Diameter Of Nanowires Research Articles

Performance analysis of ITO-free PEDOT:PSS/InP nanowire hybrid solar cell

InP nanostructure based solar cells (SCs) offer high efficiency with reduced material requirement when compared to their planar/thin-film SCs. In order to further reduce the cost and improve the effectiveness of nanostructured SCs, a new approach by combining the organic and inorganic materials in the active layer has been developed. In this study, we have replaced the indium tin oxide (ITO) with PEDOT:PSS as the transparent conducting oxide since its sheet resistance is virtually comparable to that of ITO and exhibits almost similar performance as an electrode. Geometrical parameters such as diameter (D) of InP nanowire (NW) and coating thickness (T) of PEDOT:PSS are optimized by FDTD technique to achieve best absorption and optical current density (Jsc). It is observed that for PEDOT:PSS/InP NWSCs with 160 nm of InP NW diameter and coating thickness of 80 nm for PEDOT:PSS, optical current density of 34.2 mA/cm2 is achieved, which is better than the ITO/InP NWSCs. Electrical analysis of PEDOT:PSS/p-InP/n-InP NW homojunction SCs using Charge Solver Module revealed that the power conversion efficiency (PCE) of ∼ 24% can be attained with the proposed nanostructures through a carrier lifetime of 1 ns, surface recombination velocity (SRV) of 103 cm/s of InP NW (at n-InP and p-InP interface) and core doping of 5 × 1018 cm−3. We also found out that conformally coated NWs outperform fully infiltrated NW structures in terms of optical and electrical performance.

Enhanced performance of a flexible and wearable piezoelectric nanogenerator using semi-insulating GaN:Mg/ZnO coaxial nanowires

Flexible piezoelectric nanogenerators (PNGs) with high power-conversion efficiency are of great interest. Here, we propose wearable PNGs based on pristine magnesium (Mg)-doped GaN (GaN:Mg) and GaN:Mg/ZnO coaxial nanowires (NWs) exhibiting state-of-the-art high-voltage and -current outputs. The PNGs were designed to suppress internal screening by a reduction in the diameter of the NWs, successful incorporation of Mg in GaN NWs as a p-type dopant, and deposition of a ZnO shell on the GaN:Mg NWs. The Fermi-level pinning reduces free carriers in thin NWs (diameter up to ~30 nm). By tuning the size of the metal–alloy catalyst, we obtained NWs with diameters ranging from 30 to 50 nm. To deplete the NWs fully of free carriers, Mg is incorporated without activation, which enhanced the resistance of GaN:Mg NWs by forming inactive Mg–H complexes. The flexible PNG fabricated with pristine GaN:Mg NWs exhibited the maximum output voltage and current of 52 V and 23 µA, respectively. The junction current screening was suppressed by depositing a ZnO shell with an optimized thickness of 10 nm on GaN:Mg NWs. The PNG fabricated with GaN:Mg/ZnO coaxial NWs showed an enhanced output voltage and current of 66 V and 40 µA and demonstrated a state-of-the-art high power density of 170 µW/cm2 at an optimum load resistance of 2.5 MΩ. When mounted on the wrist as a wearable healthcare monitoring device, it successfully detected the movement of tendons and muscles as soon as the fingers were moved and exhibited a corresponding change in voltage response. Additionally, the charging of a capacitor is proven by the PNG under continuous foot tapping, demonstrating its potential to charge energy storage devices by walking or jogging.

Detailed examination of domain wall types, their widths and critical diameters in cylindrical magnetic nanowires

Understanding and mastering the magnetic properties of domain walls in cylindrical nanowires is a fundamental pillar for developing novel 3D information technologies. For this purpose, a good comprehension of domain wall (DW) dynamical properties, which are strongly dependent on its type and size, is needed. In this work, by means of micromagnetic simulations, we focus on the accurate determination of DW types (transverse, vortex-antivortex, and the Bloch point) and DW widths and present a state diagram as a function of the diameter and the nanowire material. Using different initial states and trajectories we find a large region of metastability where the Bloch-point domain wall co-exists with either transverse or a more energetical vortex-antivortex one. We determine the domain wall width and its dependence on the nanowire diameter either for the transverse or the vortex-antivortex domain wall showing that it is always larger than the nanowire diameter. We also find simple expressions for the DW widths and the critical diameter for the transition between different DW types which agree well with direct simulations. Our results are useful for the experimental design of cylindrical nanowires for multiple applications.

