Ultraviolet Photoelectron Spectra of Mono Metal Atom Encapsulated Fullerenes

Abstract

Ultraviolet photoelectron spectra of mono metal atom encapsulated fullerenes, M@C₈₂ (M = La, Gd and Sc), are measured with a synchrotron radiation light source. When the excitation energy is tuned, spectral intensity oscillation is observed in these mono metal atom encapsulated fullerenes as was in empty fullerene, C₈₂. Their incident photon energy dependence is essentially the same. Their spectra deeper than 5 eV are almost identical and are similar to those of empty fullerene. The noticeable difference among the spectra is in the energy region between the Fermi level and 4 eV, which reveals the degree of electron transfer from the metal atom to the fullerene cage.     

A Spectro-Microscopic Approach for Thin Film Analysis: Grain Boundaries in mc-Si and Sn/SnO2 Nano Particles

 Synchrotron radiation based spectro-microscopy is shown to be an exciting tool for elemental analysis in the field of heterogeneous interfaces, thin films, and device technology. Results are reported, taken with a spectrometer that enables the combination of a photoemission electron microscope (PEEM) with photoelectron spectroscopies (XPS, UPS) operated at a high brilliance undulator beam line at BESSY. The properties of mc-Si (multi crystalline silicon) are of interest because of their applications in low priced photovoltaic devices. An example of how to analyze the surface potentials of such surfaces without removing the native oxide is given. Tin nano-scale particles are shown to be the decisive factor affecting the corrosion prevention of passivated tinplate surfaces.     

The production and oxidation of uranium nanoparticles produced via pulsed laser ablation

Depleted uranium samples were ablated using five nanosecond pulses from a Nd:YAG laser and produced films of ∼1600 Å thickness that were deposited with an angular distribution typical of a completely thermal ablation (cos¹ θ). The films remained contiguous for many months in vacuum but blistered due to tensile stress induced in the films several days after being brought into air. While under vacuum (2 × 10⁻¹⁰ Torr base pressure) the films were allowed to oxidize from the residual gases, of which water vapor was found to be the primary oxidizer. During the oxidation, the samples were monitored with both X-ray and ultraviolet photoemission spectroscopy (XPS and UPS) and were found to oxidize following Langmuir kinetics. That a 2D-surface growth model described the oxidation indicates that, even at these low pressures, oxygen accumulation on the surface is a much faster process than diffusion into the bulk. While bulk diffusion did occur, the oxygen present at the surface saturated the measurements taken using photoemission and diffusion was difficult to observe. A method for determining oxide concentration via photoemission from the valence level, as opposed to the more conventional core levels, is also presented.     

Ultra-thin Si overlayers on the TiO2 (1 1 0)-(1 × 2) surface: Growth mode and electronic properties

The growth of thin subnanometric silicon films on TiO₂ (1 1 0)-(1 × 2) reconstructed surfaces at room temperature (RT) has been studied in situ by X-ray and ultra-violet photoelectron spectroscopies (XPS and UPS), Auger electron and electron-energy-loss spectroscopies (AES and ELS), quantitative low energy electron diffraction (LEED-IV), and scanning tunneling microscopy (STM). For Si coverage up to one monolayer, a heterogeneous layer is formed. Its composition consists of a mixture of different suboxides SiO_x (1 < x ? 2) on top of a further reduced TiO₂ surface. Upon Si coverage, the characteristic (1 × 2) LEED pattern from the substrate is completely attenuated, indicating absence of long-range order. Annealing the SiO_x overlayer results in the formation of suboxides with different stoichiometry. The LEED pattern recovers the characteristic TiO₂ (1 1 0)-(1 × 2) diagram. LEED I-V curves from both, substrate and overlayer, indicate the formation of nanometric sized SiO_x clusters.     

Effects of rubrene mixing on the electronic structures of donor/acceptor interface in organic photovoltaic device

Rubrene mixing has been shown to be an effect mean for enhancing both the open circuit voltage (Voc) and the short-circuit current (Jsc) of copper-phthalocyanine (CuPc)/fullerene (C₆₀) based solar cell. While the increase in Jsc can be readily explained by the additional rubrene absorption and the introduction of a bulk heterojunction; causes for Voc increase are still not clear. The energy offset between the highest occupied molecular orbital (HOMO) level of donor and the lowest unoccupied molecular orbital (LUMO) level of acceptor (HOMO_D-LUMO_A) at the CuPc/C₆₀ interface was found to increase substantially upon rubrene mixing in either side of the interface. As the HOMO_D-LUMO_A is generally considered to limit the Voc, its increase agrees well with the device results. Energy level bending and associated built-in electric fields were also observed and their possible implications to device performance are discussed.     

