He beam scattering and leed evidence for partial facetting of a Pt(997) surface

Partial facetting of a Pt(997) surface is obtained by high temperature annealing in oxygen. The facets produce a characteristic, very sharp peak in the He scattering pattern. The ability of He scattering to evidence even a relatively small amount of facets is proven. LEED patterns obtained with grazing primary beam also show the simultaneous presence of facets and undisturbed stepped regions. The lack of evidence for the presence of facets in the LEED patterns obtained at normal incidence is discussed.     

Geometric and Crystallographic Characterization of WC Surfaces and Grain Boundaries in WC-Co Composites

Electron backscattered diffraction has been used to determine the orientation of WC crystals in a WC-Co composite and atomic force microscopy has been used to measure the shapes of planar sections of the same crystals. A stereological analysis has been used to determine that {101¯0} prism facets and the {0001} basal planes are the WC surfaces that are most frequently in contact with Co. Further, the WC habit is an approximately equiaxed trigonal prism bound by three prism facets and two basal facets. An analysis of 15,600 grain boundaries shows that certain interfaces occur with a frequency that is much higher than would be expected in a random distribution and that the grain boundary habit planes also have {101¯0} and {0001} orientations. Eleven percent of all the observed WC-WC interfaces are 90° twist boundaries about [101¯0]. Two types of boundaries with a 30° rotation about [0001], a twist and an asymmetric tilt, comprise 3% of the population.     

Devil's staircase-type faceting of a cubic lyotropic liquid crystal

The faceting of monocrystals of the lyotropic cubic liquid crystals in equilibrium with a humid atmosphere is observed. Experiments reveal the presence of more than 60 different types of facets on the surface of a spherical crystal of radius R = 1 mm. The devil's staircase type of faceting has been predicted theoretically when the interaction between steps on the crystal surface is repulsive.     

Helium: Solid-liquid interfaces

The static and dynamic properties of solid-liquid interfaces in helium at low temperature are reviewed. The main emphasis is on the hcp solid ⁴He-superfluid ⁴He interface. However, the bcc solid ⁴He, ³He and ³He-⁴He mixtures are also considered. Experiments and theoretical work on the dynamics of rough interfaces are first examined. For these interfaces the growth resistance, the Kapitza resistance and the Peltier coefficient are described. Then, static properties such as surface tensions, wetting and contact angles, nucleation and orientation of crystals are considered. The problem of the roughening transition, i.e. the appearance of smooth facets on the interface, is first analyzed from a theoretical point of view. The related experiments are then reviewed: they include measurements of crystal shapes and of the facet dynamics. Finally, a few other experimental and theoretical works are presented. They mainly concern ³He crystals and ³He-⁴He mixtures for which a few dynamic properties such as growth resistances or heat transport through interfaces have been analyzed.     

Precipitate orientation relationships and interfacial structures in duplex stainless steel Zeron-100

Precipitation in a commercial duplex stainless steel, Zeron-100, has been investigated using conventional and high-resolution electron microscopy. Acicular fcc precipitates of Ni-rich nphase formed in the Cr-rich fmatrix by suitable heat treatment. The orientation relationships between a large number of particles and the matrix were studied and found to be distributed in a range between the Kurdjumov-Sachs and the Pitsch relationships. All particles were observed to be bounded by two types of longitudinal facets, designated I and C, representing 'incoherent' and 'coherent'. High-resolution microscopy showed that the I facet was based on the (112) alpha /(101) nincommensurate interface between Pitsch-related crystals. The C facet exhibited a coherent terrace structure with coherency strain parallel to accommodated by a disconnection array, causing the adjacent crystals to be slightly misoriented from the Kurdjumov-Sachs relationship. The orientational incompatibility between the I and C reference structures, 5.76° about , was found to be accommodated by networks of n-crystal dislocations superimposed on the facets. These acted as tilt walls of dislocations, but, although their combined angular tilt was always observed to equal about 5.7°, this was not partitioned between the I and C facets in a unique manner. Such differential partitioning of the incompatibility offers a natural explanation for the observed variation in particle orientation. Some issues, such as the growth mechanism, were not resolved and need further work.     

Magnetic susceptibility of fluoride glasses with 3d and 4f elements

The low field ac magnetic susceptibility has been studied as a function of temperature and frequency in a series of fluoride glasses containing Mn²⁺, rare-earth ions, or an admixture of the two types. All glasses exhibit magnetic freezing in the ⁴He or ³He temperature ranges, but the nature of the freezing appears to depend on the local anisotropy. In the case of Mn²⁺ or Mn²⁺ -Gd³⁺ ions, a sharp freezing analogous to that in CuMn was observed. For Ln³⁺ or Mn²⁺ -Ln³⁺ ions (Ln=Dy, Ho), the observed progressive freezing could be of a dynamic nature.     

