G. Di Santo

Electro-chemical deposition of zinc oxide nanostructures by using two electrodes

One of the most viable ways to grow nanostructures is electro deposition. However, most electrodeposited samples are obtained by three-electrode electrochemical cell. We successfully use a much simpler two-electrode cell to grow different ZnO nanostructures from common chemical reagents. Concentration, pH of the electrolytes and growth parameters like potentials at the electrodes, are tailored to allow fast growth without complexity. Morphology and surface roughness are investigated by Scanning Electron and Air Force Microscopy (SEM and AFM) respectively, crystal structure by X-Ray Diffraction measurements (XRD) and ZnO stoichiometry by core level photoemission spectroscopy (XPS).

Review of 2H-tetraphenylporphyrins metalation in ultra-high vacuum on metal surfaces

The formation and conformational adaptation of self-assembled monolayer of 2H- tetraphenylporphyrins (2H-TPPs) on metal surfaces, as well as their metalation processes in ultra-high vacuum (UHV), are reviewed. By means of XPS, NEXAFS and STM measurements we demonstrate that, after the annealing at 550 K, a temperature-induced chemical modification of 2H-TPP monolayer on Ag(111) occurs, resulting in the rotation of the phenyl rings parallel to the substrate plane. Moreover, independently of the conformation, we report three dierent methods to metalate 2H-TPP monolayers in UHV. Experimental evidence indicates that the presence of a metal atom in the TPP macrocycle influences both the conformation of the molecule and its adsorption distance.

Formation of a quasi-free-standing graphene with a band gap at the dirac point by Pb atoms intercalation under graphene on Re(0001)

The control of the graphene electronic structure is one of the most important problems in modern condensed matter physics. The graphene monolayer synthesized on the Re(0001) surface and then subjected to the intercalation of Pb atoms is studied by angle-resolved photoelectron spectroscopy and low-energy electron diffraction. The intercalation of Pb atoms under graphene takes place when the substrate is annealed above 500°C. As a result of the intercalation of Pb atoms, graphene becomes quasi-free-standing and a local band gap appears at the Dirac point. The band gap changes with the substrate temperature during the formation of the graphene/Pb/Re(0001) system. The band gap is 0.3 eV at an annealing temperature of 620°C and it increases up to 0.4 eV upon annealing at 830°C. Based on our data, we conclude that the band gap is mainly caused by the hybridization of the graphene π state with the rhenium 5d states located near the Dirac point of the graphene π state.

Improved recovery time and sensitivity to H 2 and NH 3 at room temperature with SnO x vertical nanopillars on ITO

Nanostructured SnO2 is a promising material for the scalable production of portable gas sensors. To fully exploit their potential, these gas sensors need a faster recovery rate and higher sensitivity at room temperature than the current state of the art. Here we demonstrate a chemiresistive gas sensor based on vertical SnOx nanopillars, capable of sensing < 5 ppm of H2 at room temperature and 10 ppt at 230 °C. We test the sample both in vacuum and in air and observe an exceptional improvement in the performance compared to commercially available gas sensors. In particular, the recovery time for sensing NH3 at room temperature is more than one order of magnitude faster than a commercial SnO2 sensor. The sensor shows an unique combination of high sensitivity and fast recovery time, matching the requirements on materials expected to foster widespread use of portable and affordable gas sensors.

Dirac cone intensity asymmetry and surface magnetic field in V-doped and pristine topological insulators generated by synchrotron and laser radiation

Effect of magnetization generated by synchrotron or laser radiation in magnetically-doped and pristine topological insulators (TIs) is presented and analyzed using angle-resolved photoemission spectroscopy. It was found that non-equal photoexcitation of the Dirac cone (DC) states with opposite momenta and spin orientation indicated by the asymmetry in photoemission intensity of the DC states is accompanied by the k||-shift of the DC states relative to the non-spin-polarized conduction band states located at k|| = 0. We relate the observed k||-shift to the induced surface in-plane magnetic field and corresponding magnetization due to the spin accumulation. The direction of the DC k||-shift and its value are changed with photon energy in correlation with variation of the sign and magnitude of the DC states intensity asymmetry. The theoretical estimations describe well the effect and predict the DC k||-shift values which corroborate the experimental observations. This finding opens new perspectives for effective local magnetization manipulation.

Opposite dispersion bands at the Fermi level in ZrSe2

The electronic structure of ZrSe2 was studied by high resolution angular resolved photoemission spectroscopy (ARPES) and by density functional theory (DFT). ARPES with distinct horizontal (P) and vertical (S)-polarized synchrotron radiation was performed on the sample kept at room temperature and 20 K to unravel the electronic structure especially at the Fermi energy (EF). The DFT calculations including spin-orbit coupling using the modified Becke-Johnson potential reveal the presence of three occupied valence bands at the Γ(A)-point and show that the minimum indirect bandgap is between the Γ- and L-points of the Brillouin zone (BZ) similar to the experimental results. While the DFT calculations give only a single conduction band at the L and M-points of the BZ, the ARPES data (20 K) show two bands with opposite dispersion at EF. The observation of two bands close to EF was already reported in the charge density wave phase of TiSe2. The underlying mechanism of our observations is possibly a folding of the valence band states of ZrSe2 from the Γ(A) to M(L)-point accompanied by an energy shift due to internal dipolar momenta. Furthermore, at the A-point, the experimental dispersion of the lower occupied valence band and the size of its energy separation to the middle occupied band are not in line with the DFT calculations. Possible reasons of such discrepancies are discussed.

Electronic structure of Fe3Sion Si(100) substrates

The improved performance of large-scale integrated circuits (LSIs) by the shrinking of devices is becoming difficult due to physical limitations. Here we report, the growth and formation of Fe 3 Si on Si(100) and characterized by x-ray photoemission, UV photoemission and low energy electron diffraction to study the electronic structure. The results revealed that the DO3 phase formation is exist and photoemission results also support the electron diffraction outcome.

Electronic structure of Fe3Si on Si(100) substrates

The improved performance of large-scale integrated circuits (LSIs) by the shrinking of devices is becoming difficult due to physical limitations. Here we report, the growth and formation of Fe 3 Si on Si(100) and characterized by x-ray photoemission, UV photoemission and low energy electron diffraction to study the electronic structure. The results revealed that the DO3 phase formation is exist and photoemission results also support the electron diffraction outcome.

XPS study of 2H-TPP at Fe/Si(111) system

Metalloporphyrins control the decisive steps in various natural and technological processes, which often involve the reversible attachment of a molecular ligand to the central metal ion. Here we studied the metalation of 2HTetraphenyl Porphyrin (2H-TPP) on Fe metal films on well reconstructed Si(111)-7×7 surface. XPS results give evidence for the Fe-TPP coordination.