Low-temperature magnetoresistance due to weak localization in lightly doped semiconductors

The first observation of low-temperature magnetoresistance (MR) of interference nature in the case of a light doping is reported. The MR occurs in n- and p-type Ge samples at a frequency of 10 GHz at temperatures below 30 K in weak magnetic fields on the background of the classical MR effect associated with electrons in different valleys (n-Ge) and with heavy and light holes (p-Ge).     

Stabilisation of fcc cobalt layers by 0.4 nm thick manganese layers in Co/Mn superlattices

Epitaxial Co/Mn multilayers (0.75 to 6 nm Co, 0.4 nm Mn layer thickness) have been grown on mica substrates covered by a (0002) Ru buffer layer. The structural properties of these layers have been studied using X-ray diffraction, nuclear magnetic resonance (NMR), and high resolution transmission electron microscopy (HRTEM). The Co layers, grown as face centred cubic (fcc), were found to be stabilised by the very thin Mn layers. Data obtained using X-ray diffraction and NMR were analysed and found to be in good agreement, while Monte-Carlo simulations were used to interpret the data and calculate the expected diffracted intensity and NMR spectra. The HRTEM data show that the Mn layers give rise to a large strain contrast extending, in the growth direction, over a distance which exceeds the thickness of the Mn layers. The superlattices could be described as having an fcc structure containing randomly located stacking faults with varying densities. The results verify the presence of a dominant, almost perfect phase of fcc stacking, and of a faulted hcp phase, while the number of defects increases with the Co layer thickness. Received 27 October 1999 and Received in final form 29 May 2000     

Compact and portable holographic camera using photorefractive crystals. Application in various metrological problems

We present a compact holographic interferometer that uses a photorefractive crystal of the sillenite family as a holographic recording medium. Its development is based on a previous prototype that showed lack of flexibility and portability. We briefly discuss the main improvements leading to a compact device. Applications of this instrument in various metrological problems are shown, among which are two that were not already considered using holography, namely measurement of a thermal expansion coefficient and detection of fingerprints. Received: 20 December 2000 / Revised version: 8 February 2001 / Published online: 20 April 2001     

Frequency combinations in the magnetoresistance oscillations spectrum of a linear chain of coupled orbits with a high scattering rate

The oscillatory magnetoresistance spectrum of the organic metal (BEDO)₅Ni(CN)₄. 3C₂H₄(OH)₂ has been studied up to 50 T, in the temperature range from 1.5 K to 4.2 K. In high magnetic field, its Fermi surface corresponds to a linear chain of quasi-two-dimensional orbits coupled by magnetic breakdown (MB). The scattering rate consistently deduced from the data relevant to the basic α and the MB-induced β orbits is very large which points to a significant reduction of the chemical potential oscillation. Despite of this feature, the oscillations spectrum exhibits many frequency combinations. Their effective masses and (or) Dingle temperature are not in agreement with either the predictions of the quantum interference model or the semiclassical model of Falicov and Stachowiak.     

Ferromagnetism in Mn-doped GaAs layers: Effects of laser annealing

The properties of Mn-doped GaAs layers grown by laser deposition were investigated with measurements of Hall effect and magneto-optical Kerr effect (MOKE). The electrical and magnetic parameters of the layers were defined by growth temperature and quantity of sputtered Mn. It was shown that room-temperature ferromagnetism is revealed by MOKE and, after ruby laser 25 ns pulse annealing, by Hall effect measurements.     

Formation of a blocky ferrite in Fe–Cr–Ni alloy during directional solidification

Formation and evolution details of a blocky microstructure in AISI 304 stainless steel are studied by quenching method during directional solidification. Results show that a coupled growth microstructure, consisting of lathy ferrite and austenite, forms first from the melt. At solid-state transformation stage, most lathy ferrite disappears due to the phase transformation from ferrite to austenite. With further decreasing of the temperature, plenty of fine ferrite colonies occur in the original austenite region. The formation of the blocky ferrite indicates that reverse solid-state transformation from austenite to ferrite takes place. This transformation is due to the segregation and the instability of austenite during the growth of austenite under low cooling rate. The fine ferrite colonies transform into blocky ferrite at room temperature. TEM and EDS analyses were carried out to identify the phases and determine the phase composition, respectively.     

Adsorbate-site determination by surface-state spectroscopy?

Electronic surface states can interact with adsorbate orbitals only if they have the same symmetry with respect to the adsorption site. Therefore, the interaction between a surface state and a particular adsorbate orbital provides information about the symmetry properties of the adsorption site. This is discussed for the adsorption of hydrogen and ethylene on Ni(110).     

Nickel cluster structure determined from the adsorption of molecular nitrogen: Ni49-Ni71

The geometrical structures of nickel clusters in the size range from 49 to 71 atoms are studied by the chemical probe method. Saturation coverages of molecular nitrogen are determined for each cluster and from this data specific structures are proposed (except for Ni₆₆ and Ni₆₇). The results indicate that icosahedral packing is the dominant structural configuration throughout this size range, in agreement with earlier results based on water and ammonia adsorption. In addition, it seems that for clusters larger than Ni₅₄ the excessive strain in the surface of the 55-atom regular icosahedron often leads to rear-rangements of the surface atoms to relieve that strain. Ni₅₅, in particular, is found to have two isomers, the regular icosahedron and a structure in which a single apex atom is displaced to the center of an opposite face. Ni₇₁ occurs as a 55-atom regular icosahedron with a 16-atom cap. The results suggest that the atoms in the cap adopt an ABA configuration relative to the underlying icosahedron rather than an icosahedral arrangement. For some clusters the saturation with nitrogen causes a small degree of surface reconstruction that leads to the adsorption of additional nitrogen molecules.Work supported by the U.S. Department of Energy, Office of Basic Energy Sciences, Division of Chemical Sciences, under Contract No. W-31-109-Eng-38     

基于JSP的在线考试系统的开发与设计

基于JSP的在线考试系统的开发是为了让学校能够更好的管理学生的考试,通过互联网的方式,不仅可以方便了学生,更适合如今的网络盛行的时代。本系统分为系统管理者所辖的模块和考生用户模块两个部分。