Silicon Nanocones Research Articles

Stable field emission ofion-sputtering-induced Si nanocone arrays

Silicon nanocone arrays with metal silicide (Fe and Cr)-enriched apexes are fabricated on Si (100) substrate by the Ar+ ion bombardment method. The nanocone arrays show excellent field emission properties. A high current density (J) of ~0.33 mA/cm2 under a field of ~3 V/\mu m, a very low turn-on field of ~1.4 V/\mu m, and a very large enhancement factor of ~9466 are also obtained. The emission J of Si nanocone arrays remains extremely stable for long periods of time (24 h).

Biomimetic Antireflective Silicon Nanocones Array for Small Molecules Analysis

Biomimetic antireflective silicon nanocones array is used for analysis of small molecules by mass spectrometry. The role of the absorbed laser energy and its distribution in the laser desorption/ionization process has been investigated by varying the antireflective features precisely. By optimizing the antireflective silicon array, the absorbed laser energy can be channeled completely into the desorption/ionization of analytes. The optimized silicon array exhibits excellent performance to detect peptide, amino acid, drug molecule, and carbohydrate without any interference in the low-mass region.

Solar energy trapping with modulated silicon nanowire photonic crystals

We demonstrate the efficacy of nanostructured thin film silicon solar cells to trap and absorb approximately 75% of all sunlight incident (400 nm–1200 nm) with an equivalent bulk thickness of only 1 micron of silicon. This is achieved by sculpting the collection zone into a three-dimensional, simple-cubic-symmetry, photonic crystal consisting of modulated silicon nanowires embedded in SiO2 and sitting on a quartz substrate with no metallic mirrors. A specific modulation of the radius of nanowires provides antireflection, strong light trapping, and back-reflection mechanisms in targeted spectral regions. This modulation is linear at the top of the nano-rods leading to nanocones at the solar cell to air boundary. These silicon nanocones are very good absorbers at short wavelengths and act as broadband coupler to a light-trapping region below at longer wavelengths. In the light trapping region the modulation is periodic to form a simple cubic photonic crystal exhibiting a broad spectrum of strong parallel interface refraction resonances. Here, light incident from most angles is deflected into slow group velocity modes with energy flow nearly parallel to the interface, long dwell times, and strong light intensity enhancement (up to 150 times the incident intensity) in specific regions. Finally, a stronger and chirped modulation of the nanowire underneath provides back-reflection by means of a one-dimensional depth-dependent photonic stop-gap. The possibility of absorbing light at energies below the electronic band gap of silicon is illustrated using a graded index SixGe1−x alloy in the bottom section of each nanowire. Each nanowire is amenable to a radial P-N junction for proximal charge carrier separation and efficient collection of photo-generated current.

Robust adhesion of flower-like few-layer graphene nanoclusters

Nanostructured surface possessing ultrahigh adhesion like “gecko foot” or “rose petal” can offer more opportunities for bionic application. We grow flower-like few-layer graphene on silicon nanocone arrays to form graphene nanoclusters, showing robust adhesion. Their contact angle (CA) is 164° with a hysteresis CA of 155° and adhesive force for a 5 μL water droplet is about 254 μN that is far larger than present reported results. We bring experimental evidences that this great adhesion depends on large-area plentiful edges of graphene nanosheets tuned by conical nanostructure and intrinsic wetting features of graphene. Such new hierarchical few-layer graphene nanostructure provides a feasible strategy to understand the ultra-adhesive mechanism of the “gecko effect” or “rose effect” and enhance the wettability of graphene for many practical applications.

Lithography-free sub-100 nm nanocone array antireflection layer for low-cost silicon solar cell

A high-density and -uniformity sub-100 nm surface-oxidized silicon nanocone forest structure is created and integrated onto the existing texturization microstructures on a photovoltaic device surface by a one-step high-throughput plasma-enhanced texturization method. We suppressed the broadband optical reflection on chemically textured grade-B silicon solar cells for up to 70.25% through this nanomanufacturing method. The performance of the solar cell is improved with the short-circuit current increased by 7.1%, fill factor increased by 7.0%, and conversion efficiency increased by 14.66%. Our method demonstrates the potential to improve the photovoltaic device performance with low-cost and high-throughput nanomanufacturing technology.

