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International audience; Graphene (Gr) is known to be an excellent barrier preventing atoms and molecules to diffuse through it. This is due to the carbon atom arrangement in a two-dimensional (2D) honeycomb structure with a very small lattice parameter thus forming an electron cloud that prevents atoms and molecules crossing. Nonetheless at high an-nealing temperatures, intercalation of atoms through graphene occurs, opening the path for formation of vertical heterojunctions constituted of two-dimensional layers. In this paper, we report on the ability of silicon atoms to penetrate the graphene network, fully epitaxially grown on a Ni(111) surface, even at room temperature. Our scanning tunneling microscopy (STM) experiments show that the presence of defects like vacancies and disloca-tions in the graphene lattice favor the Si atoms intercalation, thus forming two-dimensional, flat and disordered islands below the Gr layer. Ab-initio molecular dynamics calculations confirm that Gr defects are necessary for Si intercalation at room temperature and show that: i) a hypothetical intercalated silicene layer cannot be stable for more than 8 ps and ii) the corresponding Si atoms completely lose their in-plane order resulting in a random planar distribution and form strong covalent bonds with Ni atoms.

The deposition of calcium fluoride (CaF2) on Si(111) at temperatures above 570 °C has been studied with scanning tunneling microscopy. At such temperatures, triangular calcium fluoride islands are formed both on terraces and along the phase domain boundaries of the (7 × 7) reconstruction of the Si(111) substrate. In addition to the formation of islands, we observe that CaF2 molecules react with the substrate inducing large areas of its surface to reconstruct into (√3 × √3) and c(2 × 4) phases. Upon annealing at 600 °C, the abovementioned areas of (√3 × √3) and c(2 × 4) turn into the stable (3 × 1) phase upon desorption of fluorine. Calcium fluoride islands are stable at this temperature. Depositions of calcium fluoride performed with Si substrate kept at higher temperature, namely at 680 °C, lead directly to the formation of (3 × 1) phase due to the complete desorption of fluorine, without passing through the formation of the metastable (√3 × √3) and c(2 × 4) phases. If CaF2/Si(111) is brought at even higher temperatures, Ca also starts desorbing and the (7 × 7)-Si(111) reconstruction can eventually be restored.

A dodecapeptide (AMRKLPDAPGMH) functionalized with a tetramethylrhodamine (TAMRA) chromophore at the N-terminus was immobilized on nanocrystalline TiO2. The optical and binding properties of the peptide layer immobilized on the titania surface were characterized by UV–vis absorption, steady-state fluorescence and X-ray photoelectron spectroscopies. Circular Dichroism experiments and Molecular Mechanics calculations showed that the predominant conformation populated by the peptide scaffold brings Arg3, Lys4 and Asp7 in the correct position for linking the TiO2 surface. Photocurrent generation experiments were therefore carried out to determine the photon-to-current conversion efficiency (IPCE) of a Grätzel-like Dye Sensitized Solar Cell (DSSC), the photoactive unit of which is formed by TAMRA-AMRKLPDAPGMH/TiO2. The measured IPCE amounted to 0.65%, a value that is definitely low, but superior to those previously reported for similar bioinspired DSSCs. This result can be ascribed to the light-harvesting properties of the TAMRA chromophore and to the unique structural properties of the peptide spacer. © 2017 Elsevier B.V.

