The electron and hole trapping and detrapping properties of three types of rhodium centers were determined by electron spin resonance in Rh 3ϩ -doped AgCl microcrystals. Three paramagnetic Rh 2ϩ centers were identified after ultraviolet irradiation: RhCl 6 4Ϫ , and the singly or doubly aquated RhCl 5 (H 2 O) 3Ϫ and RhCl 4 (H 2 O) 2 2Ϫ . All three defects have a 4d 7 orbital ground state in a strong ͑distorted͒ octahedral field. The RhCl 6 4Ϫ , RhCl 5 (H 2 O) 3Ϫ , and RhCl 4 (H 2 O) 2 2Ϫ centers act as deep electron traps ͑lifetime at 300 K greater than 50 min͒ and as recombination centers. These properties of the rhodium centers are consistent with photographic experiments.
During optical excitation of spectrally sensitized silver bromide microcrystals, dye radicals are generated at the surface of the crystals. For the dyes studied in this work the radicals are oxidized dye molecules, which have a hole trapped at their doubly degenerate highest occupied molecular orbital. The dye positive holes can be detected using electron spin resonance (ESR) spectroscopy. After optical excitation the oxidized form of the dye starts to decay. A new method to acquire kinetic data of formation and decay of dye positive holes is introduced, taking into account the variation in linewidth of the ESR signal. By comparing measurements in ambient air, dry air and dry nitrogen gas it is found that moisture and not oxygen influences the kinetic behavior of the radicals. A quantitative model is suggested which is able to describe the formation of dye positive holes during optical excitation. This model allows one to predict the decay of the oxidized dye molecules, using the fitting parameters of the formation curves.
An X-ray microtomograph (or micro-CT) is an instrument for high-resolution 3-dimensional reconstruction of objects internal microstructure without destruction or time consuming specimen preparation. By using modem technology in x-ray sources and detectors several micro-CT systems were created as a simply usable desktop instrument. First micro-CT system is a laboratory instrument, giving true spatial resolution over a ten million times more detailed (in the term of volume parts) than the medical CT-scanners. The instrument contains a sealed microfocus X-ray source, a cooled X-ray digital CCDcamera and a Dual Pentium computer for system control and 3D-reconstructions running under Windows NT. The instrument includes possibilities for image analysis in the non-destructively reconstructed intemal microstructure and realistic 3D visualization. During scanning objects are displaced in normal environment conditions, without vacuum or preparation. Another micro-CT scanner is a low-cost portable instrument, which can be connected to any external Pentiumbased PC. Third instrumentmicrolaminographcan create nondestructive slicing in any place of big planar objects (electronic assemblies, PCBs, etc.). This system uses principles of multilayer tomosynthesis for imaging of internal layers from noncomplete dataset. The main application areas for micro-CT and microlaminography systems are micromechanics, electronic components, material sciences, etc.
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