Silicon Nanowires Research Articles

Non-destructive characterization of silicon nanowires and nanowire coatings using mid-infrared spectroscopy

Silicon nanowires (SiNWs) have attracted much attention owing to their potential applications in electronics and photonics, while remaining as a cost-effective material platform. Key material properties in engineering SiNWs for different applications include their length, density, and presence of oxides or other chemicals on the surface. However, monitoring these properties is challenging, as scanning electron microscopy and atomic force microscopy (AFM), which directly image the wires, require destructive cleaving of the sample. This paper uses polarized, variable-angle Fourier Transform IR reflectance spectroscopy as a nondestructive technique to characterize the areal density and length of metal-assisted chemically etched SiNW arrays. In addition to the ability to characterize “as-etched” wires, we show that IR spectroscopy can also measure few-nanometer thick layers of aluminum oxide (AlOx) grown radially around the length of the SiNWs utilizing atomic layer deposition. Despite sample inhomogeneities, an effective medium theory (EMT) model can determine the length and density of the NWs for a range of lengths between 3 and 14 μm. The EMT can also reproduce the experimentally measured vibrational bands for coated NWs, demonstrating that IR spectroscopy can also evaluate the presence of molecular contaminants on the wires.

Surface plasmonic hot hole driven Ag2S/Au/Al2O3 photocathode for enhanced photoelectrochemical water splitting performance

Herein, Ag2S/Au/Al2O3 photoelectrode was fabricated for superior photoelectrochemical (PEC) water splitting response. The working electrodes were deposited using the glancing angle deposition (GLAD) method followed by RF sputtering and atomic layer deposition (ALD). The as-prepared Ag2S/Au/Al2O3 samples revealed a higher photocurrent density of 2.50 mA/cm2 (at 0.95 V Ag/AgCl) as compared to bare Ag2S (1.70 mA/cm2) with a corresponding less charge transfer resistance at the semiconducting interface. The superior PEC response may be ascribed to the synergic effect of plasmonic Au nanoparticles and the tilted Ag2S nanorods. The plasmonic effect of Au nanoparticles increases the visible-light response of Ag2S as well as provides the hot holes to enhance the photocurrent density. In addition, the increased trapping of light due to the tilted architecture of Ag2S nanorods resulted in an effective absorption of light. The theoretical simulations based on finite difference time domain (FDTD) were also performed to explore the distribution of the electric-field intensity and optical trapping of light between the nanorods of Ag2S and Ag2S/Au. The experimental and theoretical results show a deeper insight into the role of plasmonic nanostructures decorated Ag2S nanorods and shed light on designing hybrid hot hole harvesting semiconductor nanostructures for the next generation photoelectrodes.

Investigation of Physical Properties of Nanostructured Selenium-Based Compound Semiconductors

The study of physical properties of compound semiconductors plays a vital role in the device fabrication point of view. Different investigations suggest that one can tune these properties by impurity dopants, irradiation techniques, adopting different synthesis techniques, etc. In this study, the physical properties of nanostructured thin films of Se–S compound were tuned by different Hg dopant concentrations. X-ray diffraction spectra clarify the preferred crystallite growth occurs in the cubic phase of the corresponding Bravi’s crystal system. The particle size calculated from Bragg’s reflection spectra by using Scherrer’s analytical formula illustrates an enhancement of crystallite size in highly concentrated Hg-doped sample. Similar consequences are found in surface morphological micrographs. The optical band gap reduced from 1.65[Formula: see text]eV to 1.54[Formula: see text]eV on increasing the doping concentration of Hg, according to the computed optical parameters using optical transmission spectra in the wavelength range 200–1100[Formula: see text]nm. The thin-film refractive index dispersion data fits well in accordance with the single oscillator model. Investigation of electrical properties tells that there is significant improvement in electrical conductivity in highly concentrated Hg-doped samples. Therefore, the apparent tuning as observed in the physical properties of the investigated material may have practical uses in industry for a variety of optoelectronic devices.

