ESR millimeter-band spectroscopy of magnetic ordering in the low-dimensional magnet CuGeO3

Resonant absorption of microwaves in CuGeO₃ single crystals in a frequency band of 40 to 120 GHz, in magnetic field B⩽15 T, at temperatures ranging between 0.5 and 300 K, and in the configuration B∥a has been investigated. Several absorption lines (S ₀, S _a, and S _b) whose parameters strongly depend on temperature have been detected close to ESR. The temperature dependence of the total absorption in the main line S ₀ with the Landé g-factor g ₀=2.154 at temperatures above the spin-Peierls transition temperature is in good agreement with Bonner and Fisher’s theoretical prediction for a one-dimensional Heisenberg spin chain. In addition to the main resonance, a resonance of smaller amplitude, S _a, with the g-factor g _a=2.72 has been detected at temperatures ranging down to a characteristic temperature T≃1 K, below which the amplitude of this feature drops to zero. A radical restructuring of the magnetoabsorption spectrum occurs at the temperature of the spin-Peierls transition T _SP≈14 K. At T<12 K new features emerge in the spectrum, namely, a broad absorption line overlapping with the narrow lines S ₀ and S _a, and a line S _b with g _b=1.83, which is not detected at temperatures above T _SP. An analysis of amplitudes and total absorption of ESR lines as functions of temperature has shown that the temperature range below 1 K is anomalous, which may be caused by an additional ordering in the CuGeO₃ magnetic subsystem at low temperatures. Zh. éksp. Teor. Fiz. 112, 1727–1738 (November 1997)     

Growth of Cu(In,Ga)S2 on Si(100) substrates by multisource evaporation

Cu(In,Ga)S₂ films were grown on Si(100) by vacuum evaporation using the constituent elementary substances as sources. It was found from X-ray diffraction studies that orientational growth occurred in a limited temperature region. The chalcopyrite structure was confirmed by studying RHEED patterns. The existence of c-axis growth, two kinds of a-axis growth and four kinds of {112} twins which can be classified as two symmetrical pairs is proposed.     

Growth and structure of vanadium oxide on anatase (1 0 1) terraces

The interaction of vanadium oxide with epitaxial anatase films exposing (1 0 1) terraces was characterized. The TiO₂ films were grown on vicinal LaAlO₃ (1 1 0) substrates by oxygen plasma-assisted molecular beam epitaxy (OPA-MBE); reflection high energy and low energy electron diffraction (RHEED and LEED) indicated that the films exposed (1 0 1) terraces of the anatase TiO₂ polymorph. When a vanadium oxide monolayer was deposited onto the anatase surface by OPA-MBE at 725 K, only (1 × 1) RHEED and LEED patterns were observed. The V X-ray photoelectron spectroscopy (XPS) peak intensities indicated that the monolayer wetted the anatase surface and so the diffraction patterns were attributed to an epitaxial vanadia layer. Analysis of the vanadium oxide monolayer by X-ray and ultraviolet photoelectron spectroscopies revealed that the V was predominantly 5+. When the vanadia coverage was increased at 725 K, Auger electron spectra showed only very slow attenuation of the anatase Ti peaks while spots began to develop in RHEED patterns recorded along the LaAlO₃ direction; both indicative of 3-D cluster formation. In the orthogonal direction, the RHEED patterns showed unusual diagonal streaks. Meanwhile, the (1 × 1) LEED pattern persisted even after 30 nm of vanadia was deposited. This was attributed to gaps between the 3-D clusters exposing the epitaxial monolayer. Core level XPS spectra of the 3-D clusters revealed a broad V 2p_3/2 peak that was centered at the position expected for V⁴⁺ but could be deconvoluted into three peaks corresponding to V³⁺, V⁴⁺, and V⁵⁺. It is shown that crystallographic shear that accommodates such variations in the oxygen content of V oxides can lead to the diagonal streaks in RHEED patterns recorded along the LaAlO₃ [0 0 1] direction even as the pattern in the orthogonal direction shows sharp transmission spots. The results show that vanadia growth on anatase (1 0 1) proceeds through the Stranski-Krastanov mode with a strong vanadia-titania interaction stabilizing a dispersed vanadia monolayer. The results are compared with previous data for vanadia growth on anatase (0 0 1) where smooth, epitaxial VO₂ films grow ad infinitum.     

