Measurement of the absolute oscillator strengths of gadolinium using an atomic vapor produced by electron beam heating

The absolute values of the oscillator strength ƒ were measured for the six spectral lines of Gd by means of laser absorption spectroscopy with the atomic vapor produced by electron beam heating. The ƒ values obtained for the transition are 0–17381 cm⁻¹, 215–17750 cm⁻¹, 533–17795 cm⁻¹, 999–18070 cm⁻¹, 999–17931 cm⁻¹, 1719–18070 cm⁻¹ were obtained to be 0.0036, 0.012, 0.014, 0.019, 0.0075 and 0.039, respectively. The error of ƒ values was 24% due to uncertainty of metastable states' density.     

Optoacoustic study of the infrared multiphoton excitation of ethylene

The optoacoustic effect was used to detect the infrared multiphoton excitation of ethylene as a function of laser wave length and laser energy fluence. The strong absorptions were observed at 949 cm⁻¹, 953 cm⁻¹ and 939 cm⁻¹. The dependence of the energy absorption on the laser energy fluence shows that the absorption at 949 cm⁻¹ is due to the resonance of the single quantum transition whereas the absorptions at 953 cm⁻¹ and 939 cm⁻¹ are due to the resonance of the double quantum transitions. The energy shift of the later transitions was explained in terms of Fermi resonance of the overtones of v₇ and v₈ modes. The onset of highly multiple quantum transitions were observed at high laser energy fluence.     

Vibrational spectroscopy of ordered oxygen adiayers on Ni/Cu(001) and Co/Cu(001) thin film systems

We report surface vibrations in c(2 × 2) oxygen adlayers on Ni and Co thin films on a Cu(001) substrate measured at gG by high resolution EELS. For the Ni thin film surface, one phonon peak is measured for varying film thicknesses from 1.3 ML (monolayer) to 6 ML with a constant energy of 221 cm⁻¹. For the Co thin film surface, three loss peaks are found, whose relative intensities change as the film thicknesses are varied. One loss peak at ˜520 cm⁻¹ is tentatively assigned to the Fuchs-Kliewer mode of cobalt oxide (CoO). The other two peaks at 317 and 376 cm⁻¹ are likely related to different bonding sites. Surface phonons on the p(2 × 2) Co thin film (389 cm⁻¹) and a bulk resonance mode (115 cm⁻¹) are also reported.     

Dependence of the excitation wavelength on the Raman-active phonons of YBa2Cu3O7 Search for Landau damping in single-domain crystals

In single-domain crystals of YBa₂Cu₃O₇, we examine the dependence of phonon linewidth on wavevector by varying the wavelength of the exciting laser. In three crystals, we find the linewidths of the Raman-active phonons at 120 and 150 cm⁻¹ to be nearly invariant for excitation wavelengths between 647 and 413 nm. That is, we find no broadening of the phonon linewidths with increasing phonon wavevector (decreasing excitation wavelength), and thus no evidence of Landau damping in our crystals. In addition, the correlation between the intensity of the chain-related Raman feature at ≈232 cm⁻¹ and the temperature dependence of the B_1g-like phonon at 340 cm⁻¹ has been investigated. In all three crystals, we find a net sharpening of the 340 cm⁻¹ phonon below T_c and essentially no intensity for the ≈232 cm⁻¹ mode under resonance conditions.     

On the luminescence of LiBaF3:Eu

From the temperature dependence of the line—band luminescence intensity ratio of LiBaF₃:Eu²⁺ a 4f−5d activation energy (Δ) of 800 cm⁻¹ is derived, being much higher than the value reported in the literature (100 cm⁻¹). The temperature dependence of the luminescence decay can be well described with Δ = 800 cm⁻¹ and with 4f−4f and 5d−4f radiative probabilities of 4×10²s⁻¹ and 6×10⁵s⁻¹, respectively.     

