(100)Si基应变p型金属氧化物半导体[110]晶向电导率有效质量双椭球模型

利用应变技术和沟道晶向工程技术,均可有效增强Si基金属氧化物半导体器件的性能.本文提出了(100)Si p型金属氧化物半导体(PMOS)[110]晶向电导率有效质量双椭球模型,从理论上解释了Si PMOS[100]晶向沟道空穴迁移率为[110]晶向沟道空穴迁移率1.15倍的原因.基于(100)Si基应变PMOS反型层E-k关系,拓展应用该模型,首先获得了(100)Si基应变PMOS反型层价带第一子带等能图,然后给出了(100)Si基应变PMOS器件反型层[110]晶向空穴电导率有效质量模型.本文的模型方案合理可行,可为Si基应变PMOS器件的研究与设计提供有价值的参考.     

Observation of charge-density wave domains on the Cr(110) surface by low-temperature scanning tunneling microscopy

We have studied the Cr(110) surface with low-temperature scanning tunneling microscopy at 6 to 145 K. For tunneling voltages below +/-150 mV we observe a surface charge-density wave (CDW) with a wavelength of 42 A and wave fronts aligned with the [001] in-plane direction. The observed wave pattern is identified as the surface projection of the bulk CDW's arising from the spin-density wave ground state of Cr with the Q vector parallel to [100] and [010], respectively. The bulk CDW with Q parallel to the [001] in-plane direction appears, however, to be strongly suppressed at the Cr(110) surface.     

Ab initio investigation of the mechanical properties of copper

Employing the ab initio total energy method based on the density functional theory with the generalized gradient approximation, we have systematically investigated the theoretical mechanical properties of copper (Cu). The theoretical tensile strengths are calculated to be 25.3 GPa, 5.9 GPa, and 37.6 GPa for the fcc Cu single crystal in the [001], [110], and [111] directions, respectively. Among the three directions, the [110] direction is the weakest one due to the occurrence of structure transition at the lower strain and the weakest interaction of atoms between the (110) planes, while the [111] direction is the strongest direction because of the strongest interaction of atoms between the (111) planes. In terms of the elastic constants of Cu single crystal, we also estimate some mechanical quantities of polycrystalline Cu, including bulk modulus B, shear modulus G, Young’s modulus E p , and Poisson’s ratio ν.     

Strain engineering for ZnO nanowires: First-principle calculations

We employ density-functional theory to investigate the strain engineering for infinitely long [0001] ZnO nanowires with rectangular cross sections. The structural and electronic properties of ZnO nanowires with uniaxial, lateral and shear strain are systemically calculated. The results show that the band-gaps of ZnONWs will decrease (increase) with increasing (decreasing) tensile (compressive) uniaxial strain. The tensile (compressive) lateral strain on {10 1̅0} surfaces will improve (reduce) the band-gaps for ZnONW with clearly nonlinear characteristic, while the change trend of band-gaps for ZnONW with lateral strain on {1 2̅10} surfaces is basically opposite. When we enhance shear strain on ZnONWs, the band-gaps are reduced. The increasing shear strain along [10 1̅0] direction will sharply reduce the band-gap and the curve is nonlinear, while the band-gap decreases nearly linearly with the increase of shear strain along [1 2̅10] direction.     

Ab initio investigation on mechanical properties of copper

Employing the ab initio total energy method based on the density functional theory with the generalized gradient approximation, we have investigated the theoretical mechanical properties of copper (Cu) systematically. The theoretical tensile strengths are calculated to be 25.3 GPa, 5.9 GPa, and 37.6 GPa for the fcc Cu single crystal in the [001], [110], and [111] directions, respectively. Among the three directions, the [110] direction is the weakest one due to the occurrence of structure transition at the lower strain and the weakest interaction of atoms between the (110) planes, while the [111] direction is the strongest direction because of the strongest interaction of atoms between the (111) planes. In terms of the elastic constants of Cu single crystal, we also estimate some mechanical quantities of polycrystalline Cu, including bulk modulus B, shear modulus G, Young's modulus E_p, and Poisson's ratio ν.     

Hole mobility enhancement in uniaxial stressed Ge dependence on stress and transport direction

Utilizing a six-band k.p valence band calculations that considered a strained perturbation Hamiltonian, uniaxial stress-induced valence band structure parameters for Ge such as band edge energy shift, split, and effective mass were quantitatively evaluated. Based on these valence band parameters, the dependence of hole mobility on uniaxial stress (direction, type, and magnitude) and hole transport direction was theoretical studied. The results show that the hole mobility had a strong dependence on the transport direction and uniaxial stress. The hole mobility enhancement can be found for all transport directions and uniaxial stess configurations, and the hole transport along the [110] direction under the uniaxial [110] compressive stress had the highest mobility compared to other transport directions and stress configurations.     

