Valence change of europium in the Eu(Ir1−x Pd x )2Si2 silicides

Eu(Ir_1–x Pd _x )₂Si₂ solid solutions which exist only for 0x0.125 and 0.75x1 crystallize in the tetragonal ThCr₂Si₂-type structure. X-ray diffraction data, magnetic susceptibility and¹⁵¹Eu Mössbauer measurements suggest that these compounds can be characterized as homogeneous mixed valence systems. At room temperature and for 0x0.125, the europium valence decreases asx increases. For 0.75x1, a sharp continuous valence transition from Eu²⁺ to Eu³⁺ occurs near 48 K, 54 K and 78 K forx=0.75, 0.81 and 0.94 respectively. These valence changes are discussed in relation with the Eu–(Ir, Pd) interatomic distance.     

High-temperature background of internal friction in (Co45Fe45Zr10) x (Al2O3)100 − x , Co x (CaF2)100 − x , and Co x (PZT)100 − x nanocomposites

The elastic (G) and inelastic (Q ^?1) properties of (Co₄₅Fe₄₅Zr₁₀) _x (Al₂O₃)_{100 ? x} , Co _x (CaF₂)_{100 ? x} , and Co _x (PZT)_{100 ? x} (x = 23–76 at %) nanocomposites obtained by ion-beam sputtering are studied in the temperature range 300–900 K. A significant rise in the Q Q ^?1 (T) curve is observed at temperatures above 650 K, which is attributed to thermally activated migration of point defects under the conditions of confined geometry.     

Deposition behaviour of single Si adatom on p(2×2) Si(100) surface

The deposition of a single Si adatom on the p(2×2) reconstructed Si(100) surface has been simulated by an empirical tight-binding method. Using the perfect and defective Si surfaces as the deposition substrates, the deposition energies are mapped out around the research areas. From the calculated energy plots, the binding sites and several possible diffusion paths are achieved. The introduced defects will make the deposition behaviour different from that on the perfect surface.     

Mössbauer study of mixed valent silicides Eu(Ir1−x Pd x )2Si2

The solid solutions Eu(Ir_1–x Pd _x )₂Si₂, which exist for 0x0.125 and 0.75x1. cristallize with the tetragonal ThCr₂Si₂-type structure. The variation of the europium valence with composition has been thoroughly studied at temperatures 4.2T293 K by¹⁵¹Eu Mössbauer resonance. For 0x0.125 the europium valence at room temperature decreases asx increases. For 0.75x1 the valence transition temperature Eu³⁺Eu²⁺ increases asx increases.     

High-temperature ferromagnetism in Si1 ? x Mn x (x ≈ 0.5) nonstoichiometric alloys

It has been found that the Curie temperature (T _C ?? 300 K) in nonstoichiometric Si_{1 ? x} Mn _x alloys slightly enriched in Mn (x ?? 0.52?C0.55) in comparison to the stoichiometric manganese monosilicide MnSi becomes about an order of magnitude higher than that in MnSi (T _C ?? 30 K). Deviations from stoichiometry lead to a drastic decrease in the density of charge carries (holes), whereas their mobility at about 100 K becomes an order of magnitude higher than the value characteristic of MnSi. The high-temperature ferromagnetism is ascribed to the formation of defects with the localized magnetic moments and by their indirect exchange interaction mediated by the paramagnetic fluctuations of the hole spin density. The existence of defects with the localized magnetic moments in Si_{1 ? x} Mn _x alloys with x ?? 0.52?C0.55 is supported by the results of numerical calculations performed within the framework of the local-density-functional approximation. The increase in the hole mobility in the nonstoichiometric material is attributed to the decay of the Kondo (or spin-polaron) resonances presumably existing in MnSi.     

Entangled Eigenvectors of Scalar Fields φ1(x) - φ2(x) and П1(x) + П2(x)

We first demonstrate the precise Einstein-Podolsky-Rosen entanglement, which is inherent in quantum mechanics, in the context of quantum theory of complex scalar fields. We explicitly derive the entangled common eigenstates of φ₁(x) - φ₂(x) and П₁(x) + П₂(x) φ₁and φ₂ are two real components of the complex scalar field, and П₁ and П₂ are the corresponding conjugate fields) in the Fock space. The entangled eigenstates span a complete and orthonormal representation.     

