Silicon Carbon Nanotubes Research Articles

Thermal stability of compound stucture of silicon nanowire encapsulated in carbon nanotubes

To guide the experiment research, the thermal stability of composite silicon nanowire encapsulated in carbon nanotubes is investigated by computer simulation. The cubic-diamond-structured silicon nanowires with the same diameter and [111] orientationt are filled in some armchaired single-walled carbon nanotubes. The heat process of compound structure of silicon nanowire encapsulated in carbon nanotubes is simulated by classical molecular dynamic method. Through the visualization and energy analysis method, the thermal stability of composite structure is studied. The changes in the thermal stability of silicon nanowires and carbon nanotubes are explained by the relationship between carbon nanotube space constraint and van der Waals force. It is found that the diameter of the carbon nanotubes is closely related to the thermal stability of silicon nanowires inside. When the nanotube diameter is small, thermal stability of silicon nanowires increases; when the nanotube diameter increases up to a certain size, the thermal stability of silicon nanowires will suddenly drop significantly: until the distance between silicon nanowires and the wall of carbon nanotube is greater than 1 nm, the thermal stability of silicon nanowires will be restored. On the other hand, silicon nanowires filled into the carbon nanotubes have an effect of reducing the thermal stability of carbon nanotubes.

Carbon nanotube–silicon heterojunction solar cells with surface-textured Si and solution-processed carbon nanotube films

Solution-processed carbon nanotube films fit with textured Si substrates, yielding solar cells with dark surface and improved power conversion efficiency.

Nano-Bioelectronics.

Nano-bioelectronics represents a rapidly expanding interdisciplinary field that combines nanomaterials with biology and electronics and, in so doing, offers the potential to overcome existing challenges in bioelectronics. In particular, shrinking electronic transducer dimensions to the nanoscale and making their properties appear more biological can yield significant improvements in the sensitivity and biocompatibility and thereby open up opportunities in fundamental biology and healthcare. This review emphasizes recent advances in nano-bioelectronics enabled with semiconductor nanostructures, including silicon nanowires, carbon nanotubes, and graphene. First, the synthesis and electrical properties of these nanomaterials are discussed in the context of bioelectronics. Second, affinity-based nano-bioelectronic sensors for highly sensitive analysis of biomolecules are reviewed. In these studies, semiconductor nanostructures as transistor-based biosensors are discussed from fundamental device behavior through sensing applications and future challenges. Third, the complex interface between nanoelectronics and living biological systems, from single cells to live animals, is reviewed. This discussion focuses on representative advances in electrophysiology enabled using semiconductor nanostructures and their nanoelectronic devices for cellular measurements through emerging work where arrays of nanoelectronic devices are incorporated within three-dimensional cell networks that define synthetic and natural tissues. Last, some challenges and exciting future opportunities are discussed.

Effect of added silicon carbide nanowires and carbon nanotubes on mechanical properties of 0–3 natural rubber composites

In this work, the mechanical properties of 0–3 nanocomposite materials containing silicon carbide nanowires (SiCNWs), carbon nanotubes (CNTs), and natural rubber were studied. The SiCNWs and CNTs were used as reinforcement fiber whereas natural rubber was used as the matrix phase. The chemical vapor depositions (CVD) was used for synthesizing the nanowire and nanotube phases. The volume fraction of reinforcement was varied from 0 to 10%. The nanophases were mixed in the natural rubber matrix and molded by the hand lay-up technique. The mechanical properties of the samples were examined and compared with those of neat natural rubber. From the results, it was found that the hardness and density of the samples increased with the quantities of nanophases. The nanocomposites with a volume fraction of 10% exhibited maximum hardness (50.5 SHORE A). The maximum tensile strength and extent of elongation at break of the samples were obtained from the 4% volume fraction sample, which were 16.13 MPa and 1,540%, respectively.

