L.S. Caputi

Electronic structure of graphite: Single particle and collective excitations studied by EELS, SEE and K edge loss techniques

Abstract We present some EELS, SEE and K edge loss measurements on in situ cleaved graphite. Single particle excitations in the EELS measurements have been identified accordingly with some previous results on pure polycrystalline iron and are compared with available band structure calculations of graphite. The core edge loss spectroscopy performed in the reflection mode at low primary electron energy proved to be a powerful and rapid technique to study the partial density of empty states.

XPS and AFM characterization of a vanadium oxide film on TiO2(100) surface

Abstract Vanadium oxide has been grown in ultra high vacuum onto a rutile TiO2(100) surface and studied by X-ray photoelectron spectroscopy and atomic force microscopy. The AFM image showed a surface with a peculiar roughness made of three-dimensional structures having an average height of 10 nm and an average base radius of about 100 nm.

Corbonaceous layers on Ni (110) and (100) studied by AES and eels

Abstract Carbidic carbon layers, obtained on Ni (110) and (100) single crystals by exposing the samples to CO at pressures in the range 1 × 10 −6 to 3 × 10 −5 Torr at 520 K, have been studied by Auger Electron Spectroscopy (AES) and Electron Energy Loss Spectroscopy (EELS). The carbidic carbon covered surfaces have been gradually heated, and we observed new temperature-dependent carbon Auger lineshapes, which we tentatively attribute to new intermediate carbon species. At higher temperatures the carbidic carbon evolves towards graphitic carbon on Ni (110), while on Ni (100) graphitic species could not be obtained in the above pressure range.

HREELS study of Au/Fe2O3 thick film gas sensors

Abstract CO gas sensors based on Au-doped/Fe 2 O 3 thick films were studied in ultra-high-vacuum (UHV) by high resolution electron energy loss spectroscopy (HREELS). Several adsorbed species were identified on HREEL spectra collected at room temperature on thick films annealed at different temperatures. Among these, carboxylate and formate species were postulated as intermediates of the complex reactions occurring on the surface between carbon monoxide and oxygen. The catalytic and sensing properties of the Au/iron oxide samples towards CO have been also investigated showing the better performances of the co-precipitated samples in comparison to impregnated ones and the influence of annealing temperature. Data reported were correlated to the presence of oxygenate intermediates detected by HREELS.

Aluminum collective excitations: Reflection electron energy loss results

Abstract Reflection electron energy loss investigation on Al samples has been carried out with an average angle collection system from 30 to 1000 eV of primary electron energy. Plasmonic structures occur always at the same energy while their lineshape broadening increases decreasing the electron kinetic energy. The ratio between surface and bulk contributions has been exploited and reproduced with a phenomenological model. The extrinsic loss mechanism for the creation of the bulk plasmon has been investigated and compared with available theories.

Indium selenide: an insight into electronic band structure and surface excitations

We have investigated the electronic response of single crystals of indium selenide by means of angle-resolved photoemission spectroscopy, electron energy loss spectroscopy and density functional theory. The loss spectrum of indium selenide shows the direct free exciton at ~1.3 eV and several other peaks, which do not exhibit dispersion with the momentum. The joint analysis of the experimental band structure and the density of states indicates that spectral features in the loss function are strictly related to single-particle transitions. These excitations cannot be considered as fully coherent plasmons and they are damped even in the optical limit, i.e. for small momenta. The comparison of the calculated symmetry-projected density of states with electron energy loss spectra enables the assignment of the spectral features to transitions between specific electronic states. Furthermore, the effects of ambient gases on the band structure and on the loss function have been probed.

The Advent of Indium Selenide: Synthesis, Electronic Properties, Ambient Stability and Applications

Among the various two-dimensional semiconductors, indium selenide has recently triggered the interest of scientific community, due to its band gap matching the visible region of the electromagnetic spectrum, with subsequent potential applications in optoelectronics and especially in photodetection. In this feature article, we discuss the main issues in the synthesis, the ambient stability and the application capabilities of this novel class of two-dimensional semiconductors, by evidencing open challenges and pitfalls. In particular, we evidence how the growth of single crystals with reduced amount of Se vacancies is crucial in the road map for the exploitation of indium selenide in technology through ambient-stable nanodevices with outstanding values of both mobility of charge carriers and ON/OFF ratio. The surface chemical reactivity of the InSe surface, as well as applications in the fields of broadband photodetection, flexible electronics and solar energy conversion are also discussed.

HREELS investigation of COK coadsorption on Ni(111)

Abstract The coadsorption of CO and K on Ni(111) has been studied by high-resolution electron energy-loss spectroscopy. We used three precoverages, one of them (0.25 ML) corresponding to an ordered surface overlayer (p(2 × 2)) and the other two (0.3 and 0.47 ML), to an incommensurate and a disordered surface layer, respectively. Different local CO adsorption arrangements are suggested for each K coverage. The vibrational spectra show features at 27, 180 and 210 meV. The loss at 27 meV is related to a vibration of the reconstructed Ni(111) surface due to the p(2 × 2)-K layer and is damped by 3 L of CO. For the other two K precoverages, that loss exists regardless of the amount of CO. The losses at 180 and 210 meV are assigned to the CO stretching vibration corresponding, respectively, to the occupation of only one or both sites of the same p(2 × 2)-K cell. The CO saturation of the p (2 × 2)- K Ni (111) surface gives rise to a short-range interaction among CO molecules as well as between each K atom and CO molecules, which causes an overall shift of the CO stretching frequency towards higher loss energies.

Preparation of graphene oxide as biomaterials for drug adsorption

Doxorubicin hydrochloride (DOX), is a class I anthracycline antibiotic (FDA approved in the 1970s) widely used as an effective chemotherapeutic drug for the treatment of many human neoplasms. Like most anticancer drugs, DOX can provoke severe toxicity to the body when it is administered at high doses systemically. Here we report the results of an investigation of drug adsorption on graphene oxide (GO) materials prepared by the Improved Hummers method. High-purity GO has been prepared, characterized by XPS, UV-vis, FTIR-ATR, FESEM, UV- vis analyses, Zero Point Charge determinations and applied in the immobilization of doxorubicin, via simple noncovalent method. The adsorption percentage of the drug at pH 7 on GO was observed to be higher (equal to 90 %) than that obtained at acidic pH 3 (equal to 85%). Experimental result of adsorption of DOX on GO, obtained by FTIR-ATR spectroscopy analysis indicate that the inorganic material and the drug form and adduct by π-π stacking interactions.

Collective and single-particle excitations in thin layers of K on Ni(111)

Single-particle and collective excitations of KNi(111) were studied by high resolution electron energy loss spectroscopy (HREELS). Loss spectra were taken at 200 K as a function of K coverage over the 0–4 eV range of loss energy. Two peaks and a shoulder are characteristic of the submonolayer regime while, as the second atomic layer of potassium is formed, a single distinct feature dominates the loss spectrum. We assign the low-energy features in the submonolayer coverage regime to single-particle excitations: the loss at 0.5–0.6 eV is interpreted as due to electronic transitions from alkali s states to the Fermi level, while the one at about 1.68 eV (for a K coverage of 0.25 ML) is assigned to transitions from initial hybridized alkali s-Ni dz2 states, to the Fermi level. We measured the dispersion curve ω(q‖) of the single feature of the two layers of potassium. It follows the theoretical predictions for the surface plasmon of a thick K overlayer showing an initial downward dispersion versus q‖. The present results also give a hint of the nature of the alkali metal-to-substrate interactions from submonolayer regimes up to two layers of K on the Ni surface.