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In the field of sustainability, hydrogen (H2) is considered a clean fuel and a renewable energy source with no pollutant emissions. The production of H2 by water electrolysis is well-known among the scientific community. Still, alkaline electrolysis represents a challenging process and requires expensive materials have to be avoided in order to lower the impact of H2 production. This work deals with the production of copper (Cu) and nickel (Ni) nanoparticles (NPs) as catalysts for alkaline water splitting reactions. These NPs are synthesized using the pulsed laser ablation in liquid involving the ablation of Cu and Ni targets in methanol and ethanol. The morphological, structural, and compositional properties of the obtained NPs are studied. Then, a low amount of NPs-based catalyst (~1 μg/cm²) was loaded onto a nickel foam substrate and tested for both alkaline Hydrogen Evolution Reaction (HER) and Oxygen Evolution Reaction (OER). The best performance at 10 mA cm-2, in terms of overpotential (η), for OER was shown by Ni NPs, η =327 mV, while for the HER, Cu NPs reached η =211 mV at 10 mA cm-2 in aqueous 1M KOH. The ultra-low amount of the catalyst material makes these electrodes challenging in terms of mass activity [up to 14 A/mg at 10 mA cm-2] compared to the state of the art. In addition, the correlation between overpotential and the availability of electrons at the surface of the catalyst for H2 production was studied by using Mott--Schottky analysis. [ABSTRACT FROM AUTHOR]

Radio frequency magnetron sputtering is used for preparing aligned carbon nanotubes (CNTs) on a Si[O.sub.2]/Si substrate, with simultaneous in situ catalyst deposition. The structural differences are attributed to the size of the W and Ni particles and also to a different diffusion behavior of C in the two kinds of metallic clusters.

Graphene-based materials are among the most innovative and promising materials for the development of high-performance sensing devices, mainly due to the large surface area and the possibility to modify their reactivity by suitable functionalization. In the field of sensing applications, the peculiarities of innovative materials can be exploited only if chemical and physical properties are fully understood and correlated with each other. To this aim, in this work, graphene oxide (GO) and ethanol-treated GO (GOEt) were investigated from chemical and structural points of view. Electrical characterization was performed by depositing GO and GOEt between two electrodes by dielectrophoresis. All the investigations were repeated on GO materials after thermal treatment in a low temperature range (60 °C-300 °C). Furthermore, the electrical conductivity of GO was investigated by changing the temperature and the environment (air or N2) during the characterization: an increase in the conductivity of the as-deposited GO was observed when the device is cooled down and this effect is reversible with the temperature. GOEt and the thermally treated GO and GOEt show an opposite trend, confirming the key role of the oxygen functionalities in the conduction mechanisms and, therefore, in the conductivity of the GO layers. [ABSTRACT FROM AUTHOR]

O:Er concentration effects on structural, electrical and optical properties of Si:Er:O layers are examined.

The addition of a TiO2 seed layer when growing textured PbTiO3 and Pb(Zr,Ti)O3 thin films on textured Pt(111) thin film substrates allows the PcTiO3 texture to be turned from (100) to (111) orientation. X-ray photoelectron diffraction measurements indicate epitaxial ordering in the seed layer. The textured microstructure of the seed layer most probably corresponds to rutile(110). A crystalline, few nanometer thick TiO2 film has been shown to be a very efficient seed layer for the nucleation of PZT(111).

In this paper, we study the metal-catalyzed synthesis of Si nanowires (Si-NWs) in a plasma based chemical vapor deposition system. In these deposition systems due to the high efficiency of precursor molecule dissociation, both uncatalyzed and catalyzed growth mechanisms can take place. The first one gives rise to the formation of the quasi one-dimensional (1D) Si-NWs, while the second one to a continuous two-dimensional (2D) Si layer over the substrate or on the nucleated Si-NWs. The Si-NWs formation is then the result of the competition between these two processes. The control parameters ruling these two contributions are here explored. Samples with different weights of 1D and 2D growth are deposited and characterized by using a plasma based chemical vapor deposition apparatus operating at T < 400 °C. It is found that the main control parameter of these processes is the plasma power through the distribution of the precursor dissociation products. By properly tuning the power, Si-NWs with 1 × 1010 cm-2 of density, up to 1 μm long and without uncatalyzed growth are obtained. The optical functionality of the samples, grown with different 1D/2D contributions, is investigated and it is demonstrated that the uncatalyzed layer produces a total reflectance as high as ∼40%, similar to that found in a planar Si wafer, while the highly dense Si-NWs, without the uncatalyzed deposition, produce a total reflectance of ∼15%. [ABSTRACT FROM AUTHOR]

