J Forensic Sci, January 2015, Vol. 60, No. 1 doi: 10.1111/1556-4029.12599 Available online at: onlinelibrary.wiley.com
TECHNICAL NOTE CRIMINALISTICS
Stephanie F. Williams,1 M.P.S.; Drew P. Pulsifer,2 Ph.D.; Akhlesh Lakhtakia,2 Ph.D., D.Sc.; and Robert C. Shaler,3 Ph.D.
Columnar-Thin-Film-Assisted Visualization of Depleted Sebaceous Fingermarks on Nonporous Metals and Hard Plastics*
ABSTRACT: A fingermark on a nonporous substrate can be developed by depositing a columnar thin film (CTF) on it, but the CTF technique’s sensitivity for low-quality fingermarks is unknown. The optimized CTF and traditional development of several depletion series of sebaceous-loaded fingermarks were compared using a split-print methodology as well as subjective and objective grading schemes, in a limited laboratory trial. CTF development was superior to development with selected traditional techniques on brass, anodized aluminum, black acrylonitrile butadiene styrene (ABS), and white nylon. On white ABS and black nylon, the CTF technique performed poorly but still as well as the best-performing traditional development technique. The CTF technique was more sensitive on brass and anodized aluminum than, and as sensitive on the four hard plastics and stainless steel as, the best-performing traditional technique. Thus, the CTF technique is useful to develop friction-ridge detail from limited fingermark residue on some smooth substrates.
KEYWORDS: forensic science, columnar thin film, conformal evaporated film by rotation, depletion series, fingermark, nonporous substrate, physical vapor deposition, sensitivity
As fingermarks are unique to an individual and remain consistent through a person’s lifetime (1), fingermarks left on evidence or at the scene of a crime are commonly used to identify the perpetrators of that crime. Fingermarks are left on substrates because the fluid residue on an individual’s fingertips covering the frictionridge skin is transferred to a surface on the application of pressure. The most common materials present in the fingermark residue are secretions produced by the eccrine and sebaceous glands. Traditional development techniques rely on physical or chemical interactions with these secretions to visualize fingermarks. Thus, fingermarks are often developed by having ninhydrin and DFO (1,8-diazafluorene) react with amino acids contained in eccrine secretions; likewise, the reaction of silver nitrate with chloride ions in eccrine secretions is used for development (2,3). The adhesion of dusting powders and other powder formulations to 1 Forensic Science Program, Pennsylvania State University, University Park, PA 16802. 2 Department of Engineering Science and Mechanics & Materials Research Institute, Pennsylvania State University, University Park, PA 16802. 3 Forensic Science Program & Department of Biochemistry and Molecular Biology, Pennsylvania State University, University Park, PA 16802. *Supported by Award No. 2010-DN-BX-K232, awarded by the National Institute of Justice, Office of Justice Programs, U.S. Department of Justice. The opinions, findings, and conclusions or recommendations expressed in this publication are those of the authors and do not necessarily reflect those of the Department of Justice. Presented in part at the 65th Annual Meeting of the American Academy of Forensic Sciences, February 18-23, 2013, in Washington, DC. Received 17 April 2013; and in revised form 25 Dec. 2013; accepted 5 Jan. 2014.
© 2014 American Academy of Forensic Sciences
the oily emulsions in sebaceous secretions is a commonly used development mechanism (4). In fact, most on-scene development relies on (i) either a powder-based interaction with the components of sebaceous secretions (5) or (ii) fuming with cyanoacrylate (commonly called superglue) which interacts with both eccrine (6,7) and sebaceous (8,9) secretions. Instead of reliance on a physical or chemical interaction with the fingermark residue, a columnar thin film (CTF) can be conformally deposited on a fingermark, thereby allowing visualization based on the topology and surface texture of the fingermark residue (8–10). The CTF is deposited by a physical-vapor-deposition approach called the conformal-evaporated-film-by-rotation (CEFR) method. The deposition occurs inside a low-pressure chamber which contains (i) a rotatable platform to which the substrate is affixed, (ii) a metal boat containing an evaporant source material, and (iii) a quartz crystal monitor to assist in the regulation of the deposition. When an electric current of sufficiently high magnitude is passed through the metal boat, the source material evaporates. In a certain angular sector, the vapor flux is collimated. The rapidly rotating platform is positioned such that the substrate intercepts the collimated vapor flux. The vapor condenses on the rapidly rotating substrate and creates a thin film that entombs the substrate. The rapid rotation of the substrate with a nonplanar exposed surface is responsible for the coating being conformal (11). Additionally, the substrate’s rapid rotation results in the formation of the conformal thin film as a dense array of upright columns. As they grow on the fingermark, the columns copy the topology and the surface texture of the fingermark. This results in observable contrast between the ridge 179
180
JOURNAL OF FORENSIC SCIENCES
detail and the underlying substrate, while maintaining the fidelity of the topographic detail at the nanoscale (9). The CTF technique is different in at least three ways from a technique called vacuum metal deposition (VMD) often used to develop fingermarks (12,13). First, the VMD technique requires the deposition of only metals, whereas the CTF technique can use metals as well as nonmetals for deposition (8–10). Second, the thickness of the CTF ranges from 50 nm to 1000 nm (9), but the VMD deposits are
TECHNICAL NOTE CRIMINALISTICS
Stephanie F. Williams,1 M.P.S.; Drew P. Pulsifer,2 Ph.D.; Akhlesh Lakhtakia,2 Ph.D., D.Sc.; and Robert C. Shaler,3 Ph.D.
