Yb2.75C60价带光电子能谱

用角积分紫外光电子能谱技术测量了Yb_2.75C₆₀薄膜的价带电子态密度分布.相纯Yb_2.75C₆₀样品通过C1s芯态x射线电子谱峰的位移表征.结果表明Yb_2.75C₆₀是半导体，在费米能级处几乎没有电子态分布.Yb 6s电子态和C₆₀LUMO能带的杂化效应不可忽略，有部分Yb 6s电子分布在Yb-C₆₀杂化能带上. 关键词： 2.75C₆₀')" href="#">Yb_2.75C₆₀ 电子能谱 电子态密度     

DSC study of annealing and phase transformations of C60 and C70 polymerized under pressures in the range 9.5-13 GPa

C₆₀ and C₇₀ fullerenes polymerized under pressures between 9.5 and 13 GPa and temperatures between 670 and 1850 K were investigated by differential scanning calorimetry (DSC) in the range 240-640 K. Endothermal heat effects were observed with a peak maximum just below 540 K, a temperature characteristic for breakdown of (2+2) intermolecular links in dimers, 1D and 2D polymers. Exothermal effects, starting from 380 K, were observed for the first time in polymeric fullerenes. These effects are attributed to relaxation processes and to breakdown of other types of intermolecular bonds such as common four-sided rings and (3+3) interlinks.     

Metallic Rb4C60 and Rb5C60 on the top layer of C60 single crystal

Photoemission studies reveal the existences of metallic Rb₄C₆₀ and Rb₅C₆₀ surface phases on the top layer of C₆₀ single crystal. After Rb₃C₆₀ thin film with thickness of nanometers has formed on the (1 1 1) surface layers of the C₆₀ single crystal, the excess deposition of Rb atoms do not induce the bulk-like face-centered cubic to body-centered tetragonal or body-centered cubic structure transitions at room temperature. The large size of C₆₀ molecule offers the surface vacancies for the formation of Rb₄C₆₀ and Rb₅C₆₀ monolayer that is further verified by Rb 3d core-level photoemission measurements. Valence band photoemission results exhibit the surface phases are metallic.     

RHEED observation of BaTiO3 thin films grown by MBE

Ferroelectric BaTiO₃ thin films with a thickness of 10 monolayers (ML) were epitaxially grown on SrTiO₃(0 0 1) substrates by very slow deposition using molecular beam epitaxy (MBE). The investigations were carried out by two growth methods: (i) codeposition and (ii) alternate deposition of the metal elements in an oxygen atmosphere. In situ observation of reflection high-energy electron diffraction confirmed that an epitaxial cube-on-cube structure was prepared. After the deposition, X-ray diffraction measurements were carried out. The 10-ML-thick BaTiO₃ films were highly c-axis oriented single crystals with good film quality.     

The structure of C60 and endohedral C60 on the Si{1 0 0} surface

The possible structures of C₆₀ on the Si{1 0 0} surface in the four dimer position over the dimer trench have been investigated using ab initio total energy minimisations. Four possible structures have been found. The fullerenes bond to the silicon surface by breaking carbon–carbon double bonds. One electron from the broken bond is contributed to the carbon–silicon bond. The second electron is involved in forming a new π-bond within the fullerene cage. The carbon–silicon bond is primarily covalent with some charge transfer. Some discussion of endohedral fullerenes is also given.     

X-ray photoelectron and X-ray Auger electron spectroscopy studies of heavy ion irradiated C60 films

The influence of 200 MeV Au ion irradiation on the surface properties of polycrystalline fullerene films has been investigated. The X-ray photoelectron and X-ray Auger electron spectroscopies are employed to study the ion-induced modification of the fullerene, near the surface region. The shift of C 1s core level and decrease in intensity of shake-up satellite were used to investigate the structural changes (like sp² to sp³ conversion) and reduction of π electrons, respectively, under heavy ion irradiation. Further, X-ray Auger electron spectroscopy was employed to investigate hybridization conversion qualitatively as a function of ion fluence.     

