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The thermal behaviors of benzoyl peroxide (BPO) under contamination have been a topic received extensive attention. This paper attempted to examine the effect of phenol on the decomposition reaction of BPO by applying dynamic, isothermal DSC experiments and slow cook-off test. A kinetic model was further established by the Thermal Safety Software through fitting DSC curves and verified by the slow cook-off test. Moreover, the runaway reactions under different storage conditions were predicted. The results indicate that the phenol significantly reduces the thermal stability of BPO and the Benito-Perez model is credible to evaluate the decomposition process. During simulating the reaction process, it is predicted that the explosion could take place even at the 40 °C for 50 kg packaging sample. For 10% limit value, the time to conversion limit of sample is 7.49 h at 40 °C, while it just only 2.37 h at 110 °C.

Crystalline silicon thin films are promising candidates for low cost and flexible photovoltaics. Among various synthesis techniques, epitaxial growth via low temperature plasma-enhanced chemical vapor deposition is an interesting choice because of two low temperature related benefits: low thermal budget and better doping profile control. However, increasing the growth rate is a tricky issue because the agglomeration of clusters required for epitaxy leads to powder formation in the plasma. In this work, we have measured precisely the time evolution of the self-bias voltage in silane/hydrogen plasmas at millisecond time scale, for different values of the direct-current bias voltage applied to the radio frequency (RF) electrode and growth temperatures. We demonstrate that the decisive factor to increase the epitaxial growth rate, i.e. the inhibition of the agglomeration of plasma-born clusters, can be obtained by decreasing the RF OFF time or increasing the growth temperature. The influence of these two parameters on the growth rate and epitaxial film quality is also presented.

Low temperature (175°C) plasma-enhanced chemical vapor deposition (PECVD) is investigated as an alternative way to form p-n junctions for solar cells production. Compared to standard diffusion, PECVD deposition below 200°C ensures a lower thermal budget and the formation of a sharper doping profile. In this work, boron-doped epitaxial silicon films were grown by PECVD on (100) n-type Si substrates to form the emitter. We focus on the correlation between hydrogen incorporation and the structural and electrical properties of the boron-doped layers to assess their quality in view of the realization of p-n junctions. Using X-ray diffraction and electrochemical capacitance voltage, we observe that there is a strong correlation between hydrogen release (upon annealing the samples) and the activation of boron dopants in the epitaxial film. Interestingly, annealing at 300°C for 10 minutes is enough to activate boron in the emitter layers.

To study the thermal hazard of β-nitroso-α-naphthol, both dynamic and isothermal tests were performed with a differential scanning calorimeter (DSC). The dynamic tests indicated that the initial decomposition temperature of β-nitroso-α-naphthol ranged from 153 °C to 173 °C. The interrupt-rescanning method verified the autocatalytic characteristic of β-nitroso-α-naphthol decomposition. DSC curves obtained at five constant temperatures confirmed that the decomposition of β-nitroso-α-naphthol was an autocatalytic reaction. Activation energy E was 149 ± 8 kJ mol−1 calculated by Kissinger method. E values calculated by induction period method and isothermal method were in line with that obtained by Friedman method. On the basis of the kinetic analysis, the safety parameter SADT of β-nitroso-α-naphthol in 50 kg standard packaging was 81 °C based on Semenov model and 67 °C based on Frank-Kamenetskii model.

We have studied surface passivation on nanopatterned crystalline silicon (c-Si) wafers (280 µm), thin c-Si wafers (25 µm), ultrathin (~1–6 µm) low temperature epitaxial PECVD and epitaxy-free silicon. Nanopatterned front surfaces were produced by combining nanoimprint lithography with dry or wet etching. The impact of the nanopatterning on the effective lifetime is investigated by means of photoconductance and time-resolved microwave conductivity measurements. Passivation of flat ultra-thin monocrystalline layers by a-Si:H demonstrates effective lifetimes of a few µs. Flat, dry and wet etched c-Si wafers were also passivated by hydrogenated amorphous silicon, thus forming a heterojunction interface. The measured effective lifetimes were 2.2 ms for the flat, 484 μs for the dry and 709 μs for the wet etched wafers, respectively. It is noteworthy that despite the plasma damage associated with the dry etching process, the lifetime measured after passivation remains high enough for the targeted ultrathin solar cells. Solar cells fabricated on wafers nanopatterned via wet etching have reached an open circuit voltage as high as the flat sample thus demonstrating the potential of the use of wet etched nanopatterned surfaces for high efficiency solar cells.

