F. Xu

Study of Band Gap of Silver Nanoparticles—Titanium Dioxide Nanocomposites

The optical and chemical properties of Ag/TiO2 nanocomposites were investigated to explore the possibilities of incorporating these new materials in Gratzel photoelectrochemical cells. The nanocomposites were obtained doping TiO2, in both allotropic species anatase and rutile, with silver nanoparticles (grown by laser ablation process). X-ray photoelectron data indicate the absence of Ag-Ti chemical bonds, while measurements of photoluminescence and optical absorbance in UV-visible range show a quench in photoluminescence emission of about 50% and an increase in visible absorbance of about 20%. Measurements of optical band gap, obtained by Tauc’s equation, indicate a variation of about 1.6u2009eV.

Adsorption of Molecular Gases on Silver/Carbon Nanotube Composites at Low Temperatures and Low Pressures

We present an experimental study adsorption of molecular gases (N2, H2, O2, CH4, C2H4, and C2H6) on multiwalled carbon nanotubes (MWCNTs) and MWCNT doped with Ag at low temperatures (35u2009K) and pressures (10−6u2009Torr) using the temperature programmed desorption technique. Our results show that the desorption kinetics is of the first order; furthermore comparative measurements indicate that Ag/MWCNTs have an adsorption capacity higher than that of a pure sample suggesting that these composites are good candidates as gas cryosorbers for applications in cryopumps or sensor of latest generation.

Low-cost carbon-based counter electrodes for dye sensitized solar cells

In this work, we present the realization of four carbon-based counter electrodes for dye-sensitized solar cells. The photovoltaic behaviours of counter electrodes realized with graphene, multiwalled carbon nanotubes, and nanocomposites of multiwalled carbon nanotubes and metal nanoparticles are compared with those of classical electrodes (amorphous carbon and platinum). Our results show an increase of about 50% in PCE for graphene and Ag/carbon nanotube electrodes with respect to amorphous carbon and of 25% in comparison to platinum. An improvement in cell stability is also observed; in fact, the PCE of all carbon-based cells assumes a constant value during a period of one month while that with the Pt electrode decreases by 50% in one week.

Angular dependence of secondary electron emission from Cu surfaces induced by electron bombardment

We report experiments of 200 eV electron bombardment on surface of a real Cu sample used in the Large Hadron Collider (LHC) beam screen. Incidence angle dependent energy distribution curves of emitted electrons were measured and analyzed by separation into three energy regions of conventionally termed elastically reflected, rediffused and true-secondary electrons. Different angular dependences were observed for the three components. These results should have implications in simulation codes of the electron cloud effect in particle accelerators.

Study of Coating Geometries and Photoluminescence Properties of Metal Nanoparticles/Graphite Composites

In this work we present the results of a study of growth and characterization of metal nanoparticles (Ag, Au, and Co)/carbon surfaces. The nanoparticles grew by laser ablation technique and their dimensions were controlled by light scattering study and AFM microscopy before their insertion on graphite surface. Nanoparticles appear randomly disposed on carbon surfaces aggregating to form big particles only in the case of silver. The different behavior of metal nanoparticles on carbon surface was explained in terms of different metal wetting of surface, in agreement with previous theoretical results of He et al. Chemical information, obtained by X-ray photoelectron spectroscopy, indicated that the doping process is a simple physisorption while the interfacial interaction between particles and carbon layers causes local defects in graphite structure and the appearance of a strong photoluminescence signal for all composites. Moreover, the visible optical absorption decreases about 10% indicating the progressive metallization of carbon surface.