Grain-boundary faceting at a = 3, [110]/{112} grain boundary in a cubic zirconia bicrystal

The atomic structure of a = 3, [110]/{112} grain boundary in a yttria-stabilized cubic zirconia bicrystal has been investigated by high-resolution transmission electron microscopy (HRTEM). It was found that the grain boundary migrated to form periodic facets, although the bicrystal was initially joined so as to have the symmetric boundary plane of {112}. The faceted boundary planes were indexed as {111}/{115}. The structure of the {111}/{115} grain boundary was composed of an alternate array of two types of structure unit: {112}- and {111}-type structure units. HRTEM observations combined with lattice statics calculations verified that both crystals were relatively shifted by (α/4)[110] along the rotation axis to form a stable grain-boundary structure. A weak-beam dark-field image revealed that there was a periodic array of dislocations along the grain boundary. The grain-boundary dislocations were considered to be introduced by the slight misorientation from the perfect = 3 orientation. The fact that the periodicity of the facets corresponded to that of the grain-boundary dislocations must indicate that the introduction of the grain-boundary dislocations is closely related to the periodicity of the facets. An atomic flipping model has been proposed for the facet growth from the initial = 3, {112} grain boundary.     

从大气压到超低气压范围的氦等离子体发射光谱的基本特性

采用三种实验装置(介质阻挡放电装置、空心阴极放电装置和彭宁放电装置)分别测量了不同压强范围内氦等离子体的发射光谱。通过对氦等离子体发射光谱的分析,已观察到一个共同的特点,就是在三种放电条件下产生的氦等离子体中31P1→21S0的谱线强度总是最强,可以推测亚稳态氦原子的含量相当显著,但不同的装置也有不同的特点,介质阻挡放电装置能够产生准辉光放电,谱线中氦原子的谱线强度很低,而空心阴极放电与彭宁放电装置能够产生稳定均匀的等离子体,且发射足够强的光辐射。我们已对所拍摄的光谱的谱线都进行了辨认,所有结果表明原子发射光谱分析法是研究不同条件下氦等离子体状态的一种十分有效的手段。     

Gapless spin liquid behavior in two-dimensional solid 3He

Direct demagnetization has been made for two-dimensional solid 3He in both the paramagnetic and the antiferromagnetic phases. The lowest temperature is about 10 microK, judging from the observed magnetization for the paramagnetic solid 3He. The magnetization of the antiferromagnetic solid 3He shows a gradual increase to about 10 microK for the 4/7 phase adsorbed on both one layer of 4He and two layers of HD preplated graphite. This strongly suggests that the triangular antiferromagnet with the higher order multiple exchange has a quantum spin liquid ground state with nearly zero or extremely small spin gap less than 10 microK.     

NMR study of the dynamics of 3He impurities in the proposed supersolid state of solid 4He

The dynamics of (3)He atoms in solid (4)He have been investigated by measuring the NMR relaxation times T(1) and T(2) in the region where a significant nonclassical rotational inertia fraction has been reported. For (3)He concentrations x(3)=16 and 24 ppm, changes are observed for both the spin-lattice relaxation time T(1) and the spin-spin relaxation time T(2) at the temperatures corresponding to the onset of the nonclassical rotational inertia fraction and, at lower temperatures, to the (3)He-(4)He phase separation. The magnitudes of T(1) and T(2) at temperatures above the phase separation agree roughly with existing theory based on the tunneling of (3)He impurities in the elastic strain field due to isotopic mismatch. However, a distinct peak in T(1) and a less well-resolved feature in T(2) are observed near the reported nonclassical rotational inertia fraction onset temperature, in contrast to the temperature-independent relaxation times predicted by the tunneling theory.     

Faceting of copper (10,10) and (510) surfaces under lead adsorption: A LEED-AES study

Low-energy electron diffraction and Auger electron spectroscopy have been used to examine the deposition of (sub)monolayer quantities of lead onto (10,10) and (510) copper surfaces. Faceting into (100) and more complex facets is observed at ambient temperature. For the (10,10) crystal, (210), (710) and (510) facet orientations are successively identified with increasing lead coverage. For the (510) crystal, decomposition into (210) and (100) facets is followed by restoration of the initial macroscopic (510) orientation. These results are discussed in terms of the correlation between the terrace width of the observed facets and the adsorbate superstructure on the corresponding low-index plane. It is shown that the orientations stabilised at monolayer coverage cannot be entirely explained by such a correlation but the whole succession of adsorption induced facets must be taken into account.     