Carbon nanotubes@silicon dioxide nanohybrids coating for solid-phase microextraction of organophosphorus pesticides followed by gas chromatography–corona discharge ion mobility spectrometric detection

A high efficiency solid-phase microextraction (SPME) fiber coated with porous carbon nanotubes–silicon dioxide (CNTs–SiO2) nanohybrids was synthesized and applied for the determination of some organophosphorus pesticides (OPPs) in vegetables, fruits and water samples. Gas chromatography–corona discharge ion mobility spectrometry was used as the detection system. Glucose, as a biocompatible compound, was used for connecting CNT and SiO2 during a hydrothermal process. The electrospinning technique was also applied for the fiber preparation. The parameters affecting the efficiency of extraction, including stirring rate, salt effect, extraction temperature, extraction time, desorption temperature and desorption time, were investigated and optimized. The developed CNTs@SiO2 fiber presented better extraction efficiency than the commercial SPME fibers (PA, PDMS, and PDMS–DVB). The intra- and inter-day relative standard deviations were found to be lower than 6.2 and 9.0%, respectively. For water samples, the limits of detection were in the range of 0.005–0.020μgL−1 and the limits of quantification were between 0.010 and 0.050μgL−1. The results showed a good linearity in the range of 0.01–3.0μgL−1 for the analytes. The spiking recoveries ranged from 79 (±9) to 99 (±8). The method was successfully applied for the determination of OPPs in real samples.

Effect of silicon configurations on the mechanical integrity of silicon–carbon nanotube heterostructured anode for lithium ion battery: A computational study

Heterostructures of silicon and carbon nanotubes (CNT) have been widely studied as Li-ion battery anodes. The focus of the current study is to investigate the role of silicon configurations on the mechanical integrity of the Si–CNT heterostructured anodes during electrochemical cycling. We hypothesize that void nucleation and growth in silicon during electrochemical cycling of Li can induce fracture and eventual failure. To test this hypothesis, we utilized a custom developed multiphysics finite element modeling framework considering the lithium diffusion induced elasto-plastic deformation of silicon. We systematically varied the silicon component configuration and enumerated the stress field within it for one complete electrochemical cycle. Resulting evolution of stress state reveals that reducing the mechanical constraints on Si reduces the plastic flow of the material, and thus possibility of void nucleation and growth. We find that the Si droplet configuration is mechanically stable while the continuous Si coating configuration is prone to void growth induced mechanical failure. Present analysis provides a mechanistic understanding of the effect of Si configurations in heterostructured electrodes on its mechanical integrity, which can help in design of next-generation hetersostructured electrodes with improved capacity retention.

Atmospheric oxidation effect of silicon–carbon nanotube anode on Li-ion battery performance

Secondary energy storage devices are in high demand owing to recent developments in portable electronic devices and electric vehicles. In the last two decades, lithium-ion (Li-ion) battery technology has witnessed phenomenal growth. In order to cope with future requirements and to improve specific capacity, retention ability and life span of the battery, different anode materials, such as carbon nanotube (CNT), tin dioxide (SnO2), silicon (Si) and so on, were investigated. A pure Si-based anode offers maximum theoretical specific capacity of 4200 mAh/g. However, a large volume change (around 400%) during the lithiation–delithiation process hampers its wide acceptance. This problem could be addressed by incorporating different composite anode materials; Si–CNT composite is one of them. Si–CNT composite has shown great promise as a Li-ion battery anode material, but at the same time, the large surface area of Si nanoparticles makes it highly sensitive to atmospheric oxidation. This research work reports an easy and scalable method of synthesis of a Li-ion battery anode using Si–CNT composite and demonstrates the effect of atmospheric oxidation of Si nanoparticles on the performance of the Li-ion battery. The prepared anode was characterized for its structure and electrochemical performance. It offered good initial specific capacity of 663 mAh/g, though this deteriorated owing to surface oxidation.

Silicon nanowire and carbon nanotube hybrid for room temperature multiwavelength light source.

The realization of an innovative hybrid light source operating at room temperature, obtained by embedding a carbon nanotube (CNT) dispersion inside a Si nanowire (NW) array is reported. The NW/CNT system exhibits a peculiar photoluminescence spectrum, consisting of a wide peak, mainly observed in the visible range, due to quantum confined Si NWs, and of several narrower IR peaks, due to the different CNT chiralities present in the dispersion. The detailed study of the optical properties of the hybrid system evidences that the ratio between the intensity of the visible and the IR emissions can be varied within a wide range by changing the excitation wavelength or the CNT concentration; the conditions leading to the prevalence of one signal with respect to the other are identified. The multiplicity of emission spectra obtainable from this composite material opens new perspectives for Si nanostructures as active medium in light sources for Si photonics applications.

