Ultrathin Nanowires Research Articles

A Library of Rare Earth Oxide Ultrathin Nanowires with Polymer‐Like Behaviors

AbstractUltrathin nanowires (NWs) have always attracted the attention of researchers due to their unique properties, but their facile synthesis is still a great challenge. Herein we developed a general method for the synthesis of rare earth (RE) oxide ultrathin NWs at atmospheric pressure and low temperature (50 °C). The formation mechanism of ultrathin NWs lies in two aspects: thermodynamic advantage of one dimensional (1D) growth at low temperature, and supplement of effective monomers. As an extension, fifteen kinds of RE oxide ultrathin NWs were synthesized through this strategy, and they all exhibited polymer‐like behaviors. Meanwhile, the high viscosity, organic gel, wet‐ and electro‐spinning of Ce‐Mo‐O NWs were studied in detail, demonstrating the similarity of ultrathin inorganic NWs to polymers. In addition, the Ce‐Mo‐O ultrathin NWs were used as photocatalysts for toluene oxidation and showed excellent performance with toluene conversion ratio of 83.8 %, suggesting their potential application in organic photocatalysis.

Ultra‐Confined Catalytic Growth Integration of Sub‐10 nm 3D Stacked Silicon Nanowires Via a Self‐Delimited Droplet Formation Strategy (Small 42/2022)

Droplet Control In article number 2204390, Linwei Yu and co-workers successfully demonstrate stacked growth integration of ultrathin silicon nanowires, with width and height of Wnw = 9.9 ± 1.2 nm (down to 8 nm) and Hnw = 18.8 ± 1.8 nm approaching to the critical-dimension of 10 nm technology node, thanks to a self-delimited droplet control strategy, with tunable channel cross-sections, which are ideal candidates for monolithic 3D integration of logic-in-memory and neuromorphic applications.

High-Resolution Electron Tomography of Ultrathin Boerdijk-Coxeter-Bernal Nanowire Enabled by Superthin Metal Surface Coating.

The rapid advancement of transmission electron microscopy has resulted in revolutions in a variety of fields, including physics, chemistry, and materials science. With single-atom resolution, 3D information of each atom in nanoparticles is revealed, while 4D electron tomography is shown to capture the atomic structural kinetics in metal nanoparticles after phase transformation. Quantitative measurements of physical and chemical properties such as chemical coordination, defects, dislocation, and local strain have been made. However, due to the incompatibility of high dose rate with other ultrathin morphologies, such as nanowires, atomic electron tomography has been primarily limited to quasi-spherical nanoparticles. Herein, the 3D atomic structure of a complex core-shell nanowire composed of an ultrathin Boerdijk-Coxeter-Bernal (BCB) core nanowire and a noble metal thin layer shell deposited on the BCB nanowire surface is discovered. Furthermore, it is demonstrated that a new superthin noble metal layer deposition on an ultrathin BCB nanowire could mitigate electron beam damage using an in situ transmission electron microscope and atomic resolution electron tomography. The colloidal coating method developed for electron tomography can be broadly applied to protect the ultrathin nanomaterials from electron beam damage, benefiting both the advanced material characterizations and enabling fundamental in situ mechanistic studies.

Ultra-Confined Catalytic Growth Integration of Sub-10nm 3D Stacked Silicon Nanowires Via a Self-Delimited Droplet Formation Strategy.

