The mixture of a medical and legal approaches in dealing with crimes used in the United States today had its beginning in England in the 12th century, when King Richard I instituted the Office of the Coroner. Even though the coroner’s main duty was to maintain a record of all criminal matters in the county, he was also in charge for probing all deaths thought to be the result of suicide or homicide. Increasingly, the need for a more scientific investigation of unusual deaths became apparent, and coroners began calling on physicians for assistance. Over the centuries, it became obvious that medical schools needed to train doctors for this responsibility. As a consequence, in 1807 the University of Edinburgh in Scotland established a Department of Legal Medicine. As medical involvement in the investigations of violent and unexplained deaths increased, communities began to require that the individual in charge of such investigations have a specific academic background. In 1915 New York City established a comprehensive program in which the medical examiner was specifically authorized to investigate all deaths resulting from criminal violence, accidents, or suicides, and those that occurred suddenly to people who appeared to be in good health. Forensic science as practiced today is a high-technology field using electron microscopes, lasers, ultraviolet and infrared light, advanced analytical chemical techniques, and computerized databanks to analyze and research evidence.

The first electron microscope prototype was developed in 1933 by the German engineers Ernst Ruska and Max Knoll. It was based on the concepts and findings of French physicist Louis de Broglie. Even though it was primitive and not fit for practical use, the device was still capable of magnifying objects by four hundred times. Reinhold Rudenberg had patented the electron microscope in 1931. Consequently M. von Ardenne at 1938 created a scanning transmission electron microscope (STEM) by adding scan coils to a transmission electron microscope. The first STEM micrograph was of a ZnO crystal imaged at an operating voltage of 23 kV at a magnification of 8000 times, and a spatial resolution between 50 and 100 nm. The micrograph contained 400 x 400 scan lines and took 20 min to record, since the film was automatically scanned in synch with the beam. The device had two electrostatic lenses, with the scan coils positioned between them. The device also had a viewing CRT. Nevertheless, the first practical electron microscope was built at the University of Toronto in 1938, by Eli Franklin Burton and students Cecil Hall, James Hillier and Albert Prebus. Zworykin et al at 1942 having employed in the RCA Laboratories in the United States illustrated the first SEM, which was used to test the surface of a solid specimen. The electron optics of the device consisted of three electrostatic lenses with scan coils positioned between the second and third lenses. The electron gun was placed at the bottom so the specimen chamber was at a comfortable height for the operator. This was a usual way in the early days. It did suffer from the slight problem though, that the specimen might fall over the column. A resolution of approximately 50 nm was accomplished with this first SEM. By means of comparison with the fast developing TEM, this figure was considered unexciting and further development lapsed. In the late 1940s C. W. Oatley, then a lecturer in the Engineering Department of Cambridge University, England, became interested in conducting research in the field of electron optics and decided to reinvestigate the SEM as a complement to the work being done on the TEM by V. E. Cosslett, also in Cambridge at the Physics Department. One of Oatley’s students, Ken Sander, began work on a column for a transmission electron microscope using electrostatic lenses however Ken took ill after about one year and had to leave for a time. Dennis McMullan then took up this work in 1948, and he and Oatley built their first SEM. On 1952 this instrument had achieved a resolution of 50 nm, however by far the important thing about this SEM is that it produced the first micrographs viewing the striking three-dimensional imaging character of the contemporary SEM. Ken Smith who started at 1952 and took over SEM1, made a number of developments to the electron optical system, and enhanced the efficiency of secondary electron collection followed Dennis McMullan. He illustrated for the first time that an established image could be produced using the true low-energy component of the total secondary emission.

Wells who started at 1953 and built a second SEM, also incorporating electrostatic lenses; unlike SEM1, nonetheless, this instrument had the gun at the bottom of the column–a design considered better for experimental work. Wells pioneered the use of the scintillator backscattered (BSE) detector as an alternative to the secondary electron multiplier used in SEM1 and applied SEM to many new types of specimen including a large-scale study of fibers. He was also the first to use stereographic pairs to produce SEM micrographs with quantifiable depth information at 1960. The next important step was taken by Everhart who started at 1955 and improved the secondary electron (SE) detector by using a scintillator to convert electrons to photons, which were then transmitted by a light pipe directly interfaced to the photo multiplier tube. Thornley followed up this idea at 1957 and their pioneering work resulted in the publication of a much-quoted paper: “Wide-band detector for micro-microampere low-energy electron currents” (Everhart and Thornley (1960)). Substitute of the electron multiplier with the new scintillator with photo multiplier combination amplified the amount of signal collected and produced an enhancement in signal-to-noise ratio. Consequently, weak contrast mechanisms such as voltage contrast, which was discovered by Oatley and Everhart at 1957, could be better examined. The term “voltage contrast” developed from the fact that as the voltage utilized to a specimen was altered, the image contrast changed. Image analysis was also improved in this early period of research when both Everhart and Wells made the first quantitative studies of the effects of beam penetration on image creation in the SEM. Peter Spreadbury started at 1956, built a simple SEM utilizing a CRT as a display unit. Gary Stewart who started at 1958 and fitted an ion gun to the SEM specimen chamber to allow ion bombardment of the specimen opened up new fields of application. After his research, Gary went on to the Cambridge Instrument Company to pioneer the production of the Stereoscan. Alec Broers who started at 1961 and improved the ion beam optics of the instrument and added a magnetic objective lens to improve resolution later extended the ion beam work. He used this system to conduct some of the earliest experiments in electron beam micro fabrication. Another breakthrough was achieved by Haroon Ahmed who started on 1959 and modified the SEM built by Wells, which was SEM2, to enable the examination of thermionic emitters at temperatures exceeding 1000K. Fabian Pease who started at 1960 built the first SEM to achieve a resolution of 10 nm. This was an all-magnetic lens SEM, the fifth to be constructed. Although modern electron microscopes can magnify objects up to two million times, they are still based upon Ruska’s prototype and his correlation between wavelength and resolution. The electron microscope is an integral part of many laboratories. Researchers use it to examine biological materials such as microorganisms and cells, a variety of large molecules, medical biopsy samples, metals and crystalline structures, and the characteristics of various surfaces.