Adaptive photo-EMF detectors based on CdTe and their solid solutions
The complex measurements of V(Ti)-doped CdTe (crystals and films) and their solid solutions were carried out. This allowed to establish the nature and energy structure of the intrinsic defects and impurity centers and to propose the micromechsnism of photo-EMF effect. The adaptive photodetectors based on these crystals and CdTe polycrystalline films were developed.
CdTe:Ti crystals: materials for optical sensors in the near-IR region
The Ti-doped CdTe semiinsulating crystals of high optical quality were grown by the vertical Bridgman technique. The complex optical, photoelectric and photorefractive measurements of CdTe doped with Ti atoms were carried out. It allowed to our knowledge for the first time to determine the photorefractive characteristics of these crystals. Studies of the optical absorption and photodiffusion current made it possible to determine the nature and energy structure of impurity and intrinsic defects as well as to establish their role in the photorefractive effect. It was shown that the excited 3T1(P) state is in resonance with the conduction band. As a result of it the auto-ionization of electrons to the conduction band under the laser excitation take place. The energy-level diagram both of impurity and intrinsic defects in the CdTe:Ti crystals was constructed. It was shown that titanium dopant have advantage over other dopants and that CdTe:Ti has better characteristics for a potential applications. Obtained parameters: high optical holographic gain coefficient (up to 0.60 cm-1), low background absorption (about 0.1 - 0.2 cm-1), high optical quality and homogeneity, almost electronic type photoconductivity (electron-hole competition factor equals 0.94) show that this material can be effectively used as sensor components for both optical and photoelectric applications in the near infrared region.
Neutron Residual Stress Measurements on Rail Sections for Different Production Conditions
Rail sectioning with subsequent neutron diffraction experiments has been used to assess residual stresses in the rails. In this study we present the results of neutron stress measurements performed at the NIST Center for Neutron Research (NCNR) on rail sections from rails that were produced under various conditions. Specifically, these are air-cooled, air-cooled and roller-straightened, head-hardened and head-hardened and roller-straightened. More significantly, a head-hardened and roller-straightened rail was also studied after service to elucidate evolution of the service-induced residual stresses. In the latter case both a transverse-cut slice and the central region of a 0.53 m long piece were studied. Measurements on this piece are the first in which triaxial stresses have been determined for an intact rail. Neutron strain measurements with 3×3×3 mm3 spatial resolution were successfully employed for transversally cut slices to verify the difference in the stress state depending on the production process. Although examination of slices allows determination of only two-dimensional stresses in the plane of the slice, additional measurements on obliquely-cut slices, which were also carried out, and utilization of FEM gives the possibility of reconstructing the full triaxial stress distribution. Together, these approaches provide a better understanding of rail fabrication and the possibility of improving the durability and safety of rails in the future.Copyright © 2004 by ASME