Extended focused imaging for digital holograms of macroscopic three-dimensional objects

When a digital hologram is reconstructed, only points located at the reconstruction distance are in focus. We have developed a novel technique for creating an in-focus image of the macroscopic objects encoded in a digital hologram. This extended focused image is created by combining numerical reconstructions with depth information extracted by using our depth-from-focus algorithm. To our knowledge, this is the first technique that creates extended focused images of digital holograms encoding macroscopic objects. We present results for digital holograms containing low- and high-contrast macroscopic objects.     

Atomic carbon in magnesium oxide Part VI: Electrical conductivity

In the range 300–1270 K the d.c. conductivity of high-purity arc-fused MgO single crystals was found to be very different during heating and cooling and after room temperature annealing. Measurements with and without guard ring and by the 4-point method gave essentially the same results. Two distinctly different activation energies were found: the 2.5 eV mechanism, already reported in the literature, which is characteristic for high temperatures, > 1000 K, and a 1.1 eV mechanism which progressively builds up in the 700–870 K interval during heating. Between 700–870 K the conductivity rises sharply and cooling yields 1.1 eV-branches which can be cycled many times. Room temperature annealing, however, destroys the 1.1 eV mechanism and leads again to sharply rising conductivity curves in the 700–870 K interval. Remarkable instabilities and occasional short circuiting phenomena were observed during cooling from temperatures slightly above 870 K. In this temperature region the conductivity reacted very fast to a change from Ar to O₂. Together with supporting evidence provided by other methods the conductivity behavior appears to be governed by the presence of atomic carbon in the MgO.     

The surface conductivity of gamma-irradiated ceramic dielectrics

We have studied the surface dc conductivity of commercial alumina based ceramic dielectrics of the UF-46 and GB-7 types in a temperature interval from 200 to 400 K before and after gamma irradiation to a dose of 10⁴–10⁵ Gy. The two ceramics differ in the content of the α-Al₂O₃ crystal phase (72 wt % for UF-46 versus 86 wt % for GB-7) and in the total specific area of the grain boundaries (3.40 m²/kg for UF-46 versus 4.56 m²/kg for GB-7). In the temperature interval studied, the surface conductivity obeys a power law with the exponent dependent on the grain boundary area and the gamma radiation dose. Irradiation leads to a significant decrease in the exponent, the effect being more pronounced for ceramics with a greater grain boundary area. It is suggested that the electric conductivity proceeds according to a polaron mechanism, with a multiphoton character of the corresponding electron transitions.     

First study of macroscopic neutron dark field imaging using scattering grids

Instead of using the phase grating concept for dark field imaging, macroscopic scattering grids were employed at the ANTARES neutron imaging facility. Two Cadmium grids with a 1 mm gap and 1.2 mm bar were adjusted in a distance of only a few cm in order to block the direct beam. Thus, by placing the samples between these two grids only neutrons that were scattered at the samples were transmitted. A linear motion of the coupled grids allowed scanning across the samples and obtaining complete scattering projections, which delivered surprisingly sharp images. The geometric relation between grids permits determination of the transmitted scattering angles.     

Three-dimensional surface contouring of macroscopic objects by means of phase-difference images

We report a technique to determine the 3D contour of objects with dimensions of at least 4 orders of magnitude larger than the illumination optical wavelength. Our proposal is based on the numerical reconstruction of the optical wave field of digitally recorded holograms. The required modulo 2pi phase map in any contouring process is obtained by means of the direct subtraction of two phase-contrast images under different illumination angles to create a phase-difference image of a still object. Obtaining the phase-difference images is only possible by using the capability of numerical reconstruction of the complex optical field provided by digital holography. This unique characteristic leads us to a robust, reliable, and fast procedure that requires only two images. A theoretical analysis of the contouring system is shown, with verification by means of numerical and experimental results.     

