Optimized Development of Sebaceous Fingermarks on Nonporous Substrates with Conformal Columnar Thin Films

Abstract

A form of physical vapor deposition, called the conformal-evaporated-film-by-rotation (CEFR) method, was optimized for the conformal deposition of columnar thin films (CTFs) on sebaceous fingermarks. Relying on the surface topology of the fingermark, the CTF development technique is different from traditional development techniques. After the optimization of the development conditions, the CTF development technique was found to be superior to traditional development methods on several nonporous substrates: the smooth side of Scotch(®) Multitask, Gorilla(®) , and Scotch(®) Duct tapes; clear and black soft plastics; stained and sealed walnut and cherry woods; partial bloody fingermarks on stainless steel; and discharged cartridge casings. It was equally as good as other development techniques on other substrates, but worse on a few. The optimization study is expected to assist in designing a mobile CEFR apparatus capable of on-scene development of fingermarks.

Vacuum-metal-deposition and columnar-thin-film techniques implemented in the same apparatus

“…If the VMD technique is implemented first, the subsequent deposition of the CTF is similar to the deposition of the CTF only on the latent fingerprint impressed on a metal substrate [10]. If the CTF technique is implemented first, the subsequent implementation of the VMD technique is infructuous because it requires penetration of the fingerprint residue by gold.…”

“…In the CTF technique, the source material kept in a receptacle inside a low-pressure chamber is resistively heated until a collimated vapor is generated. The source material can be a metal, inorganic oxide, chalcogenide glass, or even an organic compound [10]. The vapor is launched obliquely toward the substrate which is affixed to a platform that is held at a fixed orientation quantitated by the angle χ v in Fig.…”

“…If the platform is stationary, tilted nanocolumns form on the surface of the fingerprint residue. If the platform is rapidly rotated about an axis which passes normally through it, upright and parallel nanocolumns form [8,10] and the development quality is significantly better [11]. The bottom panel in Fig.…”

Visualization of partial bloody fingerprints on nonporous substrates using columnar thin films

“…In this study, the columnar-thin-film (CTF) technique was used to exploit the topology of fingerprints [9,10,11] for development. This technique requires the heating of a source material in order to evaporate it.…”

“…Since the bloody and non-bloody parts of a fingerprint have a discernible topology due to the presence of sebaceous secretions [11], the one-step development of partial bloody fingerprints by the deposition of a CTF is promising. The differential reflection of light from the various facets of the undulating CTF allows for visualization of the fingerprint.…”