FEM study of NOW and NO2W adsorption system

Nitric oxide adsorption on tungsten and nitric dioxide adsorption on tungsten have been investigated by the FEM method. When NO or NO₂ adsorbs gradually on W at 300 K and at 80 K, the FEM patterns which appear at first are found to be similar to those which appear in N₂ adsorption on W. In the case of NO adsorption on W at 80 K, with further exposure, no further change of the FEM patterns is observed. However, in the cases of NO adsorption on W at 300 K, NO₂ adsorption on W at 300 K, and NO₂ adsorption on W at 80 K, further changes of the FEM patterns are observed with further exposure, and the FEM pattern which is obtained at the saturated state is found to be similar to the FEM pattern which appears at the saturated state of O₂ adsorption on W. From the above results it is suggested that NO and NO₂ dissociate on W at 300 and at 80 K.     

Lattice relaxation and μ+ sites in rhombohedral bismuthsites in rhombohedral bismuth

Owing to the staggered sequence of hexagonal layers in the rhombohedral crystal structure of Bi two different interstitial sites are in principle available to the μ⁺. It is found that below 10 K the μ⁺ is localized at one of these sites while above 80 K up to 110 K the μ⁺ is localized at the other site. In both instances a latticecontraction around the μ⁺ is observed, amounting to a reduction of 12% at 8 K and 7% at 100 K in the nearest Bi μ⁺ distances. At both sites the second moments reveal strong quadrupole interaction effects, which dominate at 8 K in fields up to 0.746 T but which are slightly quenched at this field strength at 100 K.     

RuFeSi — A new magnetic system

A ternary system consisting of Ru, Fe and Si is identified in which the hyperfine field at Fe is seen to evolve at a characteristic temperature, T¹, far below the magnetic ordering temperature, T_m. It is speculated that the magnetic ordering at T_m is itinerant and T¹ corresponds to the localization of the majority spin electrons at the Fe atoms.     

Adsorption of carbon monoxide on polycrystalline nickel films

The adsorption states of carbon monoxide on polycrystalline nickel films have been investigated by measuring the thermal desorption, the heat of adsorption, the change in resistivity, and the change in work function in dependence on coverage and temperature. It can be shown that there are two chemisorbed (β₂, β₂) and one weakly bound (γ) species. Desorption peaks appear at 170K, 310–360 K, and 460–490 K. The differential heat of adsorption is $\text{30}\text{kcal}\text{mole}$ at low coverages and approximately $\text{25}\text{kcal}\text{mole}$ between 0.3 and 0.6 monolayers. The resistivity of the nickel film is characteristically changed with increasing coverage, and there is a maximum of resistivity at half a monolayer. At low coverages the increase in the work function is proportional to the amount adsorbed; at a monolayer the total increase is 1.26 eV at 77 K and 1.46 eV at 273 K. The two chemisorbed species differ only in the structures they form in the adsorption phase, β₂ being the species that is stable at low coverages, β₁ being the species that is stable at high coverages. These results are in good agreement with those recently found for CO adsorption on single crystal surfaces.     

Rotational hysteresis loss and anisotropy in yttrium garnet ferrite single crystals

The rotational hysteresis loss in Y₃Fe₅O₁₂ single crystals is found to increase with the field up to 2.5–3 kOe at all temperatures between –183 and 250 ° C, this being followed by a fall, a further peak at 8–10 kOe, and a slow fall, with some residual effect even at 20 kOe. This loss is sensitive to heat treatment; annealing for 2 hr at 275 ° C greatly reduces the loss at –183 ° C and halves the main (second) peak at 20 ° C. These anomalies do not occur in ferrites with the spinel structure. The first anistropy constant is slightly reduced at all temperatures as a result of annealing.     

