Carbon nanotube/polymer composites have recently received considerable attention for thermoelectric (TE) applications. The TE power factor can be significantly improved by forming composites with carbon nanotubes. However, the formation of a uniform and well-ordered nanocomposite film is still challenging because of the creation of agglomerates and the uneven distribution of nanotubes. Here, we developed a facile, efficient, and easy-processable route to produce uniform and aligned nanocomposite films of P3HT and carbon nanotube forest (CNTF). The electrical conductivity of a pristine P3HT film was improved from ∼10–7 to 160 S/cm thanks to the presence of CNTF. Also, a further boost in TE performance was achieved using two additives, lithium bis(trifluoromethanesulfonyl) imide (LiTFSI) and tert-butylpyridine. By adding the additives to P3HT, the degree of interchain order increased, which facilitated the charge transport through the composite. Under the optimal conditions, the incorporation of CNTF and additives led to values of the Seebeck coefficient, electrical conductivity, and power factor up to rising 92 μV/K, 130 S/cm, and 110 μW/m K2, respectively, at a temperature of 344.15 K. The excellent TE performance of the hybrid films originates from the dramatically increased electrical conductivity and the improved Seebeck coefficient by CNTF and additives, respectively.
The rate of the carbon-nitrogen-oxygen (CNO) cycle of hydrogen burning is controlled by the N14(p,γ)O15 reaction. The reaction proceeds by capture to the ground states and several excited states in O15. In order to obtain a reliable extrapolation of the excitation curve to astrophysical energy, fits in the R-matrix framework are needed. In an energy range that sensitively tests such fits, new cross-section data are reported here for the four major transitions in the N14(p,γ)O15 reaction. The experiment has been performed at the Laboratory for Underground Nuclear Astrophysics (LUNA) 400-kV accelerator placed deep underground in the Gran Sasso facility in Italy. Using a composite germanium detector, summing corrections have been considerably reduced with respect to previous studies. The cross sections for capture to the ground state and to the 5181, 6172, and 6792 keV excited states in O15 have been determined at 359, 380, and 399 keV beam energy. In addition, the branching ratios for the decay of the 278-keV resonance have been remeasured. © 2011 American Physical Society.
The rate of the hydrogen-burning carbon-nitrogen-oxygen (CNO) cycle is controlled by the slowest process, 14N(p,γ)15O, which proceeds by capture to the ground and several excited states in O15. Previous extrapolations for the ground state contribution disagreed by a factor 2, corresponding to 15% uncertainty in the total astrophysical S factor. At the Laboratory for Underground Nuclear Astrophysics (LUNA) 400 kV accelerator placed deep underground in the Gran Sasso facility in Italy, a new experiment on ground state capture has been carried out at 317.8, 334.4, and 353.3 keV center-of-mass energy. Systematic corrections have been reduced considerably with respect to previous studies by using a Clover detector and by adopting a relative analysis. The previous discrepancy has been resolved, and ground state capture no longer dominates the uncertainty of the total S factor. © 2008 The American Physical Society.
The structural evolution of cobalt nanoclusters synthesized in silica glass by ion implantation has been investigated upon thermal annealing. The samples were characterized by in-situ grazing incidence X-ray diffraction, exploiting a synchrotron radiation beam and following their evolution during thermal treatments in vacuo up to T = 800 °C. Before heating, the system is composed of hcp Co nanocrystals; we have not detected the transition from hcp to fcc structure that in the bulk phase occurs around 420 °C; nevertheless, the differences in the diffraction pattern recorded at T = 800 °C with respect to the corresponding one at room temperature suggest the presence of a second crystalline phase. © 2006 Elsevier B.V. All rights reserved.
Overall water splitting represents one of the most promising approaches toward solar energy conversion and storage, which is, however, severely challenged by the four-electron/four-proton nature of the oxygen evolution reaction (OER). One option to overcome this issue is to replace OER with a more useful reaction, for simultaneous production of both hydrogen and chemicals of interest. For the purpose, in this paper a cheap, hydrothermally prepared Ti-doped nanostructured hematite photoanode was employed for the first time as highly stable, heterogeneous catalyst for the low bias, efficient and highly selective photoinduced oxidation of benzylamine to N-benzylidenebenzylamine, and for the simultaneous production of hydrogen in a double solvent/environment cell. A preliminary estimate indicates the possibility to obtain a ∼150 μmol h−1 H2 production, with the contemporary production of stoichiometric benzylidene N-benzylamine in a 5 × 5 cm2 area electrode. This study contributes to overcome the 40-year lasting issues limiting the use of hematite in industrial photoelectrochemical sunlight conversion and storage, due to poor performance of hematite and lack of economic value of oxygen production, providing solid evidence for the simultaneous use of hematite in hydrogen production and alternative oxidation reactions of industrial importance.
