ALBERT

Notes: This article addresses the effect of topographic structure of surface roughness on the flow of a thin film over a rotating disk. Six factors, namely centrifugation, surface tension, viscosity, air-shear, disjoining pressure, and surface roughness, that affect the depletion of the film are considered. Depletion histories of a thin film are given for cases involving deterministic as well as stochastic descriptions of surface roughness. It has been found that surface roughness of the disk plays a significant role in thin-film flow, and different topographic structures of the surface roughness lead to different asymptotic limits of liquid retention. The interplay of topographic parameters such as the height, skewness, and frequency of surface asperities on lubricant retention is also investigated.

Notes: A simple, practical method is described to extract the carrier concentration and mobility of each component of a multicarrier semiconductor system (which may be either a homogeneous or multilayered structure) from variable magnetic field measurements. Advantages of the present method are mainly due to the inclusion of both the longitudinal and transverse components of the conductivity tensor and normalization of these quantities with respect to the zero-field longitudinal component of the conductivity tensor. This method also provides a simple, direct criterion by which one can easily determine whether the material under test is associated with a one-carrier or multicarrier conduction. The method is demonstrated for a simple one-carrier system [GaAs single-channel high-electron-mobility-transistor (HEMT) structure] and two multicarrier systems (an InGaAs-GaAs double-channel HEMT structure and two types of carriers present in an InGaAs single-channel HEMT structure). The analysis of the experimental data obtained on these samples demonstrates the utility of the method presented here for extracting carrier concentrations and mobilities in advanced semiconductor structures.

Notes: Recognizing the potential importance of diamond thin film growth from combustion environments, a computational investigation of diamond synthesis in low pressure premixed flames has been conducted. The model employed solves the two-dimensional continuity, momentum, global energy, and species conservation equations in stagnation point flow geometry, and accounts for gas phase and surface reaction kinetics. The heterogeneous mechanism employed to describe diamond growth assumes that the methyl radical is the primary growth precursor. The gas phase mechanism includes elementary reaction pathways which generate methyl radicals from acetylene and in addition, includes a mechanism for cyclization (the formation of benzene) via acetylene and ethylene precursors. In this way, the pathway towards soot formation, which is believed to be a consequence of the formation of fused polycyclic aromatics, is shown to be a possible explanation for an eventual decrease in diamond growth rates at increasing fuel to oxygen flow ratios. A competition between oxidative pyrolysis of post flame hydrocarbons and cyclization establishes a criterion for optimum growth conditions.

Notes: The depletion of thin liquid films due to the combined effect of centrifugation, surface roughness, and air shear has recently been studied.While surface roughness of a rotating solid disk can be represented by deterministic curves, it has been argued that spatial random processes provide a more realistic description. Chiefly because of surface roughness, there is an asymptotic limit of retention of a thin film flowing on the rotating disk. The aim of this article is twofold. First, the effect of disjoining pressure on the retention of a thin film is investigated. It is found that incorporating disjoining pressure term has small but still appreciable effect on the asymptotic limits of lubricant retention. For a partially wetting lubricant, the two components of the disjoining pressure function tend to have opposite influence on the lubricant retention; one enhances the retention, while the other diminishes it. Second, the robustness of stochastic description of surface roughness is examined. For a given mean and variance, it is noted that different probability distributions of the surface fluctuations lead, in the absence of air shear, to significantly different asymptotic limits of thin-film retention. If air shear is incorporated, this sensitivity is substantially attenuated.

Notes: Photoreflectance (PR) spectroscopy, x-ray diffraction (XRD) method, and secondary ion mass spectroscopy (SIMS) were used to observe the radial distribution of the band-edge transition and modification of the band structure due to the variation of indium in 3 in. indium-alloyed semi-insulating GaAs (InxGa1−xAs) grown by the liquid-encapsulated Czochralski method. The data from room temperature PR measurements showed the variation of the transition energy with positions indicating the radial distribution of the indium content across the wafers; indium content being higher around the edge region than the central area. The splitting of the degenerate valence band around the edge region of the wafers was also shown in PR data due to the different indium content in adjacent regions where indium content varies rapidly. The XRD measurements showed the drastic change in the distribution of lattice constant on where the splitting of the heavy and light holes happened and the SIMS analysis was adopted to confirm the distribution of indium content across the wafer. The possible model was proposed from the experimental data. © 2000 American Institute of Physics.

Notes: We present contact-angle hysteresis and surface energy of differently treated indium–tin–oxide (ITO) thin films obtained from contact angles for liquids with different polar character. We find that the hysteresis and the polar and dispersion component of the surface energy depend strongly on the surface treatments. Oxygen-plasma treatments induce the highest polarity and the highest total surface energy, and we suggest that this improves the interface formation with polymers, and therefore, the performance of light-emitting diodes. We discuss the results in relation to the ITO surface roughness and chemical heterogeneity modified by the different treatments. © 1999 American Institute of Physics.

