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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 structure of thin films deposited by pulsed laser ablation (PLD) is strongly dependent on experimental conditions, like laser wavelength and fluence, substrate temperature and pressure. Depending on these parameters we obtained various kinds of carbon materials varying from dense, mainly tetrahedral amorphous carbon (ta-C), to less compact vertically oriented graphene nano-particles. Thin carbon films were grown by PLD on n-Si ?100? substrates, at temperatures ranging from RT to 800°C, from a rotating graphite target operating in vacuum. The laser ablation of the graphite target was performed by a UV pulsed ArF excimer laser (?=193 nm) and a pulsed Nd:YAG laser, operating in the near IR (?=1064 nm). The film structure and texturing, characterised by X-ray diffraction analysis, performed at grazing incidence (GI-XRD), and the film density, evaluated by X-ray reflectivity measurements, are strongly affected both by laser wavelength and fluence and by substrate temperature. Micro-Raman and GI-XRD analysis established the progressive formation of aromatic clusters and cluster condensation into vertically oriented nano-sized graphene structures as a direct function of increasing laser wavelength and deposition temperature. The film density, negatively affected by substrate temperature and laser wavelength and fluence, in turn, results in a porous bulk configuration and a high macroscopic surface roughness as shown by SEM characterisation. These structural property modifications induce a relevant variation also on the emission properties of carbon nano-structures, as evidenced by field emission measurements.

Pulsed laser ablation from a rotating graphite target operating both in vacuum (~10-5 Pa) and in He sustaining gas (~10 Pa) has been used to grow thin carbon films on Si substrates kept at temperatures from RT to 900 °C. Synchrotron and laboratory X-ray diffraction (XRD), performed at grazing incidence, established the formation of nano-sized graphene structures at higher deposition temperatures (~800 ÷ 900°C). When the carbon plume was expanding in vacuum, these structures resulted to be formed by few parallel graphene layers, characterised by an oriented growth along the graphene planes, with the ? axis parallel to the substrate. High resolution (HR) cross section TEM images of C nano-structures on grids or in film/Si substrate confirmed both size and orientation of the graphene nano-particles. The presence of He atmosphere in the reaction chamber changes basically the particle nucleation process: a clustering phenomenon of aromatic structures is promoted in the gas phase also at low temperature. The nano-structured particles, however, are characterised by a round shaped morphology and random orientation. The mass density of deposited films, measured by X-ray reflectivity, is also strongly dependent on the experimental settings: films grown in the inert gas show lower density compared to the vacuum deposited ones. The preferential vertically oriented growth of graphene layers in vacuum and high temperature can be explained as a combined effect of different processes under a fast kinetic mode: thermal surface diffusion, in-plane growth of graphene sheets and line source direction of activated carbon species of the laser plume. He deposited samples are characterised by a different nucleation and growth process and a more complex structure.

Nano-structured carbon films have been proved to be outstanding materials for different kinds of applications, mainly electronic, owing to their high electron field emission properties, but also energetic (hydrogen storage, fuel cells), catalytic (very high metal catalyst dispersion properties) or biological (very good bio-sensor support). In this work we studied the influence of experimental conditions (vs. substrate temperature, working pressure and inert sustaining gases) on the structure evolution of carbon films, from an almost amorphous material to nano-clustered graphene particles. The carbon films were grown by Pulsed Laser Ablation (Nd:YAG, 2nd harmonic: λ=532 nm, hν=2.33 eV, τ=7 ns, ν=10 Hz, Φ≈7 J/cm2), from a pyrolytic graphite target on Si substrates. PLD depositions were performed at increasing temperature, ranging from room temperature to 900 °C, both in vacuum and in He atmosphere, at ∼20 Pa. Near-edge X-ray absorption fine structure (NEXAFS) and Raman spectroscopy evidenced the aromatic ring formation and the clustering condensation process with increasing surface temperature. The surface roughness and morphology of films grown at different conditions have been characterised by atomic force microscopy (AFM) and scanning electron microscopy (SEM).

