Spreading of an SR beam spot (diameter 0.5 μm, 95 eV) photoelectron image on the surface of WO<Subscript>3 − <Emphasis Type="Italic">x</Emphasis></Subscript> films

The 2D-photoemission image of the beam spot was obtained for the first time for the W⁵⁺ oxidation state on the preliminary irradiated WO_{3 − x} thin film surface, created by scanning of the SR beam over the film surface. The W⁵⁺ beam profile intensity was found to spread up to a distance of 3.2 μm for an amorphous film and 5.5 μm for a polycrystalline film, it exceeds considerably the beam spot size. The image saturation dose was reached faster for a polycrystalline film. Among the possible mechanisms explaining this phenomenon, for the case of an almost unchangeable O2s state under irradiation, a choice was made in favor of a photon-generated charge diffusion due to low-energy secondary electrons from photoemission, which produce the “coloration” effect, e⁻ + W⁶⁺ (W⁵⁺) W⁵⁺ → W⁵⁺(W⁴⁺). The O512-eV Auger peak was found to degrade at the distance of 1.5–2 mm outside the beam spot under long-time electron beam irradiation, which is attributed to electron-stimulated oxygen desorption and outdiffusion.     

Luminescence characteristics of the Pr3+ ion in SrAlF5

The paper reports on a study of luminescence and excitation spectra of SrAlF₅:Pr³⁺ (0.5 mol %) polycrystals performed at 10 and 300 K with synchrotron radiation in the range from 5 to 25 eV. The Pr³⁺ ions in SrAlF₅ were shown to emit successively two photons in transitions from the ¹ S ₀ and ³ P ₀ levels. The main energy characteristics of the compound, namely, the position of the 4f → 5d excitation band (5.95–8.0 eV), the energy separation between the ¹ S ₀, 4f and the lowest 5d levels (～0.15 eV), and the SrAlF₅ band gap width (～12 eV), were determined. SrAlF₅:Pr³⁺ was found to possess a number of features not found in other Pr³⁺-activated fluorides.     

Two-photon time-resolved optogalvanic signals of neon

In this work, temporal evolution of two-photon laser optogalvanic signals of neon has been studied. Optogalvanic signals for four transitions from the metastable 2p⁵3s[3/2]₂ state to 2p⁵4d′[3/2]₁, 2p⁵4d′[3/2]₂, 2p⁵4d′[5/2]₃ and 2p⁵4d′[5/2]₂ states were recorded over a range of discharge currents (3.4–9 mA). It was found that the shape of the optogalvanic signal was strongly dependent on the discharge current so that its peak shifted to shorter times and its amplitude increased with the discharge current. The decay rates of the 4d states, calculated from the optogalvanic signals, were found to increase linearly with the discharge current in the range of 6.2–9 mA. However, for the range of 3.4–5.4 mA, the decay rates were observed to slightly decrease with the discharge current.     

Annealing characteristics of highly doped ion implanted phosphorus layers in silicon

A combination of sheet resistance, stripping and Hall effect measurements have been made on phosphorus layers implanted into silicon at 40 and 100 keV with doses between 1 × 10¹⁵ and 5 × 10¹⁶ atoms/cm². The implants were made at room temperature and 450°C. After annealing at 650°C, the profile of electrically active phosphorus following a high dose room temperature implant, was found to be flat topped with a concentration of approximately 5 × 10²⁰/cm³. Very little diffusion occurred when annealing to 850°C where the free electron concentration increased to approximately 1.5 × 10²¹/cm³. Highly doped channeled tails were found when implanting at 450°C along the 〈110〉 direction and damage was being continuously annealed out preventing the formation of an amorphous phase. The rapid diffusion of the profile into the bulk found when annealing between 650°C and 850°C was speculated to be due to the presence of a dense dislocation entanglement in these layers following a hot implant.     

13C NMR Chemical Shifts of Heterocycles: Empirical Substituent Effects in 5-Halomethylisoxazoles

Evaluation by empirically derived equations for the Substituent effect (α, β, γ, δ) on the ¹³C NMR chemical shifts for C-3, C-4. C-5 and halomethyl-substituent carbon (C-6) in isoxazoles 1-5 [where C-3 substituent (R¹) = H, alkyl or phenyl, C-4 Substituent (R²) = H, alkyl, and C-5 substituent (R³) = di-or trihalomethyl, methyl and H], taking as reference the compound la, is reported. From the calculated values for the α, β, γ, δ effects for each substituent it was possible to estimate the chemical shift of each carbon of the compounds 1–5. The ¹³ C chemical shifts of the C-3, C-4, C-5, C-6 of these compounds, can be estimated with good precision: 94% of the calculated chemical shifts are found to be within ±1.0ppm, and 100% are found to be within ±1.5ppm.     

