Evidence for an alkali-like conduction band in alkali graphite intercalation compounds

The valence bands of pure graphite and several alkali graphite intercalation compounds (AGIC's) were studied by UPS (hv = 21.2 eV). The most significant observation is an intensity peak at the Fermi energy E_F in the intecalation compounds. This peak is mainly due to alkali-like s-states. The density of states at E_F is enhanced by a factor of 30 compared to pure graphite. The alkali-like conduction bands in the first stage AGIC's are similar to those of pure alkali metals.     

Experimental and theoretical study of charge transfer in hydrogen ion scattering from a graphite surface

Ion scattering spectrometry (ISS) with time of flight (TOF) analysis is employed to measure the ion fraction of positively charged hydrogen (H⁺) projectiles scattered from a well characterized highly oriented pyrolitc graphite (HOPG) surface at a 45° scattering angle, various ingoing/outgoing angles and two different incoming energies (4 and 5 keV). In the theoretical approach, the negative ionization probability is calculated by employing a Green's function formalism to solve the dynamic collisional process. Both theoretical and experimental results are analyzed and contrasted. The theoretical negative ion fraction evolution during the collisional process is described in detail.     

13C MAS NMR investigations of alkali doped C60

Results of¹³C MAS NMR measurements of the Rb _x C₆₀ system (x=2.75, 3, 4, 6) and the A₆C₆₀ compounds (A=K, Rb, Cs) are presented. Special attention was paid to sample preparation in order to suppress effects of impurities and lattice defects due to imperfect C₆₀ starting material. The¹³C MAS NMR measurements of the Rb _x C₆₀ system demonstrate the usefulness of this method to reveal valuable information about its phase diagram. The existence of underdoped Rb₃C₆₀ is proved. Well resolved lines in all investigated A₆C₆₀ compounds confirm the orientational order of the C₆₀ ions. An assignment of the signals to the three magnetically inequivalent carbon atom positions in the crystal structure is proposed.     

团簇ConAgm (n +m =13)表面吸附C2H4的第一性原理研究

基于密度泛函理论的第一性原理计算方法,本文对ConAgm(n+m=13)团簇的几何结构进行优化后,研究了C2H4分子在这类团簇的表面吸附行为,讨论了团簇的平均结合能、二阶能量差分、稳定性、DOS以及吸附前后键长的变化情况。结果表明,C2H4在团簇top位的吸附主要为物理吸附,而在face位和bridge位的吸附主要为化学吸附。吸附后,C2H4@Ag13的稳定性高于C2H4@Co13,且在face位吸附时C2H4@Co2Ag11的结构最为稳定。随着Co原子数的增加,团簇中原子间成键能力减弱,而d电子轨道则呈现出较强的相互作用,并导致其向能量相对高处发生转移     

Observation of unfilled electron states in alkali graphite intercalation compounds by secondary electron spectroscopy

The energy position of distinct σ-electron energy bands above the Fermi level has been measured in pure graphite, in a variety of stage 1 alkali intercalation compounds and in several stages of C_xK. Changes of the σ-band gap between occupied and unoccupied states near the Λ-point by a nonuniform shift of the valence- and conduction-bands are small for the heavy alkali graphite intercalation compounds, whereas a change of 1 eV is observed for C₆Li.     

Variable charge transfer and band structure of graphite intercalation compounds: C8nAsF5

Using measurements of oscillatory magnetoresistance, the charge transfer in stage 2 AsF₅-graphite is found to vary over the range f ? 30–45%. By following the change of Fermi surface areas with f, a more precise determination of the band structure is possible. The band parameters are nearly identical to those of pristine graphite.     

Electronic conductivity of AgI using D.C. polarization and charge transfer techniques

A Study of electronic conductivity using the d.c. polarization technique has been carried out in α and β-AgI which shows the former is a hole and the latter an electron conductor. Activation energies of undoped and Cu-doped single crystals and polycrystalline β-AgI were found to be 0.46 eV, 0.34 eV and 0.44 eV respectively and can be related to electron trap depths. The electron transference number ($\text{σ}{}_{\mathrm{\theta }}\text{σ}{}_{\mathrm{t}}$) for polycrystalline β-AgI was found to be 0.008 at 306 K. The activation energy for hole conduction in α-AgI was determined to be 0.97 eV in agreement with previous XPS studies.Transient measurements have also been conducted using the charge transfer technique in double cells of polycrystalline β-AgI. The carrier concentration C_θ and electron mobility μ_θ, have thus been estimated to be 1.8 × $\text{10}{}^{15}\text{cm}{}^3$ and 5.14 × 10^?5$\text{cm}{}^2\text{V}$?sec. respectively at 306 K, while the double layer capacitance was 0.496 $\text{μF}\text{cm}{}^2$.     

