; one of the observed extra vibrational modes can be correlated with a permanent blue color center which is reminiscent of the electrochemically induced tungsten bronze centers.

Photochromic and electrochromic properties of tungstate glasses

Abstract Electrochromic and photochromic behavior have been observed for the first time in the Li 2 O-B 2 O 3 -WO 3 glass system. Double injection of protons and electrons results in the formation of H x WO 3 in the glass matrix which exhibits a broad absorption band peaking in the vicinity of 1.45–1.65 eV due to electron hopping between W +5 and W +6 sites. An electron diffusion coefficient of D e ∽3×10 -6 cm 2 sec -1 has been measured near the percolation threshold when the volume filling fraction f > 0.3 for WO 3 in the glass matrix. The electrochemical potential of these tungstate glasses varies as a function of coloration.

Dipole correlations in TeO2-WO3 glass☆

Abstract Capacitance and thermally stimulated depolarization current measurements on TeO 2 ·0.23WO 3 glass from 4.2–300 K reveal structure at temperatures where phase transitions are observed in crystalline WO 3 . These results indicate that the local WO 6 -octahedra determine the dielectric properties of this glass and that dipole-dipole correlations contribute to the ferroelectric-like character of this amorphous system.

Cooperative phenomena of random electric dipoles in an amorphous matrix

Abstract A ferroelectric phase transition has been observed for the first time in a series of glasses containing WO 6 -octahedra. The techniques of thermally stimulated depolarization currents were used to observe the transition from independent dipole behavior to cooperative behavior in this amorphous system as a function of concentration. These measurements yielded the activation energy Δ E =1.2eV, the pre-exponential τ 0 =2 × 10 -22 sec, and the dipole moment p =1.3 × 10 −15 esu cm for WO 3 in Li 2 B 4 O 7 . A dipole moment bearing species due to Li 2 B 4 O 7 was observed with Δ E =0.44eV and pre-exponential τ 0 =5 × 10 −8 sec. The depolarization peaks of WO 3 occur in the temperature range 265–275 K depending upon WO 3 concentration and are pressure dependent with an initial slope of 2 × 10 −5 K dyne −1 cm 2 . A model was developed for a possible phase transition associated with a random “pseudo-spin” system in an amorphous matrix.

Permanent blue coloration of (Li2B4O7)1-x(WO3)x-glasses

Abstract A permanent blue coloration is found in (Li 2 B 4 O 7 )1- x (WO 3 ) x -glasses for X ⩾ 0.44. Since this concentration limit looks like a percolation threshold and since the blue coloration is conventionally ascribed to the formation of lithium-tungsten-bronzes A x WO 3 ( A = H, Li, Na), we assume fast diffusion of lithium to decorate the WO 6 -tree once it forms in the glass matrix.

Wavelength-modulated reflectivity of the noble metals

Abstract The interband transitions of evaporated films of the noble metals copper, gold, and silver have been studied in reflectivity in the energy region 2.0 – 5.0 eV as a function of temperature, using wavelength modulation. In copper and gold, features have been observed in the imaginary part of the dielectric constant which support recent band theories as to their location in the Brillouin zone. In silver, new weak structure has been resolved near the onset of interband absorption. The surface plasmon in silver has been studied, and shown to possess a strong temperature dependence.

Raman scattering in a Ga1−xInxP strained heterostructure

Raman scattering was employed to study the optical phonon modes in Ga1−x Inx P heterostructures. The stress calculated from the pressure coefficient and the observed frequency shift for the GaP‐like LO phonon is larger than the one obtained from the lattice mismatch given by the elastic theory; the possibility of other types of defects responsible for this difference is considered. The presence of internal stress in epitaxial layers could induce a switchover from one‐ to two‐mode behavior. The modified random element isodisplacement model is used to explore this possibility.

Far-infrared cyclotron resonance in n-Ge☆

Abstract Cyclotron resonance has been performed on the conduction band of germanium using a cyanide laser at 891 GHz and a superconducting magnet of up to 110 kG. This is 2.5 times higher in frequency and 10 times higher in field than previous cyclotron resonance measurements reported for n -Ge. The effective masses do not change from their calues at lower frequencies and fields, but the scattering frequencies are 1.5 to 5 times larger. A new scattering mechansm is suggested to explain the increased scattering.

CONTINUOUS DECAY OF DRIFT MOBILITY IN INTRINSIC A-SI:H AND A-SIC:H UPON LIGHT SOAKING INVESTIGATED BY THE PHOTOMIXING TECHNIQUE

The photoconductivity, electron lifetime, and electron drift mobility in intrinsic hydrogenated amorphous silicon (a‐Si:H) and hydrogenated amorphous silicon carbide (a‐SiC:H) while light soaking were determined using a photomixing technique. In addition to the decay of the photoconductivity and electron lifetime, continuous decay of the electron drift mobility was found during the light soaking process, which reveals that the light‐induced metastable defects of the Staebler–Wronski effect results in scattering as well as recombination of charge carriers. The drift mobility decreased by a factor of 2 for 20 h light soaking at 2.5 sun intensity. Experimental data were fitted to a stretched exponential law. Different stretched‐exponential parameters for photoconductivity, lifetime, and drift mobility were obtained, which indicates the production of defects with different generation kinetics upon light soaking.

Critical point determination by derivative optical spectroscopy

Abstract The singularities of phonon-assisted transitions in Si and the reflectivity in the neighborhood of the plasma edge in Ag were determined by a method of derivative spectroscopy. The use of this technique of frequency-modulated spectroscopy enables one to readily obtain the first or higher derivatives of any optical spectra.