真空镀膜中膜系选择对潜手印显现的影响

目的探究在真空镀膜中不同镀膜材料能否显现出潜手印并比较不同镀膜金属显现手印的效果。方法使用不同的镀膜金属显现多种类型客体表面的潜手印。结果存在可替换镀膜材料。结论可替换镀膜金属对潜手印显现的效果良好,纹线清晰连贯,背景反差大,并对特定客体上的手印显现极具优势。     

真空镀膜与“502”熏显法显现非渗透性客体上汗潜手印的比较研究

目的探索真空镀膜手印显现技术,提高现场潜在手印显现率。方法通过真空镀膜与＂502＂熏显法显现常见非渗透性客体上汗潜手印的对比实验,比较二者显现效果优劣。结果真空镀膜法对于显现常见非渗透性客体上的新鲜和陈旧汗潜手印都有着明显的优势。结论真空镀膜是一种更为灵敏的非渗透性客体手印显现方法,是现有手印显现方法的重要补充。     

一种改进的碘熏法-碘锌手印显现法

目的为解决传统碘熏法显出手印容易褪色、固定困难等问题。方法提出了一种改进的碘熏法-碘锌手印显现法，实验了不同反应物配比、不同客体材质对显现效果的影响；与常规碘熏法进行了对比实验；并考察了碘锌法显出手印的稳定性。结果碘锌手印显现法可以用于常见渗透性及非渗透性客体上新鲜汗潜手印的显现。该方法不必外加热源，携带、存储和应用更加便利；该方法显出的指纹纹线保存时间与传统碘熏法相比明显延长。结论碘锌手印显现法是一种高效、实用的手印显现方法。     

物理显影液显现渗透客体表面血潜手印方法研究

目的　建立了一种物理显影液显现潮湿或者浸泡渗透客体表面血潜手印的新方法。方法　把检材浸泡在配制好的物理显影液中 ,还原的银粒子吸附在血潜手印部位显现出手印纹线。结果　显现出手印纹线为黑灰色 ,纹线连贯 ,反差明显。结论　物理显影液能够有效地显现出潮湿或者浸泡后手渗透客体表面血潜手印。     

油红O显现热敏纸上潜在手印研究

目的建立了一种油红O显现热敏纸上客体表面的潜手印的新方法。方法将检材浸泡在配制好的油红O的显现试剂中,油红可将指纹中遗留的油脂染色从而显现出手印纹线。结果显现出手印纹线为红色,纹线连贯,反差明显。结论油红O能够有效地显现出热敏纸上潜手印。     

真空镀膜技术显现疑难客体上汗潜手印

本文首先简述了真空镀膜技术原理、适用范围,而后对疑难客体上汗潜手印进行真空镀膜显现和后期加强的实验操作。通过实验验证真空镀膜技术可以成功显现如人民币、擦手纸巾、热敏纸、砂纸砂面、烟头、水浸泡过的牛皮纸信封及塑料袋等疑难客体上的汗潜手印,而且显现效果明显优于其他方法,尤其是对水浸检材。     

彩色背景客体上手印的显现方法

目的利用真空金属镀膜法和＂502＂胶熏显法之间的空间互补性原理,考察显现杂色背景客体表面潜手印过程中遇到的杂色背景干扰问题。方法对杂色背景客体表面的同一枚手印分别采用紫外照相、＂502＂胶熏显、真空镀膜方法处理,比较去除背景干扰能力。结果采用＂502＂胶熏显,真空金属镀膜后期增强处理,能够使指纹纹线清晰连贯,并能有效消除背景杂色干扰。结论该方法可有效消除背景杂色干扰,清晰显现有彩色背景的易拉罐、照片纸等客体上的指纹。     

荧光黄湿粉显现手印方法的初步研究

目的研发一种具有荧光特性的黄湿粉,以提取遗留在不同客体上的不同种类的手印。方法在100mL温水中加入适量的表面活性剂,溶解后加入100g荧光黄颜料,选用不同种类客体及不同种类物质手印进行显现实验,比较显现效果;结果遗留在光滑非渗透性客体及半渗透性客体表面的汗潜、油潜手印,显出的手印纹线流畅、反差强、荧光强;结论荧光黄湿粉可适用于光滑非渗透性客体及半渗透性客体表面新鲜或较新鲜汗潜手印、油潜手印及血潜手印的显现。     

