Fabrication Of Silicon Nanowires Research Articles

Application of Silicon Nanowires

Abstract:: Silicon Nanowires (SiNWs), a novel category of nanomaterials, exhibit several outstanding properties, including superior transistor performance, quantum tunneling effects, and remarkable electrical and optical capabilities. These properties are expected to contribute significantly to the development of future nanodevices, such as sensors and optoelectronic components. The potential for device miniaturization with SiNWs is based on their ease of monocrystallization. This leads to a reduced rate of hole-electron complexes and their extensive specific surface area that promotes boundary effects, thereby diminishing conductivity. Characterized by unique structural attributes, SiNWs hold promise for a wide range of applications in various sectors. To date, multiple methods have been established for SiNW fabrication, including solgel, electrochemical, laser ablation, chemical vapor deposition, and thermal vapor deposition techniques. Subsequently, the focus has shifted to the application of SiNWs in electronics, energy, and biomedicine. SiNWs are instrumental in producing high-performance electronic devices, such as field-effect transistors, sensors, and memory units. They also exhibit outstanding photovoltaic properties, making them suitable for high-efficiency solar cell and photocatalyst production. Additionally, SiNWs are poised to make significant contributions to biomedicine, particularly in biosensors, drug delivery systems, and tissue engineering materials. This article provides a concise review of the current status of SiNWs in electronics, sensing devices, and solar cell applications, and their roles in high-performance transistors, biosensors, and solar cells. It concludes with an exploration of the challenges and prospects for SiNWs. In summary, the unique attributes of SiNWs establish them as a versatile nanomaterial with broad applicability. This review offers a comprehensive overview of SiNW research and theoretical insights that may guide similar studies. The insights into recent SiNW research presented here are intended to inform future applications and investigations involving these nanomaterials.

Implantable pH Sensing System Using Vertically Stacked Silicon Nanowire Arrays and Body Channel Communication for Gastroesophageal Reflux Monitoring.

Silicon nanowires (SiNWs) are emerging as versatile components in the fabrication of sensors for implantable medical devices because of their exceptional electrical, optical, and mechanical properties. This paper presents a novel top-down fabrication method for vertically stacked SiNWs, eliminating the need for wet oxidation, wet etching, and nanolithography. The integration of these SiNWs into body channel communication (BCC) circuits was also explored. The fabricated SiNWs were confirmed to be capable of forming arrays with multiple layers and rows. The SiNW-based pH sensors demonstrated a robust response to pH changes, and when tested with BCC circuits, they showed that it was possible to quantize based on pH when transmitting data through the human body. This study successfully developed a novel method for SiNW fabrication and integration into BCC circuits, which could lead to improvements in the reliability and efficiency of implantable medical sensors. The findings demonstrate significant potential for bioelectronic applications and real-time biochemical monitoring.

Influence of vacuum annealing on mechanical characteristics of focused ion beam fabricated silicon nanowires

This paper describes the influence of vacuum annealing on the mechanical characteristics of silicon (Si) nanowires (NWs) fabricated using focused ion beam (FIB) technologies. Two types of Si NWs having a cross-sectional one-side length or diameter ranging from 19 to 447 nm are prepared using the direct milling and Ga ion doping functions of FIB. The Si NWs prepared are annealed at 400–700 °C in high vacuum for 10 min, followed by quasi-static uniaxial tensile testing using a microelectromechanical system based tensile test system in a scanning electron microscope. All the Si NWs fracture in a brittle manner. Young's modulus of submicrometer-sized Si NWs shows both annealing and specimen size influences in the range from 120 to 170 GPa, whereas that of nano-sized Si NWs shows only annealing influence in the range from 60 to 110 GPa. Tensile strength scatters greatly, ranging from 1.0 to 7.2 GPa, which increases with increasing the NW size. A transmission electron microscope and an atomic force microscope suggest that, by annealing, recrystallization happens in the damaged layer introduced by FIB milling and the NW surface morphology changes due to its recrystallization and gallium (Ga) ion evaporation. Fracture origin is discussed through the comparison between surface roughness and crack length estimated by the Griffith theory of brittle fracture.