During thermal decomposition of azobisisobutyronitrile (AIBN), the endothermic process of phase transition disturbed exothermic decomposition, which brought deformation in its thermal graphs. Therefore, exact kinetic parameters of the decomposition could not be obtained by the existing kinetics analytic models, and the accurate enthalpy data of the decomposition and phase transition were not available. Two methods, i.e., a solvent method and a mathematical method, were introduced in this paper to resolve the coupling phenomenon. In the former method, AIBN was dissolved into aniline to eliminate the endothermic process and obtain curves of the liquid-state decomposition. In the latter method, MATLAB software was employed to get the "pure" exothermic decomposition curve without the influence of phase transition by fitting coupling curves within the section after the transition point and extrapolating to the initial stage of decomposition. Moreover, the kinetic parameters of the "pure" exothermic decomposition of AIBN obtained by the mathematical fitting agreed with the results from the solvent method, verifying the accuracy of the decoupling. The research is of great significance for comprehending the exact characteristics of thermal behaviors and safety parameters of AIBN. It also provides a great help to determine the safe operating temperature and alarm temperature for processes in industry.

The afterburning effect of TNT and a desensitized hexogen RDX-Al explosive was studied in a defined gas volume under water. A double-layer container (DLC) filled with different gases (air, oxygen, and nitrogen) was used to control and distinguish the afterburning effect of explosives. After the charges in the DLC were initiated under water, the shock wave signals were collected and analyzed. It is shown that shock wave peak pressures are duly in compliance with explosion similarity law, pressure, and impulse histories for explosions in oxygen and air are greater than those recorded for explosions in nitrogen due to the afterburing reaction. Moreover, the afterburning energy was calculated. Results show that even though there is excess oxygen in the gas volume, the afterburning energy may not reach the theoretically maximum value. This result is different from that in confined explosion, where the presence of excess oxygen in the compressed gas filling a bomb leads to complete combustion of the detonation ...

We present our systematic work on in situ generation of In nanoparticles (NPs) from the reduction of ITO thin films by hydrogen (H2) plasma exposure. In contrast with NP deposition from vapor phase (i.e. evaporation), ITO surface can be considered as a solid reservoir of In atoms thanks to the H2 plasma reduction. On one hand, below the In melting temperature, solid In NPs formation is governed by island-growth mode, which is however a self-limiting process as H2 plasma/ITO interaction will be gradually eliminated by the growing In NPs that covers the ITO surface. On the other hand, we show that above the melting temperature, In droplets prefer to grow along the grain boundaries on ITO surface and a dramatic coalescence occurs when the growing NPs connect with each other. This growth-connection-coalescence behavior is even strengthened on In/ITO bilayers, where In particles larger than 10 μm can be formed, which are made of evaporated In atoms and in situ released ones. Thanks to this understanding, we ma...

International audience; Silicon nanowires have been grown by a plasma-assisted vapour–liquid–solid method using tin as the catalyst. Transmission electron microscopy in the [1-210] zone axis shows that the diamond hexagonal (P63/mmc) crystal structure is present in several nanowires. This is the first unambiguous proof of the natural occurrence of this metastable phase to our knowledge.

Texturing of crystalline silicon at the light wavelength scale is a promising approach for light management in ever thinner cells. However, this approach requires adapting the device design and process, which has so far revealed to be a challenging task. Indeed, successful integration requires compromising the excellent optical properties for preserving the electrical ones. We briefly summarize what has been learned so far in the community and illustrate some of these learnings with the fabrication and improvement of 1-μ m-thin monocrystalline nanotextured silicon solar cells.

Based on recent advancements of radial junction silicon nanowire (RJ SiNWs) solar cells, a demonstration of $5\mathrm{x}5 \pmb{\mathrm{cm}^{2}}$ RJ $\mathbf{SiNW}$ solar mini-module is presented in this work. The $\mathbf{SiNW}$ devices were grown by plasma-assisted vapor-liquid-solid technique at low temperature in a plasma-enhanced chemical vapor deposition reactor. The $\pmb{5\mathrm{x}5\ \mathrm{cm}^{2}}$ mini-modules have been obtained using a commercial laser scribing apparatus. The laser scribing insures a monolithic integration of electrically separated cells. We have obtained a power generation of 10 $\mathbf{mW}$ from 5 individual cells of total active area of 8.6 $\pmb{\mathrm{cm}^{2}}$. The mini-module has an open-circuit voltage of 3.85 V. The performance was evaluated using solar simulator and short comings (high series resistance) were analyzed using a home-made electroluminescence setup.

