Transmission electron microscopy imaging modes

In many ways the nanocrystal characterization problem is an ideal one for transmission electron microscopy (TEM). Here, an electron beam is used to image a thin sample in transmission mode [119]. The resolution is a sensitive fimction of the beam voltage and electron optics a low-resolution microscope operating at 100 kV might... 

Transmission electron microscopy (tern) is used to analyze the stmcture of crystals, such as distinguishing between amorphous siUcon dioxide and crystalline quartz. The technique is based on the phenomenon that crystalline materials are ordered arrays that scatter waves coherently. A crystalline material diffracts a beam in such a way that discrete spots can be detected on a photographic plate, whereas an amorphous substrate produces diffuse rings. Tern is also used in an imaging mode to produce images of substrate grain stmctures. Tern requires samples that are very thin (10—50 nm) sections, and is a destmctive as well as time-consuming method of analysis. 

High Resolution Transmission Electron Microscopy (HRTEM, Philips CM20, 200 kV) was applied to get structural and nanotextural information on the fibers, by imaging the profile of the aromatic carbon layers in the 002-lattice fringe mode. A carbon fiber coated with pyrolytic carbon was incorporated in epoxy resin and a transverse section obtained by ultramicrotomy was deposited on a holey carbon film. An in-house made image analysis procedure was used to get quantitative data on the composite. 

Transmission electron microscopy (TEM) resembles optical microscopy, except that electromagnetic instead of optical lenses are used to focus an electron beam on the sample. Two modes are available in TEM, a bright-freld mode where the intensity of the transmitted beam provides a two-dimensional image of the density or thickness of the sample, and a dark-field mode where the electron diffraction pattern is recorded. A combination of topographic and crystallographic information, including particle size distributions, can be obtained in this way [32],... 

In 2008 Shin et al. used lETS and transmission electron microscopy (TEM) to characterize the chemical integrity and morphology of rubrene (C40H24) layers after deposition of an Fe top electrode [57]. The lETS spectra were consistent with the known IR- and Raman-active normal modes, which led the authors to conclude there were no chemical reactions with Fe. Cross-sectional TEM images showed continuous rubrene layers between the bottom Co layer and top Fe layer, with no evidence for small particle formation. Similar to the study by Santos et al., they found that the presence of an AI2O3 layer had a profound effect on the tunneling... 

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). 

It is possible to distinguish between two modes of transmission electron microscopy depending on the type of sample illumination parallel beam or focused probe. These two modes, corresponding to high resolution imaging and microanalysis, arc now often combined in the same microscope using computer controlled lenses. 

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