Hemispherical Substrate Research Articles

Morphological Stability of 6H-SiC Epitaxial Layer on Hemispherical Substrates Prepared by Chemical Vapor Deposition

Morphological Stability of 6H-SiC Epitaxial Layer on Hemispherical Substrates Prepared by Chemical Vapor Deposition

Guided-light two-wave-mixing on a spherical surface

A novel guided structure is proposed which is aimed at developing integrated all-optical signal processors exploiting two wave mixing interactions. The structure is based on the whispering propagation on a hemispherical glass substrate and contains a dye-doped photoresist film as the test nonlinear material. Its functionality was demonstrated successfully with two wave mixing experiments that were performed with CW light at 1321 nm and with a probe beam at 647 nm.

Growth pyramids on Si(111) facets: A CVD and MBE study

The morphology of growth pyramids on Si(111) facets has been studied with an atomic force microscope. These facets with pyramids are formed upon chemical vapor deposition (CVD) growth on a hemispherical substrate. Spiral as well as concentric step edge patterns have been observed on the growth pyramids. Based on the step edge patterns the origin of the pyramids is attributed to different types of dislocations. Step edge patterns indicate that growth during CVD is governed by step edge processes and that surface diffusion is not rate limiting. The completely different growth mechanism of molecular-beam epitaxy (MBE) is illustrated by MBE overgrowth of a silicon layer on top of the CVD layer. MBE growth parameters have been studied by comparing the growth pyramid morphology with simulation results.

GaAs epitaxy by chemical vapour transport under high, earth and low-gravity conditions

Homoepitaxy of GaAs on hemispherical substrates have been realised by chemical vapour transport in four different gravity levels. Experiments have been performed on earth, under 5 g and 10 g acceleration conditions using a centrifuge and under a microgravity environment (EURECA-I mission). The source was either undoped GaAs or tin-doped GaAs. Analysis and comparison of the grown layers show that, in the applied conditions, the gravity level is not a relevant parameter and that tin is an inhibitor for the GaAs epitaxy.

ALPSS: A millimetre-wave aperture-coupled patchantenna on a substrate lens

The feasibility of millimetre-wave (MM-wave) aperture-coupled patch antennas, printed at the back surface of substrate-lenses is demonstrated and the corresponding radiation characteristics are investigated. A specific realisation of such an air-lens-patch-slot-strip (ALPSS) antenna on a low-permittivity /spl epsiv//sub r/=4.0 extended hemispherical lens substrate is theoretically and experimentally characterised at 70 GHz. It is demonstrated that the ALPSS antenna exhibits clean, axially symmetric patterns of low cross-polarisation (26 dB), a directivity of 30.4 dB and the 3 dB pattern full-beamwidth remains within 6/spl deg/-5/spl deg/ between 60-80 GHz. In addition, a very-high front-to-back (F/B) ratio, of the order of 50 dB is measured at 70 GHz, despite the absence of a backing ground-plane. The ALPSS antenna is well suited for low-cost broadband point-to-point communications and collision avoidance applications.

Dyscalculia and Dyslexia After Right Hemisphere Injury in Infancy

To use the findings from neuropsychological evaluation and functional magnetic resonance imaging (fMRI) to assess interhemispheric reorganization of function after early unilateral brain injury. The study focused on one case of early brain injury that resulted in both dyscalculia and dyslexia. Brain injury was studied using both structural and fMRI. Intellectual function was evaluated using the Wechsler Intelligence Scale for Children, Third Edition, while visuospatial skills were assessed using the Block Design subtest of the Wechsler Intelligence Scale for Children, Third Edition, and Judgment of Line Orientation subtest. The Selective Reminding Test and the Recurring Figures Test were used to evaluate memory and orientation; language and speech skills were evaluated using the Boston Naming Test, Controlled Oral Word Association, Gates-MacGinitie Reading Test, and color naming. Various methods were used to study arithmetic skills, including the Wide Range Achievement Test-Revised and the Peabody Individual Achievement Test. The control group for fMRI consisted of nine normal subjects. Neuropsychological laboratory in primary care hospital. A 17-year-old boy who had sustained a closed head injury associated with a partially depressed, right parietal skull fracture, and right temporal hemorrhage in a motor vehicle crash at age 7 months (November 9, 1977). Subsequent social behavior was normal, but the patient had difficulty throughout school in mathematics and spelling and was characterized as having a "short attention span." None. Standardized tests of arithmetic and reading supplemented by an assessment of calculation and quantitative skills. While performing calculations, fMRI disclosed predominantly left hemisphere activation involving the frontal and posterior parietal regions, whereas this task produced bilateral activation of the supramarginal gyrus in seven of nine normal subjects. Neuropsychological findings confirmed the presence of dyscalculia and dyslexia despite normal intellectual functioning. Visuospatial skills ranged from the low normal to average level. The fMRI findings were consistent with early interhemispheric transfer of visuospatial skills normally committed to the right parietal area to the left parietal region. The patient's dyscalculia and reading ability raise a question of acquired left parietal dysfunction as a consequence of the competition between verbal and visuospatial functions for left hemisphere representation. Interhemispheric reorganization of function may be bidirectional rather than a feature unique to the left hemisphere substrate for language.

