Carbon nitride films with the composition ratio CR(C/N)=0.5–3.0 were prepared by the ion and vapor deposition method, where carbon was evaporated on various substrates while being simultaneously bombarded with 0.5–10.0 keV nitrogen ions. The properties of the films were studied by x-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectrometry (FT-IR), ultraviolet transmission spectroscopy, x-ray diffraction, and hardness measurements. The films formed at energies lower than 0.8 keV and CR(C/N)=0.6–0.7 on tungsten carbide showed the highest Knoop harness of 6400 kgf/mm2 on films with 1 μm thickness and a maximum optical band gap of 2.7 eV. X-ray diffraction measurements demonstrated that all films have an amorphous structure. The XPS and FT-IR studies indicated that the peak newly observed at 286.3 eV in the C-1s1/2 XPS spectra arises from triple bonding C≡N.

Thallium bromide (TlBr) is a semiconductor compound with a high atomic number and a wide bandgap, being a very promising material to be used as room temperature radiation detectors. In this work, commercial TlBr powder was used for growing crystals for detector applications. To reduce impurities, this material was purified by the zone refining technique. Trace impurities at ppb/ppm level were analyzed using inductively coupled plasma mass spectroscopy (ICP-MS). The efficiency of the purification was evaluated through studies of the decrease impurities concentrations in the TlBr powder and in the purified materials. The crystal quality was verified by X-ray diffraction (XRD). To evaluate the crystal as a semiconductor detector, systematic measurements of the transmittance, resistivity, and the radiation response ( 241 Am, 57 Co, 125 I, and 133 Ba) gamma rays were carried out.

Using a generalized scheme of multiple traps, thermoluminescence (TL) glow curves are calculated for different sets of systems parameters. In particular, the conditions under which glow peaks of first-order kinetics are produced are highlighted. The major findings and conclusions are as follows. (1) In the generalized scheme the glow peaks always reduce to first order at low trap occupancies. It is therefore suggested that the peak analysis to determine the parameters should be carried out only at low doses. (2) Glow peaks which follow first-order kinetics can be obtained irrespective of whether the recombination rate is faster, equal to or slower than the retrapping rate (Rret). (3) Quasi-equilibrium (QE) of free carriers in the delocalized band, which is the essential condition for the derivation of the conventional analytical expressions of TL and thermally stimulated conductivity, can be realized irrespective of whether RrecRret. (4) The realization of the QE condition depends on the concentrations of the traps and the recombination centres (RCs) and their cross sections for free carrier capture. It is discussed and shown that, in doped insulating and semiconducting materials, the values of these parameters are sufficiently high for the QE condition to be comfortably held. It is thus concluded that the doubts raised by earlier workers regarding the validity of the QE assumption in the derivation of the analytical expressions are unnecessary as far as these materials are concerned. (5) It is shown that a system in which some of the untrapped charge carriers recombine within the germinate centres and some become delocalized may satisfactorily explain the mechanism of TL emission in most of the phosphors. The properties of first-order, supralinearity and pre-dose sensitization may be easily explained under the framework of this system. (6) Conclusions (2) and (3) above disprove those of earlier workers who had concluded that QE and fast retrapping together do not form a consistent set of conditions and that the apparent dominance of first-order kinetics in nature is due to slow retrapping.

Thin zirconium oxide films, formed on Si(111) substrate by ion-beam assisted deposition, have been investigated by x-ray diffractometry with respect to the microstructure of the films, such as preferred orientation, interplanar spacing, crystallite size. The results of the interplanar spacing and diffraction intensity analysis could be interpreted in terms of relative amount of Zr4+ ions estimated by analyses of Zr 3d x-ray photoelectron spectroscopy spectra for the films.

Strong doubts havc been expressed about the validity of the quasi-equilibrium (QE) assumption used in the derivation of the analytical expressions of thermoluminescence (TL). So far there is no established method available to check if QE actually prevails during the emission of an experimental TL signal. The present study shows that the level of QE changes with a change in the heating rate beta. The change in the level of QE in its turn gets reflected in a change in peak shape when the system turns to a non-QE condition. This property is used as the first ever experimental method to test whether or not the emission of a given glow peak occurs under the QE condition. An essential condition for holding the QE condition is found to be T(R)/taum> or = 10(-3) where T(R) and taum are the glow peak recording duration and the maximum value of the free carrier lifetime, respectively. This relation between T(R) and taum is useful in finding the approximate value of taum. The value of taum being a function of the concentration and cross section of the TL related centres, one may be able to assess these basic parameters from the study of TL glow curves. The theoretical results are discussed in the perspective of LiF (TLD-100).

Thallium bromide is a semiconductor compound with high atomic number and density. It has a CsCl-type simple cubic crystal structure and it is non-hygroscopics. The TlBr crystals are relatively soft with a knoop hardness number of 12. In this work, the TlBr commercial powder was purified by zone refining and the purest material section was used for crystal growth by Bridgman method. Efforts have been concentrated on the purification of the TlBr. The purification efficiency has been evaluated (NAA and ICP-MS) by impurities reduction results after zone refining passes. The crystalline quality was evaluated by X-ray diffraction. The characterized TlBr crystal as a detector has shown good response to gamma radiation.

Non-first order (FO) kinetics models are of three types; second order (SO), general order (GO) and mixed order (MO). It is shown that all three of these have constraints in their energy level schemes and their applicable parameter values. In nature such restrictions are not expected to exist. The thermoluminescence (TL) glow peaks produced by these models shift their position and change their shape as the trap occupancies change. Such characteristics are very unlike those found in samples of real materials. In these models, in general, retrapping predominates over recombination. It is shown that the quasi-equilibrium (QE) assumption implied in the derivation of the TL equation of these models is quite valid, thus disproving earlier workers' conclusion that QE cannot be held under retrapping dominant conditions. However notwithstanding their validity, they suffer from the shortcomings as stated above and have certain lacunae. For example, the kinetic order (KO) parameter and the pre-exponential factor which are assumed to be the constant parameters of the GO kinetics expression turn out to be variables when this expression is applied to plausible physical models. Further, in glow peak characterization using the GO expression, the quality of fit is found to deteriorate when the best fitted value of KO parameter is different from 1 and 2. This means that the found value of the basic parameter, namely the activation energy, becomes subject to error. In the MO kinetics model, the value of the KO parameter α would change with dose, and thus in this model also, as in the GO model, no single value of KO can be assigned to a given glow peak. The paper discusses TL of real materials having characteristics typically like those of FO kinetics. Theoretically too, a plausible physical model of TL emission produces glow peaks which have characteristics of FO kinetics under a wide variety of parametric combinations. In the background of the above findings, it is suggested that the kinetics analysis of the TL glow curves should be carried out straightforwardly assuming FO kinetics.

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