Femtosecond laser micro-structuring of aluminium under helium

The interaction of 180 fs, 775 nm laser pulses with aluminium under a flowing stream of helium at ambient pressure have been used to study the material re-deposition, ablation rate and residual surface roughness. Threshold fluence F_th0.4 J cm⁻² and the volume ablation rate was measured to be 30<V<450 μm³ per pulse in the fluence range 1.4<F<21 J cm⁻². The presence of helium avoids gas breakdown above the substrate and leads to improved surface micro-structure by minimising surface oxidation and debris re-deposition. At 1 kHz rep. rate, with fluence F>7 J cm⁻² and >85 W cm⁻² average power density, residual thermal effects result in melt and debris formation producing poor surface micro-structure. On the contrary, surface micro-machining at low fluence F1.4 J cm⁻² with low power density, 3 W cm⁻² produces much superior surface micro-structuring with minimum melt and measured surface roughness R_a1.1±0.1 μm at a depth D50 μm. By varying the combination of fluence/scan speed during ultra-fast ablation of aluminium at 1 kHz rep. rate, results suggest that maintaining average scanned power density to <5 W cm⁻² combined with single pulse fluence <4 J cm⁻² produces near optimum micro-structuring. The debris under these conditions contains pure aluminium nanoparticles carried with the helium stream.     

Vibrational study of silicon oxidation: H2O on Si(100)

The vibrational spectrum of water dissociatively adsorbed on Si(100) surfaces is obtained with surface infrared absorption spectroscopy. Low frequency spectra (< 1450 cm⁻¹ are acquired using a buried CoSi₂ layer as an internal mirror to perform external reflection spectroscopy. On clean Si(100), water dissociates into H and OH surface species as evidenced by EELS results [1] in the literature which show a Si---H stretching vibration (2082 cm⁻¹), and SiO---H vibrations (O---H stretch at 3660 cm⁻¹ and the Si---O---H bend and Si---O stretch of the hydroxyl group centered around 820 cm⁻¹). In this paper, infrared (IR) measurements are presented which confirm and resolve the issue of a puzzling isotopic shift for the Si---O mode of the surface hydroxyl group, namely, that the Si---O stretch of the O---H surface species formed upon H₂O exposure occurs at 825 cm⁻¹, while the Si---O stretch of the ---OD surface species formed upon D₂O exposure shifts to 840 cm⁻¹, contrary to what is expected for simple reduced mass arguments. The higher resolution of IR measurements versus typical EELS measurements makes it possible to identify a new mode at 898 cm⁻¹, which is an important piece of evidence in understanding the anomalous frequency shift. By comparing the results of measurements for adsorption of H¹⁶₂O, H¹⁸₂O and D₂O with the results from recently performed first-principles calculations, it can be shown that a strong vibrational interaction between the Si---O stretching and Si---O---H bending functional group vibrations of the hydroxyl group accounts for the observed isotopic shifts.     

NIR-FT-SERS of 4″-trimethylsilylethylsulfanyl-4,4′-di(phenyleneethynylene)benzenethiol on Au nanospheres

Oligo(phenyleneethynylene) (OPE) compounds have been identified as promising molecular electronic bridges. Self-assembled monolayers of 4″-trimethylsilylethylsulfanyl-4,4′-phenyleneethynylenebenzene thiol (OPE′) on Au were characterized by surface-enhanced Raman scattering (SERS). The FT-Raman spectrum of OPE′ shows three C–S bands at 834, 1086, and 1131 cm⁻¹. From the FT-Raman to the SERS spectra, the 1086 cm⁻¹ band exhibits a 9 cm⁻¹ red shift. Chemisorption of OPE′ to the gold surface occurs via oxidative cleavage of the disulfide bond and the formation of the Au–S bond. The Au–S vibration is visible in the SERS spectra at 257 cm⁻¹. Peaks due to the S–S and S–H stretch are observed at 544 and 2519 cm⁻¹, respectively, in the FT spectrum, but are unobserved in the surface-enhanced spectra. The C–H stretching region (2700–3350 cm⁻¹) in the spectrum of neat OPE′ shows three distinct bands, whereas the SERS spectra show a single broad band. Assignments of vibrational bands were based on DFT calculations performed at the B3LYP level with good agreement between theoretical and experimental values. An average percent difference of 2.52 was obtained for the non-CH stretching frequencies.     

