Nanocone Arrays Research Articles

Antireflection and absorption properties of silicon parabolic-shaped nanocone arrays

Adding antireflection and light trapping structures to the solar cell can decrease the optical losses and increase the efficiency of the cell effectively, the nanocone antireflection structure was paid lots of attention because of its simple manufacture processes and low reflectance. In this work, the effect of the height and diameter of the periodic unit on the reflectance, transmittance and absorptance of the parabolic-shaped nanocone (PSNC) arrays was calculated using finite-difference time-domain method. It was found that the average reflectance decreased and the average absorptance increased with the increase of height in our calculation range. The average reflectance could be decreased to 0.13% by optimizing the diameter even when the height decreased to 1μm, thus the PSNC arrays had good antireflection character. The average absorptance could reach 81.16% by optimizing the diameter when the height increased to 7μm.

High-performance MgCo2O4 nanocone arrays grown on three-dimensional nickel foams: Preparation and application as binder-free electrode for pseudo-supercapacitor

Abstract Uniform MgCo 2 O 4 nanocone arrays (NCAs) grown radially on three-dimensional (3D) nickel foams were fabricated through a facile hydrothermal process. These MgCo 2 O 4 NCAs were characterized by X-ray diffractometry, X-ray photoelectron spectroscopy, N 2 adsorption Brunauer-Emmett-Teller method, scanning electron microscopy and transmission electron microscopy. The MgCo 2 O 4 NCAs were directly used as a binder-free integrated electrode for electrochemical pseudocapacitors. The electrode yielded a high specific capacitance of 750 F g −1 with high cycling ability at a charge-discharge current density of 1 A g −1 (84.0% of initial specific capacitance was remained after 1000cycles) and it was much higher compared with the powder MgCo 2 O 4 (320 F g −1 at 0.5 A g −1 ). Evidently, MgCo 2 O 4 NCAs achieved excellent electrochemical performance owing to the unique 3D nickel-foam-based in-situ self-assembly, which accelerated electron transport and diffusion as well as intimate electrode/electrolyte contact. The remarkable performance of the aqueous symmetric supercapacitor device without addition of binders or conductive additive is attributed to the close-knit combination of MgCo 2 O 4 nanocone with highly-conductive origin nickel foam, as well as the enlarged specific surface area (335.8 m 2 g -1 ). This study approves the future applications of the MgCo 2 O 4 NCAs inspired large-scale supercapacitor grown on low-cost nickel foams.

Experimental study of heat transfer characteristics of high-velocity small slot jet impingement boiling on nanoscale modification surfaces

Jet impingement boiling is one of the most efficient methods to increase the critical heat flux. Through controlling surface chemical properties and topography, plain nickel foil surface, three kinds of plain nickel-based chemical treatment surfaces and four kinds of nickel-based electrochemical treatment surfaces with nanocone array structure were used in the jet impingement boiling experiments to investigate the quantitative effects and the effect mechanism of the surface characteristic parameters, including nanoscale roughness (Ra): solid–liquid contact angle (CA) and effective heat transfer area ratio (r: the ratio of the actual heat transfer area to its projected area) on the heat transfer coefficient (HTC) and the critical heat flux (CHF). It is revealed that: similar to the heat transfer in pool boiling, changing nanoscale Ra has little effect on the heat transfer characteristics; decreasing solid–liquid CA can enhance the HTC while worsen the CHF obviously; increasing r can intensify both the HTC and the CHF. Predictive correlations of the HTC and the CHF of jet impingement boiling which include the effects of surface characteristics are presented. The predictive correlations presented can be widely used in various conditions with different working fluids and heating surfaces.

Lithography-free wide-angle antireflective self-cleaning silicon nanocones.

Low-cost, wideband, and wide-angle antireflective layers are of prime importance to photovoltaic and other optoelectronic applications. We report a novel fabrication methodology of random textured silicon nanocones (SiNCs) array through metal-assisted chemical etching combined with oxidation. The optical properties of the fabricated structure are studied theoretically and experimentally. The random textured SiNCs array showed very promising broadband antireflective properties through the entire visible wavelength range at different incident angles up to ±60°. In addition, the nanostructures inherently could become self-cleaning due to the high contact angle. This random cheap textured SiNCs array increases the absorption efficiency of photodetectors and reduces its cost.

