The trap parameters of electrons in intermediate energy levels in quartz

The trap parameters (thermal activation energy E_t and frequency factor s) of the glow peaks of quartz, occurring in the temperature range 420–520 K and corresponding to intermediate energy levels, were evaluated using different and complementary methods of analysis: peak shift, isothermal decay and fractional glow curve. The values of E_t and of s derived with the isothermal decay method and with the peak shift technique agree quite well, within the error limits. The corresponding values obtained using the fractional glow curve analysis proved to be underestimated, probably as a consequence of the thermal quenching. Proper corrections were therefore applied to take into account this phenomenon.     

Modelling the thermal quenching mechanism in quartz based on time-resolved optically stimulated luminescence

This paper presents a new numerical model for thermal quenching in quartz, based on the previously suggested Mott-Seitz mechanism. In the model electrons from a dosimetric trap are raised by optical or thermal stimulation into the conduction band, followed by an electronic transition from the conduction band into an excited state of the recombination center. Subsequently electrons in this excited state undergo either a direct radiative transition into a recombination center, or a competing thermally assisted non-radiative process into the ground state of the recombination center. As the temperature of the sample is increased, more electrons are removed from the excited state via the non-radiative pathway. This reduction in the number of available electrons leads to both a decrease of the intensity of the luminescence signal and to a simultaneous decrease of the luminescence lifetime. Several simulations are carried out of time-resolved optically stimulated luminescence (TR-OSL) experiments, in which the temperature dependence of luminescence lifetimes in quartz is studied as a function of the stimulation temperature. Good quantitative agreement is found between the simulation results and new experimental data obtained using a single-aliquot procedure on a sedimentary quartz sample.     

Kinetic study of the thermoluminescence glow curve of natural dolerite

T _m–T _stop and glow curve deconvolution methods have been used to determine the number of glow peaks and kinetic parameters (activation energy E and frequency factor s) associated with the glow peaks in a natural dolerite. The T _m–T _stop method indicated that the glow curve of the mineral is the superposition of at least seven first-order components, whereas deconvolution analysis indicated the presence of at least eight peaks. A possible reason for this discrepancy is given. The kinetic parameters of the eight peaks are presented and used to estimate the lifetimes of the glow peaks. The lifetimes of the peaks at 120.8 and 143 °C are few days. For application in dosimetry and dating, we suggest the use of a preheat temperature around 170 °C to ensure the complete removal of these peaks with small lifetimes.     

Luminescence sensitivity changes of quartz by bleaching,annealing and UV exposure

The sensitivities of quartz luminescence signals to dose were studied after ionizing irradiation, ultraviolet (UV) exposure and different annealing conditions. The relationship between the 110 v °C thermoluminescence (TL) and optically stimulated luminescence (OSL) were studied on the same aliquot by looking at the ratio of both signals created by a test dose. It is suggested that the sensitivity changes of both signals are closely related, but not identical. Significant differences are observed when annealing to temperatures higher than 500 v °C. A modified model was proposed to interpret the observations. The similarity is interpreted as the same R hole centers are shared by both signals, whereas 110 v °C TL only uses additional R hole centers. Dramatic changes in luminescence sensitivity for quartz relate to the phase changes.     

Study of the Thermoluminescence and Optical Stimulated Luminescence properties of quartz crystal

Abstract

Thermoluminescence (TL) and Optical Stimulated Luminescence (OSL) of natural quartz crystals from sediments have been studied in order to obtain the ages of the sediments' deposition. The sediments were collected from an archaeological site, located in State of Mato Grosso do Sul, Brazil. In the present work the phototransfer TL process was observed in the 394°C TL peak, which increased 10–20% in its intensity when the sample was exposed to sunlight. As the samples did not provide a residual TL, a new methodology to evaluate the paleodose (P) was devised. Annual doses were evaluated based on uranium, thorium and potassium contents determined by neutron activation analysis. Preliminary ages were compared to those obtained by OSL and ages between (11–35) 10³ BP were obtained.     

