Structure Of Silicon Nanowires Research Articles

High-performance PANI sensor on silicon nanowire arrays for sub-ppb NH3 detection

For industrial production and disease diagnosis, real-time detection of low concentrations of NH3 is crucial, necessitating a gas-sensitive sensor compatible with integrated processes and exhibiting excellent performance. Herein, we employed wet etching and rapid in-situ polymerization on silicon nanowire substrates to grow polyaniline fibers, thereby fabricating NH3 gas sensors with p-p heterojunction and three-dimensional network structures. Characterization and gas sensing performance testing were conducted. The results demonstrate the outstanding NH3 detection capabilities of the sensor, providing stable responses down to concentrations as low as 1 ppb, which indicates its LOD is one to two orders of magnitude lower than current similar products. It also exhibits verified selectivity and long-term reliability. The excellent sensing performance is attributed to the high surface area from the silicon nanowire structure and efficient synergy of p-p heterojunction. Additionally, the influence of doping types of the substrates and annealing process were explored. This work serves as a reference for the design of silicon-based gas sensors with high sensitivity, low detection limits, and extended operational lifetimes, suitable for deployment in commercial integrated monitoring systems.

Highly Photoresponsive Vertically Stacked Silicon Nanowire Photodetector with Biphasic Current Stimulator IC for Retinal Prostheses

This paper presents an integrated approach for a retinal prosthesis that overcomes the scalability challenges and limitations of conventional systems that use external cameras. Silicon nanowires (SiNWs) are utilized as photonic sensors due to their nanoscale dimensions and high surface-to-volume ratio. To enhance these properties and achieve high photoresponsivity, our research team developed a vertically stacked SiNW structure using a fabrication method entirely based on dry etching. The fabricated SiNW photodetector demonstrated excellent electrical and optical characteristics, including linear I–V characteristics that confirmed ohmic contact formation and high photoresponsivity exceeding 105 A/W across the 400–800 nm wavelength range. The SiNW photodetector, following its integration with a switched capacitor stimulator circuit, exhibited a proportional increase in stimulation current in response to higher light intensity and increased SiNW density. In vitro experiments confirmed the efficacy of the integrated system in inducing neural responses from retinal cells, as indicated by an increased number of neural spikes observed at higher light intensities and SiNW densities. This study contributes to sensor technology by demonstrating an approach to integrating nanostructures and electronic components, which enhances control and functionality.

Density Functional Investigation of [001] and [111] SiNWs and the Effect of Doping with Boron and Phosphorus

In the present study, we investigate the influence of boron (B) and phosphorus (P) (p- and n-type, respectively) doping on the electronic properties of ultra-thin silicon nanowires (SiNWs) by gradient-corrected density functional calculations with the Perdew–Burke–Ernzerhof (PBE) approximation. In the limit of very small diameters (5–8 Å), both pristine and highly active unsaturated SiNWs with orientations along the [001] and [111] directions exhibit electronic states around the Fermi level, indicative of conductive properties. Conduction is further enhanced by the introduction of doping atoms, as demonstrated by the relative change in the band structures of SiNWs with and without B and P doping. This investigation provides an important insight into the electronic states of SiNWs, which are candidates for future electronics or sensing applications.

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.

Temperature Etching and Metallic Agent Concentration Effect on Structure, Morphology and Wettability of Silicon Nanowires

Abstract. Structural, Morphologycal and Wettability of SiliconNanowires (SiNWs) elaborated using Ag assisted electroless chemical etching are investigated. Prior the etching, Ag nanoparticles (AgNPs) were deposited at room temperature in a HF/AgNO3 solution with different concentration of AgNO3. The XRD spectra of the Ag NPs deposit show a good crystallinity. The effects of temperature etching bath and concentrations of AgNO3 on the etching process were examined. The morphological study, performed using a Scanning Electron Microscopy (SEM), shows porous silicon layer of 2µm for the lower temperature etching. For 25°C, perpendicular silicon nanowires about 15µm were formed. For the higher etching temperature (50°C), the silicon nanowire about 50 nm in diameter and 50µm in length were formed. The impact of Ag concentration on the SiNWs formation is examined in the second part of the present work. It is shown that the etching depth decreases as the Ag concentration decreases with values of 2.8 μm and 2 μm for concentrations of 0.025M and 0.0125M, respectively. The hydrophobicity of the samples was monitored by measuring the contact angle between a drop of water and the sample surface. It was established that the morphology is strongly influenced by etching conditions and their wettability changes from superhydrophilic to hydrophobic. FTIR analysis confirms the oxide-free silicon nanowires.