Fabricating ultrathin silicon (Si) channels down to critical dimension (CD) <10nm, a key capability to implementing cutting-edge microelectronics and quantum charge-qubits, has never been accomplished via an extremely low-cost catalytic growth. In this work, 3D stacked ultrathin Si nanowires (SiNWs) are demonstrated, with width and height of Wnw = 9.9 ± 1.2 nm (down to 8nm) and Hnw = 18.8 ± 1.8 nm, that can be reliably grown into the ultrafine sidewall grooves, approaching to the CD of 10nm technology node, thanks to a new self-delimited droplet control strategy. Interestingly, the cross-sections of the as-grown SiNW channels can also be easily tailored from fin-like to sheet-like geometries by tuning the groove profile, while a sharply folding guided growth indicates a unique capability to produce closely-packed multiple rows of stacked SiNWs, out of a single run growth, with the minimal use of catalyst metal. Prototype field effect transistors are also successfully fabricated, achieving Ion/off ratio and sub-threshold swing of >106 and 125mV dec-1 , respectively. These results highlight the unexplored potential of versatile catalytic growth to compete with, or complement, the advanced top-down etching technology in the exploitation of monolithic 3D integration of logic-in-memory, neuromorphic and charge-qubit applications.

A combined TEM and SAXS study of the growth and self-assembly of ultrathin Pt nanowires

Ultrathin Pt nanowires possess high activity for various electrocatalytic applications. However, little work has focused on understanding their growth mechanisms. Herein, we utilize a combination of time-dependent, ex situ transmission electron microscopy (TEM) and small angle x-ray scattering (SAXS) techniques to observe the growth process in addition to associated surfactant-based interactions. TEM images indicate that initially nanoparticles are formed within 30 s; these small ‘seed’ particles quickly elongate to form ultrathin nanowires after 2 min. These motifs remain relatively unchanged in size and shape up to 480 min of reaction. Complementary SAXS data suggests that the initial nanoparticles, which are coated by a surfactant bilayer, arrange into a bcc superlattice. With increasing reaction time, the bcc lattice disappears as the nanoparticles grow into nanowires, which then self-assemble into a columnar hexagonal structure in which the individual nanowires are covered by a CTAB monolayer. The hexagonal structure eventually degrades, thereby leading to the formation of lamellar stacking phases comprised of surfactant bilayers. To the best of our knowledge, this is the first time that SAXS has been used to monitor the growth and self-assembly of Pt nanowires. These insights can be used to better understand and rationally control the formation of anisotropic motifs of other metallic nanostructures.

Room-Temperature Interconversion Between Ultrathin CdTe Magic-Size Nanowires Induced by Ligand Shell Dynamics.

The formation mechanisms of colloidal magic-size semiconductor nanostructures have remained obscure. Herein, we report the room temperature synthesis of three species of ultrathin CdTe magic-size nanowires (MSNWs) with diameters of 0.7 ± 0.1 nm, 0.9 ± 0.2 nm, and 1.1 ± 0.2 nm, and lowest energy exciton transitions at 373, 418, and 450 nm, respectively. The MSNWs are obtained from Cd(oleate)2 and TOP-Te, provided diphenylphosphine and a primary alkylamine (RNH2) are present at sufficiently high concentrations, and exhibit sequential, discontinuous growth. The population of each MSNW species is entirely determined by the RNH2 concentration [RNH2] so that single species are only obtained at specific concentrations, while mixtures are obtained at concentrations intermediate between the specific ones. Moreover, the MSNWs remain responsive to [RNH2], interconverting from thinner to thicker upon [RNH2] decrease and from thicker to thinner upon [RNH2] increase. Our results allow us to propose a mechanism for the formation and interconversion of CdTe MSNWs and demonstrate that primary alkylamines play crucial roles in all four elementary kinetic steps (viz., monomer formation, nucleation, growth in length, and interconversion between species), thus being the decisive element in the creation of a reaction pathway that leads exclusively to CdTe MSNWs. The insights provided by our work thus contribute toward unravelling the mechanisms behind the formation of shape-controlled and atomically precise magic-size semiconductor nanostructures.

