Digital Commons Network^™

Surface Stress, Morphological Development, And Dislocation Nucleation During Sixge1-X Epitaxy, D. E. Jesson, S. J. Pennycook, J. -M. Baribeau, D. C. Houghton

Scanning Microscopy

Utilizing Ge marker layer experiments combined with atomic number contrast (Z-contrast) imaging, we have studied the evolving surface morphology of Si_xGe_1-x alloys during growth by molecular beam epitaxy. The marker layers map out the instability transition between planar two-dimensional (2D) growth and three-dimensional (3D) growth. The transition occurs via the gradual formation of a surface ripple as anticipated from instability theory. However, these undulations rapidly develop into crack-like surface instabilities which we simulate and explain by the mechanism of stress-driven surface diffusion. Finally, we model the large stresses associated with these features within a fracture mechanics formalism. …

Light Scattering And Electron Microscopy Study Of The Surface Morphology Of Gaas Films Grown By Molecular Beam Epitaxy, M. K. Nissen, C. Lavoie, S. Eisebitt, T. Pinnington, T. Tiedje

Scanning Microscopy

The surface morphology of thermally quenched GaAs films grown by molecular beam epitaxy on GaAs substrates has been studied by elastic light scattering, by scanning electron microscopy and by scanning tunneling microscopy (STM) in air. STM shows that the oxide-desorbed surface of GaAs is pitted, but smooths after deposition of a few hundred nanometers of material. Light scattering shows that, after the surface has smoothed, the power spectral density of the surface approaches a q^-2 dependence on spatial frequency over the spatial frequency range 0.2 μm^-1 < q < 20 μm^-1 that is accessible to the light scattering measurements at 488 nm. …

Ultrastructure Of Dentin Matrix In Heritable Dentin Defects, J. Waltimo, H. Ranta, P. -L. Lukinmaa

Scanning Microscopy

Heritable dentin defects form a group of diseases which exclusively affect dentin among the various dental tissues. While one type is associated with the generalized connective tissue disorder, osteogenesis imperfecta, other types occur as single traits. The clinical manifestations of the dentin defects vary from insignificant to severe enough to cause aesthetical and functional failure of the teeth. Scanning and transmission electron microscopic studies, reviewed in this paper, have markedly clarified the ultrastructure of the aberrant dentin matrix. Both similar and different changes seem to occur in the various forms of heritable dentin defects. Abnormalities in the appearance and organization …

Ionoluminescence: A New Tool For Nuclear Microprobes In Geology, C. Yang, N. P. -O. Homman, K. G. Malmqvist, L. Johansson, N. M. Halden, V. Barbin

Scanning Microscopy

When an ion beam in the energy range of a few MeV/amu impacts on a mineral, visible light can often be observed. This light, induced by energetic ions, is termed ionoluminescence (IL). The intensity and wavelength of the ionoluminescent light provide information concerning the nature of luminescence centers, such as trace substituents and structural defects, found in the mineral. This makes IL a useful complement to other methods of ion beam analysis (IBA), such as particle induced X-ray emission (PIXE) and Rutherford backscattering (RBS), in characterizing geological samples. In the present study, a proton or alpha particle beam was used …

The Morphology And Misfit Dislocation Formation Characteristics Of Strained Heteroepitaxial Layers: Ex Situ And In Situ Growth Studies, A. G. Cullis

Scanning Microscopy

Under certain regimes of heteroepitaxial layer growth, misfit stresses can lead to very significant distortions in interface morphology, which can influence strain relief and subsequent misfit dislocation introduction. These phenomena have been clearly demonstrated in the case of SiGe/Si heteroepitaxy and the way in which surface SiGe growth ripples are accompanied by strain waves has been established. The ripples provide partial elastic relief of the layer misfit stress in a manner which has been correlated with theoretical expectations. The local stress variations ultimately may influence the formation and disposition of misfit dislocations in the strained layer structures. The present paper …

Observations On Interactions Between Metal Clusters And Iii-V Semiconductor Substrates, Theodore D. Lowes

Scanning Microscopy

Interfacial reactions between deposited indium and gallium metals with GaAs(001) substrates are discussed. After Knudsen cell molecular beam epitaxy (MBE) deposition, samples were annealed in ultrahigh vacuum (UHV) and examined by ex situ electron microscopy. The resulting microstructure was compared to the microstructure of GaAs(001) substrates without metal deposition. It is shown that significant interactions occur between the deposited metal and substrate and that the final microstructure is consistent with the model for thermal decomposition of III-V compound semiconductor substrates.

