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Photoelectron Spectroscopy (PS) and Near-Edge X-ray Absorption Fine Structure (NEXAFS) spectroscopy have been used to investigate the occupied and empty density of states of biphenylene films of different thicknesses, deposited onto a Cu(111) crystal. The obtained results have been compared to previous gas phase spectra and single molecule Density Functional Theory (DFT) calculations to get insights into the possible modification of the molecular electronic structure in the film induced by the adsorption on a surface. Furthermore, NEXAFS measurements allowed characterizing the variation of the molecular arrangement with the film thickness and helped to clarify the substrate-molecule interaction. [ABSTRACT FROM AUTHOR]

The formation of the metal-organic interface depositing gold, by thermal evaporation in ultrahigh vacuum conditions, onto a copper phthalocyanine film has been studied by means of ultraviolet photoemission spectroscopy. The evolution of the valence band spectra and in particular of the highest occupied molecular orbitals (HOMO) and of the Au upper states has been followed as a function of gold film thickness. The HOMO peak position is strongly influenced by the Au deposition, suggesting an n-doping process of the organic film. The gold 6s state behavior indicates the formation of small metal clusters whose size increases as a function of the gold deposited. The doping of the organic film determines a strong reduction of the film ionization energy. [ABSTRACT FROM AUTHOR]

The electronic and structural properties of copper phthalocyanine deposited onto multiwalled carbon nanotubes were studied as a function of the deposition thickness. The valence band and core level spectra were investigated using photoemission spectroscopy. A shift of the organic highest occupied molecular level toward the Fermi level was observed for very thin film, together with a small shift of the nitrogen and copper core level peak positions. Scanning electron microscope images showed the formation of small particles around the nanotubes, forming a thin overlayer decorating the nanotube walls. An x-ray diffraction analysis reported that these particles present both the α and β crystalline phases. [ABSTRACT FROM AUTHOR]

WO3 nanofibers (NFs), with diameter of about 150–200 nm, were grown using the electrospinning technique starting from WCl6 as tungsten source. The NFs were deposited onto a patterned substrate, for gas sensing measurements, and on a silicon substrate, for chemical and structural characterizations. The chemical composition of the NFs was determined by the x-ray photoemission spectroscopy, while high spatial resolution soft x-ray photoemission spectroscopy showed a chemical image of the NF. The gas sensing properties of these NFs were checked towards NO2 and CO, showing a good response for NO2 while no effect was observed for CO. [ABSTRACT FROM AUTHOR]

The adsorption of NO2 molecules on defective multiwalled carbon nanotubes has been studied by soft-x-ray photoemission. The valence band and carbon core-level spectra have been acquired before, during, and after NO2 exposure. The spectra show a reversible decrease of the density of states at the top of the valence band when NO2 molecules are adsorbed on the (carbon nanotubes) CNTs. No shift of the C 1s spectra has been observed. Theoretical calculations, using density-functional theory, have been performed on the CNT+NO2 system, considering semiconducting nanotubes with different diameters and introducing a Stone–Wales [Chem. Phys. Lett. 128, 501 (1986)] defect. The calculation confirms the decrease of the density of states at the top of the valence band in the CNT+NO2 system, while close to the adsorption site new states appear very close to the Fermi level. [ABSTRACT FROM AUTHOR]

The electronic structure of copper-phthalocyanine (CuPc) has been studied both experimentally and theoretically. Experiments have been performed on α and β crystalline phases, using photoemission spectroscopy to probe core levels and valence band spectra. Different photon energies have been used, in order to probe different sample depths. Only minor differences have been observed in the experimental data on the two different phases, except for a small charge effect on the β phase crystal. First-principles calculations have been performed using the density functional for molecular and three-dimensional periodic solids (Dmol3) code on both the single CuPc molecule and the β phase, allowing the identification of the different atomic and angular contributions to the experimental density of states. In particular, the highest occupied molecular level is mainly due to Cu and N states. The comparison between theoretical data obtained for the CuPc in the β phase and in the single molecule shows that the interchain interaction between the molecules is negligible, whereas slightly stronger intrachain interactions occur. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

First-principles calculations within the density functional theory have been performed in order to investigate ozone adsorption on carbon nanotubes. Particular emphasis is placed on the effects of Stone–Wales-like defects on the structural and electronic properties of (i) ideal tubes and (ii) tubes in the presence of ozone. Our results show that structural deformations induced on the pure carbon nanotubes by Stone–Wales defects are similar, as expected, to those induced on graphite; for the (10,0) tube, the semiconducting character is kept, though with a small reduction of the band gap. As for the ozone adsorption, the process on ideal nanotubes is most likely physisorption, though slightly stronger if compared to other previously studied molecules and consistent with the strong oxydizing nature of O3. However, when ozone adsorbs on Stone–Wales defects, a strong chemisorption occurs, leading to relevant structural relaxations and to the formation of a CO covalent bond; this is consistent with experimental observations of CO functional groups, as well as of the liberation of CO gas phase and of the formation of C vacancies, thus explaining the consumption of the nanotube film upon ozone exposure. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

