Observation of double contours of monoatomic steps on single crystal surfaces in reflection electron microscopy

Double contours of atomic steps on single crystal surfaces are observed in the images of reflection electron microscopy in the case of enhanced Bragg reflection. The contrast of atomic steps in such a situation is discussed.     

Reflection electron microscopy (REM) of fcc metals

Reflection Electron Microscopy (REM) using diffracted beams from bulk specimens is shown to be possible with commercial electron microscopes. Surface images have been recorded from single crystal Au and Pt(111) surfaces. These images reveal growth steps, dislocations, slip traces, and other features. Geometrical restoration has been made of foreshortened images, and analysis of image contrast shows the importance of out-of-focus phase contrast and the diffraction contrast from strain fields.     

SEM electron channelling patterns as a technique for the characterization of ion-implantation damage

Electron channelling patterns (ECPs) formed in back-scattered images in the scanning electron microscope (SEM) have been used occasionally to confirm surface amorphization during ion implantation. In order to place such observations on a more quantitative basis, the study reported here has explored the variation of ECP appearance with both specimen damage levels (and thus subsurface structures) and SEM accelerating voltage (i.e. sampled depth). Polished and annealed (0001) single crystal sapphire discs were implanted to various damage levels up to both subsurface and full surface amorphization. Damage levels were measured independently by Rutherford back-scattering (RBS). Selected-area ECPs were obtained in a Jeol-840 electron microscope operating over the range 5–40 kV in 5-kV steps. Progressive ECP degradation—in terms of high-order line disappearance—was observed with increasing dose, culminating in total pattern loss when full surface amorphization occurred. However, ECP information could still be obtained from the damaged near-surface material even when a subsurface amorphous layer was present, thus demonstrating the shallow retrieval depth of information from the ECP technique. Indeed, because the spatial distribution of damage from ion implantation is both calculable and measurable, these experiments have also allowed us, for the first time, to explore and demonstrate the shallow sample depths from which the majority of ECP contrast originates (< 150 nm in sapphire at an accelerating voltage of 35 kV), even when the beam penetration is considerable by comparison (～ 5 μm). Furthermore, the way in which this sampled depth varies with SEM accelerating voltage is both demonstrated and shown to be a powerful diagnostic technique for studying the distribution of near-surface structural damage.     

Scanning electron microscopy studies of double-layer silicon structures prepar by epitaxy and direct bonding

The electrical properties of multilayer structures obtained by direct bonding of silicon wafers and epitaxial growth have been investigated. The measurements were made by scanning electron microscopy (SEM) in either secondary electron or electron beam-induced current (EBIC) regime, using cross sections of the structures with a p-n junction formed in the subsurface region of the active layer. The measurements of defect recombination activity were made using Schottky diodes formed on the active layer surfaces. Parasitic p-n junctions in some samples under a small direct voltage have been observed and the reason for the appearance of such parasitic junctions has been established. Two types of defects with different distribution densities and amplitudes of EBIC contrast have been detected.     

The scanning low-energy electron microscope: First attainment of diffraction contrast in the scanning electron microscope

Using small Pb crystals deposited in situ on a partially contaminated Si (100) crystal, we demonstrate that a commercial scanning electron microscope (SEM) can easily be converted into a scanning low-energy electron microscope (SLEEM). Although the contrast mechanism is much more complicated than that in nonscanning LEEM because not only one diffracted monochromatic beam and its close environment are used for imaging, but several diffracted beams and a wide energy spectrum of electrons of different origin (secondary electrons, inelastically andelastically scattered electrons) are used, SLEEM is a valuable addition to the standard SEM because it provides an additional structure- and orientation-sensitive contrast mechanism in crystalline materials, a low sampling depth, and high intensity at low energies.     

An analytical reflection and emission UHV surface electron microscope

An UHV surface electron microscope is described which allows the study of surfaces under vacuum conditions common in surface science with the following techniques: LEERM; LEED; photo, thermionic, secondary emission microscopy; absolute micro area work function measurements. In particular, the first LEERM of Mo(110) and Si(111) surfaces are presented. They show monoatomic steps with high contrast due to Fresnel diffraction and structural differences, respectively. Condensed silver crystallites are imaged. Gold adsorption layers on Si(111) show strong contrast in photoemission; the layer thickness is deduced from LEED.     

