Growth Of Silicon Nanowires Research Articles

Full Surface Embedding of Gold Clusters on Silicon Nanowires for Efficient Capture and Photothermal Therapy of Circulating Tumor Cells

We report on rapid thermal chemical vapor deposition growth of silicon nanowires (Si NWs) that contain a high density of gold nanoclusters (Au NCs) with a uniform coverage over the entire length of the nanowire sidewalls. The Au NC-coated Si NWs with an antibody-coated surface obtain the unique capability to capture breast cancer cells at twice the highest efficiency currently achievable (~88% at 40 min cell incubation time) from a nanostructured substrate. We also found that irradiation of breast cancer cells captured on Au NC-coated Si NWs with a near-infrared light resulted in a high mortality rate of these cancer cells, raising a fine prospect for simultaneous capture and plasmonic photothermal therapy for circulating tumor cells.

High Yield, Low Temperature and Low Pressure Growth of Silicon Nanowires (SiNW)

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Effect of Hydrogen Plasma Pretreatment on the Growth of Silicon Nanowires and Their Employment as the Anode Material of Lithium Secondary Batteries

Silicon nanowires were grown from a silane and argon gas mixture directly on a stainless steel substrate by radio-frequency plasma enhanced chemical vapor deposition (RF-PECVD) and used without any further treatment as the anode in the fabrication of lithium ion batteries. It was found that suitable pretreatment of the stainless steel substrate was required for the satisfactory growth of the silicon nanowires. In this study, the substrates were polished, etched in HF solution, coated with an aluminum catalyst layer with a thickness of c.a. 10 nm and then treated with a hydrogen plasma before the growth of the silicon nanowires. SEM (Scanning Electron Microscopy) and AFM (Atomic Force Microscopy) analyses showed that the grain size and surface roughness were increased after the hydrogen plasma pretreatment. The electrochemical performance of the silicon nanowires anode was also improved when the aluminum coated stainless steel substrate was exposed to the plasma for 20 min or longer; the initial coulombic efficiency was increased from 69.7% to 82% at a current density of 30 mA cm(-2).

A unique solid–solid transformation of silver nanoparticles on reactive ion-etching-processed silicon

Processes that combine nanoparticle suspensions with micromechanical or microelectronics platforms can reveal new phenomena unique to nanoscale objects. We report that silver nanoparticles react with silicon wafers that have been patterned by reactive ion etching (RIE) in SF6/O2 plasma. This reaction results in the localized deposition of silver on the patterns. Through the modification of the reaction conditions, the reaction mechanism was explored. Redeposition of the sputtered RIE products is suggested as the key to this transformation. The new silver deposition process was utilized to localize the growth of gold nanoparticles and silicon nanowires on the vertical sidewalls of patterns in silicon, demonstrating a simple route to the fabrication of overhanging nanoscale objects.

Recession and Characterization of Patterned Nanowires Grown by Electroless Etching of Silicon

Silicon nanowires (SiNWs) were grown by the electroless etching technique using silver nitrate (AgNO3)/hydrofluoric acid (HF) solution on a patterned p-type Silicon (Si) substrate with varying etching times and concentrations. The various etch times and concentrations produced different recession depths wherever the pattern allowed the etching solution to contact the Si substrate. At the bottom of each recession, SiNWs were produced of varying length and size, according to the depth of the recession. In this type of growth procedure, as SiNWs are grown, the tips are etched away. SiNWs grown by this method tend to agglomerate at their tips. We report that the recession and height of SiNWs grown by the electroless process can be controlled directly by the concentration of HF in the etching solution and by the etching time. Under precise conditions, the recession of SiNWs can be very nearly eliminated or nearly complete. The heights of SiNWs can also be fairly well controlled. We report that the growth of SiNWs is highly dependent on the ratio of volume of etching solution to the exposed surface area.