One of the most detrimental loss mechanisms in Luminescent Solar Concentrators (LSCs) is reabsorption of emitted light from the luminophore. Silicon Nanocrystals (SiNCs) offer a solution due to the high apparent Stokes shift, but the poor absorption properties limit their performance as LSC luminophores. Coupling an organic dye to SiNCs represents a smart approach to obtain sensitization of SiNC luminescence by the organic dyes, thus, resulting in tunable and improved optical properties of LSCs. In particular, 9,10-diphenylanthracene was employed as a UV sensitizer for SiNCs in order to produce LSCs with an aesthetic appearance suitable to smart window application and optical efficiency as high as 4.25%. In addition, the role of the energy transfer process on LSC performance was elucidated by a thorough optical and photovoltaic characterization.
While luminescent solar concentrators (LSCs) have a simple architecture—a transparent matrix embedding a luminescent fluorophore coupled with solar cells at the lateral side of the LSC slab—multiple paths for possible light losses exist. These are inherently interconnected, and in the past, limited the interest in this device, due to the gap between the theoretical possibilities and experimental achievements. This gap was a result, primarily, of the optical features of the luminescent dyes, since conventional organic luminophores are affected by limited performance in LSC devices. The rise of a wide portfolio of optically active inorganic nanomaterials in the last decade provides an alternative to organic dyes and has lead to a renaissance in the role of LSCs among the unconventional solar energy conversion devices. This paper reviews the latest results in the development of LSCs based on different classes of nanomaterials, focusing on the specific features and critically analyzing the pros and cons of the proposed structures. Particular attention is devoted to the role of the luminescence properties, e.g., the Stokes shift and the photoluminescence quantum yield, with respect to the performance of the LSC device. Future challenges to the successful employment of these devices for building integrated photovoltaics are also discussed.
Nanocrystalline CdS thin films were grown on glass substrates by a thermal evaporation method in a vacuum of about 2 × 10-5 Torr at substrate temperatures ranging between 25 °C and 250 °C. The physical properties of the layers were analyzed by transmittance spectra, XRD, SEM, and four-point probe measurements, and exhibited strong dependence on substrate temperature. The XRD patterns of the films indicated the presence of single-phase hexagonal CdS with (002) orientation. The structural parameters of CdS thin films (namely crystallite size, number of grains per unit area, dislocation density and the strain of the deposited films) were also calculated. The resistivity of the as-deposited films were found to vary in the range 3.11-2.2 × 104 Ω·cm, depending on the substrate temperature. The low resistivity with reasonable transmittance suggest that this is a reliable way to fine-tune the functional properties of CdS films according to the specific application.
Layered multi-oxide concept was applied for fabrication of photoanodes for dye-sensitized solar cells based on ZnO and SnO2, capitalizing on the beneficial properties of each oxide. The effect of different combinations of ZnO@SnO2 layers was investigated, aimed at exploiting the high carrier mobility provided by the ZnO and the higher stability under UV irradiation pledged by SnO2. Bi-oxide photoanodes performed much better in terms of photoconversion efficiency (PCE) (4.96%) compared to bare SnO2 (1.20%) and ZnO (1.03%). Synergistic cooperation is effective for both open circuit voltage and photocurrent density: enhanced values were indeed recorded for the layered photoanode as compared with bare oxides (Voc enhanced from 0.39 V in case of bare SnO2 to 0.60 V and Jsc improved from 2.58 mA/cm2 pertaining to single ZnO to 14.8 mA/cm2). Improved functional performances of the layered network were ascribable to the optimization of both high chemical capacitance (provided by the SnO2) and low recombination resistance (guaranteed by ZnO) and inhibition of back electron transfer from the SnO2 conduction band to the oxidized species of the electrolyte. Compared with previously reported results, this study testifies how a simple electrode design is powerful in enhancing the functional performances of the final device.
ZnO@SnO2 multilayered network was deposited on fluorine doped tin oxide (FTO) glass and applied as photoanode in dye sensitized solar cells whose functional performances are compared with single oxide-based photoanodes made of SnO2 nanoparticles and ZnO microparticles. Multi-oxide photoanodes provide for enhanced photoconversion efficiency (3.31%) as compared with bare SnO2 nanoparticles (1.06%) and ZnO microparticles (1.04%). Improved functional performances of the ZnO@SnO2 layered network are ascribable to partial inhibition of back electron transfer from SnO2 to the redox electrolyte, guaranteed by the ZnO, which acts as a capping layer for the underlying SnO2. © 2014 SPIE.
