Analysis Of Surface Structures Research Articles

High-resolution observation of the growth motion of elements on surfaces and at interfaces

The results of high-resolution, real-space observations of the behaviors of elements on surfaces and at interfaces during growth of Ga on Si(111)-∛×∛-Ag are presented. Site exchange and surrounding other elements were directly observed using a high-resolution ultrahigh vacuum scanning electron microscope (SEM) newly combined with characteristic x-ray spectroscopy under a grazing detection-angle condition. Compared with the resolution of conventional SEM-energy dispersive x-ray spectrometry (several μm), resolution in elementary analysis has been significantly improved due to a small beam size and cut off of x-rays from deep regions, and local elementary analysis of surface structures of only about 10–20 nm in size is possible by the present method.

Improved electrotransformation frequencies of Corynebacterium glutamicum using cell-surface mutants

The electrotransformation efficiency for homologously- and heterologously-derived plasmid DNA was determined for two families of Corynebacterium glutamicum strains derived from ATCC13059 (AS019 and auxotrophic, cell surface mutants MLB133 and MLB194) and ATCC13032 (parent strain and restriction-minus mutants RM3 and RM4), following their growth in LBG supplemented with glycine plus isonicotinic acid hydrazide (INH). Electrotransformation efficiencies of MLB133 were up to 100-fold higher than for strain ASO19 and, when using heterologously-derived plasmid DNA, MLB133 showed efficiencies comparable to or better than strains RM3 and RM4, demonstrating the relative importance of cell surface structures in impeding DNA uptake in C. glutamicum. Transmission electron microscopy analysis of cell surface structures showed that strain MLB133 has a thin cell wall relative to AS019 and growth in either glycine or INH further diminished its thickness. Both RM3 and RM4 were more sensitive to INH than ATCC13032 and growth in glycine plus INH further improved transformation efficiency. The mycolic acid composition of these strains is described and the impact of glycine and INH on this is reported.

The crystallo-chemistry of oxide-humus complexes

Complexation of humic substances with goethite, hematite, gibbsite, and boehmite has been explained from a viewpoint of crystal structure of the minerals. Theoretical analysis of crystal surface structures revealed the following. (i) Residual charge carried by O or OH on surfaces of gibbsite is –1/2; on boehmite it is –3/2 or –1/2; on goethite it is –4/3, –2/3, or –1/3; and on hematite it is –3/2, –1, or –1/2. Cations adsorbed to neutralise these charges can form bridging links with humic acid; higher charges form stronger links. (ii) Surfaces of goethite, hematite, and gibbsite also contain octahedral sites in which one O/OH position is vacant. These may provide centres for the formation of strong coordination bonds. (iii) Such vacant octahedral positions are absent in boehmite. It follows that in gibbsite, cation bridging links would be weak and vacant octahedral sites would be the dominant bonding sites; in goethite and hematite, both cation bridging and surface coordination sites would be present; in boehmite, cation bridging would be the only strong bonding mode. Derivations from crystallochemical analysis are supported by experimental observations. Infrared studies also show strong OH involvement in boehmite complexation in contrast to the weakness of OH involvement in gibbsite complexes.

Analysis of surface structures through determination of their composition using STM: Si(100)4×3-In and Si(111)4×1-In reconstructions

The advantages of scanning tunneling microscopy for the determination of the composition of the submonolayer metal/silicon interfaces has been demonstrated using Si(100)4\ifmmode\times\else\texttimes\fi{}3-In and Si(111)4\ifmmode\times\else\texttimes\fi{}1-In as sample reconstructions. It has been found that the Si(100)4\ifmmode\times\else\texttimes\fi{}3-In unit cell is built of 7 In atoms and 6 Si atoms, while the Si(111)4\ifmmode\times\else\texttimes\fi{}1-In unit cell contains 3 In atoms and 2 Si atoms in addition to the top Si(111) bilayer. The obtained quantitative information provides the ground for discussion of the plausible atomic arrangement of these reconstructions.

