SiNW Arrays Research Articles

Optical characteristics of structures with silicon nanowires and metal nanoparticles

To calculate the optical parameters, the finite difference method in the time domain (FDTD) was used, which can be applied to solve Maxwell’s equations. A large number of combinations of a planar structure with metal nanoparticles and a structure with nanowires and metal nanoparticles (NPs) were calculated. The height of nanowires h varied from 50 to 3000 nm, the period of the structure P was 100–600 nm, and the diameter of metal nanoparticles d was 50–400 nm. The reduction of light reflection was determined by the anti-reflection effect of the Si-NWs array itself and the direct scattering effect of metal nanoparticles. It was shown that all structures gave significantly lower reflection coefficients compared to that of a solid silicon plate.

Label-free identification of DNA single-base mutation for clinical diagnostics based on plasmonic SiNW@AgNP arrays

Surface-enhanced Raman spectroscopy (SERS) has exhibited great potential in deoxyribonucleic acid (DNA) analysis. Rapid and label-free identification of single-base mutation in DNA is still limited by the sensitivity and reproducibility of SERS substrates. In this work, we develope plasmonic SiNW arrays decorated with Ag nanoparticles (SiNW@AgNP arrays) via hexadecyltrimethylammonium bromide (CTAB)-assisted galvanic reaction to address these challenges, which show excellent sensitivity and reproducibility. Under optimized experimental conditions, plasmonic SiNW@AgNP arrays enable detection of DNA bases of adenine (A), guanine (G), cytosine (C), and thymine (T) in solution at concentration down to pM-μM range, and multiple detection ability with mixture of DNA bases. More significantly, our study demonstrates the SiNW@AgNP arrays may serve as excellent SERS substrates in discriminating DNA single-base mutation between sickle cell anemia gene and normal hemoglobin gene in serum samples, which can be exploited in a wide range of plasmonic enhanced sensing applications for a fast, real-time, label-free and cost-effective clinical diagnosis.

Highly sensitive detection of sarin simulant by a functional SiNW array

Highly sensitive detection of sarin simulant by a functional SiNW array

Orthogonal‐Stacking Integration of Highly Conductive Silicide Nanowire Network as Flexible and Transparent Thin Films

AbstractFlexible and transparent conductive (FTC) thin films are indispensable elements in building high‐performance flexible or soft electronics and displays. Slim inorganic nanowires (NWs), with excellent conductivity and durability, are ideal one‐dimensional ingredients to weave a quasi‐continuous FTC network. However, a precise spatial arrangement of these ultrathin NWs, to form an optimal interconnected network, represents still a difficult challenge. In this work, a catalytic growth of orderly SiNW arrays, via an in‐plane solid‐liquid‐solid mechanism, and an orthogonal‐stacking integration of the SiNWs into a 2‐layer cross‐linked network, followed by a direct alloy formation and soldering of highly conductive SiNi alloy NWs upon a flexible polyimide polymer, is demonstrated. It is also shown that the flexibility of the SiNi FTC network can be significantly enhanced with an elastic spring design of the silicide NW channels, leading to an impressive transmittance of ≈90%, a moderately equivalent sheet resistance of 130 Ω sq−1 and a durable flexibility that can sustain repetitive bending to a 2 mm radius for >1000 cycles. These results highlight the unique capabilities of an optimal spatial arrangement, precise assembly/soldering and elastic geometry design of alloy NWs to enable a new generation of high‐performance FTC thin film material for future flexible electronics, displays, and bio‐interfaced sensors.

Helical Stacking Assembly of Orderly Silicon Nanowire Multilayers for Ultrastrong Dissymmetrical Amplification of Circularly Polarized Light

