Experimental methods in chemical engineering: Transmission electron microscopy—TEM

Abstract

Thanks to an accelerating voltage in the range of 30 to 300 kV, an electron beam can pass through a thin specimen and form an image with sub-Ångström spatial resolution. When impinging on a thin crystalline specimen, the fast electrons scatter and diffract. The transmitted electron pattern depends on the local thickness, density, crystal structure, and chemical nature of the sample. The transmission electron microscope (TEM) shapes the incoming electron beam using magnetic lenses onto the specimen and, using a different set of magnetic lenses, focuses the projected electron pattern to a camera. The final image magnification and contrast are controlled using the parameters from the electron gun, apertures positioned along the optical path, and magnetic lenses. With this combination of lens and aperture, TEM offers two possible modes of operation: (a) imaging, including high-resolution electron microscopy to reveal the size, shape, crystallinity, and morphology of materials; and (b) diffraction, to determine the crystalline nature of a region of interest of a thin film, particle, or collection of particles. Chemical engineers have taken advantage of both of these modes to analyze their samples and inform their research. A bibliometric study conducted using the WoS database places TEM as one of the preferred microscopy tools to study advanced materials such as thin films, nanomaterials, and composites used in particular for the development of applications related to energy storage and conversion (catalysis, photocatalysis, electrochemistry, and batteries) and environment (adsorption, waste-water treatment, and filtration). K E Y W O R D Selectron diffraction, interfaces, metrology, nanomaterials, transmission electron microscopy

Experimental methods in chemical engineering: Scanning electron microscopy andX‐ray ultra‐microscopy—SEMandXuM

“…When resolution becomes the limiting factor, one will employ complementary techniques such as transmission electron microscopy (TEM). [ 58 ] Ultimately, one of the major limiting factors is equipment and operational costs. Although affordable benchtop SEMs are now commonplace for routine analysis, advanced microscope designs continue to strive for higher resolution and greater capability, and with that comes an increased cost.…”

Experimental methods in chemical engineering: Raman spectroscopy

“…This classification resembles that of many of the other spectroscopic techniques like FTIR, [7] x-ray diffraction, [20] x-ray photoelectron spectroscopy, [21] and transmission electron microscopy. [22] In the last four decades, researchers in chemical engineering have applied Raman spectroscopy mostly to characterize catalytic materials. [23,24] In addition to the advantages of Raman (non-destructive, small sample sizes, and minimum preparation) researchers apply it to characterize metals and oxides (bulk and supported), zeolites and other molecular sieves, some carbon materials including carbon nanotubes, heteropolyoxo anions, clays, and metal sulphides.…”

“…This classification resembles that of many of the other spectroscopic techniques like FTIR, [ 7 ] x‐ray diffraction, [ 20 ] x‐ray photoelectron spectroscopy, [ 21 ] and transmission electron microscopy. [ 22 ]…”

“…Their spatial resolution lies between SEM and XPS, while they resolve species to the same extent as XPS. [ 22 ] However, resonance and plasmonic effects boost sensitivity to the level of single molecules. The challenge is to interpret Raman signals quantitatively.…”

Issue Highlights

“…The limits of the instrument are shown along with common pitfalls such as image artefacts, electron beam damage, and lack of representativeness. Examples of applications for which TEM has contributed are commented in the framework of a bibliometric analysis …”