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1.
In molecular physisorption, beyond attractive and repulsive forces, a third contribution arises from the elastic deformation of the surface. In this paper the dimple appearing on a gold surface upon physisorption of a C60 molecule is studied and its effect on the adsorption energy is evaluated.The depth and shape of the dimple are studied on the basis of the theory of elasticity. The equilibrium equation is solved in the presence of the body forces originating from a suitable Au-C60 interaction potential and the solution for the deformation field is obtained by means of a two-step procedure. In the first step a curl-free deformation field is obtained, which takes the effects of the body forces into account, but generates mismatch of the boundary conditions. In the second step the solution of the equilibrium problem in the absence of body force is generated, which compensates the previous boundary condition violation. Thanks to linearity, the final solution is obtained as the sum of the results of the two steps. An (approximate) iterative scheme is applied for taking the surface deformation into account in imposing that no forces act on the Au surface.When the distance z0 of the centre of the C60 cage from the surface is rather large, the dimple is represented by a bulging surface, but, as the C60 approaches the Au surface, the surface recedes and a well formed dimple appears. The corresponding depth at the mechanical equilibrium position (z0 = 4.8 Å) turns out to be 36.3 pm.  相似文献   

2.
B. Ha  J. H. Rhee  Y. Li  D. Singh  S. C. Sharma   《Surface science》2002,520(3):186-192
The electronic valence band structures of polymerized thin films of C60 and La0.1C60 have been studied by using ultra-violet photoelectron spectroscopy. Additionally, the films have been characterized by using Raman spectroscopy, X-ray photoelectron spectroscopy, and X-ray diffraction. The valence band of the C60 film shows major peaks at binding energies of 2.6, 7.2, 10.3, and 12.6 eV. In the case of the doped film, we observe (i) an additional peak with a binding energy of 13.7 eV, (ii) evidence for redistribution of the density of electronic states due to hybridization between the 5d orbitals of La and the C60 cage, and (iii) significantly higher density of the electronic states near the Fermi energy. The valence band spectra of the doped film are in good agreement with recent results of the density functional theory that support strong hybridization between the d-valence orbitals of La and the C60 cage.  相似文献   

3.
Solid state 19F NMR in the temperature range from 96 to 366 K and room temperature EPR studies of fluorinated buckminsterfullerene C60F58 have been carried out. The temperature dependence of the line width and the spin-lattice relaxation time show hindered molecular motion with the activation energy of ΔEa=1.9 kcal/mol. Neither phase transition nor random rotation of C60F58 have been obtained. The spin-lattice relaxation rate is strongly affected by the presence of paramagnetic centers, namely, dangling C-C bonds yielding localized unpaired electrons. Such broken bonds are caused by C-C bond rupture in a cage-opened structure of hyperfluorinated species.  相似文献   

4.
A new molecular complex of C60 with tetrabenzo(1,2-bis[4H-thiopyran-4-ylidene]ethene), Bz4BTPE C60 (1) has been obtained. The complex has a layered structure in which closely packed hexagonal layers of C60 alternate with the layers composed of Bz4BTPE molecules. The complex has a neutral ground state according to UV-vis-NIR spectrum. It has been found that single crystals of 1 show low ‘dark’ conductivity of σ∼10−10 (Ω cm)−1. A 102 increase in photocurrent has been observed upon illuminating the crystal with white light. Photoconductivity of 1 is sensitive to magnetic field with B0<1 T and increases up to 5% in magnetic field. The photoconductivity spectra of the complex indicate that free charge carriers are generated in the UV-visible range mainly by the Bz4BTPE excitation (the peaks at 622, 562, 472 and 348 nm) with a possible contribution of charge transfer excitations between neighboring C60 molecules (the peak at 472 nm).  相似文献   

