Inversion of the electron spin resonance signal from a P1 center in a synthetic diamond crystal

We have studied the electron spin resonance (ESR) of a 0.59 carat synthetic diamond single crystal at room temperature. The crystal was grown on a “split-sphere” apparatus in the Fe-Ni-C system by the temperature gradient method. After high-temperature/high-pressure treatment of the diamond, it was observed that as the microwave power supplied to the sample increased from 70 μW to 70 mW in an H₁₀₂ cavity, the ESR signal from the P1 center (a nitrogen atom substituting for carbon at a lattice point of the diamond crystal: C-form nitrogen) is inverted. In the original diamond (before high-temperature/high-pressure treatment), no inversion of the ESR signal was observed. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 73, No. 1, pp. 9–12, January–February, 2006.     

Shaft cryostat for cooling of high-pressure chambers with diamond and sapphire anvils

A vertically loaded shaft cryostat based on a closed-cycle cryocooler built around a Sumitomo SRP-062B pulse tube has been developed. The cryostat is intended for investigating the structure and phase transformations of materials via neutron diffraction experiments on samples at pressures up to 10 GPa created in high-pressure chambers with sapphire and diamond an vils in the temperature range of 6—300 K. The cryostat has been tested with the help of the DISK diffractometer of the Russian Research Centre Kurchatov Institute. A high-pressure chamber is loaded into the cryostat through its shaft with the help of an insert. The chamber is cooled by heat-exchange gas (helium-4) an d a heat exchanger that is thermally connected with the cryocooler’s second stage. The minimum attained temperature of a sample is 6 K. The drift diameter of the shaft is 120 mm, making it possible to cool chambers with lengths up to 200 mm (in the vertical orientation) and 110 mm (in the horizontal orientation). The cryostat has been designed and manufactured at the Frank Laboratory of Neutron Physics of the Joint Institute for Nuclear Research.     

能量粒子轰击金刚石的计算机模拟

利用Tersoff势和分子动力学方法研究了初始动能为500 eV的硼粒子注入金刚石的微观行为.结果表明：硼注入后产生温度为5000 K的热峰，其寿命为0.18 ps；同时产生半径为0.45 nm局部非晶化区域，三重配位原子数占该区域原子数的7%.薄膜表层原子向内弛豫，近表层原子向外弛豫，表面层与近表层原子的间距减少了15%，表面层表现为压应力.硼原子以B<110>分裂间隙的形式存在于金刚石结构中. 关键词： 分子动力学模拟 金刚石 硼 注入     

Quantum size effects in δ-Pu (110) films

First-principles full-potential linearized-augmented-plane-wave (FP-LAPW) calculations have been carried out for δ-Pu (110) films up to seven layers. The layers have been studied at the non-spin-polarized-no-spin-orbit coupling (NSP-NSO), non-spin-polarized-spin-orbit coupling (NSP-SO), spin-polarized-no-spin-orbit coupling (SP-NSO), spin-polarized-spin-orbit coupling (SP-SO), antiferromagnetic-no-spin-orbit coupling (AFM-NSO), and antiferromagnetic-spin-orbit-coupling (AFM-SO) levels of theory. The ground state of δ-Pu (110) films is found to be at the AFM-SO level of theory and the surface energy is found to rapidly converge. The semi-infinite surface energy for δ-Pu (110) films is predicted to be 1.41 J/m², while the magnetic moments show an oscillating behavior, gradually approaching the bulk value of zero with increase in the number of layers. Work functions indicate a strong quantum size effect up to and including seven layers. The work function of the seven-layer δ-Pu (110) film at the ground state is found to be 2.99 eV.     

Crystallographic variant selection of martensite at high stress/strain

The phenomenological theory of martensitic transformation is well understood that the displacive phase transformations are mainly influenced by the externally applied stress. Martensitic transformation occurs with 24 possible Kurdjomov-Sachs (K-S) variants, where each variant shows a distinct lattice orientation. The elegant transformation texture model of Kundu and Bhadeshia for crystallographic variant selection of martensite in metastable austenite at various stress/strain levels has been assessed in this present research. The corresponding interaction energies have also been evaluated. Encouraging correlation between model prediction and experimental data generation for martensite pole figures at many deformed austenite grains has been observed at different stress/strain levels. It has been investigated that the mechanical driving force alone is able to explain the observed martensite microtextures at all stress/strain levels under uniaxial tensile deformation of metastable austenite under low temperature at a slow strain rate. The present investigation also proves that the Patel and Cohen’s classical theory can be utilized to predict the crystallographic variant selection, if it is correctly used along with the phenomenological theory of martensite crystallography.     

