Nickel and indium core-shell co-catalysts loaded silicon nanowire arrays for efficient photoelectrocatalytic reduction of CO_(2) to formate

Developing an efficient artificial photosynthetic system for transforming carbon dioxide and storing solar energy in the form of chemical bonds is one of the greatest challenges in modern chemistry.However,the limited choice of catalysts with wide light absorption range,long-term stability and excellent selectivity for CO_(2) reduction makes the process sluggish.Here,a core-shell-structured nonnoble-metal Ni@In co-catalyst loaded p-type silicon nanowire arrays(SiNWs)for efficient CO_(2) reduction to formate is demonstrated.The formation rate and Faradaic efficiency of formate over the Ni@In/SiNWs catalyst reach 58μmol h^(-1) cm^(-2) and 87% under the irradiation of one simulated sunlight(AM 1.5 G,100 mW cm^(-2)),respectively,which are about 24 and 12 times those over the pristine SiNWs.The enhanced photoelectrocatalytic performance for CO_(2) reduction is attributed to the rational combination of Ni capable of effectively extracting the photogenerated electrons and In responsible for the selective activation of CO_(2).

Effects of source-drain underlaps on the performance of silicon nanowire on insulator transistors

The effects of source-drain underlaps on the performance of a top gate silicon nanowire on insulator transistor are studied using a three dimensional(3D) self-consistent Poisson-Schrodinger quantum simulation. Voltage-controlled tunnel barrier is the device transport physics. The off current, the on/off current ratio, and the inverse subthreshold slope are improved while the on current is degraded with underlap. The physics behind this behavior is the modulation of a tunnel barrier with underlap. The underlap primarily affects the tunneling component of drain current. About 50% contribution to the gate capacitance comes from the fringing electric fields emanating from the gate metal to the source and drain. The gate capacitance reduces with underlap, which should reduce the intrinsic switching delay and increase the intrinsic cut-off frequency. However, both the on current and the transconductance reduce with underlap, and the consequence is the increase of delay and the reduction of cut-off frequency.

Preparation of high-purity straight silicon nanowires by molten salt electrolysis

Silicon nanowires of high purity and regular morphology are of prime importance to ensure high specific capacities of lithium-ion batteries and reproducible electrode assembly process.Using nickel formate as a metal catalyst precursor,straight silicon nanowires(65–150 nm in diameter)were directly prepared by electrolysis from the Ni/SiO2 porous pellets with 0.8 wt%nickel content in molten CaCl2 at 900℃.Benefiting from their straight appearance and high purity,the silicon nanowires therefore offered an initial coulombic efficiency of 90.53% and specific capacity of 3377 m Ah/g.In addition,the silicon nanowire/carbon composite exhibited excellent cycle performance,retaining 90.38%of the initial capacity after 100 cycles.Whilst further study on the charge storage performance is still ongoing,these preliminary results demonstrate that nickel formate is an efficient and effective metal catalyst precursor for catalytic preparation of high purity straight silicon nanowires via the molten salt electrolysis,which is suitable for large-scale production.

Ultra-low thermal conductivity of roughened silicon nanowires:Role of phonon-surface bond order imperfection scattering

The ultra-low thermal conductivity of roughened silicon nanowires(SiNWs)can not be explained by the classical phonon-surface scattering mechanism.Although there have been several efforts at developing theories of phonon-surface scattering to interpret it,but the underlying reason is still debatable.We consider that the bond order loss and correlative bond hardening on the surface of roughened SiNWs will deeply influence the thermal transport because of their ultra-high surface-to-volume ratio.By combining this mechanism with the phonon Boltzmann transport equation,we explicate that the suppression of high-frequency phonons results in the obvious reduction of thermal conductivity of roughened SiNWs.Moreover,we verify that the roughness amplitude has more remarkable influence on thermal conductivity of SiNWs than the roughness correlation length,and the surface-to-volume ratio is a nearly universal gauge for thermal conductivity of roughened SiNWs.

Stable Superwetting Surface Prepared with Tilted Silicon Nanowires

Large-scale uniform nanostructured surface with superwettability is crucial in both fundamental research and engineering applications.A facile and controllable approach was employed to fabricate a superwetting tilted silicon nanowires(TSNWs) surface through metal-assisted chemical etching and modification with low-surface-energy material.The contact angle(CA) measurements of the nanostructured surface show a large range from the superhydrophilicity(the CA approximate to 0°) to superhydrophobicity(the CA up to 160°).The surface becomes antiadhesion to water upon nanostructuring with a measured sliding angle(a) close to 0°.Moreover,the fluorinated TSNWs surface exhibits excellent stability and durability because strong chemical bonding has been formed on the surface.

