Surface Crystallographic Orientation Research Articles

Surface Structure Spread Single Crystals (S4C): Preparation and characterization

A set of six spherically curved Cu single crystals referred to as Surface Structure Spread Single Crystals (S4Cs) has been prepared in such a way that their exposed surfaces collectively span all possible crystallographic surface orientations that can be cleaved from the face centered cubic Cu lattice. The method for preparing these S4Cs and for finding the high symmetry pole point is described. Optical profilometry has been used to determine the true shapes of the S4Cs and show that over the majority of the surface, the shape is extremely close to that of a perfect sphere. The local orientations of the surfaces lie within ±1° of the orientation expected on the basis of the spherical shape; their orientation is as good as that of many commercially prepared single crystals. STM imaging has been used to characterize the atomic level structure of the Cu(111)±11°-S4C. This has shown that the average step densities and the average step orientations match those expected based on the spherical shape. In other words, although there is some distribution of step–step spacing and step orientations, there is no evidence of large scale reconstruction or faceting. The Cu S4Cs have local structures based on the ideal termination of the face centered cubic Cu lattice in the direction of termination. The set of Cu S4Cs will serve as the basis for high throughput investigations of structure sensitive surface chemistry on Cu.

Growth on Differently Oriented Sidewalls of SiC Mesas As a Way of Achieving Well-Aligned SiC Nanowires

Several different growth directions of SiC nanowires (NWs) determined by the substrate surface crystallographic orientation were achieved by conducting vapor−liquid−solid growth on the top surfaces and the sidewalls of the 4H-SiC mesas. When substrate- dependent (i.e., epitaxial) growth was ensured, six possible crystallo- graphic orientations of 3C-SiC NW axis with respect to the 4H-SiC substrate were realized. They all were at 20° with respect to the substrate c plane, and their projections on the c plane corresponded to one of the six equivalent ⟨101⟩ crystallographic directions. All six orientations were obtained simultaneously when growing on the (0001) top surface of the 4H-SiC wafer or on the mesa tops. In contrast, no more than two NW orientations coexisted when grown on any particular crystallographic plane of a mesa sidewall. In particular, the {101 mesa sidewall plane resulted in only one NW orientation, thereby producing well-aligned NW arrays desirable for device applications.

Fatigue Crack Initiation and Propagation Behavior of a Nickel Alloy ; A Study of Structural Integrity Assessment Method Based on Polycrystalline FE Analysis

Evaluation of fatigue crack nucleation and propagation behavior in anisotropic metals is necessary for improving an accuracy of structural integrity assessment. In this paper, high cycle fatigue tests and polycrystalline FE analyses were carried out to investigate a relationship between crack nucleation positions and stress distribution. Fatigue tests of a rectangular specimen were conducted by four-point bending under load control. Fatigue crack nucleation and propagation in the gauge region was carefully observed during the tests. Grain morphology and crystallographic orientation of tensile surface were characterized using electron beam backscattering diffraction pattern (EBSP) analysis. The size of characterized area was determined to sufficiently cover the gauge region of four-point bending inner span. Stress distribution of the specimen was computed by polycrystalline finite element analysis. Resolved shear stresses were calculated in expected twelve slip systems. Fatigue cracks were tend to be initiated in areas indicating relatively high resolved shear stresses in several slip systems.

THE EFFECTS OFTI/PTBOTTOM ELECTRODE ON CRYSTALLOGRAPHIC AND SURFACE CHARACTERISTICS OFPZTTHICK FILMS

The ceramic lead zirconate titanate ( PZT ) films near the morphotropic phase boundary are successfully integrated into MEMS devices, especially for applications in microsensors and actuators. The ferro/piezo electric properties of PZT thick films are widely dependent on its surface quality and crystallographic orientation growth. This paper indicates the influences of platinum bottom electrode on the surface and crystallographic properties of PZT . Ti (10 nm ) and Pt (100 nm ) thin films have been deposited on silicon substrate by thermal evaporation and electron beam respectively without vacuum breaking. After annealing treatment, the Pt film exhibited (111) preferred orientation. Finally one micron thick PZT (54/46) film was deposited by a RF magnetron sputtering at room temperature in pure Argon followed by a conventional post annealing treatment on silicon substrate. The XRD measurements have shown the provskite structure of PZT films with (100) preferred orientation at annealing temperatures above 600°C and (111) preferred orientation above 650°c. The SEM results demonstrate that whatever the annealing temperature is increased, recrystallization grains and black holes on Pt surface occurs and cause morphological change of PZT surface. The AFM test shows the strong RMS roughness of platinum surface after annealing temperature at 650°C.

