The nature of particles yielded during electron-stimulated desorption of samarium from oxidized tungsten surface

It is established for the first time that the yield resonances related to excitation of the core electron levels of samarium (Sm) and tungsten (W) during the electron-stimulated desorption of samarium from the surface of oxidized tungsten represent neutral particles differing in the chemical nature. Most probably, the excitation of samarium levels leads to desorption of Sm atoms, while the excitation of tungsten levels causes desorption of SmO molecules.     

Electron states of europium atoms on the oxidized tungsten surface

The charge state of europium (Eu) atoms adsorbed on the oxidized tungsten surface is evaluated. An energy band diagram of the adsorption system is proposed for large and small Eu coverages. The adsorption energy of Eu atoms is estimated.     

On the nature of concentration thresholds for the electron-stimulated desorption of europium atoms from the oxidized tungsten surface

The nature of the electron-stimulated desorption (ESD) of europium atoms from an oxidized tungsten surface for the electron energies of E _e =50 and 80 eV and some features of the yield of Eu atoms as a function of their surface concentration on this surface are discussed. It is shown that the ESD of Eu is related to the electron transitions from the core 5p of 5s shells of a surface tungsten atom to the outer unoccupied 2p level of oxygen.     

Thermodesorption of impurities from detonation nanodiamond

The molecular composition of volatile compounds belonging to the impurity subsystem of detonation nanodiamond particles has been analyzed. It is established that the main volatile impurities are water, hydrogen, nitrogen, methane, carbon dioxide, and sulfur dioxide. In the course of annealing, the concentration of these volatile impurities exhibits a significant decrease, the sample weight loss reaching up to 20%. This process is accompanied by both endo- and exothermal effects.     

Removal of surface carbides from spark-machined molybdenum and tungsten

When reactive metals such as molybdenum and tungsten are shaped by electrical discharge machining in the kerosene-based electrolytes generally employed for the process, they become covered with a thin, multiply-melted surface layer which contains carbide phases of variable composition. This surface layer is sometimes undesirable because its chemical and mechanical properties are different from the base metals. It has been demonstrated that the carbide can be removed by a high-temperature anneal in a reducing atmosphere. The anneal also removes surface cracks on molybdenum introduced by the machining, but the heat treatments employed here did not remove surface cracks on tungsten. The high-temperature anneal had the unfortunate side effect of inducing a significant degree of grain coarsening in the metals.     

Synthesis of samarium sesquioxide from the thermal decomposition of samarium oxychloride

In this work, Sm₂O₃ was synthesized from the thermal decomposition of SmOCl (P4/nmm). The process was studied by gravimetry under flowing air between 600 °C and 950 °C. Reactants and products were identified and analyzed by X-ray diffraction and energy dispersive spectroscopy. From the results, the stoichiometry of the reaction was obtained. Between 800 °C and 950 °C, the successive formation of both cubic Sm₂O₃ (Ia3) and monoclinic Sm₂O₃ (C2/m) phases was observed. Below 800 °C, no transformation of cubic Sm₂O₃ to monoclinic Sm₂O₃ was detected. Quantification of phases was made using the Rietveld Method. Combined with the analysis of the evolution of the microstructure by scanning electron microscopy, an elemental analysis of the kinetics of the reaction was made and a reaction scheme was proposed.     

The structure and composition of oxidized and reduced tungsten oxide thin films

The structure, morphology and composition of pure WO₃ thin films deposited onto vacuum-cleaved NaCl(001) single crystals have been studied at different substrate temperatures up to 580 K and under different oxidative and reductive treatments in the temperature range 373-873 K by Transmission Electron Microscopy, Selected-Area Electron Diffraction and X-ray Photoelectron Spectroscopy (XPS). A transition from an amorphous structure obtained after deposition at 298 K to a more porous structure with small crystallites at the highest substrate temperatures has been observed. XPS spectra reveal the presence of W⁶⁺ irrespective of the preparation procedure. Significant changes in the film structure were only observed after an oxidative treatment in 1 bar O₂ at 673 K, which induces crystallization of a monoclinic WO₃ structure. After raising the oxidation temperature to 773 K, the film shows additional reconstruction and a hexagonal WO₃ structure becomes predominant. This hexagonal structure persists at least up to 873 K oxidation temperature. However, these structural transformations observed upon oxidation were almost completely suppressed by mixing the WO₃ thin film with a second oxide, e.g. Ga₂O₃. Reduction of the WO₃ films in 1 bar H₂ at 723-773 K eventually induced the formation of the β-W metal structure, as evidenced by electron diffraction and XPS.     