A reversible reaction forming (---Cu---O---) strings and (Cu)6-clusters on Ag(110) shown by STM

An artificial new surface of (---Cu---O---) chains grown on Ag(110) surface was prepared by reacting a surface with Cu atoms, where the (---Cu---O---) chains grow in the [1 0] direction and are self-assembled on the Ag(110) surface in a (2 x 2)-p2mg structure. When the Cu---O/Ag(110) surface was heated in vacuum, the (---Cu---O---) chain decomposed to uniform cluster dots arranged along the [1 0] direction, where the cluster dots were composed of six Cu atoms. When the Ag(110) surface with the Cu---cluster dots was exposed to O₂, the (---Cu---O---) lines were redrawn along the [1 0] direction by reacting a s in the [1 0] direction with O₂. This is a reversible chemical reaction in one dimensional regime proved in atomic resolution.     

Ideal shear strength under compression and tension in C, Si, Ge, and cubic SiC: an ab initio density functional theory study

Ideal shear strength under superimposed normal stress of cubic covalent crystals (C, Si, Ge, and SiC) is evaluated by ab initio density functional theory calculation. Shear directions in [112] and [110] on the (111) plane are examined. The critical shear stress along the former direction is lower than that along the latter in all the crystals unless the hydrostatic tension is extremely high. In both the [112]-shear and [110]-shear, critical shear stress is increased by compression in C but is decreased in the other crystals. The different response of the critical shear stress to normal stress is due to the strength of the bond-order term, i.e., dependence of the short-range interatomic attraction on the bond-angle.     

AFM针尖纳米切削晶向和切削方向影响的分子动力学

"建立了AFM针尖切削单晶铜的三维分子动力学模型,研究了工件材料不同晶向和刀具切削方向对切削过程中工件材料变形的影响．采用EAM势计算工件原子之间的作用,采用Morse势计算刀具原子之间的作用．模拟结果表明工件材料晶向和切削方向对纳米切削过程有显著影响．沿[110]方向切削比[100]方向切削产生的切屑结合更紧密,切削工件材料(110)晶向比切削工件材料(100)晶向产生的切屑体积更小,工件材料变形区域更小．研究了工件材料晶向和切削方向组合的不同纳米切削过程中系统势能变化情况．"     

Torsional strain of TaS3 whiskers on the charge-density wave depinning

We find that an electric current I exceeding the threshold value results in torsional strain of o-TaS3 samples with one contact freely suspended. The rotation angle deltavarphi of the free end achieves several degrees and exhibits hysteresis as a function of I. The sign of deltavarphi depends on the I polarity; a polar axis along the conducting chains (the c axis) is pointed out. We associate the effect with surface shear of the charge-density wave (CDW) coupled to the crystal shear. The current-induced torsional strain could be treated in terms of enormous piezoelectric coefficients (>10(-4) cm/V) corresponding to shear. In essence, TaS3 appears to be a ready torsional actuator based on the unique intrinsic property of the CDW.     

单轴应变Si(001)任意晶向电子电导有效质量模型

单轴应变Si材料电子电导有效质量是理解其电子迁移率增强的关键因素之一, 对其深入研究具有重要的理论意义和实用价值. 本文从Schrödinger方程出发, 将应力场考虑进来, 建立了单轴应变Si材料导带E-k解析模型. 并在此基础上, 最终建立了单轴应变Si(001)任意晶向电子电导率有效质量与应力强度和应力类型的关系模型. 本文的研究结果表明: 1) 单轴应力致电子迁移率增强的应力类型应选择张应力. 2) 单轴张应力情况下, 仅从电子电导有效质量角度考虑, [110]/(001)晶向与[100]/(001)晶向均可. 但考虑到态密度有效质量的因素, 应选择[110]/(001)晶向. 3) 沿(001)晶面上[110]晶向施加单轴张应力时, 若想进一步提高电子迁移率, 应选取[100]晶向为器件沟道方向. 以上结论可为应变Si nMOS器件性能增强的研究及导电沟道的应力与晶向设计提供重要理论依据. 关键词： 单轴应变 E-k关系')" href="#">E-k关系 电导有效质量     

Diagonal antiferromagnetic easy axis in lightly hole doped Y1-xCaxBa2Cu3O6

Hole induced changes in the antiferromagnetic structure of a lightly Ca doped Gd:Y(1-x)CaxBa2Cu3O6 copper oxide single crystal with x approximately 0.008 is investigated by Gd3+ electron spin resonance. Holes do not localize to Ca2+ ions above 2.5 K since the charge distribution and spin susceptibility next to the Ca2+ are independent of temperature. Both hole doped and pristine crystals are magnetically twinned with an external magnetic field dependent antiferromagnetic domain structure. Unlike the undoped crystal, where the easy magnetic axis is along [100] at all temperatures, the easy direction in the hole doped crystal is along the [110] diagonal at low temperatures and changes gradually to the [100] direction between 10 and 100 K. The transition is tentatively attributed to a magnetic anisotropy introduced by hole ordering.     

Thermal expansion measurements of the quasi-one-dimensional conductor K0.30MoO3

The charge density wave (CDW) dynamics of the quasi-one-dimensional conductor K_0.30MoO₃ shows two different regimes depending on the temperature: a strongly damped CDW motion above ∼50 K and CDW motion with almost no damping below ∼50 K. In a search for a characterization of this CDW behaviour, we performed thermal expansion measurements on K_0.30MoO₃ single crystals in the temperature range 4-250 K. In addition to the anomaly observed at the Peierls transition at 180 K along the [102] direction, an anomaly is observed at ∼50 K along the [−201] and [102] directions. The results are discussed in relation with the change in the CDW rigidity at ∼50 K.     