Multiple-spin analysis of chemical-shift-selective (13C, 13C) transfer in uniformly labeled biomolecules

Chemical-shift-selective (13C, 13C) polarization transfer is analyzed in uniformly labeled biomolecules. It is shown that the spin system dynamics remain sensitive to the distance of interest and can be well reproduced within a quantum-mechanical multiple-spin analysis. These results lead to a general approach on how to describe chemical-shift-selective transfer in uniformly labeled systems. As demonstrated in the case of ubiquitin, this methodology can be used to detect long-range distance constraints in uniformly labeled proteins.     

C60-聚甲基丙烯酸甲脂复合膜的结构、光学和电荷转移特性

描述了通过溶胶-凝胶法制备的C60-PMMA复合膜的结构、紫外-可见吸收特性、Raman散射特性和红外吸收特性.通过对C60紫外-可见吸收光谱,Raman散射谱和红外吸收谱的实验和理论分析,研究了C60与PMMA之间的电荷转移.     

SiC bonding in ( C 60 ) n Si m clusters

This paper deals with a new type of SiC bonding where silicon atom seems to bridge C₆₀ molecules. We have studied films obtained by deposition of (C₆₀)_nSi_m clusters prepared in a laser vaporization source. Prior deposition, free ionized clusters were studied in a time-of-flight mass spectrometer. Mixed clusters (C₆₀)_nSi_m were clearly observed. Abundance and photofragmentation mass spectroscopies revealed the relatively high stability of the (C₆₀)_nSi _n ⁺ , (C₆₀)_nSi _{n - 1} ⁺ and (C₆₀)_nSi _{n - 2} ⁺ species. This observation is in favor of the arrangement of these complexes as polymers where the C₆₀ cages may be bridged by a silicon atom. Free neutral clusters are then deposited onto substrate making up a nanogranular thin film (≃ 100 nm). The film is probed by Auger and X-ray photoemission spectroscopies, but above all by surface enhanced Raman scattering. The results suggest an unusual chemical bonding between silicon and carbon and the environment of the silicon atom is expected to be totally different from the sp³ lattice: ten or twelve carbon neighbors might surround silicon atom. The bonding is discussed to the light of the so-called fullerene polymerization as observed for pure fullerite upon laser irradiation. This opens a new route for bridging C₆₀ molecules together with an appreciable energy bonding, since the usual van der Waals bonding in fullerite could be replaced by an ionocovalent bond. Such an assumption must be checked in the future by XAS and EXAFS experiments. Received 15 November 2000     

Theoretical study of charge transfer dynamics in collisions of C6+ carbon ions with pyrimidine nucleobases

A two qubit quantum gate, namely the C-phase, has been realized by exploiting the longitudinal momentum (i.e. the optical path) degree of freedom of a single photon. The experimental setup used to engineer this quantum gate represents an advanced version of the high stability closed-loop interferometric setup adopted to generate and characterize 2-photon 4-qubit phased Dicke states. Some experimental results, dealing with the characterization of multipartite entanglement of the phased Dicke states are also discussed in detail.     

Improving the charge transfer performance of Si nanomaterial through C surface modification: A first-principles study

Models of oxidized Si (111) surface under different C coverage were established to study the charge transfer ability of Si nanomaterial from strategy of C surface modification using first-principles calculation. The calculated formation energies show that structures of C surface-modified oxidized Si (111) surface are stable. The electronic properties present that the interaction between C and Si atoms is mainly contributed by the hybridization of C-2p and Si-3p states. And the interaction between C and Si atoms increases firstly and then decreases with the increasing C coverage rate. The transfer charge between C and Si reaches a maximum when C coverage rate is 0.5. We speculate that the conductivity of experimentally prepared Si nanomaterial does not monotonously enhance with the increasing C concentration, which would reach a maximum at a certain C concentration, and then decreases.     

Optical determination of the charge transfer in AsF5-graphite intercalation compounds

Optical reflectance experiments are performed on well-characterized compounds C_8nAsF₅ (n = 1, 2), in the temperature range 10–300 K. The theoretical analysis of the reflectivity spectra within the 2-D model of graphite independent subsystems [1] provides an optical determination of E_F and the charge transfer coefficient which is found independent of temperature.