Decrease In Peak Intensity Research Articles

Synthesis of Er3+ and Er3+ : Yb3+ doped sol-gel derived silica glass and studies on their optical properties

Er3+ and Er3+ : Yb3+ doped optical quality, crack and bubble free glasses for possible use in making laser material have been prepared successfully through sol-gel route. The thermal and optical, including UV-visible absorption, FTIR etc characterizations were undertaken on the samples. The absorption characteristics of Er3+ doped samples clearly revealed the absorption due to Er3+ ions. On the other hand Yb3+ : Er3+ doped samples showed enhanced absorption due to2 F 7/2 →2 F 5/2 transition. The absorption and emission cross-section for2 F 7/2 ↔2 F 5/2 of Yb3+ were estimated. FTIR absorption spectra have clearly shown the reduction of the absorption peak intensity with heat treatment in the range 3700–2900 cm−1. The 960 cm-1 band also showed progressive decrease in the absorption band peak intensity with heat treatment. The result of the investigations with essential discussions and conclusions have been reported in this paper.

Physicochemical properties and surface free energy of ground talc

When the talc was ground with the vibrating mill, a remarkable decrease in crystallinity was observed. Especially, the decrease of peak intensities at (002), (004) and (006) plane was detected. The decrease of mean particle size (D 50) and the increase of specific surface area were also observed as the increase of grinding times. The heat of immersion was significantly increased as the increase of grinding times. The surface free energy of talc was measured by the liquid penetration rate measurement. The polar part of surface free energy ( γ p) was considerably increased after 10 min of grinding ( γ p: intact talc 4.7→10 min ground talc 12.1 mN/m). The change in the polarity ( γ p/( γ p+ γ d)) was also observed by the grinding. The polarity of intact talc was 26%. The polarity was increased to 41% by 10 min of grinding of talc. The disintegration time and the dissolution rate of ethenzamide formulated with ground talc were remarkably faster than those with intact talc. It seemed that more hydrophilic surface might be appeared by the grinding of talc. By using the ground talc as a lubricant, it might be possible to control the disintegration rate and the dissolution time of drug from tablet.

기능성 Zeolite-KCIO3복합체에 의한 Chlorothalonil의 분해

Salt occlusion in Zeolite is a unique phenomenon that takes place only when the salt size is similar to the window size of host zeolite. -occluded Zeolite, as an environment-friendly oxidant, has a high potential for effective removal of various organic pollutants. This study was carried to investigate the characteristics and the removal kinetics of fungicide chlorothalonil by zeolite- complex. About 10% of was occluded in zeolite pores synthesized by salt-thermal method from fly ash, although the occlusion amount was relatively less compared to that of nitrate salts. By occlusion with , no remarkable changes were found in X-ray diffraction patterns of cancrinite, whereas some decrease of overall peak intensities was found with those of sodalite. Different releasing kinetics of ion were observed in distilled water and soil solution from zeolite- complex. Two reactions, hydration and diffusion, seem to be related with the release of . Therefore, the release isotherm of ion well fitted to the power function model which indicate the release was made by hydration and diffusion. The removal of chlorothalonil by zeolite and reached at reaction equilibrium within 6 hours by 18% and 47% respectively. However, the chlorothalonil removal by the zeolite- complex increased slowly and steadily up to 92% in 96 hours. These findings suggested that zeolite- complex could be applied for effective removal of organic contaminants in the soil and aqueous environment.