TL and PL studies on defect-assisted green luminescence from doped strontium sulfide phosphor

Defect-assisted luminescence of Pr³⁺-doped SrS has been investigated and reported in this paper. The polycrystalline sample of phosphor was prepared by conventional solid-state reaction method and checked for crystallization and phase by X-ray diffraction study. The thermally stimulated luminescence studies of the phosphor samples with various activator concentrations, irradiated by a blacklight source, are conducted and show a broad single peak around 365-382 K. Computerized glow curve deconvolution tool is used to evaluate the effective trapping parameters and suggests quasi-continuous distribution of traps in the range of 0.5−0.9 eV. A critical survey on the application of first-order kinetics in the present phosphor is undertaken. Photoluminescence studies reveal three excitation bands at 287, 314, 355 nm and defect-related emission at 517, 494 nm for two concentrations of activator atoms in the present phosphor. The 314-355 nm broad excitation bands correspond to a charge transfer transition of Pr³⁺-S²⁻.     

The annealing of damage in ion implanted gallium arsenide

Photoluminescence measurements at 77°K and Rutherford scattering of 450 keV protons were used to study radiation damage and annealing in ion implanted GaAs. The characteristic band edge luminescence (8225 Å) in GaAs is completely quenched by ion implantation. Photoluminescence measurements on samples which were isochronally annealed show a single annealing stage at 600°C. A luminescence peak at 9140 Å is introduced into the spectra of all implanted and annealed samples. This peak is attributed to an acceptor level created by As vacancies. The intensity of the peak is greatly reduced by protecting the surface of implanted layers with SiO₂ during annealing. Rutherford scattering measurements on isochronally annealed samples reveal two annealing stages. A 300°C annealing stage is observed on samples which have an initial aligned yield less than random while a 650°C stage is observed on samples which have an initial aligned yield equal to random.     

Thermoluminescence of the green emission band of calcite

The thermoluminescence (TL) characteristics of the green emission band of natural calcite are studied. The kinetic parameters of the natural and laboratory-induced defects were estimated. The γ-dose response was studied in the range of 0.01–10⁴ Gy. The fading rate at room temperature is monitored over a period of 30 days. The results showed that calcite has a potential use as a material for γ-ray TL dosimeters for food sterilization, testing of materials and other industrial or reactor procedures.     

Simulations of the effect of pulse annealing on optically-stimulated luminescence of quartz

Pulse annealing techniques are commonly used in OSL studies of quartz to obtain information on the kinetic parameters of OSL traps and hole reservoirs. In this paper, simulations of pulse annealing experiments are carried out using the comprehensive model for quartz developed by Bailey [2001. Towards a general kinetic model for optically and thermally stimulated luminescence of quartz. Radiat. Meas. 33, 17–45] for both natural and laboratory irradiated aliquots. The results of the simulations are in qualitative agreement with, and reproduce, several unusual features of the experimental data of Wintle and Murray [1998. Towards the development of a preheat procedure for OSL dating of quartz. Radiat. Meas. 29, 81–94]. The simulations are also carried out using different heating rates, and show that pulse annealing experiments can be used to recover appropriate kinetic parameters for both the OSL traps and the hole reservoirs known to exist in quartz. The results of the simulations show the importance of these hole reservoirs in determining how the OSL signal depends upon the preheat temperature.     

Reliability of single aliquot regenerative protocol (SAR) for dose estimation in quartz at different burial temperatures: A simulation study

The single aliquot regenerative protocol (SAR) is a well-established technique for estimating naturally acquired radiation doses in quartz. This simulation work examines the reliability of SAR protocol for samples which experienced different ambient temperatures in nature in the range of −10 to 40 °C. The contribution of various experimental variables used in SAR protocols to the accuracy and precision of the method is simulated for different ambient temperatures. Specifically the effects of paleo-dose, test dose, pre-heating temperature and cut-heat temperature on the accuracy of equivalent dose (ED) estimation are simulated by using random combinations of the concentrations of traps and centers using a previously published comprehensive quartz model. The findings suggest that the ambient temperature has a significant bearing on the reliability of natural dose estimation using SAR protocol, especially for ambient temperatures above 0 °C. The main source of these inaccuracies seems to be thermal sensitization of the quartz samples caused by the well-known thermal transfer of holes between luminescence centers in quartz. The simulations suggest that most of this inaccuracy in the dose estimation can be removed by delivering the laboratory doses in pulses (pulsed irradiation procedures).     