Orientation dependent surface stabilization on flame deposited diamond single crystals

In this study a model for the orientation dependent surface stabilization of diamond grown from the vapour phase is presented. The model is based on a first order broken bond analysis of the diamond crystal with additional considerations about surface reconstruction by dimer formation. Due to the formation of dimers, surface stabilization is expected for orientations corresponding to Miller indices { hhk} h < k in the 〈110〉 zones. It is demonstrated that this model gives a good description of growth phenomena like facets, curved bands and microfaceting, observed on homoepitaxially grown diamond samples. These specimens are obtained by flame deposition on cylindrical type IIa natural diamond substrates with {111}, {110} or {001} top faces. In conformation with the model the surfaces { hhk} h < k between {111} and {113} appear to be stabilized in one direction, while a discrete number of orientations between {113} and {001} are subject to two-dimensional stabilization. All other surfaces are stabilized by the development of microfacets which also have orientations close to { hhk} h ≤ k , as was determined by laser reflectometry. In addition it is shown that differences in the orientation dependent incorporation of nitrogen as nitrogen-vacancy pairs in the diamond lattice is consistent with the described model. For this purpose a single crystalline diamond layer grown on top of a hemispherical diamond substrate by the flame technique was investigated by cathodoluminescence topography.

Reduced pressure silicon CVD on hemispherical substrates

The orientation dependence of silicon crystal growth in the Si- H- Cl CVD system is studied as a function of temperature and chlorine/hydrogen ratio in the gas phase for pressures of 0.1 and 0.01 atm. This is done with the aid of hemispherical single crystal substrates. The transition from macroscopic steps at low temperatures to flat { hhk} h < k faces, viz. {113}, {337} and {771 3}, at high temperatures, as reported in an earlier paper, is reinvestigated. In accordance with the earlier study it is found that this transition is not only dependent on the chlorine/hydrogen ratio in the gas phase, but also on the pressure in the growth system. The observed trend is consistent with the idea that adsorption is responsible for the destabilization of these faces. The experimentally found pressure dependence of the transition is not as large as is predicted with the aid of the previously developed model based on Cl and/or H adsorption, however. In this paper an explanation for this discrepancy is suggested, which is based on the increasing importance of surface kinetic processes at lower pressures. As was reported before, the stability of the {001} and the { hhk} h > k faces, i.e. {331}, {551}, decreases with increasing temperature. At the lower pressures it is additionally found that the stability of these faces is lower for lower chlorine/hydrogen ratios in the gas phase; it is also lower for a lower pressure. This proves that besides thermal roughening as the main reason for the destabilization, also the decrease in the coverage of these faces, which takes place at a lower chlorine/hydrogen ratio in the gas phase or at a lower pressure in the growth system, results in less stable { hhk} h > k fac

Roughening effects during silicon CVD studied by the use of hemispherical substrates

With the aid of hemispherical substrates the morphological importance of silicon faces has been investigated as a function of fundamental gas phase parameters for epitaxial growth with the SiHCl CVD system. For moderate supersaturations it is found that the morphological importance of the {111} and {110} faces is independent of temperature, while that of the faces {001}, {551} and {331} decreases with increasing temperature. The latter temperature effect is interpreted in terms of thermal roughening. To explain the trends in the roughening temperatures, which could be derived from the decrease of the facet dimensions on the hemispheres with temperature, atomic models for the different faces are discussed. For high temperature growth at high supersaturations, kinetical roughening of the above mentioned faces is observed. The kinetical roughening of the {111} faces is accompanied by a change in the orientation of the growth hillocks on these faces: instead of being bound by (dimer reconstructed) 〈 112〉 steps, as is normally observed, at high temperature and high supersaturation the hillocks are terminated by 〈11 2〉 steps. An interpretation of these supersaturation effects is given, based on the adsorption probabilities for growth species on the different steps and faces.

