Aligned Nanowire Arrays Research Articles

Magnetic field-assisted self-assembled aligned nanowires for anisotropic strain sensor with ultrahigh resolution

Flexible anisotropic strain sensors (ASSs) are crucial for comprehending both the magnitudes and directions of complex strains. Some fabrication techniques have been employed to engineer macro-alignments of sensing materials capable of an anisotropic response to strain. However, these sophisticated processes often fail to precisely control the micro-assembly of sensing elements, thereby limiting the sensors’ ability in accurately discerning strains below 0.1 %. Here, we propose an ASS based on an aligned magnetic nanowire array (AMNWA). During the fabrication of AMNWAs, an external magnetic field facilitates the alignment of nanowires in a specific direction, while micro fields of nanowires further induce the construction of end-to-end junctions between nanowires, whose conductivity is susceptible to minimum strains. Consequently, the AMNWA demonstrates a remarkable sensitivity to strains parallel to the aligned direction (Gauge factor > 500), allowing the ASS for the discernment of subtle strains as minuscule as 0.0037 % with a theoretical resolution of 0.001 %. The response of the AMNWA presents extreme anisotropy, with negligible sensitivity to strains perpendicular to the aligned direction. By strategically arranging two AMNWAs orthogonally, the magnitude and direction of complex strains can be effectively decoupled. Notably, this configuration enables accurate recognition of strain signals generated by human joint movements. According to these excellent sensing performances, we hold an optimistic outlook on the potential inspiration and reference of AMNWAs for the design and optimization of ASSs.

Optical analysis of aligned Ni nanowire arrays with different degree of oxidation for terahertz polarizer application

The optical properties of aligned nickel nanowire arrays (NiNWAs) with different degrees of oxidation for terahertz (THz) polarizer applications have been investigated by using THz time-domain spectroscopy. In frequency-domain spectra, the full width at half maxima of transmitted peaks was broadened and the peak positions have a blue shift with increasing oxidation levels, besides the enhancement in peak intensity. It is indicated that the oxidation of Ni nanowires (NWs) has a significant influence on the interaction between Ni NWs and THz wave. The transmittance of the aligned NiNWAs increases with annealing temperature increasing. Conversely, the degree of polarization and extinction ratio (ER) decreases. A corresponding relationship between the change of ER and degree of oxidation is summarized by means of thermogravimetric analysis. The change of ER for the annealing sample with the degree of oxidation of 0.507% is 27.32%, which induced the polarization properties of aligned NiNWAs to be sensitive to the oxidation of Ni NWs. These findings can provide new positive features in the development of future polarization-based device applications for THz electronics and photonics.

Self-Assembly of Silver Nanowire Films for Surface-Enhanced Raman Scattering Applications.

The development of SERS detection technology is challenged by the difficulty in obtaining SERS active substrates that are easily prepared, highly sensitive, and reliable. Many high-quality hotspot structures exist in aligned Ag nanowires (NWs) arrays. This study used a simple self-assembly method with a liquid surface to prepare a highly aligned AgNW array film to form a sensitive and reliable SERS substrate. To estimate the signal reproducibility of the AgNW substrate, the RSD of SERS intensity of 1.0 × 10-10 M Rhodamine 6G (R6G) in an aqueous solution at 1364 cm-1 was calculated to be as low as 4.7%. The detection ability of the AgNW substrate was close to the single molecule level, and even the R6G signal of 1.0 × 10-16 M R6G could be detected with a resonance enhancement factor (EF) as high as 6.12 × 1011 under 532 nm laser excitation. The EF without the resonance effect was 2.35 × 106 using 633 nm laser excitation. FDTD simulations have confirmed that the uniform distribution of hot spots inside the aligned AgNW substrate amplifies the SERS signal.