Boron Reconstructed Si(111) Surfaces Produced By B2o3 Decomposition, J. Nogami, S. Yoshikawa, J. C. Glueckstein, P. Pianetta

Scanning Microscopy

Scanning tunneling microscopy has been used to study the growth of boron on the Si(111) surface. Boron was deposited in the form of B₂O₃ which was decomposed by heating the substrate. With this technique, it is possible to control the B coverage, and also to produce the well known √3 x √3 reconstruction at annealing temperatures as low as 600°C. The optimal conditions for the formation of the √3 x √3 surface by B₂O₃ decomposition are given. In addition, the nature of the √3 x √3 surface over …

Metastable Reconstructions On Si(111), Y. -N. Yang, E. D. Williams

Scanning Microscopy

We report unambiguous atomic scale evidence demonstrating that the atom density in the high temperature "1x1" phase of Si(111) is ~6% higher than the 7x7. Such evidence is provided by scanning tunneling microscopy (STM) observation of excess adatom density, and related island formation, on surfaces with very large terraces. The unusually large terraces were produced by heating the sample with DC current in the step-down direction at 1200°C. By trapping adatoms on the terraces through a quench, we have also created areas of metastable reconstructions, i.e., 9x9, 2x2, c2x4 and √3x√3, much larger than previously reported. For …

Microdissection And Measurement Of Polytene Chromosomes Using The Atomic Force Microscope, Curtis Mosher, Daniel Jondle, Linda Ambrosio, James Vesenka, Eric Henderson

Scanning Microscopy

A method to isolate specific regions of the Drosophila polytene chromosome using an atomic force microscope (AFM) was explored. The AFM was used for the microdissection of the locus of interest with much greater precision than standard microdissection techniques. The amplification of DNA isolated in this fashion by the polymerase chain reaction (PCR) is discussed. A study of the effect of hydration level on gross chromosome structure was carried out. It was shown that chromosome swelling is dependent upon humidity or the buffered medium. The significance of this swelling with respect to studies of chromosome structure under physiological conditions is …

Reflection High Energy Electron Diffraction (Rheed) Intensity Oscillations: Growth Modes And Growth Rates: A Critique, B. A. Joyce, X. M. Zhang, J. H. Neave, P. N. Fawcett, M. R. Fahy, K. Sato, I. Kamiya

Scanning Microscopy

The origin of and diffraction effects associated with reflection high energy electron diffraction (RHEED) intensity oscillations which occur during layer-by-layer growth of epitaxial thin films of III-V compounds by molecular beam epitaxy (MBE) are explained. It is shown that on (001) oriented substrates the period of the oscillations is in general a direct measure of the film growth rate which corresponds to the group III element flux. There are, however, exceptions to this simple concept including growth under group III rich-conditions, vicinal plane growth and growth from pulsed beams; each is considered.

On non-(001) low index orientations, the RHEED oscillation …

Epitaxial Growth Studies By Low Energy Electron Microscopy, E. Bauer

Scanning Microscopy

In spite of being a surface sensitive tool, low energy electron microscopy (LEEM) can also give information on interfaces. An example is the CoSi₂/Si(111) interface. Most of the work discussed in this paper, however, makes use of the high surface sensitivity of LEEM which makes this method an ideal tool for the study of the early growth stages in epitaxy, in particular of the growth dynamics and of the influence of misfit on the growth mode. Two prototype substrates, Mo(110) and Si(111), and three representative deposit metals, Cu, Au and Co, are used to illustrate the large variety …

The Principles Of Proton Probe Microanalysis In Biology, G. J. F. Legge, M. Cholewa

Scanning Microscopy

The proton microprobe, more correctly described as an ion microprobe which operates at MeV energies, complements its parent instrument the electron microprobe. This paper compares the basic principles and performance of the two instruments and relates the evolution of biological analysis on such ion microprobes to that on electron microprobes, covering the development of sample handling techniques and of data handling techniques and comparing beam damage studies. The paper describes the variety of techniques available to the ion microprobe - the initial techniques of Energy Dispersive X-ray analysis, Rutherford Back Scattering and Nuclear Reaction Analysis and the rapid evolution of …

X-Ray Absorption Studies Of Strain In Epitaxial (Si-Ge) Atomic Layer Superlattice And Alloy Films, T. Tyliszczak, A. P. Hitchcock, Z. H. Lu, J. -M. Baribeau, T. E. Jackman

