Simple, high current, antimony ion source.
A simple metal ion source capable of producing a continuous, uncontaminated, high current beam of Sb ions is presented. It produced a total ion current of 200 muA at 1 kV extraction voltage. A discharge occurred in the source at a pressure of 6x10(-4) Torr. The ion current extracted from the source increased with the 3/2 power of the extraction voltage. The perveance of the source and ion density in the plasma were 8x10(-9) and 1.8x10(11) cm(-3), respectively.
1 – The Technology and Design of Molecular Beam Epitaxy Systems
This chapter discusses that molecular beam epitaxy (MBE) involves the generation of fluxes of constituent matrix and doping species (molecular beam) and their reaction at the substrate to form an ordered over-layer (epitaxy). To maintain the high purity and integrity of the deposit, stringent vacuum conditions are needed. A key attribute of MBE is the precision with which the composition and doping of a structure can be tailored, such that atomically abrupt features can be produced. The evaporation procedure, flux incidence on the substrate, vacuum, and process diagnostics are controlled by a supervisory operator or computer. The MBE process is supplemented by ex situ substrate preparation and wafer introduction procedures. For a better understanding of current MBE methodology and system designs, it is useful to take a brief look at the historical development of the MBE process. Retraction of sources into small volume load-lock chambers that can be isolated from the deposition chamber with a valve permits venting and reloading of the cell without disturbing the deposition environment. The integral control term corrects for offset, a condition where the system temperature stabilizes at a fixed interval below the set point temperature.
rPET detectors design and data processing
Small animal PET systems based on rotating planar detectors posses some interesting advantages for high sensitivity, high resolution imaging. We have designed the rPET detectors based on MLS crystals assembled on a 30times30 matrix optically coupled to a flat-panel PS-PMT. Weighted position readout circuits pre-process the 64 signals from the 8times8 anodes matrix, which are digitized using a charge-integrating converter. The amplification electronics, including the trigger output for coincidence detection, and the high voltage supply are integrated in a three PCBs stack that forms the base attached to the back of the PMT. The whole assembly is enclosed in a light tight, lead (Pb) shielded aluminum box. The detectors are mounted on a rotating gantry with more than 180 degrees rotation span. The digitized events are screened and histogramed, and a modified center of gravity algorithm removes from the position calculation those signals with poor signal to noise ratio. Apparent mean crystal size on the 511 keV field-flood images is 0.6 mm, mean peak-to-valley ratio is better than 8, and intrinsic resolution is 1.5 mm at the central row, with the energy window wide open. Sensitivity (CPS) for a pair of these detectors set in coincidence at 160 mm distance is 1%