SEMs AND FORENSIC SCIENCE（sem和法医科学）.pdfVIP

SEMs ANDFORENSICSCIENCE HansKRÜSEMANN PhilipsElectronOptics,Eindhoven,theNetherlands ABSTRACT: One of the latest developments in microscopy is the Environmental Scanning Electron Microscope (ESEM). The ESEM technology allows the microscope to operate in three modes: high vacuum typically at 10–4 mbar, low vacuum typically at 0.1 to 1.0 Tr and ESEM vacuum typically between 1 and 10 mbar. ESEM technol- ogy combines three microscopy modes in one instrument and therefore allows the widestrangeofsamplestobeinvestigated. ESEM allows imaging and analysis of uncoated, otherwise vacuum unstable, specimens. The ESEM microscope offers the possibility to image the specimen sur- face in a gaseous environment (using water vapor). Imaging is done by employing backscatter detection, for atomic number contrast, or the dedicated GSED (Gaseous Secondary Electron Detector) for secondary electron imaging giving topographic in- formation. Backscatter imaging (BSI) will show elemental contrast, therefore show- ing difference between materials. Both detectors are commonly used in forensic investigationsandcanberunsimultaneously. The SEM is very suitable for imaging non-conducting materials at high kV. For many materials such as plastics, polymers, glass, wood, paints, fibers, hairs, finger- prints, insects, etc., the ESEM allows these types of specimen to be viewed in the nat- ural uncoated state. The ESEM can also be used as traditional high vacuum SEM without changing any mechanical set-up. The software automatically controls the transition from low vacuum to high vacuum mode of operation. The third mode of op- eration in the range 1 to 10 mbar is very useful for delicate samples such as pollen and fungi, wet samples, dirty and oily samples and strongly outgassing materials suchasshoes. KEY WORDS:ESEM;Specimenanalysis. ProblemsofForensicSciences,vol.XLVII,2001,110–121 Received5April2001;accepted15September2001