[en] The nature of damage in diamond and its annealing are studied by monitoring the changes in electrical conductivity, material density and Raman spectra as a function of density of defects (implantation dose) and annealing temperature. Use is made of the marked differences between the properties of diamond and graphite to study the kinetics of the structural transformation of damaged diamond upon annealing. It is found that for low dose implantations (which create damage below a certain critical density N_C) the damaged diamond is rich in point defects and anneals back to diamond, via some well-defined defect states (most likely the split interstitial <1 0 0> dumbbell). In contrast, implantation to doses which create damage in excess of N_C, results in a fully amorphized, mostly sp² bonded, material which converts to graphite upon annealing. The onset of graphitization for heavily damaged diamond is found to be at about 800 K

[en] The thermally driven structural modification of diamond damaged by low-temperature Xe ion implantation are studied by following the changes in its electrical resistivity as function of annealing temperature and time while it gradually converts to graphite. The conduction mechanism in damaged and in partially graphitized diamond is well described by the variable-range-hopping mechanism, allowing the extraction of a number of hopping sites at different stages of annealing from the temperature dependence of the resistivity. It is found that conversion of broken, metastable diamond bonds to graphitic bonds sets in already at an annealing temperature of 420 K with an activation energy of about 0.7 eV, thus giving an estimate of the height of the barrier which separates broken sp³ bonds from graphitic bonds. copyright 1997 The American Physical Society

[en] The electronic properties of polycrystalline lead oxide consisting of a network of single-crystalline α-PbO platelets and the formation of native point defects in the α-PbO crystal lattice are studied using first-principles calculations. The results suggest that the polycrystalline nature of α-PbO causes the formation of lattice defects (i.e., oxygen and lead vacancies) in such a high concentration that defect related conductivity becomes the dominant mechanism of charge transport. The neutral O vacancy forms a defect state at 1.03 eV above the valence band which can act as a deep trap for electrons, while the Pb vacancy forms a shallow trap for holes located just 0.1 eV above the valence band. The ionization of O vacancies can account for the experimentally found dark current decay in ITO/PbO/Au structures. (paper)

[en] First-principles calculations have been applied to study the crystallographic defects in α-PbO in order to understand an origin of n- and p-type conductivity in otherwise undoped α-PbO. It was found that deposition in an oxygen-deficient environment defined in our simulations by the Pb-rich/O-poor limit stimulates a formation of O vacancies and Pb interstitials both characterized by quite low formation energies ∼1.0 eV. The O vacancy, being occupied by two electrons, shifts the balance of electrons and holes between these two defects to an excess of electrons (four electrons against two holes) that causes n-type doping. For the Pb-poor/O-rich limit, an excess of oxygen triggers the formation of the O interstitials characterized by such a low formation energy that a spontaneous appearance of this defect is predicted. It is shown that the concentration of O interstitials is able to reach an extreme magnitude equal to the number of possible defect sites (∼10²² cm⁻³). The localized state formed by the O interstitial is occupied by two holes and because there are no other defects in reasonable concentration to balance the hole redundancy, p-type doping is induced. (paper)

[en] The spectral-correlation method was described for diagnostics of optically inhomogeneous biological objects and materials of natural origin. The interrelation between parameters of the studied objects and parameters of the cross correlation function of speckle patterns produced by scattering of coherent light at different wavelengths is shown for thickness, optical density and internal structure of the material. A detailed study was performed for cellulose electric insulating paper with different parameters. (paper)

[en] The electrophysical characteristics of experimental types of electrical insulating paper modified by bacterial cellulose made of nano-gel film Komagataeibacter xylinus, disintegrated in various ways, were studied. The advantage of composites over traditional electrical insulating paper made of pine cellulose is shown in terms of electrical and mechanical strength, sorption activity and heat resistance. The efficiency of using an industrial blender to grind bacterial cellulose has been confirmed, which significantly reduces the time of its high-quality grinding. (paper)

[en] A comparative study of laboratory castings of insulating paper was fulfilled: the traditional composition made of insulating cellulose of pine and cellulose, modified with the nanocellulose of the agricultural waste (composite). The positive effect of the introduction of this structure-forming modifier on the electrical and mechanical strength of the cellulose dielectric, as well as its heat resistance was revealed. Confirmation of expediency of development of works of this direction for expansion of raw material base for producing of the bio component promoting increase of working capacity of the cellulose dielectrics used in high-voltage insulation of power devices is received. (paper)

[en] Photo-induced crystallization (PC) is studied in amorphous selenium (a-Se) films deposited on glass with and without intermediate layers of indium tin oxide or polymer material. The spatial profile of PC domains is examined by co-localized scanning atomic force microscopy and Raman mapping. We also explore the thermal behavior of the onset and growth of PC in the a-Se films by Raman spectroscopy measurements at temperatures spanning the glass transition (T_g ∼ 313 K). In many films the onset time for PC shows a surprising discontinuity near T_g. Inserting a thin polyimide layer between the a-Se film and the substrate inhibits PC. Our results indicate that adhesion to a rigid substrate is important for promoting PC in a-Se films. We find that the discontinuities in the PC onset times, the shape of the mapping profiles, and the effects of having a soft polymer interface layer can be understood by a model that takes account of the substrate shear strain and its relaxation near T_g. (author)

[en] Avalanche multiplication in amorphous selenium (a-Se) can provide a large, adjustable gain for active matrix flat panel imagers (AMFPI), enabling quantum noise limited x-ray imaging during both radiography and fluoroscopy. In the case of direct conversion AMFPI, the multiplication factor for each x ray is a function of its depth of interaction, and the resulting variations in gain can reduce the detective quantum efficiency (DQE) of the system. An experimental method was developed to measure gain fluctuations by analyzing images of individual x rays that were obtained using a video camera with an a-Se target operated in avalanche mode. Pulse height spectra (PHS) of the charge produced per x ray were recorded for monoenergetic 30.9, 49.4, and 73.8 keV x-ray sources. The rapid initial decay and long tail of each PHS can be explained by a model in which positive charge dominates the initiation of avalanche. The Swank information factor quantifies the effect of gain fluctuation on DQE and was calculated from the PHS. The information factor was found to be 0.5 for a 25 μm a-Se layer with a maximum gain of ∼300. Changing the energy of the incident x ray influenced the range of the primary photoelectron and noticeably affected the tail of the experimental PHS, but did not significantly change the avalanche Swank factor

[en] Amorphous selenium (a-Se) films deposited on rigid substrates can undergo photo-induced crystallization (PC) even at temperatures (T) well below the glass transition, T_g ∼ 313 K. Substrate-generated shear strain is known to promote the PC process. In the present work, we explore the influence of different substrates (Si and glass), and different film-layer-substrate combinations, on the PC in a variety of a-Se films and film-structures. The intermediate layers (indium tin oxide and polyimide) are chosen to promote conductivity and/or to be a buffer against interface strain in structures of interest for digital imaging applications. The PC characteristics in these samples are evaluated and compared using optical microscopy, atomic-force microscopy, Raman mapping, and T-dependent Raman spectroscopy. Both the presence of a soft intermediate layer, and the thermal softening that occurs for T increasing through T_g, inhibit the tendency for the onset of PC. The extensive PC mapping results in the wide range of samples studied here, as well as the suppression of PC near T_g in this array of samples, strongly support the generality of this behavior. As a consequence, one may expect that the stability of a-Se films against PC can be enhanced by decreasing the rigidity of the film-substrate interface. In this regard, advanced film structures that employ flexible substrates, soft intermediate layers, and/or are designed to be operated near T_g should be explored