High-performance pyramid-SiNWs biosensor for NH3 gas detection

NH3 is widely existed in the environment and is closely associated with various health issues. Additionally, detecting the small amounts of NH3 exhaled by patients with liver and kidney diseases offers potential opportunities for painless early disease diagnosis. Therefore, there is an urgent need for a convenient, rapid, and highly sensitive real-time NH3 monitoring method. This work presents a high-performance NH3 sensor based on olfactory receptor-derived peptides (ORPs) on a pyramid silicon nanowires (SiNWs) structure substrate. First, we successfully fabricated the pyramid-SiNWs structure on a silicon substrate using a chemical etching method. Subsequently, by dehydrative condensation reaction between the amino groups on APTES and the carboxyl groups of ORPs, ORPs were successfully immobilized onto the pyramid-SiNWs structure. This methodology allows the ORPs sensor on the pyramid-SiNWs substrate to detect NH3 as low as 1 ppb, which was the reported lowest limit of detection, with a higher response rate compared to ORPs sensors on flat SiNWs substrates. The sensors also exhibit good sensitivity and stability for NH3 gas detection. The results show the feasibility and potential applications of ORPs-pyramid-SiNWs structure sensors, in the fields of food safety, disease monitoring, and environmental protection, etc.

Silicon Nanowire Array Weaved by Carbon Chains for Stretchable Lithium-Ion Battery Anode.

To manufacture flexible batteries, it can be a challenge for silicon base anode materials to maintain structural integrity and electrical connectivity under bending and torsion conditions. In this work, 1D silicon nanowire array structures combined with flexible carbon chains consisting of short carbon nanofibers (CNFs) and long carbon nanotubes (CNTs) are proposed. The CNFs and CNTs serve as chain joints and separate chain units, respectively, weaving the well-ordered Si nanowire array into a robust and integrated configuration. The prepared flexible and stretchable silicon array anode exhibits excellent electrochemical performance during dynamic operation. A high initial specific capacity of 2856mAhg-1 is achieved. After 1000 cycles, a capacity retention of 60% (1602mAhg-1) is maintained. Additionally, the capacity attenuation is less than 1% after 100 bending cycles. This excellent cycling stability is obtained with a high Si loading of 6.92mgcm-2. This novel approach offers great promise for the development of high-loading flexible energy-storage devices.

Influence of surface facets on the electronic structure of silicon nanowires and slabs from atomistic calculations

Fabrication of modern solid-state devices demands precise control of shape and dimensions, which requires an accurate knowledge of the role that surfaces play in such devices. To contribute to the understanding of surface effects on silicon nanowires, we present an atomistic study of the electronic properties of silicon nanostructures exhibiting surface facets over the (100), (110), (111), and (112) crystallographic planes. We calculate the electronic structure of slabs in such a way that the effect of individual facets may be observed. Subsequently, we determine the electronic structure of nanowires grown along the [100], [110], [111], and [112] directions, with surfaces defined by a combination of the mentioned facets. Our nanowires comprise diameters ranging from 1 to 6.7 nm and structures with more than 1000 atoms. We discuss the band structure, the relation between direct and indirect bandgaps, and the density of states. We base our calculations on semiempirical pseudopotentials where we implement complex potentials to describe passivants. We find that there is a transition from direct to indirect gap for the [111] direction at approximately 2 nm and that the difference between the direct and indirect gap may reach more than 300 meV depending on the diameter. We show that the occurrence of a direct bandgap is favored by the presence of the (100) facet and that it is related to a higher surface density of states. Conversely, we find that the (111) facet is the most inert surface type with a lower surface density of states.