We have investigated the formation and the morphology of carbon deposit on the cathode, after arc discharge between two graphite electrodes immersed in liquid nitrogen. We show that the deposit is mainly composed of disordered carbon structures at the bottom and at the external part of the deposit, forming like a bowl, whereas randomly oriented carbon nanotubes (CNTs) aggregated as pillars are found at the center of the deposit. The spatial distribution of the two kinds of structures in the deposit, the size and the sharpness of the CNT pillars are found to depend both on the applied voltage and the current values used for the arc discharge. A correlation between the plasma temperature field and the morphology of the deposit is reported. [ABSTRACT FROM AUTHOR]

Arc discharge between two graphite rods in liquid nitrogen has been investigated in order to identify the main factors ruling the formation of carbon nanotubes (CNTs) and linear C chains. The influence of the experimental parameters on the structural properties of the produced materials was evaluated and interpreted, taking into account the existing models. We found that the electrode size and discharge current values greatly influence the structural quality of the nanotubes (e.g., presence of carbonaceous impurities, innermost tube diameter) and a proper combination of these parameters allows one to control the synthesis of CNTs and/or CNT-linear C chain hybrid systems. [ABSTRACT FROM AUTHOR]

Radio frequency magnetron sputtering has been used for the synthesis of aligned carbon nanotubes (CNTs) on a SiO2/Si substrate, with simultaneous in situ catalyst deposition. This method allows the use of substrates without the need of a surface predeposition of catalytic particles. In particular, among the metals considered, we observed the formation of CNTs using W or Ni as catalysts. Only in the case of Ni did we find that the CNTs are aligned along the target-substrate direction, unlike the randomly oriented CNTs observed when W was used as catalyst. Scanning and transmission electron microscopies show that the catalytic Ni nanoparticle is found mostly on the tip of the obtained bamboolike CNTs, while W nanoparticles are encapsulated inside hollow nanotubes, at different points along their length. We ascribe not only the observed structural differences to the size of the W and Ni particles but also to a different diffusion behavior of C in the two kinds of metallic clusters. [ABSTRACT FROM AUTHOR]

The growth of thin cubic silicon carbide (3C-SiC) buffer layers in an horizontal hot-wall chemical vapor deposition reactor, through the carbonization of differently oriented Si surfaces, is presented. A qualitative and quantitative study has been performed on statistical parameters related to voids due to the buffer layer growth on the different substrate orientations emphasizing shape, size, and density as a function of the substrate orientation. Variation in the void parameters can be attributed to the atomic packing density related to the substrate orientations, which were (100) Si, (111) Si, and (110) Si in this study. Scanning electron microscopy and transmission electron microscopy were performed to analyze the surface and the crystalline quality of the 3C-SiC films grown and, eventually, an empirical model for the carbonization of Si surfaces formulated. Large platens characterize the 3C-SiC films with shapes related to the orientations of the substrate. These platens derive from the two-dimensional growth of different SiC islands which enlarge during the process due to the continuous reaction between Si and C atoms. The interior part of platens was characterized by the presence of a pure crystalline material with the presence of small tilts affecting some grains in the 3C-SiC layer in order to relief the stress generated with the substrate. [ABSTRACT FROM AUTHOR]

The interaction between indium and boron coimplanted in silicon has been investigated. In particular, the effects of the coimplantation on the diffusion and the electrical activation have been studied in comparison with the single B or In implanted samples. It is shown that, by means of coimplantation, it is possible to obtain p-type carrier concentration profiles with a concentration peak higher than the ones achievable by the single In doping, but with the further advantage of a shallower carrier distribution with respect to the single B implant. It is found that this is due to the formation of In–B complexes with an acceptor level deeper than the one related to substitutional B. [ABSTRACT FROM AUTHOR]