TiN thin films deposited by ion beam sputtering: effects of energetic particles bombardment

The low energy broad argon ion beam (1.35–2.0) keV was used for sputtering of a Ti target in an atmosphere of nitrogen gas to form TiN films. During deposition the growing thin film was under argon ion irradiation from the beam periphery. The influence of the ion beam energy ( E b) and average energy delivered by assisting ions to condensing film atoms ( E n) on TiN film properties was investigated. The titanium nitride thin films were deposited at a low working pressure of 1×10 −4 mbar and at ambient substrate temperature. XRD analysis revealed the formation of a δ-TiN phase with preferred (220) orientation for the stoichiometric composition of TiN films (RBS). The increase of both the intensity of the (220) peak and TiN film crystallite dimension with increasing the energy of Ti target bombarding Ar + ions ( E b) was observed. By increasing the average ion energy per deposited metal atom ( E n) the (220) peak intensity and crystallite dimension decrease and a complete loss of (220) orientation at E n close to 162 eV/at was found. In the range of E n considered, the TiN films grain size decreases leading to the nano-structured surface as revealed by the STM analysis. The incident angle and energy of the assisted bombarding strongly influence the film-preferred orientation and sub-microstructure.

Additive behavior in ultrathin polymer films investigated by ToF-SIMS

This work is part of a European research program aiming at the detection and quantification by ToF-SIMS of additives at polymer surfaces. An antioxidant has been mixed with different amorphous polymer solutions, and layers of different thickness (<1 μm) have been prepared by spin coating on silicon wafer. These samples were studied by ToF-SIMS. At constant additive concentration in solution (0.5 or 1 wt.%), SIMS peak intensities were found to depend on the film thickness. Data processing based either on univariate analyses or on multivariate analyses (principal component analysis) indicated a pronounced decrease of additive peak intensities below a critical film thickness (in the range of 10–80 nm). Within the range of studied samples, this transition did not seem to depend on the additive nature and/or concentration. However, the weight average polymer molecular weight ( M w) was seen to play a key role. This was pointed out during the analyses of a polystyrene series with M w from 8300 to 63 000 g/mol and with a constant additive concentration (1 wt.%). These results indicate that a correlation may be found between the polymer chain dimension and the critical film thickness. The change of the macrochain conformation, from a mainly surface perpendicular orientation towards a more parallel orientation below the critical thickness, is evoked to explain these results.

Thermal study of copper adsorption on montmorillonites

Copper was adsorbed onto Ca-exchanged montmorillonite (Cheto clay) under basic conditions. Differential thermogravimetric analysis (DTGA) combined with mass spectroscopy (MS) was employed as the principal technology to study the distributions and structures of adsorbed copper species on Cheto clay. The results showed that the original Cheto clay was easily rehydrated. After copper adsorption, a step-by-step replacement of hydrated calcium ions by copper–ammonia complex was observed through the gradual decrease of the first DTGA dehydration peak intensity with the increasing copper loading amount. Compared with the original Cheto clay, copper-loaded samples showed new DTGA peaks assigned to NH 3 and N 2O. The presence of N 2O peak suggested that the loaded copper species were in agglomerated copper oxide form, which dispersed well over the edge and external surface of the clay layers.

Weathering of phlogopite by Bacillus cereus and Acidithiobacillus ferrooxidans.

The purpose of this study was to assess the weathering of finely ground phlogopite, a trioctahedral mica, by placing it in contact with heterotrophic (Bacillus cereus) and acidophilic (Acidithiobacillus ferrooxidans) cultures. X-ray diffraction analyses of the phlogopite sample before and after 24 weeks of contact in B. cereus cultures revealed a decrease in the characteristic peak intensities of phlogopite, indicating destruction of individual structural planes of the mica. No new solid phase products or interlayer structures were detected in B. cereus cultures. Acidithiobacillus ferrooxidans cultures enhanced the chemical dissolution of the mineral and formed partially weathered interlayer structures, where interlayer K was expelled and coupled with the precipitation of K-jarosite [KFe3(SO4)2(OH)6].