Scanning Microscopy

The Si 1s (K-shell) X-ray absorption spectra of a series of strained Si_xGe_100-x alloy thin films and several {(Si)_m(Ge)_n}_p atomic layer superlattices (ALS) grown epitaxially on Si(100) and Ge(100) substrates have been investigated using plane polarized synchrotron radiation. Polarization dependent components of the signal are attributed to anisotropic states associated with strain-induced tetragonal distortions. The sense of the polarization is shown to be identical for all compositions (x = 25 to 92) of SiGe alloys grown on Si(100) substrates. The opposite polarization dependence is found to occur for all Si_xGe …

Interfacial Studies In Semiconductor Heterostructures By X-Ray Diffraction Techniques, J. -M. Baribeau, R. L. Headrick, P. Maigné

Scanning Microscopy

X-ray radiation is a non-destructive probe well suited to assess structural perfection of semiconductor material. Three techniques are used to study the interfacial roughness, period fluctuations and annealing-induced interdiffusion in various superlattice structures. Reflectivity of long period Si/Si_1-xGe_x multiple quantum wells reveals an asymmetry oriented along the direction of miscut in the interface roughness with the Si_1-xGe_x to Si interfaces being about twice as rough (0.5 versus 0.3 nm) as the Si to Si_1-xGe_x interfaces. For Si-Si_0.65Ge_0.35 multiple quantum wells, diffuse scattering is minimal for a growth temperature …

Reply By A. Carretero Et Al., Ana Carretero, H. Ditrich, M. Navarro, H. Splechtna, J. Ruberte

Scanning Microscopy

Dear Editor,

The study of vascular casts in the embryo by means of the scanning electron microscope represents the main subject of our research. We fully agree with DeRuiter and Gittenberger-de Groot in that corrosion casting is a valuable tool to study the early angiogenesis in embryos.

Balancing Surface Energy Terms For Stable Growth Of Planar Surfaces, M. Albrecht, P. O. Hansson, S. Christiansen, W. Dorsch, H. P. Strunk, E. Bauser

Scanning Microscopy

We investigate the driving forces that determine the growth mode of heteroepitaxial Ge layers grown from solution on Si substrates with orientations (001), (011) and (111) by transmission electron microscopy (TEM) and atomic force microscopy (AFM). Using liquid phase epitaxy, we can study the influences of strain and surface energy terms independently on effects due to limited surface diffusion. In (001) and (011) orientated layers, {111} faceted islands form (Stranski-Krastanov growth). In contrast, (111) orientated layers grow in a two-dimensional step flow growth mode (Frank-van der Merwe growth).

We model these investigations in terms of energy minimisation considering surface energy …

Znse Heteroepitaxial Growth On Si (100) And Gaas (100), D. K. Biegelsen, R. D. Bringans, J. E. Northrup, L. -E. Swartz

Scanning Microscopy

The early stages of ZnSe heteroepitaxy on Si(100), Si(100):As and GaAs(100) are compared and contrasted, based on results of scanning tunneling microscopy and photoemission spectroscopy. High Se reactivity with the substrate constituents leads to bulk phase formation which is detrimental to heteroepitaxy. As-termination of Si(100) not only passivates the surface, but also provides an ideal buffer for ZnSe overgrowth. Lacking a similar buffer layer, stoichiometric control of the GaAs(100) surface is investigated to find a means for controlled heteroepitaxy.

Recent Surface Studies Using Biassed Secondary Electron Imaging, Rajendra Persaud, Hisato Noro, Muhammad Azim, Robert H. Milne, John A. Venables

Scanning Microscopy

The growth and surface diffusion of Cs on Si(100) and Ag on Fe(110) have been studied using biassed secondary electron imaging (b-SEI) and Auger electron spectroscopy (AES).