High resolution SE-I SEM study of enamel crystal morphology

Until recently high resolution TEM was the only imaging mode capable of probing the atomic lattice structure of crystals composing tooth enamel. Studies designed to determine the polyhedral shape of normal enamel crystals and initiation of carious lesions in enamel crystals were hampered and limited by interpretation of two-dimensional TEM images from thin section and freeze fracture replica specimens lacking depth of field. The newly developed SE-I signal mode for SEM (SE-I/SE-II ratio) can produce images of enamel crystals approaching beam diameter dimensions (0.7–2.0 nm), rivaling the resolution of the TEM technique and generating topographic contrasts for three dimensional imaging at very high magnification (≈?1,000,000 X). Ultrathin chromium (Cr) films generate enriched high resolution SE-I contrasts of enamel crystal surfaces and when imaged using an immersion lens field emission SEM operated at high voltage (20–30 KeV) produce unsurpassed topographic contrasts. Since the grain size of Cr is below the resolution of any SEM and is ultrathin (≈?1 nm), then SE-I images can provide a more accurate representation of enamel crystal structure than TEM methodologies. Our SE-I SEM observations of normal human enamel crystals reveal fractured spicules which contain angled flat surfaces delineated by a prominent 2 nm wide SE-I edge brightness contrast. Although microscopic observations often show crystals which are hexagonal in cross-section, in both SEM and TEM many other growth habits, including rectangular or irregular crystals (30–40 nm in width) which contain “notches,” are also observed. More detailed morphological studies are therefore required to determine the most likely habit planes and their relevance to the function of the enamel crystals. The granular appearing fine structural contrast imposed onto <100> lattice planes of sectioned enamel in TEM micrographs is also resolved with topographic contrasts in SE-I micrographs. These granules probably represent one or both of the enamel protein classes.     

The Imaging Of Surface Step Structures By Dark Field Electron Microscopy

The dark field imaging of monatomic surface steps is studied by weak beam electron microscopy using reflections in higher order Laue zones. Dynamical theory calculations of the step intensities and of the diffuse background intensity in various diffracting conditions are in moderately good agreement with experimental observation on (111) thin films of gold. From grooving effects visible at incoherent twin boundaries, the boundary energy is estimated to be about one-third of the surface energy. The extension of the method to other crystal surfaces or other materials is discussed.     

Influence of electrical discharge machining on sliding friction and wear of WC-Ni cemented carbide

Tribological characteristics of fine-grained WC-8 wt%Ni with different surface finishing conditions corresponding to sequential wire electrical discharge machining (wire-EDM) or grinding were investigated by performing dry reciprocating sliding experiments on TE77 pin-on-plate equipment with WC-6 wt%Co as mating material. Surface finishes and wear surfaces were characterized using surface topography scanning, SEM analysis and EDX spectrometry. The decreased wear resistance due to wire-EDM could be linked to flexural strength properties as well as XRD measurements revealing tensile residual stresses on wire-EDM surfaces, in contrast with the compressive stress state on ground surfaces. Substantial improvement of wear resistance was accomplished with finer-executed EDM steps.     

Surface investigations with a combined scanning electron–scanning tunneling microscope

We have combined a scanning tunneling microscope (STM) with a scanning electron microscope (SEM) for surface investigations of atomically flat surfaces, ultrathin adsorbate films, and material surfaces. The mechanical stability of the hybrid instrument allows high-resolution SEM of samples mounted on the STM stage and atomic resolution with the STM. Experimental results of combined SEM/STM investigations on textured material surfaces, submicron structures, and atomically flat conducting surfaces are presented. An example is given for surface machining with the STM under SEM control.     

An investigation of the markings on wear and fatigue fracture surfaces

The worn surfaces of three polymers sliding against a lapped steel disk were studied by scanning electron microscopy (SEM) and transmission electron microscopy. The surfaces of polymethylmethacrylate and high density polyethylene were covered with bands of arced ripples stretched along the transverse direction. The shape of these ripples is consistent with the distribution of tensile principal stress in the contact zone for a hemispherical indenter sliding on a plane surface. The Polyvinylchloride surface suffered severe plastic deformation during sliding as discerned by the dimples on it. The fatigue fracture surfaces of these materials were also examined by SEM. The polymethylmethacrylate surface exhibited a series of striations whose spacing increased in the direction of crack propagation. The striations on high density polyethylene and Polyvinylchloride surfaces were not observed because fracture was accompanied by considerable plastic deformation. This study shows that the mechanism of the separation of a wear particle from the sliding surface is cumulative damage as encountered in fatigue.     