A Review on Silicon Nanowires and their use in the Development of Nano Piezoresistive Pressure Sensors

Abstract: Silicon has been the most trusted and used material in the fabrication of microelectronics components and systems. Recently, silicon nanowires have gained a lot of importance in the development of devices/components in many applications. SiNWs have unique attributes that are not found in bulk silicon. Their one-dimensional electronic structure provides interesting properties. Unique properties and small dimension (nm) of silicon nanowires have made them to be used as sensing elements in the development of nanosensors and devices. Silicon nanowires are now being extensively used in the development of biosensors, FETs, lithium-ion batteries, transistors, microelectronic chips, and sensors. SiNWs are used in the development of solar cells and photovoltaic batteries, because of their charge-trapping capabilities. The fabrication of silicon nanowires follows chemical etching, chemical vapor deposition (CVD), electron beam lithography, etc. The dimensions of silicon nanowires are highly compatible with the dimensions of biological and chemical species, hence making them more efficient to be used as sensing elements in bio and chemical domains. SiNWs exhibit excellent piezoresistive properties and hence are used as piezoresistors in piezoresistive sensing applications. This article presents a review of SiNWs in the development of sensors. An emphasis is given to the piezoresistive property of SiNWs. The use of SiNWs as a piezoresistor in the development of piezoresistive pressure sensors is also extensively reviewed in this article, along with the unique properties of SiNWs. Typical dimensions and applications of SiNWs are also reviewed. Moreover, this article also explores the fabrication, characterization aspects, and capabilities of SiNWs in the design and development of nanoscale devices/sensors.

Dewetting-Assisted Patterning: A Lithography-Free Route to Synthesize Black and Colored Silicon.

We report the use of thermal dewetting to structure gold-based catalytic etching masks for metal-assisted chemical etching (MACE). The approach involves low-temperature dewetting of metal films to generate metal holey meshes with tunable morphologies. Combined with MACE, dewetting-assisted patterning is a simple, benchtop route to synthesize Si nanotubes, Si nanowalls, and Si nanowires with defined dimensions and optical properties. The approach is compatible with the synthesis of both black and colored nanostructured silicon substrates. In particular, we report the lithography-free fabrication of silicon nanowires with diameters down to 40 nm that support leaky wave-guiding modes, giving rise to vibrant colors. Additionally, micrometer-sized areas with tunable film composition and thickness were patterned via shadow masking. After dewetting and MACE, such patterned metal films produced regions with distinct nanostructured silicon morphologies and colors. To-date, the fabrication of colored silicon has relied on complicated nanoscale patterning processes. Dewetting-assisted patterning provides a simpler alternative that eliminates this requirement. Finally, the simple transfer of resonant SiNWs into ethanolic solutions with well-defined light absorption properties is reported. Such solution-dispersible SiNWs could open new avenues for the fabrication of ultrathin optoelectronic devices with enhanced and tunable light absorption.

Fabrication of Silicon Nanowires by Metal-Assisted Chemical Etching Combined with Micro-Vibration.

In this work, we design a micro-vibration platform, which combined with the traditional metal-assisted chemical etching (MaCE) to etch silicon nanowires (SiNWs). The etching mechanism of SiNWs, including in the mass-transport (MT) and charge-transport (CT) processes, was explored through the characterization of SiNW's length as a function of MaCE combined with micro-vibration conditions, such as vibration amplitude and frequency. The scanning electron microscope (SEM) experimental results indicated that the etching rate would be continuously improved with an increase in amplitude and reached its maximum at 4 μm. Further increasing amplitude reduced the etching rate and affected the morphology of the SiNWs. Adjusting the vibration frequency would result in a maximum etching rate at a frequency of 20 Hz, and increasing the frequency will not help to improve the etching effects.