Instability of C 60 + on Ni (100) in surface collisions

Collisions of C ₆₀ ⁺ -ions with a nickel (100) surface in ultra high vacuum have been studied. Fullerene ions emerging from the surface after impact were not observed. Auger spectroscopy reveals an increasing carbon coverage of the surface as the exposure dose of C ₆₀ ⁺ increased until saturation is reached. Low energy electron diffraction shows formation of ac(2×2) carbon superstructure ofp4g-symmetry. There is strong evidence, that the observed instability of C₆₀ is induced by a chemical reaction at the surface and that the Ni–C bonds formed lead to the superstructure.     

Growth of wide band gap wurtzite ZnMgO layers on (0001) Al2O3 by radical-source molecular beam epitaxy

Wurtzite structure ZnMgO layers have been grown using radical-source molecular beam epitaxy on high-quality ZnO buffer layers grown on (0001) sapphire substrates. The thickness of the ZnO buffer layers is 300 nm, with full width at half maxim of the HR-XRD (0002) rocking curves as low as 25 arcsec. In-situ Reflection High-Energy Electron Diffraction (RHEED) was employed for the optimization of the ZnMgO growth. RHEED and X-Ray Diffractometry measurements did not reveal any phase change from the wurzite structure to the rocksalt structure. The C-lattice parameter of Zn_1−xMg_xO films decreased from 5.209 to 5.176 Å with increasing x to 0.2. The surface morphology of the samples was studied with atomic force microscopy. The root mean square roughness values of 200 nm thick ZnMgO (x=0.2) was less than 1 nm. The main photoluminescence peak of Zn_1−xMg_xO shifted to as high as 3.77 eV owing to the increasing Mg composition of up to x=0.2.     

In situ characterization of MBE grown GaAs and Al x Ga1−x As films using RHEED,SIMS, and AES techniques

A combination of the surface diagnostic techniques Auger electron spectroscopy (AES), reflection high energy electron diffraction (RHEED), and secondary ion mass spectroscopy (SIMS) was used in order to get more detailed information on basic processes which lead to the formation of high quality monocrystalline GaAs and Al _x Ga_1−x As films by molecular beam epitaxy (MBE) under ultra-high vacuum conditions. The formation and changes of reconstructed surface structures on (100) GaAs as a function of growth parameters were observedduring growth by RHEED. AES was used to determine the relative ratio of Ga/As on the surface for different reconstructed structures, to investigate the impurity contamination on substrate surfaces and grown films, and to study the surface segregation of Sn in MBE GaAs during doping. Finally, intentional and unintentional impurities incorporated during the growth of GaAs and Al _x Ga_1−x As by MBE were detected by the SIMS technique immediately after growth within the reaction chamber.     

Crystal Structures of Tetrakis‐(4‐chlorophenylthio)‐butatriene and Tetrakis‐(tert‐butylthio)‐butatriene

Tetrakis‐(4‐chlorophenylthio)‐butatriene (3a) and tetrakis‐(tert‐butylthio)‐butatriene (3b) were synthesized, and their crystal structures were determined. The compound 3a is monoclinic, space group P2₁/c, a=6.9785(8), b=8.6803(9), c=22.884(2) Å, β=93.887(6)^o, V=1383.0(3) ų, Z=2. The compound 3b is monoclinic, space group P2₁/n, a=11.0615(6), b=10.8507(4), c=11.2717(6) Å, β =116.427(2)^o, V=1211.5(1) ų, Z=4. The title compounds 3a and 3b reside on an inversion center so that only half of the molecule is crystallographically unique. Both compounds are not planar. The crystal structures of 3a and 3b have cumulated double bonds. The C7–C8–C8ⁱ and C5–C6–C6ⁱ angles that show the linearity in both structures, respectively, are 176.4(3)° in 3a and 175.6(2)° in 3b.     

Surface Ostwald-ripening and evaporation of gold beaded films on sapphire

The kinetics of morphological evolutions of gold nanoparticles on alumina, resulting from evaporation and surface Ostwald-ripening coarsening, have been investigated by means of Auger electron spectroscopy. When the fraction of the covered area is small, the kinetics of evaporation can be related to the desorption of adatoms. In the temperature range 943–1043 K we obtained the evaporation flux J(m^-2s^-1)=4.8×10²⁷exp[-196±9 (kJ/mol)/RT]. The experimental activation energy of evaporation of gold from a sapphire surface, Q_evap=196±9 kJ/mol, is lower than the tabulated value of enthalpy of sublimation of gold, ΔH_subl=368 kJ/mol. At lower temperatures, in the range 623–778 K, Ostwald-ripening experiments, carried out on nanosized clusters, yield the mass transfer surface diffusion coefficients of gold on alumina, D_s(m²/s)=2.6×10^-14exp[-58±9 (kJ/mol)/RT]. These results, providing information on the evolution of granular gold films such as those used in catalysts or sensors, are compared to previous data on similar systems. PACS 68.47.Jn; 68.43.Jk; 68.55.-a     

