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Carbon supported platinum (Pt/C) catalyst remains among the most preferable catalyst materials for Proton Exchange Membrane (PEM) fuel cells. However, platinum (Pt) particles suffer from poor durability and encounter electrochemical surface area (ESA) loss under operation with the accompany of Pt nanoparticle coarsening. Several proposed mechanisms have involved the Pt detachment from its carbonate support as an initial step for the deactivation of Pt nanoparticles. In this study, we investigated the detachment mechanism from the nano-adhesion point of view. Classic molecular dynamics simulations are performed on systems contain Pt nanoparticles of different sizes and shapes. A thin Nafion film (1 nm) at different hydration levels is also included in the system to study the environmental effect on nanoparticle adhesion. We found that the adhesion force strengthens as the Pt size goes up. Pt nanoparticles of tetrahedral shape exhibit relatively stronger connection with the carbon substrate due to its unique ‘anchor-like’ structure. Adhesion is enhanced with the introduction of a Nafion. The humidity level in the Nafion film has a rather complicated effect on the strength of nanoparticle adhesion. The binding energies and maximum adhesive forces are reported for all systems studied.

Nanocrystallites have garnered substantial interest due to their various applications, including catalysis and medical research. Consequently important aspects of synthesis related to control of shape and size through economical and non-hazardous means are desirable. Highly efficient bioreduction-based fabrication approaches that utilize microbes and/or plant extracts are poised to meet these needs. Here we show that the γ -proteobacterium Shewanella oneidensis can reduce tetrachloroaurate (III) ions to produce discrete extracellular spherical gold nanocrystallites. The particles were homogeneously shaped with multiple size distributions and produced under ambient conditions at high yield, 88% theoretical maximum. Further characterization revealed that the particles consist of spheres in the size range of ∼2–50 nm, with an average size of 12 ± 5 nm. The nanoparticles were hydrophilic and resisted aggregation even after several months. Based on our experiments, the particles are likely fabricated by the aid of reducing agents present in the bacterial cell membrane and are capped by a detachable protein/peptide coat. Ultraviolet–visible and Fourier transform infrared spectroscopy, X-ray diffraction, energy dispersive X-ray spectra and transmission electron microscopy measurements confirmed the formation, surface characteristics and crystalline nature of the nanoparticles. The antibacterial activity of these gold nanoparticles was assessed using Gram-negative ( Escherichia coli and S. oneidensis ) and Gram-positive ( Bacillus subtilis ) bacterial species. Toxicity assessments showed that the particles were neither toxic nor inhibitory to any of these bacteria.

A combination of the 'semi-empirical' model for secondary electron production and the TRIM routines which describe ion stopping power, scattering, and transport, has been used to construct a Monte Carlo simulation (IONiSE) that can quantitatively interpret the generation of secondary electrons (SE) from materials by fast helium ions. This approach requires that the parameters of the semi-empirical model be determined by fitting to experimental yield data but has the merit that, unlike more fundamental models, it can be applied with equal ease to both pure elements and complex compounds. The application of the model to predict the topographic yield variation of helium generated SE as a function of energy and material, and to investigate the ratio between SE generated by incident and backscattered ions, is demonstrated.

In many applications such as optoelectronic devices, three-dimensional (3D) structures are required. Examples include photonic band gap (PBG) crystals, diffractive optical elements, blazed gratings, MEMS, NEMS, etc. It is known that the performance characteristics of such structures are highly sensitive to their dimensional fidelity. Therefore, it is essential to have a fabrication process by which such 3D structures can be realized with high dimensional accuracy. In this paper, practical methods to control thickness of the remaining resist and etch depth, which may be employed for fabrication of such 3D structures using grayscale electron-beam lithography, are described. Through experiments, explicit control of the remaining resist thickness and etch depth at the resolution of 20nm for the feature sizes of 0.5@mm and 1@mm has been successfully demonstrated. Also, the 1:1 ratio of silicon to resist etching rates was achieved for transferring the remaining resist profile onto the silicon substrate.

