Effect Of Xe Research Articles

Effect of an Xe additive on the degree of translational nonequilibrium of an He-O2-H2 mixture in a shock wave front

Computer simulations of the experimentally observed detonation threshold shift upon adding small amounts of Xe with the use of the direct simulation Monte Carlo method once again confirmed that this effect is associated with a substantial increase in the degree of translational nonequilibrium in the shock wave front. It was demonstrated that, when the presence of hydrogen in the mixture is taken into account, the calculated degree of translational nonequilibrium becomes higher. In addition, the effect of Xe was observed to grow stronger as the Xe concentration was decreased from 0.5 to 0.25%.

Cell effects of xenon n vitro under hypothermal conditions

The effects of Xe on cell viability and redox balance in the culture of Wistar rat thymocytes were studied in vitro during 24-h storage under hypothermic conditions. The results indicate that after bubbling of cell suspensions (5 x 10(6) cell/ml, 4 ml medium), the weight of Xe in flasks was 15-43 mg, whereas in cell-free medium no weight increment due to gas accumulation in the system was detected. The content of Xe in cell suspension slightly decreased over 24-h culturing at ambient temperature (by 10% of initial level). Xenon significantly improved cell survival during thermal exposure of all modes. The maximum cytoprotective effect of Xe was observed under rigorous thermal conditions associated with significant cell death without chemical protectors (3 degrees C, -35 degrees C). The effect of Xe was less pronounced at mild temperatures (23-37 degrees C) or in the presence of chemical protectors (-35 degrees C with dimethylsulfoxide). The mechanisms of the effect of the inert gas are determined by its antioxidant or prooxidant action. The capacity of Xe to improve cell survival under hypothermic conditions can be used for the development of new methods for transportation and storage of cell material.

Compact High-Efficiency CO2 Slab Waveguide Lasers with Segmented RF Excitation

RF-excited slab waveguide CO2 lasers based on either internal or external electrodes were studied. A compact multisegment RF excitation configuration was used for pumping the gain medium. The use of a separate driving circuit to excite each discharge segment led to a very uniform discharge along the slab waveguide. A resultant maximum output power of 82 W with efficiency up to 20.5% was recorded from a 3 mm×10 mm×450 mm slab waveguide. The gain coefficient, saturation power and the effect of Xe in the gas mixture were also studied. These lasers can be easily scaled to obtain low-cost high-power operation.

Ion-beam-induced morphology on the surface of thin polymer films at low current density and high ion fluence

The effect of Xe+ bombardment on the surface morphology of four different polymers, polystyrene (PS), poly(phenylene oxide), polyisobutylene, and polydimethylsiloxane, was investigated in ion energy and fluence ranges of interest for secondary ion mass spectrometry depth-profiling analysis. Atomic force microscopy (AFM) was applied to analyze the surface topography of pristine and irradiated polymers. AFM analyses of nonirradiated polymer films showed a feature-free surface with different smoothness. We studied the influence of different Xe+ beam parameters, including the incidence angle, ion energy (660–4000 eV), current density (0.5 × 102 to 8.7 × 102 nA/cm2), and ion fluence (4 × 1014 to 2 × 1017 ion/cm2). Xe+ bombardment of PS with 3–4 keV at a high current density did not induce any change in the surface morphology. Similarly, for ion irradiation with lower energy, no surface morphology change was found with a current density higher than 2.6 × 102 nA/cm2 and an ion fluence up to 4 × 1016 ion/cm2. However, Xe+ irradiation with a lower current density and a higher ion fluence led to topography development for all of the polymers. The roughness of the polymer surface increased, and well-defined patterns appeared. The surface roughness increased with ion irradiation fluence and with the decrease of the current density. A pattern orientation along the beam direction was visible for inclined incidence between 15° and 45° with respect to the surface normal. Orientation was not seen at normal incidence. The surface topography development could be explained on the basis of the balance between surface damage and sputtering induced by the primary ion beam and redeposition–adsorption from the gas phase. Time-of-flight secondary ion mass spectrometry analyses of irradiated PS showed strong surface modifications of the molecular structure and the presence of new material. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 39: 314–325, 2001

Laser-Induced-Fluorescence Study of the SiH2 Density in RF SiH4 Plasmas with Xe, Ar, He, and H2 Dilution Gases