Copper Nanowire Arrays: Growth and Properties

Cu nanowire arrays of three different diameters have been synthesized via template assisted electrode position technique. Morphological, structural, optical, electrical and field emission properties were examined for these three nanowire arrays. Morphological study reveals the nanowire arrays are of uniform diameter throughout the length and of desired dimensions. Structural study shows the face centred cubic structure of nanowires. The crystallite size has been calculated using the Debye-Scherrer relation and micro strain has been calculated using Williamson-Hall analysis. The surface plasmon resonance absorption peak shifts towards red end with increase in diameter of nanowires. I-V characteristics show the ohmic behaviour. Electron field emission properties of Cu nanowire arrays have been studied using Fowler Nordheim theory. The field emission parameters like maximum emission current density, turn on field and field enhancement factor have been calculated for nanowire arrays of different diameters. Cu nanowire arrays of diameter 50 nm exhibit better field emission properties, indicating that thin nanowire arrays have great potential to be used as field emitters.

Silicon Nanowires: A Breakthrough for Thermoelectric Applications.

The potentialities of silicon as a starting material for electronic devices are well known and largely exploited, driving the worldwide spreading of integrated circuits. When nanostructured, silicon is also an excellent material for thermoelectric applications, and hence it could give a significant contribution in the fundamental fields of energy micro-harvesting (scavenging) and macro-harvesting. On the basis of recently published experimental works, we show that the power factor of silicon is very high in a large temperature range (from room temperature up to 900 K). Combining the high power factor with the reduced thermal conductivity of monocrystalline silicon nanowires and nanostructures, we show that the foreseen figure of merit could be very high, reaching values well above 1 at temperatures around 900 K. We report the best parameters to optimize the thermoelectric properties of silicon nanostructures, in terms of doping concentration and nanowire diameter. At the end, we report some technological processes and solutions for the fabrication of macroscopic thermoelectric devices, based on large numbers of silicon nanowire/nanostructures, showing some fabricated demonstrators.

Diameter dependent thermodynamics of adsorption on nanowires: A theoretical and experimental study

Because the influencing mechanism and regularity of diameter on the adsorption thermodynamics of nanowires are still unclear, the relations of adsorption thermodynamic properties of different diameters of nanowires is derived. Experimentally, we prepared CeO2 nanowires with different diameters, and then the adsorption selectivity of CeO2 nanowires to different dyes was researched. The adsorption thermodynamic properties of dyes with the best adsorption selectivity were determined, and the influences of the diameter on the adsorption thermodynamic properties were discussed. The experimental results show that the adsorption capacity for congo red is the strongest and that for methylene blue is the weakest. In addition, with the decreases of diameter of CeO2 nanowires, the adsorption capacity and the adsorption Equilibrium constant increase, while ΔadsGmo, ΔadsHmo and ΔadsSmo decrease, and this thermodynamic properties are linearly related to the reciprocal of diameter, respectively. The experimental results agree with the thermodynamic theory of nanowire adsorption.

Microstructure and mechanical properties of SiC/SiC joints reinforced by in-situ growth SiC nanowires

A novel two-step joining technology (pyrolysis and C-Si reaction bonding) was used to prepare the SiC/SiC joints with SiC nanowire reinforcements. The microstructure and phase composition of joining layers and joints were characterized, and the effects of pyrolysis temperature, SiC particle size, polycarbosilane content and filler ratio (C/SiC) were investigated. The results indicated that when the temperature was lower than melting point of catalyst, the formation mechanism of SiC nanowires was vapor-solid growth (VS); conversely, the formation mechanism was vapor-liquid-solid growth (VLS). With the increase of SiC particle size, the quantity and diameter of SiC nanowires increased and the thickness of interlayer was slightly smaller. The higher the polycarbosilane content, the thinner the as-prepared interlayer would be. The phases of joints consisted of 6H-SiC and the mixture of 3C-SiC and free Si. The highest flexural strength of joined samples can reach 289 ± 60 MPa and 368 ± 44 MPa at room temperature and 1200 °C, respectively.

