Temperature- and illumination-dependence of the work function of gallium arsenide

Contact potentials of vacuum-cleaved (110) surfaces of GaAs have been measured as functions of temperature (77 < T < 400 K) and illumination intensity by means of a transparent vibrating capacitor. Surface photovoltage as a function of wavelength and intensity of light, as well as relaxation times, have been measured at various temperatures. Samples of greater than 10¹⁸ cm⁻³ doping exhibit photovoltages of 1–2 mV or less and little variation of work function with temperature. At a doping level of 10¹⁷ cm⁻³ p-type samples display photovoltages of more than 50 mV at 77 K and up to 10 mV at room temperature. Moderately doped n-type samples (1.8 × 10¹⁶ and 2.7 × 10¹⁷) exhibit photovoltages up to 0.25 eV at room temperature. At low temperatures, their work function can have two apparently stable values: upon rapid cooling in total darkness, the work function decreases about 80 mV, but during illumination at 77 K, however weak, it decreases by an additional 0.5 V to a new value at which it remains in the dark. This behavior can be accounted for by surface photovoltage according to a simple model not requiring a temperature dependence of surface state spectra. Light is absorbed through interband transitions in the bulk, the surface charge is altered by surface recombination and the return to equilibrium occurs by thermal excitation and tunneling of carriers.     

An estimation of the number of tie molecules in semicrystalline polymers by means of neutron scattering

A new method for the evalution of neutron scattering data from semicrystalline polymers is proposed for small and intermiediate q [q = (4π/λ)sinθ/2]. It is based on the assumption that, in general, a molecule cryustallizes in various lamellae. Within one lamella the crystalline stems connected by loop or folds from intramolecular “clusters,” which are connected by tie molecules. Without further assumptions the method yields in a straightforward manner the following quantities: (i) the average number of clusters per molecule, from which the number of tie molecules can be estimated; (ii) the radius of gyration <R> of the centers of the stems belonging to one cluster; and (iii) the radius of gyration <R> of the cluster centers with respect to the center of the molecule the method was successfully tested using experimental data obtained from poly(ethylene oxide), polyethylene, and isotactic polypropylene.     

Reaction of O(1D) with N2O

O(¹D), produced from the photolysis of N₂O at 2139 Å, reacts with N₂O in accord with: We have used the method of chemical difference to obtain an accurate measure of k₂/k₃ = 0.59 ± 0.01. Furthermore, the quantum yield of production of O(³P), either on direct photolysis or on deactivation of O(¹D) by N₂O, is less than 0.02 and probably zero.     

Berechnung der Aufbauzeit eines doppeltresonanten optischen parametrischen Oszillators

The rise time for the output power of a doubly resonant optical parametric oscillator with ring resonator configuration is calculated for the special case of subharmonic generation. It is shown that the rise time decreases by increasing the pumping level (for a constant threshold power) and, for a constant pumping level, by increasing the resonator loss.     

O−−-Lücken-Dipole in Rubidiumhalogenidkristallen

Dielectric loss measurements are reported for RbCl, RbBr, and RbJ crystals containing O^??ions. The frequency and temperature dependence can be approximated by a Debye curve. The dipole moment is interpreted as being due to O^?? ions associated with anion vacancies. Activation energies for reorientation of the dipole are 0.60 eV for RbCl, 0.56 eV for RbBr, and 0.50 eV for RbJ. The deviations of the experimental dielectric loss curves from a Debye curve are interpreted. The dielectric losses decrease and the center uv absorption changes during annealing due to association of the centers into aggregates. A detailed analysis of the kinetics for RbBr indicates the formation of O^??-pair centers as the first step. The activation energy for association isE ₂=0.79 eV.     

In Process Citation

In a systematic study of the sulphonating properties of SO(3)B complexes, we have paid attention to the thiocyanosulphates KSO(3)SCN and NH(4)SO(3)SCN. We have shown conductimetrically that these salts are dissociated and that the ionic salvation is weak in the chosen solvent-sulpholane-which is strongly aprotic in character. We have determined potentiometrically the equilibrium constant K of the reaction MSO(3)SCN measured angle MSCN + SO(3), by means of the electrochemical couple Ag + SO(3)SCN(-) measured angle AgSCN + SO(3) + e(-). The values foun the ammonium and potassium salts are K = 10(-11.5 +/- 0.45) and 10(-9.7 +/- 0.7) respectively. Thiocyanosulphates appear to be stronger than chlorosulphates as sulphonating agents. Therefore SCN(-) is a weaker base than Cl(-) in sulpholane medium.     

Wasseruntersuchung

Ohne Zusammenfassung