Surface Crystallographic Orientation Research Articles

Influence of accuracy of crystallographic plane by specific crystallographic plane cutting of WEDM and post-processing of crystal surface contour

The influence of the accuracy of crystallographic plane is studied using specific crystallographic plane cutting of wire-cut electrical discharge machining (WEDM) and post-processing of crystal surface contour. First, the influence of crystallographic plane accuracy is analyzed using specific crystallographic plane cutting of WEDM. The WEDMed wafer-orientation precision is estimated using a single-point orientation error test combined with surface profile measurement. The influence of monocrystalline silicon surface outline after chemical corrosion and mechanical polishing on crystallographic orientation accuracy is examined using the same method. Results show that mechanical polishing and chemical etching only affect silicon wafer surface quality, whereas these processes have a minimal effect on silicon wafer surface contour and crystallographic orientation precision. The orientation precision of the silicon wafer surface is determined by WEDM and its contour, and subsequent processes have minimal influence on crystallographic orientation accuracy.

Influence of Si Surface Orientation on Screen-printed Ag/Al Contacts

In this study the influence of the crystallographic surface orientation of n-type Si wafers on the contact formation of Ag/Al thick film pastes to p+-type Si layers is investigated. Therefore, n-type Si wafers with two different crystallographic orientations, namely polished (111) and (100) FZ wafers, with BBr3 based emitter and 75 nm SiNx:H are screen-printed with Ag/Al paste. Then contacts are fired in either a slow firing process or a fast one with the same peak temperature. Afterwards, contacts are prepared for scanning electron microscopy (SEM) analysis. The Ag/Al contact spots show different shapes on the differently oriented surfaces. For the slow firing process, no significant difference in number and size of the contacts spots can be found for the two surfaces. For samples fired in the fast firing process, the density and size of the contact spots on (100)-oriented surfaces is strongly reduced, whereas for the (111) surfaces only a slight reduction in density is visible as compared to the slow firing process.

Heterogeneous Thermal Oxide Film Formed on Polycrystalline Pure Iron

The thermally-grown oxides formed on pure iron have characteristic composition, structure, and thickness, depending on the oxidation condition such as temperature and oxygen partial pressure. The crystallographic orientation of iron surface also affected the rate of thermal oxidation1. However, the heterogeneity on the thermal oxide film formed on polycrystalline iron has not been discussed sufficiently. In order to well understand the non-uniform oxidation that progresses on polycrystalline iron, it is important to elucidate the precise characteristics of the thermal oxide film from the viewpoint of crystallographic orientation. In this study, we investigated the heterogeneity of thermal oxide film formed on polycrystalline pure iron by using a 2D-ellipsometer and a micro-capillary-cell (MCC) method2. The sample specimen was an annealed iron plate with a purity of 99.99%. After mirror-like polishing, the surface orientations of the sample were identified by using an electron backscatter diffraction patterning. Subsequently, the sample was kept at 573 K in air for 3.6 ks to form thermal oxide film. The thickness of the oxide film on the surface was mapped with the 2D-ellipsometer. The characteristics of the oxide film formed on each single grain were evaluated by electrochemical impedance spectroscopy (EIS) by means of an MCC with an inner diameter of 180 µm. The sample surface as polished was smooth like a mirror showing metallic luster. After thermal oxidation, however, it showed various colors, depending on the surface metallographic structure due to interference of light. The colors of the sample surface indicated that the thermal oxides grew at different rate depending on the surface orientation of single grains on the substrate. The non-uniform oxide formation on the polycrystalline iron was also confirmed by two-dimensional thickness mapping with the ellipsometer. EIS measurements showed that the electric resistance and capacitive behavior of the oxide films were depended on the orientation of substrate surface. Furthermore, the results of Mott-Schottky analysis implied that the surface orientation affected the defect structure of the thermal oxides. It was considered that the grain-dependency on the thermal oxide film was originated in anisotropic growth of the oxide determined by the crystallographic orientation of the substrate iron surface. The detailed consideration of the grain-dependency on the oxide film is discussed on site.

