Phonon dispersion curves of transition metals using modified general tensor force model

The general tensor force model has been modified by incorporating separately the electron-ion interactions. The model satisfies the translational symmetry requirements of the lattice and is used to obtain the phonon dispersion curves of chromium, molybdenum and tungsten. The agreement between the theoretical and experimental frequencies is very good.     

Plasmon dispersion in simple metals

We investigate up to which value of the momentum transfer q a quadratic plasmon dispersion can be expected to be valid. We find that so far all quadratic fits rely mainly on experimental data on the dispersion curve beyond the regime of the validity of the quadratic dispersion and thus render the reported values of the dispersion constant α as very doubtful in the discussion of exchange and correlation effects. A new evaluation of α, which, from the existing measurements, is only possible in a few cases, yields considerably smaller α-values.     

Phonon dispersion relation of liquid metals

The phonon dispersion curves of some liquid metals, viz. Na (Z = 1), Mg (Z = 2), Al (Z = 3) and Pb (Z = 4), have been computed using our model potential. The charged hard sphere (CHS) reference system is applied to describe the structural information. Our model potential along with CHS reference system is capable of explaining the phonon dispersion relation for monovalent, divalent, trivalent and tetravalent liquid metals.     

APW dispersion relation for plasmon in metals

Following Ichikawa's technique we derived a dispersion relation for plasmons in metals using APW (Augmented Plane Wave) wave functions. The formula contained herein may be used to acquire information concerning the filling of the energy bands and so data needed in explaining electrical and magnetic properties of metals.     

Phonon dispersion curves of VI B group metals

The phonon dispersion curves of chromium, molybdenum and tungsten have been computed along the principal symmetry directions using an angular force model with volume forces. The results obtained are in very good agreement with the experimental observations.The author is grateful to Dr. V. Ramamurthy of I.I.T. Delhi for many valuable and stimulating discussions.     

Classical theory of spin-wave dispersion for ferromagnetic metals

The properties of the four spin-wave dispersion branches for a planar ferromagnetic metal with TEM microwave excitation at normal incidence have been examined to derive physical insight into (a) their dependence on material parameters and orientation, (b) the interaction between branches, and (c) the polarization character associated with the related ecxitations. The Larmor electromagnetic and spin-wave branches are found to exhibit a peculiar crossover effect at a critical damping value ( 0·014 for permalloy). The polarizations vary from circular for the static field normal to the surface to elliptical for an in-plane static field. For the in-plane case, the major polarization axes are parallel and perpendicular to the surface for the Larmor and antilarmor branches, respectively. The well known Ament-Rado and Vittoria formulations have also been modified to include the effect of exchange in the damping term of the Landau-Liftshitz equation. The secular determinant is simplified considerably and the form of the dispersion equations is changed significantly. The only large effect on the branches themselves is to increase the attenuating component of the propagation parameterk for large ¦k¦.     

Basic Studies of Electrohydrodynamic Atomization Process using phase Doppler measurement technique

A planar phase Doppler system is used to measure submicron droplets generated by an electrospray. Measured drop dia-meters are correlated with the liquid properties and the condition for transition of the spray from the single-jet mode to the multi-jet mode is introduced. In another set of measurements using a standard phase Doppler system, combined size and velocity data are employed to deduce the drag force on the drops. In a situation where the drag force is balanced primarily by the electric force, the phase Doppler measurements allow to estimate the power-law relationship between the charge on a drop and its diameter and hence, many provide insights into the underlying atomization mechanisms.     

Data preparation and fabrication of DOE using electron-beam lithography

The application of electron-beam lithography to the generation of diffractive optical elements topology is examined. The formula for the estimation of exposure data volume for variable-shaped electron-beam lithography is presented as a function of diffractive optical element parameters and approximation accuracy. A special software dedicated to preparing exposure data for fabrication of diffractive optical elements is developed. Diffractive optical elements with an artificial refractive index are manufactured with a feature size much less than the wavelength. Design and experimental results on photomasks fabrication for an optical element focusing radiation into a ring with pregiven parameters are presented. The photomask set is manufactured for a reflecting optical element focusing the high power CO₂ laser beam into two points with required parameters for laser welding.     

Phonon dispersion curves of V B group of metals

The phonon frequencies of vanadium, niobium and tantalum along the principal symmetry directions are computed using an angular force model. The calculated dispersion curves are in very good agreement with the experimental results.The author is grateful to Dr. V. Ramamurthy and Dr. S. B. Rajendraprasad of IIT Delhi for many valuable and stimulating discussions.     

Laser-ultrasonic surface wave dispersion measurements on surface-treated metals

Surface acoustic wave (SAW) velocity spectroscopy has been long considered to be one of the leading candidates for nondestructive characterization of surface-treated metals because of its ability to probe the material properties at different penetration depths depending on the inspection frequency. We developed a high-precision laser-ultrasonic technique to study the feasibility of SAW dispersion spectroscopy for residual stress assessment on shot-peened metals. This technique is capable of measuring SAW dispersion with a relative error of 0.1% over a frequency range from 2 to 15 MHz. Our experimental results obtained from shot-peened aluminum 2024-T351 samples indicate that the dispersion of the surface wave is a superposition of different effects of surface treatment in the material, including surface roughness, compressive residual stress, and cold work. Although the surface roughness induced component is often the dominating part of the overall dispersion, the experimental results also indicate that it is feasible to observe a perceivable change in the dispersion of the SAW when the specimen is heat-treated at different temperatures, which has no perceivable effect on the surface roughness. The part of the dispersion, which changes during annealing via thermal relaxation, is due to near-surface residual stresses and the decay of texture, although at high frequencies nonuniform grain coarsening could also play a significant role.     