AbstractCircularly polarized organic light‐emitting diodes (CP‐OLEDs) are ideal candidates to explore novel applications such as 3D displays, optical storage, and quantum computing. However, the low dissymmetry (g) factor of most chiral organic materials remains as a major challenge for practical applications. In this work, a helical stacking assembly of orderly silicon nanowires (hs‐SiNWs) into a flexible multilayer 3D superstructure is demonstrated to accomplish a strong chiroptical activity. These orderly SiNWs are batch‐fabricated via a low temperature in‐plane solid–liquid–solid growth mechanism, with precisely‐controlled spatial arrangement and mean diameter and length of Dnw = 126 ± 24 nm and Lnw > 100 µm, respectively. To construct such helically‐stacked superstructure, the SiNW arrays are transferred and stacked upon transparent glass or flexible polymer substrates, with incremental rotational angle for each layer, which can strongly augment the circularly polarized electroluminescence (CPEL) from conventional CP‐OLEDs. Strikingly, the dissymmetry factor increases with more stacking layer up to g = ±0.17, which is more than 40 times of magnitude higher than that of the original CPEL, among the highest ones reported for CP‐OLEDs. These results indicate a promising helical‐stacking avenue to boost the chiroptical performance of various CP‐OLEDs for scalable and flexible chiroptical applications.

Structure and electrical behavior of silicon nanowires prepared by MACE process

We report on the structure and electrical characteristics of silicon nanowire arrays prepared by metal assisted chemical etching (MACE) method, investigated by cross-sectional scanning electron microscopy (SEM) and high resolution X-ray diffraction (HR-XRD) methods. SEM micrographs show arrays of merged parallel nanowires, with lengths of 700 nm and 1000 nm, resulted after 1.5 min and 5 min etching time, respectively. X-ray reciprocal space maps (RSMs) around Si (004) reciprocal lattice point indicate the presence of 0D structural defects rather than of extended defects. The photoluminescence spectra exhibit emission bands at 1.70 eV and 1.61 eV, with intensity significantly higher in the case of longer wires and associated with the more defected surface. The transient photoluminescence spectroscopy reveals average lifetime of 60 ôs and 111 ôs for the two SiNW arrays, which correlate with a larger density of defects states in the latest case. The I-V characteristics of the nanowires, show a memristive behavior with the applied voltage sweep rate in the range 5–0.32V/s. We attribute this behavior to trap states which control the carrier concentration, and model this effect using an equivalent circuit. Photogeneration processes under excitation wavelengths in visible domain, 405 nm - 650 nm, and under light intensity in the range 20–100 mW/cm2 provided a further insight into the trap states.

Photoelectrochemical Nitrate Reduction to Ammonia on Ordered Silicon Nanowire Array Photocathodes.

As a new path to "green" ammonia production, photoelectrochemical nitrate reduction reaction (PEC NO3 RR) is investigated for the first time. An Au-decorated ordered silicon nanowire (O_SiNW) array photocathode demonstrates 95.6 % of Faradaic efficiency (FE) to ammonia at 0.2 VRHE , which represents a more positive potential than the thermodynamic reduction potential of nitrate by utilizing photovoltage. The high FE is possible because both Si and Au surfaces are inactive for competing water reduction to hydrogen. The O_SiNW array structure is favorable to promote the PEC NO3 RR relative to planar Si or randomly-grown Si nanowire, by enabling the uniform distribution of small Au nanoparticles as an electrocatalyst and facilitating the mass transport during the reaction. The results demonstrate the feasibility of PEC nitrate conversion to ammonia and would motivate further studies and developments.

Photoelectrochemical Nitrate Reduction to Ammonia on Ordered Silicon Nanowire Array Photocathodes

AbstractAs a new path to “green” ammonia production, photoelectrochemical nitrate reduction reaction (PEC NO3RR) is investigated for the first time. An Au‐decorated ordered silicon nanowire (O_SiNW) array photocathode demonstrates 95.6 % of Faradaic efficiency (FE) to ammonia at 0.2 VRHE, which represents a more positive potential than the thermodynamic reduction potential of nitrate by utilizing photovoltage. The high FE is possible because both Si and Au surfaces are inactive for competing water reduction to hydrogen. The O_SiNW array structure is favorable to promote the PEC NO3RR relative to planar Si or randomly‐grown Si nanowire, by enabling the uniform distribution of small Au nanoparticles as an electrocatalyst and facilitating the mass transport during the reaction. The results demonstrate the feasibility of PEC nitrate conversion to ammonia and would motivate further studies and developments.

Helical SiNW design with a dual-peak response for broadband scattering in translucent solar cells

Design of helical SiNW with broad spectrum is applied to translucent SiNW array solar cells.

Recent Advances in Structuring and Patterning Silicon Nanowire Arrays for Engineering Light Absorption in Three Dimensions.

