Silicon Nanowire Arrays Research Articles

Ultra-thin broadband solar absorber based on stadium-shaped silicon nanowire arrays

This paper investigates how the dimensions and arrangements of stadium silicon nanowires (NWs) affect their absorption properties. Compared to other NWs, the structure proposed here has a simple geometry, while its absorption rate is comparable to that of very complex structures. It is shown that changing the cross-section of NW from circular (or rectangular) to a stadium shape leads to change in the position and the number of absorption modes of the NW. In a special case, these modes result in the maximum absorption inside NWs. Another method used in this paper to attain broadband absorption is utilization of multiple NWs which have different geometries. However, the maximum enhancement is achieved using non-close packed NW. These structures can support more cavity modes, while NW scattering leads to broadening of the absorption spectra. All the structures are optimized using particle swarm optimizations. Using these optimized structures, it is viable to enhance the absorption by solar cells without introducing more absorbent materials.Graphical

Label-Free C-Reactive Protein Si Nanowire FET Sensor Arrays With Super-Nernstian Back-Gate Operation

We present a CMOS-compatible double gate and label-free C-reactive protein (CRP) sensor, based on silicon on insulator (SOI) silicon nanowires arrays. We exploit a reference subtracted detection method and a super-Nernstian internal amplification given by the double gate structure. We overcome the Debye screening of charged CRP proteins in solutions using antibodies fragments as capturing probes, reducing the overall thickness of the capture layer. We demonstrate the internal amplification through the pH response of the sensor, in static and real-time working modes. While operated in back-gate configuration, the sensor shows excellent stability (< 20 pA/min in the worst case), low hysteresis (< 300 mV), and a great sensitivity up to 1.2 nA/dec toward CRP proteins in the linear response range. The reported system is an excellent candidate for the continuous monitoring of inflammation biomarkers in serum or interstitial fluid.

Which method is more efficient on enhancing light absorption for silicon nanowires array based solar cells: Plasmonic metal nanoparticles or narrow-bandgap semiconductor quantum dots?

Being the unique physical structure and excellent optoelectronic properties, silicon nanowires (Si-NWs) array is considered to be a key nanostructure to build low-cost and high-efficiency solar cells, showing excellent performance of photons capturing and anti-reflection. In this work, the light absorption enhancement of Si-NWs array based solar cells by filling plasmonic metal nanoparticles (NPs), such as Au, Ag and Al, and/or PbS quantum dots (QDs) in the gaps of Si-NWs or depositing on the tips of Si-NWs, are simulated by using finite-difference time-domain (FDTD) software, respectively. Based on the proposed geometry of periodic Si-NWs array, our simulation demonstrates that the light absorption in the long-wavelength region can be greatly enhanced by filling suitable metal NPs or PbS QDs to form a certain thickness layer or depositing metal NPs on the tips of Si-NWs, by making good use of the localized surface plasmons and scattering generated around metal NPs, or the high absorption of PbS QDs in near-infrared region. Also, our simulation is in agreement with experimental data reported in literatures. Therefore, our work provides a valuable theoretical basis for designing high-performance Si-NWs array based solar cells.

In Situ Monitoring of Dynamic Photocatalysis of Metal-Organic Frameworks by Three-Dimensional Shell-Isolated Nanoparticle-Enhanced Raman Spectroscopy.

