NO 3 2- centers in synthetic hydroxyapatite

Physics of the Solid State - The structure and properties of NO 3 2? paramagnetic complexes formed by γ-rays and UV irradiation in synthetic hydroxyapatite have been investigated using...     

Yellow color centers in natural and synthetic quartz

Four different yellow color centers have been characterized in quartz. Citrine or heated amethyst contain inclusions of Fe₂O₃ as shown by EPR at different microwave frequencies. Slightly yellow colors can be obtained by ionizing irradiation of certain natural quartzes with aluminum and hydrogen content. Hole centers related to the well known smoky quartz centers are formed. Doping of quartz with trivalent iron during hydrothermal growth results in interstitial incorporation of this ion in sites of distorted tetrahedral symmetry. Relations to silicate glasses are discussed. Doping with trivalent cobalt results in incorporation of this ion in interstitial positions of distorted octahedral symmetry.     

Dependence of nitrogen vacancy color centers on nitrogen concentration in synthetic diamond

Crystallization of diamond with different nitrogen concentrations was carried out with a FeNiCo-C system at pressure of 6.5 GPa. As the nitrogen concentration in diamond increased, the color of the synthesized diamond crystals changed from colorless to yellow and finally to atrovirens (a dark green). All the Raman peaks for the obtained crystals were located at about 1330 cm^-1 and contained only the sp³ hybrid diamond phase. Based on Fourier transform infrared results, the nitrogen concentration of the colorless diamond was < 1 ppm and absorption peaks corresponding to nitrogen impurities were not detected. However, the C-center nitrogen concentration of the atrovirens diamond reached 1030 ppm and the value of A-center nitrogen was approximately 180 ppm with a characteristic absorption peak at 1282 cm^-1. Furthermore, neither the NV⁰ nor the NV^- optical color center existed in diamond crystal with nitrogen impurities of less than 1 ppm by photoluminescence measurement. However, Ni-related centers located at 695 nm and 793.6 nm were observed in colorless diamond. The NE8 color center at 793.6 nm has more potential for application than the common NV centers. NV⁰ and NV^- optical color centers coexist in diamond without any additives in the synthesis system. Importantly, only the NV^- color center was noticed in diamond with a higher nitrogen concentration, which maximized optimization of the NV^-/NV⁰ ratio in the diamond structure. This study has provided a new way to prepare diamond containing only NV^- optical color centers.     

Effect of copper on dislocation luminescence centers in silicon

The effect of copper on dislocation luminescence centers in silicon has been investigated using photoluminescence and transmission electron microscopy. It has been demonstrated that there exist two main mechanisms responsible for quenching of dislocation luminescence by the copper impurity. The first mechanism is dominant at high copper concentrations and associated with the decrease in the time of nonradiative recombination of nonequilibrium charge carriers due to the formation of copper precipitates in silicon. This leads to the quenching of the entire dislocation luminescence and the edge exciton luminescence. The second mechanism is associated with the interaction of individual copper atoms with deep dislocation centers D1/D2, which results in the passivation of the recombination activity of these centers. This mechanism takes place even at room temperature and is highly effective at low copper concentrations.     

预处理气氛对电子束蒸发制备YBCO薄膜性能和结构的影响

采用先电子束沉积后退火的两步法制备YBCO超导薄膜;根据薄膜的超导临界电流密度、X射线衍射(XRD)和扫描电镜(SEM)的测试结果,研究了不同预处理气氛对YBCO薄膜结构、表面形貌及超导性能的影响。     

Laser-assisted production of tricalcium phosphate nanoparticles from biological and synthetic hydroxyapatite in aqueous medium

Pulsed laser ablation technique has attracted great attention as a method for preparing nanoparticles. In this work, calcined fish bones and synthetic hydroxyapatite, have been used as target to be ablated in de-ionized water with a pulsed CO₂ laser to produce calcium phosphate nanoparticles. The obtained nanoparticles were amorphous and spherical in shape with a mean diameter of about 25 nm. The microanalyses revealed that nanoparticles obtained from the synthetic HA undergo transformation to tricalcium phosphate. While nanoparticles obtained from the biological hydroxyapatite mostly preserve the composition of precursor material.     

Effect ofV K centers on positron annihilation in KCl and Ag-doped KCl

Positron lifetime spectra have been measured at 77 K for KCl and Ag-doped KCl before and after x-irradiation at 77 K and after annealing at room temperature. Radiation at 77 K reduces the intensity of the intermediate lifetime (τ₂) component. Radiation-induced defects were monitored optically and by ESR. The experiment shows that the changes observed in the positron decay are associated with the presence ofV _K centers.     

