Analytical,structural and electrical characterization of SiGe layers by electron microbeam techniques

k-ratios of Ge-L and Si-K measured at different beam energies allow to evaluate simultaneously composition and thickness of SiGe layers on a Si substrate. A simple technique applying backscattered electrons also enables estimation of composition of bulk SiGe and of composition and thickness of relatively thick (200 nm) SiGe layers on Si. Electron channeling patterns of pseudomorphic SiGe/Si structures and of pure Si substrate show no significant differences whereas in relaxed structures a smearing of the pattern with increasing density of misfit dislocations is observed. Under particular conditions the technique of the electron beam induced current permits imaging of recombination-active misfit dislocations with a spatial resolution around 0.2 m. Moreover, a repulsion of holes due to the valence-band offset in a n-Si/SiGe heterostructure was detected.     

Mechanical properties of fiber reinforced styrene-butadiene rubbers using surface-modified UHMWPE fibers under EB irradiation

Aiming to develop a high performance fiber reinforced rubber of SBR, a special technique using electron beam (EB) irradiation-induced graft-polymerization was applied to ultra-high molecular-weight polyethylene (UHMWPE) fibers. Although UHMWPE is chemically inert, N-vinyl formamide (NVF) could be graft-polymerized onto the UHMWPE fiber surface with this special technique. A maximum grafting percentage of 23.6% was achieved. The composite of SBR and grafted UHMWPE fibers with maximum grafting indicated a linear increase in the initial modulus and strength with the fiber content. At the fiber content of 10%, the initial modulus was improved about five times with respect to that of the pure SBR, while the strength was done about twice. At this moment, only a small reduction could be observed in the strain compared with that of pure SBR. The fiber reinforced rubber with a good performance was obtained in the system of SBR and grafted UHMWPE fibers.     

Microstructural and physicochemical study of the buried Fe/AlGaAs(100) interface by transmission electron microscopy and x‐ray emission spectroscopy

Among the magnetic metal/semiconductor contacts, the Fe/GaAs system has been widely studied owing to its potential applications in electronic devices. In contrast, there are not many studies concerning the Fe/Al_xGa_1?xAs contact, and in particular there are no reports concerning the changes induced in the interfacial zone by the presence of Al. In this work, thin polycrystalline iron films were deposited by ion beam sputtering at room temperature on a 300 nm thick Al_0.25Ga_0.75As layer grown by molecular beam epitaxy onto GaAs(001). X‐ray diffraction analysis showed that the iron films are polycrystalline, and indications of a (002) texture of the film were observed. The fine scale analysis of the interface was achieved by high‐resolution transmission electron microscopy (HRTEM) observations, the results of which are compared with the physicochemical information obtained from electron‐induced x‐ray emission spectroscopy, by analysing the Al 3p valence states at the Fe/Al_xGa_1?xAs interface. The HRTEM experiments on cross‐section samples indicate that the interfacial zone between iron and AlGaAs is limited to <1.5 nm in thickness. X‐ray emission spectroscopy showed the presence of Al atoms in an FeAl‐like environment at the interface, and the existence of wrong bonds and point defects. The estimated width of the perturbed interface (2.0 ± 0.5 nm) is in agreement with the HRTEM results. Copyright © 2003 John Wiley & Sons, Ltd.     

Polarization of coherent synchrotron radiation from an electron beam rotating in a plasma

After eliminating reflections from the walls of the plasma container, we observed polarization of the coherent synchrotron radiation from a relativistic electron beam rotating in a plasma. Several features of the polarization agree well with calculations based on the single particle synchrotron radiation theory. A particular polarization ratio (Fig. 3) does not, however. We deduce from this direct diffraction of the radiation by the beam electrons. This is strong evidence for beam-particle bunches of size cm. Also, there must be some absorption of the extraordinary wave to account for the observations. We suggest a way to apply these results to measure the pitch angle of the beam.Work supported by Army Research Office.     