International audience; We fabricated (n) c-Si/ (p) GaAs heterojunctions, by combining low temperature (∼175°C) RF-PECVD for Si and metal organic vapor phase epitaxy for GaAs, aiming at producing hybrid tunnel junctions for Si/III-V tandem solar cells. The electrical properties of these heterojunctions were measured and compared to that of a reference III-V tunnel junction. Several challenges in the fabrication of such heterostructures were identified and we especially focused in this study on the impact of atomic hydrogen present in the plasma used for the deposition of silicon on p-doped GaAs doping level. The obtained results show that hydrogenation by H 2 plasma strongly reduces the doping level at the surface of the GaAs: C grown film. Thirty seconds of H 2 plasma exposition at 175°C are sufficient to reduce the GaAs film doping level from 1 × 10 20 cm −3 to

2-Ethylhexyl nitrate (EHN) is an important material, which is produced by concentrated HNO3–H2SO4 nitration process. But EHN is not a stable material, especially mixed with acids. To analyze the stability of EHN with concentrated acid under serious condition, four samples (pure EHN, concentrated sulfuric acid with EHN, concentrated nitric acid with EHN, and mixed acid with EHN) and three acids (sulfuric acid, nitric acid, and mixed acid) were measured by differential scanning calorimeter (DSC) and accelerating rate calorimeter (ARC) in this paper. The results indicated that concentrated sulfuric acid, concentrated nitric acid, and mixed acid all could decrease the onset decomposition temperature of EHN, especially concentrated sulfuric acid. DSC results also showed that the heat of EHN decomposition with nitric acid is larger than other samples. Based on ARC data, the kinetic parameters and T D24 (temperature at which TMR ad is 24 h) were calculated. The activation energy and T D24 of the EHN with acids, especially with concentrate sulfuric acid, were much lower than the pure EHN. It can be concluded that acids could decrease the stability of EHN and that is an important reason for frequent accidents.

Four widely used organic peroxides, namely DTBP, DTAP, BTDH and TBPB, were investigated for hazards caused by their thermal instabilities. Chemically pure materials without diluents were adopted to reveal their thermal decomposition and associated kinetic processes. DSC was employed to carry out experimental thermal study and the Friedman isoconversional method, the Kissinger method, as well as AKTS software were used for kinetic calculations and numerical simulations. Experimental results showed TBPB had the lowest detected “onset temperature”, and unlike DTBP, DTAP and BTDH, all of which showed a two-stage decomposition, TBPB decomposition occurred in a single stage. Heats of reactions measured by ARC were between ca. 37 and 54% of the heats of reaction measured by DSC and reported elsewhere by both, DSC and ARC. The obtained values are compared and discussed. Then, a risk diagram was established to determine the conditionally acceptable conditions of use for the OPs. Furthermore, pressure evaluation results by TSu indicated the generation of non-condensable gas during runaway reactions should be seriously considered.

We report on the fabrication, integration, and simulation, both optical and optoelectrical, of two-dimensional photonic nanostructures for advanced light trapping in thin crystalline silicon (c-Si) solar cells. The photonic nanostructures are fabricated by the combination of various lithography (nanoimprint, laser interference, and hole mask colloidal) and etching (dry plasma and wet chemical) techniques. The nanopatterning possibilities thus range from periodic to random corrugations and from inverted nanopyramids to high aspect ratio profiles. Optically, the nanopatterning results in better performance than the standard pyramid texturing, showing a more robust behavior with respect to light incidence angle. Electrically, wet etching results in higher minority carrier lifetimes compared to dry etching. From the integration of the photonic nanostructures into a micron-thin c-Si solar cell certain factors limiting the efficiencies are identified. More precisely: (a) the parasitic absorption is limiting the short circuit current, (b) the conformality of thin-film coatings on the nanopatterned surface is limiting the fill factor, and (c) the material damage from dry etching is limiting the open circuit voltage. From optical simulations, the optimal pattern parameters are identified. From optoelectrical simulations, cell design considerations are discussed, suggesting to position the junction on the opposite side of the nanopattern.

Solar cells based on epitaxial silicon layers as the absorber attract increasing attention because of the potential cost reduction. In this work, we studied the influence of the deposition rate on the structural properties of epitaxial silicon layers produced by plasma-enhanced chemical vapor deposition (epi-PECVD) using silane as a precursor and hydrogen as a carrier gas. We found that the crystalline quality of epi-PECVD layers depends on their thickness and deposition rate. Moreover, increasing the deposition rate may lead to epitaxy breakdown. In that case, we observe the formation of embedded amorphous silicon cones in the epi-PECVD layer. To explain this phenomenon, we develop a model based on the coupling of hydrogen and built-in strain. By optimizing the deposition conditions to avoid epitaxy breakdown, including substrate temperatures and plasma potential, we have been able to synthesize epi-PECVD layers up to a deposition rate of 8.3 Å/s. In such case, we found that the incorporation of hydrogen in the hydrogenated crystalline silicon can reach 4 at. % at a substrate temperature of 350 °C.