Enhanced absorption in silicon nanocone arrays for photovoltaics

Silicon nanowire arrays have been shown to demonstrate light trapping properties and promising potential for next-generation photovoltaics. In this paper, we performed systematic and detailed simulation studies on the optical properties of silicon nanocone arrays as compared to nanowires arrays. Nanocone arrays were found to have significantly improved solar absorption and efficiencies over nanowire arrays. Detailed simulations revealed that nanocones have superior absorption due to reduced reflection from their smaller tip and reduced transmission from their larger base. The enhanced efficiencies of silicon nanocone arrays were found to be insensitive to tip diameter, which should facilitate their fabrication. Breaking the vertical mirror symmetry of nanowires results in a broader absorption spectrum such that overall efficiencies are enhanced. We also evaluated the electric field intensity, carrier generation and angle-dependent optical properties of nanocones and nanowires to offer further physical insight into their light trapping properties.

Effect of incident angles on the morphology of silicon nanocone array induced by Ar+ sputtering at room temperature

The effect of incident angles on the morphology of silicon nanocone array induced by Ar + sputtering at room temperature has been investigated. The investigation of scanning electron microscopy indicates that with the increment of incident angle from 30°, 45°, 60° to 75°, the density of silicon nanocone increases from 1-2 × 10 8 cm -2 , 1-2 × 10 8 cm -2 , 6-7 × 10 8 cm -2 to 1-2 × 10 9 cm -2 , the apex angle of cone decreased from 70°, 55°, 36° to 27° and the aspect ratio of silicon nanocone decrease from 320/410 nm, 340/330 nm, 570/370 nm to 200/120 nm.

Floral-clustered few-layer graphene nanosheet array as high performance field emitter

Graphene sheet is expected to be a highly efficient field emitter due to its unique electrical properties and open surface with sharp edges. However, it is still a tremendous technical challenge to grow and align a graphene sheet in one particular direction to protrude its sharp edges for good field emission. Here, we report an ideal graphene field emitter of flower-like graphene nanosheets grown on a silicon nanocone array, wherein nanocone array guides the alignment of vertical nanosheets and produces high-density sharp edge protrusions on the conical tip. We observe high performance and stable field emission with low turn-on fields from floral-clustered graphene nanosheets. Protrusive sharp edges on the nanocone tip and optimized spacing between clusters both appear to locally enhance the electric field and dramatically increase field emission. Our new graphene emitter design provides a robust approach to the prospect for development of practical electron sources and advanced devices based on graphene field emitters.

Ordered silicon nanocones arrays for label-free DNA quantitative analysis by surface-enhanced Raman spectroscopy

Ordered vertical silicon nanocones arrays coated with silver nanoparticles (AgNPs@SiNCs) are developed as surface-enhanced Raman scattering (SERS)-active substrate, which features good uniformity and reliable reproducibility of SERS signals. Label-free DNA at low concentrations (10−8 M) could be quantitatively analyzed via SERS using the AgNPs@SiNCs. The Raman peak at 732 cm−1 due to adenine breathing mode was selected as an endogenous Raman marker for quantitative detection of label-free DNA. The AgNPs@SiNCs as high-performance SERS-active substrates are attractive for surface enhancement mechanism investigation and biochemical sensing applications.

Surface plasmon enhanced broadband spectrophotometry on black silver substrates

We demonstrate surface plasmon-induced enhancements in optical imaging and spectroscopy on silver coated silicon nanocones which we call black silver. The black silver with dense and homogeneous nanocone forest structure is fabricated with a mass-producible nanomanufacturing method. It can efficiently trap and convert incident photons into localized plasmons in broad wavelength range, permitting the enhancement in optical absorption from ultraviolet to near infrared range by 12 times, the visible fluorescence enhancement of ∼30 times and the Raman scattering enhancement factor up to ∼108. We show the potential of the black silver in high sensitivity and broadband optical sensing of molecules.

