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Development of latent fingerprints using preferential DC sputter deposition
Forensic
ELSEVIER
Science 12 (1995)
Forensic Science International
International 35-42
Development of latent fingerprints using preferential DC sputter deposition Karl Kent*, Milutin Forensic
Services
Received
Division,
10 May
Australian
Federal
1994; revision
received
Police,
Stoilovic
P.O. Box 401, Canberra
12 September
1994; accepted
ACT 2601. Australia 1 November
1994
Abstract It was shown that a DC metal sputtering process with thermalised atoms, preferentially deposits metal onto fingerprint ridges. This method can be successfully used for the development of latent fingerprints. Four target metals were tested - copper, zinc, platinum, and gold with platinum showing superior results for latent fingerprint development on clear polythene substrates. A comparison of platinum sputtering and cyanoacrylate fuming followed by rhodamine-6G staining, was conducted for l-year-old fingerprint deposits. Platinum sputtering showed significantly higher sensitivity, and produced better overall results. Keywork
Fingerprints; Sputtering; Vacuum deposition; Metals
1. Introduction If a target material being enclosed in a vacuum (lo-* Torr; 1 Torr = 133.322 Pa) is bombarded by fast heavy particles (such as inert gas ions, e.g. argon), some atoms may be ejected in all directions from the surface of this material. Some of these ejected atoms may travel to, and condense on, a given substrate material, thus forrning a thin film. In this context the sputtering process is a form of vacuum metal de-
position which is conducted at much higher pressure and with thermalised (slow) atoms rather than fast atoms as with ‘classical’ evaporation vacuum metal deposition. A schematic diagram of a typical DC sputtering apparatus is shown in Fig. 1.
* Corresponding
author.
0379-0738/95/%09.50 0 SSDI 0379-0738(94)01671-Q
1995 Elsevier
Science
Ireland
Ltd. All rights
reserved
36
K. Kent,
M. Stoilovic/Forensic
Vacuum Typical
Science
International
72 (1995)
35-42
chamber pressure: Fingerprint
sample
Fig. 1. Schematic diagram of a typical DC sputtering chamber (adapted from Chapman [I]).
A suitable source of argon ions is a glow discharge, which is created and maintained within the vacuum chamber into which argon is introduced at low pressure. The glow discharge is usually achieved by an applied high voltage (typically from 250 V to 1 kV) between the target (-ve) and the substrate (+ve). Ejected target atoms will experience many collisions prior to their arrival at the substrate. Depending upon vacuum conditions (e.g., pressure, sputtering gas, and applied voltage) these target atoms may be thermalised (very low energy and velocity) on arrival at the substrate [2]. The only use of a sputtering process for latent fingerprint development known to the authors is that reported by Edwards [2]. Edwards employed a silver sputtering process to develop nucleation sites, prior to conventional vacuum metal deposition of cadmium, for the development of latent fingerprints on polythene substrates. In this study the potential for the use of sputter deposition for the development of latent fingerprints is further investigated. 2. Materials
and methods
2.1. Apparatus
A Polaron E7480 Cryo Freeze Drier unit, equipped with an E7400 Magnetron Sputtering and E7400 Carbon Fibre Evaporation Modules, was used for this study (Fig. 2).
Fig. 2. Photograph of the sputtering apparatus used in this study, left, and close-up of sputtering chamber, right.
K. Kent.
M. Stoilovic
/ Forensic
Science
International
72 (1995)
35-42
37
This unit was chosen for a number of reasons: 0
. a
it was fitted with a substrate stage temperature controller with a digital readout, allowing for accurate substrate temperature control (using liquid nitrogen) if necessary. In these experiments the substrate temperature did not rise above room temperature for the conditions used. it had a magnetron sputtering head which operated at lower voltages than most dedicated sputtering systems (350 V max). the unit was fitted with a transfer device and airlock, which allowed for rapid sample exchanges, and reduced the time required for pumping down.