Ultrathin gold nanowires as broadband saturable absorbers for ultrashort pulsed lasers

Ultrathin gold nanowires (UGNWs) with a diameter of ⩽2 nm have attracted much attention because of their high aspect ratios, unusual physical properties and potential applications in nanoelectronics, sensors and photonics. Despite recent advances on UGNWs and the related devices, nonlinear optical properties of UGNWs and their application on photonic devices (e.g. ultrashort pulsed lasers) remain largely unexplored. Here we show that UGNWs can be used as broadband saturable absorbers (SAs) for constructing ultrashort pulsed lasers with an operating wavelength range from near-infrared to mid-infrared (MIR). UGNWs are prepared by using a silane-mediated approach, and then mixed with polyvinyl alcohol to form the UGNWs film. The UGNWs film not only show strong absorption from visible to MIR spectral region (over 25 μm), but also possess the nonlinear saturable absorption properties in the spectral region. As the UGNWs film SA is inserted into an erbium or thulium doped silica fiber laser cavity, stable passively mode-locked lasers at 1562.2 or 1970 nm with a pulse width of a few hundreds of femtoseconds is obtained, respectively. Especially, by inserting the UGNWs film SA into a holmium/praseodymium codoped fluoride fiber laser cavity, stable passively mode-locked laser at 2864 nm is achieved. Our results show that the UGNWs film are promising SAs for constructing broadband ultrashort pulsed lasers.

Defect-Rich and Single-Crystalline PdCu Ultrathin Nanowires Promoting Ethanol Oxidation Electrocatalysis

Developing high-performance electrocatalysts for the ethanol oxidation reaction (EOR) is greatly significant for the practical application of direct ethanol fuel cells, but it is still unsatisfactory. In this manuscript, we reported a facile aqueous synthesis of PdCu ultrathin nanowires (UNWs) as a highly active and stable electrocatalyst for EOR electrocatalysis. The synthesis relied on the columnar nucleation of PdCu alloys via co-reduction of Pd and Cu precursors in an aqueous solution with a highly hydrophobic dioctadecyldimethylammonium chloride as the structure-directing surfactant. PdCu UNWs featured ultrathin diameter (∼3.2 nm), defect-rich surface (high-index site), single-crystalline structure, and well-alloyed composition. They disclosed the remarkable mass activity of 3.02 A mgPd–1 and the good chronoamperometric and cycling stability for EOR electrocatalysis, both of which are better than its counterpart catalysts and commercial Pd/C. Mechanism studies further confirmed that PdCu UNWs had much better diffusion ability and lower activation energy based on their structural and compositional add-in synergies.

Synthesis of Ultrathin AuPt Alloy Porous Nanowires with Abundant Electrocatalytic Active Sites for Excellent Electrocatalysts

Synthesis of Ultrathin AuPt Alloy Porous Nanowires with Abundant Electrocatalytic Active Sites for Excellent Electrocatalysts

Alkynyl ligands-induced growth of ultrathin nanowires arrays

Ligands are almost essential in the synthesis of nanostructures. In this work, we introduce the alkynyl ligands into the synthesis of ultrathin gold (Au) nanowires arrays. The strong binding affinity of the alkynyl ligands enables one-dimensional (1D) growth via the active surface growth mechanism. The scope of the ligand generality was systematically investigated, and the alkynyl ligand-induced nanowire growth processes were compared and contrasted with those involving thiolated ligands. While strong ligands are usually difficult to dissociate from the nanostructure surface and therefore problematic for post-synthetic processing, the alkynyl ligands are readily dissociable, making the alkynyl ligand-stabilized Au nanowires potentially more modifiable and applicable. As a demonstration, direct palladium (Pd) deposition on the Au nanowires was successfully carried out without any ligand exchange process.

Tuning Catalytic Activity in Ultrathin Bimetallic Nanowires Via Surface Segregation: Application in Electrochemical Methanol Oxidation

