Forensic Applications of the Phenom Desktop Scanning Electron Microscope (SEM)

By AZoNano Staff Writers

Topics Covered

Introduction
Forensic Applications of Desktop SEM
     Gun Shot Residue (GSR)
Traffic Accidents
Animal hair
Crime Scene Investigation
Forensic Hair Analysis
Biological Evidence
Pollen
Mechanical Evidence
Asbestos
About Phenom-World

Introduction

The Phenom desktop SEM combines the best of the optical and electron-optical world. The Phenom provides useful images up to 45,000x magnification with high depth of focus. It is as simple to use as a typical laboratory-grade optical microscope, and is therefore accessible for any forensic examiner in the lab.

Using an SEM in forensic applications can be highly valuable, as the range of applications and samples that can be studied are broad. Most of these samples can be studied with the Phenom.

Forensic Applications of Desktop SEM

Gun Shot Residue (GSR)

The residue deposited on or around a gunman’s body after firing a bullet is known as gunshot residue. Detecting a significant amount of this residue can confirm that the person was either close to the crime scene or was holding the gun.

Particle analysis using the Phenom proX desktop SEM with an energy-dispersive X-ray spectroscopy detector (EDS) can be the most powerful tool for forensic scientists in establishing proximity to a discharged firearm and/or the contact with a surface exposed to GSR.

Figure 1. The image shows a potential GunShotResidue particle (6400x magnification). GSR particles can quite easily be recognized based on compositional information from the Phenom back scatter detector. The particle can be further analyzed by using the Phenom's Energy Dispersive X-Ray Detector (EDS).

Traffic Accidents

SEM is normally used to study forensic evidence in cases where a serious accident has occurred. With the Phenom desktop SEM, a light bulb filament can be imaged and elemental analysis done. The safety belt will show if it was used at the time of impact. Animal hair may also indicate the reason of the collision. Car paint flakes offer evidence of hit and run accidents.

Figure 2. This screenshot shows the Phenom image and elemental analysis of a light bulb. When a car head- or rear light or indicator is on, the lamp filament becomes hot and at the time of a crash glass particles will melt onto the filament. EDS spot analysis from the highlighted position (spot 1) inside the image clearly shows the presence of SiO2 (glass). Material contrast based on gray level is very powerful when imaging with the back scatter detector.

After a hit and run accident small car paint flakes can often be found at the crime scene. Comparisons are made between flakes from a suspect vehicle and the specimen in order to find a match.

Figure 3. The picture shows a paint flake revealing various paint layers. The numbers represent the positions where a spot mode analysis has been made.

Animal hair

Animal hair may be the reason of the popular “one vehicle” accident. Each animal species has hair of a characteristic length, color, shape and root appearance, and internal microscopic features that distinguish one animal from another.

The image in Figure 4 was taken using the charge reduction sample holder which makes it possible to image non-conductive hair in its original state (no sputter coating is required).

Figure 4. Cat hair

Crime Scene Investigation

SEMs are very useful to identify microscopic samples such as hair, diatoms or pollen. Diatoms and pollen analysis can be useful in forensic science by helping identify the provenance of individuals, clothing or materials recovered from investigation sites.

Forensic Hair Analysis

Forensic hair analysis can be used for:

  • Identification of criminal suspects
  • Identification of crime victims
  • Associating a victim or suspect with a location
  • Determining the type of crime committed

The presence of hairs can associate a suspect to a victim or a suspect to a crime scene. The types of hair recovered and the condition and number of hairs found all impact on their value as evidence in a criminal investigation.

By comparing the microscopic characteristics of questioned hairs to known hair samples helps determine whether a transfer may have occurred. Head hair in humans offer most of the required information.

Biological Evidence

Diatoms are unicellular organisms living in open water. Diatom analysis can be of further use in forensic science by identifying the provenance of individuals, clothing or materials from sites of investigation.

If a person drowns inhaling water causes penetration of diatoms into the system and blood stream, and thus their deposition into the brain, kidneys and other organs. If the victim was dead before the body was submerged, the transport of diatom cells to various organs is prevented due to a lack of circulation.

The type of diatoms found can be used to pinpoint the location at which the drowning occurred.

Figure 5. Diatoms generally range in size from approx. 2-200 pm which can make it difficult to recognize them using light microscopy. A desktop SEM is the perfect solution due to its higher magnification and depth of focus. Sample preparation is similar to that used with optical devices.

Pollen

Pollen is a fine to coarse powder that contains the micro-gametophytes of seed plants. Pollen grains come in all shapes and sizes and never decompose. Pollen can reveal the location of the person and also the season when the person picked up the pollen.

For example, a dead body may be found in a wood, and the clothes may contain pollen that was released after death, but in a place other than where the body was found. That shows that the body was moved.

Figure 6. Grass pollen

Mechanical Evidence

Most of the crimes are committed using tools such as knives, crow bars, screwdrivers and wire cutters. When criminals use these tools to commit a crime they can leave behind marks or damage to the material they come into contact with.

The marks made are generally lines (called striations) and are caused because of imperfections on the surface of the tool. In case cloth is cut with a knife the fibers will show it distinctively when compared to cutting with a scissors. Gunshots will also damage the fibers in a specific way.

The back scatter imaging detector inside the Phenom can be used in 2 modes:

  1. Compositional mode (full mode). This gives maximum signal resulting in material information by means of contrast differences. Different materials can be recognized based on the gray scale level (left side image).
  2. Topographical mode. This gives a different kind of shading resulting in a topographical image (3D effect).

Figure 7. Fiber ends from textile which have been cut by a knife.

Asbestos

Asbestos was previously used in construction materials. Forensic investigation of suspected asbestos-related deaths includes a life-time occupational history, a complete autopsy, and identification of the asbestos fiber tissue burden.

Figure 8. The screenshot shows the Phenom EDS analysis results from crocidolite, also known as "blue asbestos".

Other SEM applications in forensics include the following:

  • Classifying minerals in soil
  • Detection of small pieces of bone in debris
  • Analyzing explosive residues
  • Examining micro-traces of foreign material in forensic pathology and anthropology

About Phenom-World

Phenom™, world’s fastest Desktop Scanning Electron Microscope takes your imaging performance to a higher level. The Phenom desktop scanning electron microscope (SEM) helps customers stay competitive in a world where critical dimensions are continuously getting smaller.

The Phenom desktop SEM combines superb imaging power up to 100,000x and outstanding technical performance with better depth of focus and chemical contrast. It is the smart, affordable and market’s fastest solution that enables engineers, technicians, researchers and educational professionals to investigate micron and submicron structures.

With the Phenom proX we offer integrated, powerful EDS microanalysis to complete the optical performance of our SEM-range. Any Phenom system can be tailored to suit application and sample needs by choosing one of the many Pro Suite-based software solutions or specially designed hardware accessories.

Phenom-World helps you to stay competitive in a world where critical dimensions are continuously getting smaller. The Phenom desktop SEM offers direct access to the high-resolution and high-quality imaging necessary in a large variety of applications. It is an affordable solution that enables engineers, technicians, researchers and educational professionals to visualize micron and submicron structures.

This information has been sourced, reviewed and adapted from materials provided by Phenom-World BV.

For more information on this source, please visit Phenom-World BV.

Date Added: Feb 21, 2014 | Updated: Mar 7, 2014
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