Ordered orthorhombic phases of titanium monoxide

Symmetry analysis is carried out for the ordered phases of cubic monoxide TiO_y with relative oxygen contents y<1 and y>1. It is established that a partially ordered orthorhombic phase (space group Immm)—a derivative of the orthorhombic M₃X₂□ superstructure (at y<1.0) or the inverse superstructure M₂■X₃ (at y>1)—may arise in TiO_y. The distribution of Ti and O atoms, oxygen vacancies □, and titanium vacancies ■ in unit cells of the orthorhombic ordered phases is determined. The phases are formed through the order-disorder transition channel along two rays of a non-Lifshitz star {k ₄}, and the ordering proceeds as a first-order phase transition. The distribution functions of Ti atoms over the sites of metallic and O atoms over the sites of nonmetallic sublattices are calculated for the orthorhombic superstructures of cubic titanium monoxide TiO_y.     

Ordered phases of XXZ-symmetric spin-1/2 zigzag ladder

Using bosonization approach, we derive an effective low-energy theory for XXZ-symmetric spin-1/2 zigzag ladders and discuss its phase diagram by a variational approach. A spin nematic phase emerges in a wide part of the phase diagram, either critical or massive. Possible crossovers between the spontaneously dimerized and spin nematic phases are discussed, and the topological excitations in all phases identified.Received: 14 August 2004, Published online: 29 June 2004PACS: 75.10.Pq Spin chain models - 75.40.-s Critical-point effects, specific heats, short-range order - 75.30.Gw Magnetic anisotropy - 71.10.Pm Fermions in reduced dimensions (anyons, composite fermions, Luttinger liquid, etc.)     

Angle-resolved reflectance and surface plasmonics of the MAX phases

We investigate theoretically the optical response of bulk samples and thin films of the MAX phase materials, accounting for their large electrical anisotropy. We reveal the unusual behavior of the reflection and transmission spectra as a function of the incidence angle and predict the effect of the inverse total internal reflection. We also investigate the behavior of the surface plasmon modes in bulk samples and thin films and analyze the difference between MAX materials and conventional metals.     

The Fermi surface reconstruction in stripe phases of cuprates

Mean-field study of the stripe structures is conducted for a hole-doped Hubbard model. For bond-directed stripes, the Fermi surface consists of segments of an open surface and the boundaries of the hole pockets which appear in the diagonal region of momenta under certain conditions. Segments of the first type are due to one-dimensional bands of states localized on the domain walls. The relation of bands to the doping and temperature dependences of the Hall constant is discussed. In connection with the observation of quantum magnetic oscillations, a systematic search for the electron pockets has been carried out. It is shown that the formation of such pockets in bilayer models is quite possible.

     

The Fermi surface reconstruction in stripe phases of cuprates

Mean-field study of the stripe structures is conducted for a hole-doped Hubbard model. For bond-directed stripes, the Fermi surface consists of segments of an open surface and the boundaries of the hole pockets which appear in the diagonal region of momenta under certain conditions. Segments of the first type are due to one-dimensional bands of states localized on the domain walls. The relation of bands to the doping and temperature dependences of the Hall constant is discussed. In connection with the observation of quantum magnetic oscillations, a systematic search for the electron pockets has been carried out. It is shown that the formation of such pockets in bilayer models is quite possible. The article is published in the original.     

基于数学形态学的表面原子熔融相的 STM图像识别算法

高温扫描隧道显微镜(HT-STM)可以实时原位地捕捉到表面原子的熔化相变过程.在这一原位变温实验中,快速可靠地识别出每帧STM图像中的熔融相十分关键.传统的手工统计方法存在效率低下、随意性大等问题.我们发展出一套基于数学形态学的算法,来自动快速地识别.与人工方法相比,该算法消除了人为主观误差,使确定的边界更加准确、光滑,处理效率提高了266倍.     

Types of Fermi surface segments of cuprate stripe phases

The mean field method was used to study zones and Fermi surfaces of the stripe phases of the Hubbard model, which describes the electronic properties of cuprates. It was shown for structures with stripes parallel to bonds that the Fermi surface consisted of open surface segments and closed surfaces around hole pockets. Segments of the first type originate from quasi-one-dimensional zones of states localized on domain walls. The properties of zones in comparison with the zones observed in angle-allowed photoemission spectra and the possible influence of the corresponding two types of carriers on the dependence of the Hall constant on temperature and doping are discussed. In view of the observed magnetic quantum oscillations, the search for electron pockets was undertaken. Their formation was shown to be possible in two-layer (but not one-layer) models.     

Ordered droplet structures at the liquid crystal surface and elastic-capillary colloidal interactions

We demonstrate a variety of ordered patterns, including hexagonal structures and chains, formed by colloidal particles (droplets) at the free surface of a nematic liquid crystal (LC). The surface placement introduces a new type of particle interaction as compared to particles entirely in the LC bulk. Namely, director deformations caused by the particles lead to distortions of the interface and thus to capillary attraction. The elastic-capillary coupling is strong enough to remain relevant even at the micron-scale when its buoyancy-capillary counterpart becomes irrelevant.     