Facile Construction of Three-Dimensional Architectures of a Nanostructured Polypyrrole on Carbon Nanotube Fibers and Their Effect on Supercapacitor Performance

Conducting polymer and carbon nanotube hybrids have been researched intensively in recent years for electrodes of fiber-shaped supercapacitors (FSSCs) toward flexible and wearable energy storage devices. Here, three-dimensional (3D) hierarchical polypyrrole (PPy)/carbon nanotube fiber (CNTF) architectures have been prepared by a facial electrodeposition method for flexible FSSC electrodes. PPy nanoparticles, vertically aligned nanowire arrays (VANAs), and nanowire networks were synthesized on CNTFs, respectively, to construct three types of 3D architectures by controlling the electrodeposition condition of PPy. The influence of the 3D architectures of PPy/CNTF electrodes on the performance of the assembled quasi-solid-state FSSCs has been carefully studied. The FSSCs with PPy VANAs showed a much higher specific capacitance than that with PPy nanoparticles because the hierarchical porous structure of PPy VANAs provides a higher accessibility of electrolytic ions and a higher Coulombic efficiency than that with the PPy nanowire network. The PPy VANA-/CNTF-based FSSCs displayed high flexibility, stability, and a specific capacitance of 178.14 F g–1 at 0.4 A g–1, which is much higher than that based on common PPy cauliflower-like film/CNTF electrodes (92.06 F g–1) and pure CNTF electrodes (8.48 F g–1) under the same conditions, demonstrating the great advantages of the 3D hierarchical structure.

Chemical vapor etching of silicon wafer for the synthesis of highly dense and aligned sub-5 nm silicon nanowire arrays

We investigated the key chemical vapor etching parameters governing the morphology of Si nanowires. Highly aligned sub-5 nm Si nanowires can be achieved by controlling the oxidant gas concentration, reaction temperature, and hydrogen concentration.

Line‐Shaped Laser Lithography for Efficiently Fabricating Flexible Transparent Electrodes with Hierarchical Metal Grids across λ/10 to Microscale

AbstractHierarchical metal grids are proven to be a promising solution for achieving high‐performance flexible transparent electrodes (FTEs) due to their significantly enhanced conductivity without noticeably sacrificing transparency. This work develops a one‐step mask‐free line‐shaped laser lithography by separated pulse laser ablation to efficiently fabricate large‐area FTEs composed of hierarchical metal grids, namely microscale grids interconnected with aligned nanowire arrays. The linewidth of aligned wires is highly controllable from the nanometer scale far beyond the diffraction limit (<λ/10) to the micrometer scale. This work experimentally studies the overall performance of FTEs to provide a guideline for selecting the layout and feature sizes of hierarchical metal grids. Hierarchical metal grids with 50 nm nanowires aligned inside the microscale grids show outstanding optoelectronic properties and mechanical stability, with sheet resistance of 4.6 Ω sq−1, transmittance of 82.9%, and a tiny increase in sheet resistance less than 4% after 1000 cycles of bending tests. These results prove that the line‐shaped laser lithography technique is a facile, low‐cost, and high‐throughput fabrication method for high‐performance FTEs.

Langmuir‐Blodgett Assembly to order Nanoparticles and Colloidal Objects

Bottom-up assembly of nanoparticles and colloidal objects pose a formidable challenge when processing devices. Speed, compatibility with various materials, defect tolerance and cost effectiveness are among the desired properties of a suitable nanoscale assembly process. In this regard, the Langmuir‐Blodgett (LB) technique is a highly sought-after candidate which aids in arranging a large number of nanostructures on solid surfaces. This mini-review aims to provide a concise account on the LB technique and four distinct ways of how it allows to assemble systems made of nanoparticles and colloidal objects: namely, close-packed nanoparticle superlattices by compression, micrometer scale nanoparticle fingering patterns by dip coating, single nanoparticle lines by stick-slip deposition and one-step patterning of aligned nanowire arrays.

Light Trapping of Inclined Si Nanowires for Efficient Inorganic/Organic Hybrid Solar Cells.