Studies on sprayed lanthanum sulphide (La2S3) thin films from non-aqueous medium

Thin films of lanthanum sulphide (La₂S₃) have been deposited onto glass substrates by spray pyrolysis technique from non-aqueous (methanol) medium. The structural, morphological, optical, dielectric, electric and thermoemf properties were studied. The films were polycrystalline with an irregular shaped particles present over the porous structure within a fibrous network structure. The optical band gap was estimated to be 2.50 eV. The dielectric properties were measured in the range 100 Hz-1 MHz. The electrical resistivity was of the order of 10⁴ to 10⁵ Ω cm. Thermoemf study revealed that the La₂S₃ films exhibit p-type electrical conductivity.     

Giant fullerenes formed on C60 films irradiated with electrons field-emitted from scanning tunneling microscope tips

It has been found that spherical large clusters of carbon atoms are formed by irradiation of crystalline C₆₀ films grown on Si(1 1 1)-(7 × 7) surfaces with electrons field-emitted from a scanning tunneling microscope probe tip. The size distribution of the clusters deduced from surface profile measurements suggests that the dominant clusters were not necessarily C_60n (n = 2-4) expected from the simple fusion of C₆₀ molecules. It was proposed that electronic excitations of C₆₀ molecules caused the fragment and coalescence of the molecules to form the giant fullerenes as in the photo-induced similar effects.     

Structural evolution of low-pressure polymerised C60 with polymerisation conditions

We show in this paper that characteristic features in the Raman spectra, especially the frequency of the pentagonal pinch mode, can give information about the polymeric structure of pressure polymerised C₆₀. High-pressure treatment at 1 GPa below 510 K for 3 h results in the formation of a low fraction of dimers only, while treatment at the same pressure and time above 540 K affords a fully polymerised material. In the latter case, different relative fractions of dimers and polymer chains are obtained depending on whether the final reaction conditions were reached by isobaric or isothermal path. We suggest that this difference results from different reaction dynamics in the two cases. The polymerisation rate depends on T and p and on the rotational and orientational states of the molecules. At 1 GPa no polymerisation is observed in sc C₆₀, while in “hexagon” oriented sc C₆₀ at 1.7 GPa dimers are already formed 175 K below the fcc–sc transition and a fully polymerised material is obtained just below the transition to the fcc phase.     

Raman microprobe spectroscopy measurements of residual stress distribution along blisters in Cr2O3 thin films

Raman spectroscopy has been used to characterise the buckling phenomenon of Cr₂O₃ films obtained by oxidation in air at 900 °C of Ni33 at%Cr. The observed circular blisters are described by measuring the radius from the optical top view, the profile via an autofocus device and the residual stress in each point of the chromia film: far away from the centre of the blister, in the vicinity and across the blister. The subsequent spalls are related to the morphology of the blisters and to the stress.     

ConC3-/0和ConC4-/0(n=1~4)团簇的结构和电子特性:尺寸选择的负离子光电子能谱和密度泛函理论研究

We investigated the structural evolution and electronic properties of Co_nC₃^-/0 and Co_nC₄^-/0 (n=1-4) clusters by using mass-selected photoelectron spectroscopy and density functional theory calculations. The adiabatic and vertical detachment energies of Co_1-4C₃^- and Co_1-4C₄^- were obtained from their photoelectron spectra. By comparing the theoretical results with the experimental data, the global minimum structures were determined. The results indicate that the carbon atoms of Co_nC₃^-/0 and Co_nC₄^-/0 (n=1-4) are separated from each other gradually with increasing number of cobalt atoms but a C₂ unit still remains at n=4. It is interesting that the Co₂C₃^- and Co₂C₄^- anions have planar structures whereas the neutral Co₂C₃ and Co₂C₄ have linear structures with the Co atoms at two ends. The Co₃C₃^- anion has a planar structure with a Co₂C₂ four-membered ring and a Co₃C four-membered ring sharing a Co-Co bond, while the neutral Co₃C₃ is a three-dimensional structure with a C₂ unit and a C atom connecting to two faces of the Co₃ triangle.     