PbS/ Si NW Heterojunction on Silicon Chip Based Self-Powered Photo Detector Device for IR Radiations by Chemical Bath Deposition

PbS/ Si NW Heterojunction on Silicon Chip Based Self-Powered Photo Detector Device for IR Radiations by Chemical Bath Deposition

Anisotropy of the conductivity of silicon nanowires

ABSTRACT This study reports the findings from an investigation into charge carrier transport within a silicon nanowire layer. The samples were prepared using the metal-assisted chemical etching method applied to crystalline silicon wafers with a resistance of 10–20 Ω·cm. The resulting silicon nanowires had a diameter of about 100 nm with a resistance of approximately 15 kΩ·cm. Electrical conductivity measurements were performed in both planar and sandwich configurations, revealing analogous conductivity mechanisms across different geometries. Frequency-dependent conductivity studies unveiled the presence of hopping conductivity. A hypothesis is proposed regarding the existence of a potential barrier at the interface between the nanowire layer and the substrate.

Effect of Temperature on the Electrical and Optical Properties of Silver (Ag) Assisted Electrochemically Etched Silicon Nanowires (SINWs)

Effect of Temperature on the Electrical and Optical Properties of Silver (Ag) Assisted Electrochemically Etched Silicon Nanowires (SINWs)

Stencil-Based Selective Surface Functionalization of Silicon Nanowires in 3D Device Architectures for Next-Generation Biochemical Sensors

Stencil-Based Selective Surface Functionalization of Silicon Nanowires in 3D Device Architectures for Next-Generation Biochemical Sensors

Twisted leaf like ZnO-flake-like BiOI@CNF grown on ITO substrate as a nanostructured pioneering platform for photoelectrochemical water splitting

Despite ZnO nanostructures garnering significant attention for photoelectrochemical (PEC) water splitting, the quest for efficient ZnO-based photoelectrodes with optimal light absorption, effective electron-hole separation, and transfer remains a challenge. The formation of ZnO heterojunctions with lower bandgap nanostructures of semiconductors has emerged as a strategy to enhance charge transfer while mitigating recombination rates. Additionally, the introduction of carbon nanofibers (CNFs) to these heterojunctions serves to further suppress recombination by electron trapping and enhances catalytic active sites, thereby elevating PEC performance. In this study, twisted leaf-like ZnO, flake-like BiOI, ZnO-BiOI nanostructure heterojunctions, and ZnO-BiOI@C composites were synthesized through a solvothermal method. Notably, the ZnO-BiOI@C photoelectrode exhibited outstanding performance, achieving a photocurrent density of 5.6 mA/cm2 through linear sweep voltammetry under light illumination. Each synthesized photoelectrode demonstrated robust photocurrent responsiveness and excellent stability under chopped conditions for up to 1150 s with a 50 s interval. This remarkable stability is attributed to the unique and stable morphological characteristics and strong crystallinity of the synthesized materials. The formed heterojunction between ZnO-BiOI was found to extend light absorption capabilities, while the incorporation of CNFs effectively trapped electrons from the heterojunction's conduction band, enhancing overall water splitting performance. The results underscore the potential of the ZnO-BiOI@C composite as a high-performing photoelectrode for PEC applications, emphasizing the importance of morphological and compositional considerations in advancing PEC technologies.

Deterministic Single-Row-Droplet Catalyst Formation for Uniform Growth Integration of High-Density Silicon Nanowires.

Planar silicon nanowires (SiNWs), grown by using low temperature catalytic approaches, are excellent 1D channel materials for developing high-performance logics and sensors. However, a deterministic position and size control of the metallic catalyst droplets, that lead to the growth of SiNWs, remains still a significant challenge for reliable device integration. In this work, we present a convenient but powerful edge-trimming catalyst formation strategy, which can help to produce a rather uniform single-row of indium (In) catalyst droplets of Dcat = 67 ± 5 nm in diameter, with an exact one-droplet-on-one-step arrangement. This approach marks a significant achievement in self-assembled catalyst formation and offers a foundation to attain a reliable and scalable growth of density SiNW channels, via an in-plane solid-liquid-solid (IPSLS) mechanism, with a uniform diameter down to Dnw = 35 ± 4 nm, and do not rely on high-precision lithography techniques. Prototype SiNW-based field effect transistors (FETs) are also fabricated, with a high Ion/Ioff current ratio and small subthreshold swing of >107 and 262 mV·dec-1, respectively, indicating a reliable new routine to integrate a wide range of SiNW-based logic, sensor, and display applications.