Array density effect on the optical and photoelectric properties of silicon nanowire arrays via Ag-assisted chemical etching

Ag-assisted chemical etching (AgACE) is a low-cost method to produce silicon nanowires (SiNWs) for photoelectric applications. Structure parameters of SiNWs have great impact on their optical and photoelectric properties, which are worth studying for fabricating high-performance devices. However, array density of SiNWs via AgACE, as an important structural parameter, has not been sufficiently investigated. Here, array density effect on the optical and photoelectric properties of SiNWs is experimentally investigated. SiNW arrays with different densities (silicon occupation ratio of 7%–34.5%) were prepared through controlling the reaction time of silicon wafers in the seed solution (t seed). The SiNW array with a t seed of 90 s shows optimum light absorption over 98% in the wavelength range of 300–1000 nm, though all the samples have light absorption over 95% due to the light trapping effect of nanowire array structure. In addition, the SiNW array with a t seed of 90 s exhibits the best photoelectric property. SiNW arrays with shorter t seed and higher density suffer more surface recombination, harming the photoelectric property. In SiNW arrays with longer t seed than 90 s and lower density, some SiNWs topple down and break, which has an adverse effect on transport and collection of carriers. These results indicate that the array density of SiNWs via AgACE has obvious effect on their photoelectric property. SiNW arrays via AgACE with a t seed of 90 s are ideal for photoelectric devices. This work is potential to guide SiNW fabrication for photoelectric applications.

Fabrication of Black Silicon Microneedle Arrays for High Drug Loading.

Silicon microneedle (Si-MN) systems are a promising strategy for transdermal drug delivery due to their minimal invasiveness and ease of processing and application. Traditional Si-MN arrays are usually fabricated by using micro-electro-mechanical system (MEMS) processes, which are expensive and not suitable for large-scale manufacturing and applications. In addition, Si-MNs have a smooth surface, making it difficult for them to achieve high-dose drug delivery. Herein, we demonstrate a solid strategy to prepare a novel black silicon microneedle (BSi-MN) patch with ultra-hydrophilic surfaces for high drug loading. The proposed strategy consists of a simple fabrication of plain Si-MNs and a subsequent fabrication of black silicon nanowires. First, plain Si-MNs were prepared via a simple method consisting of laser patterning and alkaline etching. The nanowire structures were then prepared on the surfaces of the plain Si-MNs to form the BSi-MNs through Ag-catalyzed chemical etching. The effects of preparation parameters, including Ag+ and HF concentrations during Ag nanoparticle deposition and [HF/(HF + H2O2)] ratio during Ag-catalyzed chemical etching, on the morphology and properties of the BSi-MNs were investigated in detail. The results show that the final prepared BSi-MN patches exhibit an excellent drug loading capability, more than twice that of plain Si-MN patches with the same area, while maintaining comparable mechanical properties for practical skin piercing applications. Moreover, the BSi-MNs exhibit a certain antimicrobial activity that is expected to prevent bacterial growth and disinfect the affected area when applied to the skin.

Analysis of synthesized doped vertical silicon nanowire arrays for effective sensing of nitrogen dioxide: As gas sensors

In the present study, the controllable fabrication of silicon nanowires (Si NWs) with vertical alignment was accomplished using metal assisted chemical etching (MACE). The different characteristics, such as structural, morphological, chemical, optical, and dielectric properties were analyzed using X-ray diffraction (XRD), field emission scanning electron microscope (FESEM), Raman spectroscopy, ultraviolet-visible diffuse reflectance spectroscopy (UV-DRS), and LCR [inductance (L), capacitance (C), and resistance (R)] meter (volume of the gas-sensing chamber is 650 mm3). It was revealed from the morphological study i.e., from the FESEM that p-type Si NWs are smaller in size than n-type Si NWs which is attributable to the energy band gap. The optical band gap (Eg) is observed to increase from 1.64 to 1.89 eV with the decreasing of the crystallite size and the optical reflection spectra of the Si NWs show a shift toward a lower wavelength (blue shift). Moreover, Raman spectra verified the red-shifted, asymmetrically broadened Raman line-shapes, which provides information about the size confinement effect in Si NWs. The MACE approach is excellent for synthesizing nanowire structures for use in gas-sensing applications due to its flexibility. The sensitivity of synthesized Si NWs was tested for NO2 gas. The sensor method is unique based on the testing of the device in the presence of a test gas because the use of the gas-sensing setup has the potential to measure the change in resistance by varying frequency, temperature, and time.