Serial block face scanning electron microscopy (SBF-SEM) provides nanoscale 3D ultrastructure of entire cells and tissue volumes. In SBF-SEM, an ultramicrotome built into the SEM specimen stage successively removes thin sections from a plastic-embedded, heavy metal-stained specimen. After each cut, the freshly exposed block face is imaged at a low incident electron energy using a backscattered electron detector to provide 3D ultrastructure with a resolution of approximately 5 nm in the plane of the block face and around 25 nm in the perpendicular z-direction, as limited by the slice thickness. We have explored the feasibility of improving the z-resolution in SBF-SEM by recording images at multiple primary beam energies, thus sampling different depths below the block surface.A linear relationship was found between the depth of test structures, generated by Monte Carlo simulations, and the ratio of backscattered image intensities recorded at primary beam energies between 1.4 keV and 6.8 keV. This enabled us to reconstruct the 3D model within a 25-nm surface layer at a z-resolution of around 5 nm. We used a Zeiss Sigma-VP SEM equipped with a Gatan 3View SBF system to acquire 3D data from a specimen consisting of gold spheres embedded in carbon. Experiments were also performed on embedded blocks of stained biological tissues.Although damage of the block under electron irradiation limits the signal to noise ratio, the use of multiple primary beam energies, coupled with a physics-based Monte Carlo model, provides the possibility of obtaining cellular ultrastructure at nearly isotropic 3D spatial resolution.

We describe a novel, all dry approach that uses direct epitaxial growth for nanostructure fabrication. The two major requirements for achieving direct epitaxial growth are the ability to generate and to subsequently maintain and control spatial and chemical selectivity in the film growth process. The spatial selectivity is generated by pattering a surface adsorption layer on Si(100) using scanning electron beam lithography. This artificial lateral variation in surface reactivity is used as a template in subsequent epitaxy. Selective epitaxial growth on the resulting patterns is achieved by supersonic molecular jet epitaxy. Systematic investigation of the effects of various patterning and growth parameters on spatial and chemical selectivity at a sub- 100-nm feature scale using hydrogen terminated and nitrogen terminated growing Si(100) surfaces are presented.

Current materials are usually complex in chemistry, three-dimensional in form, and of rapidly diminishing microstructural scale. To characterize such materials the scanning electron microscope (SEM) now uses a wide range of operating conditions to target the desired sample volume, sophisticated modeling techniques to interpret the data. It also uses novel imaging modes to derive new types of information. These include depth-resolved three-dimensional data, and spatially resolved crystallographic data.

Low voltage scanning electron microscopy (LVSEM) is the application of the SEM at beam energies below 5 keV. The fall in electron beam range compared to its magnitude at higher energies leads to significant changes in the beam interaction volume and in the secondary and backscattered electron yields. The topographic and beam penetration contrast effects which dominate images at high energies are replaced by detector collection efficiency contrast effects giving images which are less three dimensional but which contain more detailed information on the surface morphology and, in some circumstances, the surface chemistry of the specimen. In order to observe non-conducting specimens a state of charge balance must be obtained to obviate imaging artifacts. This requires an optimized choice of the incident beam energy, sample tilt, beam current and magnification for each sample. The high stopping power of electrons at low energy can result in enhanced radiation damage. However, because of the small electron range such damage is confined to a thin, near surface, region of the specimen. The combination of a field emission gun and a high performance lens allows the probe size of the instrument to be made almost independent of the chosen beam energy over the range 1–30 keV and probable advance in electron sources and electron optics promise still better levels of performance for the LVSEM.

An electron holographic method is introduced for the study of ferroelectric domain walls. The method allows not only direct imaging of the domain wall but also the measurement of local spontaneous polarization. Preliminary results of first high-resolution imaging of ferroelectric domain walls by using this technique in BaTiO3 and quantitative measurements of electrostatic field distribution across domain walls are presented.