Study of the bandgap renormalization in Ga-doped ZnO films by means of optical absorption under high pressure and photoelectron spectroscopy

In this paper we investigate the band gap renormalization in heavily Ga-doped ZnO thin films deposited by pulsed laser deposition on C$C$-plane sapphire and mica substrates. Thin films were studied by ultraviolet photoelectron spectroscopy and also by optical measurements under high pressure. The Fermi-level shift, as obtained from ultraviolet photoelectron experiments, exhibits a relatively small and positive shift (about 0.3 eV) with respect to the valence band for increasing electron concentrations up to 10²¹ cm⁻³. The optical gap exhibits a much larger increase (0.6 eV) for the same concentration range. Absorption measurements under pressure show that the pressure coefficient of the optical gap is correlated to the electron concentration in films, decreasing with increasing electron concentration. As a consequence, the contributions of band filling and band renormalization to the optical gap shift can be separated on the basis of the different pressure behavior of the physical parameters involved in each effect.     

Surface Core Level Shifts of Yb Films in the Multilayer,Monolayer and Submonolayer Range

Surface core level shifts in Yb and other rare earth elements, as well as in their compounds, arise from a reduced band width of the 5d band, caused by the reduced coordination at surface sites, with the strength and direction of the shifts depending on the occupation of the 5d band. If the coordination, or more exactly, the local symmetry is considered to be the decisive factor for changing the band width, it is obvious to look for core level shifts even at the interface of two solids. In order to investigate such interface core level shifts, thin Yb films of thicknesses from the multilayer down to the submonolayer range, grown on a polycristalline W substrat, were investigated by photoelectronspectroscopy. It was found, that for decreasing film thicknesses, the ratio of the surface to bulk related 4f intensities increases systematically, and finally, for thicknesses of one up to two monolayers, only the broad, surface related part of the Yb 4f doublet can be observed. For Yb coverages fewer than one monolayer, there is a sudden shift of this remaining doublet towards the Fermi energy, which must result from a reduced occupation of the Yb 5d band due to an electron transfer from Yb to W at the interface.     

N-(2-溴乙基)咔唑与N-乙烯基咔唑的气相HeI紫外光电子能谱与电子结构研究

首次报道了N-(2-澳乙基)咔唑和N-乙烯基咏唑的气相Hel紫外光电子能谱(UPS),借助于Gaussian 94采用RHF/6-3lG基组优化几何构型,并用RHF/6-31G基组计算分子轨道及能级.在对咔唑和N-烷基咔唑系列分子UPS电离能变化规律研究的基础上,对这2个分子的UPS谱带给予指认,并讨论其电子结构.结果表明N-(2-溴乙基)咔唑的UPS谱与N-烷基咔唑的不同之处是在10.295,10.540Ve处出现2个Br原子的孤对轨道;N-乙烯基咔唑的UPS谱带与咔唑的相比,电离能变化的特殊性说明乙烯基与咔唑环共平面.     

系列二羰基化合物的HeI紫外光电子能谱(UPS)及量子化学研究

报道了醌及苯并酸酐等系列二羰基化合物的气相HeI紫外光电子能谱。对各体系利用Gaussian94程序RHF/3-21G进行了构型优化,对得到的优势构型采用STO-6G基组进行了轨道计算。并结合计算结果对各分子体系的UPS谱进行了分析指认。计算结果分析显示:标题化合物的第一个电离峰均是由苯环部分的共轭π键电子电离及羰基的孤对电子电离引起的,且化合物的IP~1值随羰基在HOMO轨道中权重的增大而增大。各化合物的第二、三谱带都与羰基不同类型的孤对电子峰相关联。说明羰基为此类化合物的特征基团。且分子的对称性越高,羰基的孤对电子峰n^-和n^+的平均值越大,分裂值也越大。     

1,2,5-噻二唑衍生物电子结构的紫外光电子能谱研究

首次报导了１,２,５－噻二唑衍生物３－氯－１,２,５－噻二唑（Ａ）和３,４＝二氯－１,２,５－噻二唑（Ｂ）化合物的紫外光电子能谱（ＵＰＳ）,谱带的指认建筑在对谱带形状、相对强度、实验电离能（ＩＰＳ）的分析以对研究分子Ｇａｕｓｓｉａｎ ９４ＳＴ０－６Ｇ从头计算电离能（－ε１）。化合物Ｂ ＵＰＳ谱带的ＩＰＳ比相应的化合物Ａ的ＩＰＳ均你芝归结为Ｂ分子中两个取代Ｃ１原子上电子的拥挤效应。计算的Ｂ的 有量（