INTERACTION MEAN FREE PATH OF He PROJECTILE FRAGMENTS FROM 16O-EM COLLISION AT 60 A GeV

The interaction mean free path of He projectile fragments, produced by the collisions of ^{16O at 60 A GeV in a nuclear emulsion, has been investigated. In the present analysis, 1555 He projectile fragments, giving rise to 320 secondary interactions, have been used. At a level of 3% a very weak signal of anomalons is observed, which comes mainly from the 3×He channel.}     

Distribution of the isotopes produced in the YBa2Cu3O7−x superconductor and PbZr0.54Ti0.46O3 ferroelectric by energetic charged particles

A study has been made of the concentration profiles of radioactive isotopes produced by transmutation in the YBa₂Cu₃O_7−x superconductor and PbZr_0.54Ti_0.46O₃ ferroelectric by energetic protons (10 and 15 MeV), deuterons (4 MeV), and ³He and ⁴He nuclei (20 MeV). Profiles of two types have been observed: monotonic and with a maximum. It is shown that the type of isotope concentration profile is determined by the nature of the cross-section energy dependence of the nuclear reaction producing a given isotope. Fiz. Tverd. Tela (St. Petersburg) 40, 2189–2191 (December 1998)     

Thermal faceting of the rutile TiO2(001) surface

Temperature dependent faceting of rutile TiO₂ surfaces cut to the (001) plane has been reported [Tait and Kasowski, Phys. Rev. B20 (1979) 5178]. By comparing LEED data to beam positions calculated for various sets of facet planes, the facet planes have been identified. The first ordered structure observed on annealing ion bombarded surfaces is composed of {011} facets with the facet planes in a (2 × 1) reconstruction. The high temperature structure produced on annealing above 1300K is best described as {114} facets; however, there are deviations of the observed LEED pattern from that calculated for {114} facets, possibly because of the presence of related planes. LEED data have now been obtained on the behavior of (110), (100), (011), (114), and (001) surfaces in UHV. The observed stability of TiO₂ surfaces can be related to the Ti ion coordination numbers in the surface plane as derived from stoichiometric terminations of the rutile lattice.     

一种新的量子点形成机制:表面原子的向上扩散运动

在Al(110)表面的同质外延生长中，实验上观察到许多由特殊小面围成的较大的量子点．这些长方盒形的量子点要比外延膜的平均厚度至少高十倍以上，密度泛函理论的研究发现，动力学过程是导致形成具有特定小面量子点的主要原因，其关键机制是表面原子的向上扩散运动。     

Evidence for a new low-lying resonance state in 7He

Low-lying resonance states in 7He(6He+n), formed after fragmentation reactions of a 227 MeV/nucleon 8He beam on a carbon target, have been studied. Coincidences between 6He nuclei and neutrons, corresponding to the one-neutron knockout channel in 8He, were selected. The relative energy spectrum in the 6He+n system shows a structure, which is interpreted as the 7He ( Ipi = 3/2(-)) ground state, unbound with 0.43(2) MeV relative to the 6He+n system and a width of Gamma = 0.15(8) MeV overlapping with an excited ( Ipi = 1/2(-)) state observed at 1.0(1) MeV with a width of Gamma = 0.75(8) MeV.     

Observation of cold, long-lived antiprotonic helium ions

Cold, two-body antiprotonic helium ions p 4He2+ and p 3He2+ with 100-ns-scale lifetimes, occupying circular states with the quantum numbers ni=28-32 and li=ni-1 have been observed. They were produced by cooling three-body antiprotonic helium atoms in an ultra-low-density helium target at temperature T approximately 10 K by atomic collisions, and then removing their electrons by inducing a laser transition to an autoionizing state. The lifetimes of p 3He2+ against annihilation induced by collisions were shorter than those of p 4He2+, and decreased for larger-ni states.     

In memoriam Yurii Fedorovich Smirnov: Some personal reminiscences on a great physicist

Yurii Fedorovich Smirnov (1935–2008) was a famous theoretical physicist. He achieved his career mainly at the Institute of Nuclear Physics of Moscow. These notes describe some particular facets of the contributions of the late Professor Smirnov in theoretical physics and mathematical physics. They also relate some personal reminiscences on Yurii Smirnov in connection with some of his numerous works.     

Neutron-proton final state interaction in the 3H(3He,pα)n reaction at low bombarding energies

The ³H(³He, pα)n reaction has been studied in a kinematically complete experiment at ³He bombarding energies between 0.31 and 2.80 MeV in order to detect a possible resonant energy dependence of the spin singlet (T = 1) neutron-proton final state interaction (FSI). The data in the region of low n-p relative energies have been analyzed in terms of the Watson-Migdal formalism. Only a slight relative increase of the ¹S₀ n-p FSI is observed with increasing bombarding energy. This result is not easily related to the strong isospin violations found in the two-body reaction ³H(³He, d)⁴He at similar ³He energies.     

Orthogonal-Polarization Diode Ring Laser and Its Gain Modulation

A diode ring cavity incorporating Faraday rotators and a variable phase retarder has been constructed aiming at achieving dual-frequency lasing operation with orthogonal linear polarizations. The orthogonal-polarization oscillations were observed in the 0.8-μm region with various operation wavelengths by changing the applied retardation. Furthermore the output power definitely depended on the applied retardation. Its dependence was theoretically studied, and the gain analysis taking into consideration the reflection at the laser diode amplifier facets was in good accordance with the experimental results.