Scanning Electron Microscopy in Forensic Science

Abstract

Scanning electron microscopy is providing increasingly definitive solutions to criminal problems since its commercial debut in 1965. This has been due to the ability of the scanning electron microscope (SEM) to simultaneously produce several electron probe‐induced signals from the specimen, which generate readily interpretable images of surface topography and material composition. The successful applications of these signals are determined by sample preparation and instrumental parameters. No other microbeam technology combines high resolution (2–5 nm) of the topographic (secondary) electrons with large depth of field for three‐dimensional viewing. The SEM is indeed ideal for stereomicroscopy. The versatility of the SEM stems from its additional capability to process each specimen signal by various contrast enhancement methods, such as line scanning, deflection modulation (DM), area mapping, etc. These methods allow an intuitive, stylistic, and synthetic analysis of the image and are ideal for quality control analysis. Digital SEMs have pioneered in automated image processing and unattended search and analysis of particulates. The combined SEM and energy‐dispersive X‐ray microanalysis (EDX) is the most definitive technique in testing for gunshot residue (GSR) particles, collected by the glue‐lift technique. In the analyses of other trace evidence, such as hair and fibers, in physical matching, and in nondestructive elemental analysis of physical evidence, the SEM/EDX is the most efficient of all microbeam technologies. From firearms, bullet wounds and human bones, to plants, pollen and fungi, the list of criminal evidence examined by SEM/EDX is endless. However, the SEM/EDX is not ideal for quantitative analysis of elements present as traces (<1% w/w). The SEM lacks the three‐dimensional sectioning abilities of scanning beam confocal microscopes. The imaging capabilities of the SEM surpass these limitations. The SEM is, therefore, a major tool in forensic research and investigation.

Evergreen Conventional and Modern Microscopic Methods for Solving Various Cases of Forensic Botany by Morphological and Histological Study

“…up to 2-5 nm of the secondary electrons with large depth of field for three-dimensional viewing and a magnification up to 1,00,000 times. 1 The ability of the SEM in processing each specimen signal by various contrast enhancement methods, such as line scanning, deflection modulation (DM), area mapping, etc., makes it a multipurpose tool. The combination of SEM and energy-dispersive X-ray microanalysis (EDX) is the most extensively used technique in elemental analysis.…”