Comment on “oscillatory indirect interaction between adsorbed atoms — Non-asymptotic behavior in tight-binding models at realistic parameters” by K.H. Lau and W. Kohn

A sensitive infrared reflectance accessory suitable for the study of surface films on medium size single crystals is described. Oxide films formed on the (100), (110) and (111) crystal faces of aluminum in air, at room temperature, display nearly identical behavior with films approximately 10 Å thick absorbing as a single band near 940 cm^?. After 10⁴ sec at 570 °C, in oxygen, films formed on these crystals begin to display differences in band characteristics and growth kinetics. Between 10⁴ and 4 × 10⁴ sec the rates of growth on the (110) and (111) crystal faces are much greater than on the (100) face. Beyond 4 × 10⁴ sec the growth rate on the (100) face increases while the (110) and (111) growth rates approach zero. Limiting thicknesses reached after 4 × 10⁵ sec approach 3.4 × 10², 2.1 × 10² and 2.2 × 10² Å for (100), (110) and (111) faces, respectively. Oxide compositional differences were reflected by the number and form of the infrared bands after 10⁴ sec of oxidation. After 5 × 10⁴ sec the (100) face oxide was composed of two and possibly three oxide species as evidenced by several bands. Differences in bandwidth and frequency were observed between the (110) and (111) oxide films. The significance of such differences is discussed.     

Messung der Lebensdauer angeregter Kernniveaus von Al28, Cs133, Pr141, W182 und Pt195

The halflife of excited states in some nuclei has been measured by the method of delayed coincidences. Two different experimental arrangements have been used: a conventional scintillation counter equipment and a fast gasfilled parallelplate avalanche-counter. The results of these measurements are: 31 keV-level in Al²⁸:T _1/2=(1.91±0.08) · 10^?9 sec, 81 keV-level in Cs¹³³:T _1/2=(6.25±0.05) · 10^?9 sec, 145 keV-level in Pr¹⁴¹:T _1/2=(1.85±0.03) · 10^?9 sec, 100keV-level in W¹⁸²:T _1/2=(1.45±0.04) · 10^?9 sec, 1290 keV-level in W¹⁸² T _1/2=(1.05±0.03) · 10^?9 sec, 99 keV-level in Pt¹⁹⁵:T _1/2≦1.6 · 10^?10 sec, 129 keV-level in Pt¹⁹⁵:T _1/2=(6.2±0.7) · 10^?10 sec. These experimental values are discussed and compared with theoretical model predictions.     

Measurement of the lifetime of the first excited state in17O and17F

A new version of the “recoil distance method”, making use of a gas target, has been used to determine the lifetime of the 871 keV level in¹⁷O and of the 495 keV level in¹⁷F. The measured values of the lifetimes are (2.32±0.08) · 10^?10 sec and (3.96±0.10) · 10^?10 sec for¹⁷O and¹⁷F, respectively.     

Die Erzeugung und Bewegung einzelner Versetzungen in Germaniumkristallen

Topographic X-ray pictures are presented showing dislocation sources in plastically deformed germanium crystals. Both internal Frank-Read sources as well as sources at the crystal surface have been observed. Dislocation velocities from 10^?6 to 10^?4 cm/sec have been evaluated.     

Elektronendichten und Elektronentemperaturen bei Verdichtungsstößen

Electromagnetically driven shock-waves of about Mach 50 in Helium have been spectroscopically analysed. Shape and relative intensities of the HeII-3203 and HeI-5876 lines and continuum have been measured during the first microsecond following the luminous front. From 0.15 μsec up to 0.85 μsec after luminous onset electron density decreases from 2.5·10¹⁷cm^?3 to 10¹⁷cm^?3. The electron temperature drops from 4.5 eV to 4.0 eV. Values as calculated byRankine-Hugoniot coincide with experimental results within 10%. From HeI-5876 and HeI-3889 precursor radiation and no corresponding radiation from HeII-lines it is to be concluded that the signals are due to secondary emission.     

Messung der Lebensdauer angeregter Kernniveaus von Gd155

Using two different experimental arrangements, the halflife of the following excited nuclear states in Gd¹⁵⁵ have been measured by the method of delayed coincidences: 60.0 keV-level:T _1/2=(2.4±0.6) · 10^?10 sec, 86.5 keV-level:T _1/2=(6.35±0.09) · 10^?9 sec, 105.3 keV-level:T _1/2=(1.14±0.03) · 10^?9 sec. These results are discussed and compared with the predictions of the collective model.     

Studies of relaxation times of secondary radiations in ZnTe by circular polarization correlation

Population and spin relaxation rates concerned with exciton luminescence and multiple LO-phonon emission lines are studied in ZnTe at 77 K by means of optical circular polarization correlation between the exciting and emitted lights. The decay times of the LO lines are determined to be much less than 10^-11sec, which are definitely shorter than the obtained exciton lifetime of 10^-10-10^-9sec. It is concluded that the LO lines are not due to hot luminescence but due to resonance Raman scattering.     