A comprehensive study of the silicon nanowire growth process has been carried out. Silicon nanowires were grown by plasma-assisted-vapor-solid method using tin as a catalyst. We have focused on the evolution of the silicon nanowire density, morphology, and crystallinity. For the first time, the initial growth stage, which determines the nanowire (NW) density and growth direction, has been observed step by step. We provide direct evidence of the merging of Sn catalyst droplets and the formation of Si nanowires during the first 10 s of growth. We found that the density of Sn droplets decreases from ~9000 Sn droplets/μm2 to 2000 droplets/μm2 after just 10 s of growth. Moreover, the long and straight nanowire density decreases from 170/μm2 after 2 min of growth to less than 10/μm2 after 90 min. This strong reduction in nanowire density is accompanied by an evolution of their morphology from cylindrical to conical, then to bend conical, and finally, to a bend inverted conical shape. Moreover, the changes in the crystalline structure of nanowires are from (i) monocrystalline to (ii) monocrystalline core/defective crystalline shell and then to (iii) monocrystalline core/defective crystalline shell/amorphous shell. The evolutions of NW properties have been explained in detail.

International audience

In this review, we report several rational designs of nanowire-based solar cells from single nanowire to nanowire arrays. Two methods of nanowires fabrication: via 'top-down' and 'bottom-up', and two types of configurations including axial and radial junction are presented for nanowire-based solar cells. To enhance absorption, several photon management schemes are shown in detail, including anti-reflection coating, diffractive grating, and plasmonics. Considering the rational design of nanowire arrays, we summarize a total of seven solar cell structures including axial junctions, radial junctions, substrate interfacial junctions, planar junctions, conductors, junctionless and tandem. Each type is supported by examples which are presented and discussed. Finally, a general comparison between bulk and nanowire solar cell efficiencies is given.

Unidirectional growth of silicon nanowires (SiNWs) can be achieved via a vapor–liquid–solid (VLS) mechanism. Interestingly, when adopting low surface tension metals such as tin or indium to mediate the growth of SiNWs in a plasma-assisted VLS process, the standard scenario is challenged by the fact that low surface tension metals tend to coat the high energy sidewalls of SiNWs. Moreover, we show that tin-assisted SiNW growth can continue without any apparent metal droplet on top. To address these issues, we investigate the time evolution of tin-assisted SiNW growth. We suggest that, during the initial growth phase, an ultrathin metal layer wetting the SiNW sidewalls allows silicon adatoms to diffuse toward the top of the nanowires, and thus enhances the axial growth while suppressing the radial one (in a way similar to molecular beam epitaxy growth of SiNWs). Later on, the wetting layer can assist the growth even when the tin droplets are exhausted from the top of SiNWs. We propose that this phenomenon ma...

AIBN (2,2′-azobis (isobutyronitrile)), widely used for blowing agent and initiator, is a typical self-reactive material, being capable of undergoing runaway reaction due to its self-heating during storage or transportation. In this study, the thermal decomposition process of AIBN was studied by differential scanning calorimetry at different heating rates. The kinetic parameters including the activation energy and pre-exponential factor at different stages were calculated, and the laws of parameter variation were analyzed using the software, named as Advanced Kinetics and Technology Solutions, which can also predict the thermal stability of decomposition process at actual situations, such as ton and kg scale. The results show that heating rate can influence evidently the thermal behavior of AIBN, which can decompose in liquid phase or in liquid–solid co-existing phase, or, even decomposes in solid phase; according to Friedman method, the value of the calculated activation energy is 122 kJ mol−1; according to Ozawa method, the value decreases gradually with the reaction process, and the smallest one is 124 kJ mol−1. By mg-scale prediction under isothermal condition, it is known that AIBN decomposes at 30 °C (room temperature), very slowly; by ton-scale prediction under adiabatic condition, the safety diagram of AIBN is acquired, which shows how the time to the maximum rate changes with the initial temperature under ideal adiabatic condition (Φ = 1), for example, for TMRad = 24 h, the corresponding mean temperature (i.e., TD24) is 71.23 °C, and for the initial temperature 71.23 °C, the lower and upper limits of the confidence intervals (95 % probability) are 18.5 and 31 h; by kg-scale prediction, it is obtained that the self-accelerating decomposition temperature of 50 kg AIBN with standard package is 63 °C, which is close to that of ARC.

International audience; Ultrathin c-Si solar cells have the potential to drastically reduce costs by saving raw material while maintaining good efficiencies thanks to the excellent quality of monocrystalline silicon. However, efficient light trapping strategies must be implemented to achieve high short-circuit currents. We report on the fabrication of both planar and patterned ultrathin c-Si solar cells on glass using low temperature (T < 275 °C), low-cost, and scalable techniques. Epitaxial c-Si layers are grown by PECVD at 160 °C and transferred on a glass substrate by anodic bonding and mechanical cleavage. A silver back mirror is combined with a front texturation based on an inverted nanopyramid array fabricated by nanoimprint lithography and wet etching. We demonstrate a short-circuit current density of 25.3 mA/cm2 for an equivalent thickness of only 2.75 μm. External quantum efficiency (EQE) measurements are in very good agreement with FDTD simulations. We infer an optical path enhancement of 10 in the long wavelength range. A simple propagation model reveals that the low photon escape probability of 25% is the key factor in the light trapping mechanism. The main limitations of our current technology and the potential efficiencies achievable with contact optimization are discussed.