Three-dimensional reciprocal space mapping with a two-dimensional detector as a low-latency tool for investigating the influence of growth parameters on defects in semipolar GaN

A rapid nondestructive defect assessment and quantification method based on X-ray diffraction and three-dimensional reciprocal-space mapping has been established. A fast read-out two-dimensional detector with a high dynamic range of 20 bits, in combination with a powerful data analysis software package, is set up to provide fast feedback to crystal growers with the goal of supporting the development of reduced defect density GaN growth techniques. This would contribute strongly to the improvement of the crystal quality of epitaxial structures and therefore of optoelectronic properties. The method of normalized three-dimensional reciprocal-space mapping is found to be a reliable tool which shows clearly the influence of the parameters of the metal–organic vapour phase epitaxial and hydride vapour phase epitaxial (HVPE) growth methods on the extent of the diffuse scattering streak. This method enables determination of the basal stacking faults and an exploration of the presence of other types of defect such as partial dislocations and prismatic stacking faults. Three-dimensional reciprocal-space mapping is specifically used in the manuscript to determine basal stacking faults quantitatively and to discuss the presence of partial dislocations. This newly developed method has been applied to semipolar GaN structures grown on patterned sapphire substrates (PSSs). The fitting of the diffuse scattering intensity profiles along the stacking fault streaks with simulations based on a Monte Carlo approach has delivered an accurate determination of the basal plane stacking fault density. Three-dimensional reciprocal-space mapping is shown to be a method sensitive to the influence of crystallographic surface orientation on basal stacking fault densities during investigation of semipolar (11{\overline 2}2) GaN grown on an r-plane (1{\overline 1}02) PSS and semipolar (10{\overline 1}1) GaN grown on an n-plane (11{\overline 2}3) PSS. Moreover, the influence of HVPE overgrowth at reduced temperature on the quality of semipolar (11{\overline 2}2) GaN has been studied.

Voltammetric Scanning Electrochemical Cell Microscopy: Dynamic Imaging of Hydrazine Electro-oxidation on Platinum Electrodes.

Voltammetric scanning electrochemical cell microscopy (SECCM) incorporates cyclic voltammetry measurements in the SECCM imaging protocol, by recording electrochemical currents in a wide potential window at each pixel in a map. This provides much more information compared to traditional fixed potential imaging. Data can be represented as movies (hundreds of frames) of current (over a surface region) at a series of potentials and are highly revealing of subtle variations in electrode activity. Furthermore, by combining SECCM data with other forms of microscopy, e.g. scanning electron microscopy and electron backscatter diffraction data, it is possible to directly relate the current-voltage characteristics to spatial position and surface structure. In this work we use a "hopping mode", where the SECCM pipet probe is translated toward the surface at a series of positions until meniscus contact. Small amounts of residue left on the surface, upon probe retraction, demark the precise area of each measurement. We use these techniques to study hydrazine oxidation on a polycrystalline platinum substrate both in air and in a deaerated environment. In both cases, the detected faradaic current shows a structural dependence on the surface crystallographic orientation. Significantly, in the presence of oxygen (aerated solution) the electrochemical current decreases strongly for almost all grains (crystallographic orientations). The results highlight the flexibility of voltammetric SECCM for electrochemical imaging and present important implications for hydrazine electroanalysis.