In this work we investigate the diffusion and the electrical activation of In atoms implanted into silicon with energies ranging from 40 to 360 keV and doses of 5 × 10[SUP12] and 5 ×10[SUP13]In/cm[SUP2] during rapid thermal processing. Our investigation shows a clear dependence of In outdiffusion and electrical activation on the implant depth. For a fixed dose, the electrical activation was found to increase with the implant energy. We propose that the data can be explained by considering the balance between the local In concentration and the C background. The occurrence of coupling between the C present in the substrate and the implanted In, depending on the C/In ratio, may in fact give rise to significant formation of C-In complexes. Such complexes play a role in the enhanced electrical activation due to the shallower level they introduce into the Si band gap (E[SUBν + 0.111 eV), with respect to the rather deep level (E[SUBν] + 0.156 eV) of In alone [R. Baron et al., Appl. Phys. Lett. 30, 594 (1977); R. Baron et al., ibid. 34, 257 (1979)]. The interaction of In atoms with the C background inside the silicon substrate has been, therefore, identified as the most likely origin of this behavior. In and C coimplantation has also been studied in this work, in order to further investigate the key role of C in the increase of electrical activation. A large increase of electrical activation has been detected in the coimplanted samples, up to a factor of about 8 after annealing at 900°C. However, C precipitation occurs at 1100°C, and has dramatic effects on the carrier concentration that falls by even two orders of magnitude. This limits the maximum thermal budget that can be used for In activation in C coimplanted material. [ABSTRACT FROM AUTHOR]

The thermal oxidation of Ge-implanted Si single crystals has been investigated for different Ge doses (3 × l0[sup 15] cm[sup -2] and 3 × 10[sup 16] cm[sup -2]) and different oxidation processes (in wet ambient at 920 °C for 30, 60, and 120 min, or dry ambient at ll00 °C for 30 min). The oxide roughness, the oxidation rate, the Ge diffusion, precipitation, and clustering, have been monitored by several experimental techniques: atomic force microscopy, transmission electron microscopy, Rutherford backscattering spectrometry, and x-ray absorption spectroscopy. We found that the surface roughness is related to the segregation of Ge at the oxide/substrate interface, occurring when the oxidation rate is faster than the Ge diffusion, in particular at the higher implanted dose (3 × 10[sup 16] cm[sup -2]) when processed in a wet ambient. For these conditions, we also observed an oxidation rate enhancement with respect to pure Si, and a strong indication that pure Ge clusters were formed. When a critical Ge concentration at the interface is reached, the oxidation mechanisms change and the oxidation rate is reduced, along with Ge diffusion into the substrate and a consequent reduction of the Ge fraction at the interface. Nevertheless, the oxide roughness still increases despite the Ge concentration reduction, resulting from the initial nucleation of precipitates. [ABSTRACT FROM AUTHOR]

This study reports the structural and stoichiometric modifications of bismuth oxide nanoparticles in the β phase (β-Bi2O3) by UV pulsed laser irradiation in water or ethanol solutions. Scanning electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, UV-vis diffuse reflectance and high-resolution transmission electron microscopy were used to characterize the synthesized nanomaterials. The various analyses demonstrate that the laser irradiation of β-Bi2O3 nanospheres is a green, fast and effective method to produce Bi2O2CO3 nanosheets or metallic Bi nanoparticles depending on the liquid environment used. Bi subcarbonate is obtained by laser irradiation in water, whereas metallic Bi is produced by laser irradiation in ethanol, and in particular the relative amount of metallic Bi is found to depend on the laser fluence. These typologies of materials find application in several fields, such as photocatalytic processes, light filters and environmental sensors. [ABSTRACT FROM AUTHOR]

The injection of Si self-interstitial atoms during dry oxidation at 815 °C of very shallow SiGe layers grown on Si (001) by molecular-beam epitaxy (MBE) has been investigated. We first quantified the oxidation enhanced diffusion (OED) of two boron deltas buried into the Si underlying the oxidized SiGe layers. Then, by simulating the interstitial diffusion in the MBE material with a code developed on purpose, we estimated the interstitial supersaturation (S) at the SiGe/Si interface. We found that S (a) is lower than that observed in pure Si, (b) is Ge-concentration dependent, and (c) has a very fast transient behavior. After such a short transient, the OED is completely suppressed, and the suppression lasts for long annealing times even after the complete oxidation of the SiGe layer. The above results have been related to the mechanism of oxidation of SiGe in which the Ge piles up at the SiO2/SiGe interface by producing a thin and defect-free layer with a very high concentration of Ge. [ABSTRACT FROM AUTHOR]