Imaging connected porosity of crystalline rock by contrast agent‐aided X‐ray microtomography and scanning electron microscopy

We set out to study connected porosity of crystalline rock using X‐ray microtomography and scanning electron microscopy with energy dispersive X‐ray spectroscopy (SEM‐EDS) with caesium chloride as a contrast agent. Caesium is an important radionuclide regarding the final deposition of nuclear waste and also forms dense phases that can be readily distinguished by X‐ray microtomography and SEM‐EDS. Six samples from two sites, Olkiluoto (Finland) and Grimsel (Switzerland), where transport properties of crystalline rock are being studied in situ, were investigated using X‐ray microtomography and SEM‐EDS. The samples were imaged with X‐ray microtomography, immersed in a saturated caesium chloride (CsCl) solution for 141, 249 and 365 days and imaged again with X‐ray microtomography. CsCl inside the samples was successfully detected with X‐ray microtomography and it had completely penetrated all six samples. SEM‐EDS elemental mapping was used to study the location of caesium in the samples in detail with quantitative mineral information. Precipitated CsCl was found in the connected pore space in Olkiluoto veined gneiss and in lesser amounts in Grimsel granodiorite. Only a very small amount of precipitated CsCl was observed in the Grimsel granodiorite samples. In Olkiluoto veined gneiss caesium was found in pinitised areas of cordierite grains. In the pinitised areas caesium was found in notable excess compared to chloride, possibly due to the combination of small pore size and negatively charged surfaces. In addition, elevated concentrations of caesium were found in kaolinite and sphalerite phases. The findings concerning the location of CsCl were congruent with X‐ray microtomography.     

Characterization of the annealed (0001) surface of sapphire (alpha-Al2O3) and interaction with silver by reflection electron microscopy and scanning reflection electron microscopy.

Annealed (0001) surfaces of single-crystal sapphire (alpha-Al2O3) rod have been studied in the electron microscope using reflection electron microscopy (REM), scanning reflection electron microscopy (SREM), and reflection high energy electron diffraction (RHEED). Annealed surfaces of (0001) sapphire are vicinal and characterized by close-packed (0001)-oriented terraces separated by faceted multiple-height steps, with edges parallel to energetically preferred low-index directions (less than 1010 greater than and less than 1120 greater than). These structural features are not seen on cleaved surfaces or polished surfaces treated at temperatures less than 1,250 degrees C. Oxygen-annealing produces clean surfaces which prove useful for investigating the interaction of deposited metals with the (0001) sapphire. Both REM and SREM (with microdiffraction spots) techniques have been used to observe fine structure of flat Ag islands on the scale of 1-100 nm on the (0001)-oriented terraces as well as aggregations at the steps. A preliminary result on interaction with Cu is also included.     

Electron microscopic study of novel threadlike structures on the surfaces of mammalian organs

The ultrastructures of novel threadlike structures (NTSs) and corpuscles on the surfaces of internal organs of rats were investigated using electron microscopy. The samples were studied in situ by using a stereomicroscope and were taken for further morphological analysis. Scanning electron microscope (SEM) images revealed a bundle structure of threadlike tissue, which was composed of several 10-micro m-thick subducts. The surfaces of the corpuscles were rather coarse and fenestrated. The corpuscles had cucumber-like shapes with an average length of about 2 mm and a thickness of about 400 micro m. Transmission electron microscope (TEM) images disclosed disordered collagen fibers, which formed the extracellular matrix of the threadlike tissue, and immune-function cells, like macrophages, mast cells, and eosinophils. Sinuses of various diameters, which were thought to be cross-sections of the lumens of the subducts, were observed in the TEM, cryo-SEM and focused-ion-beam SEM images. These SEM images were obtained for the first time to reveal the detailed structure of the NTSs that were only recently discovered.     

