CeO2 is an important material in many catalyst applications. CeO2, PrO2 and TbO2 are the only lanthanides known to exist as oxides in both 3+ and 4+ oxidation states. The high oxygen mobility at low temperature (≈300°C) results in easy oxidation-reduction cycles; a property utilized in the catalyst industry, especially for CeO2. Studying the oxidation-reduction behavior is thus very important to understanding the reactivity of CeO2 as a catalyst. We have studied CeO2 by in situ electron diffraction, high resolution electron microscopy (HREM) and electron energy-loss spectroscopy (EELS), not only to understand the reduction behavior but also to develop a method to quantify the reducibility of CeO2 or mixed oxides containing CeO2 by EELS. We have applied this method to study the behavior of ZrO2-CeO2 catalyst during reduction.

Experiments were performed on a PHILIPS-430 electron microscope operated at 300KV, fitted with a differentially pumped environmental cell and a Gatan Imaging Filter (GIF).

Elevated temperature scanning tunneling microscopy is used to study oxides that are room temperature insulators but become sufficiently electrically conducting at higher temperatures to allow imaging to be performed. Atomic resolution images of NiO, CoO, and UO2 have been obtained in this fashion which allow surface structure and defect determination. To complement the experiments, modeling of the electronic surface structure reveals which atomic sites give rise to the contrast observed in the images. Low voltage scanning electron microscopy is used to image small equilibrium pores in UO2 single crystals to evaluate the surface energy ratio of the (111) to (001) surfaces.

A new acoustic microscopy method was developed for providing near-surface elastic property mapping of a material. This method has a number of advantages over the traditional V(z) technique. First, it enables one to perform measurements in an automated mode that only requires user intervention in the setup phase. This automated mode makes it feasible to obtain quantitative microscopy images of the elastic property over an area on the material being tested. Also, it only requires a conventional ultrasonic system operating in pulsed mode for collecting the data, rather than a specialized tone-burst system, which is needed in the traditional quantitative scanning acoustic microscopy technique. Finally, unlike the traditional method, the new experimental process does not require calibration of the systems electronics or additional reference data taken under hard-to-duplicate identical conditions from a material that does not exhibit surface acoustic waves.

In truly standardless electron microprobe analysis, generated X-ray intensities calculated from firstprinciples are combined with a detector efficiency model. Though already used for energy dispersive (ED)analysis, the application of this concept to wavelength dispersive (WD) analysis is problematic, mainly becausethe reflectivity of spectrometer crystals is not well known. However, the need to carry out standard measurementswith every batch of WD analyses can be avoided by using stored intensity data, and interpolation maybe used when no standard is available. An empirical adjustment factor allowing for changes in spectrometerefficiency with time can be applied as necessitated by the variability of the spectrometer characteristics and theaccuracy required. A similar approach to background corrections, based on measured continuum intensities,can be used. While the convenience of standardless WD analysis is attainable only at the expense of reducedaccuracy, it can have a useful role where high accuracy is not needed or as a preliminary to applying a morerigorous routine using standards.

We report detailed experimental results on the electrochemical selective etching of doped Si. By using transmission electron microscopy analyses and spreading resistance measurements we investigated the dependence of the etching selectivity on the different parameters of the electrochemical cell, i.e., bias voltage and chemical solution. In B-doped samples immersed in buffered HF, the increase of bias voltage from 0.5 to 1 V produces a slight improvement of the etching selectivity and a B concentration as low as 1 × 1017 cm−3 can be successfully delineated at 1 V. A further improvement is achieved by using HF:HNO3:CH3COOH or HF:HCl chemical mixtures for which the delineation sensitivity approaches the value of 1 × 1016 cm−3. In buffered HF As-doped regions can be delineated to a concentration of 2 × 1017 cm−3, independently of the bias voltage, in the range 2–4 V. These results were used to measure the 2D doping diffusion profiles in silicon wafers patterned with polycrystalline Si strips and implanted with As or B, by using different tilt and twist angles. The high resolution of the electrochemical delineation allowed us to evaluate very accurately the effects of the implant angles on the lateral doping distribution.