Aligned Carbon Nanotube Thin Films from Liquid Crystal Polyelectrolyte Inks.

Single walled carbon nanotube thin films are fabricated by solution shearing from high concentration sodium nanotubide polyelectrolyte inks. The solutions are produced by simple stirring of the nanotubes with elemental sodium in dimethylacetamide, and the nanotubes are thus not subject to any sonication-induced damage. At such elevated concentrations (∼4 mg mL(-1)), the solutions exist in the liquid crystal phase and during deposition this order is transferred to the films, which are well aligned in the direction of shear with a 2D nematic order parameter of ∼0.7 determined by polarized absorption measurements. Compared to similarly formed films made from superacids, the polyelectrolyte films contain smaller bundles and a much narrower distribution of bundle diameters. After p-doping with an organic oxidizer, the films exhibit a very high DC electrical to optical conductivity ratio of σ(DC)/σ(OP) ∼ 35, corresponding to a calculated DC conductivity of over 7000 S cm(-1). When very thin (T550 ∼ 96%), smooth (RMS roughness, R(q) ∼ 2.2 nm), and highly aligned films made via this new route are used as the front electrodes of carbon nanotube-silicon solar cells, the power conversion efficiency is almost an order of magnitude greater than that obtained when using the much rougher (R(q) ∼ 20-30 nm) and less conductive (peak σ(DC)/σ(OP) ∼ 2.5) films formed by common vacuum filtration of the same starting material, and having the same transmittance.

Hydrogen physisorption and selectivity in single-walled silicon carbon nanotubes: a grand canonical Monte-Carlo study

We report grand canonical Monte-Carlo simulations of pure hydrogen physisorption and its binary mixtures with nitrogen and methane H/N2H2/CH4 in single-walled silicon carbon nanotubes (SWSiCNTs). We investigate the effect of temperature, pressure, tube diameter and the influence of the presence of the second molecule on the adsorption of hydrogen. Some obtained results have compared with that of boron nitride and carbon nanotubes and it shows that the SWSiCNT has more hydrogen adsorbable than single-walled boron nitride (SWBNNT) and carbon nanotube (SWCNT) in same chirality of nanotube and same thermodynamic conditions. Furthermore, the influence of tube length on hydrogen adsorption capacity has been illustrated in various SWSiCNT, SWBNNT and SWCNT and the calculations show that the hydrogen adsorption holds the line when the tube length increases. In addition, pure hydrogen adsorption is investigated in rhombic and square SWSiCNT arrays, while the results of this investigation illustrate that rhombic and square SWSiCNT arrays have gravimetric hydrogen capacities between rhombic and square silicon and carbon nanotube arrays, in same thermodynamics conditions and same tube diameters. The simulation data of pure hydrogen fit to Langmuir, Freundlich and Langmuir–Freundlich equations and the Langmuir–Freundlich equation has the best behavior fitting to hydrogen adsorption data; it emphasizes that the multi-layer pure hydrogen adsorptivity occurs more prominently in SWSiCNTs. Also, the excess and delivery isotherms of hydrogen were calculated for various SWSiCNTs, SWBNNTs and SWCNTs. Furthermore, the adsorption selectivity in different mole fractions of hydrogen/methane and hydrogen/nitrogen mixtures in SWSiCNTs has investigated at 77 and 298 K on (8,8) and (15,15) SWSiCNTs, and results show that selectivity-based adsorption decreases at 298 K in both mixtures while increasing pressure and temperature can increase selectivities and the selectivity is not related to the diameter of nanotubes.

Synthesis of silicon carbide at room temperature from colloidal suspensions of silicon dioxide and carbon nanotubes

Experimental and theoretical approaches were used for the investigation of mechanisms and conditions of self-organized nanostructures formation in the drying drop of the mixture of colloidal suspensions of nanoscale amorphous silicon dioxide and carbon nanotubes. The formation of rodlike structures with diameter 250-300nm and length ∼4pm was revealed. The diffraction analysis of the obtained nanostructures showed the formation of the silicon carbide phase at room temperature.