Hydrogen is an efficient, clean, and economical energy source, owing to its huge energy density. Electrochemical water splitting is a potential candidate for inexpensive and eco-friendly hydrogen production. Recently, the development of 2D transition metal chalcogenides (TMDs) nanomaterials with a variety of physicochemical properties has shown their potential as eminent non-noble metal-based nanoscale electrocatalysts for hydrogen evolution. Nanostructuring such materials induces deep modification of their functionalities, compared to their bulk counterparts. High density of different types of exposed active sites is formed, and the small diffusion paths, which enhances the electron transfer in the 2D structures, can successfully aid the charge collection process in the electrocatalytic hydrogen evolution reactions. In this review, the key parameters to improve the catalyst performance of 2D TMDs in electrochemical hydrogen evolution reaction (HER) processes are discussed in detail and the most recent developments in the field are summarized, focusing on the improvement of the electrocatalytic activity of 2D TMDs. This review delivers deep insight for the clear understanding of the potential of 2D TMDs nanoscale materials as electrocatalysts for HER, suggesting the development of new type of catalyst with efficient activity in HER as well as other renewable energy fields.
We investigated the effect of copper doping on the photocatalytic properties of TiO2 thin films. Titania thin films doped with three different copper concentrations were synthesized via radiofrequency-assisted (RF) magnetron sputtering, then annealed at 600 °C in controlled atmosphere (Ar, O2, H2 flow). The impact of the annealing in inert, oxidizing or reducing atmosphere on the crystalline and surface structure, and photocatalytic performance in the methylene blue degradation under UV light irradiation was investigated by X-ray diffraction, UV-Vis Spectroscopy, Rutherford Backscattering Spectrometry, electron scanning microscopy. Annealing induced very different crystallization in different atmospheres, with strong copper out-diffusion in samples annealed in reducing atmosphere and formation of large embedded nanoparticles. The Cu-doped titania films exhibited higher photocatalytic activity than pure titania film and the best performing catalyst, treated in H2 atmosphere, suggests that the presence of embedded copper nanoparticles (both metallic and oxidized) is able to strongly enhance the photocatalytic properties of the host titania matrix. Incorporated Cu particles can act as trapped sites for generated electrons, and this leads to the reduction of carrier recombination which, ultimately, plays a significant role in the increase of photoactivity. The recyclability of the best system was ascertained by a suitable 3-cycle stability test.
We developed a scattering layer composed of TiO2 nanocrystals assembled into a densely packed three-dimensional network of nanofibers to localize light within a photoanode used in dye sensitized solar cells (DSSCs). The electro-netting approach was applied to obtain polyamide 6 nanofibers with bi-modal diameter distribution, followed by solvothermal synthesis for the coating of TiO2 nanocrystals on the polymer template. The resulting nanofiber-structured scattering layer (NFSL) is composed of TiO2 nanofibers (200-300 nm in diameter) supporting an ultrathin nanofiber network (diameters within 10-50 nm) and exhibits strong light scattering in the visible range (400 to 700 nm). This NFSL was applied on top of a transparent active TiO2 layer (TL) forming the photoanode in DSSCs. The performance of the bi-layered photoanode was compared to its analogue, fabricated with commercial scattering layers containing different sizes of nanoparticles. The DSSCs assembled with the NFSL showed an 18% enhancement in power conversion efficiency (PCE) compared to that of DSSCs whose photoanode contained only a TL. This enhancement factor was improved up to 31% when the bi-layered structure was post-treated with TiCl4. The PCE improvement was mainly associated with the light harvesting efficiency within the photoanode because of scattering from the NFSL and increased dye adsorption due to the addition of this top layer. These conclusions were inferred from diffuse reflectance behavior, dye loading measurements, external quantum efficiency and electrochemical properties. Our work demonstrates a promising approach without the requirement of time consuming and complicated procedures for the fabrication of a densely packed 3D nanofiber network scattering layer for diverse energy conversion devices and photocatalytic applications
Pt/Pd hollow nanofibers were obtained by sputtering a Pt/Pd alloy (80/20 wt%) onto polymer nanofibers (used as sacrificial template) and were used as counter-electrodes (CEs) in dye-sensitized solar cells (DSSCs). We demonstrate that optimization of nanofiber density and Pt/Pd sputtering thickness can increase the short circuit current density and consequently lead to a ∼15% enhancement in power conversion efficiency (PCE), when compared to the commonly used flat Pt/Pd CEs with the same thickness. The processes that contribute to such PCE improvement are: (i) increased surface area provided by the high aspect ratio hollow nanofibers and (ii) improved electro-catalytic performance, as validated by electrochemical impedance spectroscopy (EIS) measurements. The latter showed a two-fold decrease in the charge-transfer resistance of the nanostructured-CE, compared to the flat CE. The contribution of the Pt/Pd hollow nanofiber to light scattering was negligible as shown by reflectance measurements. These results suggest a simple and straightforward strategy to increase PCE in DSSCs, to minimize the use of precious metals used in this kind of devices and, more generally, to tailor the CE structure in photoelectrochemical systems to boost their functional properties, thanks to the advantages afforded by this complex morphology.
