Oxygen Redistribution Research Articles

NO and Hypoxia

The transcription factor hypoxia-inducible factor (HIF) 1α plays a pivotal role in the cellular response to low oxygen levels; its activation under hypoxic conditions leads to increased transcription of genes implicated in O 2 delivery and adaptive responses to O 2 deprivation. Hagen et al . now find that HIF-1α is destabilized by nitric oxide (NO) and other inhibitors of mitochondrial respiration by an increase in HIF-1α degradation triggered by increased activity of the O 2 -dependent enzyme prolyl hydroxylase. This NO-mediated inhibition of mitochondrial O 2 consumption may increase O 2 availability for nonrespiratory functions (such as prolyl hydroxylases) and may cause the cell to fail to register hypoxia. Thus, redistribution of intracellular O 2 may be another important consequence of NO action. T. Hagen, C. T. Taylor, F. Lam, S. Moncada, Redistribution of intracellular oxygen in hypoxia by nitric oxide: Effect on HIF1α. Science 302 , 1975-1978 (2003). [Abstract] [Full Text]

Redistribution of intracellular oxygen in hypoxia by nitric oxide: effect on HIF1alpha.

Cells exposed to low oxygen concentrations respond by initiating defense mechanisms, including the stabilization of hypoxia-inducible factor (HIF) 1alpha, a transcription factor that upregulates genes such as those involved in glycolysis and angiogenesis. Nitric oxide and other inhibitors of mitochondrial respiration prevent the stabilization of HIF1alpha during hypoxia. In studies of cultured cells, we show that this effect is a result of an increase in prolyl hydroxylase-dependent degradation of HIF1alpha. With the use of Renilla luciferase to detect intracellular oxygen concentrations, we also demonstrate that, upon inhibition of mitochondrial respiration in hypoxia, oxygen is redistributed toward nonrespiratory oxygen-dependent targets such as prolyl hydroxylases so that they do not register hypoxia. Thus, the signaling consequences of hypoxia may be profoundly modified by nitric oxide.

Redistribution of ytterbium and oxygen in annealing of silicon layers amorphized by implantation

The redistribution of ytterbium and oxygen was studied in silicon layers that were implanted with 1-MeV Yb+ ions at a dose of 1×1014 cm−2, which exceeds the amorphization threshold, and 135-keV O+ ions at a dose of 1×1015 cm−2 and that were subsequently annealed at 620 and 900°C. The redistribution of Yb is due to segregation at the interface between the amorphous and single-crystal layers in solid-phase recrystallization of the buried amorphized layer. The redistribution of oxygen and its accumulation in regions with the highest concentration of Yb is associated with oxygen diffusion and the formation of YbOn complexes with n varying from 1 to 6. The parameters characterizing the dependence of the Yb segregation coefficient on the thickness of the recrystallized layer and the formation of YbOn complexes were determined.

High-Temperature Structural Disorder in R3NbO7

R3NbO7 (R = La, Nd, Gd, Y) niobates have been studied by Raman spectroscopy at 298-973 K. The temperature and composition effects on the structure of these compounds are considered. The changes observed in the Raman spectra at elevated temperatures are caused by a reversible structural disordering due to oxygen redistribution over anion sites.

Microstructural evolution of low-dose separation by implanted oxygen materials implanted at 65 and 100 keV

Thin separation by implanted oxygen substrates are attractive candidates for low-power, low-voltage electronic devices and can be obtained by low-dose, low-energy oxygen–ion implantation. We report in this study a variation of the process parameters that have never been investigated before, particularly for implantation with a high current density implanter. Characterization of the sample sets by transmission electron microscopy, secondary ion mass spectroscopy (SIMS), and Rutherford backscattering spectrometry (RBS) shows an optimum dose of 3.0 to 3.5 × 1017 O+/cm2 at 100 keV for forming a continuous buried oxide (BOX) layer compared to 2.5 × 1017 O+/cm2 at 65 keV. At this optimum condition for 100 keV, the thickness of Si top layers and BOX layers is in the range of 175–185 nm and 70–80 nm, respectively. Analysis of the breakdown voltage of small area capacitors shows a breakdown field in the range of 6.0–7.0 MV/cm, which is adequate for low-power, low-voltage devices. SIMS analysis shows that the maximum oxygen concentration of as-implanted samples is located at depths of 160 and 240 nm for the implantation energy of 65 and 100 keV, respectively. A significant redistribution of oxygen occurs at temperatures above 1300 °C during the ramping process. RBS analysis showed that a high-quality crystalline Si layer was produced after annealing at 1350 °C for 4 h. The defect density determined by the chemical etching method was found to be very low (<300 defects per cm2) for all samples with a dose range of 3.0 × 1017 O+/cm2 to 6.0 × 1017 O+/cm2 implanted at 100 keV. However, a 65 keV sample with a dose of 4.5 × 1017 O+/cm2 contains about 109 defects per cm2. The larger defect density in the 65-keV sample may be due to the shift of oxygen depth distribution toward the surface, resulting in easier defect extension during the annealing process. The oxide precipitates in the Si overlayer play a key role in defect reduction by blocking the extension of dislocations to the surface.