亮绿SF溶液增强红色光滑客体表面潜血手印技术研究

目的探索一种实验室和犯罪现场上均可使用的红色光滑表面上血潜手印新型显现技术。方法把0.2g亮绿SF溶解到容积为200m L盛有5m L蒸馏水的烧杯中,然后加入0.2g正四丁基碘化铵、93m L无水乙醇,使用玻璃棒搅拌,充分溶解后,最后加入盐酸2m L形成绿色透明溶液作为显现液,采用精细喷雾器喷涂客体增强红色光滑面潜血手印,潜血手印增强后,照相提取后并对局部放大观察效果,研究其对红色光滑表面潜血手印的增强效果。结果对遗留手印进行了批量显现与统计分析,0.2%的亮绿SF酒精显现液对红色客体表面潜血手印的反应极其敏感,实验室条件下潜血手印样本显现率可达100%,显出的手印纹线清晰连贯,反差明显,无颜色背景,且局部放大能够有效显示出纹线的细节特征。结论 0.2%的亮绿SF显现液能有效增强红色光滑客体表面潜血手印,反差极其明显,可以作为红色光滑客体表面潜血手印增强试剂。     

胶带粘面手印荧光显现剂的研发与应用

目的根据胶带粘面上潜在手印的特点,利用染料和潜手印的理化性质,研究开发胶带粘面手印荧光显现剂。方法在各种胶带粘面上显现潜在手印,并与常规的碳素墨水染色法进行比较。结果在长波紫外线照射下手印呈黄色明亮荧光,手印纹线清晰、连贯,基本不受手印遗留时间、客体表面颜色和性质的影响。结论胶带粘面上的汗潜手印和血潜手印用荧光显现剂显现效果优于碳素墨水染色法,在实际案件的侦破中有较好的应用前景。     

Latent Fingerprint Visualization using a Scanning Kelvin Probe in Conjunction with Vacuum Metal Deposition

The application of vacuum metal deposition before scanning Kelvin probe visualization of fingerprints is investigated. The potential contrast between fingerprint ridges and furrows is maximized by the use of silver deposition for non‐noble metals and gold–zinc deposition for noble metals. The higher susceptibility of eccrine fingerprints to vacuum metal overdeposition is confirmed. Additionally, fingerprints are best developed individually and by building the metal deposition slowly to protect against overdevelopment and variation in the rate of metal condensation. The progress of the metal deposition can be monitored using the scanning Kelvin probe by reference to the change in potential and continuity of the new potential on the surface. The use of acetic acid solution for the recovery of overVMD‐developed samples is shown not to be useful. Applying the metal deposition has the additional prospect of increasing surface conductivity and homogeneity and both can aid fingerprint visualization using the scanning Kelvin probe.     

Vacuum metal deposition: developing latent fingerprints on polyethylene substrates after the deposition of excess gold.

A previously identified difficulty with the development of latent fingerprints on low-density polyethylene (LDPE) by vacuum metal deposition (VMD) is that excess gold deposition prevents effective zinc deposition and so inhibits latent print development [1]. The investigation of a means to correct for excess gold deposition was the basis for this study. Exposure to zinc and the readmission of air into the vacuum chamber followed by VMD development results in the deactivation of the initial gold clusters due to the formation of zinc oxide and the adsorption of air and water molecules. As a result, the majority of the gold deposited during the second treatment creates new gold clusters rather than adding to the gold clusters previously formed. After excess gold deposition on LDPE, the deposition of 1.5 times the optimum gold amount will result in good-quality normal development. The results also indicate that, on all surfaces, at least twice the initial gold count should be used for re-treatment when further development is required after air has been readmitted to the chamber.     

Vacuum metal deposition: factors affecting normal and reverse development of latent fingerprints on polyethylene substrates

Vacuum metal deposition (VMD) is an established technique for the development of latent fingerprints on non-porous surfaces. VMD has advantages over cyanoacrylate fuming, especially in circumstances where prints are old, have been exposed to adverse environmental conditions, or are present on semi-porous surfaces. Under normal circumstances, VMD produces 'negative' prints as zinc deposits onto the background substrate and not the print ridges themselves. A phenomenon of 'reverse' development, when zinc deposits onto the print ridges and not the background, has been reported by many authors but its causes have not been conclusively identified.Four plastic substrates were used in this study and these could be easily divided into two groups based on the types of development observed as the amount of deposited gold was increased. On group I plastics, identified as low-density polyethylene (LDPE), normal development then reverse development and finally no development resulted with increasing gold. On group II plastics, identified as high-density polyethylene (HDPE), normal development then over-development and finally poor-quality normal development resulted with increasing gold. Our results suggest that the difference between these plastic types causes variations in the gold film structure which in turn dictates the nature of the zinc deposition.On group I plastics, the structure and thickness of the gold film has been identified as the critical factor in the occurrence of normal or reverse development. Thin gold films on plastic substrates form small 'clusters' (or agglomerates) rather than the atoms being uniformly spread over the surface. The size and shape of these clusters is critical. Once the clusters reach a certain morphology, they no longer act as nucleation sites for zinc, and hence, zinc will not deposit onto the substrate.On group II plastics, results suggest that the gold clusters are smaller and more densely packed. Hence, even though the same amount of gold has been deposited, the gold clusters in this case do not reach the critical morphology and so continue to act as nucleation sites for zinc.Typically, zinc will not deposit onto the fingerprint ridges as the gold nucleation sites are buried within the print residue. However, when more gold is deposited, gold emerges at the surface of the latent print allowing zinc deposition onto the ridges.The rate of gold evaporation was found not to affect the structure of the gold film, although a slower rate of evaporation resulted in more effective deposition.     