Echelon approach to areas of concern in synoptic regional monitoring

Echelons provide an objective approach to prospecting for areas of potential concern in synoptic regional monitoring of a surface variable. Echelons can be regarded informally as stacked hill forms. The strategy is to identify regions of the surface which are elevated relative to surroundings (Relative ELEVATIONS or RELEVATIONS). These are areas which would continue to expand as islands with receding (virtual) floodwaters. Levels where islands would merge are critical elevations which delimit echelons in the vertical dimension. Families of echelons consist of surface sectors constituting separate islands for deeper waters that merge as water level declines. Pits which would hold water are disregarded in such a progression, but a complementary analysis of pits is obtained using the surface as a virtual mould to cast a counter-surface (bathymetric analysis). An echelon tree is a family tree of echelons with peaks as terminals and the lowest level as root. An echelon tree thus provides a dendrogram representation of surface topology which enables graph theoretic analysis and comparison of surface structures. Echelon top view maps show echelon cover sectors on the base plane. An echelon table summarizes characteristics of echelons as instances or cases of hill form surface structure. Determination of echelons requires only ordinal strength for the surface variable, and is thus appropriate for environmental indices as well as measurements. Since echelons are inherent in a surface rather than perceptual, they provide a basis for computer-intelligent understanding of surfaces. Echelons are given for broad-scale mammalian species richness in Pennsylvania.

An XPS Analysis of the Interface between SiOx Deposited Films and Polyethyleneterephthalate (PET) Films.

Polyethylenterephtarate (PET) films with deposited Al or SiOx thin films are utilized for a wide variety of package materials. The interfacial interaction between PET films and vapor deposited thin films was investigated using X-ray Photoelectron Spectroscopy (XPS). We studied some influences of the vapor deposition process on the surfaces of PET films, using commercial samples. In order to get the information at the interface between vapor deposited thin films and PET films, analysis of PET surface structures was carried out by breaking samples in the vicinity of the interface. The XPS data, the full width of half maximum (FWHM) of C-C bonding peaks and the changes in the peak area of functional groups obtained by means of peak separation, suggested that the surface structure of PET films was influenced by vapor deposition process, and Si-C bonding was formed at the interface.

Analysis of surface structures ofCladonia mitispodetia in historic and recent collections from Greenland

Field observations in Greenland combined with a scanning electron microscopical survey have revealed a hitherto undescribed correspondence in the distribution of a brownish colour and a crust-like surface structure formed by hyphae at exposed parts of the shoot tips of podetia of Cladonia mitis. A different brownish colour pattern is caused by fungal parasites. A comparable but less prominent colour-crust syndrome was observed on C. mitis from Denmark. The colour-crust syndrome is considered an unhealthy and damaged condition, and the light microscope reveals that areas with this syndrome mainly consist of the uncovered stereome devoid of the hyphal zone containing algal colonies. In a comparative study of podetia collected up to 105 years ago in Greenland, crust-like surface structures occur more frequently since the 1970s. Key words: Arctic lichen heath, Cladonia mitis, Greenland, podetial morphology, UV-B radiation.

X-ray-scattering analysis of surface structures produced by vapor-phase epitaxy of GaAs.

We have used in situ x-ray-scattering techniques to analyze surface reconstructions and ordered steps at various stages in the growth of GaAs by organometallic vapor-phase epitaxy. In contrast to an earlier report of a c(4\ifmmode\times\else\texttimes\fi{}4) reconstruction, our current measurements reveal a related structure with 1\ifmmode\times\else\texttimes\fi{}2 symmetry. The 1\ifmmode\times\else\texttimes\fi{}2 structure is a disordered form of the c(4\ifmmode\times\else\texttimes\fi{}4) reconstruction in which long-range correlations between dimer rows are preserved but dimer vacancies are located at random. Aside from reconstructions, ordered step structures were studied on samples with both high (2.2\ifmmode^\circ\else\textdegree\fi{}) and low (0.07\ifmmode^\circ\else\textdegree\fi{}) levels of miscut. Using Gaussian step-spacing distributions with widths of order the mean terrace size, a numerical model is used to reproduce measured truncation rod profiles in scans perpendicular to steps. We also use the model to follow the narrowing of the step-spacing distribution which occurs during growth. After the growth of several hundred angstroms of GaAs, truncation-rod profiles sharpen, accompanied by a shift in peak positions. The shift is due to an asymmetric weighting of the scattering from terraces of different widths: wide terraces make a greater contribution to the structure factor. For samples with a broadened distribution of step spacings, this effect results in a smaller peak splitting than that which would occur for an ideally miscut sample.

Optimization methods and their use in low-energy electron-diffraction calculations.