Monolithical integration of III-V and Si is of strong interest to produce tandem solar cells reaching high conversion efficiencies. In the context of the French ANR research project IMPETUS, an innovative approach for III-V/Si multijunction solar cells is studied. The targeted device is a tandem cell composed of a III-V top cell (AlGaAs) and a IV bottom cell (Si 1−x Ge x ). The choice of Al y Ga 1−y As as the top material is justified because it provides the optimum bandgap combination with Si 1−x Ge x (1.63 eV/0.96 eV), with theoretical efficiencies in excess of 42% for such a tandem configuration. In our inverted metamorphic approach, we first use MOVPE to grow the AlGaAs top cell on a lattice matched GaAs substrate, and then perform low temperature PECVD heteroepitaxial SiGe on top. We show here the first structural and electrical characterizations of Si(PECVD)/III-V(MOVPE) interfaces. Furthermore, the epitaxial growth of highly doped crystalline Si by low-temperature PECVD on GaAs enables us to fabricate hybrid tunnel junctions with low resistivity and a high current, suitable to interconnect the two subcells in the tandem III-V/Si solar cell.

The integration of III-V semiconductors with silicon is a key issue for photonics, microelectronics and photovoltaics. With the standard approach, namely the epitaxial growth of III-V on silicon, thick and complex buffer layers are required to limit the crystalline defects caused by the interface polarity issues, the thermal expansion and lattice mismatches. To overcome these problems, we have developed a reverse and innovative approach to combine III-V and silicon: the straightforward epitaxial growth of silicon on GaAs at low temperature by plasma enhanced CVD (PECVD). Indeed we show that both GaAs surface cleaning by SiF4 plasma and subsequent epitaxial growth from SiH4/H2 precursors can be achieved at 175 °C. The GaAs native oxide etching is monitored with in-situ spectroscopic ellipsometry and Raman spectroscopy is used to assess the epitaxial silicon quality. We found that SiH4 dilution in hydrogen during deposition controls the layer structure: the epitaxial growth happens for deposition conditions at the transition between the microcrystalline and amorphous growth regimes. SIMS and STEM-HAADF bring evidences for the interface chemical sharpness. Together, TEM and XRD analysis demonstrate that PECVD enables the growth of high quality relaxed single crystal silicon on GaAs.

Developing structures that provide excellent light absorption while keeping a high surface passivation quality is a mandatory issue for crystalline Si solar cells. In this study, Si nanowires grown on crystalline Si wafers using plasma-enhanced chemical vapor deposition (PECVD) are used as nanostructures for an efficient light absorption. Two types of stacks with direct or decoupled growth of nanowires on crystalline Si have been studied in order to identify their influence on the light absorption, as well as on the passivation quality. By choosing appropriately the stack configuration and carefully adjusting parameters such as silicon nitride thickness, Si nanowire diameters, and lengths, we have obtained an effective carrier lifetime up to 1.7 ms. Moreover, modeling has shown that a photogeneration density above 41 mA/cm2 can be expected in the c-Si wafer.

The enhancement of light absorption via nanopatterning in crystalline silicon solar cells is becoming extremely important with the decrease of wafer thickness for the further reduction of solar cell fabrication cost. In order to study the influence of nanopatterning on crystalline silicon thin-film solar cells, we applied two lithography techniques (laser interference lithography and nanoimprint lithography) combined with two etching techniques (dry and wet) to epitaxial crystalline silicon thin films deposited via plasma-enhanced chemical vapor deposition at 175 degrees C. The influence of nanopatterning with different etching profiles on solar cell performance is studied. We found that the etching profiles (pitch, depth and diameter) have a stronger impact on the passivation quality (open circuit voltage and fill factor) than on the optical performance (short circuit current density) of the solar cells. We also show that nanopatterns obtained via wet-etching can improve solar cell performance; and in contrast, dry-etching leads to poor passivation related to the etching profile, surface damage, and/ or contamination introduced during the etching process.