The interaction of cobalt with oxidized silicon surface

The initial stages of the growth of cobalt disilicide (CoSi₂) on a 2×1 reconstructed Si(100) surface in the presence of oxygen have been studied for the first time by method of high-resolution photoelectron spectroscopy. The evolution of the electron structure of the sample surface was traced in the course of silicon oxidation, cobalt deposition, and subsequent thermal annealing. It is established that cobalt atoms penetrate to the oxide-silicon interface even at room temperature. This phenomenon favors the formation of an epitaxial CoSi₂ layer with improved morphology.     

Detection of oxidized low-density lipoproteins using surface plasmon resonance

Management of atherosclerosis is a high priority target. If this is to be achieved, the early detection of risk and risk factors are paramount and integrated with this is a need for the detection of the oxidation state of a patient's low density lipoprotein (LDL). Presently no readily usable technique exists for their rapid determination and in order to develop such a technique a monitoring system must be devised which distinguishes a parameter which changes on oxidation and distinguishes critical and noncritical oxidation products. The strategy which is investigated here is based on the use of a heparin-modified Au-surface plasmon resonance (SPR) device as a modulator of LDL binding, according to its oxidation state. Heparin is strongly negatively charged and seven binding sites for heparin have been identified on the LDL apoprotein consisting of arginine and lysine clusters; these are regarded as identical to the LDL receptor binding sites. The heparin-modified surface was calibrated for LDL and a calibration factor of 1.84 × 10(9) particles mm(-)(2) Δ(o)(-)(1) SPR and instrumental resolution of 9 × 10(6) particles mm(-)(2) obtained which gives sufficient scope to distinguish LDL dependent binding. LDL oxidation could involve the protein and/or lipoprotein, the latter being of interest for athersclerosis risk and the LDL binding to heparin was shown to decrease with degree of protein oxidation as determined by the free amino groups (fluorescamine assay), but was not influenced by lipid oxidation (determined by thiobarbituric acid reactive substances assay, TBARS). The SPR based assay was tested for LDL in plasma and the calibration found to follow that obtained in buffer, although the scatter was higher, probably due to interference from other plasma species. Nevertheless, in the context of the normal distribution of LDL in healthy patients, the assay would almost certainly be able to determine Ox-LDL in atherosclerotic patients.     

AES investigation of the stainless steel surface oxidized in plasma

Auger electron spectroscopy (AES) depth profiling was used to study the oxidation phenomena of AISI316L stainless steel during treatment with oxygen plasma. Samples were exposed to low-pressure RF plasma with a high dissociation degree, so that the flux of oxygen atoms onto the sample surface exceeded 10²⁴ m⁻² s⁻¹. A set of samples was oxidized 4 min at different temperatures up to 1300 K during plasma treatment. AES measurements showed that the oxide film thickness increased with the increasing temperature. The thickness of the oxide film on the samples oxidized in plasma at 300 K was nearly the same as for the untreated sample. The thickness of the oxide film of the samples which were oxidized at 1000 K was about 170 nm and it consisted of iron oxide. The thickest oxide film of about 350 nm was found on the samples heated in oxygen plasma to 1300 K. Depth profiling showed the uppermost layer of manganese oxide, followed by a mixture of chromium oxide and iron oxide. The scanning electron microscope analyses showed a dramatic increase of the surface roughness.     

Formation of interstitial atoms in surface layers of helium-implanted tungsten

Using a method of field ion microscopy, the atomic structure of surface and near-surface layers of a perfect dislocation-free tungsten irradiated by helium ions with energies below the threshold of displacement was studied. We have found the output of tungsten atoms from the bulk as a result of their displacement from regular lattice positions occupied by implanted helium atoms and the formation of interstitial tungsten atoms. It is shown that high concentrations of helium and the presence of image forces have a considerable effect on the development of these processes. Depleted zones consisting of helium-vacancy complexes are revealed within the irradiated near-surface layer.     