Size correlation of optical and SERS properties for highly ordered Au nanocone arrays with sub-100 nm feature size

Using ultrathin anodic aluminum oxide membranes as evaporation masks, highly ordered Au nanocone arrays with sub-100 nm feature size were fabricated on glass substrates. The size of Au nanocones was adjusted by the easily controllable nanopores’ dimension. Influences of Au nanocone size on the optical property and SERS activity were characterized by extinction and Raman spectra, respectively. For one thing, the spectral position of plasmon resonances was seen to slightly blue-shift with increasing the nanocone size, which coincided well with the result of finite-difference-time-domain simulation. For another, glass substrates patterned by Au nanocone arrays exhibited a high surface enhanced Raman scattering sensitivity to Rhodamine 6G. Compared with the bulk sample, the estimated enhancement factor was boosted from 8 × 106 to 1.79 × 107 as the diameter of Au nanocone increased from 36 to 77 nm. Such highly ordered nanocone arrays with tunable and uniform size have great potential for various optical or spectrographic applications.

The Enhanced Light Absorptance and Device Application of Nanostructured Black Silicon Fabricated by Metal-assisted Chemical Etching.

We use metal-assisted chemical etching (MCE) method to fabricate nanostructured black silicon on the surface of C-Si. The Si-PIN photoelectronic detector based on this type of black silicon shows excellent device performance with a responsivity of 0.57 A/W at 1060 nm. Silicon nanocone arrays can be created using MCE treatment. These modified surfaces show higher light absorptance in the near-infrared range (800 to 2500 nm) compared to that of C-Si with polished surfaces, and the variations in the absorption spectra of the nanostructured black silicon with different etching processes are obtained. The maximum light absorptance increases significantly up to 95 % in the wavelength range of 400 to 2500 nm. Our recent novel results clearly indicate that nanostructured black silicon made by MCE has potential application in near-infrared photoelectronic detectors.

Controllable Protein Adsorption and Bacterial Adhesion on Polypyrrole Nanocone Arrays

In this research, polypyrrole nanocone arrays doped with β-Naphthalene sulphonic acid (PPy-NSA) were built. This film was expected to control protein adsorption and bacterial adhesion by potential-induced reversibly redox. The scanning Kelvin probe microscopy (SKPM) and surface contact angles (SCA) tests suggested that the surface potential and wettability of PPy-NSA nanocone arrays could be controlled by simply controlling its redox property via applying potential. The controllable surface potential and wettability in return controlled the adsorption of protein and adhesion of bacteria. The proposed material might find application in the preparation of smart biomaterial surfaces that can regulate proteins and bacterial adhesion by a simple potential switching.

Role of nanocone and nanohemisphere arrays in improving light trapping of thin film solar cells

A new crystalline silicon solar cell with Si nanocone arrays on the top and Al nanohemisphere arrays on bottom surface were proposed. The light-trapping ability were systematically studied by COMSOL Multiphysics. The nanocone arrays benefit light-trapping by introducing gradient change of refractive index and coupling the incoming light into optical modes. The metallic nanohemisphere arrays affect the light-harvesting by surface plasmon polaritons (SPPs) and scattering effect. The numerical simulations show that the optimal parameters for the periodic nanocone arrays are 350nm in diameter and 1.1 of the pitch/diameter ratio. The optimal parameters for the nanohemisphere arrays are 160nm in diameter, 1.3 of the pitch/diameter ratio respectively. Eliminating the Ohmic Loss in metallic nanohemisphere, a 700nm thick silicon solar cell with the combination of these two nanostructures will contribute an average absorption of 72.928% and a 33.311mA/cm2 short circuit photocurrent density in the wavelength of 310–1127nm.

GaN Nano-Cones Prepared by Jet-Printed Nanospheres Arrays

Site and dimension controllable nanocone arrays have been fabricated by a combination of inkjet-printing and nanosphere lithography. Each printed array is of well-formed circular geometry with diameters of about 20 μm. The nanocones with base diameters of 500 nanometers and sharp tips are formed due to etch isotropy. Photoluminescence has been carried out to study the optical properties of the Gallium Nitride nanostructures. The approach is demonstrated to be effective for the enhancement of light extraction, as well as for the formation of site-controlled nanocavities.

Metal impurity-assisted formation of nanocone arrays on Si by low energy ion-beam irradiation

