Integrated in situ monitoring of a metalorganic vapor phase epitaxy reactor for II–VI epitaxy

The focus of this paper is the integrated use of system and wafer monitors to obtain a complete picture of the growth process and to identify the major causes of variance. In situ monitoring of a growing layer of Hg_1-xCd_xTe using laser reflectometry has been compared with the outputs of various system monitors such as pyrometer, organometallic concentration, and flow. Differences between the expected and measured concentrations were corrected by initially adjusting the organometallic flows, and the remaining variance in CdTe interdiffused multilayer process layer thickness was then corrected by increasing the CdTe cycle time. The remainder of the layer gave a homogenized alloy composition of 0.256 for a target value of 0.258. This example shows how different in situ monitors have been integrated to give a comprehensive picture of the growth process, which were then related to known kinetic behavior. As a result of this monitoring, it was possible to identify critical parameters for control.     

Experimental and CFD investigation of 100 mm size cone flow elements

This paper presents performance characteristics of 100 mm line size cone flow elements having beta ratios of 0.4, 0.5, 0.6, 0.7 and 0.8. A magnetic flow meter is used as a reference standard for flow measurement in vertical test section. A series of experiments have been conducted using water at in-house Flow Calibration Facility (FCF) to cover the Reynolds number ranging from 20,000 to 200,000. The performance characteristics of 100 mm line size cone flow elements with different beta values have been evaluated experimentally. It is found that the discharge coefficient of the cone flow element is nearly independent of the specified range of Reynolds number. Testing of the cone flow element in accordance with new API 5.7 is carried out at flow calibration facility. The testing requirements in the standard explain the conditioning effect of the cone flow element having gate valve disturbance upstream of the cone at various locations. The effect of the upstream velocity profile has been investigated by placing a gate valve upstream of the cone flow element at a distance of 0D and 28D and performing experiments at 25%, 50% and 100% opening of gate valve. The value of the discharge coefficient is not affected when the cone is placed at a distance of 0D and for 100% opening of gate valve. The uncertainty results of the cone testing are discussed. For studying pressure and velocity distributions, cone elements are modeled using computational fluid dynamics (CFD) code PHOENICS. Pressure and velocity profiles for different sizes of cone elements are plotted. From the pressure profile, it can be seen that the pressure recovery downstream of the cone is within a distance of 3D. The velocity profile downstream of the cone signifies the use of flow element as a signal conditioner. For measurement of flow through a 100 mm line, differential pressure across the cone is measured using a Differential Pressure Transmitter (DPT). Experiments were repeated by replacing the cone element for obtaining different β values.     

Investigation of the structural stability of Co2NiGa shape memory alloys via ab initio methods

CoNiGa alloys have received considerable interest due to their high-temperature shape memory properties. Although there have been many investigations on the mechanical and magnetic behavior of these materials, little is known about the microscopic basis for the observed macroscopic behavior. In this work, we discuss the stability of Co₂NiGa-based structures. The austenite phase is modeled as fully ordered L2₁ and as partially ordered B2. The stability of the austenite phase with respect to tetragonal distortions is examined. Lattice dynamics calculations suggest that the mechanism for the transformation is different from that of the much more studied and chemically similar Ni₂MnGa shape memory alloy (SMA). The electronic basis for the observed metastability of the cubic Co₂NiGa austenite is found to be qualitatively different from that observed in other ferromagnetic SMAs, especially Ni₂MnGa.     

Evaluation of total phenol content and antioxidant properties of encapsulated grape seed extract in yoghurt

The effect of encapsulated (En) and nonencapsulated (NE) grape seed extract (GSE) at 1% level added to milk before its fermentation was evaluated on the physicochemical properties, total phenolic content and antioxidant activity of the resulting yoghurt. Encapsulated GSE resulted in a product comparable to the control, based on sensory properties, acidity, water‐holding capacity, viscosity and colour, along with a threefold increase in total phenolic content and fourfold increase in antioxidant activity. The GSE addition resulted in no effect on the viability of Streptococcus thermophilus and Lactobacillus bulgaricus subsp. delbrueckii counts. The product with NE‐GSE had poor sensory properties and lesser polyphenol stability during storage as compared to En‐GSE yoghurt.     

Fracture processes and mechanisms of crack growth resistance in human enamel

Human enamel has a complex micro-structure that varies with distance from the tooth’s outer surface. But contributions from the microstructure to the fracture toughness and the mechanisms of crack growth resistance have not been explored in detail. In this investigation the apparent fracture toughness of human enamel and the mechanisms of crack growth resistance were evaluated using the indentation fracture approach and an incremental crack growth technique. Indentation cracks were introduced on polished surfaces of enamel at selected distances from the occlusal surface. In addition, an incremental crack growth approach using compact tension specimens was used to quantify the crack growth resistance as a Junction of distance from the occlusal surface. There were significant differences in the apparent toughness estimated using the two approaches, which was attributed to the active crack length and corresponding scale of the toughening mechanisms.     

