Wilbur C. Bigelow

A new MEMS-based system for ultra-high-resolution imaging at elevated temperatures

In recent years, an increasing number of laboratories have been applying in situ heating (and ultimately, gas reaction) techniques in electron microscopy studies of catalysts and other nanophase materials. With the advent of aberration‐corrected electron microscopes that provide sub‐Ångström image resolution, it is of great interest to study the behavior of materials at elevated temperatures while maintaining the resolution capabilities of the microscope. In collaboration with Protochips Inc., our laboratory is developing an advanced capability for in situ heating experiments that overcomes a number of performance problems with standard heating stage technologies. The new heater device allows, for example, temperature cycling from room temperature to greater than 1000°C in 1 ms (a heating rate of 1 million Centigrade degrees per second) and cooling at nearly the same rate. It also exhibits a return to stable operation (drift controlled by the microscope stage, not the heater) in a few seconds after large temperature excursions. With Protochips technology, we were able to demonstrate single atom imaging and the behavior of nanocrystals at high temperatures, using high‐angle annular dark‐field imaging in an aberration‐corrected (S)TEM. The new capability has direct applicability for remote operation and (ultimately) for gas reaction experiments using a specially designed environmental cell. Microsc. Res. Tech., 2009.

Electron Microscopy of Gold Soldered Joints

Electron photomicrographs were taken to examine and compare the structure of the properly heated soldered joints with that of the overheated joints. No diffusion of the solder was observed in the former group and considerable diffusion took place in the latter group. Pronounced oxide formation, micro-porosity, and alloying with the parent alloy were observed in the overheated joints.

Silicification of developing internodes in the perennial scouring rush (Equisetum hyemale var. affine)

Abstract An electron microprobe (EMP) analysis of silica (SiO 2 ) deposition in the epidermis of developing internodes of the perennial scouring rush ( Equisetum hyemale var. affine ) indicates that SiO 2 is first detected in the stomatal apparatus beginning with internode 3, then the epidermal papillae (internode 8), and finally in radial cell walls of the long epidermal cells (internode 10). This process is initiated in the intercalary growth regions at the bases of the elongating internodes. The deposition of SiO 2 in long epidermal cell walls occurs after internodal extension has ceased and should therefore be considered as one of the final stages in internodal differentiation that involves strengthening the cellulosic framework of the cell wall. EMP measurements indicate that SiO 2 in stomata is equivalent to 30% of a pure SiO 2 standard and that SiO 2 in the radial walls of long epidermal cells averages twice that measured on the tangential walls of these same cells. This study supports the view that silicification plays a major role in strengthening the developing perennial scouring rush internodal system and that regulation of this process in this and other species of Equisetum , whose SiO 2 deposition patterns are markedly different, deserves further study.

Electron-probe microanalysis of silicon in the epidermis of rice (Oryza sativa L.) internodes.

SummaryElectron-probe X-ray microanalysis showed that significant amounts of silicon are accumulated in the entire epidermal system of the rice internode except in the stomatal apparatuses. Thus, there is a lack of specific sites for Si deposition from levels just above the base to the tip of the rice internode. In the intercalary meristem region, 1 cm above the base of the internode, point-count data indicate more Si accumulation in the dumb-bell shaped silica cells than in the long epidermal cells. Above this region, Si is accumulated essentially in a uniform pattern in all epidermal cells. Such a pattern for Si accumulation in rice internodes markedly contrasts with that for Avena internodes and may explain, in part, why rice plants have a higher percentage Si (dry weight basis) in their shoots. The adaptive significance of this silicification pattern in rice is discussed.

A New Dental Superalloy System: III. Microstructure and Phase Transformations

A microstructural study was conducted on 15 cobalt-chromium-nickel alloys of the basic composition 40 Co-30 Ni-30 Cr. The alloys were strengthened by the addition of tantalum and tantalum-rich regions were found at the interdendritic spaces. The increase in Ta concentration caused a decrease in the concentration of the β phase and an increase in the amounts of the a phase. Excessive amounts of Ta resulted in formation of the σ phase. The failure of the alloy occurred as a result of the interconnection of σ regions.