Simulation of Chirped Pulse Propagation in Silicon Nanowires: Shape and Spectrum Analysis

In this paper, we simulate the propagation of chirped pulses in silicon nanowires by solving the nonlinear Schrodinger equation (NLSE) using the split-step Fourier (SSF) method. The simulations are performed both for the pulse shape (time domain) and for the pulse spectrum (frequency domain), and various linear and nonlinear effects changing the shape and the spectrum of the pulse are analyzed. Owing to the high nonlinear coefficient and a very small effective-mode area, the required length for observing nonlinear effects in nanowires is much shorter than that of conventional optical fibers. The impacts of loss, nonlinear effects, second- and third-order dispersion coefficients and the chirp parameter on pulse propagation along the nanowire are investigated. The results show that the sign and the value of the chirp parameter have important role in pulse propagation so that in the anomalous dispersion regime, the compression occurs for the up- chirped pulses, whereas the broadening takes place for the down-chirped pulses. The opposite situation happens for up- and down-chirped pulses propagating in the normal dispersion regime.

Strongly enhanced light trapping in a two-dimensional silicon nanowire random fractal array

We report on the unconventional optical properties exhibited by a two-dimensional array of thin Si nanowires arranged in a random fractal geometry and fabricated using an inexpensive,fast and maskless process compatible with Si technology.The structure allows for a high light-trapping efficiency across the entire visible range,attaining total reflectance values as low as 0.1%when the wavelength in the medium matches the length scale of maximum heterogeneity in the system.We show that the random fractal structure of our nanowire array is responsible for a strong in-plane multiple scattering,which is related to the material refractive index fluctuations and leads to a greatly enhanced Raman scattering and a bright photoluminescence.These strong emissions are correlated on all length scales according to the refractive index fluctuations.The relevance and the perspectives of the reported results are discussed as promising for Si-based photovoltaic and photonic applications.

Kinetically-Induced Hexagonality in Chemically Grown Silicon Nanowires

Various silicon crystal structures with different atomic arrangements from that of diamond have been observed in chemically synthesized nanowires.The structures are typified by mixed stacking mismatches of closely packed Si dimers.Instead of viewing them as defects,we define the concept of hexagonality and describe these structures as Si polymorphs.The small transverse dimensions of a nanowire make this approach meaningful.Unique among the polymorphs are cubic symmetry diamond and hexagonal symmetry wurtzite structures.Electron diffraction studies conducted with Au as an internal reference unambiguously confirm the existence of the hexagonal symmetry Si nanowires.Cohesive energy calculations suggest that the wurtzite polymorph is the least stable and the diamond polymorph is the most stable.Cohesive energies of intermediate polymorphs follow a linear trend with respect to their structural hexagonality.We identify the driving force in the polymorph formations as the growth kinetics.Fast longitudinal elongation during the growth freezes stacking mismatches and thus leads to a variety of Si polymorphs.The results are expected to shed new light on the importance of growth kinetics in nanomaterial syntheses and may open up ways to produce structures that are uncommon in bulk materials.

One-step growth of large-area silicon nanowire fabrics for high-performance multifunctional wearable sensors

Silicon nanowire(SiNW)fabrics are of great interest for fabricating high-performance multifunctional wearable sensors.However,it remains a big challenge to fabricate high-quality SiNW fabrics in a simple and efficient manner.Here we report,for the first time,one-step growth of large-area SiNW fabrics for multifunctional wearable sensors,by using a massive metal-assisted chemical vapor deposition(CVD)method.With bulk Sn as a catalyst source,numerous millimeter-long SiNWs grow and naturally interweave with each other,forming SiNw fabrics over 80 cm2 in one experiment.In addition to intrinsic electronic properties of Si materials,the SiNw fabrics also feature high flxibility,good tailorability and light weight,rendering them ideal for fabricating multifunctional wearable sensors.The prototype sensors based on the SiNW fabrics could efectively detect various stimuli including temperature,light,strain and pressure,with outstanding performance among reported multifunctional sensors.We further demonstrate the integration of the prototype sensors onto the body of a robot,enabling its perception to various environmental stimuli.The ability to prepare high-quality SiNW fabrics in a simple and eficient manner will stimulate the development of wearable devices for applications in portable electronics,Internet of Things,health care and robotics.

Integration of silicon nanowires in solar cell structure for efficiencyenhancement: A review

Silicon nanowires (SiNWs) are a one-dimensional semiconductor, which shows promising applications indistinct areas such as photocatalysis, lithium-ion batteries, gas sensors, medical diagnostics, drug delivery,and solar cell. From an implementation point of view, SiNWs are fabricated using either a topdownor bottom-up approach, and SiNWs are both optically and electronically active. SiNWs enhancesthe efficiency of the solar cell due to better electronic, optical, and physical properties that can becontrolled by tuning the physical dimensions of SiNWs. The SiNWs shows an inherent capability to beutilized in radial or coaxial p-n junction solar cells, to stipulate orthogonal photon absorption, antireflection,and enhanced carrier collection. This paper reviews property-control of SiNWs, theirvarious types of incorporation in a solar cell, and the reasons behind enhanced efficiency.