Metal-organic frameworks (MOFs) are promising as novel disinfectants due to the reactive oxygen species (ROS) produced in their photocatalytic processes. The optimal MOF is screened as the best disinfectant, representing high-efficacy production of ROS under photocatalytic conditions. However, current methods to screen abundant MOFs for disinfectant application are generally semiquantitative or ex situ methods [such as electron paramagnetic resonance (EPR) measurements], so achieving a strategy that can quantitatively screen an optimal MOF in situ and is reliable is demanded. Herein, we developed a three-dimensional (3D) shell-isolated nanoparticle-enhanced Raman spectroscopy (SHINERS) platform to study the dynamic photocatalytic processes of various MOFs (e.g., ZIF-67, ZIF-8, and UIO-66) in situ. This platform comprises silica shell-isolated gold nanoparticles (AuNPs) modified on silicon nanowire arrays (SiNWArs). The MOF is then self-assembled on the 3D-SHINERS substrate. Using this platform, we recorded dynamic spectroscopic evidence of ROS formation by various MOFs under sunlight irradiation. By dynamic comparison, ZIF-67 has the most robust photocatalytic efficiency, ∼1.7-fold stronger than that of ZIF-8 and ∼42.6-fold stronger than that of UIO-66. As expected, ZIF-67 displays the best antibacterial ability, up to 99% in the agar plate assay. This work provides a versatile platform for dynamically monitoring photocatalytic performance and screening antibacterial MOFs.

Recycling protein selective adsorption on fluorine-modified surface through fluorine-fluorine interaction

Low surface energy materials with micro-nano structures have been widely developed to prevent non-specific adhesion of biomolecules. Herein we put forward a new approach based on the antifouling and self-assembly properties of fluorine components, to construct a non-specific protein resistance surface with selective protein adsorption property. Briefly, the antifouling surface (SN-F) was obtained by a simple one-step modification on silicon nanowire arrays (SiNWAs) with fluorine coupling agent 1 H,1 H,2 H,2 H-perfluorodecyltrimethoxysilane (FAS). And protein was fluorinated by conjugation with an amphiphilic fluoro-copolymer, produced from 2-methacrylamido glucopyranose (MAG) and trifluoroethyl methacrylate (TFEMA) via RAFT polymerization. The properties of the materials were characterized by 1H nuclear magnetic resonance (1H NMR), infrared spectroscopy (FTIR), water contact angle, and X-ray photoelectron spectroscopy (XPS) etc., and protein adsorption was investigated by protein content measurement, fluorescence detection, and electrophoresis. It was observed that the adsorption for native proteins on SN-F was at an extremely low level, while the adsorption for the fluoro-copolymer conjugated protein (PFG-BSA) was significantly increased. When the percentage of TFEMA in the fluoro-copolymer was as high as 52.0%, the fluorinated protein adsorbed on SN-F was more than 35 times of native proteins on the surface. Moreover, the platform could resist IgG adhesion in serum after the adsorption of fluorinated protein, and it could be recycled three times after 75% ethanol treatment. In conclusion, SN-F showed non-specific protein resistance through low surface energy and specific protein adsorption by fluorine-fluorine self-assembly. The fluorinated nanostructured platform has a great potential in controlling protein adsorption and release.

Silicon nanowire arrays synthesized using the modified MACE process: Integration into chemical sensors and solar cells

In this work, the influence of the technological process for metal-assisted chemical etching on surface morphology and electrophysical properties of obtained nanostructures has been investigated. It has been demonstrated that the obtained structures with a high aspect ratio could be used both in sensors and solar cells. It has been shown that application of the metal-assisted chemical etching (MACE) process enables to significantly improve the short-circuit current density in silicon solar cells (up to 29 mA/cm2). Also, the possibility of detection of hydrogen peroxide and glucose (via enzymatic reaction) by resistor-like sensors with nanostructured silicon as the sensitive area has been demonstrated with the sensitivity up to 2.5…2.75 mA/V•%.

Effect of Surface Morphology Changes on Optical Properties of Silicon Nanowire Arrays.

The optical properties of silicon nanowire arrays (SiNWs) are closely related to surface morphology due to quantum effects and quantum confinement effects of the existing semiconductor nanocrystal. In order to explore the influence of the diameters and distribution density of nanowires on the light absorption in the visible to near infrared band, we report the highly efficient method of multiple replication of versatile homogeneous Au films from porous anodic aluminum oxide (AAO) membranes by ion sputtering as etching catalysts; the monocrystalline silicon is etched along the growth templates in a fixed proportion chemical solution to form homogeneous ordered arrays of different morphology and distributions on the surface. In this system, we demonstrate that the synthesized nanostructure arrays can be tuned to exhibit different optical characteristics in the test wavelength range by adjusting the structural parameters of AAO membranes.