Heterojunction with intrinsic thin layer (HIT) solar cells are still costly due to the use of silicon wafers that contribute to ∼30% of the final module cost. To reduce the costs, thinner wafers can be used but to the detriment of the optical absorption. This loss has to be compensated by an efficient light trapping scheme. In this paper we study HIT devices based on Si nanowire (SiNW) core–shell structures to enhance light absorption. The SiNWs are fabricated by a wet etching technique, and the heterojunction is formed using an optimized low-temperature plasma enhanced chemical vapor deposition (PECVD) process at 200 °C. The solar cells are characterized via carrier lifetime and electron beam induced current (EBIC) measurements to understand their electrical properties at nanoscale. The impact of the SiNW length on the cell performance is also investigated. The solar cells show a good performance reaching average fill factor of 81%, Voc of 0.525 V, and Jsc of 29.27 mA/cm2 giving rise to an average effici...

Silicon nanowires (SiNWs) with different surface number density are fabricated using Chemical Vapor Deposition (CVD) method by controlling the catalyst droplet number density with in-situ evaporation. For comparison, another type of SiNWs is fabricated by Molecular Beam Epitaxy (MBE) method. To study these two types of SiNWs a general growth rate model is presented. The fit curves from this model are consistent with our experimental data. In both growing conditions the SiNW growth rate as a function of their diameter are compared and discussed. The p-type SiNWs have also been prepared by adding diborane into precursor. The doping metrology in an individual SiNW is realized by laser assisted Atom Probe Tomography (APT). We have shown that the doping atoms (e.g. B) can incorporate into SiNW and an accurate quantification can be given (© 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

This paper presents calorimeter measurement for the thermal decomposition of n-propyl nitrate (NPN), isopropyl nitrate (IPN) and 2-ethylhexyl nitrate (EHN). Similar experimental results of triethylene glycol dinitrate (tri-EGDN) and tetraethylene glycol dinitrate (tetra-EGDN) are included for comparison. The potential energy surfaces (PESs) along O-NO2 bond stretch are investigated using the DFT (B3P86, B3PW91 and B3LYP), ab initio Hartree-Fock and PM3 methods. The good coincidence of experimental with theoretical results indicates that initial stage in the thermal decomposition of five nitrates is only unimolecular homolytical dissociation of the O-NO2 bonds and the activation energies of thermolysis by DSC correspond to the energies of O-NO2 bond scission of nitrates.

By correlating atom probe tomography with other conventional microscope techniques (scanning electron microscope, scanning transmission electron microscope, and scanning tunneling microscopy), the distribution and composition of Au clusters in individual vapor-liquid-solid grown Si nanowires is investigated. Taking advantage of the characteristics of atom probe tomography, we have developed a sample preparation method by inclining the sample at certain angle to characterize the nanowire sidewall without using focused ion beam. With three-dimensional atomic scale reconstruction, we provide direct evidence of Au clusters tending to remain on the nanowire sidewall rather than being incorporated into the Si nanowires. Based on the composition measurement of Au clusters (28% ± 1%), we have demonstrated the supersaturation of Si atoms in Au clusters, which supports the hypothesis that Au clusters are formed simultaneously during nanowire growth rather than during the cooling process.

JUN 14-19, 2015; International audience; We report on the fabrication and characterization of both flat and patterned c-Si solar cells on glass. We use epitaxial layers grown by plasma enhanced chemical vapor deposition at low temperature (T

Incorporation of nanostructures is a recent trend in the photovoltaic community, aimed at improving light absorption and consequently cell efficiency. In this regard, semiconductor nanowires provide an attractive research platform for a new generation of cost-effective and efficient solar cells. Thanks to their unique geometry, silicon nanowires enhance light trapping and anti-reflection effects by means of multiple scattering between individual nanowires, and by coupling the light into confined eigenmodes over a broad range of the solar spectrum. Moreover, radial junction solar cells built around nanowires decouple the light absorption and carrier collection directions, which allows for a higher internal field and better carrier collection. Thus, arrays of radial junction solar cells bring advantages of high efficiency with reduced material amount. This is particularly attractive for devices based on hydrogenated amorphous and microcrystalline silicon thin films. In this paper, after reviewing different approaches to fabricate silicon nanowires, we focus on nanowires grown using the plasma-assisted vapour–liquid–solid method because of the simplicity and compatibility with current silicon thin-film technology. Their application to a-Si : H based radial junction solar cells has already resulted in ∼8% of stable devices with an absorber layer thickness of only 100 nm. Moreover, current challenges and perspectives such as the use of a microcrystalline silicon absorber are also reviewed.

Introducing nanophotonics into photovoltaics sets the path for scaling down the surface texture of crystalline-silicon solar cells from the micro-to the nanoscale, allowing to further boost the photon absorption while reducing silicon material loss. However, keeping excellent electrical performance has proven to be very challenging, as the absorber is damaged by the nanotexturing and the sensitivity to the surface recombination is dramatically increased. Here we realize a light-wavelength-scale nanotextured monocrystalline silicon cell with the confirmed efficiency of 8.6% and an effective thickness of only 830 nm. For this we adopt a self-assembled large-area and industry-compatible amorphous ordered nanopatterning, combined with an advanced surface passivation, earning strongly enhanced solar light absorption while retaining efficient electron collection. This prompts the development of highly efficient flexible and semitransparent photovoltaics, based on the industrially mature monocrystalline silicon technology.

