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In this Letter, we investigated the photo-response of multi wall carbon nanotube-based composites obtained from in situ thermal evaporation of noble metals (Au, Ag, and Cu) on the nanotube films. The metal deposition process produced discrete nanoparticles on the nanotube outer walls. The nanoparticle-carbon nanotube films were characterized by photo-electrochemical measurements in a standard three electrode cell. The photocurrent from the decorated carbon nanotubes remarkably increased with respect to that of bare multiwall tubes. With the aid of first-principle calculations, these results are discussed in terms of metal nanoparticle-nanotube interactions and electronic charge transfer at the interface. [ABSTRACT FROM AUTHOR]

Abstract: We analyze the local microscopic deformation left by Au, Ag and Cu islands on carbon nanotube walls observed by transmission electron microscopy. We employ finite-element simulations within continuum elasticity theory to demonstrate that the observed deformation of the tube walls is the result of elastic strain energy relaxation induced by the nucleation of noble metal clusters on the graphene lattice. We find that the magnitude of the tube deformation is strictly correlated to the lattice mismatch of the metal/carbon system under study. In this context, the tube deformation under the island is a proof of the pseudomorphical character of the system, even in the case of high lattice misfit (∼15%) as for Au and Ag. [Copyright &y& Elsevier]

Abstract: 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. [Copyright &y& Elsevier]

Abstract: 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. [Copyright &y& Elsevier]

Abstract: Combined scanning tunneling microscopy, reflection electron energy loss spectroscopy and X-ray photoelectron studies have been performed in situ under ultra high vacuum condition, on tetraphenylporphyrin molecules (H2TPP) vacuum sublimated on highly oriented pyrolitic graphite. The experimental studies were performed at room temperature, as a function of the amount of deposited porphyrins. The propensity of H2TPP to self-assembly on the graphite surface could be detected after a threshold of deposited material. In this case tetraphenylporphyrin molecules arranged according to a quasi-hexagonal lattice separated from their nearest neighbours by a minimum distance of about 1nm. The formation of an additional incomplete layer, at a slightly higher coverage, was also detected where the quasi-hexagonal symmetry is retained. Finally, subsequent tetraphenylporphyrins depositions gave molecular aggregates randomly distributed on the graphite surface with subsequent loss of order. [Copyright &y& Elsevier]

Abstract: The ordering properties of tetraphenylporphyrin molecules sublimated on a highly oriented pyrolitic graphite surface have been investigated. The morphological information obtained by scanning tunneling microscopy has been linked with the optical spectra by reflectance anisotropy spectroscopy. Measurements were performed in situ as a function of the nominal coverage. [Copyright &y& Elsevier]

Abstract: 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. [Copyright &y& Elsevier]

In this paper we report on a morphological investigation of the growth mechanism of silicon carbide (SiC) on the Si(1 1 1)7 × 7 surface. The role of the substrate morphology and temperature during acetylene exposure has been studied with the aim to obtain high quality SiC films. We compared two starting points of silicon substrate: one characterised by step bunching and one by monoatomic terraces of the same width. Our results indicate that a lower density of defects and holes is present in the former case. [Copyright &y& Elsevier]

The morphology of the first stages of acetylene reaction with Si(1 1 1)7 × 7 reconstructed surface has been investigated by scanning tunneling microscopy (STM). We studied the surface modification for two substrate temperatures during reaction (650 and 700 °C) and as a function of acetylene doses. Both these parameters have been observed to play a crucial role in the carbonization reaction, the formation of nanostructures and their development. For low acetylene exposure, almost the entire surface appears √ of 3 × √ of 3-R30° reconstructed but islands, mainly decorating the step edges, are generally surrounded by 7 × 7 reconstructed areas, located deeper with respect to the plane of √ of 3 × √ of 3-R30° reconstruction. For highest acetylene dose, the surface is characterized by nanostructures and large holes (as deep as 3–5 nm) that occupy one or more terraces between the original silicon surface step edges with their inner side constituted of islands itself. For intermediate acetylene exposure, the small increase (from 650 to 700 °C) of substrate temperature during the reaction is sufficient to make the resulting carbonization mechanism switch towards the highest exposure behaviour. [Copyright &y& Elsevier]

