Density functional theory study of H,C and 0 chemisorption on UN（O01） and （111） surfaces

We performed density functional theory calculations of H, C, and O chemisorption on the UN（001） and （111） surfaces using the generalized gradient approximation （GGA） and the Hubbard U parameter and revised Perdew-Burke-Ernzerhof （RPBE） exchange-correlation functional at non-spin polarized level with the periodic slab model. Chemisorption energies vs. distance of molecules from UN（001） and UN（111） surfaces have been optimized for four symmetrical chemisorption sites, respectively. The results show that the Hollow, N-top, and Hollow adsorption sites are the most stable sites for H, C, and O atoms with chemisorption energies of 13.06, 25.50 and 27.34 kJ/mol for UN（001 ） surface, respectively. From the point of adsorbent （UN（001） and UN（111） surfaces in this paper）, interaction of O with the chemisorbed surface is of the maximum magnitude, then C and H, which are in agreement with electronegativities of individual atoms. For the UN（001） surface, U-N bond lengths change relatively little （〈 9%） as a result of H chemisorption, however C and O chemisorptions result in remarkable changes for U-N bond lengths in interlayer （〉 10%）. Electronic structure calculations indicate that Bridge position is equivalent with Hollow position, and the most stable chemisorption position for H, C, and O atoms are all Bridge （or Hollow） position for the UN（1 11） surface. Calculated electronic density of states （DOSs） demonstrate electronic charge transfer between .9, p orbitals in chemisorbed atoms and U 6d, 5f orbitals.     

Shape Co-Existence in the Transitional Nuclide 157yb

High-spin states in 157yb have been populated in the 144Sm(16O, 3n)157yb fusion-evaporation reaction at a beam energy of 85 MeV, and two rotational bands have been established for the first time. Within the framework of the triaxial particle-rotor model, the energy spectra and single-particle configurations of 157yb are investigated. The calculated energy spectra agree well with the experimental data. The newly observed vf7/2 band, and the previously known vi13/2 band in 157yb, are also discussed by means of Total-Routhian-Surface methods. The structural characters observed in 157Yb provide evidence for the shape coexistence of three distinct shapes: prolate, triaxial and oblate. At higher spins, both the vf7/2 band and the vi13/2 band in 157yb undergo a shape evolution with sizable alignments occurring.     

Evaluation of influence of surface barrier in solid on ion reflection by bipartition model of ion transport

The influence of surface barrier of solid upon ion reflection was studied in a few papers of other authors by using the Monte-Carlo simulation. Based on the bipartition model of ion transport, a new analytical theory has been developed instead of the MC simulation, due to important implication of the effect for fusion research. In the present paper we have calculated the number reflection coefficients of H , D , He and T normally incident on C, Al and Cu for ion energy from several eV to one hundred keV respectively. Our computational results accorded with the MC simulation. The results have shown that the effect of surface barrier on ion reflection becomes evident when the energy of incident ions is lower than one keV. In particular, for the ion energy from several eV to one hundred eV, the discrepancies of number reflection coefficients can increase up to 0.1-0.3, showing this influence to be very important.     

Study on Modification of Nano-Sized Anatase Titanium Dioxide by Nitrogen-Plasma

The nano-sized particles of anatase titanium oxide （TiO2） were obtained by hydrolysis of titanium ester （TNB） in basic media and dehydrated in acid media. And then the anatase titanium oxide was treated with nitrogen plasma. The effect of nitrogen plasma treating time on the activity of photo-catalytic reduction of the Cr2O7^2- for sample obtained was investigated. The samples were characterized by X-ray diffraction （XRD）, X-ray photoelectron spectroscopy （XPS）, Transmission Electron Microscope （TEM） and Ultraviolet （UV）. A peak of 396 eV in the N 1 s XPS spectra of sample obtained with nitrogen plasma treated TiO2 showed that nitrogen-doped titanium oxide （TiO2-zNx） has been obtained. The spectra of UV showed that the light absorption of TiO2-xNz obtained by nitrogen plasma treated TiO2 for 10min. had moved to the visible region. The picture of TEM and spectra of XRD indicated that the crystallographic forms and particle dimension had no apparent change for both the modified and the unmodified TiO2. When the TiO2 sample was treated for 7 min with nitrogen plasma, it exhibited best photo-catalytic activity.     