Use of quartz crystal nanobalance to study the binding and stabilization of albumin and doxycycline on a thin layer of hydroxyapatite

This study reports the use of quartz crystal nanobalance (QCN) to study the adsorption of two model molecules namely albumin and doxycycline by hydroxyapatite (HA). The work focuses on the deposition of a stable coating of HA on the quartz crystal, modification of the coating using doxycycline and its subsequent effects on albumin adsorption. The uniformity and thickness of the HA coating has been studied using atomic force microscopy (AFM). The functional groups to ascertain the presence of the selected moieties have been characterized by Raman spectroscopy. The results indicate that the mass of albumin deposited on the surface of the HA coated quartz crystal functionalized with doxycycline shows a substantial increase when compared to the standard HA coated quartz crystal. The adsorbed albumin has also been found to be retained for an enhanced period of time. This surface immobilization of doxycycline and subsequent albumin adsorption seem to be a promising approach to confer biomaterials with antithrombogenic and antibacterial surfaces.     

Paper I: The use of measurement-time dependent single-aliquot equivalent-dose estimates from quartz in the identification of incomplete signal resetting

The identification of incomplete signal re-setting of optically stimulated luminescence signals in sedimentary quartz is a vitally important step in the continued improvement of optical dating. It is shown that narrow spectrum (blue-green) laboratory partial bleaching of aliquots of natural sedimentary quartz has a significant effect on equivalent dose (measured using a single aliquot procedure) calculated as a function of measurement time (D_e(t)). The blue-green stimulation spectrum mimics that found underwater and the results suggest that incomplete re-setting of waterlain sediments may be possible using the D_e(t) method.     

Adsorption/desorption behavior of protein on nanosized hydroxyapatite coatings: A quartz crystal microbalance study

Protein separation relates closely to the interactions between proteins and various kinds of adsorbents. To obtain a direct and comprehensive understanding of the protein interaction at the solid/solution interface, quartz crystal microbalance (QCM) technique was employed to in situ investigate the adsorption process of bovine serum albumin (BSA) on nanosized hydroxyapatite coatings, and factors affecting its adsorption such as pH, solution ionic strength and temperature were discussed in detail. The adsorption kinetic parameter and the desorption of adsorbed BSA caused by phosphate buffer solution (PBS) introduction were investigated and discussed as well, and an adsorption/desorption mechanism has been proposed. The obtained information suggests that QCM is a useful method for monitoring the adsorption/desorption behavior of BSA on nanosized hydroxyapatite coating.     

Effects of electrodes with continuously varying thickness on energy trapping in thickness-shear mode quartz resonators

We study the effects of electrodes of nonuniform thickness on thickness-shear vibration frequencies and mode shapes of quartz resonators. This paper extends a previous paper from electrodes of stepped thickness to continuously varying thickness. Numerical results for electrodes of linearly varying thickness are presented. The results show that strong energy trapping can be achieved and adjusted using electrodes with variable thickness.     