In this work a new, simple and green protocol to introduce a limited content of silanol groups on the surface of an hydrophobic diatomite, in order to be slightly hydrophilic and susceptible to be silanized by bifunctional, sulfur-containing organosilanes for rubber applications, is proposed. The chemical modification was carried out at 85 °C in a solution of H 2 O:NaOH:H 2 O 2 . The modified diatomite was then silanized with bis(triethoxysilylpropyl) disulfide by a procedure that does not involve toxic solvent. Morphological features and elemental composition of diatomite were investigated by Field emission scanning electron microscopy coupled with Energy dispersive X-ray spectroscopy. The surface modification and silanization process were assessed by Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy. Diatomite was composed by micrometric frustules from different diatom species with pore size ranging from 25 nm to 1 μm. The spectroscopic characterizations confirmed the surface modification of diatomite with some silanols that acted as sites for silanization reaction. The silanized diatomite and the untreated one were used as filler in unvulcanized solvent-cast SBR films in order to verify that the modification does not negatively affect the polymer/filler interface and as consequence the mechanical properties. Mechanical properties of the realized samples were assessed by uniaxial tensile tests. Films filled with 10 wt% of diatomite (untreated or silanized) showed an increase of Elastic Modulus about of 50% and a decrease of the strain at break with respect to SBR samples, while the tensile strength was not significantly affected by the diatomite addition. SEM images of fracture surfaces of tested specimens showed a fine dispersion of both untreated and silanized diatomite in the polymeric matrix and the achieving of a good interfacial adhesion SBR/fillers. The silanized diatomite, as it is potentially able to bind chemically to elastomeric molecules during vulcanization process, could be used in rubber compounds as semi-reinforcing filler.

Carbon spheres of nanometric dimension are known since the first studies on the synthesis of fullerenes. Their shape originates from the curvature of a carbon sheet similar to fullerenes, but with numerous graphitic rings that regulate the inside structure and the formation of open edges at the surface. This paper focuses on the structural and electronic characterization of carbon spheres obtained from a targeted chemical vapor deposition synthesis process. Two different set of samples are analyzed in detail, in particular, the electron microscopies and Raman spectroscopy help understanding the morphology and the graphitic-sp2 arrangement of the carbon atoms in the architectures. In addition, the iron catalyst used during the reaction process confers the carbon spheres a ferromagnetic response at room temperature. Therefore, both the structural properties of the samples and the active contribution of iron mark the difference in the measured photoresponse as well as in the electrochemical behavior. The X-ray photoelectron spectroscopy study addresses these points by giving information on the composition and the iron chemical state in the assembly. The collected results underline the advantages offered by this synthesis route and the properties of the carbon spheres as active nanomaterial for sustainable applications.

Meso-tetraphenylporphyrin connected with a ferrocene molecule in the beta-position of the macrocycle through a triple carbon@carbon bond has been bound to carbon spheres using the Prato@Maggini reaction. The ethynyl or/and phenylene ethynylene subunits were chosen as a linking bridge to give a high conjugation degree between the donor (i. e., ferrocene), the photoactive compound (i. e., porphyrin), and the acceptor (i. e., carbon spheres). The molecular bridges have been directly linked to the beta-pyrrole positions of the porphyrin ring, generating a new example of a long-range donor@acceptor system. Steady-state fluorescence studies together with Raman and XPS measurements helped understanding the chemical and physical properties of the porphyrin ring in the new adduct. The spectroscopic characteristics were also compared with those obtained from a similar compound bearing fullerene instead of carbon spheres. &nbsp

Here we present for the first time polymer solar cells that incorporate biological material that show state of the art efficiencies in excess of 8%. The performance of inverted polymer solar cells was improved significantly after deposition of ZnO nanoparticles (ZnO-NPs) together with a thin deoxyribonucleic acid nanolayer and used as an electron extraction layer (EEL). The ZnO-NPs/DNA double layer improved the rectifying ratio, shunt resistance of the cells as well as lowering the work function of the electron-collecting contact. Importantly, the ZnO-NPs/DNA bilayer enhanced the power conversion efficiency of cells considerably compared to cells with EELs made of only DNA (improvement of 56% in relative terms) or only ZnO-NPs (improvement of 19% in relative terms) reaching a best power conversion efficiency of 8.5%. The ZnO-NPs/DNA double layer cells also outperformed ones made with one of the most efficient previous synthetic composite EELs (i.e. ZnO/PEIE(poly(ethyleneimine)-ethoxylated)). Since all fabrication procedures were carried out at low (