We developed a hierarchically assembled hybrid counter electrode (CE) based on copper sulfide (CuS) nanoplatelets grown on polymer nanofibers. The resulting CE was used in a quantum dot (QD)-based photoelectrochemical (PEC) system for H2 generation in the presence of sacrificial agents (S2−/SO32−). The concept is to increase the specific surface area of the CE, aiming at maximizing charge exchange at the electrode, which boosts efficient generation of H2 and to obtain a stable structure for long-term operation of the device. Structural and morphological characterization indicated the presence of a covellite crystalline phase (CuS). PEC tests showed that the CuS nanoplatelets grown in the CEs could replace Pt CEs in either visible-active or near infrared (NIR)-active QD-based PEC systems. Specifically, saturation of the photocurrent density (∼7.5 mA cm−2) occurred at ∼0.6 V versus the RHE, when using a NIR QD-based TiO2 photoanode and a nanofiber-supported CuS as the CE. Stability tests of the nanofiber-supported CuS CE showed that 85% of the initial photocurrent density was maintained after ∼1 h, which is similar to that obtained with the Pt foil CE (86%). In contrast, CuS nanostructures directly deposited on FTO glass without nanofibers (CuS/FTO CE) exhibited poor stability. CuS/FTO CE degraded quickly, showing a 90% drop in the initial photocurrent within 200 s testing whereas a 14% drop in the initial photocurrent was observed for the CuxS on brass within 10 min of testing. Our new nanofiber supported-CuS CE stands out due to its higher performance compared to brass and its similar stability compared to Pt during long term PEC operation. Additionally, our hybrid CE showed a better catalytic performance than the Pt CE and good stability in cyclic voltammetry tests. These results demonstrate that the nanofiber-supported CuS is a promising cost effective alternative to Pt as a highly efficient CE for PEC H2 generation
The sensing properties of titanium oxide have been tailored through doping with niobium and dispersion of nanosized Au particles. The microstructural features of the gold-titania composite system were investigated by transmission electron microscopy and the electronic properties of Au nanoparticles were specifically investigated by electron holography. Holography provides quantitative determination of the mean inner potential with the high spatial resolution attained by transmission electron microscopy. Large increase of the mean inner potential has been measured for ultra small Au particles arising from the nano-scale assembling. Electrical tests were performed at low operating temperatures and demonstrated the considerable enhancement of CO sensitivity owing to the extremely high catalytic activity of gold particles. © 2007 Elsevier Ltd. All rights reserved.
Among the existing materials for heat conversion, high-entropy alloys are of great interest due to the tunability of their functional properties. Here, we aim to produce single-phase high-entropy oxides composed of Co-Cr-Fe-Mn-Ni-O through spark plasma sintering (SPS), testing their thermoelectric (TE) properties. This material was successfully obtained before via a different technique, which requires a very long processing time. Hence, the main target of this work is to apply spark plasma sintering, a much faster and scalable process. The samples were sintered in the temperature range of 1200–1300 °C. Two main phases were formed: rock salt-structured Fm3̅m and spinel-structured Fd3̅m. Comparable transport properties were achieved via the new approach: the highest value of the Seebeck coefficient reached −112.6 μV/K at room temperature, compared to −150 μV/K reported before; electrical properties at high temperatures are close to the properties of the single-phase material (σ = 0.2148 S/cm, σ ≈ 0.2009 S/cm reported before). These results indicate that SPS can be successfully applied to produce highly efficient TE high-entropy alloys in a fast and scalable way. Further optimization is needed for the production of single-phase materials, which are expected to exhibit an even better TE functionality.