Light/matter interaction of low-dimensional silicon (Si) strongly correlated with its geometrical features, which resulted in being highly critical for the practical development of Si-based photovoltaic applications. Yet, orientation modulation together with apt control over the size and spacing of aligned Si nanowire (SiNW) arrays remained rather challenging. Here, we demonstrated that the transition of formed SiNWs with controlled diameters and spacing from the crystallographically preferred <100> to <110> orientation was realized through the facile adjustment of etchant compositions. The underlying mechanism was found to correlate with the competing reactions between the formation and removal of oxide at Ag/Si interfaces that could be readily tailored through the concentration ratio of HF to H2O2. By employing inclined SiNWs for the construction of hybrid solar cells, the improved cell performances compared with conventional vertical-SiNW-based hybrid cells were demonstrated, showing the conversion efficiency of 12.23%, approximately 1.12 times higher than that of vertical-SiNW-based hybrid solar cells. These were numerically and experimentally interpreted by the involvement of excellent light-trapping effects covering the wide-angle light illuminations of inclined SiNWs, which paved the potential design for next-generation optoelectronic devices.

Epitaxial growth of aligned MgO nanowire arrays on a single crystalline substrate.

MgO nanostructures with different morphologies were fabricated by regulating the composition of raw materials, using the chemical vapor deposition method with gold as a catalyst. Polycrystalline MgO nanopillars were prepared using only Mg3N2 as the raw material. Single crystalline nanowire arrays can be obtained by adding carbon powder into the raw material. X-ray diffraction, scanning electron microscopy, and transmission electron microscopy were used for the detailed characterization of (100) nanowire arrays. Besides the vertical growth direction [100], the nanowires change into two kinds of orientations after growing to a certain length: 〈111〉 and 〈001〉. The epitaxial growth was attributed to the lattice match and regulation of the concentration of the Mg source. The variation of growth orientations was probably caused by the difference in surface energy and reaction temperature.

Multidimensional Aligned Nanowires Array: Toward Bendable and Stretchable Strain Sensors

Micropatterns based on the oriented nanowires have attracted research interests for their unique physicochemical advantages in various applications of electric microdevices. Here, we proposed a facile fibrous dewetting strategy by spreading and dewetting of the silver nanowire (AgNW) solution on the vertical aligned carbon nanotube array (ACNTs) for preparing multidimensional aligned nanowires array, based on the elastocapillary coalescence. The unidirectional shrinking of the liquid film on the top of ACNTs happens during the dewetting process, as a result of the elastocapillary coalescence of ACNTs, which drives the AgNWs aligned along normal direction of liquid film shrinkage on the top of ACNTs. Thus, a multidimensional aligned NWs array was prepared, composing of the horizontally oriented NWs of top layer and vertical ACNT bundles of under layer connected by CNT yarns. A bendable flexible electrode was prepared using the as-prepared multidimensional aligned nanowires array, showing high stability during bending cycles (1800 cycles). Moreover, the multidimensional aligned nanowires array is also applicable for fabricating strain sensors, which show stable resistance response under strain. We envision that the as-developed approach shed new light on easy manufacture NW-based micropatterns.

Influence of wet etching in KOH on defects in silicon nanowires formed by cryogenic dry etching

The work is devoted to exploration of arrays of vertical aligned silicon nanowires (SiNWs) obtained by cryogenic dry etching in ICP mode with height of 4.5-5.5 μm and aspect ratio of 7. It was shown that geometry of nanowires has crucial influence on rate of wet etching in KOH since it is higher for 3D objects than for planar wafer, and the diameter should be the same along the nanowire for controlled wet etching. Wet etching in 4% KOH solution during 30 s allowed to save array of uniformity vertical aligned SiNWs with height of 4 μm and diameter of 500 nm. Such treatment reduced concentration of defects detected by deep-level transient spectroscopy, particularly, it drops as minimum in two times for deep level with £0=0.68-0.74 eV placed near to surface of wafer.