Thin carbon films have been deposited in vacuum (?10-4 Pa) on Si substrates by pulsed laser ablation of a graphite target using a Nd:YAG laser operating in the near infrared region (?=1064 nm). The samples have been deposited at different substrate temperatures (T sub) ranging from room temperature (RT) to 800°C. X-ray diffraction analysis established the progressive formation of nanosized graphene structures as T sub increased. In fact, film structure evolves from almost amorphous to nanostructured phase characterized by graphene layers oriented perpendicularly to the film plane. The film density, evaluated by X-ray reflectivity measurements, is strongly affected by T sub. At RT the film density is similar to the graphite one, while it decreases at higher T sub. The electrical properties of the samples have been characterized by field emission measurements. The parameters describing the emitter properties (threshold field E th and field enhancement factor ?) have been evaluated using variable anode-to-cathode distance method. Samples deposited at low T sub have shown the best emission properties, presenting lower E th and larger ? values than those deposited at higher T sub. This is mainly attributed to the sensible density variation, which is in competition with the slighter augment of mean nanoparticle size.

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.

Amorphous (a-C) Carbon thin films were deposited, using pulsed laser deposition (PLD) with a Nd:YAG laser ( 1064 nm, 7 ns), from a pyrolytic graphite target, on < 1 0 0 > silicon and refractory metal (Mo) substrates to a film thickness of 55, 400 and 500 nm. Samples were grown at RT and then annealed by a laser annealing technique, to reduce residual stress and induce a locally confined "graphitization'' process. The films were exposed to irradiation, in vacuum, by a Nd: YAG pulsed laser, operating at different wavelengths ( VIS, N-UV) and increasing values of energy from 6-100 mJ/pulse. The thinner films were completely destroyed by N-UV laser treatment also at lower energies, owing to the almost direct propagation of heat to the Si substrate with melting and ruinous blistering effects. For thicker films the Raman micro-analysis evidenced the influence of laser treatments on the sp(3)/sp(2) content evolution, and established the formation of aromatic nano-structures of average dimension 4.1 divided by 4.7 nm ( derived from the I-D/I-G peak ratio), at fluence values round 50 mJ/cm(2) for N-UV and 165 mJ/cm(2) for VIS laser irradiation. Higher fluences were not suitable for a-Carbon "graphitization'', since a strong ablation process was the prominent effect of irradiation. Grazing incidence XRD (GI-XRD) used to evaluate the dimension and texturing of nano-particles confirmed the findings of Raman analysis. The effects of irradiation on surface morphology were studied by SEM analysis.

Photocurrent generation measured with an electrochemical cell on carbon nanotubes has been obtained mainly from single-walled nanostructures. In fact, multiwall carbon nanotubes (MWCNTs) were not expected to show analogous low-dimensional effects, due to their close similarity to metallic graphite. Recently we reported on the ability of MWCNTs to generate photocurrent in the visible and ultraviolet spectral range. In this paper we show a significant enhancement in the photocurrent generation when the walls of the MWCNTs were decorated with dispersed Cu nanoparticles. This result is of particular relevance for photovoltaic nanodevices and solar energy conversion applications.

We compare the local order in single-wall carbon nanotubes (SWCNTs) and highly oriented pyrolitic graphite (HOPG) by means of nanoscale transmission extended energy loss fine structure (EXELFS) measurements above the carbon K edge. The HOPG EXELFS spectra and their Fourier transform were compared to their synchrotron extended X-ray absorption fine structure (EXAFS) counterpart and discussed within a multiple scattering framework. By comparing the experimental EXELFS data to spectra calculated using a theoretical model based on a single scattering approach, we showed the fundamental importance of considering multiple paths (involving up to eight body scattering) to reproduce the fine details of EXELFS features. Simulating EXELFS spectra of SWCNTs by our theoretical model is shown to represent a measure of their chiralities. Finally, the shrinkage of the nearest-neighbor distance in the Fourier transform observed for SWCNTs (absent in graphite) is interpreted within a simple model invoking anharmonic effects.