Nanostructured materials and nanocomposites have shown great promise for improving the efficiency of thermoelectric materials. Herein, Fe nanoparticles were imbedded into a CrN matrix by combining two physical vapor deposition approaches, namely, high-power impulse magnetron sputtering and a nanoparticle gun. The combination of these techniques allowed the formation of nanocomposites in which the Fe nanoparticles remained intact without intermixing with the matrix. The electrical and thermal transport properties of the nanocomposites were investigated and compared to those of a monolithic CrN film. The measured thermoelectric properties revealed an increase in the Seebeck coefficient, with a decrease of hall carrier concentration and an increase of the electron mobility, which could be explained by energy filtering by internal phases created at the NP/matrix interface. The thermal conductivity of the final nanocomposite was reduced from 4.8 W m-1 K-1 to a minimum of 3.0 W m-1 K-1. This study shows prospects for the nanocomposite synthesis process using nanoparticles and its use in improving the thermoelectric properties of coatings.
This work concerns with metal oxide (MOX) gas sensors based on nanowires and thin films. We focus on chemical warfare agents (CWAs) detection to compare these materials from the functional point-of-view. We work with different chemicals including simulants for Sarin nerve agents, vescicant gases, cyanide agents, and analytes such as ethanol, acetone, ammonia, and carbon monoxide that can be produced by everyday activities causing false alarms. Explorative data analysis has been used to demonstrate the different sensing performances of nanowires and thin films. Within the chosen application, our analysis reveal that the introduction of nanowires inside the array composed by thin films can improve its sensing capability. Cyanide simulants have been detected at concentrations close to 1 ppm, lower than the Immediately Dangerous for Life and Health (IDLH) value of the respective warfare agent. Higher sensitivity has been obtained to simulants for Sarin and vescicant gases, which have been detected at concentrations close or even lower than 100 ppb. Results demonstrate the suitability of the proposed array to selectively detect CWA simulants with respect to some compounds produced by everyday activities. © 2008 IEEE.
The impact of energetic ions on solid samples gives rise to the emission of visible light owing to the electronic excitation of intrinsic defects or extrinsic impurities. The intensity and position of the emission features provide information on the nature of the luminescence centers and on their chemical environments. This makes ion beam induced luminescence (IBIL) a useful complement to other ion beam analyses, like PIXE, in the cultural heritage field in characterizing the composition and the provenience of art objects. In the present paper, IBIL measurements have been performed on inorganic pigments for underlying the complementary role played by IBIL in the analysis of artistic works. Some blue and red pigment has been presented as case study. © 2006 IOP Publishing Ltd.
Solar-driven photoelectrochemical (PEC) hydrogen production is one of the most effective strategies for solar-to-hydrogen energy conversion. Among various types of semiconductors used for PEC anodes, colloidal quantum dots (QDs) have been widely used as new and promising absorbers for PEC and other optoelectronic devices. However, currently, most efficient optoelectronic devices contain toxic Pb/Cd elements or non-earth-abundant elements (In/Ag). It is still a challenge to produce Pb/Cd-free QDs without using any toxic and non-earth-abundant elements. Here, we synthesized SnSe QDs via a diffusion-controlled hot injection approach and further stabilized the as-prepared SnSe QDs via a cation exchange reaction. The as-synthesized Zn-stabilized SnSe QDs (SnSe/ZnSe) have an orthorhombic crystal structure with indirect bandgaps ranging from 1 to 1.37 eV. Zn stabilization can significantly decrease the number of QD surface metallic Sn bonds, thereby decreasing the number of recombination centers of defects/traps. As a proof-of-concept, SnSe/ZnSe QDs are used as light absorbers for PEC hydrogen production, leading to a saturated photocurrent density of 7 mA cm−2, which is comparable to best values reported for PEC devices based on toxic-metal-free QDs. Our results indicate that Zn-stabilized SnSe QDs have great potential for use in emerging optoelectronic devices.
The film thicknesses of five different layer systems on glass substrates were analyzed and determined in a multi-method approach by eight different university and industrial laboratories. The total coating thicknesses varied between a few nm up to some 100 nm. The measurements give information about the chemical composition and cover a wide spectrum of typical coating application on glasses. The results of the different laboratories and methods are compared and the challenges and limits of the various analytical techniques are discussed.
In this work we report the preparation and structural characterization of tin oxide nanowires as functional materials for the development of chemical sensors. Aspects of material preparation relevant for gas sensing applications, such as the control of the wire diameter, are emphasized. The functional characterization is focused on the detection of Chemical Warfare Agents (CWAs) simulants, with particular regard to poisoning effects induced by dimethyl methyl phosphonate (DMMP), a simulant for Sarin nerve agent. Tin oxide thin films, prepared by means of rheotaxial growth and thermal oxidation (RGTO) technique, are used as reference to better compare the performance of nanowires with thin films traditionally used in gas sensing field. © 2009 Elsevier B.V. All rights reserved.
