The stoichiometry and site distribution of metastable nickel-titanate spinel has been studied with AEM. The results of EDXS and EELS agree that the metastable spinel is nonstoichiometric and titanium-deficient relative to its hypothetical endmember composition, “Ni2TiO4”. The titanium deficiency has been determined by EELS to be Δ = 0.025 ± 0.005. Channeling-enhanced microanalysis and ELNES studies indicate that the Ti4+ and Ni2+ cations are in tetrahedral and octahedral coordination, respectively, so that the metastable spinel has the normal cation distribution: Til−Δ[Ni2(1+Δ)]O4. This result is consistent with neutron powder-diffraction studies and SiO2-solubility measurements of similar equilibrated and quenched spinel-containing specimens. Metastable nickel-titanate spinel therefore contrasts with stable stoichiometric spinels which tend to the inverse cation distribution, Me[MeTi]O4.

Secondary excitation can be a large source of inaccuracy in quantitative X-ray microanalysis of inhomogeneous specimens in the AEM. The size of the secondary excitation component in the measured X-ray spectrum is sensitive to the geometry of the thin foil specimen. Secondary excitation has been examined in a self-supporting disc specimen of composition NiO-20 wt.% TiO2 which has been partially masked by a gold slot washer. The ratio of the intensities of the characteristic Kα peaks of Ti and Ni in X-ray spectra from a periclase-structured phase, of nominal composition NiO, has been measured to be NTi / NNi ≈ 0.005. There is no apparent Ti L2,3 signal in the corresponding electron energy-loss spectrum. The secondary excitation contribution to the characteristic Ti K≈a-peak from all sources can therefore be no larger than 0.5%. It should be possible to reduce this modest level of secondary excitation still further with a better masking arrangement.

Electron excited energy dispersive X-ray spectrometry (EDS) was used to determine the atomic species present in 35 Å diameter CdSe nanocrystallites. Both theoretical modeling and experimental calibration with standard materials were used to relate the relative X-ray intensities to the atomic fractions present in the sample. The EDS results were normalized to those found by elemental analysis, which also detects light elements. With different surface models, and the atomic fractions found by EDS, the number of surface groups per nanocrystallite was determined.

Pt colloidal particles with large surface areas are effective electrocatalysts which can be applied in methanol fuel cells. The efficiency of the Pt catalyst can be greatly increased if it is incorporated with a second component such as Ru. By applying TEM, EDXS and XRD, the chemical composition, particle size and crystallinity of Pt and Pt/Ru colloidal particles during synthesis procedure are investigated in this research.

We report results of Raman spectroscopy of size selected, matrix isolated Si clusters. Cluster ions produced by laser vaporization are size selected by a quadruple mass spectrometer and co-deposited with cryogenic matrices onto a substrate at ∼15K. A surface-plasmon-polariton-enhanced Raman geometry is used to gain adequate signal.

The observed vibrational frequencies from Si4, Si6 and Si7 are compared with theoretically calculated Raman active modes based on the structures of planar rhombus, distorted octahedron and pentagonal bipyramid, respectively. The agreement is excellent. Cluster agglomeration is observed when cluster concentrations exceed ∼0.3% by volume in the matrix and/or with annealing at ∼28K, below the temperature of matrix evaporation.

Energy-filtered imaging in a transmission electron microscope provides a fast and quantitative technique for mapping the distribution of elements in solids at nm-level resolution. The technique and its instrumental requirements are reviewed, and illustrated in the context of materials science.

Parallel-detection electron energy loss spectroscopy (EELS) in the scanning transmission electron microscope provides a very sensitive means of detecting specific elements in biological systems. By analyzing EELS spectrum-image data recorded from rapidly-frozen and cryosectioned tissue it is possible to map quantitatively the distribution of the biologically important element, calcium, which is typically present at concentrations of only a few parts per million in cellular structures some tens of nanometers in diameter. A significant improvement (factor of four) in calcium detectability has been demonstrated for EELS compared with energy-dispersive x-ray spectroscopy. The spectrum-imaging technique has also been applied to map water distributions in hydrated biological specimens by utilizing the valence electron excitations.