神光-Ⅱ装置三倍频实验中靶场单元技术的改进

 主要介绍为了满足神光-Ⅱ高功率激光装置三倍频光（351nm，3ω）的物理实验要求，靶场三倍频模拟光源和瞄准监视系统两个主要单元技术的改进，即三倍频模拟光源由基频光（1 053nm，3ω）通过腔外的KTP+BBO晶体倍频获得，再经八路分光系统和主激光耦合；瞄准监视系统由透射式光学系统改进为反射式光学系统，避免原系统存在较大的色差，提高瞄准精度。     

A critique of the unsaturable trap model of radiation damage in metals

The unsaturable trap model, which attributes the increase of the electrical resistivity of fcc metals during electron irradiation in the temperature regime of Stage-II recovery to the trapping of Stage-I_E interstitials at impurity atoms, is shown to be in serious disagreement with the experiments, contrary to opposite statements in the literature. As shown recently, the predictions of the unsaturable trap model are independent of the dimensionality of the diffusion of the Stage-I_E interstitials. Previous attempts to rule out a one-dimensional migration of the Stage-I_E interstitials (and hence the two-interstitial model) on the basis of the alleged agreement of the unsaturable trap model with Stage-II damage curves are thus meaningless. On the contrary, it is demonstrated that the two-interstitial model accounts for minute details of the measured Stage-II damage curves in a natural way.     

FREE VIBRATION ANALYSIS OF LATTICE SANDWICH BEAMS UNDER SEVERAL TYPICAL BOUNDARY CONDITIONS

Free vibration problems of lattice sandwich beams under several typical boundary conditions are investigated in the present paper. The lattice sandwich beam is transformed to an equivalent homogeneous three-layered sandwich beam. Unlike the traditional analytical model in which the rotation angles of the face sheets and the core are assumed the same, different rotation angles are considered in this paper to characterize the real response of sandwich beams. The analytical solutions of the natural frequencies for several typical boundary conditions are obtained. The effects of material properties and geometric parameters on the natural frequencies are also investigated.     

Effects of physics change in Monte Carlo code on electron pencil beam dose distributions

Pencil beam algorithms used in computerized electron beam dose planning are usually described using the small angle multiple scattering theory. Alternatively, the pencil beams can be generated by Monte Carlo simulation of electron transport. In a previous work, the 4th version of the Electron Gamma Shower (EGS) Monte Carlo code was used to obtain dose distributions from monoenergetic electron pencil beam, with incident energy between 1 MeV and 50 MeV, interacting at the surface of a large cylindrical homogeneous water phantom. In 2000, a new version of this Monte Carlo code has been made available by the National Research Council of Canada (NRC), which includes various improvements in its electron-transport algorithms. In the present work, we were interested to see if the new physics in this version produces pencil beam dose distributions very different from those calculated with oldest one. The purpose of this study is to quantify as well as to understand these differences. We have compared a series of pencil beam dose distributions scored in cylindrical geometry, for electron energies between 1 MeV and 50 MeV calculated with two versions of the Electron Gamma Shower Monte Carlo Code. Data calculated and compared include isodose distributions, radial dose distributions and fractions of energy deposition. Our results for radial dose distributions show agreement within 10% between doses calculated by the two codes for voxels closer to the pencil beam central axis, while the differences are up to 30% for longer distances. For fractions of energy deposition, the results of the EGS4 are in good agreement (within 2%) with those calculated by EGSnrc at shallow depths for all energies, whereas a slightly worse agreement (15%) is observed at deeper distances. These differences may be mainly attributed to the different multiple scattering for electron transport adopted in these two codes and the inclusion of spin effect, which produces an increase of the effective range of electrons.     

Chiralization in mesogenic 1,3-diacylaminobenzenes

The effect of molecular chirality in thermotropic mesomorphic H-bonded polymeric systems has not really been investigated so far. Therefore, five new chiral mesogenic diamides have been prepared and described. Besides more ordered mesophases, the enantiomers exhibit a chiral nematic polymorphism detected by microcalorimetry and probably corresponding to different modes of chiral coiling to give these singular twisted nematic phases.     

Optical characterization of high speed microscanners based on static slit profiling method

Optical characterization of high-speed microscanners is a challenging task that usually requires special high speed, extremely expensive camera systems. This paper presents a novel simple method to characterize the scanned beam spot profile and size in high-speed optical scanners under operation. It allows measuring the beam profile and the spot sizes at different scanning angles. The method is analyzed theoretically and applied experimentally on the characterization of a Micro Electro Mechanical MEMS scanner operating at 2.6 kHz. The variation of the spot size versus the scanning angle, up to ±15°, is extracted and the dynamic bending curvature effect of the micromirror is predicted.