Etching rate of silicon nanowires with highly doped silicon during metal-assisted chemical etching

The fabrication of silicon nanowires (SiNWs) by metal-assisted chemical etching (MACE) has been widely studied in a variety of fields. SiNWs by high-doped silicon are potential materials to be applied in thermoelectric, lithium-ion batteries and sensors. However, existing studies on the etching characteristics of high-doped silicon are limited and miSunderstandings are existing. In this study, through the comparison of three types of silicon with different concentrations, it was found that the loss of SiNWs by low-doped and medium-doped was little but the loss for high-doped silicon was significant. Contrary to existing reports, we clarify that the etching rate of high-doped silicon was the highest among them through measurements and calculations, although the observed length was the smallest. The differences between supposed generated SiNWs and measured SiNWs can be assumed as the lateral etching of high-doped silicon. In addition, the cluster morphology of high-doped silicon also suggested severe lateral etching. Therefore, the etching characteristics of high-doped silicon and the mechanism need to be re-understood to control reactions and obtain expected SiNWs.

Silicon Nanowire Technologies: brief review, home-made solutions and future trends

The silicon nanowire (SiNW) is poised to become an industry standard on the upcoming technological nodes. It presents improved current drive and modulation, minimized footprint, stackability, and a host of different beneficial characteristics. The last few years of research have focused on solving the last remaining challenges of SiNW fabrication as they roll into commercial usage. Now, novel devices, as well as channel and device stacking for 3D VLSI applications is being studied. As well as how can the SiNW geometry can be harnessed for More Than Moore materials and applications. In this review, we present a sample of the range of devices, techniques and applications of SiNW structures, alongside novel developments in the research carried out at University of Campinas. Demonstrations of JLFETs fabricated using Ga+-FIB, e-beam lithography, silicon etching in NH4OH solution, FinFETs fabricated using Ga+ lithography and strained silicon structures are shown. Promising future developments in VLSI and More Than Moore applications such as vertically stacked nanowire geometries, graphene nanoribbon devices, and MagFETs are also presented.

Ammonia sensing by silicon nanowires (SINWs) obtained through metal assisted electrochemical etching

Present work reports fabrication of silicon nanowires (SINWs) through metal-assisted electrochemical etching. The process of etching is carried out with the help of dc current supplied through Agilent 6634B dc power supply on silver electroplated silicon(Si) wafer. The method provides ordered SINWs with larger surface area. Morphology, as seen from FESEM shows vertically aligned bunched SINWs of average length of 23µm with porous structure of finely distributed pores over the surface. Electrochemically etched SINWs shows high sensitivity to gas/vapors due to its highly porous nature, by capturing the gas molecules through voids present on the surface. In the present work different vapors viz. acetone, chloroform and ammonia are tested. Among these SINWs are seen to be fairly selective to ammonia. Ammonia sensing measurements are done for gas concentrations from 10 to 100 ppm. Sensitivity of the sensor increases with increasing concentrations. Electrical conductivity of SINWs is reduced in presence of ammonia. The experimental results highlight fair response and recovery times with good correlation coefficient to ensure prospect of developing SINWs based gas sensor for possible utilization in the medical and environmental fields, for example.

Removal of Ag remanence and improvement in structural attributes of silicon nanowires array via sintering

Metal-assisted chemical etching (MACE) is popular due to the large-area fabrication of silicon nanowires (SiNWs) exhibiting a high aspect ratio at a low cost. The remanence of metal, i.e., silver nanoparticles (AgNPs) used in the MACE, deteriorates the device (especially solar cell) performance by acting as a defect center. The superhydrophobic behavior of nanowires (NWs) array prohibits any liquid-based solution (i.e., thorough cleaning with HNO3 solution) from removing the AgNPs. Thermal treatment of NWs is an alternative approach to reduce the Ag remanence. Sintering temperature variation is chosen between the melting temperature of bulk-Ag (962 °C) and bulk-Si (1412 °C) to reduce the Ag particles and improve the crystallinity of the NWs. The melting point of NWs decreases due to surface melting that restricts the sintering temperature to 1200 °C. The minimum sintering temperature is set to 1000 °C to eradicate the Ag remanence. The SEM–EDS analysis is carried out to quantify the reduction in Ag remanence in the sintered NWs array. The XRD analysis is performed to study the oxides (SiO and Ag2O) formed in the NWs array due to the trace oxygen level in the furnace. The TG-DSC characterization is carried out to know the critical sintering temperature at which remanence of AgNPs removes without forming any oxides. The Raman analysis is studied to determine the crystallinity, strain, and size of Si nanocrystals (SiNCs) formed on the NWs surface due to sidewalls etching. An optimized polynomial equation is derived to find the SiNCs size for various sintering temperatures.