Notes: A new procedure for calculating the nonlinear energy transfer and linear growth/damping rate of fully developed turbulence is derived. It avoids the unphysically large damping rates typically obtained using the predecessor method of Ritz [Ch. P. Ritz, E. J. Powers, and R. D. Bengtson, Phys. Fluids B 1, 153 (1989)]. It enforces stationarity of the turbulence to reduce the effects of noise and fluctuations not described by the basic governing equation, and includes the fourth-order moment to avoid the closure approximation. The new procedure has been implemented and tested on simulated, fully developed two-dimensional (2-D) turbulence data from a 2-D trapped-particle fluid code, and has been shown to give excellent reconstructions of the input growth rate and nonlinear coupling coefficients with good noise rejection. However, in the experimentally important case where only a one-dimensional (1-D) averaged representation of the underlying 2-D turbulence is available, this technique does not, in general, give acceptable results. A new 1-D algorithm has thus been developed for analysis of 1-D measurements of intrinsically 2-D turbulence. This new 1-D algorithm includes the nonresonant wave numbers in calculating the bispectra, and generally gives useful results when the width of the radial wave number spectrum is comparable to or less than that of the poloidal spectrum. © 1996 American Institute of Physics.

Notes: A matrix formalism for the Hall effect is presented for an arbitrary J-fold multicarrier semiconductor system. Explicit formulas are derived for important transport quantities such as the sheet resistance, the Hall coefficient, and the Hall scattering factor. For J≤3, these formulas reduce to simple closed-form expressions as a function of the applied magnetic field and the carrier densities and mobilities. The closed-form formulas are useful for the correct interpretation of the Hall effect in multicarrier semiconductor systems. The field dependence and asymptotic behavior of these formulas are also discussed.

Notes: A conventional zero-dimensional (uniform plasma parameters with no spatial variations) fluid model will provide a good match with an experimental electron cyclotron resonance ion source (ECRIS) charge-state distribution (CSD) if provided with a judicious set of user inputs. However, this arbitrarily chosen set of inputs is not necessarily unique. To be truly predictive, an ECRIS model should rely on experimental parameters as inputs. A multi-species model for an ECRIS plasma using experimental parameters as inputs is under development. The model eliminates electron temperature as a user input by employing a 2 V(v,θ) Fokker–Planck code with an ECR heating term to calculate the non-Maxwellian anisotropic electron distribution function. Further arbitrary user inputs are eliminated in favor of controlled parameters by bounce averaging the Fokker–Planck coefficients for a one-dimensional (1D)/2 V axial model. The neutral gas modeling has been extended to 1D using axially coupled particle balance equations. The improved model is able to reproduce experimental Faraday cup (CSDA) from the Argonne National Laboratory's ECR-II. Further elimination of arbitrary inputs is expected when the ion model is extended to 1D. © 2000 American Institute of Physics.

Notes: The injection of Ar into the region of the DIII-D divertor is a promising technique for energy dissipation (through radiation and collisions) and consequently for reduction of the heat load on the plates. An important problem related to this technique, is the inherent poisoning of the core plasma by migrating Ar. The Ar core contamination seems also to improve the thermal transport in an advanced operating mode of the tokamak. It is therefore of great importance to measure the evolution of the impurity concentration profile within the core plasma. This goal could be achieved by using the Ross filter method in conjunction with the existing x-ray diagnostics on DIII-D. A basic Ross filter system consists of two identical detectors placed behind two different x-ray absorbing foils looking at the same plasma volume. The foils are made of different elements or compounds with adjacent or nearly adjacent atomic numbers. Their accurate thickness causes the x-ray transmission curves of the two foils to be effectively identical over the entire energy range except within the narrow region between their absorption edges. Since the transmission characteristics of the foils above and below their absorption edges are the same, any difference in the two detected signals is proportional to the total x-ray power of the emission spectrum between these two edge energies. An x-ray Ross filter with its energy pass band centered on the Ar XVII Kα line at 3.14 keV has been designed. This allows for the discrimination of the Ar Kα line only, regardless of Ar ionization state, against any background radiation with energies outside the energy pass band. The Ross filter was installed in front of two of the fan shaped poloidal x-ray arrays on DIII-D. The first measurements showed very good discrimination against Ne, another injected impurity. Emissivity profile evolution of the Kα lines and Ar enhanced continuum within the energy pass band of the Ross filter can be determined from the x-ray brightness signals by inverting techniques and by using the Te, ne, and Ar16+ profiles as measured by other diagnostics. The transport code MIST1 can be used to calculate both the emissivity profiles of the Kα of all the ions and their concentration profiles when the measured Te, and ne are used as input. The Ar16+ profiles as measured by charge exchange spectroscopy can be used as a constraint for the MIST code to accurately calculate the Ar18+ profile and thus unfold all the Ar ions Kα emissivity profiles. From these one can determine the Ar concentration profile evolution and the particle diffusion coefficient. In conclusion, using the Ross filter method with the existing x-ray imaging systems results in a powerful and cost-effective diagnostic for impurity transport studies. © 2001 American Institute of Physics.