Defective carbon nanotube-silicon heterojunctions for photodetector and chemical sensor with improved responses

The direct growth and integration of defect-modulated carbon nanotubes (CNTs) on n-type silicon (Si) microstructures for high performance photodetectors and chemiresistive sensors is presented. By devising a Si microspring that is strained by the growth force of the CNTs, a vertical load from the restoring force of the microspring is perpendicularly applied against the growth direction of the CNTs. This vertical load induces the formation of defective structures in the CNTs while the CNT–Si heterojunctions are fabricated. Under the illumination of UV light, photogenerated carriers from both the CNTs and the Si can be separated at the CNT–Si heterojunctions and at the defects in the CNTs before recombination, which contributes to a high photoresponsivity of 262.3 mA W−1 and an external quantum efficiency of 91.4%. Moreover, the adsorption of chemical species can be promoted by increasing the defects in the CNTs, thereby improving the sensing responsiveness toward ethanol and NO2 vapors. Our simple and facile growth of defect-adjusted CNTs on conductive Si microstructures would be beneficial to the scalable, high throughput manufacturing of heterojunctioned devices with tunable properties and functionalities of the CNTs.

Study of the Structural Changes Undergone by Hybrid Nanostructured Si-CNTs Employed as an Anode Material in a Rechargeable Lithium-Ion Battery

Silicon–carbon nanotube (Si-CNT) hybrid structures have been fabricated in a single step on Cu substrate by hot filament chemical vapor deposition (HFCVD). A mixture of straight chain saturated aliphatic polymer and Si nanoparticles was used as the seeding source. The material was analyzed by transmission electron microscopy (TEM) and electron energy loss spectroscopy (EELS), and the Si content in the Si-CNT was estimated to be ∼15% wt % by thermogravimetric analysis (TGA). Thereafter, the films were used for lithium-ion battery (LIB) anodes, whose cyclic voltammetry studies show redox peaks for Si and C consistent with lithium insertion/extraction, indicating good reversibility over extensive cycling. Electrochemical tests showed that Si-CNT electrodes can deliver an initial high discharge capacity of ∼700 mAh/g and a reversible capacity of ∼500 mAh/g over 520 cycles. After electrochemical cycling, the Si-CNTs were analyzed and compared to pristine material. The cycled films showed an increment of Si-CNT...

Fabrication of silicon nanowire on freestanding multiwalled carbon nanotubes by chemical vapor deposition

The multi-walled carbon nanotube-silicon nanowire (MWNT/SiNW) hybrids are important materials to meet the requirements of energy storage devices. We fabricated novel freestanding MWNT/SiNW hybrids by growing SiNWs directly on MWNT network via chemical vapor deposition. Gold (Au) was employed as catalyst and the influence of catalyst on the morphology of hybrids was investigated. The results indicated that tuning the thickness of Au layer could serve as a means to control the structure of MWNT/SiNW hybrids. The formation of SiNWs on the surface of MWNTs mainly depended on Au nanoparticles migrating into larger eutectic Au–Si alloy, and the abundant Si depositing on MWNTs improved the connections among MWNTs and SiNWs mechanically and electrically.

The Evolution of a High Capacity Electrode

Silicon can store Li+ at a capacity 10 times as high as that of graphite anodes. However, to harness this remarkable potential for electrical energy storage, one must address the multifaceted challenge of volume change inherent to high capacity electrode materials. In this talk, we present novel chemical strategies to address this challenge. Based on fundamental understanding of nanostructure interface, we have synthesized non-cracking silicon-carbon nanotube composite electrodes that electrically connect amorphous silicon beads. This synthesis is made possible by a propagative chemistry which creates regular bands of alkylcarboxyl groups along the nanotubes. The functional bands anchor the beads such that they exhibit a symmetric “radial breathing” around the CNT string, remaining crack-free and electrically connected throughout lithiation-delithiation cycling. We further show that, solely by chemical tailoring of the Si-C interface with atomic oxygen, the cycle life of the electrodes can be substantially improved, by 300%, even at high mass loadings. The evolution of this work culminates in the design and fabrication of a high capacity composite electrode that is weavable. The engineered andoe simultaneously attains high areal capacity (3.86 mAh/cm2), high specific capacity (922 mAh/g based on the mass of the entire electrode), and excellent cyclability (80% retention of capacity after 160 cycles), which are among the highest reported. This work was mainly supported as part of Nanostructures for Electrical Energy Storage (NEES), an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences under Award Number DESC0001160. We acknowledge cumulative contributions from many collaborators particularly K. Karki, M. Okada, H. Liao, H. Zhu, Z. Jia, E. Baker, Y. Zhang, K. Gaskell, A. Ghemes, P. Wang, J. Cumings, L. Hu, Y. Inoue, T. Li, Y. Qi, and G. W. Rubloff.