Evolution of the structure of Rb2ZnCl4 over the temperature range 4.2–310 K

X-ray diffraction is used to study the temperature dependence of the lattice parameters and the sequence of structural realignments in crystalline Rb₂ZnCl₄ over temperatures of 4.2–310 K. The appearance of and changes in the system of satellite reflexes indicative of structural ordering are studied. Below 74 K, on going into the monoclinic phase (space group A11a), anomalies are observed in the behavior of the lattice parameters, and superstructural reflexes develop with wave vectors q=a ^*/3+b ^*/2+c ^*/2 corresponding to an increase by a large factor in initial parameters a, b, and c of the Pnma-phase. Fiz. Tverd. Tela (St. Petersburg) 41, 1084–1090 (June 1999)     

基于电子回旋共振-等离子体增强金属有机物化学气相沉积技术生长GaMnN稀磁半导体的研究

利用电子回旋共振-等离子体增强金属有机物化学气相沉积 (ECR-PEMOCVD)方法,采用二茂锰(Cp₂Mn)作为Mn源,高纯氮气作为氮源,三乙基镓(TEGa)作为Ga源,在蓝宝石(α-Al₂O₃)(0001)衬底上外延生长GaMnN稀磁半导体薄膜.反射高能电子衍射(RHEED)、X射线衍射(XRD)、原子力显微镜(AFM)表征了GaMnN薄膜的晶体结构和表面形貌.GaMnN薄膜均表现出良好的(0002)择优取向,表明制备的薄膜倾向于 关键词： GaMnN薄膜 稀磁半导体 铁磁性 居里温度     

Auger electron spectroscopy of the kinetics of evaporation of palladium beaded films from sapphire substrate

) surface of sapphire were investigated by Auger electron spectroscopy in the temperature range of 1053–1083 K. It was found that the decrease of the effective thickness during heat treatments under 10^-8 mbar was caused by evaporation from the surface of the substrate. Using the model developed by Kaganovskii and Beke we have established that the process is controlled by surface diffusion. It was shown that the evaporation rate of palladium adatoms from an alumina surface is given by I_o=1.45×10³⁶exp{-(393±46 kJ/mol)/RT}ms, and, on the basis of an estimation of the surface diffusion length, the effective surface diffusion coefficient D_s was evaluated: Received: 30 March 1998/Accepted: 28 May 1998     

Effect of adsorbed oxygen on the properties of ytterbium nanofilms

The effect of O₂ molecules adsorbed on the surface of ytterbium nanofilms on the properties of the volume and surface of these films has been studied. It has been shown that the dependence of the work function of the films on the concentration of O₂ adsorbed molecules exhibits a nonmonotonic behavior: originally, the work function decreases, to start increasing again on passing through a minimum. At high oxygen doses, this increase stops. Adsorption of oxygen brings about a fundamental rearrangement of the Auger spectra of ytterbium; indeed, the Auger peaks observed before oxygen adsorption disappear completely after its deposition on the surface, to become replaced by other ones. The results obtained qualitatively agree with similar observations amassed by the present authors in studies of adsorption of CO molecules on the surface of ytterbium films. These results should be ascribed to a manifestation of complex processes of electron exchange between these films and adsorbed O₂ molecules. These processes end up in a qualitative rearrangement of the electronic structure of the part of film volume that borders the surface, where ytterbium transforms into the d metal.     

Study on B2 structure epitaxial Fe/Co superlattice

The B2 structure Fe₅₀Co₅₀ alloy is very attractive material as a large spin conductance asymmetry. In this study, we have tried to fabricate epitaxial Fe/Co superlattice with B2 structure. In order to investigate the relationship between the film structure and the substrate temperature, the films were prepared at different substrate temperature. The film structure of Fe/Co was evaluated by reflection high energy electron diffraction (RHEED). The in-plane lattice spacing gradually decreased to that of a bulk Fe₅₀Co₅₀ as increase in the number of layers. The B2 structure ordered phase of Fe/Co superlattice was successfully confirmed by RHEED and X-ray diffraction (XRD).     