Magnetic resonance of paramagnetic ion-nuclei in metals and superconductors

The magnetic resonance lineshape of paramagnetic ion-nuclei in metals is calculated using the temperature Green functions method and is analyzed for limiting cases of fast and slow spin lattice relaxation of localized moments. The longitudinal spin lattice relaxation rate for paramagnetic ion-nuclei in type II superconductors due to the hyperfine coupling with local moments is calculated. The influence of the fluctuation coupling of electrons on relaxation of paramagnetic ion-nuclei in “dirty” type II superconductors is investigated in magnetic field slightly above the upper critical field H_c2.     

Electron spin resonance studies of Cu2+ doped in cadmium maleate dihydrate single crystals

Electron spin resonance studies have been carried out on Cu²⁺ ion doped in single crystals of cadmium maleate dihydrate at 303 and 77K. It has been found that Cu²⁺ enters this lattice interstitially. The spin Hamiltonian parameters have been evaluated and the ground state wave function is found to be predominantly |X ² −Y ²〉 with a slight admixture of |3Z ² −r ²〉.     

Nuclear moments around the Z=40 shell closure:91mY,95Zr and97Nb

Magnetic moments around the Z=40 shell closure have been established using nuclear magnetic resonance on oriented nuclei (NMR/ON) in iron. From the resonance frequencies we established |μ(⁹¹Y;9/2⁺)|=5.96(6)μ_N, |μ(⁹⁵Zr;5/2⁺)|= 1.103(23)μ_N, | μ(⁹⁷Nb;9/2⁺)| = 6.153(5)μ_N. From the electric quadrupole alignement of⁹⁵Zr+⁹⁵Nb in a Zr single crystal Q(⁹⁵Zr)=+0.29(5)b and Q(⁹⁵Nb)<0 have been derived. The results obtained are discussed using the Nilsson deformed single particle model. It is shown that for certain deformation regions, a measurement of the magnetic moment can give information on the nuclear quadrupole deformation. the NICOLE-ISOLDE Collaboration, CERN     

金刚石/硅(001)异质界面的分子动力学模拟研究

采用分子动力学方法模拟研究了未重构的金刚石/硅(001)面相接触时界面层原子的弛豫过程及所形成的异质界面的结构特征.硅碳二元系统中原子间的相互作用采用Tersoff多体经验势描述.弛豫前沿[110]与[110]方向界面碳硅原子数之比均为3∶2.界面碳硅原子总数之比为9∶4.弛豫后金刚石与硅界面处晶格匹配方式改变为[110]方向基本上以3∶2关系对准,而[110]方向大致以1∶1关系对准.相应地,界面碳硅原子总数之比接近3∶2.界面下方部分第二层硅原子在弛豫过程中向上迁移至界面是引起这种变化的原因,同时该层其他原子及其底下一到两个原子层厚度的区域在[001]方向上出现一定程度的无序化转变倾向.金刚石/硅异质界面处的硅碳原子发生强烈键合,形成平均键长为0.189nm的硅碳键.研究证实,晶格匹配主要呈现界面及其附近硅原子迎合界面碳原子排列的特点. 关键词： 金刚石 硅 异质界面 分子动力学     

Lattice specific heat and local density of states of Ni-based dilute alloys at low temperature

A detailed theoretical study of the low-temperature lattice specific heat of Ni-based dilute alloys has been carried out. Lattice Green’s function method has been used to calculate the local density of states of substitutional impurities and lattice specific heat in different alloys. The resonance condition has been investigated for possible occurrence of resonance modes. Except in NiCr and NiMn, low-frequency resonance modes have been obtained in all the alloys. However, no localized mode was obtained. The impurity-induced increase in lattice specific heat is explained on the basis of the obtained resonance modes. The calculation shows an excellent agreement with the measured lattice specific heat in these alloys     

Pressure dependence of the lattice constant of diamond: Isotopic effects

The pressure dependence of lattice constants of ¹³C-enriched diamond and diamond of natural isotopic composition have been studied by using x-ray synchrotron radiation and the imaging plate technique. The compression curves reveal features which indicate an inversion of the isotope effect at high pressure. Pis’ma Zh. éksp. Teor. Fiz. 63, No. 2, 73–77 (25 January 1996) Published in English in the original Russian journal. Edited by Steve Torstveit.     

Magnetic anisotropy of epitaxial iron films on single-crystal MgO(001) and Al_2 O_3 (11\bar 20) substrates

The ferromagnetic resonance and magnetization of single-crystal thin (27–100 Å films grown in the (110) direction are measured in the temperature range 20–400 K. The films are prepared by molecular-beam epitaxy on single-crystal sapphire substrates with a Nb(110)buffer layer. The angular dependence of the parameters of the ferromagnetic resonance spectrum is observed to have a 180° character when the static magnetic field is rotated in the plane of the sample. It is established that this angular dependence can be described on the assumption that the lattice distortions are essentially trigonal. A comparative analysis of previous data for Fe(001) films with the data for Fe(110) films shows that the source of the corrections to the cubic anisotropy constant is the characteristic distribution of the strains along the thickness of the film. Zh. éksp. Teor. Fiz. 115, 689–703 (February 1999)     