The speed of automatic optimization procedures used in surface structure determination by low-energy electron diffraction can be greatly enhanced by the use of linear approximations in the calculation of scattering amplitudes. It is shown how linear approximations can be used in the calculation of derivatives of intensities which are required in the least-squares optimization method. The derivatives with respect to structural and nonstructural parameters are calculated applying a combination of analytic and numerical methods in connection with approximations of the sum over lattice points in the angular momentum representation. Special cases for different structural and nonstructural parameters and simplifications for special geometries are discussed. The computational effort becomes nearly independent of the number of free parameters and enables the analysis of complex surface structures.

Mesh generation with adaptive finite element analysis

This paper deals with key aspects of the coupling of automatic mesh generation with adaptive analysis and shape optimisation of planar and surface structures. Adaptive analysis requires the design of nearly optimal meshes with varying element sizes to achieve a prescribed accuracy. In any shape optimisation process as the region to be discretised changes continuously and sometimes drastically, mesh generation should ideally take place without intervention by the analyst and without any excessive distortion of elements. To carry out these processes in a fully automatic and efficient manner a highly robust, versatile and flexible mesh generator is required. A brief introduction to the features of one such automatic mesh generator, based on the advancing front method, is described. Several examples are presented exploiting the potential of this mesh generator for adaptive analysis and shape optimisation. The integration of the mesh generation with these procedures well as some issues which required special attention.

Friction Gages for In-Situ Rock-Mass Deformability and Stress Measurements

The in-situ deformability of rocks and the state-of-stress must be known for the analysis and design of surface and underground structures. This paper presents a method for determining the in-situ deformability of rock-masses using friction gages. Friction gages utilize the friction between the gage and the rock surface for detecting the strain changes. The method involves impressing friction gages on two opposite quadrants of the borehole wall, then radially loading the other two quadrants over 45-deg contact with a self-equilibrating pair of forces of sufficient magnitude to initiate and propagate tensile fractures. While loading, the friction gages detect the tangential strains on the borehole wall before, during and after fracturing of the rock. From the linear portion of the tangential stress-strain data, the elastic properties of the rock can be determined using the appropriate relationships. Furthermore, from the failure and post-failure portions of the tangential stress-strain data the tensile strength of the rock-mass and the in-situ state-of-stress can also be estimated. The theoretical basis of the method, and the fabrication, calibration and testing of the friction gage system, are described. Furthermore, practical field applications of the method are given.

Costimulatory function of APCs

interesting recent review entitled The costimulatory function of antigen-presenting cells' (Immunol. Today, 11, 49-55) by C.T. Weaver and E.R. Unanue began with c dis- cussion of the costimulatory function of interleukin 1 (IL-1). I respect the authors' desire not to present oppos- ing views to aspects of their research. However, in this case I feel it is necess- ary to point out that there remains significant controversy about the existence of a membrane form of IL-1 ano, more importantly, about the use of short-term paraforma!dehyde treatment of cells for the analysis of functional cell surface structures in

Collapse load analysis of prestressed concrete surface structures with unbonded tendons by the finite element method

The middle surfaces of curved surface structures (shells) and the axes of the tendons embedded between the two surfaces of a shell are assumed to be analytically describable. Essential features of the mathematical formulation are the exact consideration of the geometric form of the middle surface of a given shell by means of thin-shell finite elements and of the axes of the tendons. Prestress losses occuring during the tensioning operation as well as changes of the prestress forces resulting from loads applied after prestressing are taken into account. For prestressed concrete (PC) surface structures (panels, slabs and shells) with unbonded tendons, determination of these changes of forces is difficult if friction between the tendon and the duct is considered. The basis of the theoretical investigation is a formulation of the principle of virtual work which is suitable for incremental-iterative analysis of PC surface structures by the finite element method (FEM). It contains the expression for the virtual work of forces exerted by the tendons on the remaining part of the surface structure, treated as a free body. Geometric nonlinearity is considered on the basis of Koiter's shell theory of small displacements and moderately large rotations. Physical nonlinearity is taken into account by means of appropriate constitutive equations for intact and cracked concrete, respectively, reinforcing steel and prestressing steel. The numerical investigation consists of collapse load analysis of a PC slab with unbonded tendons. It demonstrates the usefulness of the theoretical concept.

