In the forensic science field there are various machines used to examine physical evidence. One of those instruments is the scanning electron microscope (SEM). This instrument can be used in examining physical evidence found at crime scenes. There have been a number of scientists that have developed and improved the SEM. SEM is very significant in forensics because it can narrow down size, shape, and chemical composition. The scanning electron microscope is always growing and becoming a great impact on forensic science.
We will start of learning where the scanning electron microscope (SEM) began. Knoll built the first scanning microscope in 1935; he was not using demagnifying lenses. Von Ardenne expressed the theoretical philosophy underlying the scanning electron microscope. Developing the first scanning electron microscope in 1942 was Zworykin. This microscope was more improved due to using an electron multiplier tube as a preamplifier off the secondary electrons emission current. The resolution on the SEM was 50 nm (Physics Emory). Improving the SEM that Zworykin had developed, Oatley used nonlinear signal amplification. He was also the first to place in a stigmator in the SEM, which was used to correct lens cylindrical imperfections. In 1960, Everhart and Thornley improved the secondary electron detection. Three years following that Pease and Nixon, combined all the improvements in one microscope. The first commercial scanning electron microscope was developed in 1965 by the Cambridge Scientific Instruments Mark I (Physics Emory).
The scanning electron microscope has 10 parts to it which are the secondary detector, x-ray detector, backscatter detector, sample chamber, objective lens, electron beam, condenser lens, anode, electron gun, and vacuum chamber. Secondary detectors generate the most detailed images of an object's surface. The backscattered electron detectors and x-ray detectors, informs researchers about the composition of a substance. The vacuum chamber is very important for the SEM; the vacuum prevents encounter that would be constant interference from air particles in the atmosphere. The electron gun is used to create a steady stream of electron. There are usually two types of electron guns, which are thermionic guns and field emission guns. Thermionic guns apply thermal energy to a filament to coax electrons away from the gun and toward the specimen under examination (Atteberry). The field emission gun creates a strong electrical field to heave electrons away from the atoms they're associated with (Atteberry). The lenses on the SEM are made of magnets, so that they can bend electron to get them accurately where they need to go. All of these parts work together for the scanning electron microscope to work.
Next, we will focus on how the scanning electron microscope works. When the beam traces over the object it interacts with the surface, dislodging secondary electrons from the specimen in distinctive patterns (Atteberry)....