Sunlight driven improved photocatalytic activity of Mn doped SnO2 nanowires

Sn1-xMnxO2 (x = 0, 0.1, 0.2 and 0.3) were successfully synthesized by simple Co-precipitation technique. The influence of Mn dopant on the crystal structure, surface morphology, optical, magnetic and electrical properties of SnO2 were investigated by various techniques like XRD, IR, TG/DSC, SEM, TEM, EDX, DRS, photoluminescence, magnetic susceptibility and electrical resistivity. XRD pattern reveal formation of tetragonal structure for undoped and Mn doped SnO2. SEM and TEM images of Mn doped SnO2 revealed formation of nanowires of different diameter and length. Mn substitution in SnO2 crystal lattice leads to widening of band gap and paramagnetic behavior. The photocatalytic activity was evaluated by the degradation of Naphthol Blue Black dye under solar light. Enhanced photocatalytic efficiency is exhibited by Sn0·7Mn0·3O2 within 180 min time. 92% reduction in COD value and presence of inorganic ions indicate complete mineralization of the NBB dye. Antibacterial activity of SnO2 towards gram positive and gram negative bacteria is also enhanced with Mn doping.

Wafer-Scale Synthesis and Optical Characterization of InP Nanowire Arrays for Solar Cells.

Nanowire solar cells have the potential to reach the same efficiencies as the world-record III–V solar cells while using a fraction of the material. For solar energy harvesting, large-area nanowire solar cells have to be processed. In this work, we demonstrate the synthesis of epitaxial InP nanowire arrays on a 2 inch wafer. We define five array areas with different nanowire diameters on the same wafer. We use a photoluminescence mapper to characterize the sample optically and compare it to a homogeneously exposed reference wafer. Both steady-state and time-resolved photoluminescence maps are used to study the material’s quality. From a mapping of reflectance spectra, we simultaneously extract the diameter and length of the nanowires over the full wafer. The extracted knowledge of large-scale nanowire synthesis will be crucial for the upscaling of nanowire-based solar cells, and the demonstrated wafer-scale characterization methods will be central for quality control during manufacturing.

Formation of nanoporous Ge layers by ion implantation at different temperatures of c-Ge substrate

The flat monocrystalline c-Ge wafers implanted by 108Ag + ions with the energy E = 30 keV, dose D = 1.3·1016 ion/cm2 and at current density J = 5 μA/cm2 for various substrate temperatures from 25 to 400 °C were studied. By scanning electron microscopy and optical reflection spectroscopy it was found that as a result of ion implantation in the temperature range from 25 to 300 °C an amorphous porous Ag:PGe layers of a spongy structure consisting of Ge nanowires on the c-Ge substrate surface are formed. The diameter of Ge nanowires increases from 16 to 24 nm with a rising of substrate temperature. It is shown that at the highest temperature of 400 °C, the porous structure does not form and the Ge surface remains flat on which the formation of Ag nanoparticles can be observed. A change in the level of the sample surface in dependence on substrate temperature due to swelling up to 280 °C was replaced by effective ion sputtering at higher temperatures.

Sensitivity and linearity enhanced wide-detection range surface-plasmon-resonance photonic-crystal-fiber sensor

A refractive-index (RI) sensor based on photonic crystal fiber (PCF) and surface plasmon resonance (SPR) is proposed and demonstrated in this paper. The influences induced by the changes of the diameter of gold nanowire, air-hole spacing, diameter of central hole and diameter of the air hole on both sides of central hole are investigated to analyze and optimize the performances of the SPR-PCF sensor. It is indicated that the proposed sensor is suitable for the detection of the RI of material in the range from 1.15 to 1.45. Moreover, the optimized RI sensitivity can reach −5893.9 nm/RIU and the optimized R2 can be larger than 0.999. Detections of the alcohol with different concentrations are carried out to demonstrate the performance of the SPR-PCF. The sensitivities in both polarization directions are −192 nm/% and −198 nm/% when the concentration is changed from 10% to 87%. Moreover, the sensitivities for RI-detection are −5900 nm/RIU and −6116 nm/RIU with the corresponding R2 larger than 0.9993 in both polarization-directions. Our detailed results will help to understand the SPR phenomenon in hexagonal PCF, and promote the realization and application of SPR-PCF sensors.

