Surface Review and Letters

This paper discusses the results obtained with a long pulse laser (such as a CO₂ laser) assisted shaping of microspherical lenses at the end face of a specialty image fiber. The 600-μm-diameter image fiber consists of 15 000 pixels (individual fibers) with a spatial resolution of 267/mm. When laser-assisted heating is induced at the surface of the fiber tip, it tends to become spherical in shape due to surface tension. The curvature formed at the surface will act as the microspherical lens. The effects of the laser repetition rate and irradiation time on the surface finish and curvature of the shaped lens are illustrated in this paper.

The p-silicon surfaces have been irradiated with ~ 100 MeV Si⁷⁺ions to a fluence of 2.2×10¹³ ions cm^-2, and surface morphology has been studied with atomic force microscopy (AFM). Interesting features of cracks of ~ 47 nm in depth and ~ 103 nm in width on the irradiated surfaces have been observed. The observed features seemed to have been caused by the irradiation-induced stress in the irradiated regions of the target surface.

Dispersion relations for two-component and three-component periodic optical semiconductor superlattices are derived. A systematic study of the interaction of bulk and surface plasmons with optical phonons is made in these superlattices to find out the factors which can influence the coupling between the two modes of vibration. Coupling between the plasmons and optical phonons in the bulk medium and surface of the two semi-infinite mediums gives rise to four modes (two symmetric and two antisymmetric) for the bulk mode and two for the mixed mode. The detailed calculation is presented for various types of multicomponent semiconductor superlattice structures.

In a recent work we have proposed a quantum-mechanical approach to explaining our resistivity experimental results for platinum and gold thin films. Good agreement was found between theory and experiment. In that work only the main features of our calculations were pointed out. In the present work the quantum approach calculations are shown in detail and the predictions are compared with our experimental data.

TiC/TiN-reinforced composite coatings were fabricated on the substrate of Ti–6Al–4V alloy using laser remelting. X-ray diffraction (XRD) was used to identify the phases in the laser-clad composite coating; the interface characterization of the dilution zone-clad zone (IDC) and the dilution zone-heat-affected zone (IDH) was observed with a scanning electron microscope (SEM). The results show that the microstructure of a cross-section has stratification characterization, and consists of the clad zone (CZ), the dilution zone (DZ), the diffusion layer (DL) and the heat-affected zone (HAZ). The layer-by-layer microstructure results from the boundary layer phenomenon of viscous melt-fluid and diffusion. The kind of reinforced particle has an effect on the interface morphology, microstructure and flow characterization of the melt-fluid. The phase constitution in the clad zone consists of (Cr–Ni–Fe), TiC, Ni₄B₃, Ti₂Ni, Cr₂B and M₂₃C₆ for TiC+NiCrBSi coating, and (Cr–Ni–Fe), TiN, NiB, Cr₂Ti and Ti₂Ni for TiN+NiCrBSi coating. The interfaces of the IDC in the NiCrBSi-clad layer is clear and clean; those of TiC+NiCrBSi and TiN+NiCrBSi are illegible. Ti–Ni phases with acicular microstructure link dilution zone and clad zone, and two kinds of phase with acicular microstructure, are similar in composition and shape.

Within the framework of the effective mass approximation, we have theoretically investigated the linear intersubband optical absorption in a quantum well under external electric and intense laser field. Results obtained show that intersubband optical transition and energy levels in quantum wells can significantly be modified and controlled by the electric field and intense laser field. Generally there is a distinct feature for the case of the intersubband absorption compared with intersubband optical absorption in a quantum well with an applied electric field.

Interference ring marks were observed on a copper substrate consisting of plated layers of Au, Pd and Ni after laser ablation of epoxy material from the top surface. These ring marks are the result of laser-induced surface oxidation and need to be avoided or minimized in order to improve the solder wettability on the treated surface. Studies of laser-induced thermal diffusion through the plated layers were carried out using a 532 nm Q-switch Nd:YAG laser. The major process variables investigated were the beam profile, pulse repetition rate and beam scan pattern. Secondary ion mass spectroscopy (SIMS) was used to obtain a depth profile of the laser-treated layers. It revealed that interfusion of Pd and Ni by diffusion occurred during laser irradiation. Calculations of thermal diffusion length and temperature rise of the metal layers without considering the accumulated thermal effect of overlapping pulses are presented in this article. The study results are useful for a better understanding of the process of laser removal of epoxy flashes on leadframe heatsink surfaces.

Two approximate expressions used to compute the interaction energy between two similar plane parallel double layers are derived by expanding the interaction energy in the power series of at low dimensionless surface potential y₀ or the power series of at high dimensionless surface potential y₀, respectively. Two series converge very fast. In the range of dimensionless surface potential of colloid particles y₀ from 1.00000×10^-1 to 3.00000×10, when C<-4.30000, the high potential expression is usable; when C≥-4.30000, the low potential expression is usable. The required series terms will not exceed four to obtain the interaction energy with six significant figures if a low potential expression and a high potential expression are combined.

The influence of extended flat interface boundaries on the scattering and localization of spin waves in disordered quasi-two-dimensional Heisenberg ferromagnets is studied. The two ferromagnets are considered as two dissimilar semi-infinite slabs in contact, joined together at an extended flat interface between two adjacent planes. The mathematical framework of the matching method is used to analyze both the localization and the scattering phenomena on the extended flat interface boundaries in the harmonic approximation with nearest neighbor magnetic exchange interactions. The energy of spin-wave-localized modes arising from the absence of magnetic translation symmetry in the direction normal to the interface boundaries is determined. The transmission and reflection probabilities, as well as the average transmittance of magnetic excitations across the interface, are calculated in full accordance with the Landauer–Büttiker description of electron transport, and numerical results are presented for the most representative sets of system parameters in a large range of scattering energies. Results show that there are several localized modes, which may be either optical or acoustical modes (depending on the system parameters), and the scattering properties of the system are a strong function of scattering energy and model parameters, which are assumed to be different at the interface compared with those of the bulk.

One type of combined magnetically modulated nanostructures is proposed that can be experimentally realized by depositing two hybrid ferromagnetic stripes on the surface of a semiconductor heterostructure. Since these two stripes induce different magnetic barriers, the electron transmission and the conductance of nanostructure are strongly dependent upon the electronic spins. Thus, in this kind of hybrid magnetic nanostructures, electrons show up a considerable spin polarization effect, which provides an alternative approach to realization of spin-polarized electrons into semiconductors and may be of practical importance for spin-based nanodevice applications.

The growth kinetics of the solid solution phase of aluminum in copper in diffusion couples of pure aluminum and copper has been investigated at 425°C using a scanning electron microscope. In the initial stage, the phase layer growth was found to obey the parabolic law, indicating that the rate-controlling process is diffusion. At longer times, the growth rate deviates from the kt^-1/2 behavior of the early stage.

Phase demixing is evaluated as a possible explanation for the anomalous temperature dependence of the Pt segregation at the Pt₅₀Rh₅₀(511), Pt₂₅Rh₇₅(110) and Pt₂₅Rh₇₅(100) surfaces. Calculations are performed in the quasichemical approximation and a broken bond scheme. Although the calculations based on systematic demixing tend to overestimate the surface enrichment, the qualitative agreement appears to be rather good.