Electrical Transport and Oxygen Disorder in YBCO

We investigated the origin of a non-linear temperature dependence of resistivity ρab(T) in the a-b planes of YBCO, frequently observed in optimally doped twinned YBCO single crystals and thin films and in untwinned YBCO crystals along the chain direction. We performed the measurements of ρab(T) in c-axis oriented YBCO thin films that were subjected to low temperature annealing at 120–140°C (400–420 K) in argon. Our results have shown that redistribution of oxygen at a fixed oxygen content in the chain layers of YBCO with a non-linear ρab(T), leads to an increase of Tc, an increase of resistivity and a reduction of the non-linear component in ρab(T).

Neuroprotection in hypothermia linked to redistribution of oxygen in brain.

Hypothermia improves the outcome of acute ischemic stroke, traumatic injury, and inflammation of brain tissue. We tested the hypothesis that hypothermia reduces the energy metabolism of brain tissue to a level that is commensurate with the prevailing blood flow and hence allows adequate distribution of oxygen to the entire tissue. To determine the effect of 32 degrees C hypothermia on brain tissue, we measured the sequential changes of physiological variables by means of PET in pigs. Cerebral blood flow and oxygen consumption (cerebral metabolic rate of oxygen) declined to 50% of the baseline in 3 and 5 h, respectively, thus elevating the oxygen extraction fraction to 140% of the baseline at 3 h. The results are consistent with the claim that cooling of the brain to 32 degrees C couples both energy metabolism and blood flow to a lower rate of work of the entire tissue.

Effect of Oxygen Redistribution on the Normal and Superconducting Properties of Yttrium High‐Temperature Superconductors

An anomaly is found in the vicinity of Tmax∼ 560$ K on electric resistance versus temperature curves for yttrium high‐temperature superconductors of the 123 phase. X‐ray phase analysis suggests a structural phase transition in the vicinity of Tmax due to oxygen redistribution in the mobile sublattice of this compound. Investigation of samples with Y partially replaced by Ca has shown that the structural phase transition does not depend on carrier concentration in the conduction band.

Cationic Ruthenium-Sulfine Complexes: Synthesis and Dynamic Behaviour

Abstract Cationic ruthenium sulfine complexes [CpRu(PR´3)2(O=S=CHR)]PF6 have been obtained by a variety of methods. Oxidation of the thioaldehyde complexes [CpRu(PR´3)2(S=CHR)]PF6 with either 2-tosyl-3-phenyl-oxaziridine (PR´3 = PMe3 ) or magnesium-monoperoxyphthalate (PR´3 = 1/2 dppm) gave complexes of arylsulfines (R = Ph, 3-C6H4F, 4-C6H4Cl, 4- C6H4OMe) selectively in their thermodynamically less stable E form. Siloxane elimination from the sulfinato complexes [CpRu(PMe3)2(SO2CHRSiMe3)] yielded complexes of aliphatic sulfines, [CpRu(PMe3)2(O=S=CHR)]PF6 (R =H,Me). Treatment of [CpRu(dppm)(SO2CH2R)] with acetyl chloride led to an oxygen redistribution giving complexes of thioaldehydes [CpRu(dppm)(η2-S=CH2)]PF6 and [CpRu(dppm)(η1-S=CHR)]PF6 (R = Ph, 4-C6H4Cl). The structure of the latter was determined by X-ray crystallography. The loss of oxygen can be suppressed by performing the acylation-elimination sequence in the presence of poly-(4-vinylpyridine). This provided a selective access to complexes of Z-sulfines, [CpRu(PMe3)2(O=S=CHR)]PF6 (R = Ph, 4-C6H4Cl) and [CpRu(dppm)(O=S=CHR)]PF6 (R = Ph, 4-C6H4Cl, COOEt, Cl). Complexes of the parent sulfine O=S=CH2 were also obtained by SO transfer to the methylene complex [CpRu(PMe3)2(CH2)]PF6 and methylene transfer to the sulfur monoxide complex [Cp*Ru(PMe3)2 (SO)]PF6. Most of the new sulfine complexes exhibit dynamic behaviour in solution, i. e. ligand rotation, ligand inversion, and η2 /η1 hapticity change. O-Alkylation provided the dicationic complex [CpRu(PMe3)2 (EtO-S=CHMe)](PF6)2, and S-oxidation gave the sulfene complexes [(C5R5)Ru(PMe3)2 (O2S=CH2)]PF6 (R = H, Me).