CuSCN/Si heterojunction near-infrared photodetector based on micro/nano light-trapping structure

In this paper, high-performance CuSCN/Si heterojunction near-infrared photodetectors were successfully prepared using nanoscale light-trapping optical structures. Various light-trapping structures of ortho-pyramids, inverted pyramids and silicon nanowires were prepared on silicon substrates. Then, CuSCN films were spin-coated on silicon substrates with high crystalline properties for the assembly of CuSCN/Si photodetectors. Their reflectance spectra and interfacial passivation properties were characterized, demonstrating their superiority of light-trapping structures in high light response. Under the irradiation of 980 nm near-infrared light, a maximum responsivity of 2.88 A W−1 at −4 V bias and a specific detectivity of 5.427 × 1010 Jones were obtained in the CuSCN/Si heterojunction photodetectors prepared on planner silicon due to 3.6 eV band gap of CuSCN. The substrates of the light-trapping structure were then applied to the CuSCN/Si heterojunction photodetectors. A maximum responsivity of 10.16 A W−1 and a maximum specific detectivity of 1.001 × 1011 Jones were achieved under the 980 nm near-infrared light irradiation and −4 V bias, demonstrating the advanced performance of CuSCN/Si heterojunction photodetectors with micro-nano light-trapping substrates in the field of near-infrared photodetection compared to other silicon-based photodetectors.

Research progress of silicon nanowires array photodetectors

As one of the most important semiconductor materials, silicon (Si) is widely used in optoelectronic devices such as solar cells and photodetectors. Owing to the difference in refractive index between silicon and air, a large amount of incident light is reflected back into the air from the silicon surface. In order to suppress the loss caused by this reflection, a variety of silicon nanostructures with strong trapping effect have been developed. Most of the dry-etching schemes encounter the problems of high cost and complex preparation, while the silicon nanowires array prepared by the wet-etching schemes has the problems of low controllability of some parameters such as the spacing between two adjacent nanowires, and the small effective area of heterojunction. The method of using polystyrene microsphere as the mask can integrate the advantages of dry-etching method and wet-etching method, and it is easy to obtain periodic silicon nanowires (pillars) array. In this paper, first, we summarize the properties and preparation methods for silicon nanowires structure, the strategies to effectively improve the performance of silicon nanowires (pillars) array photodetectors, Then we analyze the existing problems. Further, the latest developments of silicon nanowires (pillars) array photodetector are discussed, and the structure, morphology of photosensitive layer and methods to improve the performance parameters of silicon nanowires (pillars) array photodetector are analyzed. Among them, we focus on the ultraviolet light sensitive silicon based photodetector and its method to show tunable and selective resonance absorption through leaky mode resonance, the silicon nanowires array photodetector modified with metal nanoparticles and the method of improving performance through surface plasmon effect, and plasmon hot electrons. Heterojunction photodetectors composed of various low-dimensional materials and silicon nanowires (pillars) array, and methods to improve the collection efficiency of photogenerated charge carriers through the “core/shell” structure, methods to expand the detection band range of silicon-based photodetectors by integrating down-conversion light-emitting materials and silicon nanowires (pillars) array, flexible silicon nanowires array photodetectors and their various preparation methods, are all introduced. Then, the main problems that a large number of defect states will be generated on the silicon nanostructure surface in the MACE process are briefly introduced, and several possible solutions for defect passivation are also presented. Finally, the future development for silicon nanowires (pillars) array photodetectors is prospected.

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.

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.

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.

Fabrication of Graphoepitaxial Gate-All-Around Si Circuitry Patterned Nanowire Arrays Using Block Copolymer Assisted Hard Mask Approach.

We demonstrate the fabrication of sub-20 nm gate-all-around silicon (Si) nanowire field effect transistor structures using self-assembly. To create nanopatterned Si feature arrays, a block-copolymer-assisted hard mask approach was utilized using a topographically patterned substrate with well-defined Si3N4 features for graphoepitaxially alignment of the self-assembled patterns. Microphase-separated long-range ordered polystyrene-b-poly(ethylene oxide) (PS-b-PEO) block-copolymer-derived dot and line nanopatterns were achieved by a thermo-solvent approach within the substrate topographically defined channels of various widths and lengths. Solvent annealing parameters (temperature, annealing time, etc.) were varied to achieve the desired patterns. The BCP structures were modified by anhydrous ethanol to facilitate insertion of iron oxide features within the graphoepitaxial trenches that maintained the parent BCP arrangements. Vertical and horizontal ordered Si nanowire structures within trenches were fabricated using the iron oxide features as hard masks in an inductively coupled plasma (ICP) etch process. Cross-sectional micrographs depict wires of persistent width and flat sidewalls indicating the effectiveness of the mask. The aspect ratios could be varied by varying etch times. The sharp boundaries between the transistor components was also examined through the elemental mapping.

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.