In this paper, we show that it is possible to synthesize carbon-based three-dimensional networks by adding sulfur, as growth enhancer, during the synthesis process. The obtained material is self-supporting and consists of curved and interconnected carbon nanotubes and to lesser extent of carbon fibers. Studies on the microstructure indicate that the assembly presents a marked variability in the tube external diameter and in the inner structure. We study the relationship between the observed microscopic properties and some potential applications. In particular, we show that the porous nature of the network is directly responsible for the hydrophobic and the lipophilic behavior. Moreover, we used a cut piece of the produced carbon material as working electrode in a standard electrochemical cell and, thus, demonstrating the capability of the system to respond to incident light in the visible and near-ultraviolet region and to generate a photocurrent.

A helical hexapeptide was designed to link in a rigid parallel orientation to a gold surface. The peptide sequence of the newly synthesized compound is characterized by the presence of two 4-amino-1,2-dithiolane-4-carboxylic acid (Adt) residues (positions 1 and 4) to promote a bidentate interaction with the gold surface, two L-Ala residues (positions 2 and 5) and two-aminoisobutyric acid (Aib) residues (positions 3 and 6) to favor a high population of the 3(10)-helix conformation. Furthermore, a ferrocenoyl (Fc) probe was inserted at the N-terminus to investigate the electronic conduction properties of the peptide. X-Ray photoelectron spectroscopy and scanning tunneling microscopy techniques were used to characterize the binding of the peptide to the gold surface and the morphology of the peptide layer, respectively. Several electrochemical (cyclic voltammetry, chronoamperometry, square wave voltammetry) techniques were applied to analyze the electrochemical activity of the Fc probe, along with the influence of the peptide 3D-structure and the peptide layer morphology on electron transfer processes.

Large nanostructures of silicene have been successfully grown on graphene covered 6H-SiC (0001) substrates. The graphene plays an important role to obtain honeycomb structures of silicon in the sp2 configuration and acts as an ideal template for 2D materials. The scanning tunneling microscopy images showed nanosheets of silicene with a very small buckling among the Si atoms. Our scanning tunneling spectroscopy confirmed the metallic character of the deposited silicene in excellent agreement with band structure calculations that also exhibit the presence of Dirac cones.

We report on the multiwall carbon nanotube application as energy conversion material to fabricate thin film solar cells, with nanotubes acting as photogeneration sites as well as charge separators, collectors and carrier transporters. The device consists of a semitransparent thin film of nanotubes coating a n-type crystalline silicon substrate. Under illumination electron-hole (e-h) pairs, generated in the nanotubes and in the silicon substrate underneath, are split and charges are transported through the nanotubes (electrons) and the n-Si (holes). We found that a suitable thickness of the nanotube thin film, high density of Schottky junctions between nanotubes and n-Si and lowest number of nanotube walls are all fundamental parameters to improve the device incident photon to electron conversion efficiency. Multiwall carbon nanotubes have been synthesized by chemical vapour deposition in an ultra high vacuum chamber by evaporating a given amount of iron at room temperature and then exposing the substrate kept at 800 degrees C at acetylene gas. The amount of deposited iron is found to directly affect the nanotube size distribution (inner and outer diameter) and therefore the number of walls of the nanotubes.

We report on the generation of photocurrent in the visible and ultraviolet range from planar devices built from the Ge nanocrystals grown on a heavy n-doped Si(001) substrate covered with 5 nm thick thermally grown SiO2. These Ge nanostructures/SiO2/n(+)-Si devices are shown to generate photocurrent with an Incident-Photon-to-electron Conversion Efficiency (IPCE) spectral range depending on the Ge nanocrystals size. The increase of the IPCE value of our devices in the 350-600 nm range correlates well with the absorbance of Ge.