Improvement of Pulse Characteristics of Neutrons from a Decoupled Liquid-Hydrogen Moderator Using a Multi-Layer Decoupler System at a Pulsed Spallation Neutron Source

Neutron pulse shapes are important in pulsed neutron sources, especially for high-resolution neutron scattering instruments. Around the region of thermal equilibrium energy, the moderator is the main factor in deciding the neutron pulse shapes from a decoupled moderator. However, in the slowing-down energy region, the reflector also affects the pulse shapes, and the neutrons in this energy region will be increasingly important for precise neutron-scattering experiments in the future. Lead has many preferable characteristics as a reflector from a neutronic point of view, but it has a disadvantage in that it creates a long pulse tail, since it takes a very long time for a neutron in lead to slow down. To shorten this pulse tail, we propose a multi-layer decoupler system and compare its performance with that of a traditional decoupler system. The multi-layer decoupler was found to shorten the pulse tail effectively without causing a large decrease in the pulse peak intensity, whereas the traditional decoupler caused a greater decrease in this intensity. This result indicates that the multi-layer decoupler is useful for improving pulse characteristics of neutrons from a decoupled moderator at the pulsed neutron source using a lead reflector.

Improvement of Pulse Characteristics of Neutrons from a Decoupled Liquid-Hydrogen Moderator Using a Multi-Layer Decoupler System at a Pulsed Spallation Neutron Source

Neutron pulse shapes are important in pulsed neutron sources, especially for high-resolution neutron scattering instruments. Around the region of thermal equilibrium energy, the moderator is the main factor in deciding the neutron pulse shapes from a decoupled moderator. However, in the slowing-down energy region, the reflector also affects the pulse shapes, and the neutrons in this energy region will be increasingly important for precise neutron-scattering experiments in the future. Lead has many preferable characteristics as a reflector from a neutronic point of view, but it has a disadvantage in that it creates a long pulse tail, since it takes a very long time for a neutron in lead to slow down. To shorten this pulse tail, we propose a multi-layer decoupler system and compare its performance with that of a traditional decoupler system. The multi-layer decoupler was found to shorten the pulse tail effectively without causing a large decrease in the pulse peak intensity, whereas the traditional decoupler caused a greater decrease in this intensity. This result indicates that the multi-layer decoupler is useful for improving pulse characteristics of neutrons from a decoupled moderator at the pulsed neutron source using a lead reflector.

Study of copper adsorption on montmorillonites using thermal analysis methods

Copper was adsorbed onto Ca-exchanged montmorillonite (Cheto clay) under basic conditions. Differential thermogravimetric analysis (DTGA) combined with evolved gas mass spectroscopy (MS) was employed as the principal technology to study the distribution and structure of adsorbed copper species on the montmorillonite clay. The results showed that the original clay was easily rehydrated. After copper adsorption, a step-by-step replacement of hydrated calcium ions by copper–ammonia complex was observed through the gradual decrease of the first DTGA dehydration peak intensity with increasing copper loading. Compared with the original clay, copper loaded samples showed new DTGA peaks assigned to NH 3 and N 2O. The presence of the N 2O peak suggested that the loaded copper species were in agglomerated copper oxide form, which dispersed well over the edges and external surfaces of the clay layers.

Evolution and growth of ZnO thin films on GaN(0 0 0 1) epilayers via metalorganic vapor phase epitaxy

Zinc oxide thin films have been grown via metalorganic vapor phase epitaxy at 450°C and 250 Torr total pressure on O-terminated areas and micro-regions of native oxide formed on GaN(0 0 0 1) epilayers during exposure to the oxygen reactant. Analyses of the Ga3d core level spectra acquired from films grown for progressively longer times and comparisons of these data with both thermodynamic models of growth processes and associated atomic force micrographs revealed that the ZnO nucleated and grew via the Stranski–Krastanov mode. Considerations of (1) differences in surface energetics of the polar (0 0 0 1) surfaces of ZnO and GaN and that of the Ga-based oxide as well as (2) the relatively low stress generated by the moderate lattice mismatches in the a-axis lattice parameters of these compounds supported the observed growth mode. The shifts in the position of the Ga3d core level with increasing deposition time and decreasing peak intensity were caused by surface charging and increasing sampling volumes of the Ga-based oxide as well as the growing ZnO layer. The island/ocean morphology of the Ga-based oxide controlled the morphology of the initial ZnO layer, which, in turn controlled the locations and the morphologies of the subsequently nucleated ZnO islands. Scanning electron microscopy of thicker ZnO films revealed a highly textured microstructure.