Surface effect investigation for static bending of nanowires resting on elastic substrate using Timoshenko beam theory in tandem with the Laplace-Young equation

In the present study, an enriched continuum mechanics framework is employed to study the surface effects on bending behavior of silver nanowires (NWs) resting on elastic substrate. The Timoshenko beam theory and the Laplace-Young equation are employed to investigate static behavior of silver NWs lying on Winkler-Pasternak elastic substrate. Three types of boundary conditions are considered as doubly simply supported (S-S), doubly clamped (C-C) and cantilevered (C-F). Analytical solutions are obtained for NWs with surface crystallographic orientation of [001] subjected to a concentrated external force. By defining different normalized contact stiffness, extensive numerical results are carried out to study the influence of effective parameters such as substrate, surface, aspect ratio (L/D) and diameter on the stiffness of NWs. According to the obtained results, the effect of surface and its rate of variation on stiffness of NWs lying on Winkler and Winkler-Pasternak elastic foundation models are more significant in (C-F) type of boundary condition compared to the NWs without foundation. By increasing the modulus of elastic substrate, the effect of shear deformation increases which it is more considerable in (C-C) and (S-S) NWs resting on the Winkler-Pasternak and Winkler substrate models, respectively.

Extraordinary Enhancement of Raman Scattering from Pyridine on Single Crystal Au and Pt Electrodes by Shell-Isolated Au Nanoparticles

We used shell-isolated nanoparticle-enhanced Raman spectroscopy (SHINERS) to systematically study the adsorption of pyridine on low-index Au(hkl) and Pt(hkl) single crystal electrodes. Our gold-core silica-shell nanoparticles (Au@SiO(2) NPs) boost the intensity of Raman scattering from molecules adsorbed on atomically flat surfaces. The average enhancement factor reaches 10(6) for Au(110) and 10(5) for Pt(110), which is comparable to or even greater than that obtained for bare gold NPs (a widely adopted SERS substrate). 3D-FDTD simulations reveal that this large enhancement is due to the transfer of the "hotspots" from NP-NP gaps to NP-surface gaps. We also found that the SHINERS intensity strongly depends on the surface crystallographic orientation, with differences up to a factor of 30. Periodic DFT calculations and theoretical analysis of dielectric functions indicate that this facet-dependence is predominantly governed by the dielectric property of the surface. The results presented in this work may open up new approaches for the characterization of adsorbates and reaction pathways on a wide range of smooth surfaces.

Self-organization of ripples on Ti irradiated with focused ion beam

30keV focused Ga+ ions were used to raster the metallographically polished surface of commercially pure Ti (CP Ti) at various FIB incidence angles over a wide range of doses (1016–1018ions/cm2) at room temperature. The sputtered surfaces were observed in situ using FIB imaging and later carefully characterized ex situ under scanning electron microscope (SEM) and atomic force microscope (AFM). Ripples were observed on the irradiated surfaces even at the normal FIB incidence angle. The ripple evolution is analyzed as functions of surface diffusion, surface crystallographic orientation, ion dose and incidence angle. It is found that the ripple orientation was progressively influenced by the ion beam direction with incidence angle increasing and in some cases curved ripples or fragmented rods viewed from different angles occurred at high ion doses. The morphological evolution from the well-developed straight ripples to the curved ones is never observed. The formation of ripples is attributed to the competition between the formation of ripples due to anisotropic surface diffusion and the formation of incidence-angle dependent ripples determined by Bradley–Harper (BH) model.

Direct evidence of advantage of Cu(111) for graphene synthesis by using Raman mapping and electron backscatter diffraction

The advantageous crystallographic orientation of Cu surface for graphene synthesis by using thermal chemical vapor deposition (CVD) is examined by Raman mapping and electron backscatter diffraction. It is found that Cu(111) predominates over (110) and (100) for single- (SLG) or few-layer graphene (FLG) growth. To confirm this result we attempt the synthesis of graphene on Cu(111) single crystal film surfaces. We confirmed the formation of high quality and high uniformity SLG or FLG over more than 97% of the substrate surface area of 10 mm × 10 mm by Raman mapping.