Modeling and Characterization of Silicon Nanowire Networks for Thermoelectric Conversion

ABSTRACTWe report the growth of silicon nanowires by plasma assisted metal organic chemical vapor deposition. Silicon nanowires grew as three-dimensional networks in which electrical charges and heat can travel over the distance much longer than the mean length of the constituent nanowires. We studied the dependence of thermoelectric properties on two factors; nominal doping concentrations and geometrical factors within the silicon nanowire networks. The silicon nanowire networks show Seebeck coefficients comparable with that of bulk silicon for a given nominal doping concentration, allowing us to control Seebeck coefficients by tuning the doping concentrations. Rather than studying single nanowires, we chose networks of nanowires formed densely across large areas required for large scale production. We also studied the role played by intersections where multiple nanowires were fused to form the nanowire networks. Structural analysis, transport measurement, and modeling based on finite-element analysis were carried out to obtain insights of physical properties at the intersections. Understanding these physical properties of three-dimensional nanowire networks will advance the development of thermoelectric devices.

Aluminum catalyzed growth of silicon nanowires: Al atom location and the influence of silicon precursor pressure on the morphology

We study the growth of silicon nanowires (SiNWs) by chemical vapor deposition (CVD) with aluminum as catalyst. We show that for a growth temperature of 600°C, the silicon precursor partial pressure (SiH4 in this study) is a key parameter for controlling the structural quality of the resulting SiNWs. We find by transmission electron microscopy that at high SiH4 partial pressure, the SiNWs are composed of a monocrystalline core with a high density of surface defects, mainly twins, sheathed by a rough amorphous silicon layer. By contrast, at low SiH4 partial pressure, the SiNWs are monocrystalline with a lower density of surface crystalline defects and a smooth surface. For the low SiH4 partial pressure SiNWs, Al atoms have been detected at the SiNW surface by Auger spectroscopy at level around 3at% and in the SiNW core by energy dispersive X-ray spectroscopy (EDS) at levels around 1at%. Interestingly, higher Al concentrations are measured inside the nano-twin domains by EDS (around ten times increase). Two possible explanations are proposed; stacking faults are induced by Al atoms that lower their energy formation, or Al atoms can be trapped inside these stacking faults due to segregation effect during growth. These findings will be important for growing high quality SiNWs using Al as metal catalyst in reduced-pressure CVD tool.

Carbon Nanotube‐Enhanced Growth of Silicon Nanowires as an Anode for High‐Performance Lithium‐Ion Batteries

Advanced lithium-ion batteries with high energy density, highrate capability, and excellent cycling performance are critically important for automotive and stationary energy storage applications such as electric vehicles, portable electronics, power tools, and energy storage for many types of renewable energy sources.[1–3] From the materials point of view, silicon is one of the most promising candidates as an anode material for these lithium-ion batteries owing to its abundance in nature, relatively low working potential, and highest known theoretical charge capacity of 4200 mAh g−1, 11 times higher than that of commercialized graphite.[4,5] One major challenge is that the dramatic volume change (>300%) for Si during lithium insertion and extraction processes causes capacity fading due to severe pulverization and electrical disconnection from the current collector, thus hindering practical applications.[5–8] In order to overcome these drawbacks, it is highly desirable to explore nanostructured silicon anodes with more robust architectures.[9–13] So far, silicon nanostructures (and their composites) with a variety of different dimensionalities, including nanoparticles,[14–18] nanospheres,[19] nanowires,[8,20–29] nanotubes,[30–32] nanoscale thin films,[7,33–35] and three-dimensional porous particles[36] have been reported to provide improved electrochemical performance over bulk silicon materials. These results are encouraging for the development of Si nanomaterials as potential building blocks for high-performance anode materials in lithium-ion batteries. Yet, scale-up and industrial implementation of these silicon nanostructures still lag behind and further improvements in overall performance, scalability, and cost are critically required. For example, silicon thin films exhibit highly improved cycling performance,[33,34] thanks to the anisotropy of their volume change. However, the optimized film thickness is usually a few hundred nanometers, which results in an areal capacity of ≈0.1 mAh cm−2, which is insufficient for application. Anodes made from one-dimensional silicon-based nanostructures can provide open space while remaining electrically connected to current collectors, allowing designs[8,12,13,30] which accommodate the volume change of silicon during lithium insertion. These nanostructures offer good contact with the current collectors at medium charge/discharge rate without

Effect of Etching Temperature on the Growth of Silicon Nanowires

The effects of different etching temperatures (near room temperature) on the length and surface morphology of SiNWs were reported in this paper. The studies on temperature dependence of SiNWs growth rate were carried out at 20 °C, 30 °C, 40 °C, 50 °C, 60 °C, and 70 °C for n-type and p-type substrates. The results suggested that the SiNWs length could be controlled easily by the change of the etching temperature. Superlong SiNWs were also fabricated by this technique. The superlong SiNWs had the length more than 400 μm and the aspect ratios were about 2000-20000, which could be applied in nanosensors and interconnection.