Factors Affecting Oviposition by the Parasitoid Microplitis croceipes (Hymenoptera: Braconidae) in an Artificial Substrate

Several factors that may affect oviposition by Microplitis croceipes (Cresson) in an artificial oviposition substrate were investigated. Significantly fewer females oviposited in thin disks of agarose gel than in hemispheres, cylinders, or cubes, although there were no differences in numbers of eggs laid. A higher percentage of females that had oviposited in a Heliothis zea (Boddie) larva before testing oviposited in an artificial substrate than did females without oviposition experience. In addition, experienced females laid more eggs than inexperienced females. When the artificial substrate was colored with red, yellow, blue, or green food color, colored substrates elicited more ovipositions than did uncolored substrates, and the number of eggs laid was highest for the blue substrate. The mean number of eggs laid increased also with the food color concentration. The total number of eggs laid increased with the number of substrates per Petri dish. M. croceipes preferred hemispherical substrates with a volume of 35–40 μl, which were similar in height to their actual host instar preferences. A water extract of larval feces did not increase oviposition by M. croceipes . Bioassay test criteria and the use of choice tests for ovipositional response of M. croceipes are discussed.

Embedded-atom study of the spontaneous formation of misfit dislocations.

Misfit dislocations were spontaneously formed at (111) interfaces of Pd-Cu bicrystals and monolayers simulated with the embedded-atom model of Daw and Baskes. The bicrystal model contained a total of 4417 atoms (2360 Pd and 2057 Cu) in a spherical configuration; the monolayer of Cu contained 294 atoms on a hemispherical substrate of 2360 Pd atoms. In all simulations the surfaces of the models were free of constraint. The simulation conducted was a 0-K energy minimization. This indicates that thermal activation was not necessary to produce the misfit dislocations. This is the first time that the spontaneous formation of misfit dislocations has been observed in computer simulations at these low misfits (6.7%) without thermal activation, and this is the first time that the displacements at the interface have been clearly demonstrated by computer simulation.

Influence of temperature on the crystal habit of silicon in the SiHCl CVD system II. Surface tension of faces in the 〈110〉 zones

In part I, the authors reported on the appearance of a number of flat faces with indices { hhk} after growth on hemispherical substrates. Of these faces, those with indices { hhk} h< k were found to disappear at higher temperature, while those with indices { hhk} h< k only appear above a certain critical temperature. In this paper an interpretation of this phenomenon is given based on polar plots of surface tension versus crystallographic orientation, including the effects of dimer-like surface reconstructions and hydrogen adsorption. With the use of these plots it is possible to explain the observed temperature effects. The main result is that the faces in the { hhk} h< k part of the 〈110〉 zone, particularly {113}, on the one hand will be stabilized by surface re construction, but on the other hand they will be destabilized by adsorption.

Fast growth in GaAs VPE at low temperature and high partial pressures

The anisotropy in GaAs vapour phase growth by the AsCl 3 method is studied on hemispherical and lens-shaped substrates. The surface morphologies are observed by scanning electron microscopy, and the growth rate versus orientation measurements performed by a previously described method. No appreciable change in the shape of these curves is observed when the growth temperature is lowered from 750 to 630°C although the average growth rate is decreased. On the contrary, at higher AsCl 3 partial pressures a completely different shape is observed mainly characterized by two very fastly growing areas (110) to (221) and (1 1 9) to (1 1 5). In this latter case growth rates of hundreds of microns per hour can be obtained with good surface morphologies.

Vapour epitaxial growth and characterization of InAs 1- xP x

The vapour growth of InAs 1- x P x layers has been carried out by the hydride process. The phosphorus rich part of the system (0.7 ⪯ x ⪯ 1) was especially investigated. Heteroepitaxial deposits of InAs 1- x P x and InP have been performed on substrates such as InAs, GaAs and GaP. A systematic study of the influence of the substrate orientation on the quality of the layer has been carried out by growth on hemispherical substrates. Preferential planes have been pointed out: (100) and (111) A for InAs, (111) for GaAs and GaP. The band gap variation as a function of the composition has been determined by photoluminescence at 4.2 °K and X-ray diffraction measurements. It fits the equation: E G ( x) eV = 0.425 + 0.722 x + 0.273 x 2 at 4.2 °K.