Probing battery hotspots for safer energy storage

Researchers are striving to make tomorrow's batteries charge faster and store more energy. But these conveniences come with safety challenges, like more heat produced in a battery. For the first time, a team of researchers ...

Volcanic ash particles under the microscope

Volcanic ash is hazardous to many aspects of our lives. When airborne, it can damage aircraft: its particles abrade aeroplane surfaces and can even cause failure to critical instruments. Once the ash falls, it can harm our ...

A splash of detergent makes catalytic compounds more powerful

Researcher David Rosenberg examines images of a white powder under a powerful scanning electron microscope. Up close, the powder looks like coarse gravel, a heap of similar but irregular chunks. Then he looks at a second ...

Writing with the electron beam—now in silver

When it comes to extremely fine, precise features, a scanning electron microscope (SEM) is unrivaled. A focused electron beam can directly deposit complex features onto a substrate in a single step (Electron-Beam-Induced ...

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Scanning electron microscope

The scanning electron microscope (SEM) is a type of electron microscope that images the sample surface by scanning it with a high-energy beam of electrons in a raster scan pattern. The electrons interact with the atoms that make up the sample producing signals that contain information about the sample's surface topography, composition and other properties such as electrical conductivity.

The types of signals produced by an SEM include secondary electrons, back scattered electrons (BSE), characteristic x-rays, light (cathodoluminescence), specimen current and transmitted electrons. These types of signal all require specialized detectors that are not usually all present on a single machine. The signals result from interactions of the electron beam with atoms at or near the surface of the sample. In the most common or standard detection mode, secondary electron imaging or SEI, the SEM can produce very high-resolution images of a sample surface, revealing details about 1 to 5 nm in size. Due to the way these images are created, SEM micrographs have a very large depth of field yielding a characteristic three-dimensional appearance useful for understanding the surface structure of a sample. This is exemplified by the micrograph of pollen shown to the right. A wide range of magnifications is possible, from about x 25 (about equivalent to that of a powerful hand-lens) to about x 250,000, about 250 times the magnification limit of the best light microscopes. Back-scattered electrons (BSE) are beam electrons that are reflected from the sample by elastic scattering. BSE are often used in analytical SEM along with the spectra made from the characteristic x-rays. Because the intensity of the BSE signal is strongly related to the atomic number (Z) of the specimen, BSE images can provide information about the distribution of different elements in the sample. For the same reason, BSE imaging can image colloidal gold immuno-labels of 5 or 10 nm diameter which would otherwise be difficult or impossible to detect in secondary electron images in biological specimens. Characteristic X-rays are emitted when the electron beam removes an inner shell electron from the sample, causing a higher energy electron to fill the shell and release energy. These characteristic x-rays are used to identify the composition and measure the abundance of elements in the sample.

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