Specific heat and thermal conductivity measurements for anisotropic and random macroscopic composites of cobalt nanowires

We report simultaneous specific heat (c(p)) and thermal conductivity (κ) measurements for anisotropic and random macroscopic composites of cobalt nanowires (Co NWs), from 300 to 400?K. Anisotropic composites of Co NW consist of nanowires grown within the highly ordered, densely packed array of parallel nanochannels in anodized aluminum oxide. Random composites are formed by drop-casting a thin film of randomly oriented Co NWs, removed from the anodized aluminum oxide host, within a calorimetric cell. The specific heat measured with the heat flow parallel to the Co NW alignment ([Formula: see text]) and that for the random sample (c(p)(R)) deviate strongly in temperature dependence from that measured for bulk, amorphous, powder cobalt under identical experimental conditions. The thermal conductivity for random composites (κ(R)) follows a bulk-like behavior though it is greatly reduced in magnitude, exhibiting a broad maximum near 365?K indicating the onset of boundary-phonon scattering. The thermal conductivity in the anisotropic sample ([Formula: see text]) is equally reduced in magnitude but increases smoothly with increasing temperature and appears to be dominated by phonon-phonon scattering.     

Urchin-like self-supported carbon nanotubes with macroscopic shaping and fully accessible surface

A self-supported carbon nanotubes (SSCNTs) with nanoscopic properties and controlled macroscopic shape were synthesized by a Chemical Vapour Deposition (CVD) method using a mixture of ethane/hydrogen and a Fe/Al₂O₃ growth catalyst. The SSCTs were obtained in the form of beads of 6–8 mm in diameter, with a hollow core structure and a high and fully accessible specific surface area, i.e. 140–180 m².g^? 1. In addition, the macroscopic shape and open structure of these SSCNTs allow them to be efficiently used as catalyst support either in a gas-phase or in a liquid-phase configuration.     

Atomic force microscope imaging of the surface roughness of SCS- and TiB2-coated SiC fibres and uncoated sapphire fibres

To understand the role of fibre surface roughness on the toughening of composite materials, it is imperative to characterize the fibre surface structure properly. This paper presents nanometre scale images of the surfaces of SCS- and TiB₂-coated SiC fibres, and of uncoated sapphire fibres, obtained by atomic force microscopy. It is found that SCS and TiB₂ coatings deposited on SiC fibres using chemical vapour deposition methods produce fibres exhibiting surface structures that are tri-fractal over several decades of length scale. The sapphire fibre exhibited a surface structure with two scales of periodic roughness, of wavelength 60 μm and 100 nm. A roughness analysis of the experimentally obtained data at different resolutions demonstrated that the magnitudes of the conventional parameters root mean square (r.m.s.) height σ, r.m.s. slope σ′, and r.m.s. curvature σ″ for the same surface varied in some cases by more than an order of magnitude.     

Thermal conductivity surface of argon: A fresh analysis

This paper presents a fresh analysis of the thermal conductivity surface of argon at temperatures between 100 and 325 K with pressures up to 70 MPa. The new analysis is justified for several reasons. First, we discovered an error in the compression-work correction, which is applied when calculating thermal conductivity and thermal diffusivity obtained with the transient hot-wire technique. The effect of the error is limited to low densities, i.e., for argon below 5 mol·L^–1. The error in question centers on the volume of fluid exposed to compression work. Once corrected, the low-density data agree very well with the available theory for both dilute-gas thermal conductivity and the first density coefficient of thermal conductivity. Further, the corrected low-density data, if used in conjunction with our previously reported data for the liquid and supercritical dense-gas phases, allow us to represent the thermal conductivity in the critical region with a recently developed mode-coupling theory. Thus the new surface incorporates theoretically based expressions for the dilute-gas thermal conductivity, the first density coefficient, and the critical enhancement. The new surface exhibits a significant reduction in overall error compared to our previous surface which was entirely empirical. The uncertainty in the new thermal conductivity surface is ±2.2% at the 95% confidence level.     

Analysis of counterfeit pharmaceutical tablet cores utilizing macroscopic infrared spectroscopy and infrared spectroscopic imaging

Advantages and limitations of analyzing authentic and counterfeit pharmaceutical tablets with both macro (nonimaging) attenuated total internal reflection Fourier transform infrared (ATR-FT-IR) spectroscopy and micro ATR-FT-IR spectroscopic imaging have been evaluated. The results of this study demonstrated that micro ATR imaging was more effective for extracting formulation information (sourcing), whereas a macro ATR approach was better suited for counterfeit detection (screening). More importantly, this study demonstrated that a thorough analysis of the counterfeit core can be achieved by combining the results of both techniques.     

