R&D July 2007 FEI Co. - (Page 2) Tabletop SEMs can be used in forensic analysis, showing traces of materials found on clothing, such as this diatom. A quick look with a tabletop SEM at bulk particles can show their morphology. This sample has primarily spheroidal morphology. The most striking development in the new tabletop SEM is its ease of use. Although small, inexpensive SEMs have been introduced more than once over the half century history of the technology, their widespread acceptance has been hindered by their operational difficulty. One of the new tabletop SEMs, the Phenom, from FEI Co., Hillsboro, Ore., is as easy to use as an optical microscope and accepts virtually any sample that will fit into the sample holder. Achieving this level of operational simplicity required much more than simply scaling down existing SEM technology; it required a redesign of many of the microscope’s core components. Phenom cuts away the time, difficulty, and expense of the conventional SEM. The operator simply places the sample in the sample holder on the microscope. The automatically focused image is displayed less than 30 seconds later, with the resolution and depth of field typical of full-size SEMs. Improving performance To achieve this level of performance, engineers focused on a few basic requirements: size (including facility requirements), image quality, sample requirements, and easy operation. Size –Successful imaging at high magnification in a conventional SEM requires a quiet environment. The presence of general lab equipment and a lively, vocal workforce in the same room as the SEM causes vibrations that distort the image. It is not unusual for a customized SEM room to cost as much as the SEM itself. The SEM’s sensitivity to vibration is a function of the resonant frequency of the column and sample holder, determined primarily by its length and diameter. The Phenom’s miniaturized column is approximately 10 times smaller than a conventional SEM column and is energized by permanent magnets rather than the commonly used electromagnets. The sample holder is also smaller and rigidly mounted to the SEM column. The result is a dramatic increase in the resonant frequency and a system that is virtually unaffected by the noise and vibration of a typical lab environment. Image quality –The key determinants of image quality in an SEM are www.rdmag.com Back to basics Optical microscopes use transparent lenses to focus light from the specimen into a real image, either directly onto the retina of the eye or into a camera or digital imaging system for capture and storage. SEMs create a virtual image by scanning a finely focused beam of electrons over the sample surface and mapping the intensity of various signals emitted at each point into an image array that is captured and displayed electronically. Operating an optical microscope requires little more than placing the sample on the stage and focusing the image and is usually accomplished in a matter of seconds. Conventional SEMs, which require a high vacuum in the sample chamber, typically require several minutes to pump down the sample chamber in addition to any preparation required to make the sample compatible with the vacuum (cleaning, drying, coating techniques etc.). The time required to get an SEM image can easily become many minutes or hours. The 2 R&DMagazine July 2007 http://www.rdmag.com
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