Validity of the kinematical approximation in transmission electron diffraction for the analysis of surface structures

Dynamical calculation of transmission electron diffraction (TED) intensities for Si(111)7×7 surface is done using the multislice method. The intensities of the superlattice reflections of the surface structure deviate little from those calculated by kinematical theory for incident beam directions avoiding strong excitation of the Bragg reflections of the bulk silicon crystal. The analyses show that the kinematical approximation can be used to determine the atomic arrangement of surface structures within a reliability factor of 10% when TEDs are taken with properly tilted incident beams.

Analysis of surface structures in nitrogen-containing polymer systems by ion scattering spectroscopy

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTAnalysis of surface structures in nitrogen-containing polymer systems by ion scattering spectroscopyKevin J. Hook, Joseph A. Gardella Jr., and Lawrence Salvati Jr.Cite this: Macromolecules 1987, 20, 9, 2112–2117Publication Date (Print):September 1, 1987Publication History Published online1 May 2002Published inissue 1 September 1987https://doi.org/10.1021/ma00175a011RIGHTS & PERMISSIONSArticle Views114Altmetric-Citations12LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (766 KB) Get e-Alerts Get e-Alerts

Lattice Gas Model Analysis of the (111) Surface Structures of Si, Ge and Related Systems. II. On the DAS Model

The interrelation among the (7×7), (5×5) and c(2×8) reconstructions of the (111) surface of Si, Ge and related systems is discussed by extending previous analysis of the lattice gas model on a triangular net to a multi-layer model to the purpose of analyzing the DAS structure of the (7×7) restruction of Si (111) surface proposed by Takayanagi et al. It is concluded that the stacking fault characterizing the DAS structure has a good reason to appear and that it can solve the difficulties encountered in the previous analysis concerning the stability of the (7×7) state and also that of the c(2×8) state of Ge(111) whose DAS like atomic configuration is newly proposed. The atomic configuration of the (1×1) disordered state at high temperatures is discussed also. The possibility of the floating phase discussed previously is reexamined thereby.

Lattice Gas Model Analysis of the (111) Surface Structures of Si, Ge and Related Systems

The interrelation among the (2×8), (2×7) and (5×5) reconstruction states of the (111) surface of pure Ge, Si and related systems is discussed on the basis of the previously proposed lattice gas model. It is pointed out that the model corresponds to the two dimensional ANNNI model if interaction parameters stabilize these states as the ground state. It is shown that the (7×7) and (5×5) states correspond to networks of the walls separating the regions of different spin directions and the (2×8) one to a parallel configuration of the walls. It is conjectured on the basis of this correspondence that the floating phase discussed by Villain and Bak may exist in a temperature range inbetween the (2×8) phase and the disordered one in the case of Ge(111). Relevant experimental data are discussed.

Analysis of ion-implanted surface and interface structures by computer-simulated backscattering spectra

Computer codes for synthesizing random and channeling backscattering spectra have been elaborated to characterize the surface and interface structures formed or modified by ion implantation. Both effects of isotopes and energy fluctuation are taken into account in the spectrum simulation. This backscattering measurement combined with the simulation method is applied to characterization of the N+-implanted Al films and to quantitative analysis of chemical reaction and interdiffusion induced by ion-beam mixing. An ion-beam-induced damage profile and its epitaxial recovery of crystallinity are analyzed by the simulation of channeling spectra from ion-implanted Al2O3 substrates.

Analysis of surface structures and of size and shape variations in ionitrided precipitation hardening stainless steel samples

The applicability of ionitriding process to the ASTM A564 Tp 630 steel is studied. The ionitriding treatment is carried out as a phase complementary to and contemporary with the precipitation hardening. Analyses of surface structures and of size and shape variations induced by the treatment are developed with reference to varied operating conditions and component geometries.

Determination of surface topography of biological specimens at high resolution by scanning tunnelling microscopy.

Although techniques are available for the determination of the three-dimensional structure of biological specimens, for example scanning electron microscopy, they all have some serious drawback, such as low resolution, the requirement for crystals or for the sample to be analysed in a high vacuum. In an attempt to develop a technique for high-resolution three-dimensional structure analysis of non-crystalline biological material, we have tested the applicability of scanning tunnelling microscopy (STM), a method that has been used successfully in the analysis of metal and semiconductor surface structures. We report here that scanning tunnelling electron microscopy can be used to determine the surface topography of biological specimens at atmospheric pressure and room temperature, giving a vertical resolution of the order of 1 A. Our results show that quantum mechanical tunnelling of electrons through biological material is possible provided that the specimen is deposited on a conducting surface.