Aspect Ratio Of Nanowires Research Articles

Morphology-controlled copper nanowire synthesis and magnetic field assisted self-assembly.

Morphology, dimensions, crystalline structure and compositions of nanomaterials are very critical in determining their unique characteristics. Here we report how the reducing agent concentration affects the surface morphology of copper nanowires and establish the optimized reaction conditions to synthesize high aspect ratio nanowires with a smooth surface. Also, reported is the magnetic field assisted technique to control the orientational and positional ordering of cupronickel nanowires (Cu/Ni NWs) on a large-scale area. A combination of magnetic field, surface derivatization and photolithographic techniques allowed self-assembly of Cu/Ni NWs into channels. The channel resistance as a function of the applied magnetic field during fabrication shows an anomalous decrease owing to the positional end-to-end alignment of NWs. Magnetic field and areal NW density dependence of NW sheet resistance in channels is presented and analyzed using scaling theoretical models.

Insight of surface treatments for CMOS compatibility of InAs nanowires

A CMOS compatible process is presented in order to grow self-catalyzed InAs nanowires on silicon by molecular beam epitaxy. The crucial step of this process is a new in-situ surface preparation under hydrogen (gas or plasma) during the substrate degassing combined with an in-situ arsenic annealing prior to growth. Morphological and structural characterizations of the InAs nanowires are presented and growth mechanisms are discussed in detail. The major influence of surface termination is exposed both experimentally and theoretically using statistics on ensemble of nanowires and density functional theory (DFT) calculations. The differences observed between Molecular Beam Epitaxy (MBE) and Metal Organic Vapor Phase Epitaxy (MOVPE) growth of InAs nanowires can be explained by these different surfaces terminations. The transition between a vapor solid (VS) and a vapor liquid solid (VLS) growth mechanism is presented. Optimized growth conditions lead to very high aspect ratio nanowires (up to 50 nm in diameter and 3 micron in length) without passing the 410 °C thermal limit, which makes the whole process CMOS compatible. Overall, our results suggest a new method for surface preparation and a possible tuning of the growth mechanism using different surface terminations.

Quantum confinement chemistry of CdS QDs plus hot electron of Au over TiO2 nanowire protruding to be encouraging photocatalyst towards nitrophenol conversion and ciprofloxacin degradation

Solar light harvesting science is ascertained to be the topmost effective green technique in alleviating environmental pollutants. In this respect, we report a visible light active TiO2/Au/CdS QDs nanocomposite which manifested upgraded photocatalytic activity towards the transformation of 2-nitrophenol, 4-nitrophenol, and degradation of ciprofloxacin. Here, TiO2 nanowire is synthesized by a molten flux method with high product yield and crystallinity with organized dimensions. Au nanoparticles are successfully integrated in between TiO2-CdS composite by Reverse Turkevich method. The prepared composites are meticulously characterized by different physical and optoelectronic techniques to inspect the crystal structure, phase purity, optical properties, nanostructured morphology and electrochemical properties. The plasmonic direct hot electron transfer (DET) mechanism is confirmed from UV-Vis DRS spectra. The prepared composite produces 2.98 mA/cm2 of current density under light irradiation. A Longer lifetime of electrons is found from Bode phase plot i.e. 97.4 μs for TiO2/1%Au/3%CdS QDs owing to the integrative cooperation effect of high aspect ratio of TiO2 nanowire, quantum size effect of CdS and the direct hot electron transfer by Au nanoparticle.

Recent progress in the synthesis of silver nanowires and their role as conducting materials

Synthesis of silver nanowires got much attention of researchers due to their promising applications in various fields of nanoelectronic devices. Many research articles focusing on silver nanowires synthesis have been reported since past decade. A number of techniques have been applied for successful synthesis of silver nanowires. Solution-based polyol process was proved as a dominant approach to the fabrication of silver nanowires with homogeneity and high aspect ratio. Various inorganic salts have been used in solution-based polyol synthesis of silver nanowires which play a key role in controlling the final morphology of silver nanowires and lead to uniform growth of silver nanowires. The different experimental parameters have been studied, which directly influence the final morphology of silver nanowires. The research on the development of an efficient synthesis approach of silver nanowires is still in progress to accomplish the need of advanced technology for controlled morphology and highest aspect ratio of silver nanowires. Moreover, the unique applications of silver nanowires in conducting polymers composites were discussed.

