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The quantum efficiency and reflectivity of thick, back-illuminated CCD’s being fabricated at the Lawrence Berkeley National Laboratory for astronomical applications are modeled and compared with experiments. The treatment differs from standard thin-film optics in that (a) absorption is permitted in any film, (b) the 200–500 lm thick silicon substrate is considered as a thin film in order to observe the fringing behavior at long wavelengths, and (c) by using approximate boundary conditions, absorption in the surface films is separated from absorption in the substrate. For quantum efficiency measurements, the CCD’s are normally operated as CCD’s, usually at T = -140 °C, and at higher temperatures, as photodiodes. They are mounted on mechanical substrates. Reflectivity is measured on air-backed wafer samples at room temperature. The agreement between model expectation and quantum efficiency measurement is in general satisfactory. [ABSTRACT FROM AUTHOR]

Silicon detectors with very thin entrance contacts have been fabricated for use in the IMPACT SupraThermal Electron (STE) instrument on the STEREO mission and for the Solid State Telescopes on the THEMIS mission. The silicon diode detecters were fabricated using a 200 Å thick phosphorous doped polysili con layer that formed the thin entrance window. A 200 Å thick aluminum layer was deposited on top of the polysilicon in order to reduce their response to stray light. Energy loss in the entrance contact was about 350 eV for electrons and about 2.3 keV for protons. The highest detector yield was obtained using a process in which the thick polysilicon gettering layer was removed by chemical etching rather than chemical mechanical polishing. [ABSTRACT FROM AUTHOR]

We present three new autoradiography methods to map positron emission rate of a bio-specimen slice with high resolution. One is based on LBNL scientific charge coupled device (CCD) and the other two are based on conventional CCDs. High conversion efficiency (100k e-h pairs / 0.5 MeV positron) and low dark current (1.75 × 10(-4) e-/pix/sec) can be achieved using the LBNL CCD. The theoretical calculations and preliminary experiments show that an 86 μm spatial resolution can be achieved when imaging a 100 μm thick tissue soaked with (18)F which produce higher energy positron. The main disadvantage of the LBNL CCD we tested is that a very low operating temperature is required to eliminate dark current. This dramatically increases the system cost. In addition, the integration time of the CCD needs to be short enough to avoid overlapping of the positron trajectories. Conventional CCDs have lower conversion efficiency (2k e-h pairs / 0.5 MeV positron) and higher dark current (200 e-/pix/sec), but are more cost-efficient and the requirement for the readout frequency is much lower. The conversion efficiency of the conventional CCD imager can be improved by 17 times by inserting a 100 μm layer of phosphor between the sample and the imager. However, the light emitted from the phosphor screen will be ~100 μm diameter, which severely degrades the spatial resolution. A high readout frequency is also required to avoid the overlapping. The CCD systems designed in this study will be used to map positron emission rate of bio-specimens such as cancerous tissues acquired in regular biopsy procedure. They can also be used to corroborate tracer kinetic modeling at a cellular level.