Photocurrent generation of nanometric Ge dots has been investigated by using electrochemical measurements. Photocurrent features have been ascribed, for large Ge dots, to Ge bulk direct electronic transitions at L and X points as evidenced by their close correspondence with the optical absorption coefficient. A blueshift of the photocurrent features has been detected by reducing the Ge dot size. These changes have been interpreted as due to quantum confinement effect. This result suggests that Ge dots could be applied in photovoltaic nanodevices and quantum dot based lasers. [ABSTRACT FROM AUTHOR]

The electronic structure of free-standing parallel and braided bundles of single-wall carbon nanotubes (∼1.2 nm 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). [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

The initial growth of Mn on Pt(1 1 1) at room temperature has been followed by auger electron spectroscopy and scanning tunneling microscopy. In the interface formation, two distinct regimes have been observed as a function of manganese deposit, with a sharp change in the growth mode at about 1.6 ML. A model has been developed for the earlier stage of growth, suggesting the formation of an intermixed phase extending to about 14 layers, with an average composition Pt0.89Mn0.11. [Copyright &y& Elsevier]

Single molecule localization microscopy (SMLM), which can provide up to an order of magnitude improvement in spatial resolution over conventional fluorescence microscopy, has the potential to be a highly useful tool for quantitative biological experiments. It has already been used for this purpose in varied fields in biology, ranging from molecular biology to neuroscience. In this review article, we briefly review the applications of SMLM in quantitative biology, and also the challenges involved and some of the solutions that have been proposed. Due to its advantages in labeling specificity and the relatively low overcounting caused by photoblinking when photo-activable fluorescent proteins (PA-FPs) are used as labels, we focus specifically on Photo-Activated Localization Microscopy (PALM), even though the ideas presented might be applicable to SMLM in general. Also, we focus on the following three quantitative measurements: single molecule counting, analysis of protein spatial distribution heterogeneity and co-localization analysis. [ABSTRACT FROM AUTHOR]

We investigated the local order in individual iron nanoparticles (NPs) embedded in carbon nanotubes (CNTs). The NPs directly come from the CNT growth on stainless steel without addition of external metal catalyst. The structural analysis has been obtained through nanoscale transmission extended electron energy loss fine structure (EXELFS) measurements above the iron L edge. A theoretical simulation of the EXELFS features has been performed within the multiple scattering theory. By comparing the experimental data with the simulations, we found that pure γ-Fe and FeC nanoparticles are the catalysts of the CNT synthesis on the stainless steel. Moreover, from the analysis of the fine details of the EXELFS oscillations, we also estimated the value of the fcc Fe NP lattice parameter to be a = 3.61 ± 0.03 Å. This last finding suggests a high magnetic moment of the fcc Fe NPs. [ABSTRACT FROM AUTHOR]

A novel method to build bicomponent peptide self-assembledmonolayers(SAMs) has been developed, by exploiting helix···helixmacrodipole interactions. In this work, a peptide-based self-assembledmonolayer composed of two helical peptides was immobilized on a goldsurface. Specifically, a pyrene-containing octapeptide, devoid ofany sulfur atom (A8Pyr), and a hexapeptide, functionalized at theN-terminus with (S,R) lipoic acid,for binding to gold substrates (SSA4WA) via a Au–S linkage,have been employed. Both peptides investigated attain a helical structure,because they are almost exclusively formed by strongly folding inducerCα-tetrasubstituted α-amino acids. We demonstratethat the two peptides generate a stable supramolecular nanostructure(a densely packed bicomponent peptide monolayer), where A8Pyr is incorporatedinto the SSA4WA palisade by exploiting helix···helixmacrodipole interactions. The presence of both peptides on the goldsurface was investigated by spectroscopic and electrochemical techniques,while the morphology of the monolayer was analyzed by ultra high-vacuumscanning tunnelling microscopy. The composition of the bicomponentSAM on the surface was studied by a combination of electrochemicaland spectroscopic techniques. In particular, the amount of Au–Slinkages from the sulfur-containing peptides was quantified from reductivedesorption of the peptide-based SAM, while the amount of A8Pyr wasestimated by fluorescence spectroscopy. The antiparallel orientationof the A8Pyr and SSA4WA peptide chains minimizes the interaction energybetween the helix dipoles, suggesting that this kind of electrostaticphenomenon is the driving force that stabilizes the bicomponent SAM. [ABSTRACT FROM AUTHOR]

