Scanning Transmission Electron Microscopy STEM

STEM basically offers the same information as obtained with SEM, however with enhanced resolution and thus the ability to observe samples at higher magnifications. Features on pretreated surfaces can be observed at higher resolution and environmental effects on these surfaces can be studied. 

Not only can the physical picture of the adherend surface, obtained by microscopy, aid in the understanding of adhesion processes, but also a chemical picture of the surface, obtained by various spectroscopies detailed below, is needed. 

The STEM is unrivaled in its ability to obtain high-resolution imaging combined with microanalysis from specimens that can be fashioned from almost any solid. Major applications include the analysis of metals, ceramics, electronic devices 

There are three types of instruments that provide STEM imaging and analysis to various degrees the TEM/STEM, in which a TEM instrument is modified to operate in STEM mode the SEM/STEM, which is a SEM instrument with STEM imaging capabilities and dedicated STEM instruments that are built expressly for STEM operation. The STEM modes of TEM/STEM and SEM/STEM instruments provide useful information to supplement the main TEM and SEM modes, but only the dedicated STEM with a field emission electron source can provide the highest resolution and elemental sensitivity. 

The development of the STEM is relatively recent compared to the TEM and the SEM. Attempts were made to build a STEM instrument within 15 years after the invention of the electron microscope in 1932. However the modern STEM, which had to await the development of modern electronics and vacuum techniques, was developed by Albert Crewe and his coworkers at the University of Chicago.  

The most important criterion for a STEM instrument is the amount of current in the small electron probe. Generally, 1 nA of probe current is required for high- 

The major STEM analysis modes are the imaging, diffraction, and microanalysis modes described above. Indeed, this instrument may be considered a miniature analytical chemistry laboratory inside an electron microscope. Specimens of unknown crystal structure and composition usually require a combination of two or more analysis modes for complete identification. 

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The very high powers of magnification afforded by the electron microscope, either scanning electron microscopy (sem) or scanning transmission electron microscopy (stem), are used for identification of items such as wood species, in technological studies of ancient metals or ceramics, and especially in the study of deterioration processes taking place in various types of art objects. 

Scanning thermal microscopy, 3 332-333 Scanning transmission electron microscopy (STEM), 24 74... 

Substrate Characterization. Test coupons and panels of 7075-T6 aluminum, an alloy used extensively for aircraft structures, were degreased In a commercial alkaline cleaning solution and rinsed In distilled, deionized water. The samples were then subjected to either a standard Forest Products Laboratories (FPL) treatment ( 0 or to a sulfuric acid anodization (SAA) process (10% H2SO4, v/v 15V 20 min), two methods used for surface preparation of aircraft structural components. The metal surfaces were examined by scanning transmission electron microscopy (STEM) In the SEM mode and by X-ray photoelectron spectroscopy (XPS). 

To find the distribution of iron within the nanotube walls an energy dispersive x-ray spectroscopy (EDS) line scan was performed via scanning transmission electron microscopy (STEM), see Fig. 5. 55. The intensity of both the TiK and FeKa lines are maximum at the center of the wall due to its torus shape. Despite the presence of isolated hematite crystallites, a more or less uniform distribution of iron relative to the titanium can be seen across the wall. STEM line scans were performed across a number of walls, and while the average relative intensity of the TiK and FeKa lines varied from wall to wall the relative distribution across a single wall remained uniform. It appears that some of the iron goes into the titanium lattice substituting titanium ions, and the rest either forms hematite crystallites or remains in the amorphous state. 

Transmission electron microscopy (TEM) and scanning transmission electron microscopy (STEM) are recognized as powerful and versatile tools for the characterization of supported metal catalysts, because real-space images of catalysts with spatial resolution down to 0.1 nm can be recorded and combined with high-spatially resolved spectroscopic information. However, TEM has been used mainly for ex situ characterization, for example, of catalysts after gas treatments. 

Fig. 7.7 Scanning transmission electron microscopy (STEM) images of supported gold catalysts, along with particle diameter distributions, double-logarithmic plots showing how particle volume (proportional to intensity) depends on particle size, and geometric distributions of truncated octahedrons with certain edge lengths and thickness, as indicated in Figure 7.8. (Adapted from [18]).

Scanning Transmission Electron Microscopy (STEM) [22]. STEM represents a merger of the concepts of TEM and SEM. Modes of operation and mechanisms of contrast and of imaging are essentially the same as in CTEM but the main advantage of STEM is the ability to carry out microanalysis at very high resolution (see Section H). 

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