Enhanced photocatalytic activities of silicon nanowires/graphene oxide nanocomposite:Effect of etching parameters

Homogeneous and vertically aligned silicon nanowires(SiNWs)were successfully fabricated using silver assisted chemical etching technique.The prepared samples were characterized using scanning electron microscopy,transmission electron microscopy and atomic force microscopy.Photocatalytic degradation properties of graphene oxide(GO)modified SiNWs have been investigated.We found that the SiNWs morphology depends on etching time and etchant composition.The SiNWs length could be tuned from 1 to 42μm,respectively when varying the etching time from 5 to 30 min.The etchant concentration was found to accelerate the etching process;doubling the concentrations increases the length of the SiNWs by a factor of two for fixed etching time.Changes in bundle morphology were also studied as function of etching parameters.The SiNWs diameter was found to be independent of etching time or etchant composition while the size of the SiNWs bundle increases with increasing etching time and etchant concentration.The addition of GO was found to improve significantly the photocatalytic activity of SiNWs.A strong correlation between etching parameters and photocatalysis efficiency has been observed,mainly for SiNWs prepared at optimum etching time and etchant concentrations of 10 min and 4:1:8.A degradation of92%was obtained which further improved to 96%by addition of hydrogen peroxide.Only degradation efficiency of 16%and 31%has been observed for bare Si and GO/bare Si samples respectively.The obtained results demonstrate that the developed SiNWs/GO composite exhibits excellent photocatalytic performance and could be used as potential platform for the degradation of organic pollutants.

Loose-fit graphitic encapsulation of silicon nanowire for one-dimensional Si anode design

Silicon nanowires(SiNWs) encapsulated with graphene-like carbon sheath(GS) having a void space in between(SiNW@V@GS) are demonstrated for the improved electrochemical performance of Si anode in lithium ion battery. The Si NW@V@GS structure was synthesized by a scalable fabrication method including four successive reactions: metal-catalyzed CVD growth of Si NWs, controlled thermal oxidation, and deposition of the graphitic layer, to form Si NW@SiO_2@GS and additional chemical etching of sacrificial SiO_2 layer between Si NWs and carbon sheath. During the synthetic process, the thickness of the void spacing was controlled by adjusting the oxidation-dependent process. The well-controlled void space and crystalline graphitic carbon sheath of the SiNW@V@GS structure enable good reversible capacity of1444 m Ahg^(-1) and cycling stability of 85% over 150 cycles.

On-demand production of hydrogen by reacting porous silicon nanowires with water

On-demand hydrogen generation is desired for fuel cells,energy storage,and clean energy applications.Silicon nanowires(SiNWs)and nanoparticles(SiNPs)have been reported to generate hydrogen by reacting with water,but these processes usually require external assistance,such as light,electricity or catalysts.Herein,we demonstrate that a porous SiNWs array,which is fabricated via the metal-assisted anodic etching(MAAE)method,reacts with water under ambient and dark conditions without any energy inputs.The reaction between the SiNWs and water generates hydrogen at a rate that is about ten times faster than the reported rates of other Si nanostructures.Two possible sources of enhancement are discussed:SiNWs maintain their high specific surface area as they don’t agglomerate,and the intrinsic strain of the nanowires promotes the reactivity.Moreover,the porous SiNWs array is portable,reusable,and environmentally friendly,yielding a promising route to produce hydrogen in a distributed manner.

A controllable fabrication improved silicon nanowire array sensor on(111)SOI for accurate bio-analysis application

Silicon nanowire field-effect transistor(SiNW-FET)sensors possess the ability of rapid response,real-time,and label-free detection with high sensitivity and selectivity in the analysis of charged molecules.Their nano-scale size makes them well suited for ultralow detection of charged molecules,but also brings the uniformity fabrication challenging,thus limiting their large-scale application.By a horizontal control approach,highly controllable silicon nanowires arrays at the top of the silicon-on-insulator(SOI)wafer(T-SiNW)were developed in our previous work.To further improve the device uniformity,here a novel SiNW fabricated approach was carefully designed by the combination of horizontal and vertical control.The new silicon nanowires appeared at the bottom of the top silicon layer(B-SiNW).The B-SiNW has a relatively low requirement on the fabrication process and better device uniformity compared to T-SiNW.These improvements resulted in the B-SiNW device with a lower current fluctuation(4.1 nA with 5.1%variations)in the flowing liquid,compared to the T-SiNW device(4.4 nA with 11%variations).Further,in quantitative detection of 40 ng/mL MMP-9,the B-SiNW sensors provided larger signals and lower fluctuation(normalized average response value:0.57 with 4.2%variations),compared to the T-SiNW sensors(0.41 with 12.1%variations),thus indicating a more accurate bio-analysis application of the B-SiNW sensor.This work advances the nanowire sensor technology a step closer toward large-scale application to create stable sensing platforms in disease diagnosis and monitoring.