Quasi one-dimensional nanostructures of semiconducting metal oxides are promising for the development of nano-devices. Tin, indium, and zinc oxides were produced in form of single-crystalline nanowires through condensation from vapor phase. Such a growth occurs in controlled thermodynamical condition and size reduction effects on the electrical and optical response to gases have been exploited. Preparation, microstructural, and electrical characterization of nanowires are presented and the peculiarities of these innovative structures are highlighted. © 2006 Elsevier B.V. All rights reserved.
ZnO, SnO2, Indium-tin oxide (ITO) nanostructures have been produced on glass substrates coated with a transparent conducting oxide (TCO) electrode for application in dye sensitized solar cells (DSC). Quasi one-dimensional (1D) nanostructures of different TCOs have been synthesized using the vapour transport-and-condensation technique. Nanostructures with different shape and aspect-ratio can be obtained by properly tailoring of the condensation conditions and the substrate preparation. A multi technique approach, using electron microscopy and DC electrical characterization, has been applied for micro-structural and functional characterization of the nanostructures. © 2008 IEEE.
We recently suggested using short bent crystals as primary collimators in a two stage cleaning system for hadron colliders, with the aim of providing larger impact parameters in the secondary bulk absorber, through coherent beam-halo deflection [1]. Tests with crystals a few mm long, performed with 70 GeV proton beams at IEHP in Protvino, showed a channeling efficiency exceeding 85 %. We also observed disturbing phenomena such as dechannelling at large impact angle, insufficient bending induced by volume capture inside the crystal, multiple scattering of non-channeled protons and, for the first time, a proton flux reflected by the crystalline planes. Indeed, protons with a tangent path to the curved planes somewhere inside the crystal itself are deflected in the opposite direction with respect to the channeled particles, with an angle almost twice as large as the critical angle. This effect, up to now only predicted by computer simulations [2], produces a flux of particles in the wrong direction with respect to the absorber, which may hamper the collimation efficiency if neglected.
We review the experimental evidences we recorded with volume reflection and planar and axial channelings with negatively charged particles beam. High deflection efficiency was observed in all cases. The experiment was carried out by the UA9 collaboration in the external lines of the CERN SPS with a secondary beam of 150 GeV/c negative particles.
Multiple volume reflection by different planes passing through the 〈111〉 axis in a bent silicon crystal was observed for the first time for 150 GeV/c negative particles, π- mesons, at one of the secondary beams of the CERN SPS. The beam of π- mesons was deflected opposite to the crystal bend by an angle of about 48 μrad, which is 4.6 times larger than in a single volume reflection by the (110) bent planes. The one-side deflection efficiency was about 65%. Multiple volume reflection transforms to a single volume reflection when the orientation angle of the 〈111〉 axis relative to the beam direction is increased. Copyright © 2011 Europhysics Letters Association.
Deflection due to axial channeling in a silicon crystal bent along the 〈111〉 axis was observed for 150 GeV/c negative particles, mainly π- mesons, at one of the secondary beams of the CERN SPS. The whole beam was deflected to one side with the efficiency of about 90% and with the peak position at the bend crystal angle α = 43 μrad. The deflection occurs mainly due to doughnut scattering of above-barrier particles by the atomic strings of the crystal. However, due to a high probability of particle recapture into bound states with the atomic strings their contribution to the deflection should be about 15% for our case according to simulation results. © 2009 Elsevier B.V. All rights reserved.
Deflection due to planar channeling and volume reflection in short bent silicon crystals was observed for the first time for 150 GeV / c negative particles, π- mesons, at one of the secondary beams of the CERN SPS. The deflection efficiency was about 30% for channeling and higher than 80% for volume reflection. Volume reflection occurs, in spite of the attractive character of the forces acting between the particles and the crystal planes, in a wide angular range of the crystal orientations determined by the crystal bend angle. © 2009 Elsevier B.V. All rights reserved.
Multiple volume reflection by different planes in a bent silicon crystal with its 〈111〉 axis orientation close to the beam direction was observed for the first time for 400 GeV/c protons at the CERN SPS. The proton beam was deflected to the side opposite to the crystal bend by an angle of about 67 μrad, which is five times larger than in a single volume reflection by the (110) bent planes. The registered efficiency of one side deflection was about 84%. It was shown that multiple volume reflection transforms to a single volume reflection when the orientation angle of the 〈111〉 axis relative to the beam direction is increased. © 2009 Elsevier B.V. All rights reserved.