Single-Crystal Electrochemistry Reveals Why Metal Nanowires Grow

Shape-control is used to tune the properties of metal nanostructures in applications ranging from catalysts to touch screens, but the origins of anisotropic growth of metal nanocrystals in solution are unknown. We show single-crystal electrochemistry can test hypotheses for why nanostructures form and predict conditions for anisotropic growth by quantifying the degree to which different species cause facet-selective metal deposition. Electrochemical measurements show disruption of alkylamine monolayers by chloride ions causes facet-selective Cu deposition. An intermediate range of chloride concentrations maximizes facet-selective Cu deposition on single crystals and produces the highest aspect ratio nanowires in a solution-phase synthesis. DFT calculations similarly show an intermediate monolayer coverage of chloride displaces the alkylamine capping agent from the ends but not the sides of a nanowire, facilitating anisotropic growth.

Morphology control of magnetic properties in cobalt nanowires

Cobalt nanowires with different shapes and sizes were synthesized by reduction of carboxylate salts of CoII in 1, 2-butanediol using a solvothermal chemical process. The well-crystallized Co nanowires with hexagonal close-packed (hcp) phase are observed and the (002) crystalline direction is along the long axis of nanowires. The morphology control is strongly dependent on the reaction parameters. By varying the amount of capping agent in proper ranges, the effect of reaction parameters on controlling the size and shape of Co nanowires is demonstrated. With the amount of capping agent increasing, the aspect ratio of Co nanowires increases remarkably. However, the magnetic measurement of cobalt nanowires shows that the coercivity of the Co nanocrystals does not increase with the increase in aspect ratio monotonously, which suggests that the tip shape and microstructure also play an important role in the magnetization reversal process of the Co nanocrystals, and the aspect ratio plays a much less role as the ratio value exceeds 11. To further understand the effect of size on the magnetic properties in the Co nanowires, micromagnetic simulations were performed, which confirms that the magnetic properties are barely affected by the aspect ratio larger than 10. The highest coercivity of 624 kA·m−1 is obtained for ellipsoid nanowires with a mean length of 200 nm, which also displays a strong magnetic anisotropy. As a result, the highest energy product of the wires reaches 248 kJ·m−3.

Controlled fabrication of Pr(OH)3 nanowires for enhanced photocatalytic activities

In this report, praseodymium hydroxide Pr(OH)3 nanowires with different aspect ratios (length to diameter ratios) were synthesized by a facile hydrothermal approach. The variations in alkali concentration during synthesis are found to form different aspect ratios of nanowires. The X-ray diffraction and Raman spectroscopy analysis demonstrate the absence of any impurity phases in as-prepared materials. Subsequently, photocatalytic activities of as-prepared nanowires were evaluated by the degradation of methyl orange (MO). Our findings reveal that the nanowires with larger aspect ratios have higher photocatalytic efficiency than the smaller aspect ratio samples. X-ray photospectroscopy investigations reveal that the samples with higher aspect ratio are found to exhibit more oxygen vacancies as compared to lower aspect ratio samples. The enhanced photocatalytic activities can be attributed to the presence of higher percentage of active crystal facet (100), higher concentration of defects densities and narrower band gap. Thus, Pr(OH)3 nanowires can be considered as a potential candidate for the application of wastewater treatment and related technologies.