Comparative study of quantum confinements effect present in Silicon Nanowires using absorption and Raman spectroscopy

Silver-induced chemical etching (SIE) has been widely explored for developing silicon (Si) based photovoltaic devices with its benefits for low-cost and large-area fabrication of silicon nanowires (SiNWs) of high aspect ratios. Structures and optical properties of SiNWs fabricated through chemical etching are significantly affected by experimental as well as environmental conditions of etching. A comparative study of quantum confinement (QC) effect due to variation in nano crystallite size (NCS) of SiNWs samples, fabricated by SIE technique has been investigated here using ultraviolet visible (UV-VIS) spectroscopy and Raman spectroscopy. An enhanced optical band gap has been observed from the samples under UV excitation at room temperature due to QC effect. To improve the understanding of basic mechanism of QC effect present in samples has been analyzed through characteristic features of Raman line-shape like red shift, asymmetry ratio and broadening as compared to its bulk counterpart. The NCS of SiNWs present in the samples has been calculated by QC based Brus model, bond polarizability (BP) model and Raman line-shape fitting model. This study prove itself to explore a new direction towards a systematic building block for fabricating optoelectronic devices based on light - matter interactions present at the nano-scale. • Silicon nanowires (Si-NWs) onn type-Si(100) by silver-induced chemical etching. • Results obtained, indicate that the fabrication of size controlled Si-NWs. • Quantum confinements effectobserved in Si-NWs using Brus, bond polarizability and line shape model. • Estimated size from Brus and bond polarizability model using PL and Raman data were around 1.7–3.2 nm. • Theoretical estimation of size from line shape model were 2.66–3.16 nm.

Structural Properties of Alkanethiolates and Their Influence on The Stability and Reproducibility of Impedimetric Sensing

