High resolution x-ray study of microstructural changes in semiconductors and insulators subject to high electric fields

Using a high-resolution X-ray diffractometer, microstructural changes have been observed in Si-, LiF- and CdS-crystals subject to high d.c. and a.c. fields. At high fields the diffraction peaks are unstable due to inhomogeneous distribution of the electric current in the specimen. The inhomogeneous regions have been directly observed in high-resolution topographs. A correlation between current fluctuations and the diffracted beam intensity has been observed. Changes in peak shapes as a result of field have been observed.     

Oblique interaction of electrostatic nonlinear structures in relativistically degenerate dense magnetoplasmas

We have investigated the interaction of obliquely propagating ion acoustic solitary waves in a magnetoplasma with relativistically degenerate electrons. Using the quantum hydrodynamics model and by employing the extended Poincaré–Lighthill–Kuo technique, we have derived a set of Korteweg de Vries equations for two solitons. We have observed that the system under consideration allows the formation of only compressive solitons and their velocities remain in the sub-acoustic limit. Furthermore, phase shifts of solitons as a result of their interaction have been calculated. The phase shifts have been observed to be dependent on the obliqueness and the physical parameters of plasma. It has also been noticed that phase shifts remain negative for the whole range of parameters generally found in white dwarf stars. We have observed that the phase shifts enhance with the enhancement in number density, however, the converse happens when the magnetic field is enhanced. It has also been observed that the phase shift is slightly greater for the solitons that are less oblique as compared to their more oblique counterparts. Furthermore, we have estimated the spatial scales of interaction of solitons using the parameters found in white dwarf stars.     

Lifetime of negative molecular ions of tetracene and pentacene with respect to the autodetachment of an electron

The processes of nondissociative resonant attachment and autodetachment of electrons in a number of poly-cyclic aromatic hydrocarbon molecules have been investigated by mass spectrometry. Long-lived negative molecular ions of phenanthrene and triphenylene have not been observed. Such ions have been detected for anthracene, pyrene, and benzo[e]pyrene capturing thermal electrons. Negative molecular ions of tetracene and pentacene have also been observed up to 2.5–3 eV. The lifetimes of these ions with respect to the auto-detachment of an electron have been measured throughout the energy range where they are observed. This lifetime for tetracene and pentacene is more than 10 ms, which is two or three orders of magnitude larger than that for remaining compounds. Correlation between the lifetime of ions and the electron affinity of the molecules has been revealed.     

六角结构金属α—Ti中的小角晶界

本文报道了六角结构金属α-Ti中小角晶界的透射电子显微镜观察结果。除倾侧间界外,还在基面、柱面上观察到扭转晶界。在柱面上的位错网络中还观察到c型位错,但尚未观察到c型位错的运动,这可能与c型位错有较高的Peierls应力有关。 关键词：     

TiVI真空紫外光谱

用1m法向入射光谱仪观察三电极真空火花发射的Ti五次离化光谱。在24～200nm波段内观察到157条TiVI的新谱线。根据新归属的TiVI谱线定出11个新能级,并对5个有疑问的能级值作了修正。     

Locking of a cw dye laser to inverted atomic transitions

We have observed narrow line oscillation of an internally pumped cw dye laser at wavelengths which correspond to atomic transitions in the pump laser discharge. At other discharge wavelengths quenched regions in an otherwise broader dye laser output have also been observed. It is believed that the narrow lines correspond to transitions which have gain in the pump laser discharge, while the holes correspond to transition with loss.     

Electrical and optical analyses of Er-doped silicon grown by liquid-phase epitaxy

We have studied the deep levels present in Er-doped silicon epilayers grown by the liquid-phase epitaxy method by deep level transient spectroscopy (DLTS) and optical DLTS, in order to identify the majority and minority carrier traps and a possible correlation between these traps and the observed photoluminescence (PL) and cathodoluminescence (CL) spectra. Capacitance–voltage analyses have been performed to analyze uniformity and depth distribution of the existing traps and marked differences have been observed between the luminescent and non-luminescent materials.The PL and depth resolved CL revealed the presence of dislocation-related emission lines which can possibly be correlated to the broadened peaks observed in DLTS analyses of luminescent material.     