Particle size and crystallographic orientation controlled electrodeposition of platinum nanoparticles on carbon nanotubes

Platinum-coated carbon nanotubes (Pt/CNTs) with desired particle size and preferred surface crystallographic orientations have a variety of applications in diverse fields. Pt/CNTs having uniform dispersion of Pt nanoparticles are synthesized via electrodeposition route using CNT coated carbon fiber as the working electrode and H2PtCl6.6H2O as Pt precursor. Particle size and crystallographic orientation of Pt nanoparticles are controlled by using polyvinylpyrrolidone (PVP) as the protecting agent during electrodeposition in H2SO4 or HCl containing coating baths. Cyclic voltammetric study and X-ray diffraction analysis suggest Pt(100) surface enrichment of Pt nanoparticles in presence of PVP, which increases with increasing PVP concentration. Although the Pt deposition rate decreases significantly in presence of Cl− ions, the enrichment effect is observed both in the H2SO4 as well as the HCl containing baths. The Pt/CNT synthesized in presence of PVP exhibit higher oxygen reduction reaction activity (acidic media) and methanol oxidation activity compared to that synthesized without PVP. The process may be utilized to synthesize Pt based electrocatalysts with controlled particle size and preferred surface orientation.

Influence of surface structure on single or mixed component self-assembled monolayers via in situ spectroelectrochemical fluorescence imaging of the complete stereographic triangle on a single crystal Au bead electrode.

The use of a single crystal gold bead electrode is demonstrated for characterization of self-assembled monolayers (SAM)s formed on the bead surface expressing a complete set of face centered cubic (fcc) surface structures represented by a stereographic projection. Simultaneous analysis of many crystallographic orientations was accomplished through the use of an in situ fluorescence microscopic imaging technique coupled with electrochemical measurements. SAMs were prepared from different classes of molecules, which were modified with a fluorescent tag enabling characterization of the influence of electrical potential and a direct comparison of the influence of surface structure on SAMs adsorbed onto low index, vicinal and chiral surfaces. The assembly of alkylthiol, Aib peptide and DNA SAMs are studied as a function of the electrical potential of the interface revealing how the organization of these SAMs depend on the surface crystallographic orientation, all in one measurement. This approach allows for a simultaneous determination of SAMs assembled onto an electrode surface onto which the whole fcc stereographic triangle can be mapped, revealing the influence of intermolecular interactions as well as the atomic arrangement of the substrate. Moreover, this method enables study of the influence of the Au surface atom arrangement on SAMs that were created and analyzed, both under identical conditions, something that can be challenging for the typical studies of this kind using individual gold single crystal electrodes. Also demonstrated is the analysis of a SAM containing two components prepared using thiol exchange. The two component SAM shows remarkable differences in the surface coverage, which strongly depends on the surface crystallography enabling estimates of the thiol exchange energetics. In addition, these electrode surfaces enable studies of molecular adsorption onto the symmetry related chiral surfaces since more than one stereographic triangle can be imaged at the same time. The ability to observe a SAM modified surface that contains many complete fcc stereographic triangles will facilitate the study of the single and multicomponent SAMs, identifying interesting surfaces for further analysis.

Properties of Ni/Nano-TiO2 Composite Coatings Prepared by Direct and Pulse Current Electroplating

Pure nickel and nickel matrix composite coatings containing nano-TiO2 particles were produced under both direct and pulse current conditions from an additive-free nickel Watts’ type bath. The surface morphology, crystal size, crystallographic orientation, and microhardness of nickel matrix and the amount of embedded nano-TiO2 particles in the composite coatings were investigated. The corrosion performance of the coatings was investigated by potentiodynamic polarization and electrochemical impedance spectroscopy methods. The TiO2 particles embedded in the nickel matrix exerted strong influence on the texture of the growing nickel layer, changing its texture under both direct and pulse current conditions. The textural perfection of the deposits revealed that the presence of TiO2 particles led to the deteriorating of [100] preferred orientation. Under direct current conditions, the composite coating exhibited clearly [211] fiber orientation, while pulse current working exhibited a mixed crystal orientation through [100] and [211] axes. It is concluded that in the presence of TiO2 nanoparticles, the adsorption-desorption phenomena occurring on the metal surface are altered. The experimental results show that composite electrodeposits prepared under pulse plating conditions exhibited higher incorporation percentages than those obtained under direct plating conditions, at particularly 10 Hz and low duty cycles. The results revealed that pulse-plated Ni/TiO2 nanocomposite coating provided excellent anti-corrosion performance and presented higher microhardness.

