Surface Crystallographic Orientation Research Articles

Electron-Beam Exposure(EBE) and Epitaxy of GaAs Films on CaF2/Si Structures

A novel heteroepitaxial method (electron-beam exposure and epitaxy: EBE-epitaxy) has been developed for growing GaAs films on top of CaF2/Si(111) structures. In this method, the surface of CaF2 films is modified by an electron beam (e-beam) under arsenic impingement prior to the growth of GaAs films. It has been found that this EBE-epitaxy is very effective in improving the quality of the GaAs films such as surface morphology, crystallinity and crystallographic orientation. The principal effects in the EBE-epitaxy to improve the crystalline quality are considered based on these experimental results to derive a model of the growth mechanism. Other effects, such as electron energy dependence, substrate temperature dependence during e-beam exposure and GaAs growth temperature dependence, are also investigated systematically. Subsequently, the growth condition for an ideal EBE-epitaxy is discussed.

Influence of the crystallographic orientation of the surface on the potential of zero charge of silver electrodes

The variation of the potential of zero charge of silver electrodes with the crystallographic orientation of the metal surface was determined for 13 faces of low and high indices. The possible interference of the reaction of electrolytic hydrogen evolution (thermodynamically possible in the range of potential where zero charge potentials are measured) with the precise determination of the values of the zero charge potential and its influence on the shape of the capacity potential curves are discussed. The variation of the potential of zero charge with the crystallographic orientation is found to parallel that of the surface energy.

Orientation dependent adsorption of oxygen on a cylindrical Ge sample

The dependence of oxygen adsorption on the crystallographic surface orientation was studied on a cylindrical Ge sample with [1 10] as cylinder axis by Auger electron and photoelectron spectroscopy. At 300–340 K, adsorption is slowest at (110), (111) and (113) and increases in the vicinity of these orientations due to step-enhanced adsorption. At 650 K, adsorption is faster, especially at (111). The analysis of chemical shifts associated with the Ge 3d emission on six orientations yields discrete shifts towards higher binding energy for Ge atoms with 1, 2 or 3 oxygen ligands (Ge 1+, Ge 2+, Ge 3+). At 340 K, the Ge 1+ and Ge 2+ components have similar intensities. Their average positions are at about −0.7 and −1.7 eV with respect to the bulk emission (towards higher binding energy). At 650 K, The Ge 2+ component becomes more prominent, corresponding to the formation of predominantly GeO. Surprisingly, the positions of Ge 1+ and Ge 2+ become strongly orientation dependent, varying between −0.56 eV (331) and −1.17 eV (001) for Ge 1+ and −1.72 eV (331) and −2.03 eV (001) for Ge 2+. Also a weak Ge 3+ component at about −2.8 eV but no Ge 4+ component was observed. A shift of the O 2s orbital from −21.9 to −22.4 eV is observed when going from predominantly adsorbed oxygen to a GeO-like configuration.

単結晶ＣＢＮ工具による鉄系材料の精密切削

Mirror-like cutting of ferreous metals with CBN cutting tools is discussed experimentally in this paper. For the purpose of the mirror-like cutting, single crystal CBN cutting tools are developed. The wearing test of the single crystal CBN is carried out to ascertain the optimum crystallographic orientation of flank surface. The wear resistance in direction on (111) plane is the largest, so the (111) plane is chosen as the flank surface for single crystal CBN tools, and direction on (111) plane as the cutting direction on the flank surface. The polished flank surface roughness of 0.005-0.008 μmRmax can be obtained using fine diamond grinding wheel whose working surface roughness is kept within 1 μmRmax. Using this single crystal CBN cutting tool, machined surface roughness of less than 0.05 μmRmax has been achieved for hardened stainless steel (HRC 52). Although the tool lives in single crystal CBN tools have not been sufficient (about 200 m cutting length), the use of the new tools expected in a drastic reduction of the polishing time for the hardened stainless steel mold dies.

Changes in real surface area, crystallographic orientation and morphology of platinum electrodes caused by periodic potential treatments: phenomenological approach

Abstract The changes in surface structure of polyfaceted single crystal platinum spheres subjected to repetitive square-wave potential treatments in acid solution have been studied. The dependence of the prevailing type of change on symmetry, potential limits and frequency of the periodic potential has been determined. Results are discussed on the basis of different reactions occurring within definite potential windows and distinct rate controlling processes depending on the operating conditions. Accordingly, the surface restructuring involves a predominant change in either the real surface area, the crystallographic orientation or the entire surface morphology.

Effect of indenter shape and surface crystallographic orientation on frictional plastic flow and fracture in α-SiC

The effect of indenter shape on track morphology and debris shape on the (0001) surface is considered while the significant difference in the subsurface dislocation arrangement occurring between tests conducted on the (0001) and {10 1 0} surfaces is reported. For tests conducted on the (0001) surface, b = 〈2 1 10〉 dislocations on the (0001) plane dominate the flow while tests on the {10 1 0} plane, split dislocations according to the reaction of the type 1 3 〈2 1 10〉 = 1 3 〈1 100〉 + 1 3 〈10 10〉 dominate.

