Oxidation behavior of NiAl alloy at low temperatures

Oxidation behavior of NiAl alloy at low temperatures was studied. A NiAl plate was oxidized by exposure to ambient atmosphere at room temperature, heated at 473 K in air, and heated at 773 K in air. The oxide formed on the NiAl surface was investigated by angle‐resolved X‐ray photoelectron spectroscopy (AR‐XPS). Chemical composition and atomic concentration in the oxide layer were analyzed with factor analysis of XPS spectra. Exposure of the NiAl plate to the ambient atmosphere resulted in the formation of an Al₂O₃ layer along with a small amount of NiO. Oxidation of the NiAl plate at 473 K in air formed a film of double‐layered oxide; the top layer consisted of NiAl₂O₄ and a small amount of NiO, and the second layer was Al₂O₃. Successive oxidation at 773 K only changed the oxide‐layer thickness without changing the structure. Formation of oxide observed in the present study corresponds to the thermodynamic prediction for the oxidation behavior of NiAl at 1373 K. Copyright © 2007 John Wiley & Sons, Ltd.     

New experimental technique of photoelectron holography applied to Bi trimers on Si(111)

The branching ratio, the photoemission intensity ratio of two spin-orbit-split components, has been applied for the first time as a means for obtaining a photoelectron holographic image. Angle-resolved photoemission from a monolayer of Bi adsorbed on Si(111) shows fine-structure oscillations in the branching ratio of the Bi 5d core level due to diffraction effects. These oscillations as a function of photon energy are recorded for a number of emission angles. Three-dimensional holographic inversion of the data yields an atomic image which shows that the Bi adatoms are arranged in a trimer structure.     

Secondary electron emission control in X-ray photoelectron spectroscopy

Secondary electron emission (SEE) is a major player in surface charging during X-ray photoelectron spectroscopy (XPS); its characteristics and applicability as a current source for electrical measurements are studied. We employ sample biasing and a top retarding grid to control the photoelectron current, and further compare their I–V characteristics with direct spectroscopy of the secondary electrons. Using silica-coated gold substrates, the effect of sample work function on the emitted secondary electrons is shown and fine control over the surface potential gradients, in the range of 10–100 meV, is achieved. XPS-based chemically resolved electrical measurements (CREM) can thus be extended to the positive current regime.     

时间分辨傅氏变换红外光谱方法中的定时直流成分

在常规的傅里叶变换红外光谱学中，干涉图的直流成分为∫＾∞０Ｂ（σ）ｄσ，而在时间分辨ＦＴＩＲ中，直流成分Ｉｄｅ成为∫（∞，０）Ｂ（σ，τ）ｄσ，即与信号出现的时间τ有关，称为定量直流成分。     

Angle‐resolved photoemission spectroscopy and imaging with a submicrometre probe at the SPECTROMICROSCOPY‐3.2L beamline of Elettra

The extensive upgrade of the experimental end‐station of the SPECTROMICROSCOPY‐3.2L beamline at Elettra synchrotron light source is reported. After the upgrade, angle‐resolved photoemission spectroscopy from a submicrometre spot and scanning microscopy images monitoring the photoelectron signal inside selected acquisition angle and energy windows can be performed. As a test case, angle‐resolved photoemission spectroscopy from single flakes of highly oriented pyrolitic graphite and imaging of the flakes with image contrast owing to rotation of the band dispersion of different flakes are presented.     

激光诱导Al等离子体电子温度的时间空间演化特性研究

实验测定了激光烧蚀Al等离子体中Al原子在380-500nm 波长范围内的时间和空间分辨发射光谱。由Al原子390.068nm、394.4nm、396.152nm、466.3056nm、451.25nm、352 .95nm发射光谱线的强度计算了等离子体电子温度,并由实验结果讨论了激光等离子体中电子温度的时间和空间演化特性。实验结果表明,当延时在100-1500ns范围内变化时,相应的电子温度Te范围为6200K -32700K;当距离靶表面0-1.8mm范围内变化时,相应的电子温度Te范围为9800K- 32700K, 电子温度在沿激光束方向上的分布具有很好的对称性。     

Nature of charge separation and recombination processes within an organic dyad having short spacer

With the help of electrochemical, steady state and time resolved fluorescence (fluorescence lifetimes by using time correlated single photon counting technique) and nanosecond laser flash photolysis methods, the nature of charge separation along with the energy wasting charge recombination processes within a short-chained organic dyad 1-(4-Bromo-phenyl)-3-(2-methoxy-naphthalen-1-yl)-propenone (MNBA) has been revealed. In MNBA, the donor 2-methoxynaphthalene (2MNT) is connected with the acceptor p-bromoacetophenone (PBA) by an unsaturated olefinic bond. Though in the ground state elongated type structure (E-form) is observable from NMR spectra but on photoexcitation, another conformers possibly of the nature of folded type isomeric species (termed as Z-isomer) were also apparent from time resolved fluorescence measurements. However, preponderance of elongated form in the excited singlet state has been established from this time resolved measurements. NMR study on photoirradiated sample and theoretical predictions from computations using CIS method with Lanl2DZ basis set also indicate in favor of the propositions made on the formations of the two possible conformers and the stability of elongated isomeric species in the electronic excited state from the experimental results. The energy wasting charge recombination rate, k_CR, determined from the transient absorption measurements by nanosecond laser flash photolysis (LFP) technique was found to be (k_CR, ∼1.9×10⁵ s⁻¹) significantly lower than the charge-separation rate, k_cs∼9.4×10⁷ s⁻¹, measured from the time resolved fluorescence. This observation demonstrates that MNBA may serve as an efficient candidate to construct artificial light energy conversion devices or components of molecular photovoltaic cells.