Ultrahigh energy storage density at low operating field strength achieved in multicomponent polymer dielectrics with hierarchical structure

Dielectric composites with excellent capacitive energy storage capabilities have great potential applications in energy storage capacitors operating efficiently at relatively low field strengths. Herein, unlike the traditional methods via the introduction of fillers including randomly distributed ceramic nanofibers and aligned nanowires arrays into the monolayer films are simply to increase the energy storage density (Ue), both Ue and charge–discharge efficiency (η) at low electric field strengths have been improved in tri-layered all-polymer films owing to the synergistic effect of multiple interbedded interfaces and deliberately modulation of linear dielectric poly(methyl methacrylate) (PMMA) contents. The effects of film structure on the energy storage capabilities have been comparatively discussed. Consequently, an ultrahigh Ue of 15 J cm−3 accompanied with great η of 76.5% has been delivered in the resulting tri-layered film via optimizing the PMMA content (30 wt%) of out layers at 350 MV m−1, surpassing the energy storage upper limits of the reported polymer dielectrics that show the Ue of ~12 J cm−3 and η of ~70% at comparable electric fields of 310–380 MV m−1. Along with high pulsed power density, multicomponent polymer dielectrics with hierarchically structure provide an effective paradigm for achieving the low operating field strength applications of capacitive energy storage devices with excellent energy storage capability.

Stable clusters array of silicon nanowires developed by top-plating technique as a high-performance gas sensor

For a gas sensor based on aligned nanowires array, effective extraction of sensing signals produced by all of nanowires is extremely crucial to harvest high response magnitude. In this work, a stable clusters array of silicon nanowires arrays (SiNWs) with a unique aggregation interconnection (AI) configuration was proposed to boost the sensing performances of the corresponding sensor. The stable AI structure was achieved by Cu2O top-plating technique via multiple spin-coating of Cu2+ and HF solution on SiNWs. The top-plating treatment produces a unique and stable clusters array of vertical SiNWs with obvious tip AI structure of nanowires in different clusters. And the as-formed AI array is proved to be highly effective as a gas sensor in achieving highly sensitive and stable response and low detection limit at room temperature. Compared with the pristine SiNWs sensor, the AI-SiNWs sensor displayed ~64-fold enhancement in response value to 1 ppm NO2, and the limit detection concentration of NO2 gas deducted by the experiment data is 5.4 ppb. The satisfactory sensing-performances can be interpreted effectively in terms of the effectiveness of the unique AI array in extraction of electronic response signal of SiNWs sensing units and reduction of substrate resistance influence from Cu2O soldering.

Solar-blind ultraviolet photodetector based on vertically aligned single-crystalline β-Ga2O3 nanowire arrays

Abstract Vertically aligned nanowire arrays, with high surface-to-volume ratio and efficient light-trapping absorption, have attracted much attention for photoelectric devices. In this paper, vertical β-Ga2O3 nanowire arrays with an average diameter/height of 110/450 nm have been fabricated by the inductively coupled plasma etching technique. Then a metal-semiconductor-metal structured solar-blind photodetector (PD) has been fabricated by depositing interdigital Ti/Au electrodes on the nanowire arrays. The fabricated β-Ga2O3 nanowire PD exhibits ∼10 times higher photocurrent and responsivity than the corresponding film PD. Moreover, it also possesses a high photocurrent to dark current ratio (I light/I dark) of ∼104 and a ultraviolet/visible rejection ratio (R 260 nm/R 400 nm) of 3.5 × 103 along with millisecond-level photoresponse times.

(Invited) Nanopatterning Functional Metal Oxide Nanostructures By Vapor-Phase Infiltration in Polymer Templates

Infiltration synthesis is a process technique derived from atomic layer deposition (ALD), where polymeric templates, such as those lithographically patterned and self-assembled, are infiltrated by vapor-phase inorganic precursors to form novel organic-inorganic hybrids with enhanced materials properties. These hybrids can be further transformed by selectively removing the organic matrix to finally form metal oxide nanostructures with morphology and positional registry as dictated and designed by the starting polymer templates. In this talk, I will highlight a few examples of our recent efforts to generate functional inorganic nanostructures by using infiltration synthesis including, patterning arbitrary metal oxide nanostructures with sub-40 nm linewidth and over 15 aspect ratio, structural characteristics extremely difficult to achieve by conventional microfabrication techniques; fully CMOS compatible, wafer-scale synthesis and integration of in-plane aligned ZnO nanowire array phototransistors; and three-dimensional (3D) ZnO nanomesh structures derived from self-assembled block copolymer (BCP) templates with layer-number-dependent percolative electrical conductance.