Preparation of silica nanowires using porous silicon as Si source

This very paper is focusing on the preparation of silica nano-wires via annealing porous silicon wafer at 1200°C in H2 atmosphere and without the assistant metal catalysts. X-ray diffraction, X-ray energy dispersion spectroscopy, scanning electron microscopy, high-resolution transmission electron microscopy and selected area diffraction technology have been employed for characterizing the structures, the morphology and the chemical components of the nano-wires prepared, respectively. It is found that the diameter and the length of the nano-wires were about 100nm and tens micron, respectively. Meanwhile, it is also necessary to be pointed out that silica NWs only formed in the cracks of porous wafers, where the stress induced both by the electro-chemical etching procedure for the porous silicon preparation and nanowires growth procedure is believed to be lower than that at the center of the island. Therefore, a stress-driven mechanism for the NWs growth model is proposed to explain these findings.

Highly Interconnected Si Nanowires for Improved Stability Li‐Ion Battery Anodes

AbstractSilicon exhibits the largest known capacity for Li insertion in anodes of Li‐ion batteries. However, because of large volume expansion/phase changes upon alloying, Si becomes powder‐like after a few charge‐discharge cycles. Various approaches have been explored in the past to circumvent this problem, including the use of nanomaterials, particularly Si nanowires. However, even though nanowires resist cracking very well, anodes based on Si nanowires still see their original capacity fade away upon cycling, because of wire detachment from the substrate, due to the stress generated at their roots upon alloying with Li. Here, we present a silicon nanowire growth strategy yielding highly interconnected specimens, which prevents them from being individually detached from the substrate. We report a ∼100% charge retention after 40 cycles at C/2 rate, without charging voltage limitation. We also show that our anodes can be cycled at 8C rates without damage and we grow nanowires with a density of 1.2 mg/cm2, yielding anodes delivering a 4.2 mAh/cm2 charge density. Finally, we point out that a better understanding of the interactions of silicon with electrolytes is needed if the field is to progress in the future.

Statistical model on the optical properties of silicon nanowire mats

Randomly grown silicon nanowire (SiNW) mats show a high light absorption even for long wavelengths despite the small volume of silicon. We present a statistical model that gives a physical understanding of the mechanisms of the absorption and scattering of light in such SiNW mats. According to this model the two main mechanisms of the effective absorption of light are (i) resonant optical antenna effects of the absorption within the individual SiNWs and (ii) the interaction of the light with several SiNWs in the mat due to strong light scattering. The results of this model are in good agreement with the experimental reflection, transmission, and absorption spectra taken with an integrating sphere.

Low-temperature growth of In-assisted silicon nanowires

Indium-assisted silicon nanowires have been grown by plasma enhanced chemical vapor deposition at temperatures down to 330 °C without plasma pre-treatment of the In films deposited on silicon substrates before the growth. Two families of wires have been observed: thin, tapered wires that show a metallic nanoparticle at their top, and thick, almost cylindrical wires that have no metallic nanoparticle at their final end. We suggest that the two types of NWs grow after different mechanisms. Moreover, we point out important growth features that are common with Au- and self-induced nanowires.

Growth of silicon nanowires by electron beam evaporation using indium catalyst

For the first time silicon nanowires have been grown on indium (In) coated Si (100) substrates using e-beam evaporation at a low substrate temperature of 300 °C. Standard spectroscopic and microscopic techniques have been employed for the structural, morphological and compositional properties of as grown Si nanowires. The as grown Si nanowires have randomly oriented with an average length of 600 nm for a deposition time of 15 min. As grown Si nanowires have shown indium nanoparticle (capped) on top of it confirming the Vapor Liquid Solid (VLS) growth mechanism. Transmission Electron Microscope (TEM) measurements have revealed pure and single crystalline nature of Si nanowires. The obtained results have indicated good progress towards finding alternative catalyst to gold for the synthesis of Si nanowires.