Probing Co/Si interface behaviour by X-ray photoelectron spectroscopy （XPS） and atomic force microscopy （AFM）

In this work, we investigate the Co-Si reaction, the Co growth mode at room temperature, diffusion behaviour as well as morphology evolution during annealing on both H-terminated and clean Si（001） and Si（lll） surfaces. From in-situ X-ray photoelectron spectroscopy （XPS） investigation, ＂Co-Si＂ reaction appears to occur on both H-terminated and clean surfaces at room temperature （RT） and the silicide crystallinity is improved upon annealing. Co growth mode on H-terminated Si surfaces occurs in a pseudo layer-by-layer manner while small close-packed island growth mode is observed on the clean Si surface. Upon annealing at different temperatures, Co atom concentration decreases versus annealing time, which in part is attributed to Co atoms inward diffusion. The diffusion behaviour on both types of surfaces demonstrates a similar trend. Morphology study using ex-situ atomic force microscopy （AFM） shows that the islands formed on Si（001） surface after annealing at 700℃ are elongated with growth directions alternate between the two perpendicular [110 ] and [ 110] directions. Triangular islands are observed on Si （111） surface.     

Kinetic Monte Carlo Simulation of Deposition of Co Thin Film on Cu（001）

A kinetic Monte Carlo （kMC） simulation is conducted to study the growth of ultrathin film of Co on Cu（001） surface. The many-body, tight-binding potential model is used in the simulation to represent the interatomic potential. The film morphology of heteroepitaxial Co film on a Cu（001） substrate at the transient and final state conditions with various incident energies is simulated. The Co covered area and the thickness of the film growth of the first two layers are investigated. The simulation results show that the incident energy influences the film growth and structure. There exists a transition energy where the interracial roughness is minimum. There are some void regions in the film in the final state, because of the influence of the island growth in the first few layers. In addition, there are deviations from ideal layer-by-layer growth at a coverage from 0 - 2 monolayers （ML）.     

Four-Quasiparticle High-K States in Neutron-Deficient Lead and Polonium Nuclei

Configuration-constrained potential energy surface calculations have been performed to investigate four-quasiparticle high-K configurations in neutron-deficient lead and polonium isotopes. A good agreement between the calculations and the experimental data has been found for the excitation energy of the observed Kπ = 19- state in 188Pb. Several lowly excited high-K states are predicted, and the large oblate deformation and low energy indicate high-K isomerism in these nuclei.     

Influence of Different Surface Modifications on the Photovoltaic Performance and Dark Current of Dye-Sensitized Solar Cells

The TiO2 nanoporous film photoelectrode, as a crucial component of dye-sensitized solar cells, has been investigated. The photovoltaic properties and the dark current were studied by two surface modification methods. One was to apply a compact layer between the conductive glass substrate and nanoporous TiO2 film. Another was to produce TiO2 nanoparticles among the microstructure by TICl4 treatment. A suitable concentration and number of times for TICl4 treatment were found in our experiment. The dark current is suppressed by surface modifications, leading to a significant improvement in the solar cells performance. An excessive concentration of TICl4 will produce more surface states and introduce a larger dark current reversely. The dye is also regarded as a source of charge recombination in dark to some extent, due to an amount of surface protonations introduced by the interracial link in the conductive glass substrate/dye interface and dye/TiO2 interface.     

Low Pressure DC Glow Discharge Air Plasma Surface Treatment of Polyethylene (PE) Film for Improvement of Adhesive Properties

The present work deals with the change in surface properties of polyethylene (PE) film using DC low pressure glow discharge air plasma and makes it useful for technical applications. The change in hydrophilicity of the modified PE film surface was investigated by measuring contact angle and surface energy as a function of exposure time. Changes in the morphological and chemical composition of PE films were analyzed by atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS). The improvement in adhesion was studied by measuring T-peel and lap-shear strength. The results show that the wettability and surface energy of the PE film has been improved due to the introduction of oxygen-containing polar groups and an increase in surface roughness. The XPS result clearly shows the increase in concentration of oxygen content and the formation of polar groups on the polymer surface. The AFM observation on PE film shows that the roughness of the surface increased due to plasma treatment. The above morphological and chemical changes enhanced the adhesive properties of the PE film surfaces, which was confirmed by T-peel and lap-shear tests.     