Oxygen nonstoichiometry and superconductivity of the Nd 2− xCe xCuO 4− δ single crystal

Investigations of the oxygen desorption by Nd 2− x Ce x CuO 4− δ single crystals (0⩽ x⩽0.17) was carried out, and we present here a group of superconductors with an electron type of conductivity made by crystallization from a melt. It was established that, under heating of the single crystals with a constant flow rate of Ar and pO 2=100 Pa, the oxygen desorption proceeded through two maxima in the temperature range of 973–1173 K, the nature of which is related to desorption of oxygen from different crystallographic fragments. It is suggested that the problem of creation of the necessary concentration of oxygen and its ordering in the net of Cu–O 2 layers is related to the redistribution of oxygen from the 02 to the 01 structural positions in the Nd 2− x Ce x CuO 4− δ crystal. Under a schedule of three stages of thermal treatments of the single crystal, we were able to achieve superconductivity of the researched samples at temperatures of <19 K.

KINETICS OF CARBONIZATION OF TITANIUM ALLOYS IN A CARBON-OXYGEN-CONTAINING MEDIUM

We investigate the kinetics of saturation of surface layers of VT1-0 and OT4 titanium alloys in the process of carbonization from graphite in an atmosphere of argon at temperatures of 900 and 1000°C for 1 ‐ 15 h. We revealed the formation of a deep hardened zone for long-holding times. The redistribution of oxygen in the case of dissociation of a surface oxide film promotes the formation of complex TiC x O y -type compounds based on titanium carbide, which additionally harden surface layers. Thermochemical treatment, in particular carbonization, is an efficient method for increasing the durability of products made of titanium alloys [1 ‐ 3]. The rate of formation and growth of surface carbide layers, their phase composition, and the structure are determined by the activity of the saturating medium, the temperature, and the time of treatment [4]. Using the results of investigation related to carbonization, one can estimate the intensity of interaction of a metal with the environment and trace the evolution of phase transformations in its surface layers. Saturation of titanium alloys from a powder substance (graphite) in argon [4] is one of the efficient methods for their carbonization. Using this fact, we investigate the kinetics of carbonization of titanium alloys from this medium. Methodical Aspects We investigate specimens 15 × 10 × 1 mm in size made of commercial titanium VT1-0 (commercially pure titanium) and OT4 (Ti ‐ 3.5, Al ‐ 1.5 Mn) alloys. The specimens were polished ( R a = 0.4 µm ) and subjected to the thermochemical treatment at temperatures of 900 and 1000°C for an isothermal holding of 1 ‐ 15 h. The specimens were saturated from graphite in a static atmosphere of argon (100 kPa) under a partial oxygen pressure < 0.2 Pa. We determine the phase composition of surface layers performing X-ray phase analysis with a DRON-3.0 diffractograph in a monochromatic CuK α -irradiation focused according to the Bragg ‐ Bretano scheme. The voltage across the anode of the X-ray tube is equal to 30 kV and the current through it equals 20 µA. The results are processed with a software of the diffractograph. To identify the obtained diffraction spectrum of the specimen presented in the form of an array of the values of d i and T i , we compare them with the data of the JCPDS‐ASTM card file [5]. We estimate hardening on the basis of microhardness (a PMT-3 device). We identify a hardened layer with a zone whose hardness is greater than the hardness of the core by 0.2 GPa [6]. Results and Discussion

Evolution of microstructure during annealing of low-dose SIMOX wafers implanted at 65 keV