The main vacuum chamber was 22.5 cm high x 12.5 cm wide x 12.5 cm deep, being constructed of stainless steel with a single glass viewing port. The chamber was evacuated using a rotary pump to pressures no lower than 0.75 x 10m2 torr. An argon needle valve was located on the top left of the chamber, this valve being connected via plastic hosing to an argon supply cylinder, fitted with a two-stage regulator to provide about 350 x lo2 Pa secondary pressure. The sputter head cathode/anode stage separation was 40 mm. The substrate material was mounted on a brass dovetail bed, which slotted into the stage (anode) and was held firmly in position. The magnetron sputtering head (cathode) operated at a maximum of 350 V DC. The cylindrical magnetron head used an axial magnetic field, the effect of which was to increase the sputtering rate, by keeping electrons away from the chamber walls and the anode; these electrons also assist in maintaining the glow discharge. The inner cylinder of the sputtering head held the target material in position using a simple push on collar, the head diameter being 24 mm. The glow discharge current was monitored using an ammeter (O-50 mA, typically 15-20 mA), the discharge current being a function of cathode voltage, system pressure, and the particular target material being used. However, for each target material, system pressure (typically 1.5 x 10-l to 6 x 10e2 torr) and cathode/anode potential (270-320 V) were used to control the discharge current. 2.2. Target materials
Target materials of gold, platinum, zinc, and copper were used. Each target material was prepared as a 22-mm diameter, l-mm thick, highly polished disc. The purity of each target material was 99.99%. 2.3. Sample preparation
Clear plastic polythene bags (12 cm x 10 cm) were used as the substrate material. The inside surface of each bag was used to avoid contamination. Latent fingerprint samples were prepared using the right middle finger of a single donor, so as to limit the number of variables in the experiments. However, a different donor was used for the l-year-old samples. Each of the latent prints were deposited in the same manner, with four successive impressions (I-IV) being produced, I being the first impression.
38
K. Kent,
IU. Stoilovic
/ Forensic
Science
International
72 (1995)
35-42
2.4. Photography 2.4.1. Sputter developedsamples.A Rolin
PolilightTM PLlO, set at a wavelength of 505 nm, was used in the diffused reflection mode as a light source [3 1. An Olympus OM-4Ti camera, set in auto mode, using Kodak T-Max 100 black and white film, was employed to record the results. A Wild Leitz MDG 13, photomacroscope (50 x magnification) was used to observe and record the sputter developed fingerprint samples. 2.4.2. Cyanoacrylate developedsamples.The standard Australian Federal Police procedure, as described by Stoilovic [3], for cyanoacrylate (Loctite type 406) latent fingerprint development, and post-treatment using Rhodamine 6G, was employed. 3. Results 3.1. Choice of optimum sputtering conditions for each metal
The most important consideration was to maintain a steady glow discharge for each metal at the lowest possible voltage, such that sputtered metal atoms arrive at the substrate at the lowest possible speed (thermalised). This was achieved by varying the system pressure controlled by the argon flow rate into the chamber. It was found that the minimum sustainable discharge current for each metal was 15 mA, with the exception of zinc, which was 20 mA. The optimum conditions for each metal are shown in Table 1. These conditions were established prior to a sample being placed into the chamber. 3.2. Choice of optimum target materials
This experiment was conducted to choose the best two out of the four metals: gold, platinum, zinc, and copper. Four successive fresh latent fingerprints of one linger were placed onto the inside surface of clear polythene bags and left 1 h before treatment. This process was repeated four times, producing sixteen fingerprint samples for each metal. Each of the sixteen fingerprint impressions was cut out and then developed by DC sputter deposition for a particular metal. The sputtering time was varied to achieve the best result for each particular successive impression. This process was repeated for the remaining three metals. The range of sputtering times is shown in Table 2.