Effect of Ga incorporation on valence band splitting of OVC CuIn3Se5 thin films

Polycrystalline thin films of CuIn_2.95Ga_0.05Se₅ produced by the incorporation of Ga into the ordered vacancy compound CuIn₃Se₅ by a two-stage vacuum evaporation process were structurally, compositionally and optically characterized using X-ray diffraction, energy dispersive analysis of X-rays and optical absorbance measurements. From the X-ray diffraction data of the films, the structural parameters like lattice constants, tetragonal deformation, bond lengths and anion displacement were evaluated and their effect on the optical behavior of films was discussed. The Hopfields quasi-cubic model adapted for chalcopyrites with tetragonal deformation was used to elucidate the crystal field and spin orbital splitting parameters in the uppermost valence band of the compound, using the three energy gaps 1.649, 1.718 and 1.92 eV corresponding to the threefold absorption in the fundamental absorption region of the optical spectra of these films. The percentage contributions of Se p and Cu d orbitals to p-d hybridization in this compound were calculated using linear hybridization of orbitals model and the effects of p-d hybridization on the band gaps were studied.     

Core level and valence band studies of layered Ti3SiC2 by high resolution photoelectron spectroscopy

The ternary compund Ti₃SiC₂ is a prominent representative of a new class of layered ceramics whose extraordinary physical properties has attracted much attention in recent years. Ti₃SiC₂ is electrically and thermally highly conductive, elastically rigid, lightweight, and maintains its strength to high temperatures. It is furthermore damage tolerant and oxidation resistant. We have studied fractured surfaces of coarse-grained Ti₃SiC₂ by means of photoelectron spectroscopy at the MAX-lab synchrotron radiation facility in Lund, Sweden. High-resolution C 1s, Si 2p, Ti 2p, Ti 3s and Ti 3p core-level spectra are reported and interpreted in terms of crystallographic and electronic structure. Valence band spectra confirm the validity of recent band calculations.     

Growth of β-MnO2 films on TiO2(110) by oxygen plasma assisted molecular beam epitaxy

We have used oxygen plasma assisted MBE to grow epitaxial films of pyrolusite (β-MnO₂) on TiO₂(110) for thicknesses of one to six bilayers (BL). We define a bilayer to be a layer of Mn and lattice O and an adjacent layer of bridging O within the rutile structure. The resulting surfaces have been characterized in situ by reflection high-energy electron diffraction, low-energy electron diffraction, X-ray photoelectron spectroscopy and diffraction, and atomic force microscopy. Well-ordered, pseudomorphic overlayers form for substrate temperatures between 400 and 500°C. Mn–Ti intermixing occurs over the time scale of film growth (1 BL/min) for substrate temperatures in excess of 500°C. Films grown at 400–500°C exhibit island growth, whereas intermixed films grown at temperatures of 500–600°C are more laminar. 1 BL films grown at 450°C are more laminar than multilayer films grown at the same temperature, and form a well-ordered surface cation layer of Mn on the rutile structure with at most 10% indiffusion to the second cation layer.     

Electronic conduction properties of Au/C60/p-Si and C60/Au/p-Si sandwich structures: I–V and transducer characteristics

Gold-fullerite [C₆₀]-silicon (p-type) sandwich structures have been fabricated in order to investigate intrinsic cross-sectional and planar electronic conductive properties, in particular the C₆₀/p-Si p–n heterojunction. The turn-on voltage of this p–n heterojunction lies in the range 0.25–0.27 V. The I–V characteristics of the Au/C₆₀/p-Si structure are mostly defined by the bulk specific resistance of the fullerite crystal film itself (6×10⁷ Ω cm). I–V curves in the C₆₀/Au/p-Si structure are shown to be ohmic. Au/C₆₀/p-Si sandwiches irradiated with swift (300 MeV) heavy ions, (⁸⁴Kr¹⁴⁺) to a total fluence 10¹⁰ ion/cm² yield structures which are sensitive to ambient air pressure, specifically in the case of a transverse contact configuration, and if one of the contacts is located on the irradiated part of the fullerite film. The sandwich-structure sensitivity to pressure is 5×10⁻⁶ Pa⁻¹. This exceeds the sensitivity of conventional silicon pressure transducers by almost three orders of magnitude.     