Fully differential cross sections for the single ionization of helium by ionimpact

We present experimental and theoretical fully differential cross sections for the singleionization of He by heavy-ion impact for electrons emitted into the scattering plane. Datawere obtained for 2 MeV amu−1 C6+and 3.6 MeV amu−1 AuQ+(Q = 24, 53)projectiles, corresponding to perturbations (projectile charge to velocity ratio)ranging from 0.7 to 4.4, a regime which is inaccessible for electron-impactionization. We observe a decreasing recoil peak intensity (relative to the binarypeak) and at the same time an increasing peak in the forward direction withincreasing perturbations. Large discrepancies between the experimental data andtheoretical predictions are found, which can at least be partly attributed to theuse of hydrogenic wavefunctions.

Study of the origin of luminescence in high indium composition InGaN/GaN quantum wells

We report the emission properties of various InGaN/GaN quantum wells. The photoluminescence of InxGa1−xN/GaN (x&amp;gt;20%) quantum wells under varying external bias voltages has been investigated. A redshift of the photoluminescence peak position and decrease of photoluminescence peak intensity with an increase in voltage were observed regardless of the direction of external bias applied. For the sample in which the quantum dot-like region is abundant in quantum well layers, the peak position and intensity were not influenced much by the externally applied bias voltage. The results show that the origin of strong emission from InGaN/GaN quantum wells can be attributed to exciton localization in the quantum dot-like region and they are consistent with those of high-resolution transmission electron microscopy.

Comparative study of GaN/AlGaN MQWs grown homoepitaxially on [formula omitted] and (0 0 0 1) GaN

Structural and optical properties of GaN/AlGaN multiple quantum wells (MQWs) grown by plasma-assisted molecular-beam epitaxy on ( 1 1 ̄ 0 0 ) plane free-standing GaN substrates and (0 0 0 1) GaN quasi-substrates have been compared. Atomic force microscopy studies indicate that the films and MQW structures grown on both substrates replicate the surface morphology of the substrates. MQWs with AlGaN barriers grown in the presence of In flux have stronger photoluminescence (PL) intensity than those with AlGaN barriers without In. X-ray diffraction spectra of MQWs grown on the (0 0 0 1) GaN substrates show larger number of superlattices peaks than those grown on ( 1 1 ̄ 0 0 ) substrates suggesting that the former have smoother interfaces. The PL spectra of MQWs deposited on (0 0 0 1) GaN substrates, where the growth is in a polar direction, exhibit a red-shift as well as a decrease in peak intensity with increase in well widths. Similar MQW structures on the ( 1 1 ̄ 0 0 ) GaN, on which the growth is in a non-polar direction, do not exhibit this phenomenon, which we attribute to the absence of internal electric fields in these structures. PL intensity of MQWs with a well width of 75 Å is 20 times stronger for those grown on the ( 1 1 ̄ 0 0 ) plane than on the (0 0 0 1) plane GaN substrate.

Swift heavy ion induced amorphisation and chemical modification in polycarbonate

Polycarbonate (Makrofol kg) film stacks were irradiated by 15.14 MeV/amu Xe 136 and 11.4 MeV/amu U 238 in the electronic stopping power range (7.6–17.1 keV/nm) and the fluence range from 9×10 9 to 1×10 12 ions/cm 2. The chemical degradation of the function group was investigated by Fourier-transform infrared (FTIR) spectroscopy and the crystallinity was analyzed by X-ray diffraction (XRD) measurement. FTIR results reveal that the material suffers serious degradation after irradiation. The alkyne group was found after irradiation and their formation cross-sections were evaluated. XRD measurements show the decrease of the main XRD peak intensity, confirming that the material to be amorphised under irradiation. The ion induced amorphisation cross-section was extracted from the fitting of the experimental data for different electronic energy loss irradiations. The degradation cross-section, the formation cross-section and the amorphisation cross-section versus electronic energy loss were discussed.

