Photopyroelectric spectroscopy (P2ES) of electronic defect centers in crystalline n-CdS

The electrical and dielectric properties of mercuric iodide were studied at room temperature under various intensities and colours of light in the frequency range 1 Hz–10 kHz. In the high-frequency region (>40 Hz), the real part of the dielectric constant () is almost constant with frequency (f), colour and intensity of light. At lower frequencies, varies nearly as 1/f and monotonically increases with intensity (I) of the yellow (or green) light, whereas it is almost constant with red light intensity. This behaviour is discussed in the view of the different polarization contributions. The imaginary part of the dielectric constant () was found to vary as 1/f over the frequency range studied. This behaviour was observed whether the crystal was in dark or illuminated implying that the roomtemperature ac dark- or photo-conductivity () is independent of frequency. The observed variation of with intensity of yellow (or green) light was found to follow anI ^1/2 dependence and a weaker dependence for the red light. the red light. The conductivity behaviour is discussed in the view of the current theories.     

Diffusion of sulfur in nickel oxide single crystals

The diffusion of sulfur in nickel oxide single crystals has been investigated over the temperature range from 1000 to 1250°C. The measured data were found to deviate markedly from the error function complement dependence for diffusion from a constant source. The deviation is attributed to the migration of sulfur by the “double mode simultaneous diffusion mechanism.” The faster mode diffusion is suggested to be via nickel vacancies, and the slower mode diffusion is suggested to be via oxygen vacancies. The diffusivities for faster mode are given by D_f = 2.94 exp[? 86.6 kcal/RT] cm² sec^?1 and, the slower mode, D_s = 1.08 × 10^?9 exp [?32.8 kcal/RT]cm²sec^?1.     

Thermal decomposition of CO on a stepped Ni surface

The adsorption-desorption behaviour of CO on the stepped Ni(S) [5(111) × (11̄0)] and the smooth Ni(111) plane are compared by using LEED, thermal flash desorption and AES. Above room temperature flash desorption from the Ni(111) face yields a single α peak characteristic of molecularly adsorbed CO whereas from the stepped surface in addition to the a peak α second desorption peak (β2) appears around 550°C which is assigned to associative CO desorption. If carbon and oxygen are separately chemisorbed on Ni(111) associative desorption of CO leads to a desorption peak around 350° C. It is concluded that steps lower the activation energy for CO decomposition but increase the activation energy for associative desorption.     

Search for delayed fission products from superheavy nuclei in the reaction136Xe+208Pb

The production of superheavy elements in binary reactions of the type²⁰⁸Pb (¹³⁶Xe, X) Y was investigated atE _c.m.=470 MeV. The experiment was designed to search for delayed fission products from elements withZ between 108 and 116 and fission lifetimes ofΤ?10^?12 s. No fission events were observed the upper limit for the formation cross section being 1.2 Μbarn.     

Nachweis schwacher Phasenmodulationen von Lichtbündeln

We describe a piezoelectrically tuned and electronically stabilized Michelson Interferometer. The use of a compensation method together with an appropriate modulation technique enables us to measure optical phase modulation Δϕ in light beams interferometrically with a resolution of Δϕ≈3·10⁻⁹ rad, where Δϕ stands for the rms value. The sensitivity of the instrument is limited only by shot noise

Detection of Weak Phase-Modulations in Light-Beams     

Charge and mass transfer in the reaction136Xe+208Pb at energies close to the coulomb barrier

Mass and charge transfer was investigated for the system¹³⁶Xe+²⁰⁸Pb at 5.9 MeV/nucleon incident energy with aΔE —E-time of flight telescope. The angle and energy integrated cross section for the strongly damped events was found to be 510 mb, very close to the total reaction cross section. The width of the mass distribution as function of the total kinetic energy loss was measured and is compared to the width of the corresponding charge distribution. An upper limit of 1 μb has been found for processes with very large mass transfer.     

Variation of material parameters along the growth direction of liquid encapsulated Czochralski grown GaAs ingots

The variation of material properties along the growth axis of single crystal LEC GaAs ingots is studied. Parameters investigated include concentration and lateral variation of EL2, photoluminescence intensity, resistivity, the concentration of extrinsic shallow acceptors and, after test implantation, the sheet resistivity. Correlations between the observed trends are identified and discussed in terms of compensation and segregation. In general, a very satisfactory homogeneity is found. Remaining variations are identified and evaluated with respect to their device-relevant consequences.     

Euler characteristic and related measures for random geometric sets

By an elementary calculation we obtain the exact mean values of Minkowksi functionals for a standard model of percolating sets. In particular, a recurrence theorem for the mean Euler characteristic recently put forward is shown to be incorrect. Related previous mathematical work is mentioned. We also conjecture bounds for the threshold density of continuum percolation, which are associated with the Euler characteristic.