Natasha Erdman

The structure and chemistry of the TiO2-rich surface of SrTiO3 (001)

Oxide surfaces are important for applications in catalysis and thin film growth. An important frontier in solid-state inorganic chemistry is the prediction of the surface structure of an oxide. Comparatively little is known about atomic arrangements at oxide surfaces at present, and there has been considerable discussion concerning the forces that control such arrangements. For instance, one model suggests that the dominant factor is a reduction of Coulomb forces; another favours minimization of ‘dangling bonds’ by charge transfer to states below the Fermi energy. The surface structure and properties of SrTiO3—a standard model for oxides with a perovskite structure—have been studied extensively. Here we report a solution of the 2 × 1 SrTiO3 (001) surface structure obtained through a combination of high-resolution electron microscopy and theoretical direct methods. Our results indicate that surface rearrangement of TiO6-x units into edge-sharing blocks determines the SrO-deficient surface structure of SrTiO3. We suggest that this structural concept can be extended to perovskite surfaces in general.

Solution of the p(2 2) NiO(1 1 1) surface structure using direct methods

A solution for the p(2 2) NiO(1 1 1) surface reconstruction was obtained using direct methods applied to X-ray diAraction data. The solution was refined with 296 data points and 21 parameters using v 2 minimization Ov 2 a 1:82; Ra 0:17U. The surface atoms showed very small relaxation from the bulk interatomic distances (Ni‐Ni distances are 2:9 0:1 A; Ni‐Oˇ2:0 0:1 A). The solution can be characterized by alternating close-packed layers of oxygen and nickel atoms: the top surface layer is nickel terminated with 3/4 of the nickel atoms missing, the next oxygen layer is completely full, and the third, nickel layer, has 1/4 of the nickel atoms missing. The structure is consistent with theoretical predictions of octopolar termination of the surface and exhibits the features observed by previous STM studies. In addition, local density functional calculations have been carried out in this work in order to gain insights into the surface charge distribution and electronic structure of the proposed reconstruction. Calculated partial atomic charges and magnetic moments as well as densities of state are reported. The cation deficient nature of the surface requires the presence of electron holes for charge compensation, which we find mainly located on second layer oxygen atoms. The structure diAers from that recently reported for the same surface, and we are not able to reproduce the reported good fit to the (same) experimental data. ” 2000 Elsevier Science B.V. All rights reserved.

Direct synthesis of AgInO2

Potential applications as transparent conducting oxides have made the study of ternary metal oxides based on the delafossite structure very attractive. The well known and understood thermal instability of noble metal oxides, and therefore the associated problems with high-temperature solid-state techniques to yield pure complex oxides based on noble metals, clearly illustrates the need for low-temperature alternatives. For the first time, synthesis of 3R-AgInO2 at low temperature (175 8C) and pressure (,10 atm) was achieved by a single-step hydrothermal technique. Particle size of the orange crystallites ranged from 3 to 7 mm.

Nanoscale Crystallographic Analysis in FE-SEM Using Transmission Kikuchi Diffraction

Recent developments in SEM column design have led to the ability to produce nm spot sizes even at high probe currents [1], thus pushing the analytical techniques available in the SEM to conduct microanalysis with nanometer resolution. Although the limitations of microanalysis at these spatial resolution requirements stem from the physics of beam-specimen interaction and the volume from which the signal is generated during basic bulk sample observation and microanalysis, use of very thin specimens, similar to TEM, can lead to significant improvements in microanalysis resolution. This approach has been shown to be successful in for EDS analysis [2] and has been gaining prominence for crystallographic analysis using Transmission Kikuchi Diffraction (TKD, also referred to as t-EBSD) with a traditional EBSD camera [3].

New Approaches for high lateral resolution Array Tomography analysis

Recent applications of Scanning Electron Microscopy (SEM) are versatile. Nowadays, the SEM is not only a surface observation and analysis technique, but can also provide three-dimensional (3D) analysis that collects information about internal structure especially in soft materials such as biological materials. Array Tomography (AT) is one of the methods which are able to analyze large 3D area of biological materials. Ultrathin serial sections prepared with ultra-microtome are placed on substrates and then observed with SEM [1,2]. 3D images are reconstructed by stacking two-dimensional (2D) images of each section. In AT, it is possible to obtain 2D images with high lateral resolution by utilizing an incolumn electron detector. Furthermore, the charging artifacts are substantially reduced, since the substrate on which the sections are placed provides a conductive pathway. This also allows us to perform Energy Dispersive X-ray Spectrometry (EDS) analysis at high incident voltages without charging up. In this report, we present acquisition of 3D images composed of 2D images with high lateral resolution that based on AT and subsequent acquisition of 3D elemental maps by AT-EDS method.