Tailoring Morphology and Vertical Yield of Self-Catalyzed GaP Nanowires on Template-Free Si Substrates.

Tailorable synthesis of III-V semiconductor heterostructures in nanowires (NWs) enables new approaches with respect to designing photonic and electronic devices at the nanoscale. We present a comprehensive study of highly controllable self-catalyzed growth of gallium phosphide (GaP) NWs on template-free silicon (111) substrates by molecular beam epitaxy. We report the approach to form the silicon oxide layer, which reproducibly provides a high yield of vertical GaP NWs and control over the NW surface density without a pre-patterned growth mask. Above that, we present the strategy for controlling both GaP NW length and diameter independently in single- or two-staged self-catalyzed growth. The proposed approach can be extended to other III-V NWs.

Strong coupling of a plasmonic nanoparticle to a semiconductor nanowire

Abstract By placing a single Au nanoparticle on the surface of a cadmium sulfide (CdS) nanowire, we demonstrate strong coupling of localized surface plasmon resonance (LSPR) modes in the nanoparticle and whispering gallery modes (WGMs) in the nanowire. For a 50-nm-diameter Au-nanosphere particle, strong coupling occurs when the nanowire diameter is between 300 and 600 nm, with a mode splitting up to 80 meV. Using a temperature-induced spectral shift of the resonance wavelength, we also observe the anticrossing behavior in the strongly coupled system. In addition, since the Au nanosphere has spherical symmetry, the supported LSPR mode can be selectively coupled with transverse electric (TE) and transverse magnetic (TM) WGMs in the nanowire. The ultracompact strong-coupling system shown here may provide a versatile platform for studying hybrid “photon–plasmon” nanolasers, nonlinear optical devices, and nanosensors.

Simulated synthesis of silica nanowires by lyotropic liquid crystal template method

ABSTRACT Dissipative particle dynamics simulations were adopted to study the mechanism of lyotropic liquid crystal (LLC) formation and the synthesis process of silica nanowires by LLC template method. Simulation results show that the one-dimensional (1D) LLC channel can be formed at the Pluronic F127 concentration range of 61 ∼ 67%. With the increase of Pluronic F127 concentration, the diameter of LLC channel decreases and the deformation degree increases. The effect of PEO: PPO ratio on the diameter of LLC channel is slight. The appropriate PEO: PPO ratio of Pluronic is 40:70 for the formation of 1D LLC channel, as the deformation degree of channel is the smallest in this case. The effect of polymerisation degree on the diameter and deformation degree of LLC channel is both little. With the increase of TEOS concentration, the nanowire diameter increases rapidly at first, and then increases quite slowly. This work can provide guidance for silica nanowires synthesis by LLC template method.

α-MnO2 Nanowires as Potential Scaffolds for a High-Performance Formaldehyde Gas Sensor Device

Herein, we report a chemi-resistive sensing method for the detection of formaldehyde (HCHO) gas. For this, α-MnO2 nanowires were synthesized hydrothermally and examined for ascertaining their chemical composition, crystal phase, morphology, purity, and vibrational properties. The XRD pattern confirmed the high crystallinity and purity of the α-MnO2 nanowires. FESEM images confirmed a random orientation and smooth-surfaced wire-shaped morphologies for as-synthesized α-MnO2 nanowires. Further, the synthesized nanowires with rounded tips had a uniform diameter throughout the length of the nanowires. The average diameter of the α-MnO2 nanowires was found to be 62.18 nm and the average length was ~2.0 μm. Further, at an optimized temperature of 300 °C, the fabricated HCHO sensor based on α-MnO2 nanowires demonstrated gas response, response, and recovery times of 19.37, 18, and 30 s, respectively.

