John Damiano

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.

An Improved Holey Carbon Film for Cryo-Electron Microscopy

Two issues that often impact the cryo-electron microscopy (cryoEM) specimen preparation process are agglomeration of particles near hole edges in holey carbon films and variations in vitreous ice thickness. In many cases, the source of these issues was identified to be the residues and topography often seen in commercially available films. To study and minimize their impact during specimen preparation, an improved holey carbon film has been developed. Rather than using a consumable template based on soft materials that must be removed prior to grid assembly, a method was developed that uses a hard template and a water-soluble release layer to replicate the template pattern into the carbon films. The advantages of this method are the improved purity and flatness of the carbon films, and these attributes are shown to have a dramatic improvement on the distribution of single particles embedded in vitreous ice suspended across the holes. Improving particle distribution is an enabling factor toward increasing the throughput of data collection for cryoEM.

Quantitative Electrochemical Measurements Using In Situ ec-S/TEM Devices

Insight into dynamic electrochemical processes can be obtained with in situ electrochemical-scanning/transmission electron microscopy (ec-S/TEM), a technique that utilizes microfluidic electrochemical cells to characterize electrochemical processes with S/TEM imaging, diffraction, or spectroscopy. The microfluidic electrochemical cell is composed of microfabricated devices with glassy carbon and platinum microband electrodes in a three-electrode cell configuration. To establish the validity of this method for quantitative in situ electrochemistry research, cyclic voltammetry (CV), choronoamperometry (CA), and electrochemical impedance spectroscopy (EIS) were performed using a standard one electron transfer redox couple [Fe(CN)6]3-/4--based electrolyte. Established relationships of the electrode geometry and microfluidic conditions were fitted with CV and chronoamperometic measurements of analyte diffusion coefficients and were found to agree with well-accepted values that are on the order of 10-5 cm2/s. Influence of the electron beam on electrochemical measurements was found to be negligible during CV scans where the current profile varied only within a few nA with the electron beam on and off, which is well within the hysteresis between multiple CV scans. The combination of experimental results provides a validation that quantitative electrochemistry experiments can be performed with these small-scale microfluidic electrochemical cells provided that accurate geometrical electrode configurations, diffusion boundary layers, and microfluidic conditions are accounted for.

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.

Computer-Controlled In Situ Gas Reactions via a MEMS-based Closed-Cell System

Closed-cell TEM specimen holders based on MEMS-fabricated heater devices allow atomic resolution to be obtained on e.g. catalyst materials, at elevated temperatures and pressures [1-3]. We have shown that resolution in STEM imaging mode is largely unaffected by the gas pressure and cell temperature [4]. Understanding the physical characteristics and behavior of the MEMS heater devices in different gas environments has enabled development of an in situ reaction cell that is easy to use, and generates more reliable data. The holder-based approach does not require a dedicated (S)TEM, and most existing microscopes are compatible with current holder designs.

Entrepreneurship in the Microscopy Community

One highlight of the annual Microscopy & Microanalysis meeting is visiting the exhibition floor and seeing the latest product offerings. For students, post-docs, and others in the field, working for one of the large, established microscopy companies is an attractive option. Others may choose to work in academia, or at a national lab or international research consortia. An alternative to all of these choices is entrepreneurship – starting a new venture, or working for an early-stage company. Small companies create millions of jobs and bring innovative products or services to the world, playing a vital role in all markets, including microscopy.

Novel FIB-less Fabrication of Electrical Devices for in-situ Biasing

In this study, we report a novel fabrication scheme for in-situ electrical biasing of bulk material systems. This scheme integrates simple microelectronics fabrication processes with conventional TEM sample preparation through mechanical polishing, to produce electrical devices suitable for high resolution TEM/STEM studies under applied electrical bias. This is particularly crucial for applications such as quantitative STEM imaging, where FIB-induced sample damage distorts the image contrast, and prevents precise quantification.