Silicon dioxide is an important catalyst material, a mainstay insulator in microelectronics, and a widely distributed terrestrial and marine skeletal mineral. Geologically, it is found in one of a large number of polymorphic crystalline states, but can also be rendered “amorphous” by rapid cooling from the melt through a glass transition, depositing from a vapor or from solution (in radiolaria skeletons), oxidizing silicon, or irradiating with electrons, ions or neutrons. While the structures of the crystalline polymorphs are well documented, the structure of even the exhaustively studied vitreous silica remains largely enigmatic. Diffraction provides average information about short-range order—which appears to comprise [SiO4] tetrahedral units in all but a high-pressure crystalline polymorph—but is relatively insensitive to alternative medium-range arrangements of these structural units. One sensitive, but little understood, indicator is the position and shape of the first sharp diffraction peak (FSDP).

The technique of energy selected electron diffraction gives information about amorphous structures which can be used to characterize amorphous materials in terms of their structure. The diffraction data can be used to refine models obtained using molecular dynamics, resulting in physically reasonable models consistent with the diffraction data.

The effect of multiple scattering in a turbid medium on single-photon and two-photon fluorescencemicroscopy is experimentally investigated for different scattering characteristics including scattering anisotrophyand optical thickness of a turbid medium. It is demonstrated that two-photon excitation can providesignificant improvement in penetration depth through turbid media, due to reduced scattering experienced bythe excitation beam. It is also shown that the limiting factor in obtaining high-quality images under singlephotonexcitation is the fast degradation of image resolution caused by multiple scattering, while for twophotonexcitation it is limited by the degradation of image contrast due to the reduction in fluorescencestrength.

In 1999 NCEM's One Ångstrom Microscope (OAM) became fully operational. The OAM is a Philips CM300 FEG/UT field emission microscope with holographic capabilities that is equipped with a Gatan Image Filter (GIF) and operates at 300 kV. It was designed to reach a resolution close to the “magic barrier” around one Ångstrom (100 pm) by combining mid voltage technology with advanced computer processing [1,2]. Ahardware correction of the three-fold astigmatism allows for aberration free imaging down to sub Ångstrom values [3]. In this contribution it will be shown that the instrument's performance exceeded expectations because sub Ångstrom resolution can be achieved by reconstructing electron exit waves from focal series [4].

Figure la depicts a simulated [110] lattice image of a 90° partial dislocation in silicon. Tersoff potentials were used to calculate the exact atomic positions around dislocations with different core structures [5].

This article proposes a lossy three-dimensional (3-D) image compression method for 3-D secondary ion microscopy (SIMS) image sets that uses a separable nonuniform 3-D wavelet transform. A typical 3-D SIMS measurement produces relatively large amounts of data which has to be reduced for archivation purposes. Although it is possible to compress an image set slice by slice, more efficient compression can be achieved by exploring the correlation between slices. Compared to different two-dimensional (2-D) image compression methods, compression ratios of the 3-D wavelet method are about four times higher at a comparable peak signal-to-noise ratio (PSNR).

Energy-filtered transmission electron microscopy (EFTEM) can be used to acquire elemental distributionimages at high lateral resolution within short acquisition times. In this article, we present an overviewof typical problems from materials science which can be preferentially solved by means of EFTEM. In the firstexample, we show how secondary phases in a steel specimen can be easily detected by recording jump ratioimages of the matrix element under rocking beam illumination. Secondly, we describe how elemental maps canbe converted into concentration maps. A Ba-Nd-titanate ceramics serves as a typical materials science exampleexhibiting three different compounds with varying composition.