Properties of atmospheric pressure plasma oxidized layers on silicon wafers

Abstract In this research a new process of plasma oxidation of crystalline silicon at room temperature is studied. The plasma oxidation was carried out using Diffuse Coplanar Surface Barrier Discharge (DCSBD) operating in ambient air and oxygen at atmospheric pressure. The influence of exposition time, plasma parameters and crystallographic orientation of silicon on oxidized layers and their dielectric properties were investigated. Thickness, structure and morphology of these layers were studied by ellipsometry, infrared absorption spectroscopy and scanning electron microscopy. During the treatment time, from 1 to 30 minutes, oxidized layers were obtained with thickness from 1 to 10 nm. Their roughness depends on the crystallographic orientation of silicon surface and exposure time. Electrical parameters of the prepared layers indicate the presence of an intermediate layer between silicon substrate and the oxidized layer.

The dependency of diamond lapping surface morphology on crystal orientation

In mechanical lapping, diamond exhibits a highly anisotropic tribological behavior. The dependency of wear rate on crystal orientation has long been noticed by diamond polishers. However, in the diamond manufacturing, the surface quality is another side in need of attention. In this paper, the relationship between surface morphology and crystallographic orientation under a certain lapping condition was examined. It is found that a fine surface can still be obtained at the directions that deviate a lot from the “soft” directions (near crystal direction for {110} surface). But, with respect to the “hard” directions (near crystal direction for {110} surface), a bad surface finish with a fracture appears. This result comes down to two aspects. First, on {110} surface, as the lapping direction from the (soft direction) approaches (hard direction) the phase change of diamond carbon atoms gets more difficult, which causes the depth of the amorphization layer becomes thinner. Second, the energy required by diamond amorphization is lower than that by surface fracture around the soft direction, while near the hard direction, the contrary is the case. Our work provides a further understanding of the diamond tribological properties.

Surface energy and work function of fcc and bcc crystals: Density functional study

The surface energies and work functions for six close-packed surfaces of 19 common fcc and bcc metals in the periodic table have been systematically calculated by means of the density functional theory (DFT) method. The accuracy of the results is established in comparison with the experimental and other theoretical values. The variations of work functions with the surface crystallographic orientation display a good regularity. For alkali metals, the work functions follow the sequence Φ(110)>Φ(133)>Φ(311)>Φ(120)>Φ(100)>Φ(111). But for the same crystal structure of bcc transition metals (Nb, Mo, Ta, W), the order is Φ(110)>Φ(133)>Φ(120)>Φ(111)>Φ(311)>Φ(100). The work functions for 3d, 4d and 5d transition fcc metals also display an obvious regularity and ordered as Φ(111)>Φ(100)>Φ(211)>Φ(123)>Φ(310)>Φ(110). Particular attention is paid to the surface energies anisotropy with the same crystal structure metals and the variations present a good regularity, too. Especially, a roughly inverse proportional relationship between the surface energy and work function is found.

Modification of (111) and (100) silicon in atmospheric pressure plasma

In this paper the effect of plasma treatment in dependence of the different crystallographic orientation of silicon surface, (1 0 0) plane and (1 1 1) plane is studied. Plasma treatment was realized in atmospheric pressure plasma generated by diffuse coplanar surface barrier discharge in ambient air. The changes of surface morphology, wettability and chemical structure were investigated by means of the AFM measurement, contact angle measurement and XPS, respectively. It was proved that plasma roughening of c-Si depends on the crystallographic orientation. The wettability of c-Si after plasma treatment was improved independently on the orientation however oxidation of Si surface was also observed.

