Formation of nanodefects in LiF crystals under gamma irradiation

The absorption spectra, photoluminescence spectra, and microhardness of LiF crystals exposed to gamma radiation from a shutdown reactor and a ⁶⁰Co source at a dose rate of 7.65 Gy/s are investigated. The structure of these crystals is determined using x-ray diffraction analysis. It is revealed that the Li sublattice contains not only point and complex radiation-induced defects but also 28-nm LiOH particles induced by gamma radiation. It is shown that the formation of defects occurs more efficiently upon exposure to radiation from a shutdown reactor than from a ⁶⁰Co source.     

Annealing studies of electron-irradiated copper and copper-hydrogen alloys

Systematic investigations on the effect of small doses of ionizing radiation on defective semiconducting crystals have revealed an interesting feature : under a dose of 10⁴minus;10⁶r gamma-ray irradiation or 10¹²minus;10¹⁴e/cm² electron flux the number of defects does not increase but decreases, and ordering of the crystal structure takes place.¹ The number of removable defects determined by the backscattering method of channelling charged particles is 10 times higher than the number of generated electron-hole pairs. Therefore we assume that ordering of the crystal structure is taking place by chain annihilation reactions between the defects, initiated by ionization.^2,3     

Photoluminescence of bulk Eu-doped GaN crystals

A study of the variation of photoluminescence spectra of bulk Eu-doped GaN samples revealed that the dopant can reside in the crystal in various charge states depending on the total defect concentration in the starting semiconductor host matrix. In crystals with the lowest concentration of shallow-level defects, the ion can exist only in one charge state, Eu³⁺. At higher concentrations of such defects, Eu can be observed in two charge states, Eu²⁺ and Eu³⁺. A rare-earth impurity was found to act as a getter of defects in the starting GaN matrix.     

X-Ray Luminescence of Defects in Spinel Single Crystals

The flareup of x-ray luminescence in spinel single crystals (MgAl₂O₄) depending on the time of x-ray irradiation and the decay of fluorescence depending on the time elapsed after the termination of irradiation have been investigated. These dependences were measured at different powers of the irradiation dose (power of the x-ray tube) and at different temperatures of the samples. The experimental results suggest the existence of large-size complexes of defects, which include antisite defects and impurity ions, the exchange of charge carriers between which during and after irradiation leads to luminescence of the impurity ions. Transfer of charge carriers between isolated elements of the pairs of antisite defects (not interacting with the impurity ions) leads to the formation of a competing channel of recombination luminescence in the UV region of the spectra. The decay of fluorescence attributable to transitions in the Mn²⁺ and Cr³⁺ ions depending on the time elapsed after the termination of x-ray irradiation points to the existence of various combinations of antisite defects in the surroundings of these ions.     

Investigation of the radiation damage to a single crystal of KCl using the method of backward scattering and chaneling of hydrogen and helium ions

The method of channeling and backward scattering of H⁺ and He⁺ ions has been used to analyze the radiation defects in a single crystal of KCl when the crystal is irradiated with H⁺ and He⁺ ions with energies of 1 MeV. The position of the displaced atoms in the crystal lattice was determined and the value of the cross section for the formation of radiation defects and their rate of formation as a function of the radiation dose and orientation of the bombarded beam with respect to the 100 crystallographic axes of the crystal are found. The effect of an external electric field on the formation of the radiation defects was investigated. The effects of irradiation with H⁺ and He⁺ ions are compared with one another. It is shown that mechanisms connected with ionization and excitation of the crystal atoms make the main contribution to the formation of defects.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 3, pp. 49–53, March, 1980.     

