New interpretations of XPS spectra of nickel metal and oxides

A current interpretation of XPS spectra of Ni metal assumes that the main 6 eV satellite is due to a two hole c3d⁹4s² (c is a core hole) final state effect. We report REELS observation in AES at low voltages of losses (plasmons and inter-band transitions) corresponding to the satellite structures in Ni metal 2p spectra. The satellite near 6 eV is attributed to a predominant surface plasmon loss. A current interpretation of Ni 2p spectra of oxides and other compounds is based on charge transfer assignments of the main peak at 854.6 eV and the broad satellite centred at around 861 eV to the cd⁹L and the unscreened cd⁸ final-state configurations, respectively (L is a ligand hole). Multiplet splittings have been shown to be necessary for assignment of Fe 2p and Cr 2p spectral profiles and chemical states. The assignments of Ni 2p states are re-examined with intra-atomic multiplet envelopes applied to Ni(OH)₂, NiOOH and NiO spectra. It is shown that the free ion multiplet envelopes for Ni²⁺ and Ni³⁺ simulate the main line and satellite structures for Ni(OH)₂ and NiOOH. Fitting the NiO Ni 2p spectral profile is not as straightforward as the hydroxide and oxyhydroxide. It may involve contributions from inter-atomic, non-local electronic coupling and screening effects with multiplet structures significantly different from the free ions as found for MnO. A scheme for fitting these spectra using multiplet envelopes is proposed.     

Extension of the range of resonator scanning spectrometer into submillimeter band and some perspectives of its further developments

Extension of the working frequency of modern resonator spectrometers into submillimeter wave range is described. Experimental record of atmospheric absorption spectrum covering 45-370 GHz range is demonstrated for the first time, and measured water vapor J′_{ka′, kc′}-J_{ka, kc} = 5_1,5-4_2,2 at 325 GHz line parameters are presented. For the first time pressure lineshift for the 325-GHz water vapor line is measured. Further extension of working range is discussed. New estimations of physical limits of time needed for measurements of absorption in the whole Backward Wave Oscillator (BWO) range are given for phase continuous synthesizer regime. Basic schemes of fast broadband continuous phase synthesized sources are discussed. Verification of the previous measurements of water vapor 3_1,3-2_2,0 at 183 GHz line parameters is presented. Comparisons with ringdown resonator spectrometers are given.     

Electrochemical impedance spectroscopy and linear polarization applied to evaluation of porosity of phosphate conversion coatings on electrogalvanized steels

In this work, electrochemical impedance spectroscopy and linear polarization are used in determining porosity of zinc phosphates, and of nickel and manganese modified zinc phosphates on electrogalvanized steel. The porosity of the phosphate layers ranges from 0.1% for the manganese-modified hopeite to 8% for hopeite, using the linear polarization and the electrochemical impedance spectroscopy techniques. The porosity values measured using the two techniques were in agreement. All impedance spectra of coated samples showed two steps, with two capacitive arcs and an inductive looping.     

Au deposits on graphite: On the nature of high temperature desorption peaks in CO thermal desorption spectra

Due to the discovery of Au as a catalyst for low temperature CO oxidation, the adsorption of CO on Au surfaces has attracted a lot of attention recently. On stepped and rough single crystal surfaces as well as on deposited particles two characteristic desorption states above 100 K have been observed via TPD. We have studied Au deposits on graphite in order to elucidate the nature of these desorption peaks in more detail. For this purpose, Au was deposited at 100 K and 300 K on HOPG as a weakly interacting support. In analogy to other supports, we obtain two desorption states (∼140 K and ∼170 K) whose relative intensities depend strongly on the deposition temperature with the high temperature peak being much more pronounced for the 100 K deposits. After annealing to 600 K, both states drastically lose intensity. XP spectra, on the other hand, show virtually no decrease of the Au 4f intensity as would be expected for desorption or significant changes of the particle morphologies. We conclude that both desorption peaks are defect-related and connected with under-coordinated Au atoms that are lost for the most part upon annealing. These sites could be located at the perimeter of dendritic islands or on small, defect-rich particles in addition to larger particles not adsorbing CO at 100 K. Preliminary STM results are in favour of the second interpretation.     

Structural studies of Cr-doped mullite derived from single-phase precursors

Cr-doped mullites were prepared from single-phase precursors containing up to 9.60 wt% Cr₂O₃ using a sol-gel technique followed by thermal treatment. Particle induced X-ray emission spectroscopy and X-ray powder diffraction were used to characterize the samples. Mullites were orthorhombic, space group Pbam. Cr doping caused the increase of unit-cell parameters. Strongest expansion was noticed along c-axis followed by a and b (Δc/c=0.089, Δa/a=0.061, Δb/b=0.045% per mole Cr₂O₃). A second phase, namely θ-(Al,Cr)₂O₃, was revealed by XRD in the sample containing 9.60 wt% Cr₂O₃. The structure of mullites was refined by the Rietveld method, location of Cr³⁺ was performed by the EPR spectroscopy. At low chromium doping level (Cr₂O₃ content less than ∼5 wt%) Cr³⁺ ions were substituted for Al³⁺ in the AlO₆ octahedra of the mullite structure (M1 site). For higher doping level, Cr³⁺ ions were additionally substituted for Al³⁺ in the AlO₆ octahedra of the second phase [θ-(Al,Cr)₂O₃ at 1400 °C, or α-(Al,Cr)₂O₃ at 1600 °C] which segregated in the system. Substitution of Cr³⁺ for Al³⁺ on M1 site in the mullite structure resulted in increase of average distances in (M1)O₆ octahedron and decrease of average distances in T*O₄ tetrahedron, while average distances in TO₄ tetrahedron stayed almost constant.     