Imaging decorated platinum single crystal electrodes by scanning electrochemical microscopy

Platinum single crystal electrodes, Pt( h k l ), represent ideal materials where studying surface sensitive reactions such as oxygen reduction reaction (ORR). Moreover, there is a great interest in testing carbon supported electrocatalyts mixed with Nafion ® ionomer in order to directly evaluate catalysts under practical fuel cell conditions. Thus, we provide a first imaging attempt by scanning electrochemical microscopy (SECM) to locally evaluate the electrocatalytic activity during ORR on a Pt(1 1 1) single crystal electrode decorated with spots of commercial carbon supported platinum nanoparticles entrapped in Nafion ®. Both electrocatalysts present the same chemical composition and then, total surface area, particle size and crystallographic orientation at the electrode surface are the effects studied. Our SECM images prove that the peroxide pathway can also be considered a relevant reaction route on platinum electrodes. We agree with some recent reports pointing the Nafion ® content and the three-dimensional surface electrode area as key factors to control for achieving a proper evaluation of the apparent number of electrons exchanged during ORR.

The effects of mixtures of acid mist suppression reagents on zinc electrowinning from spent electrolyte solutions

The effects of Dowfroth 250 (D) and Tennafroth 250 (T) in combination with saponin (S) on zinc deposition current efficiency and power consumption during electrowinning of zinc from industrially supplied spent electrolyte solutions were investigated. The surface morphology and crystallographic orientations of the zinc deposits were also examined by scanning electron microscopy and X-ray diffraction techniques, respectively. Acid mist suppression efficiencies were measured and investigated by frothing behavior of the additives and by surface tension measurements. Concentrations of 5, 10, and 15 ppm of each of the additives were mixed with all possible combinations into spent electrolyte to study the effects. Results showed that addition of Dowfroth 250/Tennafroth 250 as well as saponin decreased the current efficiency, increased the energy consumption while maximum acid mist suppression efficiencies of 86.1% and 87.0% were obtained at D5 + S5 and T5 + S5, respectively. The increase in saponin concentration resulted a change in preferred crystal orientation from (104) (112) (103) (102) (101) at low saponin concentrations to (101) (112) at higher saponin concentration. Bright and compact deposits were obtained at a mixture concentration level of T5 + S5 and D5 + S5.

Progress in the understanding of surface structure and surfactant influence on the electrocatalytic activity of gold nanoparticles

The preparation of gold nanoparticles (Au-NPs) displaying specific shape, size and surface crystallographic domains has been investigated aiming to clarify the effect of the surface crystallographic orientation, of the synthesised nanoparticles, and surfactant influence on the electrochemical response of the ITO/Au-NPs modified electrodes. Polymorphic and nanorod-shaped Au-NPs have been obtained using distinct synthetic procedures in the presence of cetyltrimethylammonium bromide (CTAB), through seed-mediated growth methods, displaying distinct surface crystallographic domains confirmed by transmission electron microscopy, X-ray diffraction analysis and under potential deposition (UPD) of lead. The nanoparticles have been physically immobilised by casting on indium tin oxide (ITO) surfaces and the electrocatalytic activity of the Au-NPs evaluated using the ascorbic acid (AA) oxidation reaction, by cyclic voltammetry. The polymorphic and distinct surface crystallographic orientations of the Au-NPs were reflected in an irreproducible electrochemical response. Using gold nanorods comprising (1 1 1) and (1 1 0) facets and gold nanocubes consisting of faces displaying (1 0 0) surface domains, by contrasting the behaviour of CTAB-stabilised and clean particles, it has been possible to verify that the distinct voltammetric results are due to the exposure of specific crystallographic orientations owing to dissimilar interaction strength of CTAB with those facets.

The effects of deposition parameters on surface morphology and crystallographic orientation of electroless Ni-B coatings

Electroless Ni-B coatings were deposited on AISI 304 stainless steels by electroless deposition method, which was performed for nine different test conditions at various levels of temperature, concentration of NaBH4, concentration of NiCl2, and time, using the Taguchi L9(34) experimental method. The effects of deposition parameters on the crystallographic orientation of electroless Ni-B coatings were investigated using SEM and XRD equipment. SEM analysis revealed that the Ni-B coatings developed six types (pea-like, maize-like, primary nodular, blackberry-like or grapes-like, broccoli-like, and cauliflower-like) of morphological structures depending on the deposition parameters. XRD results also showed that these structures exhibited different levels of amorphous character. The concentration of NaBH4 had the most dominant effect on the morphological and crystallographic development of electroless Ni-B coatings.