Vertically aligned silicon nanowire (VA-SiNW) arrays can significantly enhance light absorption and reduce light reflection for efficient light trapping. VA-SiNW arrays thus have the potential to improve solar cell design by providing reduced front-face reflection while allowing the fabrication of thin, flexible, and efficient silicon-based solar cells by lowering the required amount of silicon. Because their interaction with light is highly dependent on the array geometry, the ability to control the array morphology, functionality, and dimension offers many opportunities. Herein, after a short discussion about the remarkable optical properties of SiNW arrays, we report on our recent progress in using chemical and electrochemical methods to structure and pattern SiNW arrays in three dimensions, providing substrates with spatially controlled optical properties. Our approach is based on metal-assisted chemical etching (MACE) and three-dimensional electrochemical axial lithography (3DEAL), which are both affordable and large-scale wet-chemical methods that can provide a spatial resolution all the way down to the sub-5 nm range.

CO2 sensing behavior of vertically aligned Si Nanowire/ZnO structures

Metal oxide nanostructures are highly attractive for the fabrication of gas sensors due to their high surface‐to‐volume ratios. The design of novel structures has great importance to improve sensing behavior. Atomic layer deposited ZnO thin film on vertically aligned silicon nanowire (Si NW) arrays were used to understand the influence of etching time on CO2 sensing behavior of the SiNW/ZnO structure. The metal-assisted chemical etching method was used to realize SiNW arrays. The etching processes were performed for 5, 10, 30, and 60 min. The linear relationship between etching time and Si NW length was reported. 30 nm ZnO thin films were deposited on Si NWs by atomic layer deposition (ALD) method using diethyl Zinc and H2O as Zn and O2 sources, respectively. The CO2 sensing properties of the SiNW/ZnO structures were examined at ambient temperature and low CO2 concentration. The testing measurement results reveal that the sensor realized on un-etched Si does not exhibit any sensitivity. While the SiNW/ZnO was sensitive to CO2, the sensor sensitivity increase with the etching time due to the increase in the specific reactive surface. Moreover, the realized sensors have a relatively low response and recovery times, in the range of 2–7 s, by comparison to the reported ones in the literature.

Efficient Charge Separation Enabled by N-Doped Graphene Quantum Dots and PCDTBT for a High-Performance Silicon Nanowire Solar Cell

Light absorption by n-silicon nanowires (SiNWs) grown by a chemical etching method is augmented by tethering photoresponsive and highly luminescent nitrogen-doped graphene quantum dots (N-GQDs) and poly[N-9′-heptadecanyl-2,7-carbazole-alt-5,5-(4′,7′-di-2-thienyl-2′,1′,3′-benzothiadiazole)] (PCDTBT) to a SiNW array. The resultant N-GQDs@PCDTBT@SiNW photoanode affords a wide, continuous, and intense absorption band spanning from ∼350 to 1200 nm wavelength range, enabling maximum light uptake, with a work function of ∼4.74 eV, deep enough to not serve as a charge-trapping state. Under illumination, efficient charge separation in this ternary composite is ensured by the p-type semiconducting nature of N-GQDs with a shallow valence band (VB) that allows for rapid hole extraction from the VBs of SiNW and PCDTBT and their rapid relay to the bromide ions in the electrolyte. This is simultaneously accompanied by fast, excited electron injection from N-GQDs and PCDTBT to the SiNW via a cascade process, thus minimizing back electron transfer to the tribromide ions. When the N-GQDs@PCDTBT@SiNW photoanode is coupled with a highly electrocatalytic and electrically conductive multiwalled carbon nanotube (MWCNT)@C-fabric counter electrode and a bromine/bromide electrolyte, a power conversion efficiency of 13.18% is achieved for this liquid junction solar cell, which is significantly enhanced compared to that of the SiNW/HBr,Br2/C-fabric cell (4.37%). The roles of N-GQDs, PCDTBT, and MWCNTs are independently quantified to explain the observed solar cell performance.