The Sensitivity Profile of the Fast Reactor k_(eff)

The nuclear design calculations have always been limited in their accuracy by both computational methods and uncertainties in cross-section data. After a period of extensive refinements in calculation methods, like the node method and MonteCarlo method, and the rapidly development in the computer, more emphasis has been directed toward improving cross-section data. For this purpose, we should     

Growth of TiO2 surfaces following low energy (<40 eV) atom and small cluster bombardment

Low energy (10-40 eV) interaction of small Ti_xO_y clusters with a rutile (1 1 0) substrate was investigated using molecular dynamics with the aim of determining the influence of various parameters on surface growth and defect formation. Rutile growth was simulated through depositing randomly selected clusters with energies in the tens of eV range. Long time scale evolution was approximated through heating the substrate. A modified second-moment-Buckingham-QEq (SMB-Q) empirical potential was developed for the purpose. Crystal growth on amorphous and anatase TiO₂ substrates was also considered. Grown lattice layers were compared by visual inspection along with radial distribution function (RDF) plots. Bombardment at an energy of around 20 eV in an oxygen rich atmosphere with a high proportion of bombarding clusters, TiO, TiO₂, as opposed to single atoms, was found to produce rutile growth with the best crystallinity.     

Optical properties of titanium oxide films obtained by cathodic arc plasma deposition

Structural and optical properties of nanometric titanium oxide(TixOy) films obtained by cathodic arc plasma deposition were investigated. Phase analysis by x-ray diffraction and Fouriertransform infrared spectroscopy showed the presence of anatase, rutile, Ti_2O_3, Ti_4O_7 and amorphous phases. Scanning electron microscopy images showed well-developed surface morphology with nano-patterns. Spectroscopic ellipsometry revealed film thicknesses of 53 and50 nm, variable refractive indices dependent on the light wavelength and close to zero extinction coefficients for wavelengths higher than 500 nm. On the basis of ultraviolet–visible spectroscopy data and using the Tauc equation, band gap values for direct and indirect electron transitions were determined.     

First-principles study of electronic structure and insulating properties of uranium and plutonium dioxides

First-principles density functional theory calculations were carried out to investigate the electronic structure and the degree of 5f states localization of the Mott-Hubbard type insulators UO₂ and PuO₂. We used the fully relativistic cluster discrete variational method (RDV) with the local exchange-correlation potential. The energies of one-electron transition between occupied and vacant 5f^5/2 states of neighboring actinide atoms were evaluated on the base of the ground state and the excited state calculations. It is found that in UO₂ and PuO₂ the energy difference between 5f^5/2 levels of nearest metal sites in the lattice are close to 1.0 eV and 0.9 eV, despite the results of conventional band structure approach predicting that both oxides are good conductors.     

Density functional theory study of H,C and O chemisorption on UN(001) and(111) surfaces

We performed density functional theory calculations of H, C, and O chemisorption on the UN(001) and(111) surfaces using the generalized gradient approximation(GGA) and the Hubbard U parameter and revised Perdew-Burke-Ernzerhof(RPBE) exchange-correlation functional at non-spin polarized level with the periodic slab model. Chemisorption energies vs. distance of molecules from UN(001) and UN(111) surfaces have been optimized for four symmetrical chemisorption sites, respectively. The results show that the Hollow, N-top, and Hollow adsorption sites are the most stable sites for H, C, and O atoms with chemisorption energies of 13.06,25.50 and 27.34 kJ/mol for UN(001) surface, respectively. From the point of adsorbent(UN(001) and UN(111)surfaces in this paper), interaction of O with the chemisorbed surface is of the maximum magnitude, then C and H, which are in agreement with electronegativities of individual atoms. For the UN(001) surface, U-N bond lengths change relatively little( 9%) as a result of H chemisorption, however C and O chemisorptions result in remarkable changes for U-N bond lengths in interlayer( 10%). Electronic structure calculations indicate that Bridge position is equivalent with Hollow position, and the most stable chemisorption position for H, C,and O atoms are all Bridge(or Hollow) position for the UN(111) surface. Calculated electronic density of states(DOSs) demonstrate electronic charge transfer between s, p orbitals in chemisorbed atoms and U 6d, 5f orbitals.     