EPR study of the effect of partial pressure of oxygen in the growth atmosphere on concentration of chromium centers in synthetic forsterite

Samples of synthetic forsterite doped with chromium and grown in an argon atmosphere with different oxygen concentrations (at a partial pressure of oxygen in the range from 0.03 to 0.78 kPa) have been studied using multifrequency electron paramagnetic resonance (EPR) spectroscopy. It has been demonstrated how the oxidizing properties of the atmosphere during the growth of crystals affect the relative concentration of di-, tri-, and tetravalent chromium ions in the samples. The structure of trivalent chromium impurity centers has been discussed.     

Simple synthetic route for hydroxyapatite colloidal nanoparticles via a Nd:YAG laser ablation in liquid medium

Pulsed laser ablation (PLA) in liquid medium was successfully employed to synthesize hydroxyapatite (HAp) colloidal nanoparticles. The crystalline phase, particle morphology, size distribution and microstructure of the HAp nanoparticles were investigated in detail. The obtained HAp nanoparticles had spherical shape with sizes ranging from 5 to 20 nm. The laser ablation and the nanoparticle forming process were studied in terms of the explosive ejection mechanism by investigating the change of the surface morphology on target. The stoichiometry and bonding properties were studied by using XPS, FT-IR and Raman spectroscopy. A molar ratio of Ca/P of the prepared HAp nanoparticles was more stoichiometric than the value reported in the case of ablation in vacuum.     

Effect of random motion on synthetic aperture radar imagery

We consider the effect of the random motion of capillary waves on the mean intensity and the contrast of the images of dynamic ocean surfaces, with such features as surface waves and current boundaries, produced by a synthetic aperture radar (SAR).     

Effect of dilute gelatine on the ultrasonic thermally assisted synthesis of nano hydroxyapatite

A series of nano hydroxyapatite-gelatine composites with different dilute solutions of gelatine concentrations were synthesized by a thermally assisted low-power ultrasonic irradiation method. The gelatine hydroxyapatite, (Gel-HAP) nanoparticles were prepared using Ca(NO(3))(2) and KH(2)PO(4) in the presence of gelatine in an aqueous solution. The synthesised products were heat treated between 100 and 400°C. The effect of the addition of gelatine on the nucleation and growth of synthesised nano HAP was investigated. Characterisation was performed using X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM) and Fourier transform infrared spectroscopy (FT-IR). The characterisation results indicate that gelatine has been appended to the nano HAP forming regular spherical shaped crystals of nano sized Gel-HAP.     

Effect of high temperature treatments on defect centers and impurities in hydrothermally grown ZnO

Deep level transient spectroscopy (DLTS) has been employed to study electron traps in hydrothermally grown n-type ZnO samples after thermal treatments up to 1500 °C. Schottky barrier contacts were formed by e-beam evaporation of Pd, followed by DLTS and secondary ion mass spectrometry (SIMS) measurements in order to investigate possible correlations between electron traps in the upper part of the band gap and the concentration of the most prominent impurities. The DLTS results show three different levels having energy positions of , , and (E_c denotes the conduction band edge). The SIMS results showed that the most pronounced impurities were Li, Al, Si, Mg, Fe, Mn, and Ni with concentrations up to . A decrease in the level is observed after temperature treatments above 1300 °C, and in the same temperature range the Li concentration drops from ∼10¹⁷ to . However, based on absolute concentration values an association between Li and the level can be ruled out. In contrast, the level, which is not stable above 1300 °C, may be associated with Li but further experimental data are needed to substantiate this assignment. The level occurred in selected samples and is presumably impurity-related but no correlation was found with the main impurities detected by SIMS. Except for Li, the concentration of all the impurities remained essentially constant as a function of heat treatment temperature.     

Corrosion of 85-5-5-5 bronze in natural and synthetic acid rain

In order to investigate the decay of bronzes exposed to acid wet depositions, a comparative study has been performed by following the corrosion behaviour of different sets of bronze specimens exposed either to natural rain or to a similar solution, without organic compounds, artificially reproduced in laboratory. The as cast G85 bronze specimens were exposed to aggressive solutions for different periods through a wet-dry technique. The pH trend of the solutions and the amount of metals transferred into the solutions were periodically monitored. OM, SEM, XRD, RAMAN analyses and ac electrochemical measurements were performed on the artificially weathered specimens. Preliminary results, showing the difference between the ageing in natural and synthetic rain, suggest the influence of the organic components on the corrosion process. In particular, the growth of a more uniform protective layer of corrosion products on the metal surface exposed to the natural rain could be attributed to these components. PACS 82.45.Bb; 82.33.Tb