The incorporation of metal atoms into silicon nanowires during metal-particle-assisted growth is a critical issue for various nanowire-based applications. Here we have been able to access directly the incorporation and redistribution of metal atoms into silicon nanowires produced by two different processes at growth rates ranging from 3 to 40 nm s(-1), by using laser-assisted atom probe tomography and scanning transmission electron microscopy. We find that the concentration of metal impurities in crystalline silicon nanowires increases with the growth rate and can reach a level of two orders of magnitude higher than that in their equilibrium solubility. Moreover, we demonstrate that the impurities are first incorporated into nanowire volume and then segregate at defects such as the twin planes. A dimer-atom-insertion kinetic model is proposed to account for the impurity incorporation into nanowires.

A quantitative structure–property relationship model for prediction of the heat capacity was developed from molecular structures. By using DRAGON 2.1, various kinds of molecular structure descriptors were calculated to represent the molecular structures of compounds, which contain 18 categories of descriptors in total. The novel variable selection method of ant colony optimization (ACO) algorithm was employed to select an optimal subset of descriptors that have significant contribution to the property from a large pool of calculated descriptors. As a result, five descriptors were screened out as input parameters. With the same five descriptors, ACO coupled with the conjugate gradient (CG) method and support vector machine (SVM) method was employed to construct the linear model (ACO-CG) and the nonlinear model (ACO-SVM), respectively. The results showed robust models and small prediction error, and the built models were very satisfying. In addition, the fitting and predicting performances of the ACO-SVM model (squared correlation coefficient, Rtrain2=0.9607, Rtest2=0.9398) are both better than that of the ACO-CG model (Rtrain2=0.9404, Rtest2=0.9281). The traditional validation parameters of Qloo2 (internal validation) and Qext2(external validation) have been supplemented with two novel parameters rm2 and cRp2 for a stricter test of validation. The developed models could achieve the required values for the novel parameters rm2 (rm2¯>0.5, Δrm2 0.5). From the preceding analysis, it can be concluded that the proposed methods can be successfully used to predict the heat capacity with preselected theoretical descriptors, which can be directly calculated solely from the molecular structure. The applicability domain of the model was assessed by the Williams plot. Copyright © 2013 John Wiley & Sons, Ltd.

Understanding and controlling effectively the behavior of metal catalyst droplets during the Vapor-Liquid-Solid growth of nanowires are crucial for their applications. In this work, silicon nanowires are produced by plasma-assisted Chemical Vapor Deposition using gold as a catalyst. The influence of hydrogen plasma on nanowire growth is investigated experimentally and theoretically. Interestingly, in contrast to conventional chemical vapor deposition, the growth rate of silicon nanowires shows a decrease as a function of their diameters, which is consistent with the incorporation of silicon via sidewall diffusion. We show that Ostwald ripening of catalyst droplets during nanowire growth is inhibited in the presence of a hydrogen plasma. However, when the plasma is off, the diffusion of Au atoms on the nanowire sidewall can take place. Based on this observation, we have developed a convenient method to grow silicon nanotrees.

Hydrogenated polymorphous silicon (pm-Si:H) is a nanostructured material consisting of silicon nanocrystals embedded in an amorphous silicon matrix. Its use as the intrinsic layer in thin film p-i-n solar cells has led to good cell properties in terms of stability and efficiency. Here, we have been able to assess directly the concentration and distribution of nanocrystals and impurities (dopants) in p-i-n solar cells, by using femtosecond laser-assisted atom probe tomography (APT). An effective sample preparation method for APT characterization is developed. Based on the difference in atomic density between hydrogenated amorphous and crystalline silicon, we are able to distinguish the nanocrystals from the amorphous matrix by using APT. Moreover, thanks to the three-dimensional reconstruction, we demonstrate that Si nanocrystals are homogeneously distributed in the entire intrinsic layer of the solar cell. The influence of the process pressure on the incorporation of nanocrystals and their distribution is also investigated. Thanks to APT we could determine crystalline fractions as low as 4.2% in the pm-Si:H films, which is very difficult to determine by standard techniques, such as X-ray diffraction, Raman spectroscopy, and spectroscopic ellipsometry. Moreover, we also demonstrate a sharp p/i interface in our solar cells.