Fundamental aspects of surface engineering of transition metal oxide photocatalysts

Many metal oxide photocatalysts exhibit strong variations in their photocatalytic activities as a function of their crystallographic surface orientation. In this Perspective possible fundamental reasons for the surface dependent photocatalytic properties are discussed. The majority of the data imply that the differing surface activities for photo-oxidation and -reduction reactions are mainly a consequence of electron and hole diffusion towards different surfaces. This is either due to directional charge carrier diffusion as a result of bulk anisotropies or it is a consequence of differing band bending (or flat band potentials) at the interface of the photocatalyst with its environment. Although the fundamental reason for the surface electronic structure must lie in the surface structure, no correlation between surface chemical properties and photochemical properties has yet been unambiguously determined. The importance of surface charge separation and charge trapping at the surface leads to new concepts for engineering surface properties with potentially increased photocatalytic activity. Consequently, enhancement can be achieved by synthesizing photocatalyst powders that expose surfaces with ‘naturally’ higher photoactivity; or in a proposed approach by modifying surfaces selectively with special surface phases or monolayer heterostructures that enhance charge separation at the surface. In addition, special surface phases with a narrowed band gap may enable visible light activity of otherwise only UV active bulk materials.

Comparison of the crystalline quality of homoepitaxially grown CVD diamond layer on cleaved and polished substrates

AbstractA transmission electron microscopy (TEM) study, comparing homoepitaxial diamond layers grown on different substrate surface preparation states and crystallographic orientation is presented. Quality of epilayers grown on {111} cleaved surface and on {001} polished one is evaluated in terms of crystalline defects. Focused ion beam (FIB‐dual beam) sample preparations are observed by TEM using the {111}, {400} and {022} reflections of the [011] pole. Burgers vector analysis allowed to conclude the presence of 60° dislocations oriented along all the different 〈110〉 directions in the cleaved sample, while no dislocations are observed on the polished one. A complete dislocation analysis is performed for that sample. The presence of dislocations in an undoped (i.e. fully lattice matched) epilayer is surprising; and is probably induced by atomic steps, generated by the cleavage process. This notes down the importance of the substrate if high quality diamond epilayers want to be grown.

Effects of surface diffusional anisotropy on the current-driven surface morphological response of stressed solids

A comprehensive analysis is presented of the effects of surface diffusional anisotropy on the morphological stability of planar surfaces of stressed crystalline solids under the simultaneous action of an electric field. The analysis is based on self-consistent dynamical simulations of driven surface morphological evolution in conjunction with linear stability theory. Results are reported of a systematic study of the effects on the surface morphological response of varying surface diffusional anisotropy parameters; these include the direction of the applied electric field with respect to fast surface diffusion directions, the surface crystallographic orientation, and the strength of the anisotropy that increases with decreasing temperature. For face-centered cubic crystalline solids under stress, we find that there exists a preferred direction for the applied electric field that optimizes their surface morphological response. In addition, we find that for these solids under given surface electromigration conditions, the morphological response of their ⟨111⟩-oriented surfaces is superior to that of their ⟨100⟩-oriented and ⟨110⟩-oriented surfaces. Furthermore, we demonstrate that increasing the strength of the surface diffusional anisotropy in these materials has beneficial effects on their surface morphological stability under the simultaneous action of an electric field. Our predictions can provide guidance for experimental studies of surface morphological response to the combined action of electric fields and mechanical stresses, as well as for tailoring operating conditions to improve the mechanical reliability of thin films in service.

Strain heterogeneities between phases in a duplex stainless steel. Comparison between measures and simulation