The feature study on the <Emphasis Type="Italic">π</Emphasis> and proton rapidity distributions at AGS,SPS and RHIC

The features of nuclear stopping power and multi-hadron production systematically are studied by making an analysis of rapidity distributions of pion and proton at AGS, SPS and RHIC in this work. It is found that nuclear stopping power increases linearly with project rapidity y _p at AGS and SPS, but that is not liner at RHIC. It is argued that the average rapidity loss is saturated at central rapidity region at RHIC. For pion distribution, it is found that the phase space of pion distribution distributes uniformly in the longitudinal direction, and a linear relationship of 〈βγ〉_L with log√s is given at AGS and SPS. Non-uniform flow model may explain the features of the distribution at AGS and SPS, but may not explain those of at RHIC. Supported by the Excellent Youth Foundation of Hubei Scientific Committee (Grant No. 2006ABB036), the Educational Commission of Hubei Province of China (Grant No. Z20081302), and the Natural Science Foundation of China Three Gorges University (Grant No. 2003C02)     

A hybrid Monte Carlo approach to molecular aggregation in a porous medium

A Monte Carlo simulation is used to study the segregation of liquid crystal molecules (short chains) in a heterogeneous matrix (of barrier concentration ) in an ordering field (E). Aggregation of molecules, pinned by the matrix barriers, is enhanced at lower temperature (T) and higher barrier concentrations via clusters of clustering growth. Variation of the radial distribution function with T and , rms displacement of molecules, and visual analysis of their distribution reveal that the size of the molecular aggregates is relatively larger and less dispersed at higher than that at a lower at T=0.2. The orientational molecular ordering is found to be lower at low temperature at higher . Molecules remain segregated at higher temperatures unless the porosity is reduced and the ordering field is increased considerably. Received 29 October 1999 and Received in final form 19 January 2000     

Measurement of low frequency absorption

Measurements in four rooms with volumes between 106 and 607 m³ give significant differences in the value of the sound absorption coefficient at low frequencies. There is little variation with volume at high frequencies. In two rooms, 204 and 607 m³ in volume, no significant change in absorption coefficient is observed at low frequencies when the amount of diffusing elements in the room is changed. This is in contrast to the well-known variation with number of diffusers that occurs at high frequencies.     

Influence of a controlled oxidation at moderate temperatures on the surface chemistry of nitinol wire

Commercial nitinol wire is oxidised at 480-530 °C/10 min in air. Surface morphology and chemistry is studied in detail using scanning electron microscopy, energy dispersive spectrometry, X-ray diffraction, Raman spectrometry and X-ray photoelectron spectroscopy. It is found that the main oxidation product at both temperatures is rutile containing a few at.% Ni. Beneath the rutile layer, there are titanium sub-oxides, showing characteristic maxima in depth profiles. Nickel in an oxidised state is present on the surface, whereas in a sub-surface region of scales, there is only metallic nickel. Thickness of the total oxide layers is 70 and 140 nm after oxidation at 480 and 530 °C, respectively. The preferential oxidation of titanium causes the formation of a Ni-enriched and Ti-depleted zone, suggesting the presence of Ni₃Ti phase. XRD reveals that the presence of cubic B2 NiTi phase in the base alloy is not affected by oxidation at 480-530 °C/10 min.     

Antiferromagnetic ordering and metamagnetism in PrCuSi

A variety of physical properties measured on the hexagonal rare-earth intermetallic compound PrCuSi are presented. We provide compelling evidence for antiferromagnetic ordering at T_N = 5.1 K in this compound, in contrast to the former claim of ferromagnetic ordering at 14 K. The antiferromagnetic order is, however, found to be unstable in applied magnetic fields, becoming ferromagnetic beyond a metamagnetic transition at a field of 0.7 T at 2 K. It is argued that the magnetism in PrCuSi has the ingredients of a tricritical phase transition at the intersection of paramagnetism, ferromagnetism, and antiferromagnetism.     

Absorption phenomena in multicomponent phosphate glasses with Mn

The absorption and ESR spectra of multicomponent alumino-phosphate glasses doped with manganese (0·2–20 mol %) has been measured and compared with the absorption spectra of manganous and manganic ions in model solutions. The unirradiated glasses show in ultraviolet region increasing absorption below 200 nm with the shoulder at 235 nm and the absorption bands due to manganous oxygen complexes in octahedral symmetry. They are similar to the absorption bands of Mn²⁺ in concentrated H₃PO₄ acid. In irradiated glasses the bands at 200, 235, 275 (only if Mn is present) and a broad band at 540 nm appear. After the annealing at 450 C all radiation-induced bands disappear and the bands at 235 nm is more pronounced. The Mn³⁺ in H₃PO₄ solution exhibit the absorption spectrum with a weak band at 530 nm and a very intense band at 270 nm. It is therefore proposed that both the 540 and 275 nm bands in irradiated glasses can be assigned to octahedral oxygen complexes of Mn³⁺, i.e. to hole centres. The band at 200 nm which is practically independent of the modifiers (Be, Mg, Ca, Sr and Ba) is, therefore, associated with electron centres (electrons trapped in non-bridging oxygen vacancies). It is suggested that the band at 235 nm in irradiated and annealed glasses is associated with irreversible structural changes.The authors wish to express their appreciation to H.Dvoáková for preparing the solutions and E.Linhartová for careful measurements.     