A Novel Heating Technology for Ultra-High Resolution Imaging in Electron Microscopes

Capabilities for in-situ studies of materials at elevated temperatures and under gaseous environments have received increasing attention in recent years [1]. With the advent of electron microscopes that provide routine imaging at the atomic level (e.g. aberration-corrected TEM and STEM instruments), it is of particular interest to be able to record images at high temperatures while retaining the inherent resolution of the microscope; that is, the resolution is not limited by drift in the heating holder or other instabilities associated with its operation. A number of commercial and experimental heating devices have been used over the years; some holders are designed with miniature furnaces that heat entire grids [2], while a more recent development used a tiny spiral filament coated with a carbon film as the heater element [3]. These devices, while very useful for some applications (particularly in “environmental microscopes” that employ differential pumping to allow gases at some elevated pressure to be injected around the specimen), are invariably not as stable as might be desired for sub-Angstrom imaging experiments. They are also limited by the speed at which the sample can be heated to temperature for stable operation. In collaboration with Protochips Inc. (Raleigh, NC), our laboratory is developing a novel new technology for in-situ heating experiments that overcomes a number of performance problems associated with standard heating stage technologies [4].

Electron microprobe analysis of silica cells in leaf epidermal cells ofCyperus alternifolius

SummaryElectron microprobe analysis was used to examine relative amounts of selected accessory elements (Ca, Mg, K, Na, P, Mn, and Fe) associated with silicon in silica cells in leaf epidermal cells ofCyperus alternifolius. In the leaf epidermal cells, silicon is localised in significant quantities in silica cells and in a few long epidermal cells. Silicon could not be detected in the stomatal apparatuses. The accumulation of significant amounts of silicon in the silica cell appears to retard the accumulation of K and to enhance the accumulation of Ca, Mg, Mn, Fe, and P. Sodium was detected in very small traces in the silica cells. The possible functional significance of the altered deposition patterns for these elements inCyperus is discussed.

Controlled In Situ Gas Reaction Studies of Catalysts at High Temperature and Pressure with Atomic Resolution

In situ reaction studies of catalyst materials using closed-cell environmental specimen holders have been shown to allow atomic resolution to be obtained on e.g. catalyst materials, at elevated temperatures and pressures [1-4]. These holders incorporate MEMS-based devices into the holder tip, which serve to encapsulate a gas layer between a thin film heater device and an ultra-thin amorphous SiN window. With a gas layer of only 5-10 μm, pressures of up to 1 atm and temperatures of 1000°C are routinely employed without significant loss in resolution, especially in scanning transmission mode in a probecorrected microscope [1]. The holder-based approach does not require a dedicated TEM, and most existing microscopes are compatible with current holder designs.

Development of a Novel Environmental Cell for In-Situ Gas Reaction Experiments via Aberration-Corrected STEM Imaging

A novel heating technology composed of a disposable MEMS-based (microelectromechanical systems) device has recently been developed and shown to provide unique in-situ heating capabilities in electron microscopes [1]. Protochips, Inc. (Raleigh, NC) provides the Aduro heater technology, composed of a disposable MEMS device that serves both as the heating element and the specimen support grid, a TEM holder with electrical feed-throughs, and an external current source. This system has been shown to provide near instantaneous (10 °C/s) heating and cooling, and is stable to the limit of the microscopes specimen stage so full sub-Ångström image resolution in highangle annular dark-field imaging mode can be achieved on our JEOL 2200FS scanning transmission electron microscope (STEM/TEM) instrument, fitted with a hexapole corrector on the probe-forming lenses (CEOS GmbH, Heidelberg, Ger.). This heating technology is being extended to function in a closed cell system that allows heating in a gaseous environment for in-situ elevated temperature reaction studies. The design concepts and early results of testing of the environmental cell (E-cell) performance are detailed here.

Effect of Tantalum Additions to a Cobalt-Chromium-Nickel Base Alloy

An investigation by electron diffraction, transmission and scanning electron microscopy, and energy-dispersive X-ray analysis has shown that Ta additions to a 40-30-30 Co-Cr-Ni-base alloy strengthen by ordering and by formation of coherent α-Co3Ta precipitate. However, increasing Ta content increases the proportion of the hexagonal phase and decreases ductility.