The utilization and commercialization of electronic based point of care (PoC) diagnostic devices has been hindered by the lack of repeatability and stability associated with such devices. Consequently, the enzyme-linked immunosorbent assay (ELISA) remains the dominant immunoassay used for the detection of serological diseases despite the numerous drawbacks associated with this platform.1, 2 Most notably, the ELISA relies on trained laboratory personnel to perform the assay in a centralized laboratory, which increases both the cost and time to actionable treatment. An electrochemical impedance biosensor is an example of a label-free biosensing platform that has high sensitivity and can be easily miniaturized and mass produced at a low cost, thus improving the time to actionable treatment.3-7 It has been shown that the repeatability and stability of electronic based biosensors is not associated with the transducing element but rather is dependent on the sensor-molecule interface.8 This interface typically consists of an alkanethiolate-based self-assembled monolayer (SAM) chemisorbed onto a gold (Au) substrate. In the case of Electrochemical Impedance Spectroscopy (EIS) sensing, the SAM forms a barrier to the ionic transport of the selected redox coupling agent. The molecular structure of the alkanethiolate determine the uniformity and density of the SAM, which directly affects its ability to impede the ionic transport of the redox coupling agent. Molecular dynamics studies have shown that shorter, less-ordered alkanethiolates rotate more easily than longer alkylthiolates.9 Their ability to rotate facilitates the gradual coverage of pinholes and defects present on the sensor-molecule interface.9 A separate study has shown that short chain (6C) alkanethiolates leads to significant drift in EIS measurements.10 The drift in charge transfer resistance of the 6C SAM was hypothesized to be associated with the surface reorganization of these thiols. The observed drift in the SAM measurements has been reported to be greater in magnitude than the measured change in charge transfer resistance upon binding of a receptor, thus compromising the reliability of biosensing measurements.10 This work uses a 16C alkanethiolate SAM to show that the stability and reproducibility of EIS measurements is directly dependent on the coverage of pinholes and defects present on the Au substrate as well as the crystallinity of the SAM. Cyclic Voltammetry (CV) and X-ray Photoelectron Spectroscopy (XPS) were used to measure the density and uniformity of the SAM, respectively. We show that stability in EIS measurements of the sensor-molecule interface directly corresponds to stable and reproducible measurements associated with the attachment of the selected receptor and lastly of the target analyte. Thus, through the rational design of a stable sensor-molecule interface we can minimize the drift associated with the SAM, and consequently the receptor interface. Thus, improving both the sensitivity and limit of detection of EIS based sensors.References Yalow, R. S.; Berson, S. A., Immunoassay of endogenous plasma insulin in man. The Journal of clinical investigation, 1960, 39 (7), 1157-1175.Prevention, C. f. D. C. a. Understanding the EIA Test. https://www.cdc.gov/lyme/diagnosistesting/labtest/twostep/eia/index.html Cui, Y., Wei, Q. Q., Park, H. K., and Lieber, C. M., Nanowire nanosensors for highly sensitive and selective detection of biological and chemical species, Science, 2001, 293, 1289-1292.Park, I., Li, Z., Pisano, A. P., and Williams, R. S., Top-down fabricated silicon nanowire sensors for real-time chemical detection, Nanotechnology, 2001, 21, 015501.Patolsky, F., Zheng, G. F., Hayden, O., Lakadamyali, M., Zhuang, X. W., and Lieber, C. M., Electrical detection of single viruses, Proceedings of the National Academy of Sciences of the United States of America, 2004, 101, 14017-14022.Pui, T. S., Agarwal, A., Ye, F., Ton, Z. Q., Huang, Y. X., and Chen, P. Ultra-sensitive detection of adipocytokines with CMOS-compatible silicon nanowire arrays, Nanoscale, 2009, 1, 159-163.Stern, E., Vacic, A., Rajan, N. K., Criscione, J. M., Park, J., Ilic, B. R., Mooney, D. J., Reed, M. A., and Fahmy, T. M. Label-free biomarker detection from whole blood, Nature Nanotechnology, 2010, 5, 138-142.Tarasov, A.; Tsai, M.-Y.; Flynn, E. M.; Joiner, C. A.; Taylor, R. C.; Vogel, E. M., Gold-coated graphene field-effect transistors for quantitative analysis of protein–antibody interactions. 2D Mater. 2015, 2, 044008.Jiang, L., Sangeeth, C. S., Yuan, L., Thompson, D., & Nijhuis, C. A. (2015). One-Nanometer thin Monolayers remove the deleterious effect of substrate defects in Molecular Tunnel Junctions. Nano Letters, 2015 15(10), 6643-6649.Xu, X.; Makaraviciute, A.; Kumar, S.; Wen, C.; Sjödin, M.; Abdurakhmanov, E.U.; Danielson, H.; Nyholm, L.; Zhang Z.; Structural Changes of Mercaptohexanol SelfAssembled Monolayers on Gold and Their Influence on Impedimetric Aptamer Sensors, Analytical Chemistry., 2019 91 (22), 14697-14704

Ultra-sensitive and fast optical detection of the spike protein of the SARS-CoV-2 using AgNPs/SiNWs nanohybrid based sensors