Metallic nanocone array photonic substrate for high-uniformity surface deposition andoptical detection of small molecules

Molecular probe arrays printed on solid surfaces such as DNA, peptide, and proteinmicroarrays are widely used in chemical and biomedical applications especially genomicand proteomic studies (Pollack et al 1999 Nat. Genet. 23 41–6, Houseman et al 2002Nat. Biotechnol. 20 270–4, Sauer et al 2005 Nat. Rev. Genet. 6 465–76) as well as surfaceimaging and spectroscopy (Mori et al 2008 Anal. Biochem. 375 223–31, Liu et al 2006Nat. Nanotechnol. 1 47–52, Liu 2010 IEEE J. Sel. Top. Quantum Electron. 16 662–71).Unfortunately the printed molecular spots on solid surfaces often suffer low distributionuniformity due to the lingering ‘coffee stain’ (Deegan et al 1997 Nature 389 827–9) problemof molecular accumulations and blotches, especially around the edge of deposition spotscaused by solvent evaporation and convection processes. Here we present, without anysurface chemistry modification, a unique solid surface of high-aspect-ratio silver-coatedsilicon nanocone arrays that allows highly uniform molecular deposition and thussubsequent uniform optical imaging and spectroscopic molecular detection. Bothfluorescent Rhodamine dye molecules and unlabeled oligopeptides are printedon the metallic nanocone photonic substrate surface as circular spot arrays. Incomparison with the printed results on ordinary glass slides and silver-coatedglass slides, not only high printing density but uniform molecular distributionin every deposited spot is achieved. The high-uniformity and repeatability ofmolecular depositions on the ‘coffee stain’-free nanocone surface is confirmedby laser scanning fluorescence imaging and surface enhanced Raman imagingexperiments. The physical mechanism for the uniform molecular deposition is attributedto the superhydrophobicity and localized pinned liquid–solid–air interface onthe silver-coated silicon nanocone surface. The unique surface properties of thepresented nanocone surface enabled high-density, high-uniformity probe spottingbeneficial for genomic and proteomic microarrays and surface molecular imaging.

Plasma-made silicon nanograss and related nanostructures

Plasma-made nanostructures show outstanding potential for applications in nanotechnology. This paper provides a concise overview on the progress of plasma-based synthesis and applications of silicon nanograss and related nanostructures. The materials described here include black silicon, Si nanotips produced using a self-masking technique as well as self-organized silicon nanocones and nanograss. The distinctive features of the Si nanograss, two-tier hierarchical and tilted nanograss structures are discussed. Specific applications based on the unique features of the silicon nanograss are also presented.

Periodic silicon nanocone arrays with controllable dimensions prepared by two-step etching using nanosphere lithography and [formula omitted] solution

An electroless chemical etching technique using polystyrene nanospheres as a self-assembled mask is developed to fabricate size-controllable, periodic silicon nanopillars (NPs) and subsequent nanocone (NC) arrays. The Si NCs are obtained based on the NPs structure using cost-effective ammonia-related etching chemistry. The diameter, height, and periodicity of the NCs can be systematically controlled. Optical measurement shows a good improvement in the reduction of reflectance properties with Si NCs structures. This method is potentially beneficial to many device applications including super-capacitors, batteries, solar cells, etc.

Influence of ambient gas on the growth kinetics of Si nanocones

Multi-segment silicon nanocones were designed and fabricated to investigate their growth kinetics. We found the ambient gas influenced the growth rates of Si nanocones remarkably. The axial growth rate increased with the total pressure of ambient gas, finally approaching saturation. Meanwhile the radial growth rate also increased with the total pressure but decreased with hydrogen content. A model was developed to study the growth kinetics by combining the effects of Langmuir adsorption, silane decomposition, and hydrogen coverage on the surface of SiNCs, which agreed with the experimental results. This paper also demonstrated the controllable cone angles by the ambient gas.

Synthesis of Pt Nanopetals on Highly Ordered Silicon Nanocones for Enhanced Methanol Electrooxidation Activity

Platinum (Pt) nanopetals were electrodeposited on highly ordered silicon nanocones (SiNCs) and explored as the electrocatalyst for methanol oxidation reaction (MOR) for direct methanol fuel cells applications. Highly ordered SiNCs array fabricated using the porous anodic aluminum oxide as the template had a high surface area. Well-dispersed Pt nanopetals possessing high electrocatalytic surface area was synthesized by pulse-electrodeposition on the SiNCs. Pt nanopetals loaded on highly ordered SiNC support exhibited very good catalytic activity for MOR and a high tolerance against CO poisoning, as compared to Pt nanoflowers/flat Si, Pt nanoparticles/flat Si, and many previously reported works. The abundance of a large surface area for facile transport of methanol, SiO(2) sites in the vicinity of the SiNCs, as well as less contact area between the Pt nanopetals catalyst and SiNCs are suggested to be the major factors enhancing the electrocatalytic performance of the Pt nanopetal/SiNC electrode. Moreover, we believe this new nanostructure (Pt nanopetals/SiNCs) will enable many new advances in nanotechnology.