Thermal- and photo-induced transformations of luminescence centers in αd-Al<Subscript>2</Subscript>O<Subscript>3</Subscript> anion-defective crystals

The thermal- and photo-induced transformations of luminescence centers in anion-defective crystals of α-Al₂O₃ have been investigated. It has been found that the exposure of crystals to ultraviolet light at temperatures in the range 50–900°C leads to substantial changes in their thermoluminescence and radioluminescence spectra. According to the optical absorption and photoluminescence data, the detected F-type centers have been identified and the temperature ranges of the F → F ⁺ → F ₂ transformations and their possible mechanisms have been determined. The special attention has been drawn to the detailed similarity in the formation of complex F ₂-type centers in the initially perfect α-Al₂O₃ crystals irradiated with fast neutrons and in the studied anion-defective crystals.     

Effect of the δ-shaped quantum well at the one-dimensional lattice boundary on properties of Tamm-type surface electronic states

The Tamm-type surface electronic states at the boundary of the one-dimensional structure with periodically potential profile have been theoretically studied under the condition that the δ-shaped quantum well is at this boundary. The properties of surface electronic states in such a structure have been compared with Tamm electronic states in the absence of a quantum well at the lattice boundary and with electronic states localized near the δ-shaped potential well deep in the lattice. In particular, it has been shown that the existence of the δ-shaped potential well at the lattice boundary facilitates a significant increase in the degree of localization of Tamm-type surface electronic states and makes possible the appearance of these states at arbitrarily small heights of lattice potential barriers.     

Transient NMRON of brute force oriented110mAgAg

A novel technique involving electrodeposition has been used to prepare an elemental silver specimen wherein radioactive^110mAg probe nuclei are confined to a surface layer of approximately 0.1 μm depth. This specimen was then brute force oriented in a field of 8T and the continuous wave (CW) nuclear magnetic resonance on oriented nuclei (NMRON) spectrum showed an integrated destruction of some 58%. Moreover the transient NMRON techniques of single and modulated adiabatic passage were successfully applied, resulting in a determination of the electric quadrupole interaction strength at the^110mAg site in polycrystalline silver of P/h=+0.74(5)kHz with a FWHM of ΔP/h=0.75(8)kHz. The resulting mode electric field gradient is V_zz=+1.87(23)×10¹⁸Vm⁻¹. Analysis of the single passage data provides an estimate for the nuclear spin lattice relaxation constant in silver at 8T of C_k=1.6(3)s.K.     

Count fluctuation analysis in the triaxial strongly deformed potential well of 163Lu

High-spin properties of the triaxial strongly deformed potential well in ¹⁶³Lu at excitation energies above resolvable bands have been investigated. Gated E _γ-E _γ spectra display clear ridges with moments of inertia corresponding to those observed for the discrete strongly deformed bands. A fluctuation analysis of the ridges yields a number of two-step paths of ≈ 40 and ≈ 20, when gating on triaxial strongly or normally deformed bands, respectively. These results show that a potential well at large deformation coexists with the normally deformed well, and indicate a mixing between states in the two wells at higher excitation energy. Received: 4 January 2002 / Accepted: 6 May 2002     

Acoustic wave propagation in barium monochalcogenides in the B1 phase

Temperature dependence of ultrasonic attenuation due to phonon-phonon interaction and thermoelastic loss have been studied in (NaCl-type) barium monochalcogenides [BaX, X = S, Se, Te], in the temperature range 50–500 K; for longitudinal and shear modes of propagation along 〈100〉, 〈110〉, 〈111〉 directions. Second and third order elastic constants have been evaluated using electrostatic and Born repulsive potentials and taking interactions up to next nearest neighbours. Gruneisen parameters, nonlinearity constants, nonlinearity constants ratios and viscous drag due to screw and edge dislocations have also been evaluated for longitudinal and shear waves at 300 K. In the present investigation, it has been found that phonon-phonon interaction is the dominant cause for ultrasonic attenuation. The possible implications of results have been discussed. The text was submitted by the authors in English.     

NMR Relaxometer Operating in a Continuous Mode upon Rapid Adiabatic Approach to Resonance

A nuclear magnetic resonance relaxometer operating in a continuous mode of the high-frequency low-power generation upon a rapid approach to resonance, and consequent “passage” through resonance for the time of the signal decay has been developed. In addition to the increased signal-to-noise ratio, the application of the periodic audio-frequency modulation of the magnetic field under adiabatic conditions has enabled us to obtain the absorption derivative, which, in turn, has allowed us to record the establishment of the thermodynamic equilibrium between spins and the lattice. Experimental data on the amplitude–relaxation response of the relaxometer are given. Spin–lattice relaxation times of some proton-containing substances have been determined as well.