A theoretical study of CHx chemisorption on the Ni(100) and Ni(111) surfaces

Cluster model calculations have been performed for CH_x, x = 0−3, chemisorbed on Ni(100) and Ni(111). The predicted chemisorption energies, at the present level of theory, based on bond-prepared clusters for Ni(100) are for carbon 150 kcal/mol, for CH 136 kcal/mol, for CH₂ 91 kcal/mol and for CH₃ 46 kcal/mol. The corresponding energies for Ni(111) are for CH 120 kcal/mol, for CH₂ 88 cal/mol and for CH₃ 49 kcal/mol. These chemisorption energies lead to similar stabilities for all CH_x fragments on both Ni(100) and Ni(111). Large basis sets and multi-reference correlation treatments are found to be very important in particular for the multiply bonded species. The vibrational C-H stretching frequencies predicted for CH_x on Ni(111) are for CH 3054 cm⁻¹ (2980 cm⁻¹), for CH₂ 3204 cm⁻¹ and for CH₃ 2709 cm⁻¹ (2680 cm⁻¹), where the available experimental values are given in parent The predicted ionization spectra of adsorbed CH_x are also in general agreement with experimental findings.     

Ionic conductivity of crystalline and glassy Mg4.5Na7(P2O7)4

In our work single crystals of Mg_4.5Na₇(P₂O₇)₄ were prepared, pulverized, pressed into pellets and sintered in order to measure the electrical conductivity of polycrystalline specimens. The conductivity was also measured on glassy specimens obtained by the melting of previously prepared crystals. The electrical conductivities at 25°C with values of the order of 10⁻¹⁶ Ω⁻¹ cm⁻¹ for polycrystalline samples and a value of the order of 10⁻¹⁴ Ω⁻¹ cm⁻¹ for glass, show that the glassy phase of Mg_4.5Na₇(P₂ because of its greater molar volume and loosely packed structure, is a better matrix for ionic motion.     

Influence of the Sb dopant distribution on far infrared photoconductivity in Ge:Sb blocked impurity band detectors

Extended long wavelength response to 200 μm (50 cm⁻¹) has been observed in Ge:Sb blocked impurity band (BIB) detectors with N_D1×10¹⁶ cm⁻³. The cut-off wavelength increases from 150 μm (65 cm⁻¹) to 200 μm (50 cm⁻¹) with increasing bias. The responsivity at long wavelengths was lower than expected. This can be explained by considering the observed Sb diffusion profile in a transition region between the blocking layer and active layer. BIB modeling is presented which indicates that this Sb concentration profile increases the electric field in the transition region and reduces the field in the blocking layer. The depletion region consists partially of the transition region between the active and blocking layer, which could contribute to the reduced long wavelength response. The field spike at the interface is the likely cause of breakdown at a lower bias than expected.     

Nombres D''ondes Absolus De La Bande ν3 De OCS Par Spectroscopie De Fourier

Absolute wavenumbers of 140 lines belonging to ν₃ band of ¹⁶O¹²C³²S, around 2060 cm⁻¹, are measured under vacuum with a high resolution Fourier Spectrometer, within ±0.11 × 10⁻³ cm⁻¹ (3.1 MHz) . They achieve a 20-fold improvement in accuracy over previous measurements and are consequently proposed as secondary infrared standards. Molecular constants are reported.     

Proton conductive amorphous thin films of tungsten oxide clusters with acidic ligands

Three kinds of peroxo-polytungstic acid (PPTA, C-PPTA and N-PPTA) were obtained by reacting hydrogen peroxide with metallic tungsten, tungsten carbide or tungsten nitride, respectively. Polytungstates, C-PPTA and N-PPTA, were found to contain oxalate and nitrate ligands. Their proton conductivities were compared using thin film specimens spin-coated from their water solution. Conductivity of each as-coated film was in the range from 10⁻³ to 10⁻⁴ S cm⁻¹ under the relative humidity of 40% (25 °C). A sharp decrease in conductivity (to less than 10⁻⁷ S cm⁻¹ at 25 °C) was observed for PPTA without acidic ligands after thermal treatment at 80 °C. However, the effect of thermal treatment on C-PPTA or N-PPTA was much milder. A 80 °C-treated C-PPTA film showed the conductivity of 1.0 × 10⁻⁵ S cm⁻¹ (25 °C) with a very weak dependency on ambient humidity.     