Sensitive detection of SARS-CoV-2 spike protein using vertically-oriented silicon nanowire array-based biosensor

The COVID-19 pandemic has caused tremendous damage to the world. In order to quickly and accurately diagnose the virus and contain the spread, there is a need for rapid, sensitive, accurate, and cost-effective SARS-CoV-2 biosensors. In this paper, we report on a novel biosensor based on angiotensin converting enzyme 2 (ACE-2)-conjugated vertically-oriented silicon nanowire (vSiNW) arrays that can detect the SARS-CoV-2 spike protein with high sensitivity and selectivity relative to negative controls. First, we demonstrate the efficacy of using ACE-2 receptor to detect the SARS-CoV-2 spike protein via a capture assay test, which confirms high specificity of ACE-2 against the mock protein, and high affinity between the spike and ACE-2. We then report on results for ACE-2-conjugated vSiNW arrays where the biosensor device architecture is based on a p-n junction transducer. We confirm via analytical modeling that the transduction mechanism of the biosensor involves induced surface charge depletion of the vSiNWs due to negative electrostatic surface potential induced by the spike protein after binding with ACE-2. This vSiNW surface charge modulation is measured via current-voltage characteristics of the functionalized biosensor. Calibrated concentration dependent electrical response of the vSiNW sensor confirms the limit-of-detection for virus spike concentration of 100 ng/ml (or 575 pM). The vSiNW sensor also exhibits highly specific response to the spike protein with respect to negative controls, offering a promising point-of-care detection method for SARS-CoV-2.

Surface-Enhanced Raman Scattering from Dye Molecules in Silicon Nanowire Structures Decorated by Gold Nanoparticles.

Silicon nanowires (SiNWs) prepared by metal-assisted chemical etching of crystalline silicon wafers followed by deposition of plasmonic gold (Au) nanoparticles (NPs) were explored as templates for surface-enhanced Raman scattering (SERS) from probe molecules of Methylene blue and Rhodamine B. The filling factor by pores (porosity) of SiNW arrays was found to control the SERS efficiency, and the maximal enhancement was observed for the samples with porosity of 55%, which corresponded to dense arrays of SiNWs. The obtained results are discussed in terms of the electromagnetic enhancement of SERS related to the localized surface plasmon resonances in Au-NPs on SiNW’s surfaces accompanied with light scattering in the SiNW arrays. The observed SERS effect combined with the high stability of Au-NPs, scalability, and relatively simple preparation method are promising for the application of SiNW:Au-NP hybrid nanostructures as templates in molecular sensorics.

Optimization of light absorption in ultrathin elliptical silicon nanowire arrays for solar cell applications

The present study proposes an elliptical silicon array for broadband absorption inside ultra-thin silicon solar cells (SCs). The simulation results suggest that breaking the arrangement of the nanowires (NWs) modifies the absorption intensities. The efficient design of irregular NWs can contribute to improved absorption of such structures in comparison with ordinary structures. Single elliptical NWs exert significant optical antenna effects, which enable higher absorption of particular frequencies. However, in the case of NW arrays enhanced absorption is the outcome of trade off between an optical antenna and diffraction effects. In this study, a structure composed of a semi-periodic NW is suggested which can achieve improved performance in ultra-thin silicon SCs.

Early Stages of Aluminum-Doped Zinc Oxide Growth on Silicon Nanowires.