The boron dopant distribution in Si nanowires grown by the Au-catalyzed chemical vapor deposition is characterized by laser-assisted atom probe tomography. A convenient and an effective method for performing the atom probe tomography of an individual nanowire is developed. Using this technique, we demonstrate that when Si nanowires are doped with boron at high silane partial pressure, the radial distribution of boron atoms is rather inhomogeneous. Much more boron atoms incorporate at the periphery than in the center, with the concentration increasing by an order of magnitude as the distance from the nanowire axis increases from zero to only 15 nm. A theoretical model is presented that is capable of describing the observed spatial inhomogeneity of boron dopant. We also consider different kinetic pathways of boron incorporation and discuss the values of diffusion length and diffusion coefficients obtained by fitting the experimental data.

Synthesis of nanostructures of uniform size is fundamental because the size distribution directly affects their physical properties. We present experimental data demonstrating a narrowing effect on the length distribution of Ge nanowires synthesized by the Au-catalyzed molecular beam epitaxy on Si substrates. A theoretical model is developed that is capable of describing this puzzling behavior. It is demonstrated that the direction of the diffusion flux of sidewall adatoms is size dependent and has a major effect on the growth rate of differently sized nanowires. We also show that there exists a fundamental limitation on the maximum nanowire length that can be achieved by molecular beam epitaxy where the direction of the beam is close to the growth axis.

International audience; Up-scaling silicon nanowire (SiNW)-based functionalities requires a reliable strategy to precisely position and integrate individual nanowires. We here propose an all-in-situ approach to fabricate self-positioned/aligned SiNW, via an in-plane solid-liquid-solid growth mode. Prototype field effect transistors, fabricated out of in-plane SiNWs using a simple bottom-gate configuration, demonstrate a hole mobility of 228 cm2/V s and on/off ratio >103. Further insight into the intrinsic doping and structural properties of these structures was obtained by laser-assisted 3 dimensional atom probe tomography and high resolution transmission electron microscopy characterizations. The results could provide a solid basis to deploy the SiNW functionalities in a cost-effective way.

In this study, we have performed nanoscale characterization of Si-clusters and Si-nanowires with a laser-assisted tomographic atom probe. Intrinsic and p-type silicon nanowires (SiNWs) are elaborated by chemical vapor deposition method using gold as catalyst, silane as silicon precursor, and diborane as dopant reactant. The concentration and distribution of impurity (gold) and dopant (boron) in SiNW are investigated and discussed. Silicon nanoclusters are produced by thermal annealing of silicon-rich silicon oxide and silica multilayers. In this process, atom probe tomography (APT) provides accurate information on the silicon nanoparticles and the chemistry of the nanolayers.

Trinitrotoluene is usually made by continuous multistage nitration of the toluene and mixed acid system, the second stage semi-batch nitration of toluene based on the first stage was studied by DSC and the reaction calorimeter(RC1e). DSC was used to test the therma1 decomposition behaviors of mixed acid and mononitrotoluene reaction system. a series of mononitrotoluene nitration experiments were carried out in RC1e to study the influences to parameters of the exothermic rate and the heat and so on by changing the different operating conditions such as stirring speed、feeding rate 、setting temperature to confirm the optimal conditions and provide the basis of technical improvement. Results indicate that temperature influent most and the optimal condition is T=80℃，R =400rpm，t =120min. By using semi-batch reaction model can effectively reduce the runaway reaction severity from medium to lower degree.

We investigated the growth of silicon nanowires from Au-rich catalyst droplets by two different methods: chemical vapor deposition (CVD) and molecular beam epitaxy (MBE). The growth rate is found to be diameter-dependent and increases with increasing precursor partial pressures. The comparison of the experimental results with models shows that the contribution of Si atoms that diffuses from the substrate and the NW sidewalls toward the catalyst droplet can be neglected in CVD for the different pressures used in this study, whereas it is the major source of Si supply for the MBE growth. In addition, by decreasing the number density of catalyst droplet prior to the NW growth in CVD, it is also found that this parameter affects the NWs morphology, increasing the tapering effect when the silane partial pressure is small enough to allow gold atom diffusion from the catalyst droplet.

We present a general model for the vapor-liquid-solid nanowire (NW) growth rates which accounts for adatom diffusion from the substrate and sidewalls into the Au catalyst drop as well as the Gibbs-Thomson effect of elevated chemical potential in the drop with a curved surface. The growth model is compared with the experimental length-diameter dependences for InP and Si NWs grown via metal organic chemical vapor deposition (MOCVD) and GaAs nanowires grown via molecular beam epitaxy (MBE). We show that MBE growth is affected mainly by adatom diffusion from the substrate, whereas MOCVD growth is affected mainly by direct Au drop impingement and sidewall diffusion. The Gibbs-Thomson effect is shown to limit growth for smaller diameter nanowires. Fits for diffusion lengths and the Gibbs-Thomson radii are determined which explain the experimental length-diameter dependence observed.