Leveraging Preconcentration and Partial Separations with Silicon Nanowire Arrays to Improve the Detection of Low Volatility Trace Explosive Vapors

Trace detection of explosive vapors in real world environments is hindered by strict sensitivity and selectivity requirements that need to be met in order for these techniques to be effective. The physical properties of most explosive molecules limit environmentally relevant vapor concentrations to the part per billion (ppbv) – part per trillion (pptv) range due to their saturated vapor pressures under real world conditions. Additionally, trace explosive vapor detectors must be able to discriminate against a number of potential chemical and biological interferents present in complex real world environments. In this work, we present silicon nanowire arrays (SiNW) as a novel tunable material aimed at providing trace explosive vapor detectors with the sensitivity and selectivity necessary for operational use.Dense, highly ordered silicon nanowires are fabricated through a nanosphere lithography process and topped with a porous gold electrode resulting in a high surface area adsorptive substrate intrinsically capable of rapid, precise temperature control via Joule heating. Explosive vapors are selectively preconcentrated onto the SiNW array by exploiting their affinities for the surface (SiO2 or otherwise functionalized) of the nanowires. Chromatographic like partial separations of preconcentrated material on the array can be achieved through careful selection of desorption parameters. Using a multichannel detector, such as an IMS or MS, we demonstrate the preconcentration of a number of explosive vapors including 2,6-DNT, TNT, and RDX, while simultaneously exploring the effects of desorption flow rates and temperatures on the partial separation of 2,6-DNT, 2,4-DNT, TNT, and RDX vapors. In addition, we provide a strategy for chemometric deconvolution of array-based partial separations based upon evolving factor analysis and multivariate curve resolution by alternating least squares. This approach enabled qualitative and quantitative analysis of individual components without target analyte libraries or complete chromatographic separation.

Fabrication and characterization of silicon nanowires with MACE method to influence the optical properties

We are presenting here fabrication of silicon (Si) nanowires (NWs) arrays by using Si (100) wafer as substrate, by metal assisted chemical etching (MACE) method. The Si-NWs growth on the Si wafer has been done by using etching time of 45 min in etching solution of hydrogen fluoride and hydrogen peroxide. X-ray diffraction (XRD) has been used for the structural analysis of NWs to estimate the crystalline size, micro-strain, dislocation density of fabricated nanostructures. The surface morphology of Si-NWs array has been studied through field effect scanning electron microscopy (FE-SEM). The optical properties like energy band gap of fabricated Si-NWs has been carried out through UV–Vis diffuse reflectance spectroscopy (UV DRS) and photoluminescence (PL) spectroscopy.

Neuron‐Gated Silicon Nanowire Field Effect Transistors to Follow Single Spike Propagation within Neuronal Network

Silicon nanowire field effect transistors (SiNW‐FETs) provide a local probe for sensing neuronal activity at the subcellular scale, thanks to their nanometer size and ultrahigh sensitivity. The combination with micropatterning or microfluidic techniques to build model neurons networks above SiNW arrays could allow monitoring of spike propagation and tailor specific stimulations, being useful to investigate network communications at multiple scales, such as plasticity or computing processes. This versatile device could be useful in many research areas, including diagnosis, prosthesis, and health security. Herein, SiNW‐based arrays enable to record electrical signals from matured neurons, such as local field potential and unitary spike within ex vivo preparations and hippocampal neurons grown on chip respectively. Furthermore, the ability to guide neurites above the sensor array during 3 weeks of cultures is demonstrated and the propagation of spikes along cells is followed. The SiNW‐FETs are obtained by a top‐down approach with complementary metal oxide semiconductor (CMOS) technology, showing the possibility to implement them at the manufacturing level. These results confirm further the potentiality of the approach to follow spike propagation over large distances and at precise locations along neuronal cells, by providing a multiscale addressing at the nano and mesoscales.

Influence of nanostructure geometry on light trapping in solar cells

The aim of this research was to detect the influence of the silicon nanowires geometry and silver nanoparticles on the wafer surface on light trapping for application in solar cells with radial p–n junction. Si-NWs arrays were fabricated on p-type (100) silicon wafers with specific resistance of 10 Ω × cm. We used MacEtch method to form Si nanowires. In our study to deposit the additional silver nanoparticles on the surface of the nanowires, the flushing time was reduced to 10 min. The structural and optical properties of silicon nanowires were studied. The absorption, transmittance and reflectance spectra for periodic nanostructures with different parameters were calculated by FDTD (Finite-Difference Time-Domain) method. The FDTD method is a powerful numerical algorithm for direct solution of Maxwell’s equations. The realization of this method is discrete both in space and in time. The presented structures are described on a discrete mesh consisting of Yee cells and the Maxwell equations. They are solved discretely over time on this grid. As a result, through the method of the catalytic etching, we obtained nanowires of 0.5–2 μm in length and diameter in range of 50–100 nm. The diameter of silver nanoparticles was in the range of 20–50 nm. The reflection coefficient of light in wide spectral range was less than 1%. Reflection spectra peaked at the wavelength of 850 nm that points out on the influence of Ag nanoparticles.