Aluminum-doped zinc oxide (AZO) is an electrically conductive and optically transparent material with many applications in optoelectronics and photovoltaics as well as in the new field of plasmonic metamaterials. Most of its applications contemplate the use of complex and nanosized materials as substrates onto which the AZO forms the coating layer. Its morphological characteristics, especially the conformality and crystallographic structure, are crucial because they affect its opto-electrical response. Nevertheless, it was difficult to find literature data on AZO layers deposited on non-planar structures. We studied the AZO growth on silicon-nanowires (SiNWs) to understand its morphological evolution when it is formed on quasi one-dimensional nanostructures. We deposited by sputtering different AZO thicknesses, leading from nanoclusters until complete incorporation of the SiNWs array was achieved. At the early stages, AZO formed crystalline nano-islands. These small clusters unexpectedly contained detectable Al, even in these preliminary phases, and showed a wurtzite crystallographic structure. At higher thickness, they coalesced by forming a conformal polycrystalline shell over the nanostructured substrate. As the deposition time increased, the AZO conformal deposition led to a polycrystalline matrix growing between the SiNWs, until the complete array incorporation and planarization. After the early stages, an interesting phenomenon took place leading to the formation of hook-curved SiNWs covered by AZO. These nanostructures are potentially very promising for optical, electro-optical and plasmonic applications.

VLS Synthesis of Silicon Nanowires Array for Photovoltaic Devices

VLS Synthesis of Silicon Nanowires Array for Photovoltaic Devices

Effect of Local Topography on Cell Division of Staphylococcus spp.

Surface engineering is a promising strategy to limit or prevent the formation of biofilms. The use of topographic cues to influence early stages of biofilm formationn has been explored, yet many fundamental questions remain unanswered. In this work, we develop a topological model supported by direct experimental evidence, which is able to explain the effect of local topography on the fate of bacterial micro-colonies of Staphylococcus spp. We demonstrate how topological memory at the single-cell level, characteristic of this genus of Gram-positive bacteria, can be exploited to influence the architecture of micro-colonies and the average number of surface anchoring points over nano-patterned surfaces, formed by vertically aligned silicon nanowire arrays that can be reliably produced on a commercial scale, providing an excellent platform to investigate the effect of topography on the early stages of Staphylococcus spp. colonisation. The surfaces are not intrinsically antimicrobial, yet they delivered a topography-based bacteriostatic effect and a significant disruption of the local morphology of micro-colonies at the surface. The insights from this work could open new avenues towards designed technologies for biofilm engineering and prevention, based on surface topography.

Localization of Dps protein in porous silicon nanowires matrix

Successful integration of the ferritin Dps protein of native origin with the developed surface of a silicon nanowires array has been demonstrated. The possibility of protein localization has been realized for different types of silicon nanostructures in terms of conductivity, different volumes of wires arrays pores available for this localization, and different wire array morphology. The observed results show the possibility of effective removal of buffer solution salts from the cultural medium, in which ferritin Dps remains on the 3D-developed porous surface of silicon nanowires. The findings demonstrate the effectiveness of a simple and affordable method to functionalize the engineered and technologically advanced silicon nanowire surface with a nanoscale ferritin Dps bioculture.

Facile Synthesis of Metal Oxide and Conductive Polymers around Silicon Nanowire Arrays for a High-Performance Aqueous Supercapacitor

Facile Synthesis of Metal Oxide and Conductive Polymers around Silicon Nanowire Arrays for a High-Performance Aqueous Supercapacitor

Rapid Formation of Uniform Cracks in Metal-Assisted Etched Silicon Nanowire Array Membranes: Implications for Transfer of Nanowires and Flexible Devices

Rapid Formation of Uniform Cracks in Metal-Assisted Etched Silicon Nanowire Array Membranes: Implications for Transfer of Nanowires and Flexible Devices

The role of quantum crystal radius on electron field emission properties of fractal silicon nanowire arrays

Here we report, the role of quantum crystal radius (QCR) on field emission (FE) properties of fractal silicon nanowire arrays (F-Si-NWAs) fabricated onto n-type Si(100) by metal electroless wet chemical etching (MEWCE). The energy band estimation from absorption spectra reveals the increment in optical band gap of F-Si-NWAs varies from 1.72 eV to 1.75 eV. Here, the band-gap dependent effective mass approximation (EMA) method are used to estimate the QCR present in F-Si-NWAs, which shows quantum confinement (QC) effect. The effect on FE properties have been studied using current–voltage (I-V) measurements followed by a theoretical analysis through the Fowler–Nordheim (F-N) equation as a function of the QCR. The FE studies show that the smaller QCR have low turn on voltage and high field enhancement factor due to QC effects.