A Brief Discussion About Image Quality and SEM Methods for Quantitative Fractography of Polymer Composites

The methodology for fracture analysis of polymeric composites with scanning electron microscopes (SEM) is still under discussion. Many authors prefer to use sputter coating with a conductive material instead of applying low‐voltage (LV) or variable‐pressure (VP) methods, which preserves the original surfaces. The present work examines the effects of sputter coating with 25 nm of gold on the topography of carbon‐epoxy composites fracture surfaces, using an atomic force microscope. Also, the influence of SEM imaging parameters on fractal measurements is evaluated for the VP‐SEM and LV‐SEM methods. It was observed that topographic measurements were not significantly affected by the gold coating at tested scale. Moreover, changes on SEM setup leads to nonlinear outcome on texture parameters, such as fractal dimension and entropy values. For VP‐SEM or LV‐SEM, fractal dimension and entropy values did not present any evident relation with image quality parameters, but the resolution must be optimized with imaging setup, accompanied by charge neutralization. SCANNING 35: 196‐204, 2013. © 2012 Wiley Periodicals, Inc.     

Nanodiamond-Based Nanolubricants: Investigation of Friction Surfaces

Synergistic compositions of detonation nanodiamond (DND) particles with polytetrafluoroethylene and molybdenum dialkyldithiophosphate were used in ring-on-ring, four-ball, and block-on-ring tests as an additive to polyalphaolefins and engine oils. Modest to significant reductions in the friction coefficients, wear, or both were observed. In the wear scars produced in the block-on-ring tests, the friction surfaces were characterized by scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), and profilometry. Significant polishing effects of the friction surfaces in lubricants containing DND were revealed in SEM observations and roughness measurements. The roughness of the scar surfaces produced in the presence of DND additives was about 35% lower than the roughness of the scars observed in pure oil experiments.     

Inflammatory cell recruitment and adhesion to methyl-terminated self-assembled monolayers: effect of implantation time

The contribution of methyl groups in implant-triggered inflammation was investigated in vivo using self-assembled monolayers (SAMs) of alkanethiols on gold. The CH(3)-coated implants were inserted in an air-pouch cavity induced in BALB/c mice. The in situ inflammatory response was monitored 24, 48, and 72 hours later. Inflammatory cells recovered from the air pouches were counted and observed by light microscopy. The cellularity of the implant surfaces was defined by scanning electron microscopy (SEM). In comparison with gold implants, the CH(3)-coated SAMs recruited a significantly higher number of inflammatory cells. Polymorphonuclear leukocytes (PMN) were more numerous than mononuclear cells (Mo) in the exudates recovered from the air pouches with CH(3)-coated SAMs. The opposite PMN/Mo proportion was observed in air pouches of the two control groups (mice receiving gold implants or sham-operated animals). A low density of adherent cells was seen on CH(3)-coated implants, with no significant quantitative differences during the time course of the study. In contrast, the gold-coated surfaces were covered with numerous cells during all of the 3 days of the inflammation. In conclusion, implants with CH(3) surfaces are likely to induce PMN-dominated local acute inflammation but these surfaces are not associated with a significant adherence of leukocytes to the implant.     

C2H2 interaction with Ni nanocrystals: towards a better understanding of carbon nanotubes nucleation in CVD synthesis

We present a study of the early stages of carbon nanotubes nucleation in CVD synthesis by combining field ion/electron emission microscopy (FIM/FEM) and atom-probe investigation (AP) of the nickel-carbon interaction. Acetylene decomposition on Ni tips at 873K is observed to induce additional step formation on an initially facetted (polyhedral) crystal. Carbon-enriched steps are then observed to act as preferential nucleation centers of graphene sheets formation. Atom-probe experiments reveal C(2) and C(3) species and frequency dependent studies demonstrate that the origin of these species is different from C(1). Experiments provide clear evidence for the crucial role of carbon-enriched steps as nucleation sites of graphene sheets on the Ni surface.     

Tilt dependence of the secondary electron emission at low excitation energy

Influence of the specimen's slope on the secondary electron emission has been experimentally studied. Strong deviations from the inverse cos law have been observed and corresponding phenomenological equation (taking into account this deviation) is suggested. The consequences of the dependence on the topography contrast of low- and high-voltage scanning electron microscopy (SEM) image, especially for three-dimensional (3-D) reconstruction, are considered.