Spatiotemporal chaos control with pinning signals in distributed systems

We suggest a local pinning feedback control for stabilizing periodic pattern in spatially extended systems. Analytical and numerical investigations of this method for a system described by the one-dimensional complex Ginzburg-Landau equation are carried out. We found that it is possible to suppress spatiotemporal chaos by using a few pinning signals in the presence of a large gradient force. Our analytical predictions well coincide with numerical observations.

Domain wall resistance in perpendicular (Ga,Mn) As: Dependence on pinning

We have investigated the domain wall resistance for two types of domain walls in a (Ga,Mn)As Hall bar with perpendicular magnetization. A sizeable positive intrinsic DWR is inferred for domain walls that are pinned at an etching step, which is quite consistent with earlier observations. However, much lower intrinsic domain wall resistance is obtained when domain walls are formed by pinning lines in unetched material. This indicates that the spin transport across a domain wall is strongly influenced by the nature of the pinning.

Photoemission study of chemisorption and Fermi-level pinning at K/GaAs(100) interface with synchrotron radiation

The adsorption of K on the n-GaAs(I 0 0) surface was investigated by X-ray photoelectron spectroscopy (XPS) and synchrotron radiation photoemission spectroscopy (SR-PES). The Ga3d and As3d core level was measured for clean and K adsorbed GaAs(I 0 0) surface. The adsorption of K induced chemical reaction between K and As, and the K-As reactant formed when the K coverage theta > I ML. The chemical reaction between K and Ga did not occur, but Ga atoms were exchanged by K atoms. From the data of band bending, the Schottky barrier is 0.70 eV. The Fermi-level pinning was not caused by defect levels. The probable reason is that the dangling bonds of surface Ga atoms were filled by the outer-shell electrons of K atoms, forming a half-filled surface state. The Fermi-level pinning was caused by this half-filled surface state. (c) 2004 Elsevier B.V. All rights reserved.

Effect of InAs quantum dots on the Fermi level pinning of undoped-n(+) type GaAs surface studied by contactless electroreflectance

Self-assembled InAs quantum dots (QDs) have been fabricated by depositing 1.6, 1.8, 2.0 and 2.5 monolayer (ML) InAs on surfaces of the undoped-n(+) (UN+) type GaAs structure. Room temperature contactless electroreflectance (CER) was employed to study the built-in electric field and the surface Fermi level pinning of these QD-covered UN+ GaAs samples. The CER results show that 1.6 ML InAs QDs on GaAs do not modify the Fermi level, whereas for samples with more than 1.6 ML InAs coverage, the surface Fermi level is moved to the valence band maximum of GaAs by about 70 meV (which is independent of the InAs deposition thickness) compared to bare GaAs. It is concluded that the modification of InAs coverage on the Fermi level on the GaAs surface is due to the QDs, rather than to the wetting layer. (C) 2003 American Institute of Physics.

Fermi-Level Pinning at Metal/High-k Interface Influenced by Electron State Density of Metal Gate

The Fermi-level pinning (FLP) at the metal/high-k interface and its dependence on the electron state density of the metal gate are investigated. It is found that the FLP is largely determined by the distortion of the vacuum level of the metal which is quantitatively ruled by the electron state density of the metal. The physical origin of the vacuum level distortion of the metal is attributed to an image charge of the interface charge in the metal. Such results indicate that the effective work function of the metal/high-k stack is also governed by the electron state density of the metal.

Enhanced Plasticity of Zr-Based Bulk Metallic Glass Matrix Composite with Ductile Reinforcement

A composite material containing uniformly distributed micrometer-sized Nb particles in a Zr-based amorphous matrix was prepared by suction cast. The resulting material exhibits high fractured strength over 1550 MPa and enhanced plastic strain of about 29.7% before failure in uniaxial compression test at room temperature. Studies of the serrations on the stress-strain curves and the shear bands on the fractured samples reveal that the amplitude of the stress drop of each serration step corresponds to the extent of the propagation of a single shear band through the materials. The composite exhibits more serration steps and smaller amplitude of stress drop due to the pinning of shear band propagation by ductile Nb particles.

Dynamic phase-mapping of domain nucleation on MgO : LiNbO3 crystal by digital holographic interferometry

The quantitative phase-mapping of the domain nucleation in MgO:LiNbO3 crystals is presented by using the digital holographic interferometry. An unexpected peak phase at the beginning of the domain nucleation is observed and it is lowered as the spreading of the domain nucleus. The existence of the nucleus changes the moving speed of the domain wall by pinning it for 3s. Such in-situ quantitative analysis of the domain nucleation process is a key to optimizing domain structure fabrication.