Table 1 Target materials and the sputtering conditions Target material
Voltage
Gold
316 271 309 300
Platinum Copper Zinc al Torr = 133.322 Pa
(V)
Current (n~4)
Pressure (Terra)
15 15 15 20
6x 1x 0.75 x 1.5 x
1O-2 10-l 10-I 10-I
K. Kent. Table 2 The range of sputtering Target
material
M. Stoilovic/
Forensic
Science Inlernational
72 (1995)
35-42
39
times for each metal Time
(s)
20-60 30-75 20-60 30-75
Gold Platinum Copper Zinc
Photomicrographs of typical developed fingerprints for each metal were taken at a magnification of 50 x , to show preferential deposition in detail. It was observed that each metal preferentially deposits along the ridges in an uneven fashion but clearly showing the pores (Fig. 3). The sputter developed fingerprints in general appeared very faint to the naked eye, and were also very fragile in nature. Illumination with the green 505-nm Polilight TM band produced the best contrast on treated latent fingerprints. Typical development achieved for each metal is shown in Fig. 4.
b
a
d Fig. 3. Photomicrographs
of typical
development
by sputtering:
a, gold; b, platinum;
c, copper;
d, zinc.
40
K. Kent.
M. Stoilovic
Gold
/ Forensic
Science
International
development
35-42
Zinc
Platinum Fig. 4. Typical
72 (1995)
achieved
for gold,
platinum,
Copper zinc and copper.
3.3. Comparisonof gold and platinum sputter target materials
A definitive comparison of gold and platinum sputter target materials was conducted. This comparison was conducted for fresh, and l-month-old latent lingerprints. Four successive impressions of one finger were placed onto the inside surface of clear polythene bags. This process was repeated four times producing sixteen fingerprint samples for fresh, and l-month-old comparisons. Each fingerprint sample was cut in half, with one half being developed with gold and the other half with platinum. Excellent results were achieved using both gold and platinum metals for all fresh samples. Typical results for one set of fresh impressions (I-IV) are shown in Fig. 5. For l-month-old samples, gold was found to produce inferior results than platinum (Fig. 6). 3.4. Comparisonof platinum sputter and cyanoacrylate development methods
A comparison of platinum sputter deposition and conventional cyanoacrylate development methods was conducted for l-year-old latent fingerprints. One set of six successive impressions from three lingers, (I) index, (II) middle, and (III) ring, were placed onto the inside surface of clear polythene bags. The fingerprint samples were kept in the open air, under laboratory conditions. Each individual fingerprint sample was cut in half, with one half being sputter developed using platinum and
II
I Fig. 5. Typical
results for one set of fresh impressions.
IV
III Left,
platinum;
right,
gold.
K. Kent.
hf. Sioilovic
/ Forensic
Science
International
72 (1995)
35-42
41
--
I Fig. 6. Typical
III
II results
for one set of l-month-old
impressions.
IV Left,
platinum;
right,
gold.
the other developed using the cyanoacrylate method followed by rhodamine-6G (R-6G) staining. Reasonable fingerprint development was obtained up to the third impression using the cyanoacrylate method. Excellent development was obtained with platinum sputtering on all six impressions. Typical results of this comparison are shown in Fig. 7. 4. Discussion
The results indicate that DC metal sputter deposition is a process that can be used to develop fresh and aged latent fingerprints on polythene substrate materials. Preferential deposition onto the fingerprint ridges was observed for all metals tested: copper, zinc, platinum and gold. For fresh fingerprints, the best target materials for this substrate, and under the conditions previously described, were gold and platinum. Whilst copper and zinc also produced good results, sputtering with these metals proved to be more difficult to control, compared with gold and platinum. However, more significantly, copper and zinc produced generally poorer results for third and fourth impressions. The comparison of gold and platinum on aged fingerprints indicated that platinum produces consistently better results on all samples.