X-ray diffraction,differential scanning calorimetric and spectroscopic studies of phase transitions in the bidimensional compound (C12H25NH3)2CdCl4

The existence of three main crystalline phases (called III, II and I) in (C₁₂H₂₅NH₃)₂CdCl₄ has been revealed by differential scanning calorimetry. X-ray diffraction and spectroscopic studies. The crystal- lographic evolution with increasing temperature appears to be monoclinic (III) → orthorhombic (II) → tetragonal (I). The low temperature phase III is the only ordered structure. The phase transition (III-II), which is of first order type, corresponds to an order-disorder mechanism involving the organic part of the structure (alkylammonium chains) whereas the phase transition (II-I), which is of second-order type, is related to the arrangement of the mineral matrix (octahedra of perovskite layers). An intermediate disordered form II', stable in a very narrow temperature range and structurally similar to the form II, has also been observed, so that the transformation (III-II) proceeds, in fact, in two steps (III-II'-II). The variation enthalpies observed at the transitions (III-II'-II) and analyzed through an order-disorder mechanism demonstrate the high disorder of the alkylammonium chains in form II, in agreement with spectroscopic results. No thermal anomaly or spectroscopic modification is observed for the high temperature transition (II-I).     

Photoelectron diffraction study of a catalytically active overlayer: C2H2 on Pd{111}

A quantitative structure determination of a newly discovered (2×2) adsorption phase of acetylene chemisorbed on Pd{111} has been performed by scanned-energy mode photoelectron diffraction: this phase corresponds to the threshold coverage for the catalytic conversion of acetylene to benzene. The carbon atoms in the C₂H₂ molecule are located almost over bridge sites with a C–C bond length of 1.34+0.10 Å, the centre of the molecule being positioned almost over a hollow site. Of the two hollow sites the hcp site (directly above a second layer Pd atom) is favoured, particularly by a subset of the data most sensitive to this aspect of the structure, but the full analysis indicates that the fcc site (above a third layer Pd atom) cannot formally be excluded. The adsorption site adopted by acetylene in the higher coverage phase on Pd{111} is essentially identical. This is the dominant structure in the coverage regime which is catalytically active for the conversion of acetylene to benzene. The implications of these findings for acetylene coupling reactions over Pd{111} are discussed.     

Gold cluster formation on C60 surfaces observed with scanning tunneling microscopy: Au-cluster beads and self-organized structures

The growth mechanism of Au-clusters on fullerene layers has been investigated by scanning tunneling microscopy in ultrahigh vacuum at room temperature. The fullerene layers, which serve as substrates, are formed on a graphite surface and exhibit the typical combination of round and fractal shapes, and small sections of the original graphite substrate are exposed. The immobile Au-clusters are concentrated on the C₆₀ terminated surface section, and the original fullerene island structures are preserved. A preferential nucleation of Au-clusters is observed at the C₆₀-graphite edges while the C₆₀-C₆₀ edges remains undecorated. These Au-clusters are placed directly on the edge and shared by the graphite and fullerene layer. They form bead-like structures, which densely populate this edge, while the first layer C₆₀ islands are clearly depleted of Au-clusters. A roughness analysis of the fullerene surface indicates the presence of Au atoms (or very small clusters), which are embedded in the fullerene surface, and likely situated in the troughs in between the large molecules. These Au atoms are highly mobile and cannot be individually resolved at room temperature. The analysis of the spatial and size distributions of Au-clusters provides the basis for the development of a qualitative model, which describes the relevant surface processes in the Au-fullerene system. The simultaneous deposition of Au and fullerene on graphite leads to the formation of highly organized structures, in which Au-clusters are embedded in a ring of fullerene molecules with a constant width of about 4 nm. The mechanism for the formation of these structures is highly speculative at present and further experiments will be pursued in the near future. A comprehensive analysis of the Au-C₆₀ system is presented, which contributes to the advancement in our understanding of the metal-fullerene interaction and furthers the development of composite materials of interest in the synthesis of solar cells and metal contacts to organic materials.     

Spectroscopic and X-ray diffraction study of high Tc epitaxial YBCO thin films obtained by pulsed laser deposition

We report spectroscopic characterization of epitaxial YBCO thin films grown on LaAlO₃ by pulsed laser deposition. Raman spectroscopy and spectroscopic ellipsometry were used for film characterization and the results were correlated with X-ray diffraction measurements. The mentioned techniques allowed us to analyze crystallographic, micro-structural, and morphological properties of YBCO thin films. We also demonstrated that relatively low resolution Raman spectroscopy and spectroscopic ellipsometry are reliable techniques for a rapid and non-destructive characterization of epitaxial YBCO thin films.