Semi-conducting CdZnTe (or CZT) crystals can be used in a variety of detector-type applications. CZT
shows great promise for use as a gamma radiation spectrometer. However, its performance is adversely
affected by point defects, structural and compositional heterogeneities within the crystals, such as twinning,
pipes, grain boundaries (polycrystallinity), secondary phases and in some cases, damage caused by external
forces. One example is damage that occurs during characterization of the surface by a laser during Raman
spectroscopy. Even minimal laser power can cause Te enriched areas on the surface to appear. The Raman
spectra resulting from measurements at moderate intensity laser power show large increases in peak intensity
that is attributed to Te. Atomic Force Microscopy (AFM) was used to characterize the extent of damage to the
CZT crystal surface following exposure to the Raman laser. AFM data reveal localized surface damage in the
areas exposed to the Raman laser beam. The degree of surface damage to the crystal is dependent on the laser
power, with the most observable damage occurring at high laser power. Moreover, intensity increases in the Te
peaks of the Raman spectra are observed even at low laser power with little to no visible damage observed by
AFM. AFM results also suggest that exposure to the same amount of laser power yields different amounts of
surface damage depending on whether the exposed surface is the Te terminating face or the Cd terminating face
of CZT.
Epitaxial single-crystal chemical-vapor-deposited diamond with (100) crystal orientation is obtained from Element Six (Ascot, United Kingdom) and Apollo Diamond (Boston, Massachusetts). Both companies supply 5×5-mm squares with thicknesses of 0.35 to 1.74 mm. Element Six also provides disks with a state of the art diameter of 10 to 11 mm and a thickness of 1.0 mm. The absorption coefficient measured by laser calorimetry at 1.064 µm is 0.003 cm−1 for squares from Element Six and 0.07 cm−1 for squares from Apollo. One Apollo specimen has an absorption coefficient near those of the Element Six material. Absorption coefficients of Element Six disks are 0.008 to 0.03 cm−1. Each square specimen can be rotated between orientations that produce minimum or maximum loss of polarization of a 1.064-µm laser beam transmitted through the diamond. Minimum loss is in the range 0 to 11% (mean=5%) and maximum loss is 8 to 27% (mean=17%). Element Six disks produce a loss of polarization in the range 0 to 4%, depending on the angle of rotation of the disk. Part of the 0.04 to 0.6% total integrated optical scatter in the forward hemisphere at 1.064 µm can be attributed to surface roughness.
Epitaxial single-crystal chemical-vapor-deposited diamond was obtained from Element Six Ltd. (Ascot, UK) and from
Apollo Diamond (Boston, MA). Both companies provided 5 x 5 mm squares with thicknesses ranging from 0.5 to 1.5
mm. In addition, Element Six provided 10-mm-diameter disks with a thickness of 1.0 mm. The absorptance of all
specimens at 1064 nm was measured by laser calorimetry, with good agreement between independent measurements at
the University of Central Florida and at QinetiQ (Malvern, UK). Depolarization at 1064 nm and ultraviolet absorption
properties are also reported.
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