Extended abstract of a paper presented at Microscopy and Microanalysis 2012 in Phoenix, Arizona, USA, July 29 – August 2, 2012.

Extended abstract of a paper presented at Microscopy and Microanalysis 2012 in Phoenix, Arizona, USA, July 29 – August 2, 2012.

It has long been thought that (111) surfaces of rock salt oxides microfacet to neutral surfaces upon annealing because of the very large energies involved in bulk terminating a layer of like ions. However in a recent reflection electron microscopy (REM) study Gajdardziska-Josifovska et al. found that MgO(lll) surfaces annealed in flowing oxygen furnaces at 1500°C not only did not microfacet, but displayed a √3×√3R30° surface periodicity that was stable in air. To determine the structure of this unusually stable surface MgO (111) transmission electron microscopy (TEM) samples were annealed in a vacuum furnace in the present study and their transmission electron diffraction (TED) patterns were analyzed with direct phasing methods.

The TEM samples were prepared by orienting a MgO single crystal and sawing lmm wafers along a (111) plane. Disk samples were then ultrasonically drilled, dimpled, mechanically polished and/or hot nitric acid etched, and milled with 5 KeV Ar+ ions.

Many industrial catalysts have a complex geometric structure to enable reacting gases or fluids to reach as much of the active surface of the catalyst as possible. The catalyzing surface frequently consists of a complex chemical mixture of different phases produced by an evolved chemical process. The active components are often very small particles dispersed on high-surface-area supports. The catalytic properties of this type of catalyst depend on the structure, composition, and morphology of the active species as well as the supports. TEM/STEM and associated techniques have been used extensively to characterize the structure and composition of supported catalysts. Surface morphology of supported catalysts is generally examined by secondary electron imaging, especially at low incident beam energies. It is, however, frequently found that small metal particles are not usually seen in SE images because of the complication of support topography

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The issue of specimen contamination becomes more important at a rate proportional to the use of high-brightness electron source Transmission Electron Microscopes (TEM). These TEMs combine smaller electron probes with increased current, allowing high resolution specimen imaging and enhanced analytical data collection. Small, high current electron probes tend to increase the detrimental effect of hydrocarbon presence on the specimen's surface. The subsequent formation of carbon deposits caused by the focused probe often times obstructs imaging and precludes acceptable analytical results. by plasma cleaning the specimen, contamination is removed and the results obtained by high resolution electron microscopy (HREM), scanning transmission electron microscopy (STEM) and analytical electron microscopy (AEM) using EDS or electron energy loss spectroscopy (EELS) are greatly enhanced. Recent instrumentation developments have resulted in the application of a high frequency, low energy, reactive gas plasma generated in an oil-free vacuum that chemically removes hydrocarbon contamination from both the TEM specimen holder and the specimen without altering its properties.

Zeolites are crystalline aluminosilicates possessing a regular microporous channel network. Unique properties of zeolites such as the presence of framework cations, acid sites, and their well-defined porous structure-with pore sizes similar to those of small molecules-account for their traditional utilization in ion exchange, catalysis, and separation. in addition, zeolites are being investigated for novel emerging applications in a diversity of areas including optoelectronic devices and reactive membranes because they provide for discrimination, recognition, and organization of molecules with a precision of less 1 Å. However, their applications are limited by the relatively small pore openings; therefore, pore enlargement was one of the main aspects in zeolite chemistry. A new class of porous materials, which contain large uniform spaces in the mesopore size regimen (15-100 Å), was reported. These so-called mesoporous materials have two different characters, disorder at the atomic scale but long range order at the atomic scale but long range order at the mesoscopic scale.

The distribution of small amounts of alloying elements or impurities to interfaces can have a major influence on the properties of a material and the atom probe field ion microscope technique is well suited for the study of such segregation effects, where structural and compositional changes often take place over regions only a few nanometers wide.

Many features of the atom probe technique make it very useful in studies of interfaces:

1. i) high spatial resolution, about lnm laterally and 0.2 nm in depth

2. ii) equal sensitivity for all elements, including the lightest

3. iii) no specimen contamination, surface artifacts from the specimen preparation are removed by field evaporation,

4. iv) low temperature operation, negligible diffusion during analysis

A ncessary prerequisite for any systematic analysis is the ability to prepare suitable specimens. The volume accessible for analysis by APFIM is orders of magnitude smaller than a typical grain size, so a specimen preparation technique was developed that could bring features of interest sufficiently close to the apex (see Fig. la).

The cloning and expression of GFP in heterologous systems introduced a fantastic tool for studying specific gene expression and protein localization inside living cells. However, one aspect of GFP that has not been exploited to its full potential is its use as a quantitative imaging tool. To determine its quantitative usefulness, we have addressed five points that are important in GFP imaging: detectable signal over background, photostability, pH stability of the molecule, temperature dependence of chromophore formation, and estimation and normalization of GFP levels.

To determine the quantitative limits of GFP in cells, several GFP versions (wtGFP, αGFP (F99S/M153T/V163A), S65T, EGFP (F64L/S65T), and a blue-shifted variant, EBFP (F64L/S65T/Y66H/Y145F)) were compared by imaging of GFP expressing cells or by spectroscopic measurements of purified proteins. When imaged, the GFP signals are contaminated by the naturally occurring background autofluorescence, but improved detection can be achieved for each green GFP by combination of confocal microscopy using 488 nm excitation, a rapid cut-on dichroic mirror, and a narrow bandpass emission filter (Figure l).

