GoEvidence Forensic Laboratories multiple chambers including one of the largest chambers ever designed and developed for forensic use.
Vacuum Metal Deposition (VMD) was first discovered as a potential process for latent print development in 1964. Serious research into the process began in 1968. Since then, extensive published research and equipment development has been done in the United Kingdom, Canada, United States, and Australia demonstrating that VMD is a highly sensitive and effective method of latent print development.
A vacuum chamber is a ridged enclosure typically made of metal. Stainless steel is the most common choice for high vacuum and ultra-high vacuum chambers. Chambers often have multiple ports allowing for instruments and viewing.
The vacuum is achieved with a series of pumps. A roughing pump is used in the first stage. The term ‘roughing pump’ refers to the vacuum range that it works in, above 1x10-3 torr. Rotary vane pumps are typically used for this purpose. A rotary vane pump is a positive-displacement pump that consists of vanes mounted to a rotor that rotates inside of a cavity.
An oil diffusion pump is needed to achieve high vacuum inside the chamber. The diffusion pump uses the vapor of boiling fluid to capture air molecules. The fluid is then moved to another location and cooled. The cooling forces the air molecules to be released. The combination of gravity and the downward direction of the vapors move the air molecules toward the bottom of the pump. A diffusion pump can achieve a high vacuum in the range of 10-4 - 10-8 Torr.
A high powered energy source is used to evaporate the metals. Vacuum Metal Deposition uses resistive evaporation. An electrical current is passed through a resistive element that can generate enough heat to melt and evaporate many materials. The evaporated metals can then condense on to any given substrate.