Electrodeposition in Supercritical Fluids

Supercritical fluids possess several characteristics which make them interesting for electrodeposition. Supercritical fluids have low viscosity, allowing fast mass transport and therefore rapid deposition. Additionally, adjusting the pressure and temperature influences the density and viscosity of the solvent, therefore allowing tuning of the solvent properties1 2. Low surface tension and phase separation also allows penetration of electrolyte into porous templates, meaning high aspect ratio nanowires can be deposited, with reported diameters as low as 3 nm3. This is a capability pertinent to the manufacture of the next generation of p-block based electronic devices, such as thermoelectric or phase change memory materials. As the current fabrication methods begin to reach their limits of size and control capabilities, extracting the maximum potential from these materials requires a new approach. Where possible, aqueous conditions remain the most popular for electrodeposition, however its small cathodic limit can put refractory metals out of reach. Supercritical difluoromethane (scR32) is a promising solvent for supercritical electrodeposition. It has a large cathodic limit (-2 V), and a high enough dielectric constant to provide reasonable conductivity, and coordinates poorly with reagents1. Electrodeposition from scR32 has yielded films and nanowires of several p-block metals, including Te, Bi, Sb and Ge4-6. Extending this capability to alloys and compounds is the next challenge. We present an introduction into the practical aspects of electrochemistry in supercritical fluids, often a non-trivial task. We will also present preliminary results concerning electrodeposition from a bismuth and tellurium electrolyte. The films produced were of varying, controlled composition. Bismuth telluride is a thermoelectric material, with the highest known room temperature thermoelectric figure of merit7, and is currently the subject of significant research efforts. The combination of supercritical fluids and electrodeposition holds significant promise for the fabrication of nanostructured materials. This work has been supported by the EPSRC Programme Grant, Advanced Devices by Electroplating (EP/N0354371/1). Work from the EPSRC Programme Grant EP/I013394/1 also contributed. 1 Abbott A. P., Eardley C. A., Tooth R., J. Chem. Eng. Data, 1999, 44, 112 2 Abbott A. P., Hope E. G., Palmer D. J., Anal. Chem., 2005, 77, 6702 3 Ke J. et al., Phys. Chem. Chem. Phys., 2012, 14, 1517 4 Bartlett P. N. et al., Phys. Chem. Chem. Phys., 2014, 16, 9202 5 Bartlett P. N. et al., Chem. Eur. J, 2016, 22, 309 6 Bartlett P. N. et al., RSC Adv., 2017, 7, 40720 7 Rosi F., Abeles B., Jensen R., J. Phys. Chem. Solids, 1959, 10, 191 Figure 1

Environmentally friendly synthesis and formation mechanism of copper nanowires with controlled aspect ratios from aqueous solution with ascorbic acid

Copper (Cu) nanowires (NWs) were synthesized by the reduction of Cu–chloride complexes using ascorbic acid (AA) as a mild reducing agent, polyvinylpyrrolidone (PVP) as a capping agent, and NaCl as an additive under atmospheric conditions at 80 °C. Surface analyses revealed that both Cl ions and PVP were required for the synthesis of Cu NWs. Together, the Cl ions and PVP capped the Cu (1 0 0) side faces, leading to anisotropic growth of Cu NWs along the [1 1 0] direction. To obtain Cu NWs with high aspect ratios, we evaluated the synthetic mechanism under different reaction conditions. The results indicated that the presence of dissolved oxygen (DO) was the dominant factor affecting aspect ratio of Cu NWs. DO and hydrogen peroxide resulting from the reaction between DO and AA oxidized the surfaces of the growing Cu NWs, preventing further growth. Decreasing the amount of oxides on the Cu NW surfaces and removing DO increased the aspect ratios of the Cu NWs. The results indicated that DO should be removed from the reaction solution to obtain high-aspect-ratio Cu NWs in aqueous solutions containing AA.

Effect of elastic modulus mismatch of epoxy/titanium dioxide coated silver nanowire composites on the performance of thermal conductivity

The effect of elastic modulus mismatch of epoxy/silver nanowires (epoxy/AgNWs) composites on thermal conductivity was critically evaluated by synthesizing a stiff titanium dioxide (TiO2) coating on the surface of AgNWs (designated as AgNWs@TiO2) with different length/diameter aspect ratio. Compared to epoxy/AgNWs composites, AgNWs@TiO2 could be more uniformly dispersed in epoxy matrix. However, the TiO2 intermediate layer with a higher elastic modulus increased the modulus mismatch with epoxy, exacerbating the interfacial phonon scattering, and the thermal conductivity of the epoxy/AgNWs@TiO2 composites was decreased. Moreover, the epoxy/AgNWs@TiO2 composites possessed enhanced volume electrical resistivity and reduced dielectric properties relative to the epoxy/AgNWs composites. These observed results on thermal conductivity, electrical insulation, dielectric loss and dielectric constant due to TiO2-coated AgNWs are more prominently displayed at higher nanowire loading (4 vol%) and aspect ratio (1000).

Stable and High Piezoelectric Output of GaN Nanowire-Based Lead-Free Piezoelectric Nanogenerator by Suppression of Internal Screening.