Behavior of hydrogen in stainless steel under irradiation

A nondestructive method of the simultaneous analysis of hydrogen and helium in combination with the technique of studying hydrogen migration provides fundamentally new information about the hydrogen behavior in metal-hydrogen systems: about hydrogen migration in metals directly under irradiation and about the mutual effect of implanted hydrogen and helium in constructional materials of nuclear and thermonuclear reactors. The irradiation of metals and alloys with ionizing radiation (ion beams, electrons, and x-ray quanta) causes intense hydrogen migration due to the excitation of electron states from metal-hydrogen bonds whose lifetime is sufficient for hydrogen to leave its regular positions and for nonequilibrium migration. Hydrogen migration over and escape from metals and alloys under the action of electrons and x-ray quanta with an energy below the threshold of defect formation are accompanied by the rearrangement of the defect structure of the material: the annealing of defects of the hydrogen origin due to the annihilation of defects (interstitial atoms and hydrogen-free vacancies). Hydrogen dissolved in metals and alloys reduces the trapping coefficient of the implanted helium, which is due to the formation of fine complexes HV and HV₂ and, as a result, to a decrease in the probability of formation of large vacancy complexes which are effective traps for helium.     

Surface polished of bulk methylammonium lead tribromide single crystal

Organic-inorganic halide perovskite materials have been demonstrated with wide applications in optoelectronics and ionization radiation detection. For bulk as-grown crystals, the existence of surface cracks and defects can significantly increase charges recombination and reduce the performance of the device. Herein, we polished the crystal surfaces with both mechanical and chemical mechanical methods at room temperature. After been chemical-mechanical polished, the crystal surface with root mean square roughness about 0.5 nm was obtained. Optical transmission and photoluminescence spectra indicate that chemical mechanical polishing technology can effectively reduce the density of crystal surface defects. The achieved low leakage current density on the surface and bulk crystal is 0.05 nA mm⁻² and 0.07 nA mm⁻², respectively. Furthermore, the current-voltage curve under visible photons and X-ray photons reveals that surface polishing treatment can suppress the charges recombination and increase the charges transportation.     

Influence of the defect state of samples on the luminescence spectra of CdS single crystals irradiated by electrons

The photoluminescence spectra of CdS single crystals irradiated by electrons (E = 1.2 MeV, Φ = 2×10¹⁷ cm^?2) are investigated in the visible and near-infrared regions of electromagnetic radiation. Some samples of the CdS single crystals are preliminarily irradiated by neutrons (E = 2 MeV, Φ = 2 × 10¹⁸ cm^?2) with the aim of increasing the concentration of initial structural defects. From analyzing the peak intensities of photoluminescence in the irradiated single crystals at the wavelengths λ_m = 0.720, 1.030, and 0.605 μm, it is concluded that the CdS samples with a low concentration of structural defects in the initial state possess the highest resistance to electron radiation. It is assumed that the observed transformation of the photoluminescence spectra of the imperfect CdS single crystals subjected to electron irradiation is determined by either the mechanisms of subthreshold defect formation or the transformation of the defect complexes in elastic and electric fields near the large structural damages of the crystal lattice.     

Particle track phenomena and radiation power effects at the formation of radiation defects in ionic crystals

The mechanisms of the radiation defect formation in alkali halide crystals are studied in an extremely wide range of the absorbed radiation dose rate (10¹–10¹² Gy/s). It is found that the power dependence of color centers accumulation is described by a curve with a maximum at a dose rate of about 10¹⁰ Gy/s. The electron and proton track parameters for ionic crystals are calculated in the context of the theory of ionization losses of charged-particle energy. Proceeding from the concept of the charged-particle track overlap, the theoretical relations are obtained that explain the radiation power effect in all dielectric materials including alkali halide crystals. The suppression of color center accumulation in these crystals under high-power electron irradiation is due to a more regular topography of the radiation defect formation. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 2, pp. 10–21, February, 2007.     