Valence state and magnetic interactions in magnetically ordered Eu(Pd1−x Au x )2Si2

X-ray diffraction,¹⁵¹Eu Mössbauer effect (ME) and magnetic susceptibility measurements have been performed to investigate the valence behavior and the magnetic interactions of the Eu ions in the intermetallic series Eu(Pd_1–x Au _x )₂Si₂ (0x1) as a Forx>0.4 all experimental techniques are in agreement with each other and suggest a divalent 4f ⁷ ground state of the Eu ion. Belowx=0.4 the different methods lead to different results: while the lattice parameters and the ME isomer shift suggest an instable behavior of the valence the magnetic susceptibility proves a pure divalent 4f ⁷ ground state. These differences can be explained by assuming a partial extension of the 4f-shell radius such that the localized character of the 4f-electrons is preserved.Dedicated to B. Mühlschlegel on the occasion of his 60th birthday     

Mechanism of H2 desorption from monohydride Si(100)2 × 1H

Most recent experimental work on H₂ desorption from the monohydride Si(100) surface seems to point to a pairwise desorption mechanism involving the concerted desorption of two hydrogen atoms on different Si atoms of a single dimer. Using ab initio SCF and CI theory and a cluster model of the surface, the present work finds that the lowest energy pathway is symmetric rather than asymmetric. The desorption energy barrier is calculated to be 3.7 eV. Compared with an experimental value of 2.6 eV, the large barrier suggests that this direct desorption mechanism is not applicable. A multi-step desorption mechanism which involves a delocalized process in the formation of dihydride SiH₂ and a localized desorption of H₂ is proposed and is shown to explain the experimental observations.     

The ferromagnetic to antiferromagnetic transition in La1−x Y x Mn2Si2(57Fe) compounds

A set of La_1–xY_xMn₂Si₂(⁵⁷Fe) samples withx=0, 0.1, 0.15, 0.2, 0.25, 0.3, 0.5 and 1.0 have been prepared with the tetragonal ThCr₂Si₂ structure.⁵⁷Fe Mössbauer spectra have been collected at 4.2 K for all samples. The spectra can be well fitted by two sextets, the predominant one (90% of the spectral area) being associated with⁵⁷Fe atoms in the Mn 4d site, with the remainder located in the Si 4e site. The analysis shows that there are distinct changes in the hyperfine interaction parameters for samples above and below the critical concentrationx _c 0.15, at which a transition from ferromagnetism to antiferromagnetism occurs. This transition is a result of a change in the exchange interactions linked with changes in the interatomic distances, due to the smaller atomic volume of Y compared to that of La.On leave from Applied Acoustics Institute, Shaanxi Teachers University, Xian, PR China.     

Thermoelectric power of Ba(Fe1−x Co x )2As2 (0 ≤ x ≤ 0.05) and Ba(Fe1−x Rh x )2As2 (0 ≤ x ≤ 0.171)

Temperature-dependent, in-plane, thermoelectric power data are presented for single crystals of Ba(Fe_1?x Co _x )₂As₂ (0?≤?x?≤?0.05) and Ba(Fe_1?x Rh _x )₂As₂ (0?≤?x?≤?0.171). Given that previous thermoelectric power and angle resolved photoemission spectroscopy studies of Ba(Fe_1?x Co _x )₂As₂ delineated a rather large Co-concentration range for Lifshitz transitions to occur, and the underdoped side of the phase diagram is poorly explored, new measurements of thermoelectric power on tightly spaced concentrations of Co, 0?≤?x?≤?0.05, were carried out. The data suggest evidence of a Lifshitz transition, but instead of a discontinuous jump in thermoelectric power in the range 0?≤?x?≤?0.05, a more gradual evolution in the S(T) plots as x is increased was observed. The thermoelectric power data of Ba(Fe_1?x Rh _x )₂As₂ show very similar behavior to that of Co substituted BaFe₂As₂. The previously outlined T–x phase diagrams for both systems are further confirmed by these thermoelectric power data.     