Hydrogen absorption in Pd thin-films

Hydrogen absorption isotherms for Pd thin films were modeled at atomistic scale by Monte Carlo (MC) simulation in the TPμN ensamble and by Molecular Dynamics (MD) simulations at 300 K. The interaction among atoms was modeled by embedded atom method (EAM) potentials. Simulated samples consisted of monocrystalline nanofilms with different thickness (2–8 nm) and two crystallographic surface orientations, (001) and (111). The isotherms were compared to bulk Pd and a few available experimental results. Instead of the plateau corresponding to the α-β PdH equilibrium in the bulk, the isotherms at nano-films show a two-plateaux behavior: a small one corresponding to a surface–subsurface hydride formation, and a larger one for the subsequent bulk hydride formation. This is strongly correlated with the atomic stress distribution induced within the thin film. The equilibrium pressures at the isotherms depend on the thin-film thickness, with pressure being larger for thicker films. The isotherms of the (001) films display lower equilibrium pressures than those for (111) films.

Influence of cetyltrimethylammonium bromide and sodium lauryl sulfate on production of zinc powders by alkaline electrowinning

The effects of cetyltrimethylammonium bromide (CTABr) and sodium lauryl sulfate (SLS) on the current efficiency, cell voltage, voltammetric behavior, and deposit character during production of zinc powder by alkaline electrowinning were investigated. Surface morphologies, crystallographic orientations, and grain size distributions of zinc powders were examined by Scanning Electron Microscopy, X-ray Diffraction, and Malvern Laser Particle Size Analyzer, respectively. Maximum current efficiencies of 97.5 and 98.3% were obtained at 1 mg/L CTABr and 10 mg/L SLS, respectively. Voltammetric studies indicated that the surfactants polarized the cathode, which was reflected in powder character. The surfactants dramatically changed the surface morphology and decreased the grain size. Zinc powders with an average grain size of 34.7 μm were obtained in the presence of 10 mg L−1 CTABr. At 0–10 mg L−1 CTABr/SLS, zinc powders exhibited an orientation dominated by (101) (002) (100). 1 mg L−1 SLS hadapositive effect on counteracting the influence of Sb.

Effect of solution concentration on surface morphology and photocatalytic activity of ZnO thin films synthesized by hydrothermal methods

ZnO thin films were synthesized via hydrothermal method on silicon substrate at various solution concentrations. The thin films were characterized by X-ray diffraction, field-emission scanning electron microscope and UV–Vis spectrophotometer. The results show that the thin films are polycrystalline with wurtzite hexagonal structure. The Tc values of (101) surface of the thin film increase from 0.929 to 1.840 at first, and then decrease to 0.779 with increasing solution concentration. The preferential orientation along the (101) crystal surface can be controlled by changing the solution concentration. Solution concentration has a significant effect on surface morphology of the thin films. The optical band gap of the thin films decreases, when the solution concentration of zinc nitrate hexahydrate increases from 0.01 to 0.06 mol/L and then increases when the solution concentration of zinc nitrate hexahydrate further increases to 0.08 mol/L. Photocatalytic activity of the thin films on degradation of methyl orange under UV light irradiation was studied in detail. The ZnO thin film with many cracks prepared from 0.01 mol/L shows the higher photocatalytic activity but the tower-like ZnO thin film prepared from 0.08 mol/L reveals the lower photocatalytic activity. Therefore, the photocatalytic activity of the thin films are mainly relate to surface morphology and crystallographic orientation.

Regular arrays of triangular‐microstructure formed on silicon (111) surface via ultrafast laser irradiation in KOH solution

The regular micrometer‐scale triangular arrays were formed using ultrafast femtosecond laser irradiation on (111) surface of silicon wafer immersed in KOH solution (0.1 g/ml). At low laser fluence, the resulting surface is covered by triangular pits microstructures, whereas at high laser fluence, the structures are transformed to multilayer‐triangular stacks‐microstructures. The number of triangular stacks layer increased as the laser fluence increased. The formation of triangle microstructure arrays depends on both silicon surface crystallographic orientation and the concentration of KOH solution. Either for lower KOH solution concentration (0.02 g/ml) or other silicon crystallographic orientation, triangle arrays cannot be obtained. We attribute the formation of triangular microstructure arrays to the laser‐assisted chemical etching process. Copyright © 2013 John Wiley & Sons, Ltd.