Artificial photosynthetic approach steers hydrogen evolution with bismuth selenide nanoflakes decorated silicon nanowires

Photoelectrochemical (PEC) water splitting offers a promising path toward green hydrogen production, but developing efficient photocatalysts remains a critical hurdle for large-scale adoption. In this study, we introduced a novel hybrid heterostructure for PEC water splitting, consisting of bismuth selenide (Bi2Se3) decorated silicon nanowires (Si NWs). This configuration achieved a high current density of 10.3 mA/cm2 at −1.2 V vs. RHE, along with an ABPE of 2.5 % at −0.8 V vs. RHE. Notably, these performance metrics surpass those of pristine Si NWs. The topological surface states in Bi-based layered chalcogenides, Bi2Se3 as cocatalysts with Si NWs, demonstrate robust charge transport which improves the conductivity of photoelectrodes in electrochemical reactions with high stability. Thus, the present study exploits the layered chalcogenides as an excellent cocatalyst for Si NWs that may lead to further advances in the hydrogen evolution reaction.

The structure, morphology, and optoelectronic properties of silicon nanowires decorated with GaN and Ag for single nanowire solar cell applications

This study focuses on the synthesis of a single Si-nanowire solar cell decorated with gallium nitride and silver nanoplasmons. The Si-nanowires were grown using the CVD approach followed by the decoration of their surfaces with GaN and Ag using a polyol approach. The structure of the developed GaN@Si and Ag@Si core/shell quantum wires was studied using X-ray diffraction. The morphology was investigated using scanning and transmission electron microscopy. The oxidation states were emphasized using X-ray photoelectron spectroscopy. The GaN and Ag nanoplasmons cause a modulation of the bandgap energy of the Si NWs. The growth of GaN and Ag nanoplasmons on the surface of Si nanowires increases the charge carrier density, photocurrent, and optical hole mobility. The plasmonic Ag nanoparticles suppress the nonlinear optical susceptibility of the Si nanowire compared to GaN-decorated Si NWs. The combination of quantum confinement and plasmonic effects of the proposed Ag@Si heterostructure nanowires offers great energy absorption and highly efficient separation of photogenerated electron/hole pairs. The developed single Ag@Si nanowire heterostructure exhibits photoconversion efficiency larger than GaN@Si NWs by one order of magnitude and larger than the un-decorated Si nanowires by 20-fold.

Protection of Si Nanowires against Aβ Toxicity by the Inhibition of Aβ Aggregation.

Alzheimer's disease (AD) is a progressive neurodegenerative disease characterized by the accumulation of amyloid beta (Aβ) plaques in the brain. Aβ1-42 is the main component of Aβ plaque, which is toxic to neuronal cells. Si nanowires (Si NWs) have the advantages of small particle size, high specific surface area, and good biocompatibility, and have potential application prospects in suppressing Aβ aggregation. In this study, we employed the vapor-liquid-solid (VLS) growth mechanism to grow Si NWs using Au nanoparticles as catalysts in a plasma-enhanced chemical vapor deposition (PECVD) system. Subsequently, these Si NWs were transferred to a phosphoric acid buffer solution (PBS). We found that Si NWs significantly reduced cell death in PC12 cells (rat adrenal pheochromocytoma cells) induced by Aβ1-42 oligomers via double staining with 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) and fluorescein diacetate/propyl iodide (FDA/PI). Most importantly, pre-incubated Si NWs largely prevented Aβ1-42 oligomer-induced PC12 cell death, suggesting that Si NWs exerts an anti-Aβ neuroprotective effect by inhibiting Aβ aggregation. The analysis of Fourier Transform Infrared (FTIR) results demonstrates that Si NWs reduce the toxicity of fibrils and oligomers by intervening in the formation of β-sheet structures, thereby protecting the viability of nerve cells. Our findings suggest that Si NWs may be a potential therapeutic agent for AD by protecting neuronal cells from the toxicity of Aβ1-42.