Columnar-Thin-Film-Assisted Visualization of Depleted Sebaceous Fingermarks on Nonporous Metals and Hard Plastics*
ABSTRACT: A fingermark on a nonporous substrate can be developed by depositing a columnar thin film (CTF) on it, but the CTF technique’s sensitivity for low-quality fingermarks is unknown. The optimized CTF and traditional development of several depletion series of sebaceous-loaded fingermarks were compared using a split-print methodology as well as subjective and objective grading schemes, in a limited laboratory trial. CTF development was superior to development with selected traditional techniques on brass, anodized aluminum, black acrylonitrile butadiene styrene (ABS), and white nylon. On white ABS and black nylon, the CTF technique performed poorly but still as well as the best-performing traditional development technique. The CTF technique was more sensitive on brass and anodized aluminum than, and as sensitive on the four hard plastics and stainless steel as, the best-performing traditional technique. Thus, the CTF technique is useful to develop friction-ridge detail from limited fingermark residue on some smooth substrates.
KEYWORDS: forensic science, columnar thin film, conformal evaporated film by rotation, depletion series, fingermark, nonporous substrate, physical vapor deposition, sensitivity
As fingermarks are unique to an individual and remain consistent through a person’s lifetime (1), fingermarks left on evidence or at the scene of a crime are commonly used to identify the perpetrators of that crime. Fingermarks are left on substrates because the fluid residue on an individual’s fingertips covering the frictionridge skin is transferred to a surface on the application of pressure. The most common materials present in the fingermark residue are secretions produced by the eccrine and sebaceous glands. Traditional development techniques rely on physical or chemical interactions with these secretions to visualize fingermarks. Thus, fingermarks are often developed by having ninhydrin and DFO (1,8-diazafluorene) react with amino acids contained in eccrine secretions; likewise, the reaction of silver nitrate with chloride ions in eccrine secretions is used for development (2,3). The adhesion of dusting powders and other powder formulations to 1 Forensic Science Program, Pennsylvania State University, University Park, PA 16802. 2 Department of Engineering Science and Mechanics & Materials Research Institute, Pennsylvania State University, University Park, PA 16802. 3 Forensic Science Program & Department of Biochemistry and Molecular Biology, Pennsylvania State University, University Park, PA 16802. *Supported by Award No. 2010-DN-BX-K232, awarded by the National Institute of Justice, Office of Justice Programs, U.S. Department of Justice. The opinions, findings, and conclusions or recommendations expressed in this publication are those of the authors and do not necessarily reflect those of the Department of Justice. Presented in part at the 65th Annual Meeting of the American Academy of Forensic Sciences, February 18-23, 2013, in Washington, DC. Received 17 April 2013; and in revised form 25 Dec. 2013; accepted 5 Jan. 2014.
© 2014 American Academy of Forensic Sciences
the oily emulsions in sebaceous secretions is a commonly used development mechanism (4). In fact, most on-scene development relies on (i) either a powder-based interaction with the components of sebaceous secretions (5) or (ii) fuming with cyanoacrylate (commonly called superglue) which interacts with both eccrine (6,7) and sebaceous (8,9) secretions. Instead of reliance on a physical or chemical interaction with the fingermark residue, a columnar thin film (CTF) can be conformally deposited on a fingermark, thereby allowing visualization based on the topology and surface texture of the fingermark residue (8–10). The CTF is deposited by a physical-vapor-deposition approach called the conformal-evaporated-film-by-rotation (CEFR) method. The deposition occurs inside a low-pressure chamber which contains (i) a rotatable platform to which the substrate is affixed, (ii) a metal boat containing an evaporant source material, and (iii) a quartz crystal monitor to assist in the regulation of the deposition. When an electric current of sufficiently high magnitude is passed through the metal boat, the source material evaporates. In a certain angular sector, the vapor flux is collimated. The rapidly rotating platform is positioned such that the substrate intercepts the collimated vapor flux. The vapor condenses on the rapidly rotating substrate and creates a thin film that entombs the substrate. The rapid rotation of the substrate with a nonplanar exposed surface is responsible for the coating being conformal (11). Additionally, the substrate’s rapid rotation results in the formation of the conformal thin film as a dense array of upright columns. As they grow on the fingermark, the columns copy the topology and the surface texture of the fingermark. This results in observable contrast between the ridge 179
180
JOURNAL OF FORENSIC SCIENCES
detail and the underlying substrate, while maintaining the fidelity of the topographic detail at the nanoscale (9). The CTF technique is different in at least three ways from a technique called vacuum metal deposition (VMD) often used to develop fingermarks (12,13). First, the VMD technique requires the deposition of only metals, whereas the CTF technique can use metals as well as nonmetals for deposition (8–10). Second, the thickness of the CTF ranges from 50 nm to 1000 nm (9), but the VMD deposits are