In this work a combined experimental and theoretical study on carbon nanotube (CNT) based system for gas sensing applications is reported. Carbon nanotubes thin films have been deposited by plasma-enhanced chemical vapor deposition on Si[sub 3]N[sub 4]/Si substrates provided with Pt electrodes. Microstructural features as determined by scanning electron microscopy, transmission electron microscopy, and Raman spectroscopy highlight the growth of defective tubular carbon structures. The electrical resistivity of the CNT film shows a semiconductinglike temperature dependence and a p-type response with decreasing electrical resistance upon exposure to NO[sub 2] gas (100 ppb). No response has been found by exposing the film to CO gas in the temperature range between 25 and 250 °C. In order to obtain a theoretical validation of the experimental results, the equilibrium position, charge transfer, and density of states are calculated from first principles for the CNT+CO and CNT+NO[sub 2] systems. Our spin-unrestricted density functional calculations show that NO[sub 2] retains its spin-polarized state upon adsorption. Both CO and NO[sub 2] molecules adsorb weakly on the tube wall, with essentially no charge transfer between the tube and molecules. The electronic properties of CNTs are sensitive to the adsorption of NO[sub 2], due to an acceptorlike peak close to the tube valence-band maximum, while they are insensitive to the CO adsorption. According to the experimental findings, our theoretical results suggest that gas-induced modification of the density of states close to the Fermi level might significantly affect the transport properties of nanotubes. © 2003 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The growth behavior of carbon nanotubes (CNTs), produced by radio frequency plasma enhanced chemical vapor deposition, is studied here as a function of the CH[SUB4]/N[SUB2] ratio and Ni catalyst layer thickness. Scanning electron microscopy shows that by employing a suitable deposition (methane) to etching (nitrogen) gas fatio, it is possible to obtain the growth of nanotubes with a limited presence of amorphous carbon on the substrate surface. In particular a progressive transition from random to aligned CNTs is observed when nitrogen is added to the plasma atmosphere. The electronic structure was then investigated by C Is and valence band photoemission spectroscopy. The results show a shift of the overall spectral to a higher-binding-energy side and a larger density of the states at the Fermi level indicating the formation of metallic aligned tubes with increasing nitrogen fraction in the plasma atomsphere. The electronic structure indicates the insertion of odd-member rings in the graphene network leading to an improvement ofthe mechanical properties. The thickness of the Ni layer has a strong influence on the CNTs growth showing maximum value for nanotube formation at 20 nm. [ABSTRACT FROM AUTHOR]

Hydrogenated amorphous carbon (a-C:H) films were deposited, at room temperature, from a CH[sub 4]/Ar plasma produced by a radio frequency (rf) glow discharge system at 13.56 MHz, and different power values. X-ray reflectivity and Brillouin light scattering have been used to investigate the relationship between deposition conditions and elastic properties of hydrogenated amorphous carbon films. The composition of the initial gaseous mixture and the rf power input are shown to affect significantly both the mechanical and the microstructural properties of deposited films. As the fraction of methane in the feed gas is increased, both the film density and the phase velocity of the surface Rayleigh wave exhibit an enhancement, thus indicating the production of a harder material. On the other hand, x-ray reflectivity measurements suggest the occurrence of a higher degree of structural order in the sp[sup 2] lattice. Experimental findings are discussed in terms of the different chemical composition of the plasma. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Improving the quality factor (Q) of electromechanical resonators is of paramount importance for different applications, ranging from RF filtering to sensing. In this paper, we present a modified fabrication process flow for contour mode resonators to simultaneously obtain the (i) Q insensitive to the Si undercut geometry and (ii) in-phase reflectors for anchor loss control and Q optimization. To assess the potential of the reflector, we vary its distance from the resonator's anchor. This results in a periodic trend of Q when the distance between the anchor and the reflector changes. Further confirmation of the trend is obtained via a finite element (FE) model. Interestingly, when in the FE model, the step between consecutive reflectors is decreased by a factor of 6× with respect to the experimental step, we observe a fast modulation of Q, superimposed onto that seen experimentally. The origin of this fast modulation is likely the coexistence of waves with different wavelengths traveling through the released region. Our results show that the profile of the region undergoing Si undercutting (released area) can be easily set by design. Furthermore, engineering the introduced acoustic mismatch provides unprecedented control of anchor loss. [ABSTRACT FROM AUTHOR]

Presents a study which examined the bonding of palladium atoms evaporated on a thin layer of silicon intermediate oxidation states using core level and valence band photoemission spectroscopy. Theoretical background; Methodology; Results.