Abstract: Multiwall carbon nanotubes are found to generate photocurrent in the visible and near ultra violet spectral range using a photoelectrochemical technique. Peaks in the photocurrent are observed at excitation energies in the visible region. Their electron energy loss spectra exhibit the π plasmon feature, typical of graphite layers, and a peak at lower energy. Features at energies between 0 and 4eV have been already observed for single wall carbon nanotubes and ascribed to interband electronic transitions due to the reduced dimensionality of these systems. The present measurements suggest that the usual identification of multiwall carbon nanotubes electronic density of states with that of graphite layers is not sufficient and more theoretical investigations are necessary to shed light on this point. [Copyright &y& Elsevier]

Different amounts of single wall carbon nanotubes (SWCNTs) have been sprayed on amorphous silicon substrates to form Schottky barrier solar cells. The measured external quantum efficiency showed a spectral behavior depending on the SWCNT network optical transparency, presenting a maximum up to 35% at a wavelength of about 460 nm. Ultrathin network of SWCNTs acts as semitransparent electrode and forms Schottky barrier with amorphous silicon, enabling new generation low cost amorphous silicon based solar cells. Numerical simulations show a poor efficiency of SWCNT contacts in collecting holes suggesting that improvement in contact quality is needed to further improve solar cell efficiency. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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 forming an electron cloud that prevents atoms and molecules crossing. Nonetheless at high annealing 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 dislocations in the graphene lattice favor the Si atoms intercalation, 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. Image 109 [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Films of multiwall carbon nanotubes (CNTs), arranged on Si/SiO 2 substrates, are used as templates for Nb films with thickness in the range 3–50 nm deposited by sputtering. The resulting aggregates show normal state and superconducting properties similar to those observed in networks of superconducting nanowires (SNW) obtained by other methods. Decreasing the Nb thickness, when the normal state resistance becomes larger than the quantum resistance, a superconductor-insulator transition is observed. Moreover, thermally activated phase slips in thicker samples, evolving in quantum phase slips in thinner nanowires, are observed in the superconducting state. The experimental results indicate that the template method based on CNTs is a promising alternative to the much more expensive nanolithography techniques for obtaining SNWs. Even more important, they indicate CNT films as versatile elements in nanostructured electronic devices. [ABSTRACT FROM AUTHOR]

With the advent of single-molecule localization microscopy (SMLM) techniques, intracellular proteins can be imaged at unprecedented resolution with high specificity and contrast. These techniques can lead to a better understanding of cell functioning, as they allow, among other applications, counting the number of molecules of a protein specie in a single cell, studying the heterogeneity in protein spatial organization, and probing the spatial interactions between different protein species. However, the use of these techniques for accurate quantitative measurements requires corrections for multiple inherent sources of error, including: overcounting due to multiple localizations of a single fluorophore (i.e., photoblinking), undercounting caused by incomplete photoconversion, uncertainty in the localization of single molecules, sample drift during the long imaging time, and inaccurate image registration in the case of dual-color imaging. In this paper, we review recent efforts that address some of these sources of error in quantitative SMLM and give examples in the context of photoactivated localization microscopy (PALM). [ABSTRACT FROM AUTHOR]

The bulk synthesis of freestanding carbon nanotube (CNT) frameworks is developed through a sulfur-addition strategy during an ambient-pressure chemical vapour deposition process, with ferrocene used as the catalyst precursor. This approach enhances the CNTs’ length and contorted morphology, which are the key features leading to the formation of the synthesized porous networks. We demonstrate that such a three-dimensional structure selectively uptakes from water a mass of toxic organic solvent (i.e. o-dichlorobenzene) about 3.5 times higher than that absorbed by individual CNTs. In addition, owing to the presence of highly defective nanostructures constituting them, our samples exhibit an oil-absorption capacity higher than that reported in the literature for similar CNT sponges. [ABSTRACT FROM AUTHOR]