Multi-parametric growth of silicon nanowires in a single platform by laser-induced localizedheat sources

Nanoscale-synthesized materials hold great promise for the realization of futuregeneration devices. In order to fulfil this exceptional promise, new techniques must bedeveloped that will enable the precise layout and assembly of the heterogeneouscomponents into functional ‘superblocks’. Direct synthesis of nanostructures via alaser-assisted chemical vapor deposition process is one promising route. In this paper,laser-assisted silicon nanowire growth based on a vapor–liquid–solid (VLS) mechanism isstudied. Spatial confinement of the nanowire growth region via focused laser beamillumination provides a convenient way to examine multiple growth parameters(temperature, time, illumination direction, gas species composition, and pressure),thereby elucidating fundamental mechanisms of laser-assisted growth in a singlesample configuration. Furthermore, the work demonstrates an advanced method fordirect synthesis of nanostructures for the purpose of practical rapid patterning.

Gold catalysed growth of silicon nanowires and core–shell heterostructures via solid–liquid–solid process and galvanic displacement

Silicon nanowires (SiNWs) were first synthesised using Au coated p type Si (100) substrate via the solid–liquid–solid (SLS) process. The growth parameters were selectively varied to achieve various stages of growth for studying their effects on the morphology and microstructures of the nanowires (NWs). The SLS growth of SiNWs is discussed in the context of the experimental conditions used. Straight NWs of large aspect ratios, good crystallinity and morphology were generally obtained at a growth temperature of 1000°C along with some worm-like amorphous structures. Te–Si NW core–shell structures were subsequently obtained via post-growth galvanic displacement of the SiNWs in an acidic HF electrolyte containing ions. The core–shell structures obtained were decorated with Te nanoparticles. This increases the NW surface areas and should have great potential in non-reflecting, photovoltaic and thermoelectric applications. Growth study on the SiNWs and Te–Si core–shell structures is presented using various microscopy, diffraction and probe based techniques for structural, morphological and chemical characterisations.

Low Temperature Growth of Silicon Nanowires Supported by Cu-Based Catalyst Suitable for Microelectronic Applications

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Growth Time-Dependent Density and Surface Evolution of Silicon Nanowires in a Vapor–Liquid–Solid Process

Single crystalline silicon nanowires (SiNWs) were grown on Si(100) substrate using a gold (Au)-catalyzed vapor-liquid-solid (VLS) approach. The dependence of the growth time (i.e., the time of exposure to the Si source) on the density and surface evolution of the grown SiNWs is considered. It was observed that the density of grown SiNWs on Si substrate increased with increasing growth time. The highest density (approximately 1.1 x 10(6) mm(-2)) was reached at 4 hr. Upon further exposure to the Si source, we observed that the density was maintained for up to 9 hr. We suggest that the increased Si chemical potential in Au-Si droplets with increased growth time enhanced the SiNW growth rate at the interfaces between Au-Si droplets and SiNWs, and enhanced the transition of the NWs from the existing Au-Si droplets onto Si substrate. This allows the SiNW density to increase with increased growth time of up to 4 hr. Moreover, we examined the influence of the growth time on surface evolution including Au diffusion, facet and taper formation, and vapor-solid (VS) growth of the SiNWs. To explain the behavior of the grown SiNWs in the VLS process, we propose a combined model using the VLS and VS growth mechanisms.

Al catalyzed growth of silicon nanowires and subsequent in situ dry etching of the catalyst for photovoltaic application

AbstractAluminum‐catalyzed epitaxial growth of silicon nanowire (SiNW) arrays was performed on Si wafer by chemical vapor deposition at 600 °C. The arrays showed a low optical total reflectance in the visible light spectrum, with a minimum of 2% around 450 nm wavelength. Following SiNW growth, dry etching of the Al catalyst was performed in situ using HCl chemistry at 600 °C. The effectiveness of aluminum etching was assessed by energy dispersive X‐ray spectroscopy, by high resolution transmission electron microscopy and by a controlled growth experiment. This SiNW array growth and subsequent catalyst dry etching opens up the possibility of an all in vacuum fabrication process of radial junction solar cells.Al catalyst dry etching following growth using HCl gas at 600 °C.magnified imageAl catalyst dry etching following growth using HCl gas at 600 °C.

Gas phase equilibrium limitations on the vapor–liquid–solid growth of epitaxial silicon nanowires using SiCl4

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