Annular dark field scanning transmission electron microscopy (ADF STEM) is chemically sensitive at high spatial resolution (e.g., 1.8ë at 100keV). Images can be digitally acquired and recorded, permitting quantitative analysis. It is particularly powerful when used in combination with complementary analysis modes such as x-ray microanalysis and transmission electron energy loss spectroscopy. Critical to the interpretation of these data is an understanding and determination of the electron probe intensity, shape and propagation characteristics inside the specimen. Quantitative measurements of diffraction patterns and images in comparison with computer-based simulations (including phonon scattering) provide a basis for developing that information. Results of a series of studies are reviewed that address questions such as defocus and other instrumental factors, and also the formation of channeling peaks that appear on the atomic columns along zone axes. For example, along Si(100) a peak forms and penetrates over 500ë whereas along Ge(100) it developes rapidly but disappears in less than 200ë. In higher atomic number elements, the penetration is even less (e.g. 1 O0ë for In).

We describe how general lattice images may be used to measure the variation of the potential in crystalline solids in any projection, with no knowledge of the imaging conditions. This approach is applicable to structurally perfect samples, in which interfacial topography, or changes in composition are of interest. We present the first atomic-level topographic map of a Si/SiO2 interface in plan-view, and the first microscopic compositional map of a Si/GeSi/Si quantum well in cross-section.

Quantitative electron energy-loss spectrometry was applied to a range of ceramic materials at a spatial resolution of <5 nm. Analysis of Fe L23 white lines indicated a low-spin state with a charge transfer of ∼1.5 electrons/atom onto the Fe atoms implanted into (amorphized) silicon carbide. Gradients of 2 to 5% in the Co:O stoichiometry were measured across 100-nm-thick Co3O4 layers in an oxidized directionally solidified CoO-ZrO2 eutectic, with the highest O levels near the ZrO2. The energy-loss near-edge structures were dramatically different for the two cobalt oxides: those for Co3O4 have been incorrectly ascribed to CoO in the published literature. Kinetically stabilized solid solubility occurred in an AIN-SiC film grown by low-temperature molecular beam epitaxy (MBE) on α(6H)-SiC, and no detectable interdiffusion occurred in couples of MBE-grown AIN on SiC following annealing at up to 1750°C. In diffusion couples of polycrystalline AIN on SiC, interfacial 8H sialon (aluminum oxy-nitride) and pockets of Si3N4-rich β'sialon in the SiC were detected.

We use electrochemical methods to control the adsorption of molecules onto an electrode for imaging in-situ by scanning tunneling microscopy. Measurements of the barrier for electron tunneling show that the mechanism of electron transfer differs from vacuum tunneling. Barriers depend upon the direction of electron tunneling, indicating the presence of permanently aligned dipoles in the tunnel gap. We attribute a sharp dip in the barrier near zero field to induced polarization. We propose a ‘tunneling’ process consisting of two parts: One is delocalization of quantum-coherent states in parts of the molecular adlayer that hybridize strongly (interaction ≥ kT) with Bloch states in the metal. This gives rise to a quantum-point-contact conductance, Gc ≤ 2e2/h at a height zo. The other part comes from the exponential decay of the tails of localized states, G = Gc exp{−2K(z − z0)}. Because measured decay lengths, (2K‘)−1, are small (≈ 1 Å), STM contrast is dominated by the contour along which G[z0 (x,y)] = Gc. Measured changes in z0 are used to calculate images which are in reasonable agreement with observations. We illustrate this with images of synthetic DNA oligomers.

The design of a low voltage point-projection field-emission transmission electron microscope is described and images showing 0.7nm resolution at 100 volts are given. A scheme for low voltage reflection electron holography from bulk samples in UHV is outlined. A new STM is described which allows atomic clusters to be transferred onto the tip, then introduced into a time-of-flight analyser for species identification.