A Sustainable Molten Salt Leaching-Electrodeposition Route Toward Converting Rice Husks into Functional Silicon Nanowires and Porous Carbon

A Sustainable Molten Salt Leaching-Electrodeposition Route Toward Converting Rice Husks into Functional Silicon Nanowires and Porous Carbon

Antenna Effect in Large Area Palladium-Coated Electrostatically Formed Silicon Nanowire for Ppb Level Hydrogen Sensing

Antenna Effect in Large Area Palladium-Coated Electrostatically Formed Silicon Nanowire for Ppb Level Hydrogen Sensing

2D Semiconductor Nanostructures for Solar‐Driven Photocatalysis: Unveiling Challenges and Prospects in Air Purification, Sustainable Energy Harvesting, and Water Treatment

AbstractThe use of solar light to accelerate chemical processes (photocatalysis) has the potential to alleviate the pollution and energy crises. Thanks to their large surface area, unusual electronic structure, and abundance of low‐coordinate surface atoms, 2D semiconductors have shown enormous promise in photocatalytic applications. The synthesis, photoexcitation processes, design, and development of 2D semiconductor photocatalysts are thoroughly examined in this perspective, as well as their possible applications in air purification, solar energy conversion, organic synthesis, carbon capture and storage, and water treatment. This work highlights ongoing research efforts focused on improving the selectivity and efficiency of photocatalytic applications based on 2D semiconductors by means of hybrid systems, heterostructures, doping, and computational methodologies, together with open challenges. Finally, the integration of 2D semiconductor photocatalysts into indoor and outdoor environments is discussed, thereby facilitating the purification of air and water and generating clean energy, which assists in the pursuit of sustainable development objectives.

Nonvolatile Phase-Only Transmissive Spatial Light Modulator with Electrical Addressability of Individual Pixels.

Active metasurfaces with tunable subwavelength-scale nanoscatterers are promising platforms for high-performance spatial light modulators (SLMs). Among the tuning methods, phase-change materials (PCMs) are attractive because of their nonvolatile, threshold-driven, and drastic optical modulation, rendering zero-static power, crosstalk immunity, and compact pixels. However, current electrically controlled PCM-based metasurfaces are limited to global amplitude modulation, which is insufficient for SLMs. Here, an individual-pixel addressable, transmissive metasurface is experimentally demonstrated using the low-loss PCM Sb2Se3 and doped silicon nanowire heaters. The nanowires simultaneously form a diatomic metasurface, supporting a high-quality-factor (∼406) quasi-bound-state-in-the-continuum mode. A global phase-only modulation of ∼0.25π (∼0.2π) in simulation (experiment) is achieved, showing ten times enhancement. A 2π phase shift is further obtained using a guided-mode resonance with enhanced light-Sb2Se3 interaction. Finally, individual-pixel addressability and SLM functionality are demonstrated through deterministic multilevel switching (ten levels) and tunable far-field beam shaping. Our work presents zero-static power transmissive phase-only SLMs, enabled by electrically controlled low-loss PCMs and individual meta-molecule addressable metasurfaces.

