High vacuum metal deposition

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As a high-vacuum metal deposition (English: Vacuum metal deposition ) is used in forensics , a thermal coating process referred to fingerprints to make them visible on surfaces.

Procedure

In the first process step, the surface to be examined is placed in a high vacuum chamber (approx. 10 −5 hPa) and a monatomic gold layer is evaporated. The gold in the impurities is absorbed in the areas where the fingerprint has left grease on them. In the gaps, the gold can be deposited directly on the surface. In the second process step, a thicker layer of zinc is vapor deposited. Zinc binds primarily to other metals, i.e. more strongly in the spaces between the fingerprint. This increases the contrast between the fingerprint and the surface and a negative of the fingerprint becomes visible. The imprint made visible is then saved photographically.

The method can be used on surfaces that are not too porous, especially plastics, e.g. B. on plastic bags made of polyethylene , but also on glass and paper. It has advantages over cyanoacrylate vapor deposition if the impressions have aged or the cyanoacrylate process is impaired by the slight porosity of the surface.

For some surface materials (e.g. LDPE ) a positive fingerprint is also observed.

The forensic technique of high vacuum metal vapor deposition was first used around 1976 in Great Britain, and since 1991 also in Germany. In laboratory tests, the process also proved to be suitable for making prints on textiles visible.

literature

Individual evidence

  1. ↑ X Dai, M Stoilovic, C Lennard, N. Speers: Vacuum metal deposition: visualization of gold agglomerates using TEM imaging. In: Forensic Sci Int. , 2007 May 24 ;, 168 (2-3), pp. 219-222, Epub 2006 Feb 28, PMID 16513309 .
  2. ↑ Naomi Jones, Milutin Stoilovic, Chris Lennardemail, Claude Roux: Vacuum metal deposition: factors affecting normal and reverse development of latent fingerprints on polyethylene substrates. In: Forensic Science International , Volume 115, Issue 1, January 1, 2001, pp. 73-88.
  3. ^ Forensic Breakthrough: Recovering Fingerprints On Fabrics Could Turn Clothes Into Silent Witnesses . In: ScienceDaily , February 2, 2011 (English).
  4. ^ Forensics: fingerprints on textiles reveal the perpetrator . welt.de, February 2, 2011.
  5. ↑ Fingerprints in a high vacuum . dradio.de, May 13, 2008.