Effect of surface crystallographic orientation upon specific adsorption of azide at silver electrodes as examined by potential-difference infrared spectroscopy

The specific adsorption of azide anions on the three low-index faces of silver, having (111), (100), and (110) orientations, has been studied by means of potential-difference infrared spectroscopy using an FTIR spectrometer in order to examine the influence of surface crystallography upon the adsorbate binding. Bipolar infrared spectra were obtained in the 2050–2100 cm −1 region, with a negative-going (i.e., decreased transmittance) feature, v a (sur), at 2075–2100 cm −1 due to the asymmetric N-N-N vibration for adsorbed azide, and its positive-going band partner, v a (sol), at 2048 cm −1 arising from the corresponding loss of an equal amount of solution azide in the thin-layer cavity brought about by the positive alteration in electrode potential. Information on the adsorbate structure was obtained from the relative intensities, I sur and I sol, as well as frequencies, of v a(sur) and v a(sol). For the Ag (111) and (100) faces, I sur⪡ I sol small azide surface concentrations (Γ ⩽ 4×10 −10 mol cm −2), whereas I sur≈ I sol at higher coverages. These findings are interpreted in terms of the surface infrared selection rule as indicting a prominence of “flat” and “vertical” orientations, respectively, of adsorbed azide under these conditions; the presence of the latter, end-on bonded, form is also consistent with the observed v a(sur) frequencies. In contrast, for the Ag (110) face, I sur⪡ I sol over the entire accessible coverage range (up to Γ ≈ 1×10 −9 mol cm −2, indicating that a flat azide orientation is especially favored at this surface. This is attributed to the adsorption of the linear N 3 − ions along the atomic-scale “furrows” which characterize the (110) face. Polycrystalline silver exhibited spectral behavior that is in some respects intermediate between that observed for the low-index single-crystal faces. Comparisons are also made between the surface infrared results and corresponding capacitance-potential data.

Observation of Surface Micro-Structures by Micro-Probe Reflection High-Energy Electron Diffraction

A new micro-probe reflection high-energy electron diffraction technique has been developed for observing micro-structures on crystal surfaces. In this technique, an electron beam of diameter 20 nm at a beam current of 8 nA and a beam angular divergence of 2 mrad has been achieved by using a field emission gun, making it possible to obtain bright, sharp diffraction patterns from surface micro-areas. A diffraction spot on a fluorescent screen is focused on an apperture by an optical lens; and part of the intensity is used as a signal to produce a scanning electron microscope image. This image is very sensitive to changes in surface crystallographic orientation, and can show areas in which the orientation change is of the order of 0.1 mrad. When the technique was used to observe Si(111) surfaces and metal-deposited Si(111) surfaces, image contrasts caused by screw dislocations, atomic steps and domain structures on the surfaces were obtained.

Underpotential deposition of lead on single crystal faces of gold Part I. The influence of crystallographic orientation of the substrate

The influence of the crystallographic orientation of the gold substrate surface on lead deposition and removal in the underpotential region is studied in detail. In order to observe systematic changes in the cyclic voltammograms, the faces of the three main zones of the unit projected stereographic triangle are grouped into five sections following bond order notation or a notation based on the TLK model of the surfaces. Correlations with the potential of zero charge are discussed. A comparison with ionic adsorption is made.

Underpotential deposition of lead on single crystal faces of gold: Part I. The influence of crystallographic orientation of the substrate

The influence of the crystallographic orientation of the gold substrate surface on lead deposition and removal in the underpotential region is studied in detail. In order to observe systematic changes in the cyclic voltammograms, the faces of the three main zones of the unit projected stereographic triangle are grouped into five sections following bond order notation or a notation based on the TLK model of the surfaces. Correlations with the potential of zero charge are discussed. A comparison with ionic adsorption is made.

The crystallographic orientation of gold surfaces at the gold-aqueous solution interphases

In order to gain further understanding of the capacity-potential curves observed at the single crystal gold-aqueous solution interphases, the five faces (100), (110), (111), (311) and (210) which should have extreme electrochemical behaviour are discussed. Correlations are established between hysteresis, of C(E) curves and current peaks. A surface reconstruction exists for the three faces of lowest indices, as is observed in ultra-high vacuum (UHV) for 5d metals. The behaviour of the (311) and (210) faces is analysed. The results obtained for each face form a sequence dependent on the adsorbability of the anions. The explanation given in this paper for secondary phenomena observed on C(E) curves for gold faces, coordinates the results obtained.

Formation and characterization of catalytic carbons obtained from co disproportionation over an iron nickel catalyst—II: Characterization

The metal-carbon composites obtained by CO disproportionation (2 CO→ CO 2 + C) over an iron-nickel (containing 75 Wt%Ni) are characterized by T.E.M., X-ray diffraction and krypton adsorption at 77 K. Besides the now well known carbon filaments, two other types of morphology are described and the experimental conditions of their formation determined: the bitubes and bifilaments as low temperature products and carbon shells as high temperature products. X-Ray diffraction studies show that the structure of the alloy is not modified by fragmentation and deposition and that the d 00.2 spacing is about 3.42 Å when formed below 500°C and about 3.38 Å when formed above 500°C. Krypton isotherms confirm that the mean size of the carbon particles increases with temperature of their formation. The filamentous-shell morphology transition suggests that a change in the mechanism of metal fragmentation occurs around 500°C which is also observed in the deposition kinetics. Finally we propose two semi quantitative index numbers for characterization of the crystallographic orientation of surfaces, the two numbers being derived from the shape of krypton adsorption isotherms.

