Scanning transmission electron microscope

Crewe A V, Wall J and Welter L M 1968 A high resolution scanning transmission electron microscope J. Appl. Phys. 39 5861-8... 

Figure 1 Signals generated when the focussed electron beam interacts with a thin specimen in a scanning transmission electron microscope (STEM).

By use of a scanning transmission electron microscope, with the incident beam grazing the crystal surface, the structural features on surfaces have also been revealed with a resolution of I08 or better... 

Analysis of individual catalyst particles less than IMm in size requires an analytical tool that focuses electrons to a small probe on the specimen. Analytical electron microscopy is usually performed with either a dedicated scanning transmission electron microscope (STEM) or a conventional transmission electron microscope (TEM) with a STEM attachment. These instruments produce 1 to 50nm diameter electron probes that can be scanned across a thin specimen to form an image or stopped on an image feature to perform an analysis. In most cases, an electron beam current of about 1 nanoampere is required to produce an analytical signal in a reasonable time. 

The scanning transmission electron microscope (STEM) was used to directly observe nm size crystallites of supported platinum, palladium and first row transition metals. The objective of these studies was to determine the uniformity of size and mass of these crystallites and when feasible structural features. STEM analysis and temperature programmed desorption (TPD) of hydrogen Indicate that the 2 nm platinum crystallites supported on alumina are uniform In size and mass while platinum crystallites 3 to 4 nm in size vary by a factor of three-fold In mass. Analysis by STEM of platinum-palladium dn alumina established the segregation of platinum and palladium for the majority of crystallites analyzed even after exposure to elevated temperatures. Direct observation of nickel, cobalt, or iron crystallites on alumina was very difficult, however, the use of direct elemental analysis of 4-6 nm areas and real time Imaging capabilities of up to 20 Mx enabled direct analyses of these transition metals to be made. Additional analyses by TPD of hydrogen and photoacoustic spectroscopy (PAS) were made to support the STEM observations. 

Figure 5 shows the Z-contrast scanning transmission electron microscope (STEM) image of a Ru/Sn02 nanocomposite catalyst prepared by the assembly process [18]. A combined EDX analysis, using an electron beam of... 

There are two types of electron energy loss spectroscopy currently in use. The first of these is found in scanning transmission electron microscopes. As indicated in Figure 5.1, compositional information may be obtained in the TEM by measuring the energy loss of the inelastically scattered electrons transmitted through a thin specimen. 

The scanning transmission electron microscope (STEM) combines the two modes of operation. Here, the scanning coils are used to illuminate a small area of... 

Wall, J. S., and Hainfeld, J. F. (1986). Mass mapping with the scanning transmission electron microscope. Annu. Rev. Biophys. Biophys. Chem. 15, 355—376. 

Analytical electron microscopy of individual catalyst particles provides much more information than just particle size and shape. The scanning transmission electron microscope (STEM) with analytical facilities allows chemical analysis and electron diffraction patterns to be obtained from areas on the order of lOnm in diameter. In this paper, examples of high spatial resolution chemical analysis by x-ray emission spectroscopy are drawn from supported Pd, bismuth and ferric molybdates, and ZSM-5 zeolite. 

The Use of Scanning Transmission Electron Microscopes to Study Surfaces and Small Particles... 

Atomic Number Imaging of Supported Catalyst Particles by Scanning Transmission Electron Microscope... 

Over the past decade increasing use has been made of the scanning transmission electron microscope (STEM) for examining catalysts(20). Owing to the increased efficiency with which scattered electrons and associated signals such as X-rays, secondary and Auger electrons may be collected, the STEM offers greater analytical flexibility compared with the CTEM (21). 

Powder X-ray diffraction (XRD) data were collected via a Siemens D5005 diffractometer with CuKa radiation (A. = 1.5418 A). Routine transmission electron microscopy (TEM) and Z-contrast microscopy were carried out using an HITACH HD-2000 scanning transmission electron microscope (STEM) operated at 200 kV. Nitrogen gas adsorption measurements (Micromeritics Gemini) were used to determine the surface area and porosity of the catalyst supports. Inductively coupled plasma (ICP) analysis was performed via an IRIS Intrepid II XSP spectrometer (Thermo Electron Corporation). 

Mass determination of unstained virus specimens in the scanning transmission electron microscope gives a value of 35 7 x 10 daltons (Freeman and Leonard, 1981). 

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