A large-scale use of nanotechnology for photocatalysis-based water purification requires to identify simple, reliable and low cost processes for the production of the photocatalytic materials. To this aim we have investigated the possibility to deposit, by electrophoresis, composite layers formed by multi-walled carbon nanotubes (MWCNTs) and anatase-type titanium dioxide nanoparticles (np-TiO 2 ), with different weight ratios. This method allows one to obtain photocatalytic layers on any conductive substrates that in principle can be re-used several times. The photocatalytic efficiency for each C-nanostructure/np-TiO 2 composite layer is evaluated by measuring the degradation of methylene blue (MB) dye induced by the light of a solar simulator or UVA/blue light irradiation. The morphology and the composition of the deposited layers are studied by scanning electron microscopy and energy dispersive X-ray analyses, respectively, while photoluminescence spectra were acquired in order to explain the different photocatalytic behaviors observed for each material. [ABSTRACT FROM AUTHOR]

In this work we report on the development of back-gated carbon nanotube-field effect transistors (CNT-FETs), with CNT layers playing the role of the channel, and on their electrical characterisation for sensing applications. The CNTs have been deposited by electrophoresis on an interdigitated electrode region created on a SiO2/Si substrate. Different kinds of CNTs have been used (MWCNTs by arc discharge in liquid nitrogen and MWCNTs by chemical vapour deposition, CVD) and the electrical characterisation of the devices was performed in a NH3- and NO2-controlled environment. Preliminary data have shown an increase in the channel resistance under NH3 exposure, whereas a decrease is observed after exposure to NO2, and the sensitivity to each gas depends on the kind of CNTs used for the device. Furthermore, the defect formation by Si ion implantation on CNTs was investigated by high-resolution transmission electron microscopy (TEM) and Raman analysis. The behaviour observed for the different devices can be explained in terms of the interaction between structural or chemical defects in CNTs and the gas molecules. [ABSTRACT FROM AUTHOR]

Multi-wall carbon nanotubes (MWCNTs) produced by the arc discharge between two graphite rods in liquid nitrogen have been investigated with the use of Raman spectroscopy and transmission electron microscopy (TEM). The effects of the applied voltage on the structural properties of the produced MWCNTs have been observed, in particular, as it concerns the size of the innermost and outermost diameters. The apparent discrepancies observed between the Raman and TEM results are explained through the observation of a selective response of the MWCNTs to the excitation laser energy in Raman spectroscopy, similar to the case of single-wall CNTs. Electronic structure calculations correlate such behavior with optical transitions, in the presence of strong electronic localizations, spatially confined in a few neighboring walls. Copyright © 2011 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

We have produced silver colloids by ablating metal targets in water and using two different laser wavelengths. The obtained sols have been characterized by optical spectroscopy and electron microscopy, revealing a definite double size distribution centered at a few tens and a few hundreds of nanometers with a mild difference between the two wavelengths employed. On the contrary, a marked difference in shape has been found for the biggest aggregates, revealing sharp cubic or octahedral structures when visible or infrared radiations are used, respectively. This fact is explained by the re-irradiation processes induced on the already formed colloid and taking place during the ablation. [ABSTRACT FROM AUTHOR]

The formation of polycrystalline Si layers on flexible plastic substrates, through plasma enhanced chemical vapor deposition and excimer laser annealing, is investigated. Combining low-temperature (300°C) annealing with laser dehydrogenation/crystallization produces good-quality polycrystalline silicon with a reduced shot density. By using optimal crystallization conditions it is possible to achieve a superlateral growth crystallization regime, with a grain, size up to 1μm, and void-free material, as confirmed by the presented structural analysis. The beneficial effect of the low-temperature thermal annealing has been related to the removal of nonbound hydrogen, as supported by the elastic recoil detection analysis and JR analysis of the samples. To validate the process, we fabricated non-self-aligned polysilicon thin-film transistors (TFTs) directly on spin-coated polyimide substrates, with a maximum processing temperature of 300°C and with a relatively low shot density (<10 shots/point). The TFTs presented good electrical characteristics with an on/off ratio > 106, a field-effect mobility up to 65 cm[sup2]/V s, and a threshold voltage of 7 V. These results confirmed that the developed crystallization process is suitable to fabricate polysilicon TFT's on polymeric substrates, allowing an increased process throughput. [ABSTRACT FROM AUTHOR]