Microwave Spectroscopic Study of NiF in the Electronic Ground and Lowest Excited States

The rotational spectra of NiF in the electronic ground (2)Pi state and the lowest electronically excited (2)Sigma state have been observed. The source of nickel atom was sputtering from a nickel electrode or nickel powder placed on a stainless steel electrode. The molecular constants have been determined by a least-squares analysis of the observed transition frequencies. The rapid increase in the Lambda-type splittings in the ground state reveals that the observed rotational transitions are ascribed to the spin substate (2)Pi(3/2). The rotational transitions corresponding to the other substate,(2)Pi(1/2), have not been observed. The large spin-rotation interaction constant gamma in the electronically excited (2)Sigma state is consistent with that from the electronic spectroscopy. Copyright 2001 Academic Press.     

Emission spectroscopy of ν10 band of vinyl bromide

By pumping with a pulsed CO₂ laser we have observed many FIR emissions in vinyl bromide that we have assigned to the ν₁₀ band at 942 cm⁻¹. We have been able also to assign many other FIR lines observed in previous works, so that we have derived new spectroscopic constants for the vibrational excited level.     

Ultrashort pulse compression and delivery in a hollow-core photonic crystal fiber at 540 nm wavelength

We have fabricated a bandgap-guiding hollow-core photonic crystal fiber (PCF) capable of transmitting and compressing ultrashort pulses in the green spectral region around 532 nm. When propagating subpicosecond pulses through 1 m of this fiber, we have observed soliton-effect temporal compression by up to a factor of 3 to around 100 fs. This reduces the wavelength at which soliton effects have been observed in hollow-core PCF by over 200 nm. We have used the pulses delivered at the output of the fiber to machine micrometer-scale features in copper.     

A HeI photoelectron spectroscopic study of polyunsaturated fatty acids

HeI photoelectron spectra of some unsaturated fatty acids except of docosahexaenoic acid have been observed in the gas phase for the first time, by using an infrared heating device that was developed in this laboratory. The first vertical ionization energies (I_obs) of oleic acid, linoleic acid, linolenic acid, and docosahexaenoic acid have been determined to be 8.85, 8.80, 8.77, and 8.75 eV, respectively. Several higher ionization energies have also been observed. The valence electronic structures associated with the observed ionization energies and the optimum geometries have been elucidated by ab initio calculations carried out in the present study.     

Reversible stress relaxation during precoalescence interruptions of volmer-weber thin film growth

From in situ stress measurements, we have observed that a large component of the precoalescence compressive stress that develops during Volmer-Weber growth of polycrystalline Cu films relaxes reversibly. This phenomenon is similar to the reversible stress relaxation previously observed in the postcoalescence regime. We have also observed that less than a tenth of a monolayer of deposition leads to an instantaneous stress of order 1 GPa. The stress changes in both the precoalescence and postcoalescence regimes of growth are explained by changes in the adatom population during and after deposition.     

Observation of compressional Alfvén modes during neutral-beam heating on the national spherical torus experiment

Neutral-beam-driven compressional Alfvén eigenmodes at frequencies below the ion cyclotron frequency have been observed and identified for the first time in the National Spherical Torus Experiment. The modes are observed as a broad spectrum of nearly equally spaced peaks in the frequency range from approximately 0.2omega(ci) to approximately 1.2omega(ci). The frequency has a scaling with toroidal field and plasma density consistent with Alfvén waves. The modes have been observed with high bandwidth magnetic pickup coils and with a reflectometer.     

The 116Sn(d,t)115Sn reaction at 23 MeV

The levels of ¹¹⁵Sn up to 4 MeV excitation energy have been studied with 15–18 keV energy resolution, and many previously unreported levels have been observed. Angular momentum transfers and spectroscopic factors have been determined for most of the levels up to 3 MeV. The main features of the observed fragmentation of the strength are rather well reproduced by means of a weak coupling calculation.     

Cylindrical GaAs quantum wires incorporated within chrysotile asbestos nanotubes: fabrication and polarized optical absorption spectra

GaAs has been injected into chrysotile asbestos channels. GaAs quantum wires (nanocylinders) with diameters ∼ 6 nm have been observed in the channels by means of transmittance electron microscopy. Polarized optical absorption spectra of asb-GaAs (chrysotile asbestos containing GaAs wires) have been studied. A high anisotropy of the absorption has been observed, and intersubband transitions in the visible light region due to a strong quantum size effect have been found.     

