Migration of latent fingermarks on non-porous surfaces: Observation technique and nanoscale variations

• Fingermark components migrate across non-porous surfaces post-deposition.
• Over 61 days a 4 nm thick uniform layer extends from the fingermark ridge edge.
• The spread, speed and degradation of intermediate layer is dependent on surface.
• The intermediate layer may affect deposition of visualisation agents such as VMD.

Latent fingermark morphology was examined over a period of approximately two months. Variation in topography was observed with atomic force microscopy and the expansion of the fingermark occurred in the form of the development of an intermediate area surrounding the main fingermark ridge. On an example area of a fingermark on silicon, the intermediate region exists as a uniform 4 nm thick deposit; on day 1 after deposition this region extends approximately 2 μm from the edge of the main ridge deposit and expands to a maximum of ∼4 μm by day 23. Simultaneously the region breaks up, the integrity is compromised by day 16, and by day 61 the area resembles a series of interconnected islands, with coverage of approximately 60%. Observation of a similar immediate area and growth with time on surfaces such as Formica was possible by monitoring the mechanical characteristics of the fingermark and surfaces though phase contrast in tapping mode AFM. The presence of this area may affect fingermark development, for example affecting the gold distribution in vacuum metal deposition. Further study of time dependence and variation with donor may enable assessment of this area to be used to evaluate the age of fingermarks.

Figure optionsDownload high-quality image (118 K)Download as PowerPoint slide