Silicon nanowires decorated with platinum nanoparticles were applied for photothermal-enhanced sonodynamic therapy.

Sonodynamic therapy (SDT) triggered by ultrasound (US) can overcome pivotal limitations of photo-therapy owing to its high depth-penetration and low phototoxicity. However, there is still a need to develop more efficient sonosensitizes to enhance the therapy efficiency.Methods: In this study, Pt nanoparticles (Pt NPs) are reduced on silicon nanowires (SiNWs) by in situ reduction to prepare Si-Pt nanocomposites (Si-Pt NCs).Results: Si-Pt NCs can produce reactive oxygen radicals (ROS) under ultrasound (US) irradiation, which have sonodynamic therapy (SDT) effect. Meanwhile, Si-Pt NCs can convert excess hydrogen peroxide (H2O2) into ROS in the tumor microenvironment, which endow strong chemodynamic therapy (CDT) effect. Taking the advantages of the mesoporous structure of SiNWs, the SDT and CDT effects of Si-Pt NCs are stronger than those of the pure Pt NPs and SiNWs. Besides, the mild photothermal effect of Si-Pt NCs further improves the SDT&CDT activity and realizes the combined cancer therapy.Conclusion: The developed Si-Pt NCs with the ability of photothermal enhanced SDT/CDT combined therapy play a momentous role in the novel cancer treatment.

Preparation of Silicon Nanowires and Porous Silicon Composite Structure by Electrocatalytic Metal Assisted Chemical Etching

Preparation of Silicon Nanowires and Porous Silicon Composite Structure by Electrocatalytic Metal Assisted Chemical Etching

SOI-Nanowire Biosensor for the Detection of Glioma-Associated miRNAs in Plasma

Herein, we report the development of a highly sensitive nanotechnology-based system—silicon-on-insulator nanowire biosensor for the revelation of microRNAs (miRNAs), associated with the development of glioma in the human. In this system, a sensor chip, bearing an array of silicon nanowire structures, is employed. The sensor chip is fabricated using a top-down technology. In our experiments reported herein, we demonstrated the detection of DNA oligonucleotide (oDNA), which represents a synthetic analogue of microRNA-363 associated with the development of glioma. To provide biospecific detection of the target oligonucleotides, the surface of the nanowire structures is modified with oligonucleotide probes; the latter are complementary to the target ones. The concentration limit of the target oligonucleotide detection, attained using our nanowire biosensor, is at the level of DL~10−17 M. The revelation of the elevated level of glioma-associated miRNA in plasma is also demonstrated.

Thermally induced evolution of the structure and optical properties of silicon nanowires

In the present paper, we report on the investigation of thermal annealing (TA) effect on structural and optical properties of crystalline silicon nanowires produced by metal-assisted chemical etching approach. In particular, the impact of TA on nanowire length, relative volume and size distribution of voids is described in terms of Lifshitz-Slyozov-Wagner theory considering the TA induced Oswald ripening in the SiNW arrays. It was also found that TA leads to a decrease of the SiNWs total reflection in the wide UV–VIS-IR spectral range. The reported effects can be used for tuning of crystalline SiNWs arrays in view of their further applications in photonics related fields.

Optimization and characterization of silicon nano-grass antireflection layer on textured silicon wafer

We propose in this paper silicon nano-grass layer as an alternative of conventional black silicon nanowire structure. Conventional metal-assisted chemical etching process by HF produces porous silicon nanowire structure. This is due to uncontrollable chemical reaction making long-heighted nanowires which causes detrimental effect on further solar cell processing. The shape and height of silicon nanostructure was reduced by new chemical solution to minimize the porosity. Silicon nano-grass layer was grown on textured silicon surface and investigated in detail. The structure was formed by NH4F/H2SO4/H2O2 solution at room temperature. Substantial reflectance reduction with broadband spectral range was observed. The etching mechanism and the effect of etch constituents of the etching solution on the structure of nano-grass were studied elaborately. Reflectance and photoluminescence were studied accordingly, and the variations in the surface porosity and light absorbance property have been monitored. At the very end, a comparative study of conventional black silicon etching process by HF/H2O2 and nano-grass on textured silicon by NH4F solution has been investigated. The etch rate and the optical superiority of nanostructures formed by both the solutions have been manifested and explained. For the commercial production level, silicon nano-grass structure is much persistent than silicon nanowire.