5.
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.  相似文献   

6.
Song Guo 《Surface science》2007,601(4):994-1000
Scanning tunneling microscopy (STM) is used to characterize partial monolayers of C60, C70, and C84 adsorbed on the Au(1 1 1) surface at room temperature and under ambient conditions. A high degree of structural polymorphism is observed for monolayers of each of these fullerenes. For C60, three lattice packings are observed, including a previously unreported 7 × 7 R21.8° structure that is stabilized by adjacent surface step defects. For C70, two lattice packings are observed, and analysis of molecular features in STM images allows molecular binding geometry to be determined. In one of the two observed lattice structures, C70 molecules align their long axis along the surface normal, while in the other, molecules align parallel to the surface and along a gold lattice direction. The parallel geometry is also preferred for isolated and loosely packed molecules on the surface. C84 exhibits a large number of lattice orientations and no long-range order, and likely binds incommensurately on Au(1 1 1). Time series of images of partial C70 monolayers show progressive surface modification as a result of perturbation by the STM tip; this is in contrast to the behavior of C60, where alterations in surface structure at room temperature are thermally driven.  相似文献   

7.
We have studied the ultraviolet laser induced desorption of NO/Cr2O3(0001), K/Cr2O3(0001) and the coadsorbate system NO/K/Cr2O3(0001) using resonance enhanced multiphoton ionization spectroscopy for state selective detection of the desorbing species after excitation with nanosecond laser pulses. The goal of our experiments was to study the influence of surface electronic modifications via alkali adsorption on the photodynamics of a simple molecule. The photochemistry of the isolated and the coadsorbate systems is strongly dependent on the coverage of the diverse components. In this paper we shall mainly focus on data for the low coverage regime of potassium. From the two adsorbate species of NO, a chemisorbed and a physisorbed species, we present data of the chemisorbed species. The velocity distributions show a strong dependence on the excitation energy which we interpret on the basis of electron energy loss spectra as being due to surface charge transfer states. This is corroborated with our coadsorption experiments with low coverages of potassium which alter the velocity distributions.  相似文献   

8.
The thermal chemistry of perfluoroethyl iodide (C2F5I) adsorbed on Cu(1 1 1) has been investigated by temperature-programmed reaction/desorption (TPR/D), reflection-absorption infrared spectroscopy (RAIRS), and X-ray photoelectron spectroscopy (XPS). I 4d and F 1s XPS spectra show that dissociative adsorption of C2F5I to form the surface-bound perfluroethyl (Cu-C2F5) moieties occurs at very low temperature (T < 90 K), while the C-F bond cleavage in adsorbed perfluroethyl (Cu-C2F5) begins at ca. 300 K. XPS and TPR/D studies further reveal that the reactions of βCF3αCF2(ad) on Cu(1 1 1) are strongly dependent on the surface coverage. At high coverages (?0.16 L exposure), the adsorbed perfluroethyl (Cu-C2F5) evolves, via α-F elimination, into the surface-bound tetrafluoroethylidene moieties (CuCF-CF3) followed by a dimerization step to form octafluoro-2-butene (CF3CFCFCF3) at 315 K as gas product. The surface-bound (Cu-C2F5) decomposes preferentially, at low coverages (?0.04 L), via consecutive α-F abstraction to afford intermediate, trifluoroethylidyne (CuCCF3), resulting in the final coupling reaction to yield hexafluoro-2-butyne (CF3CCCF3) at 425 K. However, at middle coverages (ca. 0.08-0.16 L exposure), the adsorbed perfluroethyl (Cu-C2F5) first experiences an α-F elimination and then prefers to loss the second F from β position to yield the intermediate of Cu-CF2-CFCu (μ-η,η-perfluorovinyl), which may further evolve into hexafluorocyclobutene (CF2CFCFCF2) at 350 K through cyclodimerization reaction. Our results have also shown that the surface reactions to yield the products, CF3CFCFCF3 and CF3CCCF3, obey first-order kinetics, whereas the formation of CF2CFCFCF2 follows second-order kinetics.  相似文献   

9.
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.  相似文献   

10.
The adsorption of the aromatic amino acid, phenylalanine on a TiO2 rutile (1 1 0) single crystal surface has been investigated with photoemission and NEXAFS (near edge X-ray absorption fine structure) spectroscopy. The results indicate initial adsorption via the carboxylate group in a bidentate configuration with the phenyl ring oriented at approximately 25° to the surface normal. The amino group remains as NH2. Subsequent layers of phenylalanine appear to adsorb as neutral molecules with H-bonding between NH2 and CO groups.  相似文献   

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