The silylene ( SiH2) density in a parallel-plate RF (13.56 MHz) discharge using monosilane ( SiH4) gas has been measured by using laser-induced fluorescence spectroscopy. The effect of Xe, Ar, He and H2 dilution gases on the SiH2 density was investigated at a total gas pressure of 40 mTorr. In all dilution cases, the SiH2 density was relatively insensitive to the SiH4 fraction (x) in the mixtures for x\\gtrsim0.5; however, except in the case of H2 dilution, marked increase of the SiH2 density was observed with decreasing x for x\\lesssim0.5. The production and loss mechanisms for SiH2 are discussed on the basis of the observed SiH2 density and supplementary optical emission measurements. The results indicate that, in highly diluted ( x\\lesssim0.1)SiH4/Xe and SiH4/Ar mixtures, the production of SiH2 via energy transfer from excited Xe and Ar atoms to SiH4 is dominant over direct electron impact dissociation of SiH4.

MAC of xenon and halothane in rhesus monkeys.

Local cerebral blood flow (LCBF) maps produced by 33% xenon-enhanced computed tomographic scanning (Xe/CT LCBF) are useful in the clinical diagnosis and management of patients with cerebrovascular disorders. However, observations in humans that 25-35% xenon (Xe) inhalation increases cerebral blood flow (CBF) have raised concerns that Xe/CT LCBF measurements may be inaccurate and that Xe inhalation may be hazardous in patients with decreased intracranial compliance. In contrast, 33% Xe does not increase CBF in rhesus monkeys. To determine whether this interspecies difference in the effect of Xe on CBF correlates with an interspecies difference in the anesthetic potency of Xe, we measured the minimum alveolar concentration (MAC) of Xe preventing movement to a tail-clamp stimulus in rhesus monkeys. Using a standard protocol for the determination of MAC in animals, we first measured the MAC of halothane (n = 5), and then used a combination of halothane and Xe to measure the MAC of Xe (n = 7). The halothane MAC was 0.99 +/- 0.12% (M +/- SD), and the Xe MAC was 98 +/- 15%. These results suggest that the MAC of Xe in rhesus monkeys is higher than the reported human Xe MAC value of 71%. Thus the absence of an effect of 33% Xe on CBF in the rhesus monkey may be related to its lower anesthetic potency.

Effect of Stable Xenon Inhalation on Internal Carotid Artery Blood Flow in Unanesthetized Monkeys

Stable xenon (Xe) gas, at inspired concentrations above 30%, reportedly increased cerebral blood flow (CBF) in animals and humans. An unpredictable Xe-induced elevation of CBF could result in erroneous CBF values being measured by Xe-enhanced computed tomography (Xe-CT). In order to detect a potentially rapid and transient effect of Xe on CBF, estimations of supratentorial CBF were obtained by Doppler flow probes chronically and bilaterally implanted on the internal carotid arteries of five adult monkeys. The unanesthetized monkeys with a clear plastic helmet were equilibrated for 15 min on a control gas (33% N2/67% O2) randomly exposed for 5 min to gas mixtures of either 33% Xe/67% O2 or 10% CO2/23% N2/67% O2. The mean control bilateral internal carotid artery blood flow (ICABF) was 23 +/- 10 ml/min (mean +/- SD), mean arterial pressure (MAP) was 101 +/- 13 mm Hg, and PaCO2 was 34 +/- 6 mm Hg. Inhalation of 33% Xe in O2 did not change the ICABF, MAP, or PaCO2. Inhalation of 10% CO2 in O2 increased the ICABF to 39 +/- 15 ml/min (p <0.001), MAP to 112 +/- 16 mm Hg (p <0.05), and PaCO2 to 54 +/- 5 mm Hg (p <0.001). The lack of change in ICABF and PaCO2 with 32% Xe inhalation suggests that a clinically relevant change in CBF is unlikely.