The b-SEI technique was found capable of detecting Cs on the Si surface with a 0.5% ML sensitivity. Unusual diffusion profiles containing linear sections were obtained for coverages (θ) < 1/2 ML. The general form of these profiles were reproduced using a 2-phase model, where Cs chains act as sources of mobile adatoms, in conjunction with a diffusion coefficient of the form D ~ θ (1- Cθ). This form of D, obtained from Boltzmann-Matano analysis, is consistent with diffusion theory including strongly repulsive Cs-Cs interactions. An adatom diffusion energy, E_d, = 0.47 ± 0.05 eV was found to be consistent with measurements …

Predicting Relaxation In Strained Epitaxial Layers, R. Beanland, D. J. Dunstan, P. J. Goodhew

Scanning Microscopy

Strained epitaxial semiconductor layers, much thicker than the critical thickness, have been used as "strain-relief" buffer layers for many years. The most successful structure developed so far dates back to the 1960's, and consists of a very thick ( ~30 μm) layer in which the misfit is gradually and continuously increased. These structures relax completely and have a sufficiently low threading dislocation density to allow a device structure to be grown on top. This process requires a very high growth rate to produce the buffer layer in a reasonable time, which is only provided by hydride vapourphase epitaxy. Recently, there …

New Applications Of The Nuclear Microprobe For Biological Samples, Jan Pallon, Klas Malmqvist

Scanning Microscopy

The continuing development of the Nuclear Microprobe (NMP) has opened up new fields of applications in biology and medicine. Quantitative multielemental analysis in small sections of samples can be performed routinely. The use of techniques such as scanning transmission ion microscopy makes imaging as well as mass normalization possible at submicron resolution. Recent medical applications include studies on thin cryosections prepared from autopsies and biopsies, as well as single cells grown directly on the backing foil used in the NMP analyses. The purpose of the single cell analysis is often pharmacological, e.g., testing of new drugs, their uptake and distribution. …

Scanning Electron Microscopic Study Of The Collagen Sheath Of The Human Thyroid Gland And Its Disorders, Masao Morita, Takuro Ogata, Keijiro Araki

Scanning Microscopy

A cell-maceration/scanning electron microscope (SEM) method was employed to demonstrate the collagen sheath around follicles (perifollicular sheath) of the human thyroid gland and its disorders. In the normal thyroid gland, the follicles were surrounded by spherical collagen sheaths composed of a framework of thick collagen bands 1-5 μm in width and fine solitary collagen fibrils 50-70 nm in diameter. In benign thyroid diseases (Graves' disease, Hashimoto's thyroiditis and adenomatous goiter), the perifollicular sheaths differed in size and in shape according to the disease, but they were always composed of thick collagen bands and fine fibrils as in the normal thyroid. …

Application Of Lawn Fertilizers And Pesticides In Salt Lake Valley Recharge Areas, Ghassan R. Musharrafieh, Larry Sager, Howard M. Deer, Richard C. Peralta

Civil and Environmental Engineering Faculty Publications

Homeowners, chemical applicators, and commercial lawncare companies apply chemicals to lawns and ornamentals overlying the recharge zone of Salt Lake Valley's principal aquifer. These applied fertilizers, herbicides, insecticides, and fungicides can potentially leach far enough to contaminate ground water. This report summarizes a study conducted in 1993-1994 to determine the type, rate, and frequency of applying chemicals to lawns and ornamentals in the recharge zone. Surveyed are lawncare companies, chemical applicators, schools, churches, hospitals, parks, homeowners, and government documents and community and state regulations. Results will help assess the potential impact of these applications on future ground water quality.

Modelling For Optimal Conjunctive Water Management: Irrigated Crop Production Versus Nps Pollution Prevention, O. H. Daza, Richard C. Peralta

Civil and Environmental Engineering Faculty Publications

Conjunctive water management{CWM)involves coordinating use of ground and surface water sources. Agricultural (A) and nonagricultural {NA)users compete for available water of adequate quality. A Simulation/Optimization (S/0) conjunctive water management model was developed to aid estimating the effects of water and environmental management decisions on crop yield and water quality. Included subsystems are groundwater, surface water, reservoir, delivery system, drainage, and A and NA water users. The nonlinear model addresses flows described by nonsmooth piecewise-linear functions which have discontinuous derivatives. Embedded constraints describe all significant subsystem flows. For example 1 deep percolation and runoff from surface irrigation are explicitly described as …

Formation And Structure Of Dentine In The Rat Incisor After Chronic Exposure To Sodium Fluoride, J. Appleton

Scanning Microscopy

Weanling rats were chronically exposed to sodium fluoride by feeding them for eight weeks with a standard powdered diet incorporating sodium fluoride at 0.025% , 0.05% and 0.1% by weight. After eight weeks blood was removed by cardiac puncture and the levels of plasma calcium and phosphate determined. The incisor teeth were removed and their structure examined in the scanning electron microscope (SEM) using backscattered electron imaging to determine the relative concentration and distribution of the mineral phase in the dentine. There was no significant alteration to the normal serum calcium and phosphate levels. Small scattered interglobular spaces were seen …