International audience; Multi wall carbon nanotubes (MWCNTs) were grown on a stainless steel (SS) sheet by chemical vapor deposition without the addition of external metal catalyst. We found that the key for highly efficient growth includes the nanoscale roughness of the SS surface, as shown by scanning tunneling microscopy, that acts as catalyst/template in the nanotube formation. Raman spectroscopy and electron microscopy were used to check the nature and quality of the synthesized nanotubes. We conclude that stainless steel favors a base-growth mechanism. Transmission electron energy loss spectroscopy performed on single metallic particles found inside the nanotubes clarified the atomic nature of the catalytic particles supplied by the steel. Only unoxidized iron was found and no traces of nickel and chromium were detected. In addition, the SS substrate has been used for a second growth process after carefully removing the synthesized CNTs, proving that a continuous production of CNTs from the same substrate is achievable.

We show that when a soft polymer like Poly(3-hexyl-thiophene) wraps multiwall nanotubes by coiling around the main axis, a localized deformation of the nanotube structure is observed. High resolution transmission electron microscopy shows that radial compressions of about 4% can take place, and could possibly lead to larger interlayer distance between the nanotube inner walls and reduce the innermost nanotube radius. The mechanical stress due to the polymer presence was confirmed by Raman spectroscopic observation of a gradual upshift of the carbon nanotube G-band when the polymer content in the composites was progressively increased. Vibrational spectroscopy also indicates that charge transfer from the polymer to the nanotubes is responsible for a peak frequency relative downshift for high P3HT-content samples. Continuously acquired transmission electron microscopy images at rising temperature show the MWCNT elastic compression and relaxation due to polymer rearrangement on the nanotube surface.

Controlled synthesis of carbon nanotubes (CNTs) is highly desirable for nanoelectronic applications. To date, metallic catalyst particles have been deemed unavoidable for the nucleation and growth of any kind of CNTs. Ordered arrays of nanotubes have been obtained by controlled deposition of the metallic catalyst particles. However, the presence of metal species mixed with the CNTs represents a shortcoming for most electronic applications, as metal particles are incompatible with silicon semiconductor technology. In the present paper we report on a metal-catalyst-free synthesis of CNTs, obtained through Ge nanoparticles on a Si(001) surface patterned by nanoindentation. By using acetylene as the carbon feed gas in a low-pressure Chemical Vapor Deposition (CVD) system, multi-walled carbon nanotubes (MWNT) have been observed to arise from the smallest Ge islands. The CNTs and the Ge three-dimensional structures have been analysed by SEM, EDX and AFM in order to assess their elemental features and properties. EDX and SEM results allow confirmation of the absence of any metallic contamination on the surface, indicating that the origin of the CNT growth is due to the Ge nanocrystals.

In this work we show that a sizeable enhancement in the photocurrent over the visible and near ultraviolet energy range can be obtained from multi-wall carbon nanotubes when decorated with Cu-nanoparticles. The result has been obtained both from electrochemical and solid state cells measurements. The photoactive metal nanoparticles do not change the intrinsic ability of multi-wall carbon nanotubes to behave as an efficient low dimensional media for generating e–h carriers. This result further confirms that multi wall carbon nanotubes can be used in photovoltaic nano-devices and solar energy conversion applications.

The photocurrent generation of nanometric Ge droplets has been investigated by using electrochemical measurements. Dots have been grown by annealing Ge layers of different nominal thicknesses (ranging from 0.5 to 5 nm) deposited on clean SiO2 surface at room temperature. The photocurrent signals for the largest dots show features, which can be ascribed to the Ge nanocrystals direct electronic transitions. Only in the case of 0.5 nm Ge film a broad and intense feature at 2.4 eV has been observed while the peaks at higher energy result to be dramatically reduced. Since this last sample is characterized by (5±1) nm nanodots size (the smallest among the measured samples) the appearance of this broad band in the photocurrent active spectrum can be ascribed to quantum confinement effect.