2D-Heterostructure assisted activation of MoS2 basal plane for enhanced photoelectrochemical hydrogen evolution reaction

As a potential catalyst of hydrogen evolution reaction (HER), molybdenum disulfide (MoS2) is known to have active sites at the edges, whereas its basal plane is inert. Thus activation of basal plane of MoS2 is essential to intensify the HER catalytic activity. Among various strategies, activation of MoS2 basal plane includes defects engineering via sulfur vacancies and hetero-atom doping. However, for optimal activation, requirements of defect concentration become impractically high, which increases defect-induced high charge carrier recombination loss in photoelectrochemical (PEC) HER. Herein, we report basal plane activation of MoS2 by heterostructuring with two-dimensional (2D) MoSe2 for enhanced photoelectrochemical HER. MoS2/MoSe2 heterostructure grown on silicon nanowire (SiNW) array shows 1.2 times higher photocurrent density and 1.36 times higher incident photon-to-current efficiency (IPCE) than pristine MoS2 grown on SiNW array along with 4.44 times higher H2 evolution rate compared to pristine SiNW photocathode. Density functional theory calculations of heterostructure reveal that charge transfer from the MoSe2 layer to the basal plane of MoS2 increases overall electron density resulting in its increased affinity towards proton reduction, which supports the experimental findings. These findings will boost the strategy for basal plane activation by 2D heterostructuring for efficient photoelectrochemical HER.

Selective electrochemical deposition of indium in-between silicon nanowire arrays fabricated by metal-assisted chemical etching

Indium electrodeposition in-between silicon nanowire arrays fabricated by silver-assisted chemical etching of lightly-doped (100)-oriented silicon wafers is evaluated. It is concluded based on SEM and EDX analysis of indium's distribution that, by utilizing pulsed-mode electrodeposition and maintaining a sufficiently low duty cycle value, indium particles can be formed exclusively at the very bottom of each consecutive pore on the residual silver particles left over from metal-assisted etching. This result differs significantly from irregular pore filling along with surface and subsurface deposition observed in the cases of continuous galvanostatic deposition regimes at prolonged durations or in the absence of residual silver particles. Bottommost fusible metal deposit localization, which is unattainable on porous silicon fabricated by electrochemical anodization, is presumed to be optimal for the growth of germanium crystallites inside the pores via the electrochemical liquid-liquid-solid approach and subsequent silicon-germanium alloy formation through thermal annealing.

Wetting behavior of silicon nanowires array fabricated by Metal-assisted chemical etching

A silicon (Si) substrate exhibits a hydrophobic surface (contact angle, CA ∼ 90.2⁰), and upon anodization, the porous Si (PSi) also possesses a hydrophobic surface (CA ∼ 142.4⁰). Silicon nanowires (SiNWs) array, also known as black silicon, exhibits lotus effect, i.e., water droplet role-over the surface without penetrating inside the surface. An array of SiNWs, fabricated by metal-assisted chemical etching (MACE) of Si, act as a superhydrophobic surface (i.e., CA > 150⁰) without using any functionalization material. The MACE fabricates etched-Si, using PSi substrate that also possesses a superhydrophobic surface. Trapped air, present among the conical tips of the densely formed SiNWs array, reduces the solid–liquid contact area and improves the de-wetting behavior. The trapped air increases on increasing the length of SiNWs, which further enhances the de-wetting behavior. The wetting behavior changes to hydrophobic/hydrophilic when kept for a longer duration due to the aging effect. Oxidation causes aging and changes the conical/dendrite structure of the SiNWs/etched-Si surface. The Fourier transform infrared spectroscopy confirms the hydrogen passivation on the surfaces of SiNWs because of HF etching and highly oxidized surfaces due to the effect of aging.