Boosting electrocatalytic selectivity in carbon dioxide reduction:The fundamental role of dispersing gold nanoparticles on silicon nanowires

Carbon dioxide electrochemical reduction(CO_(2)RR)has been recognized as an efficient way to mitigate CO_(2)emissions and alleviate the pressure on global warming and associated environmental consequences.Gold(Au)is reported as stable and active electrocatalysts to convert CO_(2)to CO at low overpotential due to its moderate adsorption strength of^(*)COOH and^(*)CO.The request for improved catalytic performance,however,is motivated by current unsatisfied catalytic selectivity because of the side hydrogen evolution reaction.In this context,the design of Au based binary catalysts that can boost CO selectivity is of great interest.In the present work,we report that Au nanoparticles can be feasibly dispersed and anchored on silicon nanowires to form Au-Si binary nanomaterials.The Au-Si may stably drive CO_(2)RR with a CO Faraday efficiency of 95.6%at−0.6 V vs.RHE in 0.5 mol/L KHCO_(3)solution.Such selectivity outperforms Au particles by up to 61%.Controlled experiments illustrate that such catalytic enhancement can chiefly be ascribed to electronic effects of binary catalysts.Theoretical calculations reveal that spontaneously produced silicon oxide may not only inhibit hydrogen evolution reaction,but also stabilize the key intermediate^(*)COOH in CO formation.

Multi-time scale photoelectric behavior in facile fabricated transparent and flexible silicon nanowires aerogel membrane

In recent years,transparent and flexible materials have been widely pursued in electronics and optoelectronics fields for usage as planar electrodes,energy conversion components and sensing units.As the most widely applied semiconductor material,the related progress in silicon is of great significance although with large difficulty.Herein,we report a one-step method to achieve flexible and transparent silicon nanowires aerogel membrane.A competitive carrier kinetics involving interfacial trapped carriers and the valence electrons transition is demonstrated,according to the photoelectric performance of a sandwiched graphene/silicon nanowires membrane/AI device,i.e.,rapidly positive photoresponse dominated by laser excited^ee-carriers generation(〜500 ms)and subsequent slow negative photocurrent evolution due to laser heating involved multi-levels process(>10 s).These results contribute to fabrication of silicon nanowire self-assembly structures and also the exploration of their optoelectrical properties in flexible and transparent devices.

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

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

Single-electron transport through single and coupling dopant atoms in silicon junctionless nanowire transistor

We investigated single-electron tunneling through single and coupling dopant-induced quantum dots(QDs) in silicon junctionless nanowire transistor(JNT) by varying temperatures and bias voltages. We observed that two possible charge states of the isolated QD confined in the axis of the initial narrowest channel are successively occupied as the temperature increases above 30 K. The resonance states of the double single-electron peaks emerge below the Hubbard band, at which several subpeaks are clearly observed respectively in the double oscillated current peaks due to the coupling of the QDs in the atomic scale channel. The electric field of bias voltage between the source and the drain could remarkably enhance the tunneling possibility of the single-electron current and the coupling strength of several dopant atoms. This finding demonstrates that silicon JNTs are the promising potential candidates to realize the single dopant atom transistors operating at room temperature.

Gate-regulated transition temperatures for electron hopping behaviours in silicon junctionless nanowire transistors

We investigate gate-regulated transition temperatures for electron hopping behaviours through discrete ionized dopant atoms in silicon junctionless nanowire transistors.We demonstrate that the localization length of the wave function in the spatial distribution is able to be manipulated by the gate electric field.The transition temperatures regulated as the function of the localization length and the density of states near the Fermi energy level allow us to understand the electron hopping behaviours under the influence of thermal activation energy and Coulomb interaction energy.This is useful for future quantum information processing by single dopant atoms in silicon.

Application and prospect of semiconductor biosensors in detection of viral zoonoses

The rapid spread of viral zoonoses can cause severe consequences,including huge economic loss,public health problems or even global crisis of society.Clinical detection technology plays a very important role in the prevention and control of such zoonoses.The rapid and accurate detection of the pathogens of the diseases can directly lead to the early report and early successful control of the diseases.With the advantages of being easy to use,fast,portable,multiplexing and cost-effective,semiconductor biosensors are kinds of detection devices that play an important role in preventing epidemics,and thus have become one of the research hotspots.Here,we summarized the advances of semiconductor biosensors in viral zoonoses detection.By discussing the major principles and applications of each method for different pathogens,this review proposed the directions of designing semiconductor biosensors for clinical application and put forward perspectives in diagnostic of viral zoonoses.