The adsorption of CO on Ir(111) investigated with FT-IRAS

The adsorption of CO on Ir(111) has been investigated with Fourier transform infrared reflection-absorption spectroscopy, temperature programmed desorption, and low-energy electron diffraction. At sample temperatures between 90 and 350 K, only a single absorption band, above 2000 cm⁻¹, has been observed at all CO coverages. For fractional coverages above approximately 0.2, the bandwidth becomes as narrow as 5.5 cm⁻¹. The linewidth is attributed mainly to inhomogeneous broadening at low CO coverages and to the creation of electron-hole pairs at higher CO coverages. The coverage-dependent frequency shift of the IR band can be described quantitatively using an improved dipolar coupling model. The contribution of the dipole shift and the chemical shift to the total frequency shift were separated using isotopic mixtures of CO. The chemical shift is positive with a constant value of approximately 12 cm⁻¹ for all coverages, whereas the dipole shift increases with coverage up to a value of 36 cm⁻¹ at a coverage of 0.5 ML.     

Far-infrared and millimeter wave spectroscopy of superionic copper conductors

Far-infrared and millimeter wave spectra of copper ion conducting crystal RbCu₄Cl_3+xI_2−x, which has the same structure as the room temperature silver ion conductor RbAg₄I₅, were investigated. Broad absorption peaks observed around 40, 80, and 110–200 cm⁻¹ at room temperature show doublet structures at low temperature; this may be attributed to the difference of local structure by chlorine and iodine ion. The 110–200 cm⁻¹ bands seem to be symmetric breathing modes of CuX₄ (X = Cl or I) tetrahedron and the frequency shift coincides with the square root of the mass ratio of conduction ions. The 80 cm⁻¹ band seems to be Rb-X vibration in RbX₆ octahedron. The 40 cm⁻¹ band seems to be the attempt mode which is an outward motion of the mobile ion in halogen cage. The increase of the absorption intensity at the low energy side with temperature corresponds to an increase of the DC conductivity. Plasmon fitting in energy loss function spectra was attempted.     

Raman study of HgBa2Can−1CunO2n+2+δ (n=1,2,3,4 and 5) superconductors

Polarized micro-Raman scattering measurements have been performed on the five members of the HgBa₂Ca_n−1Cu_nO_2n+2+δ (n=1,2,3,4 and 5) high-T_c superconductor family using different laser frequencies. Local laser annealing measurements were carried out to investigate the variation of the Raman spectra with the excess oxygen content, δ. A systematic evolution of the spectra, which display mainly peaks near 590, 570, 540 and 470 cm⁻¹, with increasing number of CuO₂ layers has been observed; its origin has been shown to lie in the variation of the interstitial oxygen content. In addition to confirming that the 590 cm⁻¹ mode represents vibration of apical oxygens in the absence of neighboring excess oxygen, the 570 cm⁻¹ mode, which may be composed of some finer structures, has been assigned to the vibration of the apical oxygen modified by the presence of the neighboring excess oxygens. The 540 and 470 cm⁻¹ modes may represent the direct vibration of excess oxygens. The implication of possible different distribution sites of excess oxygens is discussed. All other observed lower-frequency modes are also assigned.     

HREELS of H/GaN(0001): evidence for Ga termination

Two issues relevant to the growth and processing of GaN are the termination of the GaN(0001) surface and its reaction with hydrogen. We have used high-resolution electron energy loss spectroscopy (HREELS), low-energy electron diffraction (LEED), and Auger electron spectroscopy (AES) to study the adsorption of hydrogen on MOCVD-grown GaN(0001). LEED of the sputtered and annealed surface shows evidence of facetting. No adsorbate vibrations are observed on the clean surface by HREELS, only Fuchs–Kliewer phonons at intervals of 700 cm⁻¹. Following exposure of the clean GaN surface to hydrogen atoms, HREEL spectra show adsorbate loss peaks at 2580, 3280, and 3980 cm⁻¹. The Ga–H stretching vibration at 1880 cm⁻¹ becomes evident when the HREEL spectrum is deconvoluted to remove the phonon multiple-loss peaks. We assign the 2580, 3280, and 3980 cm⁻¹ peaks to combination modes of the Ga–H stretch and phonon(s). Upon dosing with deuterium, the Ga–D bending mode is observed at 400 cm⁻¹. No vibrational peaks due to N–H (N–D) species are observed after H (D) exposure. We conclude that sputtered and annealed GaN(0001) is Ga-terminated.     