Different kinds of deflection in a silicon crystal bent along the 〈111〉 axis was observed for 150 GeV/. c negative particles, mainly π- mesons, at one of the secondary beams of the CERN SPS. The whole beam was deflected to one side in quasi-bound states of doughnut scattering (DSB) by atomic strings with the efficiency (95.4 ± 0.2)% and with the peak position close to the bend crystal angle, α=185 μrad. It was observed volume capture of π- mesons into the DSB states with a probability higher than 7%. A beam deflection opposite to the crystal bend was observed for some orientations of the crystal axis due to doughnut scattering and subsequent multiple volume reflections of π- mesons by different bent planes crossing the axis. © 2010 Elsevier B.V.
Multiple volume reflections of the 400 GeV / c proton beam by the sequence of fourteen bent silicon strips has been studied at the CERN SPS. The sequence is close to be parallel that is the spread of the strip orientation angles is much smaller than their bend angle and eleven strips working coherently in the regime of volume reflections deflected the beam by 110 μrad with the efficiency 88%, which is significantly larger than the estimation based on independent reflections. The mechanism giving the efficiency increase has been studied by simulation. It appears that many particles volume captured in one of the strips take part in volume reflections in the subsequent ones. Such a crystal multi reflector can be successfully used as a primary collimator for the beam halo collimation of high-energy accelerators. © 2010 Elsevier B.V. All rights reserved.
The interactions of 400 GeV protons with different sequences of bent silicon crystals have been investigated at the H8 beam line of the CERN Super Proton Synchrotron. The multiple volume reflection of the proton beam has been studied in detail on a five-crystal reflector measuring an angular beam deflection θ=52.96±0.14μrad. The efficiency was found larger than 80% for an angular acceptance at the reflector entrance of 70μrad, with a maximal efficiency value of ε=0.90±0.01±0.03. © 2009 The American Physical Society.
The radiation emitted by 180-Ge/c volume-reflected electrons and positrons impinging on a bent crystal has been measured by the H8RD22 Collaboration on the H8 beamline at the CERN SPS. A dedicated spectrometer has been developed to measure high-energy photon spectra (up to ∼100 GeV) under volume reflection: photon and charged particle beams have been separated by a bending magnet and leptons were detected and tagged by microstrip silicon detectors and a Pb-scintillator sampling calorimeter. A comparison between the experimental and analytical data for the amorphous and volume-reflection cases is presented and the differences are discussed. © 2009 The American Physical Society.
Channeling in a short bent silicon crystal was investigated at the CERN SPS using 400-GeV/c protons with an angular spread much narrower than the critical channeling angle. Particle dechanneling due to multiple scattering on the atomic nuclei of the crystal was observed and its dechanneling length was measured to be about 1.5 mm. For a crystal with length comparable to such dechanneling length, an efficiency of 83.4% was recorded, which is close to the maximum value expected for a parallel beam and exceeds the previously known limitation of deflection efficiency for long crystals. © 2009 Elsevier B.V. All rights reserved.
This paper presents a detailed study of the deflection phenomena of a 400GeV/c proton beam impinging on a new generation of bent silicon crystals; the tests have been performed at the CERN Super Proton Synchrotron H8 beam line. Channeling and volume reflection angles are measured with an extremely precise goniometer and with high resolution silicon microstrip detectors. Volume reflection has been observed and measured for the first time at this energy, with a single-pass efficiency as large as 98%, in good agreement with the simulation results. This efficiency makes volume reflection a possible candidate for collimation with bent crystals at the CERN Large Hadron Collider. © 2008 The American Physical Society.
The doubling of the angle of beam deflection due to volume reflection of protons by a sequence of two bent silicon crystals was experimentally observed at the 400 GeV proton beam of the CERN SPS. A similar sequence of short bent crystals can be used as an efficient primary collimator for the Large Hadron Collider.
A high performance apparatus has been designed and built by the H8-RD22 collaboration for the study of channeling and volume reflection phenomena in the interaction of 400 GeVc protons with bent silicon crystals, during the 2006 data taking in the external beamline H8 of the CERN SPS. High-quality silicon short crystals were bent by either anticlastic or quasimosaic effects. Alignment with the highly parallel (8 μrad divergence) proton beam was guaranteed through a submicroradian goniometric system equipped with both rotational and translational stages. Particle tracking was possible by a series of silicon microstrip detectors with high-resolution and a parallel plate gas chamber, triggered by various scintillating detectors located along the beamline. Experimental observation of volume reflection with 400 GeVc protons proved true with a deflection angle of (10.4±0.5) μrad with respect to the unperturbed beam, with a silicon crystal whose (111) planes were parallel to the beam. © 2008 American Institute of Physics.