Severe acute respiratory syndrome SARS-CoV-2 virus led to notable challenges amongst researchers in view of development of new and fast detecting techniques. In this regard, surface-enhanced Raman spectroscopy (SERS) technique, providing a fingerprint characteristic for each material, would be an interesting approach. The current study encompasses the fabrication of a SERS sensor to study the SARS-CoV-2 S1 (RBD) spike protein of the SARS-CoV-2 virus family. The SERS sensor consists of a silicon nanowires (SiNWs) substrate decorated with plasmonic silver nanoparticles (AgNPs). Both SiNWs fabrication and AgNPs decoration were achieved by a relatively simple wet chemical processing method. The study deliberately projects the factors that influence the growth of silicon nanowires, uniform decoration of AgNPs onto the SiNWs matrix along with detection of Rhodamine-6G (R6G) to optimize the best conditions for enhanced sensing of the spike protein. Increasing the time period of etching process resulted in enhanced SiNWs’ length from 0.55 to 7.34 µm. Furthermore, the variation of the immersion time in the decoration process of AgNPs onto SiNWs ensued the optimum time period for the enhancement in the sensitivity of detection. Tremendous increase in sensitivity of R6G detection was perceived on SiNWs etched for 2 min (length=0.90 µm), followed by 30s of immersion time for their optimal decoration by AgNPs. These SiNWs/AgNPs SERS-based sensors were able to detect the spike protein at a concentration down to 9.3 × 10−12 M. Strong and dominant peaks at 1280, 1404, 1495, 1541 and 1609 cm−1 were spotted at a fraction of a minute. Moreover, direct, ultra-fast, facile, and affordable optoelectronic SiNWs/AgNPs sensors tuned to function as a biosensor for detecting the spike protein even at a trace level (pico molar concentration). The current findings hold great promise for the utilization of SERS as an innovative approach in the diagnosis domain of infections at very early stages.

Fabrication of Needle-Like Silicon Nanowires by Using a Nanoparticles-Assisted Bosch Process for Both High Hydrophobicity and Anti-Reflection.

In this work, a modified Bosch etching process is developed to create silicon nanowires. Au nanoparticles (NPs) formed by magnetron sputtering film deposition and thermal annealing were employed as the hard mask to achieve controllable density and high aspect ratios. Such silicon nanowire exhibits the excellent anti-reflection ability of a reflectance value of below 2% within a broad light wave range between 220 and 1100 nm. In addition, Au NPs-induced surface plasmons significantly enhance the near-unity anti-reflection characteristics, achieving a reflectance below 3% within the wavelength range of 220 to 2600 nm. Furthermore, the nanowire array exhibits super-hydrophobic behavior with a contact angle over ~165.6° without enforcing any hydrophobic chemical treatment. Such behavior yields in water droplets bouncing off the surface many times. These properties render this silicon nanowire attractive for applications such as photothermal, photocatalysis, supercapacitor, and microfluidics.

ALD-passivated silicon nanowires for broadband absorption applications

Silicon photonics enables the fabrication of optical devices with standard semiconductor processing technology. With high transparency and modal confinement, Si has matured into a well-established infrared optical material. Nanostructured silicon has been studied extensively due to its optical properties, especially silicon nanowires due to the myriad of available fabrication techniques, the broad range of physical dimensions, and the resulting optical characteristics. In this study, we fabricate silicon nanowires using a wet chemical process and modify their absorptive properties via atomic layer deposition passivation. The passivated nanowires absorb 95% of light from the visible to infrared, with a minimal angular dependence, making them excellent candidates for broadband absorber applications.

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.

Replacing Metals with Oxides in Metal-Assisted Chemical Etching Enables Direct Fabrication of Silicon Nanowires by Solution Processing.

Metal-assisted chemical etching (MACE) has emerged as an effective method to fabricate high aspect ratio nanostructures. This method requires a catalytic mask that is generally composed of a metal. Here, we challenge the general view that the catalyst needs to be a metal by introducing oxide-assisted chemical etching (OACE). We perform etching with metal oxides such as RuO2 and IrO2 by transposing materials used in electrocatalysis to nanofabrication. These oxides can be solution-processed as polymers exhibiting similar capabilities of metals for MACE. Nanopatterned oxides can be obtained by direct nanoimprint lithography or block-copolymer lithography from chemical solution on a large scale. High aspect ratio silicon nanostructures were obtained at the sub-20 nm scale exclusively by cost-effective solution processing by halving the number of fabrication steps compared to MACE. In general, OACE is expected to stimulate new fundamental research on chemical etching assisted by other materials, providing new possibilities for device fabrication.