Strain-induced changes to the electronic structure of germanium

Density functional theory calculations (DFT) are used to investigate the strain-induced changes to the electronic structure of biaxially strained (parallel to the (001), (110) and (111) planes) and uniaxially strained (along the [001], [110] and [111] directions) germanium (Ge). It is calculated that a moderate uniaxial strain parallel to the [111] direction can efficiently transform Ge to a direct bandgap material with a bandgap energy useful for technological applications.     

Electronic structures of RTe2 (R = La,Ce): a clue to the pressure-induced superconductivity in CeTe1.82

Electronic structures of RTe2 (R=La,Ce) have been investigated by using the local spin density approximation (LSDA) and the LSDA + U (U: on-site Coulomb interaction) band methods. Both LaTe2 and CeTe2 show the very similar Fermi surface nesting features along the [100] direction, which drive the charge-density wave (CDW) instability in the Te(1) sheets. The contribution near E(F) from Ce 4f states is negligible in agreement with the measured ARPES spectra. In the semimetallic CDW-distorted RTe2, both Te vacancy and pressure induce the charge transfer from Te(1) 5p to R 5d states, producing the enhanced density of states at E(F). We suggest that these increased self-doped Te(1) 5p hole carriers are responsible for the pressure-induced superconductivity in nonstoichiometric CeTe1.82.     

Fabrication and magnetic properties of metallic nanowires via AAO templates

Metallic (Ni, Co, Cu and Fe) nanowires were fabricated by electrodeposition into anodic aluminum oxide (AAO) template. In this work, we have studied the effect of the electrode potential on the microstructure and magnetic properties of nanowires. Transmission electron microscopy (TEM) results showed that the metal nanowires were single-crystal. Cu and Ni nanowires had the same orientation along the [2 2 0] direction, while Co had a preferred orientation along the [1 0 0] direction. Fe nanowires had a preferred orientation along the [2 0 0] direction. The growth mechanisms are probably due to the competition growth of the adjacent grains and the confinement of growth in the nano-sized hole of the AAO template. Results showed that single crystal or highly textured nanowires had better magnetic properties compared with that of polycrystal nanowires in terms of coercivity and squareness.     

Lateral and vertical ordered one-dimensional InGaAs/GaAs quantum structures

Lateral and vertical ordered one-dimensional quantum structures, i.e. InGaAs/GaAs(001) quantum dot chains and quantum wires, have been obtained using molecular beam epitaxy. It was found that the InGaAs wires or dot chains sit on two-dimensional wetting layers and run along the [-110] direction, as the result of anisotropic strain and in-plane adatom diffusion. This anisotropic nature produces a model system for studying the electronic properties of one-, two-, and three-dimensional quantum confinements and related optical responses. The strain anisotropy is of importance in determining the electronic states of the quantum structures and the surrounding strained barrier. The strain-induced effects, such as change of band-gap and splitting of heavy–light hole states, were studied experimentally and theoretically. Optical anisotropy of these quantum structures is also discussed.     

Quantum melting of the charge-density-wave state in 1T-TiSe2

We report a Raman scattering study of low-temperature, pressure-induced melting of the charge-density-wave (CDW) phase of 1T-TiSe2. Our measurements reveal that the collapse of the CDW state occurs in three stages: (i) For P<5 kbar, the pressure dependence of the CDW amplitude mode energies and intensities are indicative of a "crystalline" CDW regime; (ii) for 525 kbar, the absence of amplitude modes reveals a metallic regime in which the CDW has melted.     

Visible Luminescence of SiGe/Si Quantum Wells Under an External Anisotropic Deformation

We realize for the first time an experimental investigation of the IR and visible luminescence of SiGe/Si heterostructures with quantum well subjected to an external anisotropic deformation. We show that tensile strain along the [100] direction enhances the absolute and relative intensities of visible luminescence by a factor of 7/3 at a temperature of 5 K. This effect is absent for a tensile strain along the [110] direction. We explain the phenomenon observed in view of the model of single-photon biexciton recombination for the system in which the bottom of the conduction band is formed by only two opposite electronic valleys.     

Interface roughness of GaAs/AlAs superlattices MBE-grown on vicinal surfaces

The interface morphology of GaAs/AlAs superlattices grown by molecular beam epitaxy on misoriented (001) GaAs substrates has been investigated using X-ray diffraction techniques in addition to high-resolution transmission electron microscopy (HRTEM). We observe that the width and intensity of the satellite peaks are very sensitive to the step-edge orientation. Among the investigated ones ([ 110], [100], [110]), it is the [ 10] step-edge direction which is the most favourable to a regular growth of superlattice structures. Structural models based on HRTEM observations (step distribution at interfaces and local fluctuation of layer thickness) have been constructed, allowing an explanation of the X-ray diagrams.