Anisotropic electric conductivity of In-Si(111) surface phases

The dependence of the electric conductivity of Si(111)√3 × √3-In and Si(111)4 × 1-In surface phases on the substrate surface orientation has been studied using low-energy electron diffraction, scanning tunneling microscopy, and four-point probe conductivity measurements. It is established that the directions of maximum conductivity in the Si(111)√3 × √3-In superlattice coincide with the directions of the maximum number density of In atoms, and in the Si(111)4 × 1-ln superlattice, with the directions of one-dimensional In atomic chains.     

Effect of adsorption on the surface conductivity and work function

Analytical expressions describing the change in the surface conductivity (ΔG) as a result of the adsorption of positively and negatively charged atoms are obtained. It is shown that the ratio of ΔG to the adsorption-induced change in the work function (Δ?) rather weakly depends on the surface coverage with adatoms.     

Effects of thickness on surface potential and surface conductivity in non-insulating Langmuir-Blodgett multilayers of porphyrins

The surface potentials of Langmuir-Blodgett multilayers of several porphyrins on aluminium were measured as a function of thickness using the Kelvin technique. The in-plane d.c. conductivity on insulating substrates and its variation with thickness were also measured wherever possible. Insulating long-chain and metal-free porphyrins showed almost no change in surface potential over a wide thickness range, whereas non-insulating silver mesoporphyrins showed a change of 600–800 mV relative to the potential of the aluminium substrate. The change in potential with thickness was paralleled by a change in conductivity for each material, and both changes occurred over a smaller thickness range as the bulk conductivity increased. It is suggested that a Schottky-type depletion region is responsible for the main effects observed and that the conduction is characterized by a high carrier (or defect) density but a low mobility.     

Wavelength-scanning surface plasmon resonance imaging

A new surface plasmon resonance (SPR) imaging technique was proposed. After measurements were conducted at varying wavelengths, the wavelength affording the minimum brightness (SPR wavelength) was determined at each pixel of the image. A two-dimensional map of the SPR wavelength could be converted to a thickness profile by use of a nonlinear calibration curve, which was obtained by Fresnel calculation. An array of protein thin layers on a gold film was evaluated in air to present the layers' surface structure in nanometer scale.     

Stabilizing diamond surface conductivity by phenol-formaldehyde and acrylate resins

H-terminated undoped nano-crystalline diamond films of 200 nm thickness are deposited by microwave plasma chemical vapor deposition on fused silica substrates seeded by a diamond powder. The films exhibit surface conductivity 10^? 7 (Ω/□)^? 1. Phenol-formaldehyde and acrylate resins are spin-coated on the diamond films in the thickness of 0.2–1.7 μm. After the coating, the surface conductivity changes by ? 12% to + 52% compared to a bare diamond surface. It also exhibits significantly higher temporal stability. These effects are attributed to an encapsulation of the surface conductive channel from the ambient and to an electrostatic field of molecular dipoles in the resins.     

Wide-field optical imaging of surface nanostructures

We present a new technique that increases the sensitivity of incoherent light optical microscopy to a point where it becomes possible to directly visualize ultrathin films (approximately nanometers) and isolated nano-objects. The technique is based on the use of nonreflecting substrate surfaces for cross-polarized reflected light microscopy. These surfaces generate a contrast enhancement of about 2 orders of magnitude, extending the application field of wide-field optical microscopy toward the nanoworld. The efficiency of the method is proven experimentally on well-characterized samples. Wide-field imaging of a nonlabeled lambda-DNA molecule is also presented.     

HRTEM surface profile imaging of solids

As an important supplementary technique in surface science, surface profile imaging by high resolution transmission electron microscopy provides surface structural information as well as subterranean structures of solids. The surface-related properties of materials can therefore be better understood. In particular, the application of this technique to the characterisation of nano-scale materials has increased significantly in recent years.