Ripening of surface phases coupled with oscillatory dynamics and self-induced spatial chaos through surface roughening

Some pattern formation processes on single-crystal catalytic surfaces involve transitions between alternative surface phases coupled with oscillatory reaction dynamics. We describe a two-tier symmetry-breaking model of this process, based on nanoscale boundary dynamics interacting with oscillations of adsorbate coverage on microscale. The surface phase distribution oscillates together with adsorbate coverage, and, in addition, undergoes a slow coarsening process due to the curvature dependence of the drift velocity of interphase boundaries. The coarsening is studied both statistically, assuming a circular shape of islands of the minority phase, and through detailed Lagrangian modeling of boundary dynamics. Direct simulation of boundary dynamics allows us to take into account processes of surface reconstruction, leading to self-induced surface roughening. As a result, the surface becomes inhomogeneous, and the coarsening process is arrested way before the thermodynamic limit is reached, leaving a chaotic distribution of surface phases. (c) 1999 American Institute of Physics.     

Determination of the surface tension at the boundary of solid phases

The results are given of an experimental investigation of the kinetics of isothermal coalescence of disperse phases in AI-Mg alloy and in vanadium steel. A method is described of processing the kinetic curves to evaluate the magnitude of the specific surface energy () at the boundary of the solid phases. The reasonableness of the values of obtained atthe boundary-Al-- phase (Al₃Mg₂) and -Fe-cementite (Fe₃C) confirms our calculation of the solubility of the disperse phase.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 4, pp. 114–120, April, 1972.     

Ordered arrays of myoglobin adsorbed on the surfactant modified surface by scanning tunneling microscopy

Myoglobin molecules were deposited on a surfactant sodium dodecyl sulfate modified HOPG surface and imaged in air with a high resolution scanning tunneling microscope (STM) for the first time. STM images exhibit not only ordered arrays of the surfactant molecules but also regular two-dimensional arrays of myoglobin molecules. From STM images, the myoglobin molecule can be described as an ellipsoid-shaped pattern for the tertiary structure. In this study the dimensions of a myoglobin molecule were determined approximately as 43.0 × 36.2 × 8 ų, which are in good agreement with the known data from X-ray analysis, except for the height of a molecule which cannot be estimated from STM.     

New surface phases for potassium adatoms on cleaved Si(111)

In a previous study (B. Reihl and K.O. Magnusson, Phys. Rev. B 42 (1990) 11 839) no change was observed in the LEED pattern from the 2 × 1 pattern of the clean Si(111) surface upon potassium adsorption. In contrast to this paper, we observe six surface phases during room temperature dosing of K on the cleaved Si(111) surface. In addition, we observe a 3 × 1 pattern on the cleaved K/Si(111) surface upon annealing. This paper will provide photographs of the new phases observed with LEED. It also will set limits on the K coverage required for these phases using results from photoemission and secondary electron cutoff measurements. Tentative models for these surfaces will be proposed. These new LEED results show a more complex interaction between K and the cleaved Si(111) surface than previously thought and hopefully will encourage further exploration of adsorption on the cleaved Si(111) surface.     

Displacive surface phases formed by hydrogen chemisorption on W {001}

A detailed LEED study is reported of the surface phases stabilised by hydrogen chemisorption on W {001}, over the temperature range 170 to 400 K, correlated with absolute determinations of surface coverages and sticking probabilities. The saturation coverage at 300 K is 19(± 3) × 10¹⁴ atoms cm^?2, corresponding to a surface stoichiometry of WH₂, and the initial sticking probability for both H₂ and D₂ is 0.60 ± 0.03, independent of substrate temperature down to 170 K. Over the range 170 to 300 K six coverage-dependent temperature-independent phases are identified, and the transition coverages determined. As with the clean surface $\text{(}\text{2}\text{×}\text{2}\text{)R45°}$ displacive phase, the c(2 × 2)-H phase is inhibited by the presence of steps and impurities over large distances (～20 Å), again strongly indicative of CDW-PLD mechanisms for the formation of the H-stabilised phases. These phases are significantly more temperature stable than the clean $\text{(}\text{2}\text{×}\text{2}\text{)R45°}$, the most stable being a c(2 × 2)-H split half-order phase which is formed at domain stoichiometries between WH_0.3 and WH_0.5. LEED symmetry analysis, the dependence of half-order intensity and half-width on coverage, and I-V spectra indicate that the c(2 × 2)-H phase is a different displacive structure from that determined by Debe and King for the clean $\text{(}\text{2}\text{×}\text{2}\text{)R45°}$. LEED I-V spectra are consistent with an expansion of the surface-bulk interlayer spacing from 1.48 to 1.51 Å as the hydrogen coverage increases to ～4 × 10¹⁴ atoms cm^?2. The transition from the split half-order to a streaked half-order phase is found to be correlated with changes in a range of other physical properties previously reported for this system. As the surface stoichiometry increases from WH to WH₂ a gradual transition occurs between a phase devoid of long-range order to well-ordered (1 × 1)-H. Displacive structures are proposed for the various phases formed, based on the hypothesis that at any coverage the most stable phase is determined by the gain in stability produced by a combination of chemical bonding to form a local surface complex and electron-phonon coupling to produce a periodic lattice distortion. The sequence of commensurate, incommensurate and disordered structures are consistent with the wealth of data now available for this system. Finally, a simple structural model is suggested for the peak-splitting observed in desorption spectra.     

Identification of nickel silicide phases on a silicon surface from Raman spectra

We have demonstrated the effectiveness of Raman spectroscopy for monitoring nickel silicide formation processes on the surface of silicon wafers, with deposition of a composite metal layer (nickel, platinum, and vanadium) under industrial process conditions in microelectronics. The observed shift of all the NiSi lines toward lower energies is associated with formation of the metastable silicide phase Ni_1?x Pt _x Si, which leads to the presence of stresses in the lattice as a result of the increase in the distances between atoms.