Phase mapping of domain kinetics in lithium niobate by digital holographic interferometry

The phase mapping of domain kinetics under the uniform steady-state electric field is achieved and investigated in the LiNbO3 crystals by digital holographic interferometry. We obtained the sequences of reconstructed three-dimensional and two-dimensional wave-field phase distributions during the electric poling in the congruent and near stoichiometric LiNbO3 crystals. The phase mapping of individual domain nucleation and growth in the two crystals are obtained. It is found that both longitudinal and lateral domain growths are not linear during the electric poling. The phase mapping of domain wall motions in the two crystals is also obtained. Both the phase relaxation and the pinning-depinning mechanism are observed during the domain wall motion. The residual phase distribution is observed after the high-speed domain wall motion. The corresponding analyses and discussions are proposed to explain the phenomena.

Structure and magnetic properties of CoNiP nanowire arrays embedded in AAO template

Ternary CoNiP nanowire (NW) arrays have been synthesized by electrochemical deposition inside the nanochannels of anodic aluminum oxide (AAO) template. The CoNiP NWs deposited at room temperature present soft magnetic properties, with both parallel and perpendicular coercivities less than 500 Oe. In contrast, as the electrolyte temperature (T-elc) increases from 323 to 343 K, the NWs exhibit hard magnetic properties with coercivities in the range of 1000-2500 Oe. This dramatic increase in coercivities can be attributed to the domain wall pinning that is related to the formation of Ni and Co nanocrystallites and the increase of P content. The parallel coercivity (i.e. the applied field perpendicular to the membrane surface) maximum as high as 2500 Oe with squareness ratio up to 0.8 is achieved at the electrolyte temperature of 328 K. It has been demonstrated that the parallel coercivity of CoNiP NWs can be tuned in a wide range of 200-2500 Oe by controlling the electrolyte temperature, providing an easy way to control magnetic properties and thereby for their integration with magnetic-micro-electromechanical systems (MEMS). (C) 2008 Elsevier B.V. All rights reserved.

Electronic properties of sulfur passivated undoped-n(+) type GaAs surface studied by photoreflectance

Photoreflectance (PR) has been used to study surface electronic properties (electric field, Fermi level pinning, and density of surface states) of undoped-n(+) (UN+) GaAs treated in the solution of ammonium sulfide in isopropanol. Complex Fourier transformation (CFT) of PR spectra from passivated surface shows that the sulfur overlay on GaAs surface makes no contribution to Franz-Keldysh oscillations (FKOs). The barrier height measured by PR is derived from surface states directly, rather than the total barrier height, which includes the potentials derived from Ga-S and As-S dipole layers. Comparing with native oxidated surface, the passivation leads to 80 meV movement of surface Fermi level towards the conduction band minimum, and reduction by more than one order in density of surface states. (C) 2003 Elsevier Science B.V. All rights reserved.

Effects of annealing on properties of spin-valve pinned with FeMn alloy

The magnetic properties of spin-valve pinned by FeMn layer were investigated after it was annealed at different temperatures. Its property was dependent on the vacuum annealing temperature. The pinning field could be increased through annealing at a temporature lower than 200degreesC;the pinning field would reduce and other properties be deteriorated as the annealing temperature was higher than 200degreesC; the pinning effect lost and giantmagnetic resistance disappeared at 300degreesC. Based on the results of AES analysis it was concluded that the diffusion in spin-valve multilayer was along grain boundary.

Modulation spectroscopy of GaAs covered by InAs quantum dots

Contactless: electroreflectance has been employed at room temperature to study the Fermi level pinning at undoped-n(+) GaAs surfaces covered by 1.6 and 1.8 monolayer (ML) InAs quantum dots (QDs). It is shown that the 1.8 ML InAs QD moves the Fermi level at GaAs surface to the valence band maximum by about 70 meV compared to bare GaAs, whereas 1.6 ML InAs on GaAs does not modify the Fermi level, It is confirmed that the modification of the 1.8 ML InAs deposition on the Fermi level at GaAs surface is due to the QDs, which are surrounded by some oxidized InAs facets, rather than the wetting layer.