Photoluminescence of polycrystalline cadmium sulfide films at 77 °K

The absorption, reflection, emission, and luminescence spectra of polycrystalline cadmium sulfide films have been studied at 77 deg K at 4500–5500 A. The films were prepared by sublimination of the powder in argon, hydrogen sulfide, or vacuum, followed by crystallization on a heated or unheated substrate.Specimens deposited on substrates below 350 deg C had simple absorption and emission spectra no matter which medium was used, but ones coated on substrates above 350 deg C had absorption, reflection, luminescence, and emission spectra with fine structure, which was due to transitions between the 5s²¹S₀ ground state and 5s5p³P₁, 5s5p³P₂, and 5s5p³P₀ excited states of atomic excess cadmium.Four maxima were found in the excitation spectrum of the blue luminescence (4545, 4605, 4670, and4740 A). The spectrum of the luminescence is independent of exciting wavelength in the range 2200–4900 A.This structure was observed only for films with hexagonal lattice symmetry.     

多晶Li3+xV1-xTxO4(T=Ge,Si)离子导电性能的改善

本文用阻抗谱方法研究了Li_3+xV_1-xT_xO₄(T=Si,Ge)多晶的离子导电性,发现一些工艺条件如成型压强、烧结时间和烧结程序对电导率有很大影响。注意分析了这些影响的物理起因。最佳工艺条件是:在大约8t/cm²压强下成型样品。在1000℃连续烧结5至6天,烧结过程中,应尽量避免温度波动。在此条件下制备的Li_3.5V_0.5Ge_0.5关键词：     

Slowdown of atomic diffusion in liquid gallium–indium alloy under different nanoconfinements

NMR studies were carried out on three isotopes, ⁷¹Ga, ⁶⁹Ga, and ¹¹⁵In, in liquid gallium-indium (Ga–In) alloy embedded into porous glasses with 200 and 5 nm pore sizes at two magnetic fields, 9.4 and 17.6 T. Spin-lattice relaxation and the Knight shift were found to depend on pore size. For porous glass with 5 nm pores the relaxation rate was field-dependent which evidenced that the extreme narrowing limit was no longer valid. Magnetization recovery data were used to evaluate the correlation times of atomic mobility and the quadrupole constants under nanoconfinement.     

Impact broadening of Sr 5sns 1 S 0, 5snd 1D2 and 5snd 3 D 2 levels by He and Xe

The impact broadening of strontium 5sns ¹ S ₀, 5snd ¹ D ₂ and 5snd ³ D ₂ levels by He and Xe have been studied by measuring the collisional half-widths of Doppler-free two-photon absorption lines from the 5s ^{2 1} S ₀ ground state in a thermionic diode. Large inelastic contributions to the broadening rates of the levels have been found where the moduli of the quantum defects of different level series are close to each other. A similar but continuousn-mixing behaviour along the series has also been found in our recent investigation on the broadening of Rb levels by noble gases. The broadening rates of the very high levels in Sr were found to be independent on the principal quantum number and the angular momentum of the levels and in good agreement with our recent broadening data of the Rb-He and Rb-Xe systems and the data for Na-He and Na-Xe found by the Columbia group.     

On the velocity distribution of excited Fe-atoms by sputtering of iron

From the velocity distribution of excited sputtered particles detailed information on the excitation process can be obtained. In the present paper the first direct measurement of velocity distribution of excited atoms sputtered from a metal target is presented. The irradiation of the Fe-target was performed with 10keV Ar⁺-ions. The sputtered atoms were detected using pulsed laser induced fluorescence (LIF). The sputtered Fe atoms in the metastable statea ⁵ F ₅ at 0.86 eV shows a much broader distribution, than found for the ground-state atoms, but no energy threshold, implied in the statistical excitation models, was found.     

The decay of45Ti to45Sc

The low intensity β⁺/E.C. branches in the decay of⁴⁵Ti to excited states of⁴⁵Sc have been reinvestigated in order to resolve discrepancies in reported branching ratios. A new branch to the 974 keV level, having an intensity of 9.9±1.2×10^?5/decay has been found. A previously reported branch to the 1237 keV level was found to be in error. The intensities for decay to the levels at 720, 1408 and 1661 keV levels were determined to be 154±12, 90.2±9.7 and 52.5±5.6, respectively, in units of 10^?5 per decay.     

The electron affinity of tungsten

The electron affinity of tungsten has been measured using laser photodetachment threshold spectroscopy in a collinear geometry. The electron affinity was determined to 6583.6(6) cm^-1 by observing the onset of the process when W^- ions in the 5d⁵6s²5d^56s^2 ⁶S_5/2 ground state are photodetached producing neutral W atoms in the 5d⁴6s²5d^46s^2 ⁵D₀ ground state. The measured value is in agreement with previous measurements and improves the accuracy by almost two orders of magnitude. Further, a photodetachment signal below the ground state photodetachment threshold was found, which indicates the existence of a bound excited state in W^-.     

