Thin Film Boosts Forensic Analysis Of Fingerprints

Forensic analysis of fingerprint traces may benefit from a method for depositing thin films that conform to and thereby highlight the microscopic morphology of fingerprint residue (J. Vac. Sci. Technol. B 2014, DOI: 10.1116/1.4867440). The technique, which can be carried out with common deposition equipment, may help convert faint and hard-to-analyze prints to usable legal evidence. Fingerprint residues (or latent prints) typically consist of inorganic salts, urea, and amino acids secreted by eccrine glands in fingertips. They also contain saturated fats and other secretions of sebaceous glands. Common methods for enhancing fingerprint visibility include dusting with colored powders and applying reagents that react with residue components. But those methods do not capture the often hidden detailed ridge-and-valley topology of fingerprints. To highlight those diagnostic features, Pennsylvania State University’s Akhlesh Lakhtakia and coworkers developed a deposition procedure in which a flux of a germanium-antimony-selenium material impinges upon the residue and forms a film of 60-nm-diameter columns. Tests comparing several variations of the method show that the trick to enhancing subtle topology details is to rotate the surface containing the print at high speed while directing the flux toward that surface at an oblique angle.