Further study on the influence of thermal treatments on the glow curve structure in LiF:Mg,Cu,P (GR-200A)

The influence of various annealing treatments with heating temperatures (T_A) from 240 to 700 °C, with re-annealing at 240 °C, and with a combined re-annealing procedure of 20 min at 270 °C followed by 10 min at 240 °C on LiF:Mg,Cu,P (GR-200A) was investigated. As the T_A increased, the intensity decreased rapidly to almost no signal at 340–380 °C then increased clearly and achieved a maximum at 540 °C. The position of the maximum intensity of the glow curve shifted basically in the direction of higher temperatures with an increase at T_A and achieved a maximum of 279 °C when annealed at 460 °C. The re-annealing influenced both the intensity and the glow curve structure at certain degree. The effect of re-annealing on the glow curve depended markedly on the T_A. With re-annealing at 240 °C, the intensity decreased as T_A increased up to 360 °C then increased and achieved a maximum at 540 °C. The intensity could be restored fully when annealed at above 500 °C, however, the glow curve couldn't be restored fully. With a combined annealing, the shape of glow curve of a sample annealed at above 540 °C or below 320 °C was similar to that of the standard glow curve of LiF:Mg,Cu,P and the intensity and glow curve could be restored completely when annealed in the range 620–660 °C. It seems that the main roles of the re-annealing at 240 °C are to restore partially the intensity of peak 4 and peak shape for LiF:Mg,Cu,P when annealed at above 260 °C, and restore fully the total TL intensity of LiF:Mg,Cu,P when annealed at above 500 °C and the main roles of the combined re-annealing are to reduce the intensity of peak 5 and the total TL intensity, increase the intensity of peak 4 and restore the glow curve shape.     

低温冷风与传统加工对磨削质量的对比分析

针对磨削加工传统方法的不足设计了一种新型低温冷风加工磨削装置,能够提供0～-80℃连续低温,压力在0.3～0.5MPa范围内变化,结构简单,操作控制方便,加工成本低。通过对比工件的表面粗糙度,发现使用低温冷风磨削效果优于传统磨削,并且低温冷风温度越低,压力越高则工件表面质量越好,机床参数与低温冷风参数相比对工件的表面粗糙度影响不很明显。     

An erosion sensor based on a quartz crystal microbalance for quantitative determination of the cleaning efficiency in an ultrasonic vessel

The efficiency of ultrasonic cleaning vessels cannot be measured directly in an easy way. In the presented work, a sensor is developed which quantitatively measures the ablation of a test layer. The sensor element is a quartz crystal which is coated with a sacrificial layer. Small changes in mass of this layer can be measured by a frequency shift of the crystal oscillation. For measurements, a 10 MHz AT-cut quartz crystal was used in a cleaning vessel working at 44.9 kHz. To determine the frequency shift by the ablation of the test layer, the quartz crystal was driven by a frequency generator sweeping the frequency in the range of the resonance frequency and a characteristic frequency was determined. The test layer which was applied to the quartz crystal consisted of silica microparticles suspended in varnish. In a preliminary experiment using a commercial cleaner it could be shown that significant changes in resonance frequency by cavitation effect could be detected. The initial frequency shift of the sacrificial layer is reproducible within 10%. The test layer can be adapted to the conditions of the cleaning vessel. By changing the electrical input power of the vessel, a threshold in the cavitation erosion was found.     

Comparative study of annealing and gold dopant effect on DC sputtered vanadium oxide films for bolometer applications

Vanadium oxide (VO_x) thin film has been widely used for IR detectors and it is one of the promising materials for THz detectors due to its high temperature coefficient of resistance (TCR) values. VO_x films with proper TCR values have also high resistance and it restricts bolometer performance especially for uncooled bolometers. To overcome this problem, deposition at elevated temperatures or annealing approach has been accepted and used but gold co-deposition approach has been proposed recently. In this study, vanadium oxide films were fabricated on high resistivity silicon substrates by reactive direct current magnetron sputtering in different O₂/Ar atmosphere at room temperature. We investigated influence of oxygen partial pressure during deposition process and fabricated VO_x thin films with sufficient TCR values for bolometer applications. In order to decrease resistivity of the deposited films, post annealing and gold doping approaches were performed separately. Effect of both post annealing process and gold doping process on structural and electrical properties of VO_x thin films deposited at room temperature were investigated and detailed comparison between these methods were presented. We obtained the best possible approach to obtain optimum conditions for the highly reproducible VO_x thin films which have the best resistivity and suitable TCR value for bolometer applications.