Carbon films were deposited by pulsed laser ablation on Si substrates, heated at temperatures increasing from RT to 800 °C, from a pure graphite target, operating in vacuum (~ 10− 4 Pa). The laser ablation was performed by an Nd:YAG laser, operating in the near IR wavelength (λ = 1064 nm). Micro-Raman and grazing incidence X-ray diffraction analysis (GI-XRD) established the progressive formation of ordered nano-sized graphitic structures, increasing substrate temperature. The surface morphology is characterised by macroscopic roughness (SEM, AFM) while the low temperature samples are characterised by very smooth surface. The film density, evaluated by X-ray reflectivity measurements, is also affected by the substrate temperature. This structural property modification induces relevant variation on the emission properties of carbon films, as evidenced by Field Emission measurements. The film structure and texturing is also strongly related to laser wavelength: the low energy associated to the IR laser radiation (1.17 eV) causes an early aromatic cluster formation at T = 400 °C associated to a sensible increase in the aromatic plane stacking distance (d002 ~ 0.39 nm), compared to graphite. These density decrease shows a direct correlation with the electron emission properties. Roughness and presence of voids play a negative role both on the threshold electric field Eth and enhancement factor (β) The density decreasing and graphitic layer widening are notably to be ascribed to the very fast out-of-equilibrium growth and to the presence of large activated carbon species in the “plume”.

Thin nano-structured carbon films have been deposited in vacuum by pulsed laser ablation, from a rotating polycrystalline graphite target, on Si (1 0 0) substrates, kept at temperatures ranging from RT to 800 degrees C. The laser ablation was performed by a Nd:YAG laser, operating in the near IR (lambda = 1064 nm). X-ray diffraction analysis, performed at grazing incidence angle, both in-plane (ip-gid) and out-of-plane (op-gid), has shown the growth of oriented nano-sized graphene particles, characterised by high inter-planar stacking distance (d(c) similar to 0.39 nm), compared to graphite. The film structure and texturing are strongly related both to laser wavelength and substrate temperature: the low energy associated to the IR laser radiation (1.17 eV) generates activated carbon species of large dimensions that, also at low T (similar to 400 degrees C), easy evolve toward more stable sp(2) aromatic bonds, in the plume direction. Increasing temperature the nano-structure formation increases, causing a further aggregation of aromatic planes, voids formation, and a related density (by X-ray reflectivity) drop to very low values. SEM and STM show for these samples a strongly increased macroscopic roughness. The whole process, mainly at higher temperatures, is characterised by a fast kinetic mode, far from equilibrium and without any structural or spatial rearrangement.

Aiming at the production of image-enhancing devices (electron multipliers) to amplify the backscattered electron signal in scanning electron microscopy, a study of the stationary secondary electron emission from CVD diamond films, irradiated by a high-energy primary electron beam, was performed in order to deepen the understanding of the specific material characteristics that appear to control the electronic emission. An extensive analysis of the secondary electron emission yield 6, as a function of the primary electron beam energy, was performed on polycrystalline CVD samples of different thickness. The emission yield was observed to increase up to a maximum value corresponding to a film thickness of about 15 mu m and to decrease at larger thickness values. The experimental results are analyzed according to a theoretical model previously developed [P. Ascarelli, E. Cappelli, F. Pinzari, M.C. Rossi, S. Salvatori, P.G. Merli, A. Migliori, J. Appl. Phys. 89 (2001) 689] and extended within this work. We realized that the most important material parameter controlling the secondary electron emission yield as a function of the primary electron energy is the mean escape depths of the secondary electrons. The obtained lambda(S) values were found to be adequate to explain the film emission performance dependence on its thickness d. Moreover, using the atomic force microscopy technique and developing an algorithm based on a three-points method to identify the mean orientation of crystal facets in space, we observed that the S(a) (and consequently the secondary electron emission performance) evolution during the growth process may be largely explained by a variation of the film surface mean orientation and a concomitant variation of the film quality.

