1,720,990 research outputs found
The evolution of benzenethiol self assembled monolayer on the Cu(100) surface
No full textBenzenethiol (C6H5SH) adsorption on the Cu(100) surface at room temperature has been studied using high resolution UV photoelectron spectroscopy (HRUPS), low energy electron diffraction (LEED) and work function change . Benzenethiol reacts with the copper surface, forming an S–Cu bond and an ordered thiolate layer. Two subsequent phases of the self-assembled monolayer formation have been clearly identified as a function of exposure. At low coverage, a c (4 x 4) reconstruction is observed in the LEED pattern, and the valence photoemission signals are consistent with flat molecular arrangement on the Cu(100) surface, where the phenyl group interacts via the p orbitals. At higher coverage, the LEED pattern shows a high density phase with c (2 x 6) symmetry; in the photoemission spectra the signals coming from the molecular orbitals localized on the benzene ring closely resemble the features observed in the gas phase spectra, thus suggesting an upright position of the molecule
Anchoring methane-thiol on Cu(100) in different structural configurations: electronic state dispersion
No full textMolecular orientation of 2-mercaptobenzoxazole adsorbed on Cu(1 0 0) surface
No full textThe long range ordered p(2 × 2) self-assembled monolayer formed by dosing 2-mercaptobenzoxazole (MBO, C7H5NOS) on the Cu(1 0 0) surface at room temperature has been investigated by means of near edge X-ray adsorption fine structure (NEXAFS) technique at the sulphur K-edge. NEXAFS S–K-edge spectra have been recorded at different incident photon angles with respect to the Cu(1 0 0) surface, using linearly polarised synchrotron radiation. A clear spectral feature has been observed close to the absorption edge, with higher intensity at grazing incidence, assigned to the σ*(S–C) resonance, corresponding to the transition from the S 1s core level to the σ*(S–C) antibonding molecular state. The angular dependence of the σ*(S–C) resonance intensity clearly indicates that the S–C axis is nearly perpendicular to the surface (13° ± 13°), confirming the major role of S in bonding to the surface, and the influence of the π–π interaction between the molecules in driving the almost upright position at saturation coverage
Effect of thermal treatment on morphology and electrical transport properties of carbon nanotubes film
No full textCarbon nanotubes have been synthesised with high density on a large area of platinum pre patterned layer of silicon nitride solid substrate by means of chemical vapour deposition of acetylene at 500 C in ammonia ambient. The effect of the microwave induced thermal annealing, in atmospheric air, on the morphology and electrical transport properties of nanotubes films has been evaluated. At increasing annealing time the thermal treatments leads to a progressive reduction of the nanotubes' mean diameter and to a dramatic change in the electrical conductivity of the film. Such modifications have been directly attributed to a strong reduction of the amorphous carbon amount as a consequence of the thermal annealing by microwave
Mn doping of germanium nanowires by vapour-liquid-solid deposition
No full textGermanium nanowires doped with manganese have been synthesized by thermal co-evaporation of Ge and Mn powders onto silicon oxide substrates with Au catalyst nanoparticles. Scanning electron microscopy images show a uniform and highly dense distribution of germanium nanowires with typical diameter and length of 40 nm and few tenths of micron respectively. Transmission electron microscopy and X-ray diffraction indicate that the nanowires are single crystals grown along the [100] axis. Energy dispersive X-ray results demonstrate the effectiveness of Mn doping of the nanowires
Tuning electromechanical response of individual CNT by selective electron beam induced deposition
No full textCarbon nanotubes have been recognized as one of the most promising materials for developing nanoelectromechanical systems. In particular, the electron beam induced deposition (EBID) process of amorphous carbon under scanning electron microscopy (SEM) represents a very well known and suitable technique for the realization of a stable mechanical and electrical contact between CNTs and the supporting material. Within this context, the effect of the EBID process on the electromechanical response of an individual multiwalled CNT was directly investigated by using a piezoelectric nanomanipulation system operating inside an SEM chamber. The experimental system ensures a high control capability on the geometric parameters of the as fabricated cantilevered CNT based structure, thus allowing a precise modelization of the electrostatic CNT deflection process. The amorphous carbon coating was found to produce a variation of the mechanical response of the CNT cantilevered system, suggesting the use of EBID under SEM as an effective method for tuning the electromechanical properties of single CNT based nanostructures. (C) 2010 Elsevier B.V. All rights reserved
3D island growth of 6,13 Pentacenequinone on silicon oxide and gold
No full textWe investigated the morphological and structural properties of 6,13 Pentacenequinone thin films (5-50 nm) grown by vacuum thermal evaporation on SiO(2) substrates with pre-patterned gold electrodes at room temperature using atomic force microscopy, scanning electron microscopy and X-ray diffraction. The X-ray diffraction always revealed the coexistence of two different crystalline phases, namely the bulk crystal phase and the thin film phase. A comparison of the diffraction data with atomic force microscopy and scanning electron microscopy measurements allowed assigning needle-like (compact) crystallites to the thin film (bulk) phase. The needle-like crystallites started to grow on flat two-dimensional islands lying on an initial wetting layer of Pentacenequinone. This is observed both on the bare silicon oxide substrate and on the polycrystalline gold electrodes. (C) 2010 Elsevier B.V. All rights reserved
In situ manipulation and electrical characterization of multiwalled carbon nanotubes by using nanomanipulators under scanning electron microscopy
No full textThe results of in situ manipulation and electrical transport characterization of individual multiwalled carbon nanotubes (MWCNTs) grown on a nickel tip by using a piezoelectric nanomanipulation system operating in a scanning electron microscope chamber have been reported. The growth of MWCNT directly on nickel wire by chemical vapor deposition technique ensures good electrical contact with the catalyst substrate. Using the electron beam induced welding, a full characterization of electronic properties of several MWCNTs has been explored without the usual postprocessing methods which may alter, in principle, the intrinsic properties of the carbon nanotube (CNT). Thanks to the high mechanical and electrical stability ensured by the electron beam welding procedure, a detailed study of the modification of CNT electrical transport properties under CNT buckling has been performed. The crucial role played by the structural defects in determining an irreversibility of a long MWCNT I-V characteristic under mechanical stress has been clearly evidenced. Finally, by a proper sequence of CNT/tip welding and movement, the potential in creating an Ohmic junction between two nanotubes has been demonstrated, opening the route to a systematic investigation of one of the most fundamental aspect of CNT physics
Self-assembly of an aromatic thiolate on Cu(1 0 0): the local adsorption site
No full textThe long-range ordered p(2 × 2) self-assembled monolayer formed by dosing 2-mercaptobenzoxazole (MBO, C7H5NOS) on the Cu(1 0 0) surface at room temperature has been structurally characterised by means of normal incidence X-ray standing wavefield absorption (NIXSW) at both (2 0 0) and (1 1 1) reflections. The results show that the S atom, through which the adsorbed molecular thiolate species bonds to the surface, has an interlayer spacing of 1.33 ± 0.05 Å relative to the extended bulk scatterer planes (2 0 0) parallel to the surface and occupies the four-fold coordinated hollow site, with no evidence of major reconstruction. These results are entirely consistent with previous findings for a number of thiolates formed on (1 0 0) noble metal surfaces. The role of the head-group to surface potential corrugation and intermolecular interactions in determining the adsorption site and ordering of this aromatic molecular adsorbate is discussed
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