Extended abstract of a paper presented at Microscopy and Microanalysis 2011 in Nashville, Tennessee, USA, August 7–August 11, 2011.

In recent years, a number of different groups(1) have investigated and reported on implementing Web-based controls for SEMs and TEMs. Through telemicroscopy, as the field is often known, they have demonstrated that expensive microscopy resources can be shared and the experience of remote experts utilized in an efficient, cost-effective manner. Up to this point most technological demonstrations of telemicroscopy have been implemented as retrofits to existing microscopes. As retrofits, these demonstrations had limitations which a system designed from day one as a networked instruments could avoid. present here details of an ongoing project at R.J. Lee Instruments to redesign the software interface to our Personal SEM product around a TCP/IP link between the SEM hardware and the user interface. All communications between the SEM and console, including commands and image data are transmitted over a single 10-BaseT Ethernet link using the connection-oriented TCP protocol.

One of the most challenging tasks for high-resolution electron microscopy (HREM) is the atomistic investigation of defects and interfaces in thin films of semiconductors and ceramics. In particular, the application of these materials in electronic devices requires the understanding of the atomistic structure responsible for electronic and optical properties. The imaging of these structures requires a point resolution down to 0.1 nm. For example the smallest atomic spacing of GaAs in the (110) projection is 0.14 nm. According to Scherzer the point resolution of the TEM is proportional to spherical-aberration coefficient Cs1/4 and to the wave length λ3/4. Commercial medium-voltage microscopes up to 400 kV offer only a point resolution of 0.16 nm due to the high spherical-aberration constant Cs of the electromagnetic objective lens. Decreasing the wave length λ by increasing the electron energy improves the point resolution, but has the drawback of severe radiation damage and high costs.

Sample preparation for transmission electron microscopy (TEM) has been a source of speculation with regards to potential for the creation of artifacts which may confound data gleaned from TEM analysis. For semiconductor integrated circuit (IC) materials characterization, the most common sample preparatory methods are based on final thinning by ion beam milling. The latest shift towards Copper / low dielectric constant (k) composite systems in the semiconductor IC industry provides several challenges for TEM sample preparation resulting from differences in milling rates and materials properties for neighboring features.

In conjunction with process development for integration of Cu / low-k materials, conducted at SEMATECH, we have systematically studied the effects of TEM sample preparation by ion milling in order to search for artifacts that could result from sample thinning procedures. For this purpose we have studied wafers with patterned copper lines isolated by a low-k polymer. One sample was stressed by thermal and electronic bias, while a second was subjected to only thermal stress.

In flowering plants, pollination and the process of fertilization are complex processes involving a series of cell-to-cell communication events. Though details of the progression of the pollen tube through the pistil, beginning with germination of the pollen grain on the stigma and culminating with delivery of the sperm cells to the embryo sac, are well established for several higher plant species, the mechanisms involved have yet to be elucidated. It has been shown that the transmitting tissue, which coincides with the path of pollen tubes in the gynoecium, is composed of highly secretory cells characterized by an extensive extracellular matrix (ECM). The actual roles that this ECM plays in pollination are currently unknown, although functions proposed include mechanical and/or chemotropic pollen tube guidance as well as pollen tube nutrition.

High electron mobility structures have been built for several years now using strained silicon layers grown on SixGe(1-x) with x in the 25-40% range. In these structures, a thin layer of silicon is grown between layers of unstrained GeSi alloy. Matching of the two lattices in the plane of growth produces a bi-axial strain in the silicon, splitting the conduction band and providing light electron levels for enhanced mobility. If the silicon channel becomes too thick, strain relaxation can occur by injection of misfit dislocations at the growth interface between the silicon and GeSi alloy. The strain field of these dislocations then gives rise to a local potential variation that limits electron mobility in the strained Si channel. This study seeks to verify this mechanism by measuring the absolute conduction band shifts which track the local potential near the misfit dislocations.

Today material science requires the use of increasingly powerful tools in material analysis. The last twenty years have witnessed the development of a number of analytical techniques. However, among these techniques, only a few allow observation and analysis of materials at the nanometer level ; one can mention scanning transmission electron microscopy coupled with electron energy loss spectrometry (STEM-EELS), SIMS and atom-probe techniques. In the STEM combined with electron energy loss spectrometry the spatial resolution can be better than one nanometer on a wide scanning area. However the in-depth spatial resolution is limited by the specimen thickness and therefore strongly depends on samples preparation. On the contrary, In SIMS techniques the in-depth spatial resolution can be as good as one nanometer but the lateral resolution is set by the ion beam diameter.

A great deal can be learned about integrated circuits (ICs) and microelectronic structures simply by imaging them in a focused ion beam (FIB) system. FIB systems have evolved during the past decade from something of a curiosity to absolutely essential tools for microelectronics design verification and failure analysis. FIB system capabilities include localized material removal, localized deposition of conductors and insulators, and imaging. A major commercial driver for FIB systems is their usefulness in the design debugging cycle by (1) rewiring ICs quickly to test design changes and (2) making connection to deep conductors to facilitate electrical probing of complex ICs. FIB milling is also used for making precision cross sections and for TEM sample preparation of microelectronic structures for failure analysis and yield enhancement applications.

Extended abstract of a paper presented at Microscopy and Microanalysis 2007 in Ft. Lauderdale, Florida, USA, August 5 – August 9, 2007