Abstract: The realization of a Silicon Carbon Nanotube heterojuntion opens the door to a new generation of photodetectors (Si-CNT detector) based on the coupling between this two materials. In particular the growth of Multiwall Carbon Nanotubes on the surface of a n-doped silicon substrate results on a Schottky diode junction with precise rectifying characteristics. The obtained device presents a low dark current, high efficiency in the photoresponsivity, high linearity and a wide stability range. The junction barrier is about 3.5V in reverse polarity with a breakdown limit at more than 100V. The spectral behavior reflects the silicon spectral range with a maximum at about 880nm. [Copyright &y& Elsevier]

Abstract: A new class of radiation detectors based on carbon nanostructures as the active photosensitive element has been recently developed. In this scenario the optimization of the device, both in dark and on light irradiation, is a crucial point. Here, we report on electrical measurements performed in dark conditions on carbon nanofibers and nanotubes deposited on silicon substrates. Our experimental results were interpreted in terms of a multistep tunneling process occurring at the carbon nanostructures/silicon interface. [ABSTRACT FROM AUTHOR]

Abstract: 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. [Copyright &y& Elsevier]

Negative differential resistance (NDR), for which the current is a decreasing function of the voltage, has been observed in the current–voltage curves of several types of structures. We measured tunnelling current and NDR by illuminating large area heterojunction obtained by growing Multi Wall Carbon Nanotubes on the surface of n-doped Silicon substrate. In the absence of light, the current flow is null until a junction threshold of about 2.4 V is reached, beyond which the dark current flows at room temperature with a very low intensity of few nA. When illuminated, a current of tens nA is observed at a drain voltage of about 1.5 V. At higher voltage the current intensity decreases according to a negative resistance of the order of MΩ. In the following we report details of tunneling photodiode realized and negative resistance characteristics. [ABSTRACT FROM AUTHOR]

The first stages of acetylene reaction with the Si(1 1 1)7 × 7 reconstructed surface kept at 600 °C are studied by recording scanning tunneling microscopy (STM) images during substrate exposure at a C2H2 pressure of 2 × 10−4 Pa (2 × 10−2 mbar). We observed the progressive substitution of the 7 × 7 reconstruction with a carbon induced Si(1 1 1)√3×√3R30° reconstruction characterized by an atomic distance of 0.75 ± 0.02 nm, very close to that of the silicon 7 × 7 adatoms. This means that a carbon enrichment of the silicon outermost layers occurs giving rise to the formation of a Si–C phase different from the √3×√3R30° reconstruction typical of Si terminated hexagonal SiC(0 0 0 1) surface with an atomic distance of 0.53 nm. To explain STM images, we propose a reconstruction model which involves carbon atoms in T4 and/or S5 sites, as occurring for B doped Si(1 1 1) surface. Step edges and areas around the silicon surface defects are the first regions involved in the reaction process, which spreads from the upper part of the step edges throughout the terraces. Step edges therefore, progressively flakes and this mechanism leads, for the highest exposures, to the formation of large inlets which makes completely irregular the straight edge typical of the Si(1 1 1)7 × 7 terraces. These observations indicate that there occurs an atomic diffusion like that driving the meandering effect. Finally, the formation of a few crystallites is shown also at the lowest acetylene exposures. This is the first STM experiment showing the possibility to have carbon incorporation in a Si(1 1 1) matrix for higher amounts than expected, at least up to 1/6 of silicon atomic layer. [Copyright &y& Elsevier]

Abstract: We first investigate the spontaneous formation of nanometric and highly dense (∼3×1012 cm−2) Ge droplets on SiO2/Si(001) by scanning tunnelling microscopy and spectroscopy. Ge dots are grown using a two-step process: first, Ge deposition on the clean SiO2 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 SiO2/Si(001) 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. [Copyright &y& Elsevier]

Abstract: The SiC formation on a ordered Si(100) substrate at low temperatures (980–1180K) and low total pressures (10−6 mbar) has been investigated by in situ X-ray photoemission spectroscopy (XPS) and ex situ scanning tunneling microscopy (STM). SiC was grown by chemical vapor deposition (CVD) from C2H2 and Si2H6 as the precursor gases. At all the temperatures and in presence of both C2H2 and Si2H6 XPS data showed the formation of sub-stoichiometric Si1−x C x alloys characterized by excess silicon. By exposing to C2H2 only, stoichiometric SiC could be synthesized up to 1080K. At 1180K the formation of a Si1−x C x alloy was observed. STM analysis has pointed out the role of silicon from the gas phase in the growth mechanisms and it has shown that uniform films with low roughness and small nanostructures can be obtained by tuning the acetylene/disilane ratios independently from the temperature selected in the investigated range. [Copyright &y& Elsevier]