Growth of aligned SnS nanowire arrays for near infrared photodetectors

Aligned SnS nanowires arrays were grown via a simple chemical vapor deposition method. As-synthesized SnS nanowires are single crystals grown along the [111] direction. The single SnS nanowire based device showed excellent response to near infrared lights with good responsivity of 267.9 A/W, high external quantum efficiency of 3.12 × 104 % and fast response time. Photodetectors were built on the aligned SnS nanowire arrays, exhibiting a light on/off ratio of 3.6, and the response and decay time of 4.5 and 0.7 s, respectively, to 1064 nm light illumination.

High extinction ratio terahertz broadband polarizer based on the aligned Ni nanowire arrays.

We present a broadband terahertz (THz) polarizer based on the stacks of aligned Ni nanowire (NW) arrays. We demonstrated that the polarizer has an extinction ratio of 58.8 dB and an average extinction ratio of 46.6 dB throughout a frequency range of 0.3-2.3 THz. Compared to carbon-nanotube and metallic wire-grid polarizers, our Ni-NW polarizers with rapid, reliable, low-cost fabrication processes are ideal candidates for emerging THz technologies.

Photo electrochemical ability of dense and aligned ZnO nanowire arrays fabricated through electrochemical anodization

In the present study, dense and aligned zinc oxide nanowire arrays annealed at 350 °C, with an average diameter of 99 ± 6 nm measured from histogram by Lorentz curve fitting, are fabricated through electrochemical anodization in a potassium bicarbonate aqueous solution at room temperature. During anodization, a transition in the surface morphology from nanoflowers to aligned nanowires with respect to growing time was observed. Photocurrent density of as fabricated ZnO nanowires were studied using three-electrode electrochemical cell using aqueous 1.0 M of Na2SO4 electrolyte and was found to be 30 μA/cm2 which indicates its competence to be used in UV–visible driven photoelectrode material applications.

Vertical-Aligned Silicon Nanowire Arrays with Strong Photoluminescence Fabricated by Metal-Assisted Electrochemical Etching

Metal-assisted chemical etching of silicon is a commonly used method to fabricate vertical aligned silicon nanowire arrays. In this report we show that if in the above method the chemical etching is replaced by the electrochemical one, we can also produce silicon nanowire arrays, but with a special characteristic-extremely strong photoluminescence. Further research showed that the huge photoluminescence intensity of the silicon nanowire arrays made by metal-assisted electrochemical etching is related to the anodic oxidation of the silicon nanowires which has occurred during the electrochemical etching. It is most likely that the luminescence of the silicon nanowire arrays made with metal-assisted electrochemical etching is the luminescence of silicon nanocrystallites (located on the surface of silicon nanowire fibers) embedded in a silicon oxide matrix, similar to that in a silicon rich oxide system.

Enhanced electron acceleration in aligned nanowire arrays irradiated at highly relativistic intensities

We report a significant enhancement in both the energy and the flux of relativistic electrons accelerated by ultra-intense laser pulse irradiation (>1 × 10 21 W cm−2) of near solid density aligned CD2 nanowire arrays in comparison to those from solid CD2 foils irradiated with the same laser pulses. Ultrahigh contrast femtosecond laser pulses penetrate deep into the nanowire array creating a large interaction volume. Detailed three dimensional relativistic particle-in-cell simulations show that electrons originating anywhere along the nanowire length are first driven towards the laser to reach a lower density plasma region near the tip of the nanowires, where they are accelerated to the highest energies. Electrons that reach the lower density plasma experience direct laser acceleration up to the dephasing length, where they outrun the laser pulse. This yields an electron beam characterized by a 3× higher electron temperature and an integrated flux 22.4× larger respect to foil targets. Additionally, the generation of >1 MeV photons were observed to increase up to 4.5×.