Structural state of III nitride layers implanted with erbium ions

The defect structure of AlGaN/GaN superlattices and GaN layers grown through vapor-phase epitaxy from organometallic compounds is investigated using x-ray diffraction analysis before and after implantation with erbium ions at an energy of 1 MeV and a dose of 3 × 10¹⁵ cm^?2, as well as after annealing. For a superlattice with a total thickness larger than the implantation depth, the satellites of the superlattice region strained under the action of ions disappear in the x-ray diffraction pattern after annealing at temperatures higher than 900°C. This suggests that the radiation-induced defects responsible for the positive deformation in the layer are annealed at these temperatures. However, annealing even at a temperature of 1050°C does not lead to complete recovery of the initial state and the positive deformation in the remaining regions is caused by residual defects. An analysis of the x-ray diffraction patterns demonstrates that, in samples with thin superlattices located at the depth corresponding to maximum radiation damage, the periodic structure that disappears after implantation at a dose of 3 × 10¹⁵ cm^?2 is not recovered even after annealing at a temperature of 1050°C. This inference is confirmed by the results of examinations with an electron microscope.     

KTP(001)晶体分光性能研究

根据同步辐射光源对软X射线分光晶体的性能要求,分析了软X射线能区常用分光晶体的性能优劣,指出对于晶格常数值大的分光晶体,KTP(KTiOPO₄)(011)是该能区比较理想的分光晶体. 同时提出了一种利用同步辐射光源测量晶体衍射效率的实验方法,指出光源的发散度与晶体的衍射效率密切相关. 测量了KTP(011)晶体的晶格常数,给出了KTP(011)晶体的实测衍射效率. 关键词： 同步辐射 KTP(011)晶体 衍射效率 光源发散度     

Photoluminescence of ZnTe crystals grown under deviation from thermodynamic equilibrium

Crystalline textured and columnar structures, as well as needlelike ZnTe single crystals, were grown from the vapor phase and in a tellurium melt under deviation of the growth conditions from equilibrium. Low-temperature photoluminescence and x-ray structural studies showed the samples thus grown to exhibit high structural perfection, a uniform impurity distribution, and weak interaction between impurities and defects of the crystal structure. Polariton scattering from neutral donors was detected in structures having a noticeable residual concentration of donors in the substituted state. It is shown that the spectrum of samples grown under nonequilibrium conditions exhibits transitions that are not typical of equilibrium crystals. Measurements of the luminescence spectra as a function of temperature, excitation level, and annealing conditions made it possible to draw tentative conclusions about the nature of these transitions.     

Magnetic structure and transport properties of atomically disordered crystals of two-dimensional manganites La2−2x Sr1+2x Mn2O7

The magnetic structure and transport properties of partially disordered crystals of two-dimensional manganites La_2?2x Sr_1+2x Mn₂O₇ (x = 0.3, 0.4) are studied over a wide range of temperatures. The crystals are transformed into an atomically disordered state under irradiation with fast neutrons at a dose of 2 × 10¹⁹ cm^?2. The average concentration of substitutional defects in the crystal is ≈4%. It is found that substitutional defects are responsible for the transition of these manganites from the ferromagnetic metal state to the insulator state with a spin glass structure. The results obtained are discussed in terms of the ratio between the kinetic energy of charge carriers and the exchange energy of localized spins.     

The influence of low x-ray doses on the properties of chromium-doped triglycine sulfate

The influence of low x-ray doses on pulsed polarization switching in triglycine sulfate crystals at different chromium impurity concentrations is investigated. It is demonstrated that the activation field α in the temperature range 20.0°C-T _c ambiguously depends on the radiation dose for pulses of switching currents of different polarities. It is found that the unipolarity associated with the presence of chromium ions in impurity triglycine sulfate crystals decreases as a result of the interaction between radiation-induced and impurity defects.     