The magnetic domains configuration in arrays of rectangular prisms of permalloy with lateral sizes of 1100 nm × 300 nm, and 800 nm × 550 nm, inter-dot spacing of 200 nm and thickness of 30 nm, has been investigated by magnetic force microscopy (MFM) at room temperature and at zero applied magnetic field. In order to have further information on the static magnetic properties of these dots, longitudinal magneto-optical Kerr effect experiments and micro-magnetic theoretical simulations have been performed. [Copyright &y& Elsevier]

Quantum dots (QDs) are actually easily produced by self-assembling during heteroepitaxial growth of semiconductors. In order to exploit the unique electronic properties of semiconductor QDs in novel quantum effect devices, the lateral dimensions of these structures have to be reduced to the order of tens of nanometers, which is the range of the De Broglie wavelength of electrons inside these materials. Moreover, millions of QDs must be arranged in dense ordered arrays to achieve the necessary active volume for optoelectronic applications. Nowadays it is possible to control size and shape of the nanocrystals, but it is still difficult to decide their nucleation site. Many approaches have been undertaken to overcome this problem, like using regular dislocation networks, lithographically and Atomic Force Microscopy (AFM) patterned substrates, naturally patterned surfaces. We present results obtained by some of these methods, visualized by Scanning Tunnelling Microscopy (STM) or AFM microscopy. STM measurements at high temperature during the epitaxial growth are of great help in these studies. Images and movies of the growth of Ge on Si help to identify the real nucleation sites of the islands and to follow their evolution. The influence of the ‘step bunching’ on the self-organization of Ge islands on Si(111) surfaces will be analysed, as an example of growth on self-nanostructured surfaces. [Copyright &y& Elsevier]

Abstract: The properties of carbon nanotubes (CNTs), the new allotropic status of carbon discovered in 1991, have been widely investigated in all possible application field. This new material in fact can be easily obtained chemically by CVD (Chemical Vapour Deposition) as a layer of nanotubes growth on a wide variety of materials. When growth on a silicon surface, CNTs create a semiconductor heterojunction with peculiar photoresponsivity properties. We studied this heterojunction with the purpose to realize a large photocathode with high quantum efficiency in a large wavelength range from UV to IR. Results obtained up to day allowed us to build a new kind of photodetector very cheap, stable and easy to manage. Recently this new device has been proposed as one of candidates for the beam monitor system of SuperB. [Copyright &y& Elsevier]

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. [ABSTRACT FROM AUTHOR]

We report photocurrent generation in entangled networks of multiwall-carbon nanotubes (MWCNTs) grown on TiN/Si substrates by an all-laser process. By integrating these MWCNTs into planar devices, we demonstrate that they generate photocurrent over all the visible and near-ultraviolet range, with maximum efficiency around 420 nm. Photocurrent is obtained even at zero applied voltage, pointing to a true photovoltaic (PV) effect. The extracted photocurrent as a function of applied voltage exhibits nonlinear behavior for voltages ≥2 V, suggesting that the devices do not behave as pure photoresistances. Other mechanisms (e.g., Schottky barriers imbalance) are invoked to describe current flow in these PV devices. [ABSTRACT FROM AUTHOR]

The spontaneous formation of nanometric and highly dense (∼3×1012 cm-2) Ge droplets on thin SiO2 film on Si(001) is investigated by scanning tunneling microscopy and spectroscopy. Ge dots have been grown by depositing Ge on the clean SiO2 surface at room temperature and then annealing the sample at 500 °C. Ge dots appear to be free of germanium oxides and characterized by a flat surface with the onset of {113} faceting. I-V curves show that they have an energy gap of approximately 1.8 eV, well above that of bulk Ge. Fabrication of nanometer-sized, highly dense pure Ge droplets is very promising for nanoelectronics applications. [ABSTRACT FROM AUTHOR]