Dangling-bond logic gates on a Si(100)-(2 × 1)-H surface

Atomic-scale Boolean logic gates (LGs) with two inputs and one output (i.e. OR, NOR, AND, NAND) were designed on a Si(100)-(2 × 1)-H surface and connected to the macroscopic scale by metallic nano-pads physisorbed on the Si(100)-(2 × 1)-H surface. The logic inputs are provided by saturating and unsaturating two surface Si dangling bonds, which can, for example, be achieved by adding and extracting two hydrogen atoms per input. Quantum circuit design rules together with semi-empirical elastic-scattering quantum chemistry transport calculations were used to determine the output current intensity of the proposed switches and LGs when they are interconnected to the metallic nano-pads by surface atomic-scale wires. Our calculations demonstrate that the proposed devices can reach ON/OFF ratios of up to 2000 for a running current in the 10 μA range.     

SrAl_(2x)O_(3x+1):Eu~(2+),Dy~(3+)(x=1～2)合成及其余辉特性分析

通过调节基质组份比例,研究了SrAl2xO3x+1∶Eu2+,Dy3+(x=1~2)荧光粉晶体结构,发光性质及长余辉特性。选取硝酸锶和硝酸铝作为基质原材料,硼酸氨和氟化铝作为助溶剂,采用阳离子草酸盐共沉淀,湿法预先混合原材料及分步合成等方法,制备了亮度高、余辉长及良好粒径分布的系列长余辉发光材料。基于对样品X射线衍射(XRD)图谱,扫描电子显微镜(SEM)照片,激发、发射光谱及余辉衰减曲线分析,发现SrAl2xO3x+1∶Eu2+,Dy3+具有良好的结晶状态;随x增加,发射光谱峰值从520 nm蓝移至470 nm;衰减到可辨认发光强度0.32 mcd/m2,余辉时间可相应地从30 h延长到60 h以上。通过分析发现表现不同余辉特性的主要原因是Eu2+在基质中具有不同浓度、不同衰减寿命的蓝、绿两种发光中心造成的,其中蓝发光中心寿命明显高于绿发光中心。     

A transmission electron microscopy study of composition in Si1− x Ge x /Si (001) quantum dots

A finite-element programme has been developed to model strain relaxation in the case of epitaxial Si_{1? x} Ge _x /Si coherent quantum dots either with or without compositional inhomogeneities. The resulting elastic displacement fields are used to calculate the intensity of dynamical plan view TEM images of such quantum dots. Various types of linear or parabolic compositional inhomogeneities are studied. TEM images of quantum dots with such inhomogeneities are calculated as well as those of quantum dots with a homogeneous composition. They are then compared with experimental images. It is shown how the analysis of the main features of these experimental images (black/white lobes and moiré-like fringes) enables us to determine the conditions in which it is possible to distinguish quantum dots with a homogeneous composition from those with compositional inhomogeneity.     

Formation of Ti1–x Si x and Ti1–x Si x N films by magnetron co-sputtering

The paper reports on surface morphology, structure and microhardness of TiSi–N films formed by cosputtering from two target-facing unbalanced magnetrons, equipped with pure Ti and Si targets, on an unheated substrate rotating in front of both targets. The ratio Si/Ti in the TiSi–N film was achieved by modifying the magnitude of currents in the individual magnetrons and by the addition of nitrogen to the film. The rotation of the substrate has a strong effect on the film deposition rate and its morphology. The deposition rate is 3 times lower than that of the film deposited on a stationary substrate. The surface roughness of a polycrystalline Ti film deposited on the rotating substrate is considerably higher than that on a stationary substrate. On the contrary, the surface of an amorphous Si film is smooth and there is no difference between the roughness of Si films sputtered on stationary and on rotating substrates. The hardness of the film increases with increasing Si content and with the addition of nitrogen to the TiSi film. The Ti(26 at.%)Si(8.5 at.%)N(65 at.%)-film sputtered on an unheated rotating steel substrate, held at a floating potential, exhibited the best result with a hardness of 29 GPa.     