Electronic properties of graphene nano-structures are highly anisotropic and correlated to their basal plane orientation. In this work, we tried to study and explain how deposition temperature can draw a definite plane growth direction. Carbon films have been deposited by Pulsed Laser Ablation (Nd:YAG, 2nd harmonic: λ=532 nm, hν=2.33 eV, τ=7 ns, ν=10 Hz, Φ ≈7 J/cm2), from a pyrolytic graphite target on Si substrates. PLD depositions were performed in vacuum, at increasing substrate temperature, ranging from room temperature (RT) to 900 °C. Near-edge X-ray absorption fine structure (NEXAFS), SEM and Raman spectroscopy have been used to characterise the films. Using linearly polarized Synchrotron radiation and HOPG (Highly Oriented Pyrolytic Graphite) as a reference system, we investigated, ex situ, the occurrence of an average orientation distribution of the nano-sized graphene clusters, grown at high temperature. The results of the angle-dependent study by NEXAFS of film grown at 900 °C provide evidence that at high temperature the graphene sheets show a tendency to grow with basal planes oriented perpendicularly to the substrate surface. At low temperature, the film is less structured. The features ascribable to graphitic character are less pronounced and broadened; the absence of an angle dependence of NEXAFS measurements suggest that C-structures are randomly oriented. The corresponding Raman spectrum substantiates the prevailing amorphous nature of the film.

PLD and CVD methods, plasma or bias assisted, have been used to prepare thin films of nano-clustered graphite. The experimental conditions (vz. deposition apparatus, substrate temperature, working pressure, inert sustaining gases parent species, and applied voltage) have been changed with the final aim of obtaining small graphene particles with the basal planes oriented along the growth vector and perpendicular to the n-Si substrate. Pulsed laser ablation (Nd:YAG, 2nd harmonic: lambda=532 nm, hnu=2.33 eV, tau=7 ns, nu=10 Hz, Phiapproximate to7 J/cm(2)), assisted by an RF-plasma, of a pyrolytic graphite target gave good results for nano-structure formation, provided high substrate temperature and high inert gas pressure are maintained. CVD methods, in the presence of high substrate temperature and a DC bias, showed a good attitude to drive a longitudinal growth of graphene layers and nano-wires from a reactive gas flow of Argon/Hydrogen and Methane. The morphology of the films grown at different conditions have been characterised by scanning electron microscopy (SEM). Film quality and nano-particle dimensions have been estimated by Raman spectroscopy.

An rf-SQUID under appropriate temperature and bias conditions can be used to perform tests on macroscopic quantum coherence, or as a qubit element for quantum computing. For both these purposes it is necessary a readout system allowing to discriminate stroboscopically the rfSQUID state with high fidelity. This task can be performed by means of a hysteretic dc-SQUID inductively coupled to the rf-SQUID and turned on by a fast bias current pulse. We have proposed and realized an integrated system where all the devices, the rf-SQUID, the hysteretic dc-SQUID, and a SQUID magnetometer are on the same chip. This system can perform single-shot detection of the rf-SQUID state with a fidelity better than 98%. The rf-SQUID has been coupled to a high-frequency line working in the microwave region (2–26 GHz), and has been tested and characterized from 4.2 K to the mK region of temperatures.

Owing to their outstanding properties, many research efforts have been focused on the growth and application of carbon based materials, mainly single or multi-wall carbon nano-tubes, nano-horns and cones, fibres . Nano-structured carbon films have also been proved to be a very promising field emitting material, providing the nano-graphene structure have the constituting basal plane oriented perpendicular to the substrate. Pulsed Laser Deposition (PLD) and Chemical Vapour Deposition (CVD) methods have been used to prepare carbon films of different nano-structure ranging from amorphous carbon to nano-clustered graphite and nano-wires. The influence of experimental conditions (v.z. deposition system and parent species, substrate heating, working pressure, inert sustaining gases, RF or DC plasma assisted deposition) on the carbon atom clustering, particle aggregation and structure evolution has been thoroughly analysed. Nd:YAG pulsed laser ablation of a graphite target produced nano-structured films when assisted by plasma or at high substrate temperature. Hot Filament CVD was able to grow nano-graphite "petal"-like structures vertically oriented at moderate substrate temperature ( 650 °C) and sharp graphite tips and cones at high T (1650 °C). The presence of a DC plasma was able to produce big "urchin" structures characterised by long, entangled, tubular wires (stripes), without any catalyst addition. The film morphology have been characterised by SEM; film quality and nano-particle dimension have been estimated be Raman spectroscopy. Field emission properties have been measured by a planar / spherical configuration.