Effects of crystal orientation on the dissolution of calcite by chemical and microscopic analysis

The purpose of this work was to examine the effects of polished crystal-surface orientation and degree of solution undersaturation on the dissolution kinetics of calcite. Crystallographic surface orientations utilized in this study included natural calcite specimens polished approximately parallel to the (104) plane, giving rise to surfaces with flat terraces with few steps, as well as fully kinked surfaces created by sectioning approximately parallel to the (001) plane. Results from inductively coupled plasma optical emission spectroscopy (ICP-OES) and vertical scanning interferometry (VSI) investigations revealed how crystallographic orientations of calcite with initially higher energy surface morphologies were associated with greater extent of reaction, greater surface retreat, and therefore, greater initial transient dissolution rates than those with lower energy initial surface morphologies. However, both the ICP-OES and atomic force microscopy (AFM) results confirm that the effects of crystal orientation become minimal under long-term conditions because (1) variously oriented calcite surfaces exhibited similar “long-term” rates and (2) orientations with high initial reactive site densities developed lower energy morphologies. Estimating a step rate coefficient from the experimental data from a miscut sample suggest that these coefficients may be highly morphology dependent. Results from this study are significant for predicting long term calcite dissolution rates because they suggest that the “long-term” dissolution rate of calcite will be governed by the rates of the rhombohedral faces and microfacets and the time-scale for approaching such conditions is of the order of days at room temperature and slightly alkaline solution conditions.

Controlled Rotation and Collection of Electron Backscattered Diffraction Patterns from Complex Test Samples

Abstract This article discusses the development and use of a nondestructive evaluation (NDE) method that allows researchers to compare surface crystallographic orientations before and after mechanical testing to determine the impact of surface orientation on material response. Two gage samples were tested, one rectangular (Ti-Al), the other round (IN100). The samples were placed in a SEM equipped with an EBSD detector and a motorized fixture that rotates the test piece as EBSD and imaging data are collected. Inverse pole figure maps of both gage samples are presented.

Current-driven morphological evolution of single-layer epitaxial islands on crystalline substrates

We develop and validate a nonlinear model for the current-driven dynamics of single-layer epitaxial islands on crystalline substrates. Simulations based on the model show that the dependence of the stable steady island migration speed vm on the inverse of the island size is not linear for larger-than-critical island sizes. In this nonlinear regime, we report morphological transitions, Hopf bifurcations, and instabilities for various surface crystallographic orientations and island misfit strains. Proper rescaling of vm gives a universal linear relationship for its dependence on island size.

Self cleaning behaviour of Ni/nano-TiO2 metal matrix composites

Titanium dioxide (TiO2) nano-particles were immobilized in nickel matrix coatings using the direct current electrodeposition technique. The influence of nickel surface morphology and crystallographic orientation on the photocatalytic activity and photo-induced hydrophilicity of the composite coatings were investigated under UVA illumination. The overall self-cleaning character of the composites was improved following the titania codeposition, as both hydrophilic and photocatalytic effects are present. Simultaneous optimization of the two functionalities was possible via tuning the titania percentage, indicating that the corresponding properties of the composite coatings are associated also to the induced crystalline nickel orientation and the nickel grain size. In particular, the data indicate that both enhanced photocatalytic activity and photo-induced hydrophilicity are achieved by increasing amounts of titania nano-particles embedded in the Ni matrix in combination with reduced grain size of nickel crystallites that are oriented towards the [110] axis.