Fig. 7. Typical fingerprint development of 5 successive (II-VI) platinum sputtering; right, cyanoacrylate followed by R-6G.
impressions
of I-year-old
fingerprints:
left,
42
K. Kent,
M. Stoilovic
/ Forensic
Science International
72 (1995)
35-42
The comparison of platinum sputtering and cyanoacrylate followed by rhodaminedG on l-year-old samples showed that the cyanoacrylate method developed up to the third impression. Platinum sputtering successfully developed all impressions showing the much higher sensitivity of this method. We suggest that this higher sensitivity may be explained by the fact that platinum sputtering develops latent tingerprints with platinum atoms, whilst the cyanoacrylate method develops latent fingerprints with cyanoacrylate molecules. It may be expected that the much smaller platinum atom would detect a very small amount of fingerprint deposit, whilst the much larger cyanoacrylate molecule is not able to ‘see’ such a small fingerprint residue. We do not at this stage have a satisfactory theoretical explanation for preferential deposition of metal atoms onto the fingerprint ridges. The comparison of this technique to ‘classical’ vacuum metal deposition has not been done. We intend to conduct this study in the near future. Acknowledgments
The authors wish to express their gratitude to Dr James Robertson, Head, Forensic Services Division (FSD), Mr John Horswell, Officer in Charge, Training and Standards Branch, FSD, and Dr Chris Lennard, Officer in Charge, Scientific Branch, FSD, of the Australian Federal Police, for their support and encouragement of our experimental work, and their assistance in the preparation of this paper. The authors would also like to thank the dedicated staff of the Australian National University, Research School of Biological Sciences, Electron Microscopy Unit, for their continual support, assistance and encouragement, throughout the project. In particular, we thank Dr Sally Stowe, Roger, Michael, and David. References [I] [2] [3]
B. Chapman, P.F. Edwards, and Polythene. M. Stoilovic, Federal Police,
Glow Discharge Processes, Wiley & Sons, New York, 1980. The Use of Sputtered Thin Films in the Development of Latent Fingerprints on Glass Home Oflice Technical Memorandum, 43, 1976. A Modern Approach to Latent Fingerprint Development, Second Edn., Australian 1993.
ELSEVIER
Science 12 (1995)
Forensic Science International
International 35-42
Development of latent fingerprints using preferential DC sputter deposition Karl Kent*, Milutin Forensic
Services
Received
Division,
10 May
Australian
Federal
1994; revision
received
Police,
Stoilovic
P.O. Box 401, Canberra
12 September
1994; accepted
ACT 2601. Australia 1 November
1994
Abstract It was shown that a DC metal sputtering process with thermalised atoms, preferentially deposits metal onto fingerprint ridges. This method can be successfully used for the development of latent fingerprints. Four target metals were tested - copper, zinc, platinum, and gold with platinum showing superior results for latent fingerprint development on clear polythene substrates. A comparison of platinum sputtering and cyanoacrylate fuming followed by rhodamine-6G staining, was conducted for l-year-old fingerprint deposits. Platinum sputtering showed significantly higher sensitivity, and produced better overall results. Keywork
Fingerprints; Sputtering; Vacuum deposition; Metals
1. Introduction If a target material being enclosed in a vacuum (lo-* Torr; 1 Torr = 133.322 Pa) is bombarded by fast heavy particles (such as inert gas ions, e.g. argon), some atoms may be ejected in all directions from the surface of this material. Some of these ejected atoms may travel to, and condense on, a given substrate material, thus forrning a thin film. In this context the sputtering process is a form of vacuum metal de-
position which is conducted at much higher pressure and with thermalised (slow) atoms rather than fast atoms as with ‘classical’ evaporation vacuum metal deposition. A schematic diagram of a typical DC sputtering apparatus is shown in Fig. 1.
* Corresponding
author.
0379-0738/95/%09.50 0 SSDI 0379-0738(94)01671-Q
1995 Elsevier
Science
Ireland
Ltd. All rights
reserved
36
K. Kent,
M. Stoilovic/Forensic
Vacuum Typical
Science
International
72 (1995)
35-42
chamber pressure: Fingerprint
sample
Fig. 1. Schematic diagram of a typical DC sputtering chamber (adapted from Chapman [I]).