We first investigate the spontaneous formation of nanometric and highly dense (∼3×10 12 cm −2 ) Ge droplets on SiO 2 /Si(0 0 1) by scanning tunnelling microscopy and spectroscopy. Ge dots are grown using a two-step process: first, Ge deposition on the clean SiO 2 surface at room temperature (RT) and second, thermal annealing at 500 °C. Ge dots appear free of germanium oxides. Then we show the ordering of Ge nanocrystals (NCs) on SiO 2 /Si(0 0 1) substrates patterned by focused ion beam (FIB). Lateral ordering of the ultra-dense Ge nanodots was achieved by the combination of the following technological steps: (a) use of a FIB to create ordered two-dimensional (2D) arrays of regular holes on a field oxide on the silicon substrate, (b) chemical cleaning and restoring of the Si surface in the holes, (c) further oxidation to transfer the pattern from the field oxide to the silicon substrate, (d) removal of the field oxide and thermal re-oxidation of the sample in order to create a tunnelling oxide of homogeneous thickness on the patterned silicon surface and (e) self-assembly of the 2D arrays of Ge dots on the patterned tunnelling oxide. We show that Ge NCs are ordered in the FIB holes whatever is their dimension/density.

Transmission electron microscopy (TEM) and electron energy loss near-edge structure (EELNES) revealed the presence of mostly non-oxidised silicon tubular structures among the reaction products synthesized by gas phase condensation technique. Scanning tunneling microscopy (STM) showed a hexagonal atomic arrangement for straight ones. The presence of Y-, T-branched and coiled tubular structure, like in carbon nanotubes, suggests a partially sp2 hybridization. Reflection energy loss measurements confirmed the presence of thin tubular structures and gave hint of sp3 bonds.

A novel hexapeptide was functionalized at the N-terminus by a lipoyl group for binding to gold substrates. Owing to the high content of α-aminoisobutyric acid residues, the peptide adopts a rigid helical conformation despite the shortness of its main chain. Binding of the peptide to gold was investigated by quartz crystal microbalance, cyclic voltammetry, X-ray photoelectron spectroscopy, and scanning tunneling microscopy under ultra-high vacuum conditions. Scanning tunneling microscopy experiments revealed that the peculiar self-assembly properties of this short helical peptide determine the complex morphology of the monolayer, showing ‘stripes’, i.e. peptide aggregates horizontally layered on the gold surface, and ‘holes’, i.e. Au vacancy islands coated by the peptide monolayer.

Ge nanodots, produced by solid phase crystallization of amorphous Ge layers deposited at room temperature on SiO 2 thermally grown on a Si(100) surface, generate a photocurrent in the visible and ultraviolet range. The photocurrent signal was detected by measuring the current flowing through the sample under irradiation either in planar or in up-down geometry. In both cases the quantum efficiency of the bare SiO 2 /Si(100) substrate was dramatically enhanced up to a factor of 10 3 . Current–voltage curves were acquired in the latter geometry, evidencing an increase in the short circuit current induced by the Ge nanodots presence.

Zirconia-based Ormosil planar waveguides with different ZrO 2 contents were produced by a low temperature sol–gel process and subsequent spin coating on microscope glass slides. Propagation losses as low as 0.5 dB/cm or less were found at 488 nm for films with low ZrO 2 content; in contrast, worse waveguide quality was observed with increasing ZrO 2 doping level. A morphological investigation by atomic force microscopy confirmed such result, giving evidence of an increase of surface roughness with ZrO 2 percentage. The feasibility of organic dye doping of the films for active waveguides was also demonstrated by incorporation of DODCI saturable absorber: fluorescence spectra were registered both in bulk and guided-wave configuration.

Surface chemical composition and topography of thin films grown by radiofrequency (rf) reactive sputtering on two different substrates (rough and mechanically polished) were investigated by x-ray photoemission spectromicroscopy (XPSM) and atomic force microscopy (AFM). XPSM measurements showed, for both substrates, a homogeneous chemical composition of the films. The only difference was the observation of different charging in different areas of the film grown on rough alumina substrates, due, presumably, to a non-continuous film. AFM showed large topographical variations (several hundred nanometres) for the film grown on a rough alumina substrate, due to structures already present on the substrate. The estimated roughness of the sensor was 20% larger for the film grown on a rough alumina substrate. The response to carbon monoxide was 30% higher for the sensor grown on rough alumina than that on polished alumina, reflecting the larger exposed sensor area.