The electron-optical parameters required to generate an electron hologram are discussed. It is shown that the new generation of commercial field emission transmission electron microscopes (FEG TEM) meet the conditions required. Practical details of the procedures to set up and record a hologram are described. The steps necessary to reconstruct the hologram are also discussed and an outline is provided of a program for the Apple Macintosh™ personal computer which implements these operations. The integrity and accuracy of the reconstruction program has been tested by means of a detailed simulation of high-resolution holograms starting from dynamical multi-slice calculations of the exit wavefront.

Recent advances in instrumentation have produced the first commercial examples of what can justifiably be called high-resolution scanning electron microscopes. The key components of such instruments are a cold field emission gun, a small-gap immersion probe-forming lens, and a clean dry-pumped vacuum. The performance of these microscopes is characterized by several major features including a spatial resolution, in secondary electron mode on solid specimens, which can exceed 1 nm on a routine basis; an incident probe current density of the order of 10 6 A/cm 2 ; and the ability to maintain these levels of performance over an accelerating voltage range of from 1 to 30 keV. This combination of high resolution, high probe current, low contamination and flexible electron-optical conditions provides many new opportunities for the application of the SEM to materials science, physics, and the life sciences.

In this paper equations which govern the detectable limits in a transmission electron energy loss experiment, where inner-shell edges are used for micro-elemental analysis, are derived. The minimum detectable number of atoms and the minimum mass fraction are evaluated for several model cases, including the variation with spectrometer acceptance angle and accelerating voltage.

Plural scattering is a significant limit to the accuracy of ELS quantitation. A simple deconvolution technique, sufficiently rapid for incorporation in an interactive quantitation routine, has been developed. The application of this approach improves the reliability of quantitation and, by yielding edge profiles which are reproducible, makes it possible to use computed (or previously stored) edge shapes for quantitation or background fitting.

As the size of microcircuit elements continues to decrease it is important to attempt to determine what factors ultimately limit the width of the finest line that could be fabricated by electron lithography and conventional polymer resists. Since the line profiles in an exposed and developed resist are determined by the contours of equal absorbed energy density this can be done by modelling the scattering which occurs in the polymer. We consider here the idealised case of a thin resist layer supported on a substrate of negligible scattering power, and irradiated with a beam of electrons in the energy range 30 to 100 keV, and calculate the minimum line width attainable under these optimum conditions.In the absence of any backscattering from the substrate it might be expected that the energy deposition profiles would be determined by elastic scattering in the resist.

Computer control of an electron microscope makes it possible to centralize the display of the important operating parameters, and to make provision for the storage and retrieval of sets of operating conditions. A Vacuum Generators HB5 STEM has been interfaced with a commercial microcomputer to perform these functions. Although fully automatic operation has not been provided, the ease of use of the microscope is considerably enhanced. The same computer can be used to produce special scan rasters, such as vector scans for electron lithography, and to provide a simple, software controlled, image storage system.

Convergent-beam electron diffraction (CBED), which is one of the techniques available on a modern transmission electron microscope (TEM), is sensitive to small localized lattice parameter changes and its application is therefore important in the characterization of sub-micron device structures. Unfortunately, dynamical diffraction effects prevent direct extraction of changes in the lattice parameter from CBED patterns which are obtained from high atomic number materials such as compound semiconductors. Therefore, in order to measure the relative lattice mismatch of a quaternary (InGaAsP) device structure grown on InP, we have opted to calibrate the relative position of CBED features with X-ray lattice parameter measurements which were obtained from planar quaternary layers grown on InP substrates. Three parameters from bright-field CBED patterns were measured as a function of the X-ray determined lattice mismatch in order to establish three separate calibration curves. CBED measurements taken from a device structure were found to produce similar values of lattice mismatch when interpreted using the calibration curves. The close correspondence of these three values of the lattice mismatch ((4.541 ± 2.119) × 10−4, (5.158 ± 2.881) × 10−1 and (4.819 ± 4.021) × 10−4), enhances the credibility of this approach for the characterization of sub-micron device structures.