The objective of this task was to develop a unique identifier (tag) for Treaty-Limited Items (TLIs) in arms control applications. This tag is authenticated by the direct attachment of a portable Scanning Electron Microscope (SEM) to the TLI. It is an intrinsic tag with two distinct TLI surface-authentication signatures, consisting of topography and atomic composition. Authentication is accomplished by comparing the field-inspection signature with the baseline signature. Because this tag has two unique signatures, it is considered extremely resistant to counterfeit attempts. Since commercial SEMs are large instruments intended to observe small samples introduced into a vacuum chamber integral to the instrument, it was initially necessary to demonstrate that interfacing an SEM to a large TLI was feasible. The first phase demonstrated that an SEM could obtain high- resolution images of a large, curved, simulated TLI surface. A used commercial SEM was modified to accomplish the first phase. The second phase began with a systematic evaluation of the design alternatives necessary to produce a portable SEM suitable for TLI tag authentication. Since the electron column design of the SEM was the central component that drove the selection of the rest of the system, this phase continued with a preliminary design of the column. A novel design of the column's electromagnetic lenses combined both permanent magnets and magnetic coils, significantly reducing the required lens power and weight. Prototype condenser and objective lenses were built and tested to prove that this approach was viable. Based upon the results of the second phase, a 0.1-micrometer (4-micro-inch) resolution SEM is feasible. The total system would weigh 52-Kg including a 7-Kg electron column.
展开▼