Crystallinity and interdiffusion in InP/InGaAs quantum wells grown by Hydride VPE

This paper reports the results of a study on interfacial quality and thermal interdiffusion for InP/InGaAs Quantum Wells (QW) grown by hydride VPE. By controlling well layer as thin as 25 Å, it was estimated that island and valley, whose height was one monolayer and whose lateral size was one third of exciton radius, existed at the interface. For the first time, interdiffusion coefficients for InP/InGaAs QW were obtained from 77K PL peak energy shift. Typical values were 2.5×10⁻¹⁹ cm²/sec and 1.5×10⁻¹⁸ cm²/sec for the annealing temperature of 700°C and 750°C, respectively. These values are over 10² times larger than that in AlGaAs/GaAs QW, and less 10⁻² times smaller than that in InAlAs/InGaAs QW.     

Implant redistribution in high-dose ion implanted and annealed silicon

Abstract

Diffusion constants of helium in gold, silver and aluminium are determined from thermal desorption experiments, giving:

Au: D ₀ = 10^?1.0 cm²/sec, ΔH = 1.70 eV

Ag: D ₀ = 10^?1.2 cm²/sec, ΔH = 1.50 eV

Al: D ₀ = 10^+0.1 cm²/sec, ΔH = 1.35 eV

The results are compared to self-diffusion and to the diffusion of other light elements in metals. Possible diffusion mechanisms are discussed.     

Higher order averages of primary recoil distributions

A molecular beam detector is described which ionizes by electron bombardment. The ions are then separated in a quadrupole mass filter and detected by a multiplier. The special advantages of the mass filter allow a high overall transmission so that every 1000th molecule of the beam is measured as an ion. The ion current due to the residual gas is reduced by a factor of 10^?6 for all masses >45. These results were achieved without separately pumping or baking out the ionisation chamber. Since magnets are not used the detector is comparatively light and small in size. The smallest detectable beam was found to have a current density of 1,8·10^?6 molecules/sec mm² corresponding to 4·10³ molecules/cm³, at a vacuum pressure of 8·10^?7 torr in the apparatus, and using a time constant of 1,25 sec.     

Electronic energy transfer from Cd(53P1 to Popop vapor

Quenching of Cd(5³P₁) by POPOP and sensitization of POPOP by Cd(5³P₁) have been investigated in the vapor phase at total pressures of 10^-1 to 10^-2 torr. Quenching of Cd is observed to occur at a rate of 5.9 X 10^-10 cm³/sec and sensitization of POPOP at a rate of 4.2 X 10^-11 cm³/sec. The sensitized fluorescence rate has been found to be consistent with Forsters long-range dipole-dipole mechanism. Selection of a donor for a possible energy transfer, vapor phase, dye laser is discussed.     

Fluoreszenz hydroxydhaltiger Alkalihalogenide

Alkali halides doped with OH^?-ions show a characteristic fluorescence in the near UV which is excited in the ultraviolett OH^?-absorption band. It consists of several equidistant broad bands, the spacing of which corresponds to the infrared OH^?-absorption. The temperature dependence of the half width, the quantum yield and the decay time was measured in various alkali halides. A radiationless process obeying an Arrhenius law with an activation energy between 0.03 and 0.33 eV depending on the lattice, quenches the fluorescence at high temperature. Just before its onset the decay time amounts to 4 · 10^?5 sec in KI, 6 · 10^?5 sec in KBr and 10^?6 sec in KCl and the quantum yield is approx. 1/3 in KI and KBr and 10^?3 in KCl. At low temperatures the decay time in KI and KBr increases considerably and the quantum yield in KCl decreases still more. The radiative process obviously has to be activated thermally. In KCl it is always by far exceeded by another radiationless process.     

Zur Halbwertszeit des 1,49 MeV-Niveaus im Co57

For the halflife of the 1,49 MeV state in Co⁵⁷ an upper limit of 3,0 × 10^?10 sec. has been found.     

A direct comparison of the visible and ultraviolet reflectance of aluminum films evaporated in conventional and ultra-high vacuum systems

Aluminum was evaporated in a conventional evaporator using an oil diffusion pump (p=3 × 10^-6torr) and in an ultra-high vacuum system evacuated by ion and titanium sublimation pumps (p=5 × 10^-9torr) and deposited at rates ranging from 2.5 Å/sec to 500 Å/sec. For aluminum deposited at rates of 300 Å /sec and greater there is no measurable difference in the visible and ultraviolet reflectance of the two types of films. However, if lower deposition rates are used the reflectance of aluminum films deposited at 5 x 10^-9 torr is much less dependent on deposition rate than that of films condensed at 3 x 10^-6 torr. Aluminum films deposited at high rates, both in conventional and ultra-high vacuum systems, show less degradation of reflectance during exposure to air than the films deposited at low rates.     