A piezoelectric nanogenerator (PNG) that is based on c-axis GaN nanowires is fabricated on flexible substrate. In this regard, c-axis GaN nanowires were grown on GaN substrate using the vapor-liquid-solid (VLS) technique by metal organic chemical vapor deposition. Further, Polydimethylsiloxane (PDMS) was coated on nanowire-arrays then PDMS matrix embedded with GaN nanowire-arrays was transferred on Si-rubber substrate. The piezoelectric performance of nanowire-based flexible PNG was measured, while the device was actuated using a cyclic stretching-releasing agitation mechanism that was driven by a linear motor. The piezoelectric output was measured as a function of actuation frequency ranging from 1 Hz to 10 Hz and a linear tendency was observed for piezoelectric output current, while the output voltages remained constant. A maximum of piezoelectric open circuit voltages and short circuit current were measured 15.4 V and 85.6 nA, respectively. In order to evaluate the feasibility of our flexible PNG for real application, a long term stability test was performed for 20,000 cycles and the device performance was degraded by less than 18%. The underlying reason for the high piezoelectric output was attributed to the reduced free carriers inside nanowires due to surface Fermi-level pinning and insulating metal-dielectric-semiconductor interface, respectively; the former reduced the free carrier screening radially while latter reduced longitudinally. The flexibility and the high aspect ratio of GaN nanowire were the responsible factors for higher stability. Such higher piezoelectric output and the novel design make our device more promising for the diverse range of real applications.

Nitrogenated Urchin‐like Nb2O5 Microspheres with Extraordinary Pseudocapacitive Properties for Lithium‐Ion Capacitors

AbstractRecently, lithium‐ion capacitors (LICs) combining the complementary characteristics of both lithium‐ion batteries (LIBs) and supercapacitors, have received exhaustive investigation to meet the increasing demands for clean energy. However, their commercial application has been limited by the mismatch of charge‐storage capacity and electrode kinetics between the capacitor‐type cathode and battery‐type anode. Thus, developing a novel high‐power insertion anode material is the key to realizing excellent energy and power densities for LICs. Here, 3D hierarchical Nb2O5 microspheres assembled by surface‐nitrogenated nanowires have been synthesized through a unique anti‐solvent precipitation‐assisted solvothermal route accompanied by a nitrogenization treatment, which can be successfully used for advanced LICs configuration. Owing to the high aspect ratio of ultrathin nanowires, unique pore structures caused by nitridation, improved electronic conductivity, and favorable kinetic stemming from pseudocapacitive behavior, the resultant nitrogenated Nb2O5 microspheres can deliver a high capacity of 205.3 mAh g−1 with remarkable rate capability and long lifespan. When constructed into a new LIC device with peanut‐shell derived carbon (PSC) cathode, an exceptionally high energy density of ∼83.5 Wh kg−1 and a high power density of 10 kW kg−1 with prominent cycling stability are realized. Significantly, the simultaneous manipulation of superstructure design and surface nitrogenization in novel anode material provides new opportunities to boost the energy and power densities for hybrid‐ion capacitors.

Effect of 1D Diffusion Channel Size and Ionic Content on Li+ Ion and Na+ Ion Diffusion in Tunnel Manganese Oxides

