Raffaele G. Agostino

Catanionic Tubules with Tunable Charge

Thethree-dimensionalstructureswithnanoscopicdimensionsthat are yielded by the self-assembly of lipids and surfactantsare of particular interest for their applications in nano-technology.Intheseapplications,thepossibilityofcontrollingthe charge of the particles allows the regulation of funda-mental aspects, such as the ability of the particles to loadmolecules (drugs, DNA, proteins, etc.), to aggregate, and topenetrate membranes. Within the possible surfactant supra-molecular architectures, tubular structures have recentlydrawn much research interest.

Cu-BTC/Aminated Graphite Oxide Composites As High-Efficiency CO2 Capture Media

CO2 adsorption isotherms on Cu-BTC/aminated graphite oxide composites were measured in the pressure range up to 1.5 MPa at three different temperatures close to ambient. Adsorption capacity, isosteric heat of adsorption, and regenerability were investigated. They are considered as significant factors determining the practical application of materials for CO2 capture. The results indicate a significant improvement in the performance of the composites as CO2 adsorbents in comparison with the parent Cu-BTC MOF. Among all samples analyzed, the composite of Cu-BTC and modified graphite oxide with the highest N content (MOF/GO-U3) is the best performing sample. On its surface 13.41 mmol/g CO2 was adsorbed at room temperature and 1.5 MPa. A high selectivity for CO2 adsorption over that of CH4 was found. The selectivities for CO2 adsorption over N2 are governed by the properties of the MOF phase. A relatively low heat of CO2 adsorption and the high degree of surface homogeneity cause that the composites can be fully regenerated and used in multicycle adsorption with the minimum energy demand.

Electronic and vibrational excitations in carbon nanotubes

We investigated the electronic and vibrational properties of single wall carbon nanotubes by reflection electron energy loss and X-ray absorption spectroscopies. We report on single particle excitations measured at the C-1s edge and on collective excitations of the valence band region. The comparison between the two techniques allows us to locate empty electronic states of the carbonaceous sample. Loss spectra taken in the infrared region reveal two loss features at 90 and 170 meV assigned to the excitation of optical phonon modes.

Writing submicrometric metallic patterns by ultraviolet synchrotron irradiation of nanostructured carbon and TiOx–carbon films

Nanostructured carbon and carbon–TiOx films produced by supersonic cluster beam deposition have been characterized by spatially resolved (0.5 μm lateral resolution) photoemission spectroscopy with synchrotron light. We have found that pure and TiOx-containing nanostructured carbon is modified under high flux UV exposure showing the onset of a metallic character near the Fermi level. We have studied the spectroscopic features, the spatial confinement, and the kinetics of this metallization process of the irradiated regions. This effect allows one to write metallic patterns in the TiOx-containing films with a submicrometric resolution and with a fast kinetic.

Island organization of TiO2 hierarchical nanostructures induced by surface wetting and drying.

We report on the reorganization and bundling of titanium oxide nanostructured layers, induced by wetting with different solvents and subsequent drying. TiO(2) layers are deposited by pulsed laser deposition and are characterized by vertically oriented, columnar-like structures resulting from assembling of nanosized particles; capillary forces acting during evaporation induce bundling of these structures and lead to a micrometer-size patterning with statistically uniform islands separated by channels. The resulting surface is characterized by a hierarchical, multiscale morphology over the nanometer-micrometer length range. The structural features of the pattern, i.e., characteristic length, island size, and channel width, are shown to depend on properties of the liquid (i.e., surface tension) and thickness and density of the TiO(2) layers. The studied phenomenon permits the controlled production of multiscale hierarchically patterned surfaces of nanostructured TiO(2) with large porosity and large surface area, characterized by superhydrophilic wetting behavior without need for UV irradiation.

Thermally induced modifications of the optic properties of lead zirconate titanate thin films obtained on different substrates by sol-gel synthesis

Lead zirconium titanate PbZr0.53Ti0.47O3 (PZT) thin films have been obtained by sol-gel synthesis, deposited on different substrates [float glass, indium tin oxide (ITO)-coated float glass, and intrinsic silicon wafer], and later subjected to different thermal treatments. The morphologic and the structural properties of both PZT thin films and substrates have been investigated by scanning electron microscope and their composition was determined by energy dispersive x-ray (EDX) analysis. Moreover, variable angle spectroscopic ellipsometry provides relevant information on the electronic and optical properties of the samples. In particular, the optical constant dispersion of PZT deposited on ITO-coated float glasses shows a small absorption resonance in the near IR region, not observed in PZT films deposited on the other substrates, so that such absorption resonance can be explained by interfacial effects between ITO and PZT layers. This hypothesis is also supported by EDX measurements, showing an interdiffu...