A suitable source of argon ions is a glow discharge, which is created and maintained within the vacuum chamber into which argon is introduced at low pressure. The glow discharge is usually achieved by an applied high voltage (typically from 250 V to 1 kV) between the target (-ve) and the substrate (+ve). Ejected target atoms will experience many collisions prior to their arrival at the substrate. Depending upon vacuum conditions (e.g., pressure, sputtering gas, and applied voltage) these target atoms may be thermalised (very low energy and velocity) on arrival at the substrate [2]. The only use of a sputtering process for latent fingerprint development known to the authors is that reported by Edwards [2]. Edwards employed a silver sputtering process to develop nucleation sites, prior to conventional vacuum metal deposition of cadmium, for the development of latent fingerprints on polythene substrates. In this study the potential for the use of sputter deposition for the development of latent fingerprints is further investigated. 2. Materials
and methods
2.1. Apparatus
A Polaron E7480 Cryo Freeze Drier unit, equipped with an E7400 Magnetron Sputtering and E7400 Carbon Fibre Evaporation Modules, was used for this study (Fig. 2).
Fig. 2. Photograph of the sputtering apparatus used in this study, left, and close-up of sputtering chamber, right.
K. Kent.
M. Stoilovic
/ Forensic
Science
International
72 (1995)
35-42
37
This unit was chosen for a number of reasons: 0
. a
it was fitted with a substrate stage temperature controller with a digital readout, allowing for accurate substrate temperature control (using liquid nitrogen) if necessary. In these experiments the substrate temperature did not rise above room temperature for the conditions used. it had a magnetron sputtering head which operated at lower voltages than most dedicated sputtering systems (350 V max). the unit was fitted with a transfer device and airlock, which allowed for rapid sample exchanges, and reduced the time required for pumping down.
The main vacuum chamber was 22.5 cm high x 12.5 cm wide x 12.5 cm deep, being constructed of stainless steel with a single glass viewing port. The chamber was evacuated using a rotary pump to pressures no lower than 0.75 x 10m2 torr. An argon needle valve was located on the top left of the chamber, this valve being connected via plastic hosing to an argon supply cylinder, fitted with a two-stage regulator to provide about 350 x lo2 Pa secondary pressure. The sputter head cathode/anode stage separation was 40 mm. The substrate material was mounted on a brass dovetail bed, which slotted into the stage (anode) and was held firmly in position. The magnetron sputtering head (cathode) operated at a maximum of 350 V DC. The cylindrical magnetron head used an axial magnetic field, the effect of which was to increase the sputtering rate, by keeping electrons away from the chamber walls and the anode; these electrons also assist in maintaining the glow discharge. The inner cylinder of the sputtering head held the target material in position using a simple push on collar, the head diameter being 24 mm. The glow discharge current was monitored using an ammeter (O-50 mA, typically 15-20 mA), the discharge current being a function of cathode voltage, system pressure, and the particular target material being used. However, for each target material, system pressure (typically 1.5 x 10-l to 6 x 10e2 torr) and cathode/anode potential (270-320 V) were used to control the discharge current. 2.2. Target materials
Target materials of gold, platinum, zinc, and copper were used. Each target material was prepared as a 22-mm diameter, l-mm thick, highly polished disc. The purity of each target material was 99.99%. 2.3. Sample preparation
Clear plastic polythene bags (12 cm x 10 cm) were used as the substrate material. The inside surface of each bag was used to avoid contamination. Latent fingerprint samples were prepared using the right middle finger of a single donor, so as to limit the number of variables in the experiments. However, a different donor was used for the l-year-old samples. Each of the latent prints were deposited in the same manner, with four successive impressions (I-IV) being produced, I being the first impression.