Atmospheric oxidation effect of silicon-carbon nanotube anode on Li-ion battery performance

Atmospheric oxidation effect of silicon-carbon nanotube anode on Li-ion battery performance

Implementation of antireflection layers for improved efficiency of carbon nanotube–silicon heterojunction solar cells

We explore the use of antireflection polymer layers on n-type silicon solar cells that use a carbon nanotube (CNT) front electrode. Three different types of polymer were studied; polydimethylsiloxane (PDMS), poly(methyl methacrylate) (PMMA) and polystyrene (PS). The influence of polymer type and thickness on device performance has been assessed. The performance degradation with ageing of Si–CNT, Si–CNT–PDMS, Si–CNT–PMMA and Si–CNT–PS solar cells has been compared. Based on the analysis of the results, antireflection polymer layers are able to reduce the reflectance of the cell surface and subsequently improve the amount of solar energy absorbed by the silicon without any detrimental effect on the photovoltaic junction. With the addition of a 75nm PS antireflection layer, devices achieved a photovoltaic conversion efficiency of up to 7.8% under standard AM 1.5G conditions.

Bio-inspired Hierarchical Nanowebs for Green Catalysis.

Bio-inspired 3D hierarchical nanowebs are fabricated using silicon micropillars, carbon nanotubes (CNT), and manganese oxide. The Si pillars act as artificial branches for growing CNTs and the secondary metal coating strengthens the structures. The simple but effective structure provides both chemical and mechanical stability to be used as a green catalyst for recycling waste polymers into raw materials.

Steering the efficiency of carbon nanotube-silicon photovoltaic cells by acid vapor exposure: a real-time spectroscopic tracking.

Hybrid carbon nanotube-silicon (CNT-Si) junctions have been investigated by angle resolved photoemission spectroscopy (AR-XPS) with the aim to clarify the effects of a nonstoichiometric silicon oxide buried interface on the overall cell efficiency. A complex silicon oxide interface has been clearly identified and its origin and role in the heterojunction have been probed by exposing the cells to hydrofluoric (HF) and nitric (HNO3) acid. Real-time monitoring of the cell efficiencies during the steps following acid exposure (up to 1 week after etching) revealed a correlation between the thickness and chemical state of the oxide layer and the cell efficiencies. By matching the AR-XPS and Raman spectroscopy with the electrical response data it has been possible to discriminate the effects on the cell efficiency of the buried SiO(x) interface from those related to CNT acid doping. The overall cell behavior recorded for different thicknesses of the SiO(x) interface indicates that the buried oxide layer is likely acting as a passivating/inversion layer in a metal-insulator-semiconductor junction.

Sensory properties of hybrid composites based on poly(3,4-ethylenedioxythiophene)-porous silicon-carbon nanotubes.

In this work, we have prepared film sensor elements based on a hybrid system poly(3,4-ethylenedioxythiophene)-porous silicon nanocrystals-carbon nanotubes on flexible polymer substrates. Our FTIR spectroscopy-based studies for the molecular structure of the materials obtained suggest some interaction of their components in the hybrid layer. The influence of adsorption of water molecules on the conductivity and capacitance of the hybrid composites has been investigated in the temperature range of 20°C to 40°C. We have detected essential changes in the electrical conductivity and capacitance which depend on the humidity of the surrounding atmosphere. For estimating the sensing properties of our composites, we have analyzed the sensing abilities of the hybrid systems and their dynamic characteristics. The hybrid composites as working materials for the sensors provide improved performance of the latter. In particular, the response time is reduced by 3 to 5 times.PACS73.63.-b, 73.61.Ph, 82.35.Np, 81.05.Rm