Variation of radon concentrations in soil and groundwater and its correlation with radon exhalation rate from soil in Budhakedar, Garhwal Himalaya

Radon was measured in soil-gas and groundwater in the Budhakedar area of Tehri Garhwal, India in summer and winter to obtain the seasonal variation and its correlation with radon exhalation rate. The environmental surface gamma dose rate was also measured in the same area. The radon exhalation rate in the soil sample collected from different geological unit of Budhakedar area was measured using plastic track detector (LR-115 type II) technique. The variation in the radon concentration in soil-gas was found to vary from 1098 to 31,776 Bq.m⁻³ with an average of 7456 Bq.m⁻³ in summer season and 3501 to 42883 Bq.m⁻³ with an average of 17148 Bq.m⁻³ in winter season. In groundwater, it was found to vary from 8 to 3047 Bq.l⁻¹ with an average value 510 Bq.l⁻¹ in summer and 26 to 2311 Bq.l⁻¹ with an average value 433 Bq.L⁻¹ in winter. Surface gamma dose rate in the study area varied from 32.4 to 83.6 μR.h⁻¹ with an overall mean of 58.7 μ-R.h⁻¹ in summer and 34.6 to 79.3 μR.h⁻¹ with an average value 58.2 μR.h⁻¹ in winter. Radon exhalation rate from collected soil samples was found to vary from 0.1 × 10⁻⁵ to 5.7 × 10⁻⁵ Bq.kg⁻¹.h⁻¹ with an average of 1.5 × 10⁻⁵ Bq.kg⁻¹.h⁻¹ in summer season and 1.7 × 10⁻⁵ to 9.6 × 10⁻⁵ Bq.kg⁻¹.h⁻¹ with an average of 5.5 × 10⁻⁵ Bq.kg⁻¹.h⁻¹. A weak negative correlation was observed between radon exhalation rate from soil and radon concentration in the soil. Radon exhalation rate from the soil was also not found to be correlated with the gamma dose rate, while it shows a positive correlation with radon concentration in water in summer season. Inter-correlations among various parameters are discussed in detail.      

Experimental limits on the production of fractionally charged particles in proton-nucleus and neutrino-nucleus collisions

A search for fractionally chargedQ=1/3 (2/3) particles of different properties of interaction produced in (anti)neutrino-nucleus and in protonnucleus collisions was performed using the scintillator system of the CHARM neutrino detector at the CERN SPS. No events of the cases considered were found. In (anti)neutrino beams production was found to be less than a few times 10^?5 per interaction of a beam particle. In a proton beam an upper limit on the production cross section of ～10^?40 cm² was obtained.     

Femtosecond laser ablation of cemented carbides: properties and tribological applications

Laser ablation with fs laser pulses was performed in air on cobalt cemented tungsten carbide by means of a Ti : sapphire laser (800 nm, 100 fs). Small and moderate fluences (2, 5, 10 J/cm²) and up to 5×10⁴ pulses per irradiated spot were used to drill holes with aspect ratios up to 10. Cross-section cuts from laser-irradiated samples were produced and they were analysed with optical microscopy and SEM. EDX analyses were carried out on selected zones. Quasi-cylindrical holes were found for 2 J/cm², whereas for 5 and 10 J/cm² irregular shapes (lobes, bottoms wider than hole entrances) were found to occur after a given number of incident pulses. Layers with modified structure were evidenced at pore walls. SEM revealed a denser structure, while EDX analyses showed uniform and almost similar contents of W, C, and Co in these layers. As a direct application, patterning of coated WC-Co was carried out with 2 J/cm² and 100 pulses per pore. The resulted surfaces were tribologically tested and these tests revealed an improved friction and wear behaviour. PACS 42.65.Cs; 79.60.Ds     

A study of energy transfer phenomenon leading to photon up-conversion in Ho3+:Yb3+:CaF2 crystalline powders and its temperature sensing properties

When Ho³⁺:Yb³⁺:CaF₂ crystalline powders prepared by combustion synthesis were exposed to near-infrared (λ ～ 975 nm) radiation, intense photon up-conversion (UC) was observed at the visible with emission bands peaked at ～ 545, ～650 and ～750 nm identified as 4f-4f transitions from higher levels (⁵F₄, ⁵S₂) and ⁵F₅ to lower levels ⁵I₈ and ⁵I₇ of Ho³⁺. The emission bands at the green and red, in particular, have been demonstrated to be useful for temperature sensing based on luminescence intensity ratio technique. However, no model is available in literature to explain the change of the electronic populations of states (⁵F₄, ⁵S₂) and ⁵F₅ with temperature. The UC phenomenon was studied from both theoretical and experimental points of view. A rate equation model with temperature dependent parameters for Ho³⁺ and Yb³⁺ electronic populations considering a high sensitization of Ho³⁺ ions by Yb³⁺ ions was used. High Yb³⁺ → Ho³⁺ energy transfer efficiency was found (～88% at room temperature). The change with temperature predicted by the model for the luminescence intensity ratio of the UC green and red emission lines agrees well with the experimental data.     