Cryo-Jet Preservation Of Calcium In The Rat Spinal Cord, William B. Greene, Lyle G. Walsh

Scanning Microscopy

In order to determine the distribution of diffusible ions, especially calcium, in rat spinal cord axons before and after trauma, sham, 6 hours post 6 gm/cm and 20 gm/cm trauma cords were cryo-jet frozen in situ and cryo-sections were subjected to electron probe X-ray microanalysis. The results confirm part of the Ca hypothesis, i.e., some spinal cord axons accumulate intracellular Ca after traumatic injury. In addition, 6 hours after trauma, Ca is only accumulated by axons that have also lost homeostasis. Thus, it is likely that observations of the continual rise of Ca in the traumatized spinal cord are due …

Morphologic Changes Of Apoptosis Induced In Human Chronic Myelogenous Leukemia "Blast" Cells By Sc41661a (Searle), A Selective Inhibitor Of 5-Lipoxygenase, K. M. Anderson, T. M. Seed, J. Peng, A. Jajeh, J. Meng, J. E. Harris

Scanning Microscopy

Several inhibitors of the arachidonic acid-metabolizing enzyme, 5-lipoxygenase reduce proliferation of hematopoietic and non-hematopoietic cells and cell lines and some cells undergo limited differentiation. Cells were cultured from patients with chronic myelogenous leukemia in "blast" crisis with the selective inhibitor of 5-lipoxygenase,SC41661A[3-{3,5-bis(1,1-dimethyl)-4-hydroxyphenyl}hiol]-N-methyl-N-[2-(2-phridinyl-propanamide)]. Cells cultured for 3 to 5 days with 40 μM SC41661A exhibited reduced cellular numbers along with ultrastructural changes and DNA laddering characteristic of apoptosis. Similar culture conditions reduced proliferation of U937 monoblastoid cells. In U937 cells, the ultrastructural features of apoptosis were not observed at 72 hours, when DNA laddering was present and cell numbers were reduced, …

Urinary Glycosaminoglycans Are Selectively Included Into Calcium Oxalate Crystals Precipitated From Whole Human Urine, Koji Suzuki, Keiko Mayne, Ian R. Doyle, Rosemary L. Ryall

Scanning Microscopy

Urinary glycosaminoglycans are selectively included into calcium oxalate (CaOx) crystals precipitated from whole human urine: The presence of glycosaminoglycans (GAGs) in the organic matrix of urinary stones, and their known effects on CaOx crystallization have prompted speculation regarding their role in CaOx urolithiasis. The aim of this study was to examine the involvement of GAGs in the early stages of CaOx crystallization in human urine. Urine samples were collected from healthy men and CaOx crystallization was induced by the addition of a sodium oxalate load. The crystals were harvested and demineralized, and the GAG content of the resulting extract analysed …

Cell Injury And Apoptosis, Andrejs Liepins, J. Omar Bustamante

Scanning Microscopy

Various forms of cellular injury, whether induced by immune effector cells, aberrant metabolic processes, chemotherapeutic drugs or temperature shifts, result in common morphological changes consisting of the formation and shedding of membrane vesicles from the injured cell surfaces, i.e., apoptosis. This dynamic cell surface membrane behavior appears to be dependent on the disruption of cytoplasmic microtubules. Concomitant with the altered cell surface morphology, certain physiological and biochemical events have been found to be associated with cell injury. These include changes in membrane permeability, elevated oxygen consumption rates and nuclear DNA fragmentation. However, it remains to be experimentally established which of …

The Classification Of Old World Anthidiini (Hymenoptera, Megachilidae), Charles D. Michener, Terry L. Griswold

Mi

No abstract provided.

Distribution Of Sodium, Magnesium, Chlorine, Calcium, Potassium, Phosphorus And Sulphur In Z-, I- And A-Bands In Mammalian Striated Muscle, Romuald Wróblewski, Lars Edström

Scanning Microscopy

The regularity of the striation of skeletal muscle offers a unique possibility to analyze different bands of the sarcomere in longitudinally cut semithin cryosections. The aim of the present study was to investigate the elemental content of the Z-, I- and A-bands within the sarcomere which may be related to the affinity of an element to different contractile elements and the water content in different bands. The highest potassium levels were found in the Z-band {802 mmol/kg dry weight (d.w.)} as compared to the I-band (697 mmol/kg d.w.) and the A-band (731 mmol/kg d.w.). The difference between A-band and Z-band, …