Nanoscale Observations of Fingerprints on Brass Substrates

The recovery and visualisation of fingerprints on brass substrates by traditional methods is frequently unsatisfactory, particularly when the samples have been subjected to extreme environmental conditions. This includes items for which surface morphology or exposure to non-ambient conditions compromises traditional recovery methods. To address this challenge, the work in this thesis aims to understand the physical and chemical changes occurring for fingerprint sweat deposited onto brass substrates. This was accomplished by monitoring samples using a range of different surface sensitive techniques, based on optical, physical and chemical phenomena. The main aspects explored were surface structure (topography and morphology, using various microscopies), surface composition (using XPS) and surface dynamics (evolution of surface composition and structure with exposure to diverse conditions). The amount and viscosity of fingerprint sweat deposit changed over time; this was detectable at both the nanoscale (by AFM) and macroscale (optically). The visualisation rate of the fingerprint mark could be enhanced by storage in warm humid environments. The chemical surface composition was also subject to change: this applied to both the substrate and the fingerprint sweat deposit. The Cu:Zn ratio of the substrate was affected by both the sweat type and the storage conditions employed. Surface species also changed when subjected to different storage environments. The fingerprint sweat deposit present on the substrates was difficult to remove; even washing in warm soapy water failed to remove detectable levels of the fingerprint. Non-visible fingerprints could still be detected by surface chemical composition and also revived by storage in warm humid environments. The detailed findings should influence laboratory experiment protocols and evidence processing. The outcomes of this work should improve the recovery of fingerprints from brass substrates by optimisation of storage environments and new fingerprint detection methodology.