Effect of reaction medium on radical copolymerization of acrylonitrile with vinyl acids

Radical polymerization of acrylonitrile (AN) with methacrylic acid (MAA) and itaconic acid (IA) was carried out in a mixture of dimethylformamide (DMF) and water at 70°C using α, α′‐azobisisobutyronitrile (AIBN) as an initiator. Monomer feed in the polymerization vessel was 98:2 (AN:MAA/IA) in the molar ratio, and the DMF:H₂O ratio was varied between 20:80 and 80:20 (w/w). Copolymers were characterized by FTIR, carbon, hydrogen, nitrogen elemental CHN analysis, ¹H‐ and ¹³C‐NMR, and viscometry. The rate of polymerization (R_p) was found to decrease with an increase in DMF concentration in the reaction medium, that is, in 20% DMF for AN–MAA system, the R_p is 1.23% min⁻¹ in 1 h of polymerization, while in 80% DMF, R_p is reduced to 0.37% min⁻¹. The nature of the vinyl acid also affects the R_p. It has been shown that the rate of polymerization is higher for an AN–MAA system as compared to an AN–IA system (R_p = 1.0% min⁻¹) and the methacrylic or itaconic acid content in the copolymer increases with an increase in the DMF concentration. The MAA content in the poly(AN–MAA) polymer produced in 20% DMF is 3.2 mol %, which increases to 6.1 mol % (calculated through FTIR spectra) when DMF is increased to 80% in the reaction medium. The intrinsic viscosity [η] of the poly(AN–IA) and poly(AN–MAA) copolymers in DMF was found to be in the range of 0.67–2.90 dLg⁻¹ depending on the reaction medium. In determining the intrinsic viscosity, a definite deviation from rectilinearity of the concentration dependence in the high‐dilution region is observed, thereby demonstrating the polyelectrolyte behavior of these polymers. Through FTIR and NMR spectral studies, PAN homopolymer and other copolymers have shown the formation of a small quantity of acrylamide units. In addition copolymer P₁₀, which contains 10.1 mol % IA, has shown anhydride formation. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 79: 1640–1652, 2001     

Second harmonic operation at 460 GHz and broadband continuous frequency tuning of a gyrotron oscillator

We report the short-pulse operation of a 460 GHz gyrotron oscillator both at the fundamental (near 230 GHz) and second harmonic (near 460 GHz) of electron cyclotron resonance. During operation in a microsecond pulse length regime with 13-kV beam voltage and 110-mA beam current, the instrument generates several watts of power in two second harmonic modes, the TE/sub 2,6,1/ at 456.15 GHz and the TE/sub 0,6,1/ at 458.56 GHz. Operation in the fundamental modes, including the TE/sub 0,3,1/ mode at 237.91 GHz and the TE/sub 2,3,1/ at 233.15 GHz, is observed at output powers up to 70 W. Further, we demonstrate broadband continuous frequency tuning of the fundamental modes of the oscillator over a range of more than 2 GHz through variation of the magnetic field alone. We interpret these results in terms of smooth transitions between higher order axial modes of the resonator. The 460 GHz gyrotron is currently being processed for continuous duty operation, where it will serve as a microwave source for sensitivity-enhanced nuclear magnetic resonance (dynamic nuclear polarization) studies at 16 T (700 MHz /sup 1/H), a field strength which is two-fold higher than has been accessible with previous technology.     

InAsSb/InTISb superlattice: A proposed heterostructure for long wavelength infrared detectors

A novel superlattice (SL) heterostructure, comprising of InTlSb well and InAsSb barrier lattice matched to InSb, is proposed for long wavelength 8−12 urn detectors. Improvements in the InTlSb epilayers’ structural quality are expected, as it will be sandwiched between higher quality zinc-blende InAsSb epilayers. Preliminary energy band calculations of 30? InAs_0.07Sb_0.93/100? In_0.93Tl_0.07Sb SL show the band alignment favorable to type I with three heavy-hole subband confinement in the valence band and a partial electron subband confinement in the conduction band due to the small conduction band offset. Including the effect of strain indicates significant changes in the band offsets, with optical bandgap essentially unaltered. The optical band gap of this SL was computed to be 0.127 eV (9.7 μm) at OK, indicating its potential for long wavelength applications.     

Molecular beam epitaxy HgCdTe growth-induced void defects and their effect on infrared photodiodes

We have carried out a study and identified that MBE HgCdTe growth-induced void defects are detrimental to long wavelength infrared photodiode performance. These defects were induced during nucleation by having surface growth conditions deficient in Hg. Precise control and reproducibility of the CdZnTe surface temperature and beam fluxes are required to minimize such defects. Device quality material with void defect concentration values in the low 10² cm² range were demonstrated.     

Volumetric video compression for interactive playback

We develop a volumetric video system which supports interactive browsing of compressed time-varying volumetric features (significant isosurfaces and interval volumes). Since the size of even one volumetric frame in a time-varying 3D data set is very large, transmission and on-line reconstruction are the main bottlenecks for interactive remote visualization of time-varying volume and surface data. We describe a compression scheme for encoding time-varying volumetric features in a unified way, which allows for on-line reconstruction and rendering. To increase the run-time decompression speed and compression ratio, we decompose the volume into small blocks and encode only the significant blocks that contribute to the isosurfaces and interval volumes. The results show that our compression scheme achieves high compression ratio with fast reconstruction, which is effective for interactive client-side rendering of time-varying volumetric features.