Straight and coiled single-wall carbon nanotubes (SWCNTs) synthesized by laser vaporization were dispersed on highly oriented pyrolitic graphite. Their morphology and electrical properties were investigated by scanning tunneling microscopy (STM). STM images revealed that the SWCNTs (either straight or coiled) often self-organize into bundles of two or more tubes and are rarely found alone. The conductance measured along a periodically coiled CNT was found to increase at locations where the CNT is squeezed, while it decreases significantly in unsqueezed regions characterized by an unperturbed hexagonal network. This provides experimental evidence of significant conductance modulation along a one-dimensional system on the nanometer scale.

The relaxation dynamics of unaligned multi-walled carbon nanotubes decorated with metallic nanoparticles have been studied by using transient optical measurements. The fast dynamics due to the short-lived free-charge carriers excited by the pump are not affected by the presence of nanoparticles. Conversely, a second long dynamics, absent in bare carbon nanotubes, appears only in the decorated samples. A combination of experiment and theory allows us to ascribe this long dynamics to relaxation channels involving electronic states localized at the tube-nanoparticle interface.

We have investigated the morphology, chemical bonds and electronic states of CVD carbon grown on silicon (111) substrates by means of scanning electron microscopy (SEM), Auger electron spectroscopy (AES), ultraviolet photoemission spectroscopy (UPS) and optical reflectivity. Both AES and UPS techniques show variations in the observed spectra if referred to samples at different stages of growth. The optical reflectivity technique has also been used in order to study the diamond-substrate interface and to quantify the film thickness.

Among the carbon allotropes newly discovered during the last few decades, carbon nanotubes (CNTs) have attracted enormous attention due to their structural and electronic properties with strong one dimensional character. The physical and chemical features of such systems are intrinsically rich and complex, and can only be probed by using multiple experimental and theoretical techniques. In this feature, we focus on the structural and electronic properties of CNTs that can be accessed by using transmission electron energy loss spectroscopies. The latter are complementary to optical and X-ray absorption techniques, yet allow to obtain the electronic structure with nanoscale spatial resolution. An improved understanding of the structure-electronic properties relationship of these unique 1D systems would represent a fundamental advance, and holds the promise of using CNTs in future applications.

In the present paper, we report on a metal-catalyst-free synthesis of carbon nanotubes (CNTs) on a pre-patterned Si(001) surface. Arrays of triangular-shaped holes were created by nanoindentation in specific sites of the sample. After germanium deposition and chemical vapor deposition (CVD) of acetylene, a few CNTs nucleated and grew from germanium nanoparticles. This result illustrate how it is possible to control the growth of CNTs without the use of a metal catalyst, by leading the assembly of Ge nanoparticles with a patterning technique.

Si(111) and Si(100) surfaces have been observed by an air-operating scanning tunneling microscope (STM). On the cleaved Si(111) surface STM topographic images show predominantly [2¯11]-oriented monatomic steps. The distribution of the width of the terraces is centered around 4 nm. Si(100) surfaces have been hydrogen-terminated by a treatment with fluoridic acid (HF). The surface appears in the topographic STM images to be quite stable and smooth with presumably no oxide.

We have determined the screened on-site Coulomb repulsion in graphite and single wall carbon nanotubes by measuring their Auger spectra and performing a new theoretical analysis based on an extended Cini-Sawatzky approach where only one fit parameter is employed. The experimental lineshape is very well reproduced by the theory and this allows to determine the value of the screened on-site repulsion between $2p$ states, which is found to be 2.1 eV in graphite and 4.6 eV in nanotubes. The latter is robust by varying the nanotube radius from 1 to 2 nm., 5 pages, 3 figures, to appear in Phys. Rev. B