Deep-reactive ion etching of silicon nanowire arrays at cryogenic temperatures

The pursuit of sculpting materials at increasingly smaller and deeper scales remains a persistent subject in the field of micro- and nanofabrication. Anisotropic deep-reactive ion etching of silicon at cryogenic temperatures (cryo-DRIE) was investigated for fabricating arrays of vertically aligned Si nanowires (NWs) of a large range of dimensions from micrometers down to 30 nm in diameter, combined with commonly used wafer-scale lithography techniques based on optical, electron-beam, nanoimprint, and nanosphere/colloidal masking. Large selectivity of ∼100 to 120 and almost 700 was found with resists and chromium hard masks, respectively. This remarkable selectivity enables the successful transfer of patterned geometries while preserving spatial resolution to a significant extent. Depending on the requirements by applications, various shapes, profiles, and aspect ratios were achieved by varying process parameters synchronously or asynchronously. High aspect ratios of up to 100 comparable to the best result by metal-assisted wet-chemical etching and sub-μm trenches by DRIE were obtained with NW diameter of 200 nm, at an etch rate of ∼4 μm/min without being collapsed. At the same time, low surface roughness values were maintained on the NW top, sidewall, and bottom surface of ∼0.3, ∼13, and ∼2 nm, respectively, as well as high pattern fidelity and integrity, which were measured using angle-resolved Fourier microscopy, combined atomic force, and scanning electron microscopy on selected NWs. This work establishes the foundation in the controllable development of Si nanoarchitectures, especially at sub-100 nm structures, for energy-harvesting and storage, damage-free optoelectronics, quantum, photovoltaics, and biomedical devices.

Silicon Nanowires as Anodes for Lithium‐Ion Batteries: Full Cell Modeling

Silicon (Si) anodes attract a lot of research attention for their potential to enable high‐energy density lithium‐ion batteries (LIBs). Many studies focus on nanostructured Si anodes to counteract deterioration. Herein, LIBs are modeled with Si nanowire anodes in combination with an ionic liquid (IL) electrolyte. On the anode side, elastic deformations to reflect the large volumetric changes of Si are allowed. With physics‐based continuum modeling, insight into usually hardly accessible quantities like the stress distribution in the active material can be provided. For the IL electrolyte, the thermodynamically consistent transport theory includes convection as relevant transport mechanism. The volume‐averaged 1d+1d framework is presented and parameter studies are performed to investigate the influence of the Si anode morphology on the cell performance. The findings highlight the importance of incorporating the volumetric expansion of Si in physics‐based simulations. Even for nanostructured anodes — which are said to be beneficial concerning the stresses — the expansion influences the achievable capacity of the cell. Accounting for enough pore space is important for efficient active material usage.

Electron-donor-impurity polarizability in a semiconductor nanostructure under electric field: Geometrical effects in ellipsoidal quantum dots

The features of electron-impurity polarizability in a quantum nanostructure are investigated from the knowledge of allowed electron states coupled to a shallow-donor impurity. The influence of geometry on the carrier confinement and the presence of external probes such as electric fields are explicitly considered. For the sake of illustration, the example of CdS/ZnSe-based prolate ellipsoidal core/shell quantum dot (PECSQD) configuration is chosen. This problem allows to consider a finite confinement potential model, employing both the finite element method and the effective mass approximation. Within this framework, impurity-related energies and associated polarizability for the lowest states were determined as functions of the shell thickness, core dimensions, impurity position, and applied electric field strength - while keeping the shell dimensions fixed. Electron-impurity energies are largely affected by electric field values. Under thinner shell conditions, polarizability shows variations with field strength that include “anomalous” negative values for certain states. Then, the increase in shell thickness causes a significant increment in the polarizabilities, regardless impurity position.

Electronic states in GaAs/AlGaAs/GaAs core/shell cylindrical quantum wires

Cylindrical quantum wires (CQWRs) based on GaAs/ AlxBGa1−xBAs /GaAs core/shell semiconductors are multilayer semiconductor nanostructures that exhibit interesting electronic properties. In this study, we explore in detail the electronic band structure and electronic transmission spectrum in these core/shell CQWRs in relation to various parameters such as inner and outer shell radius and aluminum-doping rate. Using Green’s function formalism, an advanced theoretical approach to solving Schrödinger’s equation in the effective mass approximation, taking into account the confinement potential of the cylindrical geometry. The results show that as the difference between the outer and inner radii of the shell increases, the number of electronic states increases due to the weakening of geometric confinement. In addition, as the concentration of Aluminum in the shell increases, the electronic states move to higher energies, due to the increase in confinement by the height of the potential. This study aims to provide an overview of the electronic states in core/shell nanowires, due to modification in Al molar concentration and shell size; they offer advantages such as better electronic transmission. We can control the electronic band structure of this nanowire, which can be used to fabricate high-performance electronic devices such as transistors, diodes and sensors.