Strong L=5 transition in Te(p,p′) reactions

Strong L=5 transitions have been found in the (p, p′) reaction on ^{122,124,126,128,130}Te. The possible 2⁵-pole collective motion in Te nuclei is discussed.     

Electron paramagnetic resonance studies in photorefractive crystals I: Hyperfine interaction and photoinduced charge transfer in233U5+ and238U5+ doped LiNbO3

Electron paramagnetic resonance studies were conducted on the photoinduced charge transfer and also hyperfine interaction of U⁵⁺ stabilized in photorefractive matrix LiNbO₃. This work deals with: (i) first observation of hyperfine structure due to²³³U (I=5/2) in its pentavalent state at octahedral sites and comparison with other possible site symmetries, (ii) photoinduced charge transfer as observable by EPR and its relevance to photorefractive behaviour of LiNbO₃. The effect of chemical bonding on the hyperfine interaction of 5f ¹ configuration was also studied by converting the existing literature data on²³⁵U⁵⁺ to that of²³³U⁵⁺ by standard methods. This suggests that progressive substitution of oxygen by F⁻, in the series UO ₆ ⁷⁻ , (UO₅F)⁶⁻ and (UO₄F₂)⁵⁻ drastically decreases the hyperfine coupling constantA _∥, along the local distortion axis. This trend is explained as being due to the absence of ligand ion along the distortion axis at U⁵⁺ site in trigonal LiNbO₃. The effects of illumination by copper vapor laser (CVL) on the intensity of the U⁵⁺ signal was studied in the 10–300K region. The kinetics of decay and restoration of U⁵⁺ was also studied between 10–100K range. The decay kinetics was found to obey double exponential. The reduction of concentration of U⁵⁺ with CVL-illumination and its restoration in the absence of light show that pentavalent uranium takes part in the photorefractive effects in LiNbO₃.     

Calcination temperature optimization,energy transfer mechanism and fluorescence temperature dependence of KLa(MoO4)2:Eu3+ phosphors

The optimum calcination temperature for KLa(MoO₄)₂:Eu³⁺ phosphor was confirmed to be 1000 °C via checking the XRD patterns, SEM images and fluorescence spectra for the samples derived from solid state reaction. The energy transfer behavior between Eu³⁺ ions was studied. It was found that electric dipole–dipole interaction is responsible for the fluorescence quenching of ⁵D₂ and ⁵D₁ levels, but exchange interaction is in charge of ⁵D₀ fluorescence quenching. It was also observed that color coordinates of the studied phosphor can be tuned when the doping concentration is relatively low. The fluorescence thermal quenching process was investigated. It was found the thermal quenching followed well crossover model. Judd–Ofelt parameters of Eu³⁺ in KLa(MoO₄)₂ were obtained, and the optical transition properties were further discussed.     

An XPS study of the UV photoreduction of transition and noble metal oxides

The photoreduction of polycrystalline samples of MoO₃, WO₃, Cu₂O, CuO, PdO and PtO by UV irradiation was investigated by X-ray photoelectron spectroscopy (XPS). Photoreduction of these metal oxides was found upon irradiation with the emission lines from a mercury vapor lamp (2537 Å) at room temperature. Other oxides, like ZnO and V₂O₅, where not photoreduced. Mo⁶⁺ and W⁶⁺ were observed to partially photoreduce to Mo⁵⁺ and W⁵⁺. In the case of the copper oxides, both Cu²⁺ and Cu¹⁺ were found to completely photoreduce to the metallic state. The photoreduction of PdO and PtO was observed to proceed slowly through the first few monolayers and was 75% completed within the XPS sampling depth ( ∼ 40 Å) after long irradiation times. All photoreduced species were observed to reoxidize upon exposure to the atmosphere. The oxidation of photoreduced metallic Pt and Pd at room temperature is unique since those metals usually do not oxidize in air. A model has been developed to explain and predict the extent of reduction of metal oxides surfaces by UV irradiation. It shows that depending on band gap and chemical stability, complete or partial reduction of many oxide surfaces can be achieved.