Vacuum metal deposition: visualisation of gold agglomerates using TEM imaging

Vacuum metal deposition (VMD) is a well-established technique that can be used for the development of latent fingermarks on a range of polymer surfaces, including polyethylene (PE) bags exposed to harsh environmental conditions. The technique has also proved to be effective on difficult semi-porous surfaces such as the polymer banknotes in circulation in Australia and in an increasing number of other countries. VMD is a two-stage technique. In the first stage, a small amount of gold is deposited under high vacuum onto the exhibit. This is then followed by the deposition, onto the gold layer, of a much thicker layer of zinc. Normal VMD development is characterised by zinc depositing all over the surface except on the fingermark ridges themselves. A phenomenon of reverse development (zinc on the ridges but not on the surface) has been reported by many authors. Recent studies indicated that this phenomenon might occur on low-density polyethylene (LDPE) when the amount of deposited gold is above an optimum quantity. The results suggested that the size of the gold agglomerates formed on the surface of the polymer plays a critical role. This preliminary study was aimed at visualising, by transmission electron microscopy (TEM), the formation of gold agglomerates on polymer surfaces to gain an appreciation of how the density and size of these agglomerates changes with an increasing amount of evaporated gold.     

Enhanced Visualization of Latent Fingermarks on Rough Aluminum Surfaces Using Sequential Au and Zn/ZnS/ZnO Depositions

Detection and visualization of fingermarks on rough and diffuse surfaces is a relatively challenging task. We succeeded in developing latent fingermarks on scratched and rough aluminum surfaces by sequential deposition of a thin layer of gold followed by one of zinc or zinc‐based compounds on the fingermarks. The best image enhancement was achieved with sequential Au and ZnS depositions. Using this combination, we could enhance the visualization of latent fingermarks aged over 65 days in normal conditions. The optical reflectance from the fingermarks with the deposited layers of metal/dielectric is analyzed as a stratified medium. Significant contrast in the reflectance from the regions of the ridges and the valleys of the fingermark would enhance the visualization. Our results show that the Au and ZnS bi‐layer combination can have a large reflection contrast and improved fingermark visualization at wavelengths corresponding to the green light for specific thickness of ZnS.     

An efficient strategy to detect latent fingermarks on metallic surfaces

The aim of this work is to use metal sputtering for the development of latent fingermarks on metallic surfaces by taking advantage of the prints' topography. In order to promote the preferential deposition onto fingerprints' ridges the deposition parameters should be optimized. After a previous selection, copper and gold thin films were deposited by magnetron sputtering onto stainless steel substrates where fingermarks were intentionally placed. After optimizing the deposition parameters, the influence of the fingermarks' age was studied. The quality of the developed fingermarks was evaluated visually and through optical and scanning electron microscopy. The morphology of the copper and gold thin films was examined by high resolution scanning electron microscopy. The preferential magnetron sputtering deposition of copper and gold thin films, 20-30 nm thick, allows latent fingermarks to be successfully developed. The gold films are more promising, especially for detecting non-fresh fingermarks and for conserving the developed marks. It was possible to detect the contours of the ridges and localize minutiae features in a one-month aged impression developed by gold deposition. These films present discontinuous surface and columnar cross-sections, while copper thin films have a featureless morphology.     

The influence of polymer type, print donor and age on the quality of fingerprints developed on plastic substrates using vacuum metal deposition.

This study investigated fingerprint development on five different polymer substrates using vacuum metal deposition (VMD). The conditions required for optimum development are shown to depend on a number of factors. No one set of conditions will result in good development in all situations. Polymer type has been confirmed as a major factor in determining the types of development that will occur and the optimum VMD conditions required. For more consistently successful VMD development, polymer type should be determined before selecting conditions. While polymer type is a key factor in determining optimum development conditions, there may be variation of the optimum conditions within a polymer type, most likely due to the presence of additives in the plastic. The heaviness of a latent print, i.e. amount of residue that constitutes the print, also affects the VMD conditions required. The donor, manner of deposition, and age of a print affect the heaviness of the deposit. The heavier the print, the higher the gold count necessary for successful VMD development. The occurrence of 'empty prints' (i.e. zinc deposition on the general background but not on or between the print ridges) was found to be related to polymer type and print heaviness. Heavy prints on PVC and PET are the most likely to be 'empty' after VMD treatment. The development of empty prints may be due to the diffusion of print residue into the print valleys. Pre-treatment with cyanoacrylate fuming was also found to affect VMD development. In particular, it was shown that cyanoacrylate pre-treatment was beneficial for print development on PET and PVC. The results of this study were used to formulate guidelines for use as an aid by laboratories using VMD in casework.