Potential applications of scanning probe microscopy

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Potential Applications of Scanning Probe Microscopy in Forensic Science

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IOP Publishing doi:10.1088/1742-6596/61/1/247

Journal of Physics: Conference Series 61 (2007) 1251–1255 International Conference on Nanoscience and Technology (ICN&T 2006)

Potential Applications of Scanning Probe Microscopy in Forensic Science
G S Watson1 and J A Watson
Nanoscale Scienceand Technology Centre, School of Science, Griffith University, Kessels Rd, Nathan, QLD, 4111 Australia E-mail: G.Watson@griffith.edu.au
Abstract. The forensic community utilises a myriad of techniques to investigate a wide range of materials, from paint flakes to DNA. The various microscopic techniques have provided some of the greatest contributions, e.g., FT-IR (Fourier-transform infrared)microspectroscopy utilised in copy toner discrimination, multi-layer automobile paint fragment examination, etc, SEM-EDA (scanning electron microscopy with energy dispersive analysis) used to investigate glass fragments, fibers, and explosives, and SEM in microsampling for elemental analysis, just to name a few. This study demonstrates the ability of the Scanning Probe Microscope (SPM) to analysehuman fingerprints on surfaces utilising a step-and-scan feature, enabling analysis of a larger field-of-view. We also extend a line crossings study by incorporating height analysis and surface roughness measurements. The study demonstrates the potential for SPM techniques to be utilised for forensic analysis which could complement the more traditional methodologies used in such investigations.

1.Introduction Various techniques utilised by forensic scientists allow detailed studies of a multitude of materials. As science advances so do the tools of the trade. Any additions to these techniques may enhance the existing results building upon the evidence in order to convict or acquit a suspect in a crime. This study expands upon a relative newcomer to the Forensic field, Scanning ProbeMicroscopy (SPM), demonstrating its various modes of operation. The merits of SPM lie in its ability to characterise surfaces based on topographical features as well as chemical and physical properties. 2. Experimental details 2.1. Materials preparation The fingerprints were deposited onto new, clean microscope slides, with no further alteration or manipulation. The surface lines were created on glossyphotographic printer paper using a standard blue ink ball-point pen. 2.2. SPM instrumentation and probes The probes utilised for this study consisted of a beam-shaped lever with an integral conical tip attached at its free end. Beam-shaped Si levers were supplied by Ultrasharp NT-MDT. The length (L), width (w), thickness (t), tip height (h), normal spring constant (kN) and tip radius of curvature(RTip) values were 350 m, 35 m, 1 m, 15-20 m, 0.01-0.08 Nm-1 and 20-30 nm, respectively, as supplied by the manufacturer. Forces acting between the tip and the sample will result in deflections of the cantilever. The lever bends vertically, i.e., in the z-direction (normal to the sample plane), in response to attractive and/or repulsive forces acting on the tip. When the tip is in contact with asample, the deflection of the lever from

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© 2007 IOP Publishing Ltd


its equilibrium position is proportional to the normal load applied to the tip by the lever. As well as the measurement of normal forces, the simultaneous measurement of frictional forces is also possible as a result of a twisting motion of the lever from...
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