Two-dimensional correlation relaxation studies of cement pastes

Two-dimensional nuclear magnetic resonance relaxation correlation studies of cement pastes have been performed on a unilateral magnet, the Surface GARField. Through these measurements, the hydration process can be observed by monitoring the evolution of porosity. Characteristic relaxation time distributions have been observed in different cement pastes: fresh white cement, prehydrated white cement and ordinary Portland cement. The observed T(1)/T(2) ratio in these cements has been shown to agree with expectations based on high field values.     

Vibrational Spectra of a Linear Alternating L,D Hexapeptide with a Type II β-Turn Structure

Raman and infrared spectra of Boc-(D-aIle-L-Ile)₃-OMe (ILEU-6) and its N-deuterated derivative have been measured. Conformationally sensitive amide vibrations have been identified and compared with the observed and calculated frequencies of Pro-Leu-Gly-NH₂ which has a type II β-turn structure. The observed frequencies of ILEU-6 have also been compared with the normal mode calculations of a standard model type II β-turn structure and a good agreement has been found in these comparisons. The additional frequencies observed for this particular structure are assigned to the residues that are not involved in the β-turn.     

Devaluation of the gold standard in x-ray photoelectron spectroscopy

The value of vapor-deposited gold as a standard in x-ray photo-electron spectroscopy has been studied. During the deposition gold may react with the sample giving consequent shifts and/or broadening of the Au 4f peaks. Shifts to higher binding energies have been observed with KCN and NACl and to lower energies with Na₂S₂O₃ and copper phthalocyanine. The An 4f peaks have been investigated over the temperature range ?50 to 200°C. At higher temperatures peaks due to metallic gold are observed. Anomalous effects have been observed in the XPS spectrum of gold plated copper phthalocyanine in the binding energy range 650–950 eV.     

Scaling properties of percolation models for multifragmentation

We have used scaling properties of nuclear multifragmentation, which have been observed with emulsion data, to investigate the properties of some approaches based on percolation. We have studied different percolation models on a cubic lattice and shown that they can rather well reproduce the data except for binary break up. We have described what the mean field approximation would give in this context and showed that it cannot reproduce the experimental results. Most of the paper is focused on the restructured aggregation model introduced earlier which allows to well reproduce the scaling properties observed experimentally. This model has been studied in details and extended to take account of bonds breaking. It is shown that, in some cases, a nucleus can break up in two pieces. This process cannot be obtained in conventional percolation or aggregation but is observed experimentally in the emulsion data. Other features like the dimensionality of the aggregation model, the restructuration of the clusters and a schematic constraint in momentum space have also been investigated.     

Raman scattering as a probe of the tensile strain distribution in GaAs grown on Si(111) by molecular beam epitaxy

Epitaxial layers of GaAs grown on Si substrates, where the layer thickness greatly exceeds any critical thickness based on mismatch in lattice constant alone, have been shown to be under tensile strain for temperature at or below 300 K. This "thermal" strain arises from the difference in thermal expansion coefficients between GaAs and Si. We have performed Raman experiments on GaAs layers grown on both Si (001) and Si (111) substrates. We have observed a shift in the optical modes towards lower frequencies which is indicative of tensile strain in the GaAs layers, this is greater in the (111) growth direction than in the (001) one. In order to investigate the strain distribution as a function of distance from the GaAs/Si interface we have measured Raman spectra after successive removing of the epitaxial layer by chemical etching. We have found out that the strain decreases with increasing distance from the interface. We have developed the theory of Cerdeira et al. (1) to determine quantitatively the strain present in the heteroepitaxial layers. We have used, for the first time, polarization selection rules to separate the various components of the optical phonon modes. According to the theory we have observed that the doubly degenerate TO phonon line exhibits both a splitting and shift with strain, while only a shift is observed for the LO phonon line. In conformity with Cerdeira we have remarked that the strain dependence of the LO phonon is equal to that of the TO phonon mode observed in crossed polarization configuration.