Well-aligned TiO2 nanofibers were grown using the near-field electrospinning technique onto a silicon dioxide substrate. These nanofibers were several millimeters long with a diameter of about 200–400 nm. The scanning electron microscopy showed the presence of microcystallites, whose crystalline structure was evaluated by x-ray diffraction measurements after a thermal process was performed to remove the solvent used in the solution. The chemical composition was investigated by x-ray photoemission spectroscopy showing the presence of TiO2. [ABSTRACT FROM AUTHOR]

The electronic structure of thin blend films composed of copper phthalocyanine (CuPc) and fullerene (C60) have been studied by x ray, soft-x-ray photoemission spectroscopy, and by theoretical simulations. Samples with different C60/CuPc concentration ratios were prepared by thermal evaporation in ultrahigh vacuum conditions. A strong shift of the highest occupied molecular orbital (HOMO) of CuPc towards the Fermi level and of the HOMO C60 states towards higher binding energy was observed. The comparison between valence band structures and core level line shape indicates that the central part of the CuPc molecule is lightly modified by the presence of the C60 molecule. The theoretical analysis, performed using density functional theory, confirms this small interaction between the two molecules, with a small charge density localized between the two molecules and a structural modification of the CuPc molecule. [ABSTRACT FROM AUTHOR]

Tungsten tips used in scanning tunneling microscopy (STM) (prepared via electrochemical etching with a 2 N KOH or NaOH solution) have been studied with state of the art scanning Auger microscopy (SAM) with chemical lateral resolution of 10 nm. The experiments were focused on the investigation of the W tips' apex shape and surface composition, for tips as etched, or after various postetching treatments performed for cleaning, sharpening, and surface oxide removal purposes. Ultrasonic cleaning likely bend the tip apex. Hydrofluoride etching successfully removes the native WO[SUB3] oxide layer, but this happens at the expense of the tip sharpness. Ion sputtering in ultrahigh vacuum is not always effective in sharpening and cleaning the tungsten tip apex, and we sometimes observed the formation of needle like nanotips, mostly composed of WO[SUB3]. Direct resistive annealing of the tip (operated in the STM at 10 V, 50 nA set-point sample bias voltage and current, respectively) to remove the oxide layer, produces a coiling of the tip apex. In this case, atom transfer from the sample to the tip is directly demonstrated with Auger spectra taken at the tip apex. [ABSTRACT FROM AUTHOR]

The electronic structure of thin blend films composed by copper phthalocyanine (CuPc) and fullerene (C60) have been studied by soft x-ray photoemission spectroscopy. Several samples with different C60/CuPc concentration ratios were prepared by thermal evaporation in ultrahigh vacuum conditions. As the C60 concentration increases, strong shifts of the CuPc highest occupied molecular orbital (HOMO) level towards the Fermi level and of the C60 HOMO level to higher binding energies have been observed. This experimental result suggests that there is a sizeable interaction between CuPc and C60 molecules that can be interpreted in terms of a charge transfer from C60 to CuPc. These shifts play an important role in the application of the CuPc:C60 blend films for instance in the construction of solar cells on flexible substrates. [ABSTRACT FROM AUTHOR]

Carbon nanotubes (CNTs) deposited by plasma-enhanced chemical vapor deposition on Si[sub 3]N[sub 4]/Si substrates have been investigated as resistive gas sensors for NO[sub 2]. Upon exposure to NO[sub 2], the electrical resistance of the CNTs was found to decrease. The maximum variation of resistance to NO[sub 2] was found at an operating temperature of around 165°C. The sensor exhibited high sensitivity to NO[sub 2] gas at concentrations as low as 10 ppb, fast response time, and good selectivity. A thermal treatment method, based on repeated heating and cooling of the films, adjusted the resistance of the sensor film and optimized the sensor response to NO[sub 2]. [ABSTRACT FROM AUTHOR]

A correction to the article "Symmetry breaking effect in the ferrocene electronic structure by hydrocarbon-monosubstitution: An experimental and theoretical study" published in volume 128, issue 15 of the journal is presented.

Explores the reactivity of gold on cleaved 2212 BiCaSrCuO by synchrotron-radiation photoemission spectroscopy. Formation of a localized nonmetallic phase; Measurement of the overlayer thickness; Importance of temperature regulation in low temperature manufacturing.