The microstructural changes that occur during annealing of ultra-thin oxygen-implanted silicon-on-insulator have been studied using transmission electron microscopy (TEM), Rutherford backscattering spectrometry (RBS), and Auger electron spectroscopy (AES). Silicon substrates were implanted at 65 keV with a dose of 4.5×1017 O+ cm−2, followed by annealing at various temperatures. TEM results show that the defects observed in the as-implanted material (stacking faults and {1 1 3} defects) were reduced after annealing at 900 °C for 2 h and were eliminated after annealing at 1100 °C for 2 h. A continuous buried oxide (BOX) layer was formed after annealing at 1300 °C for 6 h. Numerous silicon islands were present in the BOX layer. The silicon islands can be traced to a precursor structure that developed at the implantation step. RBS results indicate that the crystallinity of the top Si layer is significantly restored after annealing at 1100 °C for 2 h and is completely restored after annealing at 1300 °C for 6 h. It was also found through AES analysis that the redistribution of oxygen during annealing is initiated at 1100 °C.

Boron and Oxygen Redistribution during Silicidation Process of Titanium-Silicon System

Redistribution behavior of B and O during silicidation process of titanium-silicon system at 923 K has been examined by secondary ion mass spectrometry and transmission electron microscopy. Amorphous like TiSix forms between unreacted Ti and TiSi2. B accumulates in TiSix and O accumulates in unreacted Ti. The solubility of B and O in Ti and TiSix causes the difference of redistribution behavior of B and O during Ti silicidation.

Normal-state Hall effect inHgBa2CaCu2O6+δandTlBa2CaCu2O7−δ

The normal-state Hall effect is studied in thin-film samples of the isomorphic pair of superconductors ${\mathrm{HgBa}}_{2}{\mathrm{CaCu}}_{2}{\mathrm{O}}_{6+\ensuremath{\delta}}$ (Hg-1212) and ${\mathrm{TlBa}}_{2}{\mathrm{CaCu}}_{2}{\mathrm{O}}_{7\ensuremath{-}\ensuremath{\delta}}$ (Tl-1212). A comparison of the slopes of inverse Hall mobility $H\mathrm{cot}{\ensuremath{\theta}}_{H}{(T}^{2}),$ together with a comparison of characteristic temperature ${T}^{*}{/T}_{c}$ below which there is a systematic deviation from ${T}^{2},$ suggests that Hg-1212 has twice the charge-carrier density of Tl-1212 for samples with close to optimal ${T}_{c}.$ This is attributed to the significant role played by the redistribution of oxygen as a result of exchanging Hg and Tl cations.

Oxidation and phase transitions of epitaxial tin oxide thin films on (1̄012) sapphire

We studied the structural behavior and electrical transport properties of epitaxial α-SnO thin films grown on the (1̄012) α-Al2O3 (sapphire) substrate. Hall effect measurements revealed that the epitaxial as-deposited SnO film is a p-type semiconductor. In situ x-ray diffraction studies show that the α-SnO phase is metastable and will transform into SnO2 with the rutile type structure when annealed at high temperatures in air. The onset of this phase transformation was observed to begin approximately at 300 °C during heating. Shortly thereafter, rutile SnO2 was observed to coexist with α-SnO and intermediate products such as Sn and Sn3O4. After being annealed at temperatures above 600 °C, the film then fully transformed into the rutile SnO2 phase. Our results show that the α-SnO to SnO2 structural transformation proceeds initially by the localized disproportionate redistribution of internal oxygen at low temperature, followed by the transformation of the remaining SnO phase and intermediate phases into SnO2 via the inward diffusion of external oxygen at higher temperatures. Most of the SnO2 crystallites nucleate epitaxially on α-SnO with the orientation relationship of (101)SnO2//(001)SnO and their growth processes are controlled by the (101)SnO2//(001)SnO interfaces, leading to a (101) texture and a laminar grain shape for SnO2. The relationship between the electrical transport properties and the structural evolution of the film has also been investigated.