Fabrication of nanocone arrays on Si surfaces was demonstrated using grazing incidence irradiation with 1keV Ar+ ions concurrently sputtering the surface and depositing metal impurity atoms on it. Among three materials compared as co-sputtering targets Si, Cu and stainless steel, only steel was found to assist the growth of dense arrays of nanocones at ion fluences between 1018 and 1019ions/cm2. The structural characterization of samples irradiated with these ion fluences using Scanning Electron Microscopy and Atomic Force Microscopy revealed that regions far away from co-sputtering targets are covered with nanoripples, and that nanocones popped-up out of the rippled surfaces when moving closer to co-sputtering targets, with their density gradually increasing and reaching saturation in the regions close to these targets. The characterization of the samples' chemical composition with Total Reflection X-ray Fluorescence Spectrometry and X-ray Photoelectron Spectroscopy revealed that the concentration of metal impurities originating from stainless steel (Fe, Cr and Ni) was relatively high in the regions with high density of nanocones (Fe reaching a few atomic percent) and much lower (factor of 10 or so) in the region of nanoripples. Total Reflection X-ray Fluorescence Spectrometry measurements showed that higher concentrations of these impurities are accumulated under the surface in both regions. X-ray Photoelectron Spectroscopy experiments showed no direct evidence of metal silicide formation occurring on one region only (nanocones or nanoripples) and thus showed that this process could not be the driver of nanocone array formation. Also, these measurements indicated enhancement in oxide formation on regions covered by nanocones. Overall, the results of this study suggest that the difference in concentration of metal impurities in the thin near-surface layer forming under ion irradiation might be responsible for the differences in surface structures.

Synthesis of copper nanocone array electrodes and its electrocatalytic properties toward hydrogen peroxide reduction

The copper nanocone (Cu-NC) array electrodes were successfully synthesized by metal sputtering on Al2O3/Al substrate with conical nanopores followed by electrodeposition of Cu. To fabricate the conical pores on aluminum substrate, repeated and alternating anodizations and pore widening treatments were performed. Each anodization step was conducted at 45V in a 0.3M oxalic acid solution at 9°C. After that, the holes were widened by immersion in a 5vol% phosphoric acid solution at 30°C. The effect of different number of alternating anodization-etching cycles on the shape, diameter and height of pores in anodic aluminum oxide (AAO) template was studied. After the electrochemical deposition of Cu, free standing Cu-NC arrays were obtained by chemical etching of Al2O3 templates in dilute phosphoric acid. The dimensions of copper nanocones correspond closely with used Al2O3 templates. The morphology and structural characterization of fabricated Al2O3 templates and Cu-NC arrays were performed. The electrocatalytic activity of the Cu-NC array electrodes toward hydrogen peroxide reduction was investigated.

High performance thin film solar cells on plastic substrates with nanostructure-enhanced flexibility

Plastic substrates possess conspicuous advantages for flexible thin film solar cell applications due to their superior flexibility and light weight characteristics. However, there are several challenges of using plastic substrates for high performance thin film solar cells since they usually have low melting/softening temperature and high coefficient of thermal expansion (CTE). In this work, we demonstrated a low cost process to achieve regular nanocone arrays on polyimide (PI) substrates which have unique photon management property and excellent mechanical flexibility. To leverage these benefits of the nanocone substrates, flexible amorphous Si solar cells were fabricated on the structures. Intriguingly, it was discovered that properly designed nanocones can significantly improve solar cell device performance via light management. And the fabrication yield of properly designed nanocone solar cells is much higher than that of planar devices. In addition, the nanocone plastic solar cells possess much improved bendability and robustness verified by both experiment and mechanical modeling, showing unique stress release mechanism originated from three-dimensional nanostructure design. This property is of practical significance for flexible electronics not limited to solar cells.

Facile fabrication of binder-free NiO electrodes with high rate capacity for lithium-ion batteries

NiO nanocone arrays are fabricated on nickel foam substrate by a simple hydrothermal synthesis and a subsequent annealing in air. The obtained architecture is directly used as an anode for lithium-ion batteries without any binder. It delivers a capacity of 969mAhg−1 in the 120th cycle at a current density of 0.5C. Even at 10C, the electrode can still deliver a capacity as high as 605.9mAhg−1. The excellent electrochemical performance could be ascribed to the integrity and porosity of the cycled electrodes.

Structural colour printing from a reusable generic nanosubstrate masked for the target image

Structural colour printing has advantages over traditional pigment-based colour printing. However, the high fabrication cost has hindered its applications in printing large-area images because each image requires patterning structural pixels in nanoscale resolution. In this work, we present a novel strategy to print structural colour images from a pixelated substrate which is called a nanosubstrate. The nanosubstrate is fabricated only once using nanofabrication tools and can be reused for printing a large quantity of structural colour images. It contains closely packed arrays of nanostructures from which red, green, blue and infrared structural pixels can be imprinted. To print a target colour image, the nanosubstrate is first covered with a mask layer to block all the structural pixels. The mask layer is subsequently patterned according to the target colour image to make apertures of controllable sizes on top of the wanted primary colour pixels. The masked nanosubstrate is then used as a stamp to imprint the colour image onto a separate substrate surface using nanoimprint lithography. Different visual colours are achieved by properly mixing the red, green and blue primary colours into appropriate ratios controlled by the aperture sizes on the patterned mask layer. Such a strategy significantly reduces the cost and complexity of printing a structural colour image from lengthy nanoscale patterning into high throughput micro-patterning and makes it possible to apply structural colour printing in personalized security features and data storage. In this paper, nanocone array grating pixels were used as the structural pixels and the nanosubstrate contains structures to imprint the nanocone arrays. Laser lithography was implemented to pattern the mask layer with submicron resolution. The optical properties of the nanocone array gratings are studied in detail. Multiple printed structural colour images with embedded covert information are demonstrated.