Morphology characterization and growth of GaAs nanowires on Selective-area substrates

Gold (Au)-catalyzed and catalyst-free gallium arsenide (GaAs) nanowires (NWs) were grown on GaAs substrates with mask patterns by metal–organic chemical vapor deposition (MOCVD). Catalyst-free GaAs NWs with hexagonal prism morphology were observed by scanning electron microscopy (SEM). The growth rate of catalyst-free GaAs NWs was reduced to nearly 5.5% of that of NWs grown using a vapor–liquid–solid (VLS) mechanism. By coating Au as a catalyst on selective-area substrates with the same thickness of Au film, an increased growth was observed. The diameter of the Au-catalyzed NWs grown on selective-area substrates was roughly reduced to 40%, resulting in multiple NWs being squeezed into the same hole. GaAs NWs with cylindrical geometry on selective-area substrates were produced by adjusting the thickness of the Au film, and thus, a single NW could be contained in one hole as the Au film thickness increased.

Hybrid ZnO/MoS2 Core/Sheath Heterostructures for Photoelectrochemical Water Splitting

The rational synthesis of semiconducting materials with enhanced photoelectrocatalytic efficiency under visible light illumination is a long-standing issue. ZnO has been systematically explored in this field, as it offers the feasibility to grow a wide range of nanocrystal morphology; however, its wide band gap precludes visible light absorption. We report on a novel method for the controlled growth of semiconductor heterostructures and, in particular, core/sheath ZnO/MoS2 nanowire arrays and the evaluation of their photoelectrochemical efficiency in oxygen evolution reaction. ZnO nanowire arrays, with a narrow distribution of nanowire diameters, were grown on FTO substrates by chemical bath deposition. Layers of Mo metal at various thicknesses were sputtered on the nanowire surface, and the Mo layers were sulfurized at low temperature, providing in a controlled way few layers of MoS2, in the range from one to three monolayers. The heterostructures were characterized by electron microscopy (SEM, TEM) and spectroscopy (XPS, Raman, PL). The photoelectrochemical properties of the heterostructures were found to depend on the thickness of the pre-deposited Mo film, exhibiting maximum efficiency for moderate values of Mo film thickness. Long-term stability, in relation to similar heterostructures in the literature, has been observed.

Effects of gold film thickness and annealing time on diameter of silicon nanowires grown by VLS process

In this paper, silicon nanowires were prepared by chemical vapor deposition (CVD) in the presence of gold catalyst. We discussed the effects of gold film thickness and annealing time on droplet diameter and silicon nanowire diameter. The study revealed that the diameter of silicon nanowires increases with the increase of the thickness of the gold film. With the increase of annealing time, the number of alloy droplets decreases, and the diameter increases. The average diameter of silicon nanowires decreases first and then increases. The results provide useful information for long-time annealing of silicon nanowires.

Tuning surface-enhanced Raman scattering activity of silver nanowires

Silver nanostructure has excellent surface-enhanced Raman scattering (SERS) properties. However, the influence of the diameter of silver nanowires on the SERS is still unclear. To this end, four Ag NWs with diameters of 20, 25, 31, and 38 nm were designed and fabricated. The effects of diameter on the SERS were studied experimentally and simulated theoretically. The results indicate that the SERS activities of the Ag NWs increase with the diameter within a certain range. The highest EF value is up to 5.0 × 109. These results may provide a reference for the design of high-performance Ag NWs SERS substrates.

Fabrication and characterization of GaN-based nanostructure field effect transistors

Two different types of GaN-based nanostructure FETs, such as FinFETs and gate-all-around (GAA) nanowire FETs, have been investigated along with discussing their important performances for a possible new application. The GaN-based FinFETs have better electrostatic control compared to conventional planar-type GaN-based HEMTs, which offers great performance improvement such as very low off-state leakage current, high breakdown voltage, high linearity with broad transconductance. Recent investigation demonstrated that an appropriately designed AlGaN/GaN-FinFETs could exhibit low saturation drain voltage and very fast switching characteristics with subthreshold swing of sub-60 mV dec, which indicates that they can be a promising candidate for low voltage/power logic application. GAA GaN nanowire FETs have even better electrostatic control and exhibit excellent device performances showing their potential low voltage/power logic applications. For clear understanding of the device performances, simulation including two models concerning the multi-level trapping effects and the self-heating effects has been conducted, which leads to good agreement with the experimental results. Negative transconductance and offset-like output characteristics, observed in the narrow nanowire devices, have been well explained using the deep trapping effect and the built-in potential at ohmic contact. Scaling of the nanowire FET has been implemented such as channel length, doping concentration, and diameter of nanowire, which helps to predict further improvement of the device performance.