Many studies aimed at understanding the strain and damage micro-mechanisms in low-cycle fatigue in duplex stainless steels. Different methods allow the evaluation of the strains on the microstructural scale, some are surface techniques (AFM, EBSD, DIC) and others are bulk techniques (TEM, XRD). Recently, some works have analyzed the plastic strain sharing between austenitic and ferritic phases using one or several of these experimental methods (TEM, XRD, AFM, EBSD, etc.). The present work proposes to analyze the strain fields measured by digital image correlation (DIC) on the microstructural scale at the surface of a specimen cyclically strained in low-cycle fatigue, and to compare it with that obtained by a polycrystalline bi-phased microstructure numerical calculation.A cyclic mechanical test was carried out at room temperature on a forged duplex stainless steel. Before the test, a surface crystallographic orientation measurement was performed by EBSD analysis in the central part of the specimen. A specific in-situ optical microscopic device equipped with a CCD camera was used in order to observe and take digital images of the specimen surface on the microstructural scale, at different number of cycles. The displacement and strain fields of a representative surface zone were obtained by DIC using the specific software CORRELIQ4. The strain distribution and the strain sharing between austenitic and ferritic phases were analyzed from mechanical fields obtained between images taken at different number of cycles. In parallel, a quasi-2D microstructure finite element calculation of a small zone experimentally analyzed was performed. Numerical microstructure and grain orientations were obtained from EBSD measures. Two crystal plasticity constitutive laws were used to model the behaviors of austenitic (FCC) and ferritic (BCC) grains, respectively. The mechanical fields and the strain distributions per phase were compared to those obtained by DIC on the first hysteresis loop.

Adenine Adsorption at Single Crystal and Thin-Film Gold Electrodes: An In Situ Infrared Spectroscopy Study

Adenine adsorption at gold electrodes is studied in neutral sodium fluoride solutions by cyclic voltammetry and in situ infrared spectroscopy. External reflection measurements were performed with Au(111) and Au(100) single crystal electrodes in D2O solutions, whereas surface enhanced infrared reflection absorption spectroscopy experiments under attenuated total reflection conditions were carried out with sputtered gold thin-film electrodes, both in D2O and H2O solutions. The results clearly show the specific adsorption of the molecule providing significant surface enhancement of the strong ring stretching band and the scissoring mode of the amino group. On the basis of the results, an adsorption model is proposed in which the molecular plane and the C−N(H2) bond are tilted on the electrode surface. Coordination is proposed to take place via the N(amino) atom upon sp3 hybridization and the N7 atom of the ring. The model applies irrespective of the surface crystallographic orientation of the electrode or the applied potential. The influence of the reconstructed or the unreconstructed state of the surface is inferred from the analyses of the spectra recorded while scanning the potential in opposite directions.

Growth Model of MOCVD Polycrystalline ZnO

A growth model for the low pressure chemical vapor deposition (LPCVD) of polycrystalline ZnO thin films is proposed. This model is based on experimental observations of the surface morphology and crystallographic orientations of the layers at different thicknesses and growth temperatures. It is shown that the films preferred orientation evolves from c-axis to a-axis as the growth temperature is increased from 110 to 220 °C and then goes back to c-axis at 380 °C. At the same time, when the film thickness increases, the surface morphology evolves from small rounded grains to large pyramids at a growth temperature of 150 °C. The selection of various preferential orientations under different deposition conditions is attributed to growth competition between clusters initially formed with different crystallographic orientations.

Electrowinning of zinc from sulphate solutions in the presence of perfluoroglutaric acid

This paper deals with the effect of perfluoroglutaric acid in the presence and absence of antimony(III) on the cathodic current efficiency, energy consumption and polarisation behaviour of the cathode during electrowinning of zinc from acidic sulphate solutions. Surface morphologies and crystallographic orientations of the zinc deposits were also examined using scanning electron microscopy and X-ray diffraction analysis. Perfluoroglutaric acid was found to increase the current efficiency, decrease the energy consumption and produce better surface morphologies. Voltammetric studies revealed that perfluoroglutaric acid when present in the solution depolarised the cathode which was also reflected in the deposit morphologies showing bigger size crystal planes than the deposit obtained in its absence. Presence of antimony(III) in the solution deteriorated the deposit quality and resulted in corrugated deposits at higher concentrations.

Magnetic-field-dependent morphology of self-organized Fe on stepped Si(111) surfaces

The present work reports on Fe thin films grown on vicinal Si(111) substrates via rf magnetron sputtering. The dependencies of the growth mode and magnetic properties of the obtained iron nanostructures on both crystallographic surface orientation and on the direction of the very weak stray magnetic field from the magnetron gun were studied. Scanning tunneling microscopy images showed strong dependence of the Fe grains’ orientation on the stray field direction in relation to the substrate’s steps demonstrating that, under appropriately directed magnetic field, Si surfaces can be used as templates for well-defined self-assembled iron nanostructures. Magneto-optical Kerr effect hysteresis loops showed an easy-axis coercivity almost one order of magnitude smaller for the film deposited with stray field applied along the steps, accompanied with a change in the magnetization reversal mode. Phenomenological models involving coherent rotation and/or domain-wall unpinning were used for the interpretation of these results.