38
K. Kent,
IU. Stoilovic
/ Forensic
Science
International
72 (1995)
35-42
2.4. Photography 2.4.1. Sputter developedsamples.A Rolin
PolilightTM PLlO, set at a wavelength of 505 nm, was used in the diffused reflection mode as a light source [3 1. An Olympus OM-4Ti camera, set in auto mode, using Kodak T-Max 100 black and white film, was employed to record the results. A Wild Leitz MDG 13, photomacroscope (50 x magnification) was used to observe and record the sputter developed fingerprint samples. 2.4.2. Cyanoacrylate developedsamples.The standard Australian Federal Police procedure, as described by Stoilovic [3], for cyanoacrylate (Loctite type 406) latent fingerprint development, and post-treatment using Rhodamine 6G, was employed. 3. Results 3.1. Choice of optimum sputtering conditions for each metal
The most important consideration was to maintain a steady glow discharge for each metal at the lowest possible voltage, such that sputtered metal atoms arrive at the substrate at the lowest possible speed (thermalised). This was achieved by varying the system pressure controlled by the argon flow rate into the chamber. It was found that the minimum sustainable discharge current for each metal was 15 mA, with the exception of zinc, which was 20 mA. The optimum conditions for each metal are shown in Table 1. These conditions were established prior to a sample being placed into the chamber. 3.2. Choice of optimum target materials
This experiment was conducted to choose the best two out of the four metals: gold, platinum, zinc, and copper. Four successive fresh latent fingerprints of one linger were placed onto the inside surface of clear polythene bags and left 1 h before treatment. This process was repeated four times, producing sixteen fingerprint samples for each metal. Each of the sixteen fingerprint impressions was cut out and then developed by DC sputter deposition for a particular metal. The sputtering time was varied to achieve the best result for each particular successive impression. This process was repeated for the remaining three metals. The range of sputtering times is shown in Table 2.
Table 1 Target materials and the sputtering conditions Target material
Voltage
Gold
316 271 309 300
Platinum Copper Zinc al Torr = 133.322 Pa
(V)
Current (n~4)
Pressure (Terra)
15 15 15 20
6x 1x 0.75 x 1.5 x
1O-2 10-l 10-I 10-I
K. Kent. Table 2 The range of sputtering Target
material
M. Stoilovic/
Forensic
Science Inlernational
72 (1995)
35-42
39
times for each metal Time
(s)
20-60 30-75 20-60 30-75
Gold Platinum Copper Zinc
Photomicrographs of typical developed fingerprints for each metal were taken at a magnification of 50 x , to show preferential deposition in detail. It was observed that each metal preferentially deposits along the ridges in an uneven fashion but clearly showing the pores (Fig. 3). The sputter developed fingerprints in general appeared very faint to the naked eye, and were also very fragile in nature. Illumination with the green 505-nm Polilight TM band produced the best contrast on treated latent fingerprints. Typical development achieved for each metal is shown in Fig. 4.
b
a
d Fig. 3. Photomicrographs
of typical
development
by sputtering:
a, gold; b, platinum;
c, copper;
d, zinc.
40
K. Kent.
M. Stoilovic
Gold
/ Forensic
Science
International
development
35-42
Zinc
Platinum Fig. 4. Typical
72 (1995)
achieved
for gold,
platinum,
Copper zinc and copper.
3.3. Comparisonof gold and platinum sputter target materials
A definitive comparison of gold and platinum sputter target materials was conducted. This comparison was conducted for fresh, and l-month-old latent lingerprints. Four successive impressions of one finger were placed onto the inside surface of clear polythene bags. This process was repeated four times producing sixteen fingerprint samples for fresh, and l-month-old comparisons. Each fingerprint sample was cut in half, with one half being developed with gold and the other half with platinum. Excellent results were achieved using both gold and platinum metals for all fresh samples. Typical results for one set of fresh impressions (I-IV) are shown in Fig. 5. For l-month-old samples, gold was found to produce inferior results than platinum (Fig. 6). 3.4. Comparisonof platinum sputter and cyanoacrylate development methods
A comparison of platinum sputter deposition and conventional cyanoacrylate development methods was conducted for l-year-old latent fingerprints. One set of six successive impressions from three lingers, (I) index, (II) middle, and (III) ring, were placed onto the inside surface of clear polythene bags. The fingerprint samples were kept in the open air, under laboratory conditions. Each individual fingerprint sample was cut in half, with one half being sputter developed using platinum and
II
I Fig. 5. Typical
results for one set of fresh impressions.