The cracking of zinc spangles on hot-dipped galvanized steel

The cracking of zinc spangles on hot dipped galvanized sheet steel was studied under controlled conditions. It was confirmed that there are two major modes of failure—boundary cracking and intragranular basal cleavage. There are four types of surface topographiesviz “mirror-like”, “feathery”, “dimpled” and “ridged”. Of these only the last type, “ridged”, was found to have its basal planes lying at an angle to the plane of the sheet. These spangles also tended to fracture most readily when strained. Hence a relationship between surface topography, crystallographic orientation and fracture behavior has been established. The implications of these findings for paint adherence is discussed.

Structural investigations of metal adsorbates on single crystal surfaces using reflectance spectroscopy

We determined the relative reflectance change. ΔR R , for various adsorbates on single crystal surfaces of Pt and Ag as a function of coverage. The measurements were done with linearly polarized light at normal-incidence where any anisotropy in the optical response of adsorbate covered surfaces is easily detected by rotating the electric vector of the probing light with respect to the surface crystallographic orientation. The anisotropy in ΔR R for adsorbates such as H, Cu and Pb on Pt(110) and Pb on Ag(110) is shown and discussed as well as compared with systems where such effects are not observed.

Surface composition and surface cluster size distribution of Cu-Ni alloys via a monte carlo method

A Monte Carlo simulation of the Cu-Ni alloy surface was performed in order to determine surface composition and surface atom arrangement as a function of bulk composition, surface crystallographic orientation and temperature. The highly surface active nature of copper demonstrated in previous studies was confirmed, and surface nickel atom arrangement was shown to be a sensitive function of first-layer composition and of crystallographic orientation. Configurational energies were computed in a manner which accounted for the variation of atom-atom bond energies with coordination number. The effect of this method of computation on first-layer composition and composition profile was shown to be significant. Based upon the computed composition profile, an estimate of “surface” composition as it would be determined by Auger electron spectroscopy was made and was shown to be in reasonable agreement with published experimental results.

Crystallography of epitaxially grown molybdenum on sapphire

Molybdenum thin films were deposited onto (0001), ( 1012 ) and (10 12 ) sapphire substrates by electron-beam evaporation in ultrahigh vacuum. The surface morphology and crystallographic orientation of these films were characterized by electron microscope replication and reflection electron diffraction. The effect of the crystallographic plane of the sapphire substrates as well as that of the deposition rate on the crystallographic orientation of the deposited molybdenum films were examined in the temperature range 25°-1000°C. The epitaxial temperature range was 600°-900°C for basal plane substrates and 300°-1000°C for ( 1 012) and (10 1 2) substrates. The orientation of the deposited film was strongly dependent on that of the sapphire substrate.

A method of orienting hexagonal crystal surfaces from surface trace observations

Manual methods employing the Wulff net and stereographic projections are used to determine the crystallographic orientation of hexagonal crystal or grain surfaces from observations of traces of crystallographic planes. Equations are developed which enable such determinations to be carried out easily and precisely with computers for many kinds and combinations of traces observed. A method of this nature should reduce considerably the labour in the single-surface trace analysis of hexagonal crystals or grains.

The influence of sound waves on the growth of zinc single crystals

Abstract The growth of zinc single crystals (purity 99.993%) in sonic and ultrasonic fields of 0.1 to 50 watts/cm2 was studied at frequencies within the range of 100 to 25 000 cycles per second using a modified Czochralski technique. Changes in surface roughness, crystallographic orientation and critical shear stress appeared, depending upon the intensity of the applied sound field. An attempt is made to discuss the results on the basis of concepts that involve the influence of sound on the conditions of vacancy supersaturation during cooling of the crystal, and the formation of dislocation networks during homogenization behind the solid-liquid interface.

An Electromechanical Effect in Semiconductors

The resistance of semiconducting crystals to indentation deformation has been found to be lowered significantly (up to 60%) by the simultaneous presence of a small potential (0.05 to 10 V) between the indenter and the crystal surface. This electromechanical effect appears to be confined to the plastic strain region of a surface layer of material 2–3 μ deep. A large body of experiments of varied nature have established that the effect is real and not spurious. Similar effects are observed in a number of different semiconductors (Ge, Si, InSb and SiC) but not in metals or ionic crystals. The effect disappears at elevated temperatures but becomes enhanced below room temperature. It is not sensitive to the type of current carrier. The roles of surface preparation, crystallographic orientation, kind and concentration of charge carrier, geometry, and time have also been examined. Other and possibly related experiments show significant enhancement of the surface photovoltage (the Dember potential) by a longitudinal electric field. All of these experiments are extensively documented and discussed but no satisfactory model or mechanism has yet been conceived.