An improved synthesis of the electron-rich N,N-chelating ligand, 2-(1-t-butyl-1H-1,2,3-triazol-4-yl)pyridine (L), has been developed by coupling t-butyl-azide with ethynylpyridine in the presence of a Cu(I) catalyst. L has been employed in the preparation of lanthanide coordination compounds having formulae [Ln(κ2-NO3)3L2] and [Eu(dbm)3L] (Ln = Eu, Tb; dbm = dibenzoylmethanate). The molecular structure of [Eu(dbm)3L] has been determined by X-ray diffraction studies. All the new complexes exhibit good photoluminescence properties and [Eu(dbm)3L] has been successfully used as the dopant for the preparation of luminescent plastic materials.
We report the synthesis and characterization of new metal-free organic dyes (namely B18, BTD-R, and CPTD-R) which designed with D-π-A concept to extending the light absorption region by strong conjugation group of π-linker part and applied as light harvester in dye sensitized solar cells (DSSCs). We compared the photovoltaic performance of these dyes in two different photoanodes: a standard TiO2 mesoporous photoanode and a ZnO photoanode composed of hierarchically assembled nanostructures. The results demonstrated that B18 dye has better photovoltaic properties compared to other two dyes (BTD-R and CPTD-R) and each dye has higher current density (Jsc) when applied to hierarchical ZnO nanocrystallites than the standard TiO2 mesoporous film. Transient photocurrent and photovoltage decay measurements (TCD/TVD) were applied to systematically study the charge transport and recombination kinetics in these devices, showing the electron life time (τR) of B18 dye in ZnO and TiO2 based DSSCs is higher than CPTD-R and BTD-R based DSSCs, which is consistent with the photovoltaic performances. The conversion efficiency in ZnO based DSSCs can be further boosted by 35%, when a compact ZnO blocking layer (BL) is applied to inhibit electron back reaction
A transparent conductive graphene film is investigated as front contact in dye-sensitized solar cells (DSSCs), as an alternative to traditional transparent conducting oxides (TCO). The film is composed of poly-crystalline few-layers graphene, covering homogeneously an area of 1 cm2, deposited by chemical vapour deposition (CVD) technique on larger area Cu catalyst substrate and transferred on glass. DSSC photoanode is then fabricated, according to consolidated procedure, by sequential casting of TiO2 films through tape casting technique, followed by annealing at 500 °C, and sensitization with N719 dye. An outstanding value of photoconversion efficiency as high as 2% is recorded for the best cell, under one sun irradiation (AM 1.5 G, 100 mW cm−2), which is the highest ever reported for this kind of devices using graphene as front conducting film. Compared to previous results in the literature, the application of a large area continuous graphene film, guaranteed by the CVD deposition, definitely outperforms graphene layers composed by smaller graphene platelets (at micrometer scale). Morphological and electrical characterizations of graphene are reported and the functional performances of the best cell are compared with those obtained from classical DSSC exploiting fluorine-doped tin oxide. Obtained results encourage further investigation of graphene homogeneous thin film as viable alternative to standard TCOs for application in advanced devices, requiring high temperature processing or flexible substrates, incompatible with standard TCO films.
The availability of a well-established procedure for fabricating reliable and reproducible counter electrodes for quantum dot sensitized solar cells is currently an issue, limiting both the functional performances of these devices and the possibility to compare results obtained in different laboratories. We present here a simple, cheap and fast method for Cu2S counter electrodes fabrication based on spray pyrolysis deposition. Application of prepared counter electrodes to SILAR-sensitized quantum dot solar cells results in high performance devices (photoconversion efficiencies as high as 3.75% and impressive incident photon-to-current-efficient higher than 90%) as well in excellent reproducibility. © 2014 Elsevier Ltd.
Photoelectrochemical (PEC) catalysis provides the most promising avenue for producing value-added chemicals and consumables from renewable precursors. Over the last decades, PEC catalysis, including reduction of renewable feedstock, oxidation of organics, and activation and functionalization of C─C and C─H bonds, are extensively investigated, opening new opportunities for employing the technology in upgrading readily available resources. However, several challenges still remain unsolved, hindering the commercialization of the process. This review offers an overview of PEC catalysis targeted at the synthesis of high-value chemicals from sustainable precursors. First, the fundamentals of evaluating PEC reactions in the context of value-added product synthesis at both anode and cathode are recalled. Then, the common photoelectrode fabrication methods that have been employed to produce thin-film photoelectrodes are highlighted. Next, the advancements are systematically reviewed and discussed in the PEC conversion of various feedstocks to produce highly valued chemicals. Finally, the challenges and prospects in the field are presented. This review aims at facilitating further development of PEC technology for upgrading several renewable precursors to value-added products and other pharmaceuticals.