After describing some recent developments in atomic force microscopy (AFM), a specific application to the study of shell ultrastructure is examined in detail. By embedding bleached nacreous tablets in epoxy and imaging them with the atomic force microscope (AFM) during in situ dissolution, it was possible to visualize the topography of both the top faces of the tablets and the impressions in epoxy made by the bottom faces of the tablets. This epoxy imprint reproduced tablet features down to the 10 nm scale. Using this technique it should be possible to measure correspondence between topographic features on the proximal and distal faces of tablets, which is necessary to form a three-dimensional picture of the nacreous region. In addition to these dissolution experiments, growth experiments (in modified sea water) on bleached, embedded tablets indicated that aragonite grows on a tablet as asperities oriented along the c axis, normal to the tablet surface. No change was seen on the surface of the epoxy, which confirmed that the crystals were growing on the tablet surface, not spontaneously nucleating out of solution.

Recent progress in the field of liquid crystal materials and oriented polymers studied by nearfield scanned probe microscopies (SPM) is presented here. The investigations were focused on scanning tunneling microscopy (STM) results of antiferroelectric liquid crystalline molecules observed at different elevated temperatures corresponding to different bulk mesophases of the material, and on surface morphological studies of a liquid crystalline polymer by scanning force microscopy (SFM). In the field of oriented thermoplastic polymers, SFM images of the morphology and molecular packing in the outermost surface of poly(butene-1) films are presented.

The Atomic Force Microscope (AFM) has created exciting new possibilities for imaging thin organic films under ambient conditions at length scales ranging from tens of microns to the sub - molecular scale. We present images of thin organic films prepared by the Langmuir-Blodgett (LB) technique that demonstrate the possibilities of the AFM.

The design and operation of a number of techniques in near field optical microscopy are described. Specific attention is paid to the three modalities of polarization, interference contrast, and photoluminescence imaging. By premodulating the polarization state of the sample beam, pure, linear, polarizing microscopy is performed. In addition, polarization anomalies are observed in the focal plane of a high numerical aperture lens. Amplitude and phase contrast imaging is performed in a feedback stabilized Mach-Zehnder interferometer. Magneto-optically induced polarization shifts are detected interferometrically, resulting in linear sensitivity. Localized photoluminescence is induced in porous silicon, and the results are correlated with the topography of the sample.

With photon tunneling microscopy (PTM), dielectric, semiconductor, and other surfaces are imaged by means of the phenomenon of photon tunneling (or evanescent waves). Vertical resolution is detector limited to one nanometer and the vertical range is λ/2. Lateral resolution is better than λ/4 with a field-of-view up to approximately 125 µm. PTM produces images of samples independent of size and thickness in real-time without metallization, shadowing, vacuum, electrons, or scanning probes. Tunneling images are analog processed for realtime 3-D topographic imaging with continuous viewpoint and magnification control. In this paper PTM images of a variety of samples are presented and briefly discussed.

The scanning electron microscope (SEM) is the most widely used, as well as the most versatile, of electron-optical instruments. In all of the imaging modes of the instrument it is now possible to achieve a spatial resolution on the nanometer scale from a bulk specimen, provided that the electron-optical performance of the instrument is of the necessary quality. In practice this means that a field emission gun (FEG) as well as a highly excited probe forming lens must be used. With state-of-the-art instrumentation, image resolutions as good as 4 - 5 nm at lkeV, and lnm at 20keV, are now achievable. This paper outlines the design criteria for a high resolution FEG SEM and discusses the type of image information available. The performance achieved is compared to that of other types of microscope that offer similar capabilities.

We have used nanometer spatial resolution secondary electron and Auger electron imaging in an ultra-high vacuum scanning transmission electron microscope to characterize microstructure in ultrathin films of Fe/Cu(100) grown at room temperature and Fe/CaF2/Si(111) grown at room temperature and 150 C. Thin film microstructure was correlated in situ with magnetic properties by using the surface magneto-optic Kerr effect.

Photo-induced conduction in thin insulating films of diamond was used to obtain STM images indicative of film morphology. UV light was used to generate carriers in the conduction band of diamond films grown on Si (111). Tunneling currents could only be established when the tunnel junction was illuminated. Without the light, no current was measured even with the tip in contact with the surface. Two types of films were studied. A CVD grown diamond film with nitrogen impurities and a diamond-like film grown by laser ablation of graphite. Topological detail was compared to that obtained with an AFM. The correspondence between AFM and photoinduced STM images suggests that the STM images are indicative of film morphology.