In situ real-time environmental high resolution electron microscopy (EHREM) under controlled reaction environments permits direct atomic resolution imaging of dynamic surface and sub-surface microstructures of reacting catalysts. Using the EHREM and complementary microscopy methods, we have investigated selective hydrogenation reaction mechanisms over novel xerogel catalysts of ruthenium and Ru with Co and Au promoters on titania supports, and report an alternative heterogeneous catalytic process for the hydrogenation of adiponitrile (ADN) in the manufacture of Nylon 6,6. The direct EHREM observations are supported by ultra-high resolution low voltage scanning electron microscope (SEM) of spatial distributions of the highly dispersed nanometer-size catalyst particles and parallel chemical studies. The results demonstrate the important role of in situ EHREM in the design of heterogeneous catalytic hydrogenation processes on the nanoscale.

One of the great challenges of nanotechnology is how to produce and modify objects at nanoscale dimensions. The search for physical and chemical methods for controlled synthesis, modification and characterization of semiconductor nanocrystals is of special interest due to their novel electronic and optical properties. Recently we have achieved the first laser-induced phase transformation in semiconductor nanocrystals [1], irradiating colloidal solutions of CdS nanocrystals with 7 ns pulses of 532 nm wavelength. We used established wet-chemistry methods to synthesize the CdS nanocrystals, and a combination of electron microscopy methods to determine the structure, size and composition of the nanocrystals. In the present paper we report a wavelength dependence of the laser-induced phase transformations in CdS. We also explore electron-induced transformations in comparison with their photon counterparts.

Aqueous colloidal solutions of CdS nanocrystals were prepared by mixing of CdCl2 with Na2S in the presence of Sodium Mercaptoacetate and HC1 [2].

When Pt particles of sub-nanometer dimensions are inserted into the linear channels of the potassium ion form of zeolite L, the resultant Pt/KL catalyst converts linear n-C6 hexane into cyclic C6 benzene with remarkable efficiency [1,2].

However, a drawback to Pt/KL catalysts is that they are exquisitely sensitive to sulfur contamination in the n-hexane feed. The catalyst deactivates rapidly when there are trace amounts (> 50 parts per billion) of sulfur in the feed. Bright field TEM studies show that the Pt particles remain finely dispersed within the channels after sulfur poisoning, with typical particle widths < 1.5 nm, implying that a large percentage of the Pt atoms still reside on the surfaces of the particles. For heterogeneous catalysts such as Pt/γ-alumina, where the Pt particles are always readily accessible on the external surface of the alumina support, such sulfur concentrations are tolerated.

We show that in the limit of a large objective (probe-forming) aperture, relevant to a spherical aberration corrected microscope, the Z-contrast image of a zone-axis crystal becomes an image of the 1s Bloch states. The limiting resolution is therefore the width of the Bloch states, which may be greater than that of the free probe. Nevertheless, enormous gains in image quality are expected from the improved contrast and signal-to-noise ratio. We present an analytical channeling model for the thickness dependence of the Z-contrast image in a zone-axis crystal, and show that, at large thicknesses, columnar intensities become proportional to the mean square atomic number, Z2.

Confocal laser scanning microscopy (CLSM) has been used to generate three dimensional projection maps of less fluorescent domains caused by asphaltene aggregates in the autofluorescent matrix of crude oil. Heavy crude oils contain asphaltene particles resulting in the production of optically observable micron sized asphaltene aggregates. This technique has been employed to determine the volume fraction of aggregated asphaltenes, øagg, and the time evolution of this phenomenon. The measurements cover a range of various concentrations of asphaltene volume fractions of the heavy asphaltenic oil, øm, from øm = 0 to øm = 0.6.

Examining crude oils for asphaltenes aggregates using CLSM presents a challenge due to the strong absorption of the oils. This is because some molecules of the crude oil fluoresce when excited by optical laser light used as a source in the CLSM. Other molecules of the crude oils absorb light at similar wavelengths.

Very high angle (~100 mrad) annular dark-field (HAADF) images in a dedicated scanning transmission electron microscope (STEM) can be used to quantitatively measure the number of atoms in a cluster on a support material. We have developed a computer program which will automatically find the location of the particles and then integrate the intensity to find the number of atoms per cluster. We have examined ultra-small Pt clusters on a C substrate by this novel mass-spectroscopic technique. We discovered that the Pt clusters maintain their three-dimensional shape, and are probably spherical.