Fabrication of nanocone arrays by two step metal assisted chemical etching method

This work develops a novel method for preparing a moth eye structure, which has a sub-wavelength periodical Si nanocone structure on Si(100) substrate, using two-step metal assisted chemical etching (MACE). The 1st MACE and 2nd MACE were respectively performed with the intention to form perpendicular Si nanowire arrays on a Si substrate and sharpening the Si nanowire arrays. We found that the inhomogeneous absorption and aggregation of Au particles used as a catalyst for the 2nd MACE was important to obtain the nanocone shape. The obtained Si nanocone arrays showed superior anti-reflecting properties especially in a wavelength below 600nm compared with the Si nanowire arrays. A possible mechanism involved in the formation of the nanocone structure by the 2-step MACE is discussed in this paper.

Correction: Corrigendum: Three Dimensional Hybrids of Vertical Graphene-nanosheet Sandwiched by Ag-nanoparticles for Enhanced Surface Selectively Catalytic Reactions

Three dimensional (3D) plasmonic nanostructure is perfect for the surface-enhanced Raman scattering (SERS) and also very suitable for surface catalytic reaction, but how to design and fabricate is still a robust task. Here, we show a 3D plasmonic nanohybrid of vertical graphene-nanosheet sandwiched by Ag-nanoparticles on the silicon nanocone array substrate for enhanced surface catalytic reaction. By SERS detection, we find that this hierarchical nanohybrid structure is highly efficient in the enhancement of catalytic reaction, even at a very low concentration of 10−11 M, which is far better than previous reports by four orders of magnitude. A strong electric field enhancement produced in the 3D framework nanohybrids of graphene nanosheet/Ag-nanoparticles is responsible for this great enhancement of catalytic reaction, due to larger electron collective oscillation in the composite system. Especially the oxygen adsorbed on the graphene and Ag nanoparticles can be excited to triplet excited states, and the electrons on the graphene and the nanoparticles can be effectively transferred to the oxygen, which plays very important role in molecular catalytic reactions. Our results demonstrate the contribution of graphene in plasmon-driven catalytic reactions, revealing a co-driven reaction process.This excellent SERS substrate can be used for future plasmon and graphene co-catalytic surface catalytic reactions, graphene-based surface plasmon sensors and so on.

Enhanced charge separation of vertically aligned CdS/g-C3N4 heterojunction nanocone arrays and corresponding mechanisms

Vertical-aligned CdS/g-C3N4 heterojunction nanocone arrays have been fabricated on silicon(100) substrates by a plasma sputting reaction deposition and pulsed laser deposition, successively.

The morphologies and optical properties of three-dimensional GaN nano-cone arrays

Three-dimensional GaN nanostructures with well-aligned nano-cones were fabricated via laser interference lithography + inductively coupled plasma etching techniques.

Broadband bidirectional visible light absorber with wide angular tolerance

A wide-band bidirectional visible light absorber has been developed based on a quasi-periodic nanocone array coated with a dielectric-loaded Au monolayer.

Nanoscale patterning of biopolymers for functional biosurfaces and controlled drug release.

We compare the rates of drug release from nanopatterned and flat biodegradable polymer surfaces, and observe significantly lower release rates from the nanopatterned surfaces. Specifically, we nanopattern poly(l-lactic acid) (PLLA), a biodegradable polymer frequently used for fabricating drug-eluting coronary stents, through microtransfer molding and solvent casting and investigate the nanopattern's impact on the release of sirolimus, an immunosuppressant agent, coated on the PLLA surface using high performance liquid chromatography/mass spectrometry. We find that PLLA surfaces nanopatterned with 750 nm-pitch nanocup or nanocone arrays exhibit drug release rates significantly lower (25-30%) than that of the flat surface, which is counter-intuitive given the nanopattern-induced increase in their surface areas. Based on diffusion and meniscus curvature minimization analyses, we attribute the decreased drug release rate to the incomplete wetting of the nanopatterned surface. These results provide new insights on how the surface nanopatterning of biomaterials can functionalize the surface and tailor the release kinetics of therapeutic agents coated on it for controlled drug elution.