低能氦等离子体低温条件下钨材料的表面形貌

为研究氦等离子体在钨表面造成的表面纳米结构,利用荷兰基础能源研究所Pilot-PSI直线等离子体发生装置在673 K温度下,对钨材料进行了低能（40 eV）高束流强度（4×10²³ m^-2•s^-1）氦等离子体辐照。实验结果表明,辐照后钨材料表面出现了多种不同形态的纳米结构,表面纳米结构和晶粒的表面法向之间存在明显关联。在表面法向为［111］的晶粒表面出现三角形的纳米结构,在［110］取向的晶粒表面出现条带状的纳米结构,而在［001］取向的晶粒表面没有明显的结构出现。晶粒表面的纳米结构尺寸在50 nm左右,高度起伏在5 nm以下。另外,氦等离子体辐照会造成晶界处的高度差,在25 nm左右。分析推测氦等离子体辐照造成的晶粒表面和晶界的形貌可能是由近表面的气泡所导致的。     

Synthesis of Cu-Doped Mixed-Phase TiO2 with the Assistance of Ionic Liquid by Atmospheric-Pressure Cold Plasma

An atmospheric-pressure dielectric barrier discharge(DBD) gas-liquid cold plasma was employed to synthesize Cu-doped TiO_2 nanoparticles in an aqueous solution with the assistance of[C_2MIM]BF_4 ionic liquid(IL) and using air as the working gas.The influences of the discharge voltage,IL and the amount of copper nitrite were investigated.X-ray diffraction,N_2adsorption-desorption measurements and UV-Vis spectroscopy were adopted to characterize the samples.The results showed that the specific surface area of TiO_2 was promoted with Cu-doping(from 57.6 m~2·g~(-1) to 106.2 m~2·g~(-1) with 3%Cu-doping),and the content of anatase was increased.Besides,the band gap energy of TiO_2 with Cu-doping decreased according to the UV-Vis spectroscopy test.The 3%Cu-IL-TiO_2 samples showed the highest efficiency in degrading methylene blue(MB) dye solutions under simulated sunlight with an apparent rate constant of 0.0223 min~(-1),which was 1.2 times higher than that of non-doped samples.According to the characterization results,the reasons for the high photocatalytic activity were discussed.     

Energy loss in grazing proton-surface collisions

The energy loss of fast protons, with energy E>100 keV, specularly reflected on a solid surface with glancing angle of incidence of the order of a mrad is analysed on theoretical grounds. Two different contributions can be distinguished: i) energy losses originating from the interaction with the valence band, accounted for through an induced force, and ii) the excitation of electron bound states of the target atoms. The results are compared with available experimental data.     

O2在UC(001)表面吸附的第一性原理研究

本文使用GGA+U方法研究了O₂在UC(001)表面的吸附、解离过程。结果表明：U_eff=1.5 eV能很好地再现晶格常数a和内聚能E_coh的实验结果;经过离子弛豫,最表面的两个原子层出现分层现象,各自形成两个亚层;O₂分子的吸附构型对吸附过程影响较大,吸附能在2.21～8.55 eV之间变化。通过Bader电荷、差分电荷和态密度分析,可确定O₂分子的解离活化机理为U的5f/6d电子转移至O₂的π2p和π*2p轨道。     

Broadening effects in Auger neutralization of 130–430 eV Ar ions at Al surfaces

We present a model for electron emission from Al surfaces by Auger neutralization of 130–430 eV Ar⁺ ions, that includes the singular response of the metal conduction band to the abrupt change of the surface potential caused by electron capture by the incident ion. This effect, previously identified in X-ray studies, produces a broadening that plays a significant role in reproducing the higher energy part of the experimental electron kinetic energy distributions.     

镧系裂变产物（La、Ce、Pr和Nd）在α-U表面偏析行为的第一原理研究 #br#

镧系裂变产物引起的燃料肿胀及包壳脆化是UZr金属燃料服役中的主要问题。其快速扩散通常借助于裂变气体释放通道,实验可观察到镧系裂变产物会在UZr金属燃料氙气泡处偏析。为理解裂变产物扩散机理及表面偏析现象,本文采用第一原理方法,对低温α-U中（100）、（112）、（001）、（021）、（110）、（010）表面的原子结构及形成能进行了研究,并讨论了常见镧系裂变产物La、Ce、Pr和Nd在不同表面的偏析行为。计算结果表明,（110）表面的形成能最低,为1.75 J/m²,（112）、（021）和（001）表面的形成能次之,为1.81~1.83 J/m²,（010）和（100）表面的形成能最高,分别为1.96 J/m²和2.04 J/m²。4种裂变产物在6种表面都表现出明显的偏析效应,对于同一种表面,其偏析驱动力排序为：La>Ce>Pr>Nd。对于同一种镧系裂变产物,偏析能随层间距的增加而减小。此外,采用Mc-Lean方程从热力学上评估了4种裂变产物在α-U表面的占据率,结果表明在服役温度范围内,4种镧系裂变产物均表现出明显的表面偏析。