Monitoring an insulator-metal transition in icosahedral AlPdRe by neutron irradiation

The intrinsic disorder effect on the electrical resistivity and magnetoresistance (MR) of icosahedral AlPdRe is studied by use of high-energy neutron irradiation. The icosahedral phase is preserved under irradiation with a decrease of x-ray peak intensity and volume of the coherent icosahedral phase. An insulator-metal transition, as observed in the MR, can be driven by the irradiation and is monitored by the resistance ratio R[=rho(4.2 K)/rho(295 K)]. The relation of MR vs R was found to be similar for samples of a widely different history.

Quench–jump sequence in phase separation in polymer blends

A two-step process of phase separation–mixing is analyzed for binary mixtures. The system is first quenched into the thermodynamical instability region (temperature T), where the mixture undergoes a process of spinodal decomposition, characterized for short times by the growth of the Cahn peak of a scattered intensity at fixed scattering wave vector. Next we heat up a system (make a temperature jump to temperature T1) above the spinodal line (temperature Ts) and compute the decay of this peak. The peak intensity decreases and the peak position moves toward short wave vectors. The integrated peak intensity decreases exponentially at short times with a characteristic decay time that depends on T, T1, and Ts. The increase of the Euler characteristic from large negative values toward zero suggests that the shift of the peak toward short wave vectors is associated with the disappearance of small connections in a bicontinuous structure formed in the early stages of spinodal decomposition. Slow decay of the surface area indicates that the domains keep their shape for a long time, despite the fast decay of the saturation of the concentration field inside them.

Raman scattering studies on B + implanted Cd 0.96Zn 0.04Te thin films

Cd 0.96Zn 0.04Te thin films were prepared by vacuum evaporation onto glass substrates kept at room temperature. X-ray diffraction (XRD) studies revealed that the as-deposited films have zinc blende structure with preferential (1 1 1) orientation. Raman peak of the as-deposited film appeared between 139.88 and 163.40 cm −1 for the transverse optic and the longitudinal optic phonons, respectively. These films were implanted with 100 keV boron ions to various doses from 10 12 to 10 14 ions/cm 2. The XRD patterns of the irradiated films exhibited a decrease in peak intensity and increase in the FWHM of the (1 1 1) peak. The Raman peak position did not change appreciably whereas the FWHM increases with the ion dose and the results are attributed to the effect of implantation-induced lattice damage.

Thermoluminescence characteristics of K2Ca2(SO4)3 doped with rare earths Eu and Dy

The effects of Dy co-doping on the thermoluminescence (TL) characteristics of K2Ca2(SO4)3 : Eu phosphor are studied. Though the sensitivity of the K2Ca2(SO4)3 : Eu phosphor is decreased by five times to get the sensitivity slightly less than that of CaSO4 : Dy, the broadness of the glow peak is increased. The decrease in peak intensity of the phosphor on co-doping it with Dy gives an insight into the emission mechanism of the phosphor which involves energy transfer from Eu2+ to Dy3+. The phosphor has a simple TL glow curve structure with a single prominent peak at around 430 K. The photoluminescence emission spectra has three peaks (440, 475 and 570 nm) which could be attributed to the Eu2+ and Dy3+ emissions. Fading and reusability characteristics of the new phosphor are also studied and it is found that the phosphor is quite suitable for use in dosimetry of ionizing radiations.

X-RAY ABSORPTION STUDY OF Mg1-xAlxB2 AT B K-EDGE

We have measured B K-edge X-ray absorption spectra of Mg 1-x Al x B 2 (x=0.0 ~ 0.4) using bulk-sensitive total fluorescence yield (TFY) at room temperature and 30 K. In contrast to previous reports no peaks near 192 eV and 194 eV could be observed after repeated scraping, indicating their origin being due to surface contamination. These clean spectra show a peak right above the absorption threshold, anticipated from transition to the unoccupied B 2p states. Except in the intermediate Al doping range of x ~ 0.1 to 0.28 the threshold peak intensity decreases, consistent with pσ-hole filling. The increase of peak intensity in the intermediate range is correlated with structural phase transition.