Estimation of hydroxyl free radicals produced by ultrasound in Fricke solution used as a chemical dosimeter

Hydroxyl free radicals produced in Fricke solution exposed to 80 kV X-rays or 23 kHz ultrasound (intensity 3 W cm⁻²) or 20 kHz ultrasound (intensity 18.9 W cm⁻²) or 3.5 MHz clinical ultrasound (intensity 1.47 W cm⁻²), as estimated from the Fricke dosimetric data, exhibited a linear dose-response relationship. The dosimeter was found to be effective in the concentration range 1.0–8.0 mM of FeSO₄ solution. The hydroxyl radicals produced in Fricke solution were inhibited by the OH radical scavengers dimethyl sulfoxide (200 mM), -histidine (10 mM) and sodium benzoate (10 mM) in a manner proportional to the rate constants of their reaction with the OH radicals. The power threshold for OH radical formation, which is presumably the threshold for cavity formation, was estimated for 23 kHz ultrasound by this dosimeter as 1.28 W cm⁻² for a 4 cm³ sample volume.     

The adsorbate-induced removal of the Pt{100} surface reconstruction Part I: NO

The molecular adsorption of NO on both the reconstructed (hex) and unreconstructed (1 × 1) surfaces of Pt{100} has been studied using a combination of infrared reflection-absorption spectroscopy (IRAS) and low energy electron diffraction (LEED) at temperatures between 90 and 300 K. On the (1 × 1) surface at 300 K adsorbed NO gives rise to an N-O stretching band at initially 1596 cm⁻¹ shifting to 1641 cm⁻¹ at a coverage of θ = 0.5. The LEED pattern at this coverage is interpreted in terms of a c(4 × 2) structure in which all the molecules occupy a single type of adsorption site between the on-top and bridge positions. At temperatures below 300 K, a higher coverage disordered phase is observed, giving rise to an N-O stretching band at 1680 cm⁻¹ associated with an on-top NO species. On the (hex) phase surface above 210 K, NO adsorption gives rise to bands characteristic of adsorption on the (1 × 1) phase indicating that the reconstruction is immediately lifted. Below 200 K initial adsorption actually occurs directly on the (hex) phase, resulting in a band at 1680 cm⁻¹, which is assigned to on-top NO. This band increases in intensity until, at a critical coverage dependent on temperature, the (hex) → (1 × 1) surface phase transition is induced. This is indicated by the disappearance of the band at 1680 cm⁻¹ and its replacement by bands characteristic of adsorption on islands of the (1 × 1) structure.     

Impedance studies on polyacrylonitrile–CuX2–DMSO (X=Cl, Br, CF3SO3) solid polymer electrolyte

A series of polyacrylonitrile–dimethylsulfoxide–CuX₂ (X=CF₃SO₃⁻, Cl⁻, Br⁻), films (foils) were prepared by means of the solution cast technique. The thickness of the foils was between 0.04 and 0.09 cm and they contained 70–80 wt.% of the solvent. Conductivities of the solid electrolytes were obtained from impedance measurements. The conductivity increases with the increase of the salt content up to 8 wt.%; at higher concentrations (>8 wt.%) the conductivity is more or less stable, and reaches, in the case of Cu(CF₃SO₃)₂ and CuCl₂, the level of ca. 10⁻³ Ω⁻¹ cm⁻¹ at room temperature. The foils based on the CuBr₂ show even higher conductivity, close to 10⁻² Ω⁻¹ cm⁻¹ at room temperature, a value comparable to that characteristic for liquid solutions. The temperature variation of the conductivity for all the systems studied is of the Arrhenius type. The activation energy, determined from linear plots lnσ=f(T⁻¹), is of the order ca. 14 kJ mol⁻¹ for the PAN/CuBr₂/DMSO and of ca. 21 kJ mol⁻¹ for the PAN/CuCl₂/DMSO and the PAN/Cu(CF₃SO₃)₂/DMSO systems.