Study of nitrogen ion implantation and diffusion phenomena on thin chromium layers followed by the atomic force microscopy and secondary ion mass spectroscopy techniques characterization

This research investigates the effect of ion implantation dosage level and further thermal treatment on the physical characteristics of chromium coatings on Si(1 1 1) substrates. Chromium films had been exposed to nitrogen ion fluencies of 1 × 10¹⁷, 3 × 10¹⁷, 6 × 10¹⁷ and 10 × 10¹⁷ N⁺ cm⁻² with a 15 keV energy level. Obtained samples had been heat treated at 450 °C at a pressure of 2 × 10⁻² Torr in an argon atmosphere for 30 h. Atomic force microscopy (AFM) images showed significant increase in surface roughness as a result of nitrogen ion fluence increase. Secondary ion mass spectroscopy (SIMS) studies revealed a clear increased accumulation of Cr₂N phase near the surface as a result of higher N⁺ fluence. XRD patterns showed preferred growth of [0 0 2] and [1 1 1] planes of Cr₂N phase as a result of higher ion implantation fluence. These results had been explained based on the nucleation-growth of Cr₂N phase and nitrogen atoms diffusion history during the thermal treatment process.     

The structure of monolayer SiO2 on Mo(1 1 2): A 2-D [Si-O-Si] network or isolated [SiO4] units?

In this letter, atomically resolved scanning tunneling microscopic (STM) images obtained from monolayer SiO₂/Mo(1 1 2) are presented. The results are consistent with a previously proposed structural model of isolated [SiO₄] units based on vibrational features observed by high-resolution electron energy loss spectroscopy (HREELS) and infrared reflection-absorption spectroscopy (IRAS), and oxygen species identified by ultra-violet photoemission spectroscopy (UPS). These results are inconsistent with a structural model that assumes a two-dimensional (2-D) [Si-O-Si] network. These data illustrate that a metal substrate, although coated with an oxide thin layer, can be directly imaged at the atomic-scale with STM.     

ICLAS of weak transitions of water between 11 300 and 12 850 cm: Comparison with FTS databases

Very weak water vapor absorption lines have been investigated by intracavity laser absorption spectroscopy (ICLAS) in the 11 335-11 947 and 12 336-12 843 cm⁻¹ spectral regions dominated by the ν₁ + 3ν₂ + ν₃ and ν₂ + 3ν₃ bands, respectively. A detectivity on the order of α_min ∼ 10⁻⁹ cm⁻¹ was achieved with an ICLAS spectrometer based on a Ti: Sapphire laser. It allowed detecting transitions with an intensity down to 5 × 10⁻²⁸ cm/molecule which is about 10 times lower than the weakest line intensities previously detected in the considered region. A line list corresponding to 1281 transitions with intensity lower than 5 × 10⁻²⁶ cm/molecule has been generated. A detailed comparison with the line lists provided by the HITRAN database and by recent investigations by Fourier transform spectroscopy associated with very long multi pass cell is presented. The rovibrational assignment performed on the basis of the ab initio calculations of Schwenke and Partridge, has allowed for determining 176 new energy levels belonging to a total of 16 vibrational states.     

New feature in the Auger peak of adsorbed oxygen

Recent joint theoretical and experimental investigations of Auger core-core-valence spectra of alkali adatoms on simple metals have revealed that such technique is capable to ascertain contributions from different adsorption environments in the signal [M.I. Trioni, S. Caravati, G.P. Brivio, L. Floreano, F. Bruno, A. Morgante, Phys. Rev. Lett. 93 (2004) 206802]. Consequently, to verify if such an effect is present also for other chemical species, we study theoretically the KLV transition of oxygen either as a bulk impurity or as an adsorbate in/on Al and Ag (jellium-like). We make use of the Fermi golden rule in which the matrix elements of the interaction are calculated within DFT. We verify that the relevant physical quantity of this phenomenon is the excited local density of states (LDOS), calculated within a region centered on the core ionized atom. The Auger rate for oxygen in Ag bulk displays a single asymmetric peak, while for adsorbed oxygen a second smaller feature at lower energies, and very close to the first one, appears. This unexpected result follows from the removal of the degeneracy of the m quantum number of the 2p states of oxygen at the surface. It is only displayed on the electronically less dense metal (Ag), but not on Al.     

无催化纳米氧化锌的制备及其光学性质研究

本文采用无催化剂直接蒸发高纯Zn粉,在800℃氧气氛条件下,在Si(111)衬底上生长得到以四角状为主的纳米ZnO(T-ZnO)。T-ZnO纳米线每个角约互成110°,长度约为1.5μm,直径100nm左右;Raman分析表明E2(H)普遍存在于各形态的ZnO;光致发光光谱表明,T-ZnO纳米线的光致发光除了与材料性质有关,还与杂质缺陷有关,蓝绿光带是ZnO的缺陷产生的。