Novel ternary iron-rich,rare-earth iron silicides: R3(Fe1−x Si x )22 (x ∼ 0.16)

In our search for new ternary rare-earth (R) iron silicon intermetallic compounds, a novel ternary phase with the chemical formula R₃Fe_18.5Si_3.5 has been identified with the RFeSi ratio in the range of 12–1574–7810–12. We have studied compounds with R=Gd, Tb, Dy, Ho, Er, Tm and Lu. All of the samples, except for R=Lu, form the new ternary phase3–22. X-ray diffraction data suggest that for R=Gd and Tb, the crystal structure is the rhombohedral Th₂Zn₁₇-type structure and for R=Dy, Ho, Er and Tm, the hexagonal Th₂Ni₁₇-type structure. We suggest that a 1/4 replacement of the R sites by Fe(Si) dumbbells in the CaCu₅-type structure leads to the new3–22 phase, which is an ordered version of the TbCu₇-type structure.⁵⁷Fe Mössbauer spectroscopy has been used to determine the hyperfine parameters of the⁵⁷Fe nuclei in the3–22 compounds. At 295 K, the average hyperfine field of the new3–22 phase ranges from 19.8 T (R=Ho) to 22.2 T (R=Gd). Thermogravimetric analysis (TGA) of these compounds gives Curie temperatures in the range 467 K (Tm)–549 K (Gd). Furthermore, our Mössbauer analysis enables us to investigate the preferential site occupancy shown by Si in these structures.     

双层钙钛矿锰氧化物Nd_(2-2x)Ca_(1+2x)Mn_2O_7(x=0.4,0.5)的磁相变特性

利用固相反应法制备了Nd2-2x Ca1+2x Mn2O7(x=0.0-0.9)多晶样品,通过FULLPROF程序对样品X射线衍射图谱进行了精修,样品的空间群为14/mmm.测量了样品x=0.4,0.5的磁性(5K相似文献   

Subsurface localization of charge carriers in Si/SiO2/Si x Ge1 − x nanostructures

Analysis of the capacitance-voltage (C-V) characteristics reveals an elevated concentration of charge carriers under the surface of a silicon substrate due to the formation of elastically stressed regions induced in the substrate by Si _x Ge_{1 ? x} nanoislands grown on the preliminarily oxidized Si surface. The C-V characteristics exhibit charge density peaks at a depth from 700 to 1000 nm for Si/SiO₂/Si _x Ge_{1 ? x} structures with various thicknesses of the SiO₂ layer. The results of theoretical calculations of the electron density distribution in the bulk of the silicon substrate correspond on the whole to the C-V characteristics. The state of the interfaces in the structures with different thicknesses of the oxide layer, which determines the effects of surface and interfacial recombination as well as charge carrier scattering, is studied by analyzing the kinetics of decay of a photo-emf signal and the photo-emf distribution over the surface of the structure. The results can be used in the development of various devices based on SiGe with inclusions of oxide layers.     

Structural, thermal, and electrical properties of (100?x) ZrO2 (x) Bi2O3 compound

Composition (100?x) ZrO₂ (x) Bi₂O₃ (x?=?15, 20, 25) is synthesized by solid-state reaction method to study the effect of Bi₂O₃ doping on ZrO₂. The as-prepared samples are characterized by various methods. The X-ray diffraction pattern of all these samples exhibits three phases, namely, m-ZrO₂, ??_III-Bi₂O₃, and ??-Bi₂O₃. The differential thermal analysis curves do not show any phase transition/decomposition, which clearly indicated the stabilization of ??-Bi₂O₃ phase. The conductivity changes in all the samples are discussed in terms of different phase formations and their volume fractions. The microstructural and energy dispersive analyses indicate the presence of different phases. A maximum conductivity at high temperature (800?°C) was observed for the x?=?25 composition, i.e., ???=?4.21?×?10^?2 S/cm.