Biomimetic corrugated silicon nanocone arrays for self-cleaning antireflection coatings

Corrugated silicon nanocone (SiNC) arrays have been fabricated on a silicon wafer by two polystyrene-sphere- monolayer-masked etching steps in order to create high-performance antireflective coatings. The reflectance was reduced from above 35% to less than 0.7% in the range 400-1050 nm, and it remained below 0.5% at incidence angles up to 70° at 632.8 nm for both s- and p-polarized light. The fluorinated corrugated SiNC array surface exhibits superhydrophobic properties with a water contact angle of 164° .

Cones fabricated by 3D nanoimprint lithography for highly sensitive surface enhancedRaman spectroscopy

We demonstrated a cost-effective and deterministic method of patterning 3D cone arraysover a large area by using nanoimprint lithography (NIL). Cones with tip radius ofless than 10 nm were successfully duplicated onto the UV-curable imprint resistmaterials from the silicon cone templates. Such cone structures were shown to bea versatile platform for developing reliable, highly sensitive surface enhancedRaman spectroscopy (SERS) substrates. In contrast to the silicon nanocones,the SERS substrates based on the Au coated cones made by the NIL offeredsignificant improvement of the SERS signal. A further improvement of the SERSsignal was observed when the polymer cones were imprinted onto a reflectivemetallic mirror surface. A sub-zeptomole detection sensitivity for a model molecule,trans-1,2-bis(4-pyridyl)-ethylene (BPE), on the Au coated NIL cone surfaces was achieved.

Aluminum-enhanced sharpening of silicon nanocones

Here we report on the fabrication of high-density aligned Si nanotip arrays by chemical vapor deposition followed by dry oxidation and an etching treatment. The dry oxidation investigations indicated that Al-catalyst particles located at the tip of Si nanocones enhance their sharpening. This oxidation behavior is quite different from that of Au-catalyzed Si nanowires and is more favorable to form very sharp Si nanotips. Field emission from an individual Si nanotip showed good field-emission characteristic with a high emission current density of 1×104 A/cm2 because of its sharp tip geography, suggesting their potential application for field emitters. Our work provides an effective approach to fabricate high-density Si nanotip arrays, which overcomes some problems in the conventional fabrication approaches, such as high cost, poor controllability, and complicated process.

Interference lithographically defined and catalytically etched, large-area silicon nanoconesfrom nanowires

We report a simple and cost effective method for the synthesis of large-area, preciselylocated silicon nanocones from nanowires. The nanowires were obtained fromour interference lithography and catalytic etching (IL-CE) method. We foundthat porous silicon was formed near the Au catalyst during the fabrication ofthe nanowires. The porous silicon exhibited enhanced oxidation ability whenexposed to atmospheric conditions or in wet oxidation ambient. Very well locatednanocones with uniform sharpness resulted when these oxidized nanowires wereetched in 10% HF. Nanocones of different heights were obtained by varying thedoping concentration of the silicon wafers. We believe this is a novel method ofproducing large-area, low cost, well defined nanocones from nanowires both interms of the control of location and shape of the nanocones. A wide range ofpotential applications of the nanocone array can be found as a master copy fornanoimprinted polymer substrates for possible biomedical research; as a candidate formaking sharp probes for scanning probe nanolithography; or as a building block forfield emitting tips or photodetectors in electronic/optoelectronic applications.

Silicon Nitride Nanopillars and Nanocones Formed by Nickel Nanoclusters and Inductively Coupled Plasma Etching for Solar Cell Application

The external quantum efficiency of solar cells can be improved by using textured surface with minimum reflection. We have fabricated nanopillars and nanocone structures on silicon nitride surface by means of self-assembled nickel nano particle masks with single step inductively coupled plasma (ICP) ion etching and double step ICP etching, respectively. Thus, sub-wavelength nanopillar and nanocone-like structures displaying low reflectance were obtained readily without the need for any lithography equipment. The formation mechanism of nanopillar and nanocone like structures fabricated on silicon nitride surface has been discussed. The relationship of etching time with structure height and average reflectance spectra has been drawn.