Nanowire Array-based MOSFET for Future CMOS Technology to Attain the Ultimate Scaling Limit

Silicon nanowire (SiNW) structures are the essential foundations of the next generation highly efficient and lowcost electronic devices because of their specific chemical, optical, and electrical properties. In recent decades, the production of pure Si NW arrays with the ability to tune the wire density and dimensions has been intensively studied. This paper demonstrates the performance of silicon nanowire (Si NW) array based cylindrical gate all around (GAA) MOSFET using quantum transport model in lower technology nodes. With an improvement in drain current and lower value of threshold voltage, the proposed structure is proving itself as one of the leaders in GAA MOSFET family. Again the study includes the effect of variation in gate voltage on the electrostatic potential of individual nanowires and the potential developed at the channel-source/drain interface. The improved ON current with superior electrostatic integrity due to silicon pillars is showing the possibility of this device towards future development in CMOS technology. Finally, the article includes the integration of nMOS and pMOS to realize the CMOS inverter for high speed and noise immune characteristics.

The analysis of fabricated silicon nanowires with various techniques: a roadmap to energy saving world

The fabrication of silicon nanowire has been reported in our research study. The synthesis of functionalized-silicon nanowire (f-SiNWs) array which is currently an intense subject of research with its various vast technological applications. We are presenting here SiNW arrays having various applications in electronic and optical devices which were fabricated by a metal-assisted chemical etching (MACE) of silicon (100) wafers. The varying parameter we have taken for the SiNW growth is its etching duration. Analysis of various deposition parameters has been carried out to optimize the growth of SiNW. Surface morphology of etched Si wafer has been carried out by field effect scanning electron microscopy, Photoluminescence (PL) spectroscopy and XRD. For energy saving world the basic stepping stone is Si based nano regime which is emerging vastly on the basis of silicon nanowire. By analyzing the results we reach in the conclusions that with SiNW we will lead to the energy saving era.

Functionalized aluminum-catalyzed silicon nanowire formation and radial junction photovoltaic devices.

Vertical-oriented silicon nanowire (SiNW) arrays with shaped smooth, nanodot-, or NW-structured surfaces offer many desirable advantages for advanced device applications. In this study, these functionalized SiNW formations were simplified by ex situ preparation of an aluminum (Al) catalyst along with optimization of the substrate temperature and time during vapor-liquid-solid chemical vapor deposition as a one-step process. SiNW-based photovoltaic cells were demonstrated with minimized NW surface defects through NW surface modification, opening a new path for the development of versatile Al-catalyzed SiNWs as a material of choice for on-chip integration in future nanotechnologies.

Broadband (Ultraviolet to Near-Infrared) Photodetector Fabricated in n-ZnO/p-Si Nanowires Core–Shell Arrays with Ligand-Free Plasmonic Au Nanoparticles

We report a high response optical detector based on n-ZnO/p-Si NWs core-shell arrays decorated with plasmonic Au nanoparticles (NPs), that works in the broad frequency range from UV (300 nm) to NIR (1100 nm) and consumes low power (few μW). The optical detector combines the visible and NIR detectability of Si NWs with the UV detectivity of ZnO through the core- shell structure and broad band detectivity in the visible range has been achieved by decorating core -shell arrays with ligand-free Au NPs synthesized by using pulsed laser ablation in liquid. The photo-detector uses n-ZnO as the active photoconductive channel that is sensitive in UV region. However, using photo-gating as well as favourable band alignments the carriers generated at longer wavelengths in visible and NIR in Au NPs and Si NWs arrays were introduced into the conduction band of ZnO leading to its broad band performance. We observed significant enhancement of responsivity R not only in visible range but also in UV and NIR region with a high detectivity of 1011 (cmHz1/2W-1). The responsivity of the detector ~ 1 A/W from 700nm to longer wavelength (at bias of 1V) and in the visible region the responsivity of the photo detector with Au NPs is > 0.5 A/W and increases to > 1 A/W at UV region.