D.C.隶属函数模糊集及其应用(Ⅱ)--D.C.隶属函数模糊集的万能逼近性

本文是D．C．隶属函数模糊集及其应用系列研究的第二部分。指出在实际问题中普遍选用的三角形、半三角形、梯形、半梯形、高斯型、柯西型、S形、Z形、π形隶属函数模糊集等均为D．C．隶属函数模糊集，建立了D．C．隶属函数模糊集对模糊集的万有逼近性。探讨了D．C．隶属函数模糊集与模糊数之间的关系，给出了用D．C．隶属函数模糊集逼近模糊数的e-Cellina逼近形式，得到模糊数与D．C．函数之间的一个对应算子，指出了用模糊数表示D．C．函数的问题。     

Microstructure and wear properties of laser clad Cuss/Cr5Si3 metal silicide composite coatings

Wear resistant Cu-based solid solution (Cu_ss) toughened Cr₅Si₃ metal silicide composite coatings were fabricated on austenitic stainless steel AISI321 by laser cladding process. Due to the rapidly solidified microstructural characteristics and the excellent toughening effect of Cu_ss on Cr₅Si₃, the Cu_ss/Cr₅Si₃ coatings have outstanding wear resistance and low coefficient of friction under room temperature dry sliding wear test conditions coupling with hardened 0.45% C steel.     

Preparation of Fe–Si–B–Nb amorphous powder cores with excellent high-frequency magnetic properties

FeSiBNb amorphous powder cores were prepared with the amorphous powder by gas atomization and subsequent hot pressing of resulting powder after creating oxide layers on the amorphous powder. Fully amorphous FeSiBNb powders with good soft magnetic properties were successfully obtained in the particle size range below 100 μm. FeSiBNb amorphous powder cores exhibit stable permeability up to 10 MHz, showing excellent high-frequency characteristics.     

Magnetic properties of HITPERM-type alloys at high temperature

(Fe,Co)–Zr,Hf)–Cu–B (HITPERM-type) alloys with variable Hf, Zr and Co content were isothermally crystallised at 500–650 °C for 1 h, and the optimum nanocrystallisation temperature was selected on the basis of the minimum coercive field at room temperature. The quasistatic hysteresis loops were measured at temperature from 20 to 650 °C. Subsequently, the optimally annealed alloys were subjected to long-term annealing at 500, 550 and 600 °C. Working temperature of 600°C is too high for the investigated alloys to maintain stable magnetic properties. Temperature of 550 or 500 °C permits the material to be magnetically stable for a long period. The magnetic hysteresis loops recorded for the nanocrystalline alloys, where Fe:Co ratio is close to 1 and refractory metals content is 7 at.%, prove that coercive field increases slightly with temperature, but remains in the range of 20–40 A/m (depending on the alloy composition) from 20 to 550 °C. This proves that the investigated alloys, after optimisation of chemical composition, may be suitable for high temperature use.     

Equilibrium and kinetic surface segregation in binary alloy thin films

A general theoretical analysis of the effect of film thickness on equilibrium and kinetic surface segregation in binary alloy thin films is presented. In this analysis, a constrained condition that represents the finite size of thin film system has been introduced to the modified Darken model, which has been used to describe both equilibrium and kinetic surface segregation in bulk materials. Simulation of surface segregation for alloy thin films can be carried out for all composition ranges and all film thicknesses if only knowing the surface segregation parameters for bulk materials. Simulations of equilibrium and kinetic surface segregation in Cu(1 1 1)Ag binary alloy thin film are presented.     

Infrared reflection absorption study of carbon monoxide adsorption on Pd/Cu(1 1 1)