Metallic Tin-Filling Effects on Carbon Nanotubes Revealed by Atomically Resolved Spectro-Microscopies

The identification of features in the Local Density of States (LDOS) of carbon nanotubes (CNTs) obtained by Scanning Tunneling Spectroscopy (STS) is of great importance in order to understand their properties. In this work, Single- and Multi-Wall Carbon Nanotubes are compared with Multi-Wall CNTs filled with tin nanowires (Sn@CNTs) in order to investigate the effect on morphological and electronic properties of the CNTs metallic filling. The LDOS of CNTs, together with topology changes, is investigated by using spatially resolved STM/STS at room temperature and in air and compared to the LDOS of highly oriented pyrolitic graphite (HOPG). The LDOS of CNTs is dominated from different electronic states filling the C 2pσ-2pσ* band gap. The appearance of those states is linked to the diameter and the defects of the CNTs. In fact, Snnanowires encapsulation induces changes in the structure of the CNTs and the appearance of electronic states in the LDOS inside the band gap. A more extensive description of the samples is obtained depicting the morphological features and the vibrational structure on wider areas using Scanning Electron Microscopy (SEM) and Raman spectroscopy, respectively.

Enhanced hydrogen and methane storage of hybrid mesoporous organosilicas

In this study, hybrid mesoporous organosilicas (HMOs) were synthesized by using tetraethyl orthosilicate (TEOS) as the silica source and 1,4-bis(triethoxysilyl)benzene (BTB) in various ratios of BTB to TEOS. The two extreme cases of 0 and 100 mol% BTB were compared with the partial addition of BTB (25 mol%) and the partial absence of TEOS (75 mol% BTB). The synthesized mesoporous materials were characterized by means of powder X-ray diffraction (PXD), scanning electron microscopy (SEM) and helium pycnometry for the determination of skeletal density. The Brunauer–Emmett–Teller (BET) method was used for the determination of the specific surface area (SSA) and non-local density functional theory (NLDFT) calculations were employed for the determination of the pore size distribution (PSD). The hydrogen and methane sorption properties were investigated using a Sieverts apparatus under isothermal sorption equilibrium conditions at cryogenic and close to ambient temperatures, respectively. For hydrogen, the combination of phenyl rings with pores at the micro/mesopore border resulted in an increase in sorption capacity. The simultaneous presence of two different precursors increased the surface inhomogeneity, which led to a wider distribution of adsorption sites close to the micro/mesopore border, which favored the hydrogen sorption properties. The presence of the phenyl rings doubled the number of methane molecules that the material surface could accommodate. The partial substitution of TEOS by BTB (25 mol%) gave the same density of adsorbed methane as the non-hybrid material, which consisted of 100% BTB. The materials exhibited excellent reversibility and sorption stability upon aging. Their sorption performance was evaluated using the Toth model and was correlated with their structural characteristics. The fraction of micropores among the total number of pores was quantitatively correlated with the maximum storage capacity and the adsorbate–adsorbent interaction strength. Finally, for a low coverage of methane the enthalpy of adsorption was calculated by the Clausius–Clapeyron equation.

Electrical conductivity of cluster-assembled carbon/titania nanocomposite films irradiated by highly focused vacuum ultraviolet photon beams

We investigated the electrical transport properties of nanostructured carbon and carbon/titanium oxide nanocomposite films produced by supersonic cluster beam deposition and irradiated by highly focused vacuum UV photon beam. We have observed a relevant increase of the density of states at Fermi level, suggesting that the films acquire a “metallic” character. This is confirmed by the increment of the conductivity of four orders of magnitude for pure nanostructured carbon films and at least eight orders of magnitude for films containing 9at.% of titanium. A partial reversibility of the process is observed by exposing the modified films to molecular oxygen or directly to air. We demonstrate the capability of writing micrometric conductive strips (2–3μm width and 60μm length) and controlling the variation of the conductivity as a function of the titanium concentration.

Time-of-Flight Neutron Imaging on IMAT@ISIS: A New User Facility for Materials Science

The cold neutron imaging and diffraction instrument IMAT at the second target station of the pulsed neutron source ISIS is currently being commissioned and prepared for user operation. IMAT will enable white-beam neutron radiography and tomography. One of the benefits of operating on a pulsed source is to determine the neutron energy via a time of flight measurement, thus enabling energy-selective and energy-dispersive neutron imaging, for maximizing image contrasts between given materials and for mapping structure and microstructure properties. We survey the hardware and software components for data collection and image analysis on IMAT, and provide a step-by-step procedure for operating the instrument for energy-dispersive imaging using a two-phase metal test object as an example.