An Examination of the Surface and Sub-Surface of Modern and Historical Platinum Photographic Prints Using Low Vacuum High-Resolution Scanning Electron Microscopy

Photographic prints of platinum metal on paper supports are some of the most exquisite and expressive in the world of fine art photography. Platinum prints were produced from about 1890 to 1920 in the USA and Europe. The chemical and material nature of these valuable prints is of great interest to many who are interested in their long-term preservation, in the intersection of science and art, and in the scientific and technical study of cultural heritage. This paper presents the results of a characterization study using newer electron microscopy techniques. In this study, a low vacuum high-resolution scanning electron microscope was used to study the surface and sub-surface of historic and modern platinum and/or palladium print samples. Using environmental SEM pressures allowed us to investigate the actual top surface and sub-surface with cross-sections without any preparation; no coatings of carbon or other material. Cross-sections were prepared using an argon plasma cross-polishing system. This study shows that the photographic image of platinum prints is composed of platinum nanoparticles embedded in the upper layers of the papers cellulosic fibers.

Investigation of Multiple, Large Area EDS Detectors on an SEM Capable of Various Mounting Geometries for Optimal EDS Analysis

It is common knowledge that collecting EDS data with dual large area SDD detectors from 180 degree opposing geometries has proven extremely beneficial with highly topographic samples [REF 1]. Traditionally, using high kV, the high count rates achievable from today’s SDD EDS detectors have been used to significantly reduce the time needed to acquire the statistical data necessary for X-ray analysis and mapping. Moreover, the use of low kV EDS for high spatial resolution analysis with minimized specimen damage has been recently gaining prominence [REF 2, 3]. When low kV microanalysis is performed, there can be a significant contribution from topography variations within the sample that can affect the quality and interpretation of the collected EDS data. Utilization of multiple large area EDS detectors can help alleviate some of these issues. In this paper the benefits of large area collection at low kV will be demonstrated on the next generation SEMs using conditions conducive to minimizing sample damage and contamination and to increasing spatial resolution. We will explore the benefits of multiple geometries with a variety of topographic samples. Special attention will be paid to detector positioning in these analyses and different geometries will be compared.

Ultra Low Voltage Secondary and Backscatter Imaging in FE-SEM - Successes and Challenges.

In the last decade there has been a quantum leap in the ability of the scanning electron microscope (SEM) to observe a variety of materials and biological specimens with ultra-high resolution and exceptional surface detail, in particular employing low voltage SEM. Low voltage imaging has been successfully employed as a key technique for charge control and reduction. Improvements in electron column optics towards smaller chromatic and spherical aberration coefficients, with improved ability to deal with charging specimens via precise control of the landing energy of impact electrons and electron signal detection through in-column signal filtering or signal collection angle control have opened new avenues for specimen observation [1]. In particular, these new design improvements have significantly advanced the ability to image insulating specimens with previously unattainable nanometer scale resolution [2] at landing voltages as low as 10V (Fig. 1).

Ultra High Solid Angle EDS System Advanced STEM Analysis for FE-SEM

EDS (Energy dispersive X-ray spectrometry) is a technique used for elemental analysis of a sample, through detection of characteristic X-rays generated from a sample impacted by an electron beam. STEM (Scanning Transmission Electron Microscopy) is a method to obtain high spatial resolution images with Z-contrast [1]. STEM-in-SEM has recently become a technique of choice for high spatial resolution imaging in SEM of ultra-thin specimens and can be combined with the EDS for compositional analysis of nanostructures, with the ability to resolve structures previously unattainable with bulk EDS analysis.

Crystal Grain Observation Using a Segmented Backscattered Electron Detector

Analyzing grain size in metallic specimens is important for quality-control of metal alloys. In the case of a scanning electron microscope (SEM), an electron backscatter diffraction (EBSD) system is generally used for grain structure analysis. In EBSD, the crystal orientation is determined by analyzing Kikuchi bands with an electron beam scanned over a tilted specimen. The electron beam is scanned on the specimen and a crystal orientation map, known as inverse pole figure (IPF) map, can be obtained. The grain sizes are determined by the IPF map.