Effect of surface condition on the transport properties of tungsten

Measurements are presented of the low-temperature electrical and thermal resistivities andW, of several high-purity, single-crystal tungsten rods of various orientations for which the electron mean free path l is larger than the sample diameterd. For the highest-purity samples oriented with a [110] direction parallel to the rod axis we observe several effects of surface condition on the electron transport properties. First, both the electrical and thermal resistivities areincreased substantially by sandblasting or electroetching the surface andreduced correspondingly by electropolishing the surface. Second, the temperature-dependent part of the electrical resistivity ( — ₀ ) isreduced by sandblasting or electroetching the surface andincreased by electropolishing the surface. The corresponding effect is not observed for the thermal resistivity. Third, the Lorenz number extrapolated toT=0 K,L(T 0)=(/WT) ₀ , is found to equal the standard valueL ₀ =2.445 × 10 ^–8 W /K² for the sandblasted or electroetched surface, but is reduced significantly (up to 18%) below this value for the electropolished surface. In the latter case application of a longitudinal magnetic field strong enough to prevent many of the conduction electrons from striking the surface is observed to increaseL(T0) toL ₀, confirming that this is, indeed, a surface effect.Work supported by the U.S. Atomic Energy Commission under Contract Number AT(11-1)-3150, Technical Report #COO-3150-11.     

Growth of single-walled carbon nanotube arrays from samarium on substrates

In this letter, it is reported for the first time that samarium is an effective catalyst for single-walled carbon nanotubes(SWNTs) growth via a chemical vapor deposition(CVD) process. Horizontally superlong well-oriented SWNT arrays can be generated under suitable conditions by using ethanol as carbon source. The single-wall structure was characterized by scanning electron microscopy, Raman spectroscopy and atomic force microscopy. The results show that the SWNTs from samarium have better conductivity and better structural uniformity with less defects. This rare earth metal element provides not only an alternative catalyst for SWNTs growth but also a possible way to generate high percentage of superlong semiconducting SWNT arrays for various applications of nanoelectronic device.     

TA4电化学抛光和阳极氧化处理表面生物相容性的比较

比较了TA4纯钛材电化学抛光表面和阳极氧化表面的形貌、抗腐蚀性能、微动摩擦磨损性能和生物活性。结果表明,与阳极氧化表面相比,电化学抛光表面具有较多纳米尺度孔穴(孔穴总数较低),较低的表面粗糙度(低约一个数量级),较低的抗腐蚀性能(后者的腐蚀速率比前者的稍大),较低的摩擦系数(0.134vs.0.286),较差的耐磨性能,以及较高的生物活性(模拟体液中Ca-P层的生长速率)。     

Thermodesorption examination of interaction of hydrogen with traps in silver

Translated from Fiziko-Khimicheskaya Mekhanika Materialov, Vol. 27, No. 6, pp. 79–81, November–December, 1991.     

Electroless coating of tungsten oxide on the surface of copper powder

Tungsten oxide was successfully deposited on the surface of copper powder and the thickness of coating layer was dependent on deposition time. Because a spontaneous reaction occurred on the interface between copper and tungsten-peroxo electrolyte, there was a maximum thickness that could be obtained, as confirmed from XRD and EDX results. Mesoporous tungsten oxide was also deposited using SDS as a structure directing agent. As-synthesized tungsten oxide was amorphous and, after calcination at 450 °C, crystallized tungsten oxide was produced. Compared to pure tungsten oxide, the tungsten oxide coated copper oxide showed enhanced absorption in the visible region.     

Oxygen-containing functional groups on the oxidized surface of a carbon nanomaterial

The composition of the oxygen-containing surface functional groups produced by the oxidation of the Tekhnosorb carbon nanocomposite material is studied using chemical analysis and titrimetry. The oxygen-containing groups on the carbon surface are identified by IR spectroscopy. The oxygen content of the surface functional groups is determined as a function of oxidation conditions, and the static exchange capacity of the material is shown to correlate with its surface composition.     

Field reconstruction of close-packed atomic complexes at the surface of tungsten

The observation of low-temperature reconstruction of atomic clusters at a close-packed metal face using field ion microscopy is reported. An analysis is made of the configuration of nonclose-packed zigzag atomic chains formed as a result of the decay of clusters. Pis’ma Zh. Tekh. Fiz. 24, 1–6 (December 26, 1998)     

The preparation of tungsten oxide powders with high specific surface areas

Tungsten oxide powders with high specific surface areas (50 m²g^–1) are prepared by using a variation on the hot kerosene drying technique. It is also shown that the use of a water in oil emulsion in the hot kerosene drying technique has no effect on the specific surface areas of the resultant powders. The reason for the absence of any effect is explained. The difference between the powders prepared by the hot kerosene drying technique and the variation of this, is the high specific surface area due to the porous structure of the powders prepared by the latter method.