Thermoelectric temperature measurements in laser pulsed heating of metals

Measurements of temperature pulses following focused laser irradiation on metals were performed with a specially designed thermocouple. This detector had a hot junction of an average of 5 μ in size and a rise time of less than 1 μsec. Experimental results are compared to thermal-model predictions calculated numerically. Thermal responses were also measured for laser intensities above the damage threshold of the material, in close vicinity of the damaged area. This demonstrates possible applications of the experimental technique to the investigation of damage mechanisms.     

电液动力微泵的改进

介绍了微型电液动力泵的优化设计和工艺改进。电液动力微泵制作工艺的改进包括:材料的选择,微电极的优化设计和封装工艺的改进。使用聚二甲基硅氧烷(PDMS)作为构建微流道的材料,采用浇注法制作了PDMS微流道,并采用阳极键合方式进行微泵的封装。使用无水乙醇为工作流体对微泵进行流动实验,在驱动电压为90 V时,电液动力微泵驱动流体的最大流速可以达到92 uL/min。     

Phonon dispersion for the bcc metals Mo and Cr

In this paper the phonon dispersion for the bcc metals Mo and Cr is calculated based on the pair potentials obtained from cohesive energies and the Slater-Kirkwood- type three body interaction. In the calculation of the pair potentials the Möbius transform in the number theory is used and the cohesive energy is evaluated by the LMTO method. The results show a good agreement with inelastic neutron scattering data and indicate that the three-body interaction is necessary to account for the phonon dispersion.     

Electrohydrodynamic flow analysis in a circular cylindrical conduit using Least Square Method

In this article, Electrohydrodynamic flow (EHD flow) in a circular cylindrical conduit is studied by a semi-exact and high efficient weighted residual method called Least Square Method (LSM). A principle of LSM is briefly introduced and later is employed to solve the described problem. Furthermore, the effects of the Hartmann electric number (Ha) and the strength of nonlinearity (α) on velocity profiles are discussed and presented graphically. Results are compared with numerical solution and obtained residuals are compared with those of HAM which previously were done by Mastroberardino in Ref. [3]. Outcomes reveal that LSM has an excellent agreement with numerical solution; also depicted residual functions showed that LSM is more acceptable than HAM especially for large values of Ha and α numbers, also it is simpler and needs fewer computations.     

Electrohydrodynamic micropatterning of silver ink using near-field electrohydrodynamic jet printing with tilted-outlet nozzle

This paper introduces for the first time near-field electrohydrodynamic jet printing with tilted-outlet nozzle to obtain the fine and highly conductive patterns of silver (Ag) ink. Line widths produced by near-field electrohydrodynamic jet printing are less than 6 μm, which is approximately twenty times smaller than that of inkjet printing. Under optimized Ag ink annealing ranges 3–9 min for 30 wt% at 150°C, we observed Ag line pattern resistivities as low as 7×10⁻⁶ Ω⋅cm. Ag ink conduction mechanisms were brought to light from microstructure analysis and post-thermal-annealing examination of electrical characteristics.     

Investigation of the influence on graphene by using electron-beam and photo-lithography

The changes in Raman spectra of graphene flakes after lithography processing are systematically investigated. It is found that substantial changes in the intensity of several Raman peaks are observed after lithography processes involving electron-sensitive and photon-sensitive resists. This finding is related to the generation of disorder and introduction of impurities in the graphene flakes. It is observed that the disorder induced after spin coating PMMA resist on the graphene flakes cannot be removed by acetone but can be eliminated by means of an annealing process. The use of the AZ6624 photo-sensitive resist produces Raman changes typical for amorphization. When using this resist, the disorder-induced changes in the Raman spectra persist even after the same annealing process, implying that the contamination caused by the used photo-sensitive resist is more difficult to eliminate. The present results emphasize the important role played by the lithography process, often taken for granted, in the physical properties of graphene.     

基于Kramers-Kronig关系建立金属太赫兹色散模型

提出了一种基于测量反射率谱、使用Kramers-Kronig(KK)关系建立金属太赫兹色散模型的方法.结合合金铝和合金铜4—40 THz的测量反射率谱,通过反射系数振幅和相位的KK关系,采用高频端指数外推,低频端常数外推的方法,反演金属复折射率.以KK反演的复折射率作为实验值,以拟合复折射率和实验值误差最小为准则,使用遗传优化算法,拟合了合金铝和合金铜的Drude色散参数(等离子频率和碰撞频率).基于优化的Drude模型计算了0.1—40 THz材料的复折射率,与椭偏仪的实测结果符合,验证了模型的准确性.该方法理论与实验相互验证,以测量的复折射率作为实验定标,将远红外频段的色散信息拓展到太赫兹频域,确定了太赫兹频段金属的微观物理参数,提供了太赫兹频段色散和散射机理的研究依据.     

Band structure effects on the plasmon dispersion in simple metals

The real part of the effective dielectric function is derived analytically in the pseudopotential approximation. For anyk-direction, the theory allows the evaluation of the plasmon dispersion, _p (k), which is found to be anisotropic in general due to band structure effects. Application of the theory to Al yields an isotropic shift atk=0 of _p (0) _v – 0.3 eV and explains the recently observed anisotropic behaviour of the dispersion very well fork < 0.6k _F .