Advanced X-Ray Detectors for Transmission Electron Microscopy

70369S02-II In materials research, the current generation of detectors used for Transmission Electron Microscopy (TEM) are Si[Li] cryogenically cooled devices. Their count rate is severely limited to about 3K/sec making two-dimensional elemental mapping extremely time consuming. For example, this low count rate makes it impossible to acquire elemental maps simultaneously with near-real-time images, thereby impeding the analysis of data. Furthermore, current detectors are prone to radiation damage caused by high-energy backscattered electrons. This project will develop silicon drift detector (SDD) technology and produce a new type of detector that has a very low capacitance and can achieve low noise at short shaping times. This feature will allow the simultaneous attainment of very high-count rates and excellent energy resolution, required for elemental mapping. The SDD device is expected to yield electronic noise better than 10 electrons RMS (70 eV FWHM) at optimum peaking times of ?500 ns and posses an active area up to 0.5 cm2. Also, the implanted contact technology used for SDDs should have better radiation resistance than the Schottky-barrier type used with Si[Li] detectors. Phase I developed a prototype detector package that was inserted into a TEM at Argonne National Laboratory for testing. The performance of the system has exceeded all measures of success. Phase II will further optimize the detector structure through detailed computer simulations and modeling. Optimized devices will be constructed, and the improved detectors will be assembled into a specialized spectrometric package for use in TEM instruments. Commercial Applications and Other Benefits as described by awardee: This technology has the potential to replace cryogenically cooled Si[Li] detectors in electron beam instrumentation, x-ray fluorescence spectrometry, x-ray diffraction, x-ray physics experiments, etc. The overall market for the instrumentation in these areas is in the hundreds of millions of dollars.