Multifrequency EPR of four triarylmethyl radicals

Continuous-wave spectra at W-band of four triarylmethyl (trityl) radicals at 100 K in 1∶1 water-glycerol exhibit rhombic electron paramagnetic resonance spectra. The rigid-lattice line widths at W-band are only 3 to 5 times larger than at X-band or S-band, and fluid-solution line widths are much narrower than those for rigid lattice, which indicates that unresolved anisotropic nuclear hyperfine couplings make significant contributions to the rigid-lattice line widths. Spin-flip lines are observed in glassy-solution spectra at X-band and S-band, but not at W-band or 250 MHz. At 100 KT _m is dominated by spin diffusion of solvent protons and is independent of microwave frequency. Between about 130 and 170 K, 1/T _m for trityl-CH₃ is enhanced by rotation of the methyl groups at a rate comparable to inequivalences in the hyperfine interaction. Motional averaging of anisotropic interactions enhances spin echo dephasing between about 200 and 300 K. The temperature dependence of 1/T ₁ is similar for the four radicals and is consistent with assignment of the Raman process and a local mode as the dominant relaxation processes. The similarity inT ₁ values at W-band and X-band supports this assignment.     

First principles study of structural,magnetic and electronic properties of half-metallic CrO<Subscript>2</Subscript> under pressure

A first-principles tight-binding linear muffin tin orbital (TB-LMTO) method within the local-density approximation is used to calculate the total energy, lattice parameter, bulk modulus, magnetic moment, density of states and energy band structures of half-metallic CrO₂ at ambient as well as at high pressure. The magnetic and structural stabilities are determined from the total energy calculations. From the present study we predict a magnetic transition from ferromagnetic (FM) state to a non-magnetic (NM) state at 65 GPa, which is of second order in nature. We also observe from our calculations that CrO₂ is more stable in tetragonal phase (rutile-type) at ambient conditions and undergoes a transition to an orthorhombic structure (CaCl₂-type) at 9.6 GPa, which is in good agreement with the experimental results. We predict a second structural phase transition from CaCl₂- to fluorite-type structure at 89.6 GPa with a volume collapse of 7.3%, which is yet to be confirmed experimentally. Interestingly, CrO₂ shows half metallicity under ambient conditions. After the first structural phase transition from tetragonal to orthorhombic, half metallicity has been retained in CrO₂ and it vanishes at a pressure of 41.6 GPa. Ferromagnetism is quenched at a pressure of 65 GPa.     

Blue up-conversion with excitation into Tm ions at 808 nm in YVO4 crystals co-doped with thulium and ytterbium

The up-conversion of infrared radiation at 808 nm, emitted by a diode laser, into blue emission centered at 480 nm in 1 at.% Tm, 5 at.% Yb: YVO₄; 1 at.% Tm, 8 at.% Yb: YVO₄ and 2 at.% Tm, 5 at.% Yb: YVO₄ has been studied. The highest intensity of blue emission is found for the 1 at.% Tm, 8 at.%Yb: YVO₄ system. The power dependence of up-converted emission upon continuous-wave excitation as well as the time evolution of its intensity upon short-pulse excitation were found to be consistent with a two-step excitation mechanism in which the forward Tm³⁺–Yb³⁺ energy transfer is followed by the back Yb³⁺–Tm³⁺ energy transfer. The effect of dopant concentrations on the up-conversion process is interpreted taking into account dynamics of the excited states involved.     