In this report, we show how controlling the size and ionic content of 1D diffusion channels in tunnel manganese oxides affects the diffusion of charge-carrying Li+ and Na+ ions. Manganese oxides are of significant interest for Li-ion and Na-ion batteries (LIBs and SIBs, respectively) due to their low cost, environmental friendliness, and high electrochemical activity. Specifically, tunnel manganese oxides are attractive candidates for intercalation-based batteries due to their one-dimensional (1D) diffusion channels built from corner and edge sharing MnO6 octahedra arranged around stabilizing cations and water molecules. Hydrothermal synthesis methods are used to synthesize tunnel manganese oxides with high aspect ratio nanowire morphologies. By controlling the time, temperature, and precursors during hydrothermal synthesis, the size, shape, and ionic content of the tunnels can be carefully controlled. Here, we synthesize three tunnel manganese oxides with different size 1D diffusion channels and ionic content and compare their rate performance in LIBs and SIBs with apparent Li+ ion and Na+ ion diffusion coefficients calculated from the galvanostatic intermittent titration technique (GITT). GITT consists of a repeated sequence of a current pulse to allow a set amount of charge to titrate into the cell, followed by a relaxation period to allow the electrochemical cell to return to equilibrium (Weppner and Huggins, J. Electrochem. Soc., 1977, 124, 1569). From the changes in voltage during each step, the apparent diffusion coefficient of the charge-carrying ion can be calculated. The three different tunnel manganese oxide phases studied are α-MnO2, consisting of 2 octahedra by 2 octahedra tunnels stabilized by K+ ions, todorokite MnO2, consisting of 3xn (n = 3, 4, 5, 6, 7) octahedra tunnels stabilized by Mg2+ ions, and a newly reported phase 2xn-MnO2, which consists of an ordered array of 2x2, 2x3, and 2x4 octahedra tunnels stabilized by Na+ ions. The apparent Li+ and Na+ diffusion coefficients are shown in Figure 1. In LIBs, todorokite MnO2 demonstrates an initial Li+ ion diffusion coefficient of 1e-7 cm2 s-1, an order of magnitude higher than α-MnO2 and 2xn-MnO2. This result indicates the diffusion channels in todorokite MnO2, which are larger than in the other two phases studied, are advantageous for Li+ ion diffusion. This is also reflected in the superior rate performance demonstrated by todorokite MnO2 in LIBs. In SIBs, 2xn-MnO2 demonstrates an initial Na+ ion diffusion coefficient of nearly 1e-7 cm2 s-1, one order of magnitude higher than α-MnO2 and nearly two orders of magnitude higher than todorokite MnO2. This superior Na+ ion diffusion coefficient is supported by the greater capacity demonstrated at higher current rates by the 2xn-MnO2. Thus, despite containing smaller structural tunnels than the tunnels in todorokite MnO2, the 2xn-MnO2 demonstrates more facile Na+ ion diffusion. This observation is attributed to the fact that the 2xn-MnO2 structure is stabilized by Na+ ions that create more well-defined diffusion channels and insertion sites favored by Na+ ions. This is further supported by the Li+ diffusion coefficient for 2xn-MnO2, which is an order of magnitude lower than the Na+ ion diffusion coefficient. Thus, we find that the mobility of charge-carrying ions is not only determined by the size of the 1D diffusion channels in tunnel manganese oxides, but also by the ionic content stabilizing the channels. In summary, by utilizing the GITT, we show how 1D diffusion channel size and ionic content affects the diffusion coefficient of charge-carrying ions in tunnel structured materials. Figure 1

Magnetic Iron Oxide Nanowires Formed by Reactive Dewetting

The growth and reactive dewetting of ultrathin films of iron oxides supported on Re(0001) surfaces have been imaged in situ in real time. Initial growth forms a nonmagnetic stable FeO (wüstite like) layer in a commensurate network upon which high aspect ratio nanowires of several microns in length but less than 40 nm in width can be fabricated. The nanowires are closely aligned with the substrate crystallography and imaging by X-ray magnetic circular dichroism shows that each contain a single magnetic domain. The driving force for dewetting appears to be the minimization of strain energy of the Fe3O4 crystallites and follows the Tersoff and Tromp model in which strain is minimized at constant height by extending in one epitaxially matched direction. Such wires are promising in spintronic applications and we predict that the growth will also occur on other hexagonal substrates.

One-pot rapid synthesis of high aspect ratio silver nanowires for transparent conductive electrodes

Silver nanowires (AgNWs) with high aspect ratio were rapidly one-pot synthesized by a polyol process in the presence of polyvinylpyrrolidone (PVP) as a stabilizer as well as the anisotropic agent, and the corresponding transparent conductive films were prepared by spin-coating method. The effects of PVP molecular weight and concentration on the morphology and aspect ratio of AgNWs were investigated in detail, and the optoelectrical properties of the transparent conductive films were briefly introduced. The presence of PVP induces the growth of silver directed to form high aspect-ratio nanowires by a high anisotropic mode. Appropriate PVP molecular weight and concentration allows the rapid synthesis of AgNWs with the diameter of about 78.2 nm, the length of 79.52 μm and the aspect ratio as high as 1009.2. The as-prepared AgNWs films possess a transmittance of 81.6% and a sheet resistance of 11.36 Ω/sq. The resultant AgNWs with high aspect ratio can be applied to prepare transparent conductive electrodes.