Pd-Cu bimetallic surfaces formed through a vacuum-deposition of Pd on Cu(1 1 1) have been discussed on the basis of carbon monoxide (CO) adsorption: CO is used as a surface probe and infrared reflection absorption (IRRAS) spectra are recorded for the CO-adsorbed surfaces. Low energy electron diffraction (LEED) patterns for the bimetallic surfaces reveal six-fold symmetry even after the deposition of 0.6 nm. The lattice spacings estimated by the separations of reflection high-energy electron diffraction (RHEED) streaks increase with increasing Pd thickness. Room-temperature CO exposures to the bimetallic surfaces formed by the Pd depositions less than 0.3 nm thickness generate the IRRAS bands due to the three-fold-hollow-, bridge- and linear-bonded CO to Pd atoms. In particular, on the 0.1 nm-thick Pd surface, the linear-bonded CO band becomes apparent at an earlier stage of the exposure. In contrast, the bridge-bonded CO band dominates the IRRAS spectra for CO adsorption on the 0.6 nm-thick Pd surface, at which the lattice spacing corresponds to that of Pd(1 1 1). A 90 K-CO exposure to the 0.1 nm-thick Pd surface leads to the IRRAS bands caused not only by CO-Pd but also by CO-Cu, while the Cu-related band is almost absent from the spectra for the 0.3 nm-thick Pd surface. The results clearly reveal that local atomic structures of the outermost bimetallic surface can be discussed by the IRRAS spectra for the probe molecule.     

Study of the order–disorder transition and martensitic transformation in a Cu–Al–Be alloy by EELS

Changes in 3d states occupancy associated with order–disorder transition and martensitic transformation in a Cu–Al–Be alloy was investigated by electron energy loss spectroscopy (EELS) in both high energy and low energy loss regions. From the high energy loss region, the Cu L_2,3 white-line intensities, which reflect the unoccupied density of states in 3d bands, was measured for three states of the alloy: disordered austenite, ordered austenite and martensite. It was found that the white-line intensity remains the same during order–disorder transition but appears slightly smaller in martensite, indicating that some electrons left Cu 3d bands or some hybridization took place during phase transformation. From the low energy loss region, the optical joint density of states (OJDS) was obtained by Kramers–Kronig analysis. As maxima observed in the OJDS spectra are assigned to interband transitions, these spectra can be used to probe changes in the electronic band structure. The analysis shows that during the martensitic transformation, the peaks positions and relative intensities in the OJDS spectra undergoes noticeable changes, which are associated with interband transitions.     

Enhanced hardness in B-doped ZnO thin films on fused quartz substrates by pulsed-laser deposition

B-doped ZnO thin films have been fabricated on fused quartz substrates using boron-ZnO mosaic target by pulsed-laser deposition technique, and the mechanical properties have been studied by nanoindentation continuous stiffness measurement technique and transmission electron microscope (TEM). Nanoindentation measurement revealed that the hardness of B-doped ZnO films, 9.32 ± 0.90 to 12.10 ± 1.00 GPa, is much greater than that of undoped ZnO films and very close to that of traditional semiconductor Si. The mean transmittance (%) is larger than 81% in the visible range (380-780 nm) for all the films, and the Hall effect measurement showed that the carrier density is around 2 × 10²⁰ cm⁻³ and the resistivity lower than 3 × 10⁻³ Ω cm. TEM characteristics show undoped thin films have more amorphous area between grains while the B-doped ZnO films have thin grain boundaries. We suggest that the grain boundaries act as the strain compensation sites and the decrease in thickness of grain boundaries enhances the hardness of the B-doped ZnO films.     

Design and Fabrication of 1.06 μm Resonant-Cavity Enhanced Reflective Modulator with GaInAs/GaAs Quantum Wells

A resonant-cavity enhanced reflective optical modulator is designed and fabricated, with three groups of three highly strained InGaAs/GaAs quantum wells in the cavity, for low voltage and high contrast ratio operation. The quantum wells are positioned in antinodes of the optical standing wave. The modulator is grown in a single growth step in an molecular beam epitaxy system, using GaAs/AlAs distributed Bragg reflectors as both the top and bottom mirrors. Results show that the reflection device has a modulation extinction of 3 dB at -4.5 V bias.     

Theoretical estimates for proton-NMR spin–lattice relaxation rates of heterometallic spin rings

Heterometallic molecular chromium wheels are fascinating new magnetic materials. We reexamine the available experimental susceptibility data on MCr₇ wheels in terms of a simple isotropic Heisenberg Hamiltonian for M=Fe, Ni, Cu, and Zn and find in that FeCr₇ needs to be described with an iron–chromium exchange that is different from all other cases. In a second step we model the behavior of the proton spin lattice relaxation rate as a function of applied magnetic field for low temperatures as it is measured in nuclear magnetic resonance (NMR) experiments. It appears that CuCr₇ and NiCr₇ show an unexpectedly reduced relaxation rate at certain level crossings.