Carbon Enhancement of SiO2 Nucleation in Buried Oxide Synthesis Computer Simulations and Secondary Ion Mass Spectroscopy Depth Profiling

Physical mechanisms of oxygen transport and precipitation in silicon during the synthesis of buried oxide layers are reviewed. Different effects caused by the interaction of weakly bonded oxygen with mobile point defects and static defect complexes are analyzed. As a result, the possibility of controlling the evolution of the spatial distribution of implanted oxygen by means of gettering and defect engineering are studied and validated by computer simulations based on a quasi-chemical description of the kinetics. Special attention is given to carbon induced gettering mechanisms involved in the buried oxide synthesis known as low-dose approach combined with defect engineering. Secondary ion mass spectroscopy profiling data together with the results of computer simulations show a rather complicated behavior of the carbon and point toward an important role of the carbon-vacancy and carbon-oxygen complexes in the oxygen accumulation. Some effects in the early stage of the oxygen redistribution are revealed and discussed. The influence of an inhomogeneous distribution of bonded oxygen in silicon on the yield of different single atomic and cluster secondary ions (SIs) during oxygen sputtering is studied. The role of different oxygen containing phases in SI formation is discussed. It is shown that carbon acts on precipitates not only in a local but also in a global manner. © 2001 The Electrochemical Society. All rights reserved.

デュアルスピンバルブタイプ強磁性二重トンネル接合の熱処理による特性変化

Exchange-biased dual spin-valve type magnetic double tunnel junctions (DSV-MTJs) of Ir-Mn/Co-Fe/AlOx/Co-Fe/AlOx/Co-Fe/Ir-Mn were annealed at 175-400°C. After annealing at 325°C, the magnetoresistance (MR) ratio and bias voltage Vh, at which the MR ratio is reduced by 50%, in the DSV-MTJs were greatly increased to 42% and 930 mV, respectively. After annealing above 325°C, the MR ratio and Vh decreased. This degradation of DSV-MTJs annealed above 325°C was investigated using X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM). The XPS spectra and TEM images showed that an AlOx/MnOx composite tunnel barrier was formed due to the diffusion of Mn through the Co-Fe layer and oxygen redistribution above 300°C. Taking into account the spin-independent two-step tunneling via defect states in the barrier, we considered that this AlOx/MnOx composite barrier leads to decreasing the MR ratio and Vh and increasing the tunnel resistance.

Small signal response of the BiCuVOx/noble metal/oxygen electrode system

The electrode properties of the Bi 2Cu 0.1V 0.9O 5.35/noble metal/oxygen system have been studied by impedance spectroscopy and polarisation measurements in a three-electrode cell. Little difference was observed in the performance of Au, Pt and Ag electrode metals. Gold showed the lowest electrode resistance, silver the highest, but these differences are most likely due to differences in the microscopic electrode geometry. The impedance spectra indicate three distinct electrode processes. A fourth process, identified by a negative loop, must be ascribed to ‘cross talk’ between reference and working electrode. The main feature in the impedance is a Warburg like, P O 2 and polarisation dependent diffusion element, in parallel with a charge transfer type resistance. The observed electrode behaviour is similar to what has been found previously for the rare earth stabilized bismuth oxide electrolytes. This indicates that the electrolyte surface exposed to the ambient is the active area for the oxygen and charge transfer. At moderate temperatures a competition exists between oxygen exchange and oxygen redistribution (reduction/oxidation in the electrode-interface regions of the bulk), which is due to a small electronic conductivity.

Pressure induced transformation of the superconducting state of underdoped La 1.985Sr 0.015CuO 4+δ ( δ

We have studied the superconducting (sc.) transition in La 1.985Sr 0.015CuO 4+δ by using different high-pressure techniques. At zero pressure the transition is observed at 15 K for δ < 0.025 and at 30 K for δ > 0.025. The application of hydrostatic pressure at room temperature results in a positive shift of T c and a crossover from the 15 K to the 30 K state. At about 0.7 GPa the 30 K state quickly grows at the expense of the original 15 K state. If pressure is changed at low temperature (77 K) no such change in the sc. state can be detected. The data are explained in terms of pressure-induced redistribution of oxygen and charge carriers.

Effect of oxygen redistribution in Bi-based high- Tc superconductors on their normal and superconducting properties

Bi-based high- T c superconductors of three types, Bi 2Sr 2CuO 6.13 (2201), Bi 2Sr 2CaCu 2O 8.24 (2212), and Bi 1.9Pb 0.3Sr 1.8Ca 2Cu 3O 10+ x (2223), has been investigated. The temperature dependence of resistivity ρ( T) has been measured during slow heating of samples (∼2 K/h) up to 600 K in air. The maximum of ρ( T) at T max>400 K is observed for all samples. T c increases for overdoped samples (2201 and 2212) and does not change in the optimal doped sample (2223) after cooling from T max, and hole concentration decrease for all samples. ρ and T c return to initial states after the heating of samples up to 600 K. Powder X-ray diffraction is carried out during slow heating of Bi based samples.