Controlled Synthesis of Uniform Silver Nanowires via a Simple Polyol Process

Uniform silver nanowires were synthesized via a simple polyol process. Different aspect ratio of silver nanowires was obtained by regulating the concentration of ferric chloride and polyvinyl pyrrolidone, the maximum aspect ratio of synthesized silver nanowires is 570. The silver nanowires film with the aspect ratio of 240 was prepared and its conductivity was measured by four probe method. Controlled synthesis of uniform silver nanowires is crucial, silver nanowires will be the most promising material in the optical, electrical and photonic fields.

Nanoparticle-induced inflammation can increase tumor malignancy.

Many different types of nanoparticles have been shown to possess immunomodulatory properties, depending on their physicochemical parameters. This can potentially be harnessed as a possible antitumor therapy. However, in the current work we show that inflammation elicited by nanomaterials can have grave effects in pathophysiological conditions, where non-specific inflammation was found to increase cancer cell mobility and tumor malignancy. These data show that immunomodulatory properties of nanomaterials must be carefully controlled to avoid any undesired side-effects.

Controlled and Selective Growth of 1D and 3D CdTe Nanostructures through a Structurally Engineered Porous Alumina Template for Enhanced Optical Applications

Current manuscript describes porous alumina (PA) template assisted electrodeposition of high aspect ratio nanowires and dense hierarchical structures of CdTe. We demonstrate here for the first time that simple structural engineering of a PA template can lead to electrochemical growth of diverse shapes of CdTe nanostructures. Facile and cost-effective modifications have been implemented for the fabrication of self-organized through-hole PA membrane and its transfer onto any rough substrate. These modifications have facilitated extended duration (30 minute to 1 hour) electrodeposition of CdTe nanostructures at high bath temperature of 60°C without delaminating the PA membrane. High aspect ratio nanowires of 60 nm diameter and 2.8 μm length were growth through the self-ordered PA membrane without any underlying metal coating i.e. without altering its optical properties. An average of 56% optical absorption (within 350 nm – 1400 nm wavelength) and a moderate photoluminescence was observed for the CdTe nanowires. Minor variation in the anodization process resulted into a non-uniform/branched PA template that enabled the formation of dense 3D hierarchical structures of CdTe using similar electrodeposition conditions as that used for CdTe nanowires. The hierarchical CdTe nanostructures exhibited very high total optical absorption of ∼90% within 350 nm – 1400 nm wavelength and a strong photoluminescence was also demonstrated that was almost 10 fold more intense than the CdTe nanowires.

Different growth regimes in InP nanowire growth mediated by Ag nanoparticles

We report on the existence of two different regimes in one-step Ag-seeded InP nanowire growth. The vapor–liquid–solid-mechanism is present at larger In precursor flows and temperatures, ∼500 °C, yielding high aspect ratio and pure wurtzite InP nanowires with a semi-spherical metal particle at the thin apex. Periodic diameter oscillations can be achieved under extreme In supersaturations at this temperature range, showing the presence of a liquid catalyst. However, under lower temperatures and In precursor flows, large diameter InP nanowires with mixed wurtzite/zincblende segments are obtained, similarly to In-assisted growth. Chemical composition analysis suggest that In-rich droplet formation is catalyzed at the substrate surface via Ag nanoparticles; this process might be facilitated by the sulfur contamination detected in these nanoparticles. Furthermore, part of the original Ag nanoparticle remains solid and is embedded inside the actual catalyst, providing an in situ method to switch growth mechanisms upon changing In precursor flow. Nevertheless, our Ag-seeded InP nanowires exhibit overall optical emission spectra consistent with the observed structural properties and similar to Au-catalyzed InP nanowires. We thus show that Ag nanoparticles may be a suitable replacement for Au in InP nanowire growth.

Catalyst-Free Vapor Phase Growth of Ultralong SnSe Single-Crystalline Nanowires

Herein, high quality ultralong tin selenide (SnSe) nanowires (NWs) have been synthesized via physical vapor deposition (PVD) without catalyst. The length of the synthesized SnSe NWs are hundreds of microns and even up to one millimeter, while the mean diameter is about 270 nm, and the aspect ratio of ultralong SnSe NWs can be over 3000. The microstructural characterizations indicate that the SnSe NWs are well-crystallized single crystals with growth direction along the normal {011} planes. The formation of the SnSe NWs is addressed by an oriented one-dimensional growth driven by the dynamic factors in the vapor–solid process. The near-infrared optical band gap of the SnSe NWs has been determined.