Growth of InSe:Mn semiconductor crystals by Bridgman–Stockbarger technique and analysis of electron irradiation effects on Sn/InSe:Mn Schottky diodes

Mn-doped p-InSe semiconductor crystals were grown by Bridgman –Stockbarger technique. The crystals were analyzed by X-ray diffraction (XRD), scanning electron microscopy (SEM) and fabricated Sn/InSe:Mn Schottky diodes. The current–voltage (I–V) and capacitance–voltage (C–V) measurements of diodes were investigated to determine the response of devices to electron irradiation with 9?MeV energy and 1.2?×?10¹⁰?e^??cm^?2 dose. After irradiation, the ideality factor and barrier height of the Sn/InSe:Mn Schottky diode were determined as 1.66 and 0.85?eV, respectively. Before irradiation, they were determined as 1.37 and 0.90?eV, respectively. It has been concluded that the radiation with high energy may contribute to form defects at the interface of the Sn/InSe:Mn device.     

Time-resolved spectroscopy of natural and synthetic BeO crystals

The results of comparative luminescence investigation of natural and synthetic BeO crystals are presented. Time-resolved luminescence (2.5–8 eV) and luminescence excitation spectra, and the kinetics of glow decay were measured using ultraviolet-vacuum-ultraviolet (VUV) synchrotron radiation (5–22 eV) or x-radiation (50–620 eV or 3–62 keV) ranges. X-ray and thermostimulated luminescence of natural BeO crystals were compared to the glow of additively colored synthetic crystals. The characteristic luminescence of F and F ⁺ centers was found in natural crystals. In synthetic crystals similar luminescence is observed only after additive or radiation coloration by virtue of the creation of F ⁻ and F ⁺ centers on anion vacancies. The defects found in the crystal lattice of a natural BeO crystal testify to the degree of mineral metamictization of the given deposit.     

Recombination processes in europium-doped cadmium iodide crystals

Results of comprehensive research into optical and luminescent-kinetic characteristics of europium-doped cadmium iodide crystals excited by nitrogen laser radiation, α-particles, and x-rays are presented. Crystals under study have been grown by the Bridgman–Stockbarger method. The doping EuCl₃ admixture was introduced into the charge in quantities of about 0.05 and 1.0 mol%. Impurity absorption detected in the near-edge region of the crystals is interpreted as part of the Eu²⁺ ion long-wavelength band associated with f–d-transitions. The cation impurity and matrix defects in CdI₂:Eu²⁺ crystals create complex centers responsible for emission with a maximum in the 580–600-nm region. The short component in the luminescence decay kinetics of weakly-doped crystal excited by α-particles and x-ray photons is due to the exciton emission characteristic of CdI₂. The slow component in the scintillation pulse results from recombination of charge carriers followed by creation of exciton-like states on the defect-impurity centers. Laser or x-ray excitation induces light-sum accumulation on the trapping levels at a depth of 0.2–0.6 eV that is mainly related to matrix microdefects. Trapping centers associated with the chlorine impurity are observed in the heavily-doped crystal. Photostimulated luminescence at 85 K arising at the electron stage of the recombination process is caused by recombination of electrons released from F-type centers with holes localized near the activator. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 76, No. 3, pp. 358–364, May–June, 2009.     

Structural homogeneity of photorefractive LiNbO<Subscript>3</Subscript> crystals doped with 0.03–4.5 mol % of ZnO

Using the electronic spectroscopy method, the laser-conoscopy method, and the Raman light-scattering method, we have studied the structural homogeneity of LiNbO₃ crystals doped with 0.03–4.5 mol % of ZnO. We have found that, as the laser radiation power is increased to 90 mW, the conoscopic patterns of crystals show additional distortions, which are attributed to the manifestation of the photorefractive effect. For the LiNbO₃ crystal doped with 4.5 mol % of ZnO, in which the photorefractive effect is low, we have revealed a considerable shift (compared to the remaining crystals) of the optical absorption edge toward the shortwavelength range, which indicates a high structural homogeneity of this crystal. We have shown that, in the LiNbO₃ crystal doped by 0.05 mol % ZnO, due to the displacement of Nb_Li and Li□ structural defects by Zn²⁺ cations, the crystal structure is ordered and, simultaneously, the number of defects with localized electrons decreases.