Proton spin-lattice relaxation by critical polarization fluctuations in KH2PO4

The observed anomalous decrease in the proton spin-lattice relaxation timeT ₁ on approaching the Curie point in a rather pure KH₂PO₄ single crystal is explained by magnetic dipolar coupling to the ferroelectric mode. The isolated “non-interacting” O?H...O proton flipping time is estimated from theT ₁ data as τ=0.66·10^?12 sec for the paraelectric phase and τ=2.24·10^?12 sec for the ferroelectric phase, in good agreement with the results obtained from other methods.     

Positron annihilation in solid krypton and xenon

A computation of the life time of positrons as well as the angular distribution of the resulting gamma pair for polycrystalline krypton and xenon has been made. The calculations are based on the technique employed by Salvadori and Carbotte for the case of solid argon. The field seen by the positrons is constructed from the charge densities derived from Herman-Skillman wave functions. The positron wave functions are obtained using the Wigner-Seitz approximation. For electrons Herman-Skillman wave functions have been used. The computed distributions, when the effects of correlation are ignored, are wider than the experimental ones. The calculated values for the mean lives of positrons for krypton and xenon are 2.2×10⁻⁹ sec and 2.7×10⁻⁹ sec, respectively, and that for xenon is, as usual, longer than the measured value of 0.43×10⁻⁹ sec. Effects of electronpositron correlations on the angular distribution and the life time have been calculated for the case of krypton. When these corrections are taken into account, the life time of positrons in krypton is reduced by a factor of about eight and the angular distribution shows a slight narrowing. Paper A24 presented at 3rd Internat'l Conf. Positron Annihilation, Otaniemi, Finland (August 1973).     

Elektronenverluste in einem abklingenden Wasserstoffplasma

The time dependence of the electron density in the afterglow period of an electrodeless discharge in hydrogen was measured by means of 4- and 8-mm microwave interferometry. An exponential decay was observed in the late afterglow permitting the evaluation of a time constant in the density range from 10¹²–10¹⁰ electrons per cm³. The decay time of the plasma was influenced by the discharge conditions. Electron losses could be explained by ambipolar diffusion and attachment to impurities. Two diffusion coefficients were found correlated to the discharge duration. The mobility value H₀=10.1±1.0 cm²/V · sec calculated from the diffusion coefficient found for short discharge pulses agrees with Saporoschenkos mobility value μ₀=10.2 cm²/V · sec for the H ₃ ⁺ -ion. A second mobility value μ₀=14.8±1.2cm²/V · sec found for longer discharge pulses might refer to the H⁺-ion.     

Molecular motion on surfaces as investigated by saturation transfer EPR

Saturation Transfer Electron Paramagnetic Resonance (ST-EPR) spectroscopy has been used to investigate the rate of angular reorientation of O₂^? adsorbed on supported metallic silver surfaces at a variety of temperatures. Computer simulations of the ST-EPR spectra were compared with those obtained experimentally, and correlation times for reorientation (τ_c) in the range between 10^?6 sec at 273 K to greater than 10^?4 sec at 173 K were calculated. Comparison of these results with a simple Langmuir model of surface mobility for O₂^? on silver yields good agreement.     

Diffusion behavior of tungsten clusters on the tungsten (110) planes

Diffusion of tungsten diatomic clusters on the W (110) exhibits comparable prefactor (1.6×10^-4 cm²/sec) as single W atoms, but with slightly higher activation energy. Clusters with three atoms are unstable with respect to diffusion.     

Bestimmung von Oszillatorenstärken durch Lebensdauermessungen der ersten angeregten Niveaus für die Elemente Ba,Sr, Ca,In und Na

The lifetimes of the first excited state of the elements Ca, Sr, Ba, In and Na were measured with the method ofOsberghaus ¹. Oscillator strengthes (f) of resonance lines were computed from the measured lifetimes (τ). The measurements were corrected for imprisonment of radiation in the investigated vapor. The error of the τ-values was estimated to be approximately three percent. We got following resultslifetimes for Ca 4¹ P ₁ (4·67±0·11)·10^?9sec, for Sr 5¹ p ₁ (4·56±0·21)·10^?9 sec, for Ba 6¹ p ₁ (8·36±0·25)·10^?9sec, for In 6² S _1/2 (8·531±0·085)·10^?9sec and for Na 3² P-dublett (1·59±0·039)·10^?8sec. For the Na 3² P-dublett the dependency of the lifetime on the pressure of foreign gases (N₂, C₃H₈, C₆H₅?CH₃) was studied.