Effect of Xe + ion bombardment during titanium deposition in nitrogen atmosphere

Bombardment of evaporated titanium films with energetic Xe + ions deposition in nitrogen atmosphere has a marked effect on film properties. In comparison with evaporated titanium films, the Xe + ion-bombarded films contained more nitrogen and thus TiN films, instead of titanium films, have been formed. There were very small amounts of oxygen and xenon retained in the film. We also observed compressive stress in the Xe +-ion-bombarded films, whereas the evaporated films were nearly stressless. The critical load, determined by the scratch test, to damage the Xe +-ion-bombarded TiN films on steel and silicon substrates was twice that for evaporated films, which indicated that the adhesion of the film to the substrates was greatly promoted by Xe + ion bombardment. The hardness of the TiN films formed by Xe + ion bombardment reached 2200 kgf mm −2, which was not only much higher than that of the evaporated films, but also higher than those of films formed by bombardment with N + ions in the same condition. The results are explained from the viewpoint of the difference in energy deposited in the films by incident ions.

The effect of ion beam treatment and subsequent annealing on Au/GaAs contacts

The effect of Xe++ and Ar+ ion beam treatment and subsequent annealing on the Au (55 nm)/n-GaAs system was studied using cross-sectional transmission electron microscopy. The maximum depth of observed defects caused by Xe++ ions (700 keV, 1×1014 ions/cm2) was about 400 nm from the interface in excellent agreement with the results of capacitance-voltage measurements. The formation of about 50-nm-thick polycrystalline region of GaAs was observed. The ion beam treatment resulted in the formation of defects (stacking faults, twins) down to a depth of 200 nm measured from the interface. Between 200 and 400 nm depth dislocation loops were formed. Amorphization has not been observed. The sharp Au/GaAs interface has been only slightly destroyed in the as-implanted sample. In contrast to pits in unirradiated samples, large flat grains of Au(Ga) solid solution grown into the highly damaged region of GaAs were found in the samples annealed at 450 °C after the ion beam treatment. The formation of a regrown GaAs covering layer was observed on the top of the reacted metallization. High dose implantation of Xe++ ions resulted in the formation of an amorphous GaAs layer with a thickness of about 750 nm. A phase transition caused by the ion beam was observed in this sample. During annealing at 400 °C the whole amorphous GaAs region recrystallized to single-crystal GaAs. Ion beam treatment with Ar+ ions (400 keV, 2×1014 ions/cm2) caused the formation of dislocation loops. In this case the growth of pits is similar to the case of simple annealing without bombardment.

119Sn conversion electron Mössbauer study of Fe/Sn bilayers irradiated by Xe ions

The effect of Xe+ irradiation and that of subsequent annealings on Fe/Sn bilayer have been studied by119Sn conversion electron Mossbauer spectroscopy. It seems that the effectiveness of ion-beam mixing is comparable to the thermal treatment of the bilayer.

Effect of rare gas implantation on the magnetic properties of amorphous CoTi thin films

We report here on the effect of Xe+ ion irradiation on the magnetic properties of amorphous CoTi thin films. With increasing fluence range the in-plane K u or perpendicuIar anisotropy K p decreases continuously and disappears for 5×1015Xe+/cm2, while the magnetization remains unchanged. Resonance measurements shows that even for low fluences the homogeneity along the film thickness is improved. In comparison with thermal annealing the much higher efficiency of ion irradiation in order to suppress K u is displayed. Discussions on the physical origin of K u are also given.

The reactivity effect of Xe

The reactivity effect of Xe

Temperature dependent preferential sputtering in CoSi2 and NbSi2

Sputtering of CoSi2 and NbSi2 has been carried out by Xe ion bombardment at room temperature, as well as at elevated temperatures putting these systems in their radiation-enhanced diffusion regimes. The range of the Xe ions (at 200–260 keV) was appreciably less than the thickness of the silicides. The samples were analyzed by 2 MeV He+ backscattering spectrometry, x-ray diffraction and optical microscopy. The ratio of the sputtering yield of Si to that of the metal (i.e., Co or Nb) always exceeds the stoichiometric ratio 2∶1, leading to Si depleted surface layers. The amount of the sputtered species increases almost linearly with dose until intermixing of the silicide with the underlying Si becomes appreciable. This happens at lower doses in the radiation-enhanced diffusion regime than at room temperature. Irradiation of CoSi2 samples at high temperature leads to a broadening of the implanted Xe profile compared to the room temperature profile. No such phenomenon has been found in NbSi2. The effect of Xe broadening on the sputtering yields is discussed.