Sputter damage in Si surface by low energy Ar+ ion bombardment

The damage distributions in Si(1 0 0) surface after 1.0 and 0.5 keV Ar⁺ ion bombardment were studied using MEIS and Molecular dynamic (MD) simulation. The primary Ar⁺ ion beam direction was varied from surface normal to glancing angle. The MEIS results show that the damage thickness in 1.0 keV Ar ion bombardment is reduced from about 7.7 nm at surface normal incidence to 1.3 nm at the incident angle of 80°. However, the damage thickness in 0.5 keV Ar ion bombardment is reduced from 5.1 nm at surface normal incidence to 0.5 nm at the incident angle of 80°. The maximum atomic concentration of implanted Ar atoms after 1 keV ion bombardment is about 10.5 at% at the depth of 2.5 nm at surface normal incidence and about 2.0 at% at the depth of 1.2 nm at the incident angle of 80°. However, after 0.5 keV ion bombardments, it is 8.0 at% at the depth of 2.0 nm for surface normal incidence and the in-depth Ar distribution cannot be observable at the incident angle of 80°. MD simulation reproduced the damage distribution quantitatively.     

Nucleation of the D1a type ordered phase in the near-surface of A4B alloy: II. Nucleation at surface

Nucleation in the D1_a type A₄B ordering alloy was investigated by means of an atomistic calculation based on a phenomenological nucleation theory and the Bragg-Williams approximation. The nucleation rate at the Ni₄Mo surface is presented as a function of temperature, surface orientation, and type of the plane to which the surface is parallel (fundamental plane or superlattice plane). The radius, degree of order and activation free energy of the critical nucleus are also given as a function of temperature. The value of the nucleation rate at the surface is compared with that in the bulk. The results are as follows: (i) at temperatures near T_c. the nucleation rate is higher at the surfaces than in the bulk and the {200}_FCC surfaces are the highest in nucleation rate; (ii) however, at temperatures near the instability temperature t₀, the nucleation rate is lower at the surface than in the bulk; (iii) the present calculated results give reasonable explanations to our experimental results on the Ni₄ Mo alloy: (a) preferential surface ordering at high temperatures near T_c; (b) surface disordering at intermediate temperatures near the nose temperature.     

Diagnostics of an O<Subscript>2</Subscript>(<Superscript>1</Superscript>Δ) generator using multichannel recording of oxygen emission spectra

The concentrations of water vapor and O₂(¹Δ), as well as the temperature in the gas flow at the exit of a singlet oxygen generator, are determined using multichannel recording of the singlet oxygen emission spectrum in the bands at 634, 703, 762, and 1268 nm. The water vapor concentration is found from the intensity ratio of the 762-nm band, which corresponds to the ¹Σ → ³Σ transition of the oxygen molecule, and the dimole emission band at 634 nm. From the ratio of the integrated intensities of the bands at 634 and 1268 nm, the O₂(¹Δ) concentration is determined and it is shown that the yield of O₂(¹Δ) at the exit from the gas generator is about 52%. The temperature of the gas flow, determined by the rotational structure of the oxygen emission spectrum in the band at 762 nm, is about 300 K under the nominal conditions of the gas generator operation. The ratio of the photon fluxes in the 703 and 634nm bands of the O₂(¹Δ) dimole emission is 1.06. The temperature dependence of the dimole emission bandwidths is determined, which can be used for estimating the gas temperature at the exit of the O₂(¹Δ) generator.     

A 20.1 W solid-state laser pumped by 887 nm with high efficiency and TEM<Subscript>00</Subscript> mode

High efficiency, TEM₀₀ mode, high repetition rate laser pumped by 887 nm is reported. 20.1 W output laser emitting at 1064 nm is achieved in a 0.3 at % Nd-doped Nd:YVO₄, which absorbs pumping light of 30.7 W at 887 nm. The opto-optic efficiency and the slope efficiency are 65.5 and 88.5%, respectively. The stable Q-switching operation worked well at 100 kHz and the beam quality is near diffraction-limit with M² factor measured as M² ≈ 1.2. And the pulse waveform is analyzed in this paper.     

Low-frequency internal friction of polycrystalline ZrO2-4 mol % Y2O3 in the temperature range 273–373 K

The specific features in the low-frequency internal friction, structure, and phase composition of polycrystalline ZrO₂-4 mol % Y₂O₃ are investigated in the temperature range 273–373 K. It is demonstrated that the low-frequency internal friction exhibits two peaks upon heating and cooling. The former peak is observed at a temperature of approximately 293 K, and the latter peak is revealed at 313 K. It is assumed that the peak observed in the low-frequency internal friction at a temperature of 293 K is attributed to relaxation dissipation of energy during motion of twin boundaries in the monoclinic phase, whereas the peak at 313 K is associated with relaxation processes due to displacement of the boundaries of tetragonal T′ domains.