稀土过渡金属复合氧化物的制备结构，电学性质及气敏性研究

本文首次合成了Lar_xSr_xFe_yCor_yO_3(x、y:0.1、0.3、0.5、0.7、0.9)系列化合物和Lar_xBa_xFe_yCor_yO_3(x、y:0.1、0.3、0.5、0.7、0.9)系列化合物，并对其结构，电性及气敏性质进行了研究。关于ABO_3型稀土过渡金属复合氧化物的结构研究，文献上报道比较混乱，不同的人在进行结构研究中采用不同的结构基元得到了不同的晶型和相应的晶胞参数。本文根据上述化合物的X射线谱图，对其进行指标化，得到了上述两系列化合物为主方晶系结构，晶胞参数计算结果表明：在Y = 0.7时，化合物Lar_xSr_xFe_(0.7)Co_(0.3)O_3的晶胞参数随X值的增大而减小。化合物Lar_xBa_xFe_(0.7)Co_(0.3)O_3的晶胞参数随X值的增大而增大。在X = 0.3时，上述两条系列化合物的晶胞参数均随Y值的增大而增大。对以上两系列化合物所表现出的结构变化规律，我们用起决定作用的离子半径大小进行了解释。针对上述两系列化合物，我们研究了它们的电学性质，研究结果表明，上述两系列化合物，在Y = 0.7时，其室温电阻率均随X在 0 < x < 0.5内增大而减小。在0.5 < x < 1内随X值增大而增大。在X = 0.5时的两个化合物具有最小的室温电阻率。在此方面，其电阻率变化规律与LarxMxBO_3(M:Ca、 Sr、 Ba、 B:Fe Co)化合物的变化规律相似。在X = 0.3时，上述两系列化合物的室温电阻率均随Y值的增大而增大，上述两系列化合物所表现出的室温电阻率变化规律可以运用C. Zener的双交换模型加以解释，同时，低温电阻率测定表明：上述两系列化合物在温度100-263K内，表现半导体性质。液氮温度下它们不具有超导性。除以上研究之外，我们针对Lar_xSr_xFe_yCor_yO_3 (X = 0.3、 Y:0.1、0.5、 0.9, Y = 0.7, X:0.1、 0.9）系列化合物初步地进行了气敏性研究。结果为：化合物La_(0.7)Sr_(0.3)Fe_yCor_yO_3 (Y:0.1、 0.5、 0.9)都不同程度地对乙醇、石油醚、 乙炔、烟具有气敏性，它们对乙醇的气敏响应时间约为1分钟，而对石油醚、乙炔和烟的气敏响应时间要用5分钟左右，在上述化合物中，La_(0.7)Sr_(0.3)Fe_(0.5)Co_(0.5)O_3化合物表现出最强的对乙醇、石油醚、乙炔的气敏性。对化合物La_(0.7)Sr_(0.3)Fe_(0.5)Co_(0.5)O_3的进一步研究表明，在乙醇气氛下，化合物La_(0.7)Sr_(0.3)Fe_(0.5)Co_(0.5)O_3在工作电流I_(Dn) = 0.20A时具有最佳的气敏数应。工作电流高于或低于此值都将导致其气敏效应的大小顺序为La_(0.7)Sr_(0.3)Fe_(0.5)Co_(0.5)O_3 > La_(0.7)Sr_(0.3)Fe_(0.9)Co_(0.1)O_3 > La_(0.7)Sr_(0.3)Fe_(0.1)Co_(0.9)O_3对化合物Lar_xSr_xFe_(0.7)Co_(0.3)O_3 (X:0.1、 0.9)的气敏性研究表明：它们只对乙醇和烟具有气敏性。对上述两种气氛的气敏响应时间为5分钟。上述两种化合物中，La_(0.1)Sr_(0.9)Fe_(0.7)Co_(0.3)O_3气敏效应最强。

Growth of high-quality relaxed In0.3Ga0.7As/GaAs superlattices

With a low strained InxGa1-xAs/GaAs(x similar to 0.01) superlattice (SL) buffer layer, the crystal quality of 50 period relaxed In0.3Ga0.7As/GaAs strained SLs has been greatly improved and over 13 satellite peaks are observed from X-ray double-crystal diffraction, compared with three peaks in the sample without the buffer layer. Cross-section transmission electron microscopy reveals that the dislocations due to superlattice strain relaxation are blocked by the SLs itself and are buried into the buffer layer. The role of the SL buffer layer lies in that the number of the dislocations is reduced in two ways: (1) the island formation is avoided and (2) the initial nucleation of the threading dislocations is retarded by the high-quality growth of the SL buffer layer. When the dislocation pinning becomes weak as a result of the reduced dislocation density, the SLs can effectively move the threading dislocations to the edge of the wafer.