IV
III Left,
platinum;
right,
gold.
K. Kent.
hf. Sioilovic
/ Forensic
Science
International
72 (1995)
35-42
41
--
I Fig. 6. Typical
III
II results
for one set of l-month-old
impressions.
IV Left,
platinum;
right,
gold.
the other developed using the cyanoacrylate method followed by rhodamine-6G (R-6G) staining. Reasonable fingerprint development was obtained up to the third impression using the cyanoacrylate method. Excellent development was obtained with platinum sputtering on all six impressions. Typical results of this comparison are shown in Fig. 7. 4. Discussion
The results indicate that DC metal sputter deposition is a process that can be used to develop fresh and aged latent fingerprints on polythene substrate materials. Preferential deposition onto the fingerprint ridges was observed for all metals tested: copper, zinc, platinum and gold. For fresh fingerprints, the best target materials for this substrate, and under the conditions previously described, were gold and platinum. Whilst copper and zinc also produced good results, sputtering with these metals proved to be more difficult to control, compared with gold and platinum. However, more significantly, copper and zinc produced generally poorer results for third and fourth impressions. The comparison of gold and platinum on aged fingerprints indicated that platinum produces consistently better results on all samples.
Fig. 7. Typical fingerprint development of 5 successive (II-VI) platinum sputtering; right, cyanoacrylate followed by R-6G.
impressions
of I-year-old
fingerprints:
left,
42
K. Kent,
M. Stoilovic
/ Forensic
Science International
72 (1995)
35-42
The comparison of platinum sputtering and cyanoacrylate followed by rhodaminedG on l-year-old samples showed that the cyanoacrylate method developed up to the third impression. Platinum sputtering successfully developed all impressions showing the much higher sensitivity of this method. We suggest that this higher sensitivity may be explained by the fact that platinum sputtering develops latent tingerprints with platinum atoms, whilst the cyanoacrylate method develops latent fingerprints with cyanoacrylate molecules. It may be expected that the much smaller platinum atom would detect a very small amount of fingerprint deposit, whilst the much larger cyanoacrylate molecule is not able to ‘see’ such a small fingerprint residue. We do not at this stage have a satisfactory theoretical explanation for preferential deposition of metal atoms onto the fingerprint ridges. The comparison of this technique to ‘classical’ vacuum metal deposition has not been done. We intend to conduct this study in the near future. Acknowledgments
The authors wish to express their gratitude to Dr James Robertson, Head, Forensic Services Division (FSD), Mr John Horswell, Officer in Charge, Training and Standards Branch, FSD, and Dr Chris Lennard, Officer in Charge, Scientific Branch, FSD, of the Australian Federal Police, for their support and encouragement of our experimental work, and their assistance in the preparation of this paper. The authors would also like to thank the dedicated staff of the Australian National University, Research School of Biological Sciences, Electron Microscopy Unit, for their continual support, assistance and encouragement, throughout the project. In particular, we thank Dr Sally Stowe, Roger, Michael, and David. References [I] [2] [3]
B. Chapman, P.F. Edwards, and Polythene. M. Stoilovic, Federal Police,
Glow Discharge Processes, Wiley & Sons, New York, 1980. The Use of Sputtered Thin Films in the Development of Latent Fingerprints on Glass Home Oflice Technical Memorandum, 43, 1976. A Modern Approach to Latent Fingerprint Development, Second Edn., Australian 1993.