We have taken advantage of the native surface roughness and the iron content of AISI 316 stainless steel to direct grow multi-walled carbon nanotube (MWCNT) random networks by chemical vapor deposition (CVD) at low-temperature ($< 1000^{\circ}$C), without the addition of any external catalysts or time-consuming pre-treatments. In this way, super-hydrophobic MWCNT films on stainless steel sheets were obtained, exhibiting high contact angle values ($154^{\circ}$) and high adhesion force (high contact angle hysteresis). Furthermore, the investigation of MWCNT films at scanning electron microscopy (SEM) reveals a two-fold hierarchical morphology of the MWCNT random networks made of hydrophilic carbonaceous nanostructures on the tip of hydrophobic MWCNTs. Owing to the Salvinia effect, the hydrophobic and hydrophilic composite surface of the MWCNT films supplies a stationary super-hydrophobic coating for conductive stainless steel. This biomimetical inspired surface not only may prevent corrosion and fouling but also could provide low-friction and drag-reduction., 6 pages, 3 figures

Tungsten tips obtained through electrochemical etching have been characterized by scanning electron microscopy, scanning Auger microscopy, and scanning tunneling microscopy. While such tips resulted to be very sharp, a thick oxide layer (∼10 nm) is present at the apex. High‐vacuum annealing at 1800 K removes most of such oxide.

The dependence of electrical conductivity on compression of a freestanding three-dimensional carbon nanotube (CNT) network is investigated. This macrostructure is made of mm-long and entangled CNTs, forming a random skeleton with open pores. The conductivity linearly increases with the applied compression. This behaviour is due to increase of percolating pathways—contacts among neighbouring CNTs—under loads that is highlighted by in situ scanning electron microscopy analysis. The network sustains compressions up to 75% and elastically recovers its morphology and conductivity during the release period. The repeatability coupled with the high mechanical properties makes the CNT network interesting for pressure-sensing applications.

The discovery and understanding of nanoscale phenomena and the assembly of nanostructures into different devices are among the most promising fields of material science research. In this scenario, carbon nanostructures have a special role since, in having only one chemical element, they allow physical properties to be calculated with high precision for comparison with experiment. Carbon nanostructures, and carbon nanotubes (CNTs) in particular, have such remarkable electronic and structural properties that they are used as active building blocks for a large variety of nanoscale devices. We review here the latest advances in research involving carbon nanotubes as active components in electronic and optoelectronic nano-devices. Opportunities for future research are also identified.

We report on the significant generation of photocurrent (PC) from planar devices built from the drop casting of UV-laser-synthesized single-wall-carbon-nanotubes (SWCNTs) onto n-Si substrate. These SWCNTs/n-Si hybrid devices are shown to generate PC with external quantum efficiencies (EQE) reaching up to ∼10%. Their EQE has been optimized by controlling the amount of deposited SWCNTs, and is shown to be significantly enhanced over all the spectral range with a pronounced boost (up to ∼25× times) around 460 nm. The extension of the photoresponse of these devices toward UV correlates well with the absorbance of SWCNTs.

Scanning tunneling spectroscopy was performed on a (15,0) single wall carbon nanotube partially wrapped by poly(3-hexyl-thiophene). On the bare nanotube section, the local density of states is in good agreement with the theoretical model based on local density approximation and remarkably is not perturbed by the polymer wrapping. On the coiled section, a rectifying current-voltage characteristic has been observed along with the charge transfer from the polymer to the nanotube. The electron transfer from poly(3-hexyl-thiophene) to metallic nanotube was previously theoretically proposed and contributes to the presence of the Schottky barrier at the interface responsible for the rectifying behavior.

The authors demonstrate the ability of multiwall carbon nanotubes to generate photocurrents in the near ultraviolet and visible spectral ranges using electrochemical photocurrent measurements. The photogenerated current depends on the excitation wavelength similar to that for single wall carbon nanotubes. Its intensity and modulation can be related to the carbon nanotubes morphology. The maximum photon-to-current conversion efficiency is approximately 7%, about 50 times higher than that reported for single wall carbon nanotubes. This result is of particular relevance for photovoltaic nanodevices and solar energy conversion applications.