Effect of growth defects on microwave properties in epitaxial Ba0.5Sr0.5TiO3 thin films grown on (001) MgO by pulsed laser deposition

Ba_0.5Sr_0.5TiO₃ (BSTO) films have been grown heteroepitaxially on (001) MgO substrates by pulsed laser deposition (PLD) to fabricate microwave phase shifters for the wide frequency range 45 MHz–50 GHz. Both as-grown and ex situ annealed films have a cube on cube epitaxial relationship with ?100?BSTO//?100?MgO. Threading dislocations are the dominant defects, mostly with Burgers vectors b = ?101?. Growth at 10^?1 mbar oxygen pressure, compared to 10^?4 mbar, resulted in significantly better properties. Ex situ annealing of the film grown at 0.1 mbar resulted in a reduction of 40% in threading dislocation density and a 40% increase in dielectric tunability.     

高气压反射式高能电子衍射仪监控脉冲激光外延氧化物薄膜

在超高真空分子束外延（MBE）生长技术中，反射式高能电子衍射仪（RHEED）能实时显示半导体和金属外延生长过程，给出薄膜表面结构和平整度的信息，成为MBE必备的原位表面分 析仪.为了研究氧化物薄膜如高温超导（YBa₂Cu₃O₇） 、铁电薄膜（Sr_1-xBa_x TiO₃）及它们的同质和异质外延结构的生长机理，获得高质量的符合各种应用 需要的氧化 物多层薄膜结构，在常规的制备氧化 关键词： 高温超导薄膜 RHEED     

Sr2CoO4-δ薄膜中的自旋玻璃态的磁性质研究

用脉冲激光沉积方法(PLD)在铝酸镧衬底上制备了c取向的高氧空位含量的锶钴氧薄膜.X射线衍射分析表明薄膜单一取向且没有明显杂相.原位的高气压反射式高能电子衍射仪(RHEED)监测显示,薄膜为层状生长.通过对薄膜磁化强度随温度、磁场及时间的变化曲线进行测量,发现零场冷曲线上可能存在两个特征温度:T_f和T_a.T_f为对应玻璃态的冻结温度而T_a对应少量的不缺 关键词： 自旋玻璃 超交换相互作用 双交换相互作用 脉冲激光沉积     

Diffuse scattering in RHEED induced by linear disorders of sulphur segregated on nickel (111) surface

RHEED diffuse scattering intensity is related to the growth of one-dimensional sulphur chains segregated on a nickel (111) surface. These linear disorders lead to wall domains in the reciprocal lattice which give the well-known “arching” phenomenon in RHEED patterns. The diffuse scattering process disappears when the (5√3 × 2)R30° superstructure is obtained. Knowing the absolute coverage of sulphur by calibrated Auger spectroscopy, it is possible to give a new high symmetry model for this superstructure.     

蓝宝石衬底上Gd2O3掺杂CeO2氧离子导体电解质薄膜的生长及电学性能

采用反应磁控溅射方法,在(0001)蓝宝石单晶衬底上,制备了纳米多晶Gd₂O₃掺杂CeO₂(GDC)氧离子导体电解质薄膜,采用X射线衍射仪(XRD)、原子力显微镜(AFM)对薄膜物相、结构、粗糙度、表面形貌等生长特性进行了表征,利用交流阻抗谱仪测试了GDC薄膜不同温度下的电学性能;实验结果表明,GDC薄膜为面心立方结构,在所研究的衬底温度范围内,均呈强(111)织构生长;薄膜表面形貌随衬底温度发生阶段性变化：衬底温度由室温升高到300℃时, 关键词： 2O₃掺杂CeO₂电解质薄膜')" href="#">Gd₂O₃掺杂CeO₂电解质薄膜 反应磁控溅射 生长特性 电学性能     

Superconducting and magnetic properties of Nb/Pd 1-xFex/Nb triple layers

The superconducting and magnetic properties of Nb/Pd_1-xFe_x/Nb triple layers with constant Nb layer thickness d_Nb=200 ? and different interlayer thicknesses 3 ?≤ d_PdFe ≤ ? are investigated. The thickness dependence of the magnetization and of the superconducting transition temperature shows that for small iron concentration x the Pd_1-xFe_x layer is likely to be in the paramagnetic state for very thin films whereas ferromagnetic order is established for x ≥ 0.13. The parallel critical field B_c2||(T){B_{c2||}}(T) exhibits a transition from two-dimensional (2D) behavior where the Nb films are coupled across the interlayer, towards a 2D behavior of decoupled Nb films with increasing d_PdFeand/or x. This transition allows a determination of the penetration depth x_F{\xi _F} of Cooper pairs into the Pd_1-xFe_x layer as a function of x. For samples with a ferromagnetic interlayer x_F{\xi _F} is found to be independent of x.