The electronic structure of free-standing parallel and braided bundles of single-wall carbon nanotubes (∼1.2nm diameter) was probed by transmission electron microscopy and electron energy loss spectroscopy. The observed dramatic changes in the carbon K(1s) near-edge structures are attributed to the tubes’ structural packing in bundles which consequently alters their electronic structure. The π*- and the σ*-states are shown to be strongly affected by the way the tubes are packed in the bundles (i.e., parallel, braided, turned, or twisted).

Transmission electron microscopy (TEM), electron energy loss near edge structures (EELNES) and scanning tunneling microscopy (STM) were used to distinguish silicon nanotubes (SiNT) among the reaction products of a gas phase condensation synthesis. TEM images exhibit the tubular nature with a well-defined wall. The EELNES spectra performed on each single nanotube show that they are constituted by nonoxidized silicon atoms. STM images show that they have diameter ranging from 2 to 35 nm, have an atomic arrangement compatible with a puckered structure and different chiralities. Moreover, the I-V curves showed that SiNT can be semiconducting as well as metallic in character.

Dried, fixed uncoated neuron granule cells and their neurites have been imaged in air by an atomic force microscope (AFM) in the repulsive regime of contact mode. Neurons have also been observed after swelling with glutamate or decapping. Modifications induced by glutamate resulted in a drastic reduction in the cell body height (from 1.5 to 2.0 mu m for the untreated ones down to 0.7-1.0 mu m) and in an increased corrugation of the granule cell membrane. In the decapped neurons AFM revealed decreasing cell body height for an increasing amount of removed material during the decapping procedure. These results demonstrate that AFM is the ideal technique to observe cell corrugation and height modifications during cell treatments of neurobiological interest. (C) 1996 American Vacuum Society.

We used an atomic force microscope, in the repulsive regime of contact mode, to take images of uncoated neurons fixed in glutaraldehyde on a gold covered stainless steel substrate. We observed granule cells and their axons with a resolution better than 20 nm. The good stability of the sample and the mechanical reproducibility of the microscope allowed the imaging of a neuron culture area of several square microns. Modifications induced by glutamate on the neuronal culture resulted in observing a drastic reduction in cell granule height (from 1.5–2.0 μm for the unperturbed ones down to 0.7–1.0 μm) and in an increased corrugation of the surface membrane. The atomic force microscope images were very reproducible over repeated scanning acquisition, demonstrating a very good mechanical and thermal stability of the instrument‐sample system.

The interaction between lymphocyte cell and human immunodeficiency virus (HIV) has been studied at membrane level by atomic force microscopy (AFM) in the repulsive regime of contact mode. Morphological characteristics of noninfected lymphoid cells and HIV infected cells were easily imaged from fixed and dried cell preparations. After HIV exposure we observed a decrease in surface protrusions (lost of microvilli) and the creation of many dips. Some particles, presumably of viral origin (120–130 nm size), were also observed in proximity of the cell surface. Similar changes have been observed by AFM on cells exposed to intense electromagnetic field thus indicating that such cells undergo modifications of their morphology upon suffering from an external agent.

By properly tuning the photon energy of a femtosecond laser pump, we disentangle, in carbon nanotube–Si (CNT/Si) heterojunctions, the fast relaxation dynamics occurring in CNT from the slow repopulation dynamics due to hole charge transfer at the junction. In this way we are able to track the transfer of the photogenerated holes from the Si depletion layer to the CNT layer, under the action of the built-in heterojunction potential. This also clarifies that CNT play an active role in the junction and do not act only as channels for charge collection and transport.

We present a combined experimental and theoretical investigation of the early carbonization stages of the Si(111)-(7x7) surface upon acetylene exposure. Scanning tunneling microscopy images reveal the formation of a (root3xroot3)R30degrees reconstruction. Ab initio calculations allow us to characterize this reconstruction as a carbon-rich silicon phase due to subsurface incorporation of C atoms.