The reaction kinetics and efficiency in any catalytic process is controlled by the adsorption and desorption of reactant and intermediates on the surface of catalyst. As a consequence, the surface properties, composition and geometry of the catalyst dictates the mechanism of reactions. The surface electronic structure is modulated by variations in surface and subsurface atomic configurations, e.g., ordering and surface segregation, which in turn can vividly affects catalytic properties.1,2 A great deal of efforts are being devoted to develop efficient heterogenous catalyst by critically controlling the surface structure and chemistry. Here, I would like to present results on two different strategies for controlling the surface composition in ultrathin bimetallic AuPd nanowires. Au nanowire template-based method was used to grow AuPd wires by gradually increasing the amount of Pd.3 Percentage of composition of Au and Pd in AuPd nanowires gave either alloy nanowires with Au-rich compositions or core-shell structure at higher Pd compositions with Au-rich core and Pd-rich shell. Surface morphology of alloyed nanowires were induced through segregation of Pd to the surface by annealing under controlled CO atmosphere. High resolution microscopic imaging was possible due to the fact of substantial difference in the atomic number between Au and Pd. Electrocatalytic methanol oxidation reaction (MOR) in alkaline medium is important for energy conversion and was selected to study the catalytic activity of AuPd nanowires. A nearly monotonic increase of MOR potential was observed with increase in Pd content. Interestingly, a typical volcano type behavior of the specific activity was observed with different composition and with 40 and 50% Pd samples showed the optimum values in terms of current, potential and If/Ib values. Owing to a higher Pd content of CO-annealed nanowires, a lowering of potential was observed though the specific activity was maintained. These findings provide clear strategies to independently control the reaction potential and the activities of nanocatalysts with smaller amounts of the expensive active metal. The compositional effects on the electronic structure of the AuPd nanowires (catalyst surface) as well as binding energy of intermediates involved in the MOR was investigated using DFT calculations. d-band center analysis was employed to check interaction of CO* which a major intermediate of MOR with the catalyst surface. The theoretical investigation align well with the experimental results where it was found that the MOR potential increases with increasing amount of Pd and for the Au rich case the reaction does not reach up to CO2 but yields HCHO as a product at lower potentials. From our experimental finding it was evident that it is possible to lower the MOR potential to attain comparable or better activity through enrichment with the precious metal on the surface while essentially dropping the real quantity used.

Cold welding of ultrathin metallic glass nanowires with side-to-side contact using molecular dynamics simulations

Cold welding can effectively join a wide variety of components, forming high quality assemblies. In this work, the cold welding behaviors of Cu-Zr metallic glass nanowires (MGNWs) in the form of side-to-side contact are investigated by molecular dynamics simulation. The mechanical performance of the welded MGNW is inspected by uniaxial tensile tests. Cold welding processes of MGNWs with various sizes and under different welding conditions are explored. Our results show that the strength of the welded MGNW at 50 K is less than 60% of that of the crude nanowire. At the same welding velocity, the change of welding time within a certain range does not influence the welding quality obviously. The increase in overlap width makes the welded MGNW stronger. The enhancement of welding temperature facilitates the atom diffusion activity, and thus strengthens the contact regions, improving the welding quality. We also compare the side-to-side contact and head-to-head contact cold welding. It is found that the former endows the welded MGNW with lower strength but better plasticity. This work provides a preliminary theoretical guideline on the cold welding of MGNWs for further experiments and to facilitate the engineering practice of cold welding.

Surface Coordination Decouples Hydrogenation Catalysis on Supported Metal Catalysts

Surface Coordination Decouples Hydrogenation Catalysis on Supported Metal Catalysts

Polarization-dependent photoluminescence properties of fab-compatible nanowire-based nanophotonic structures

Semiconductor nanowires show great potential for controlling light–matter interactions. Moreover, their polarization-dependent optical properties, primarily enabled by their dielectric mismatch, are a significant requisite for a plethora of emerging applications spanning from polarized photodetection to quantum photonics and quantum communication. Herein, we study the polarization dependence of photoluminescence (PL) properties from fab-compatible nanophotonic structures, comprising arrays of ultrathin (20 nm) silicon carbide nanowires (NWs) doped with oxygen and erbium ions. Polarization-resolved PL studies demonstrate a significant excitation polarization anisotropy (∼0.7) of the visible NW PL for light polarized parallel and perpendicular to the NWs' long axis. This anisotropic behavior agrees with our simulations and with the classical dielectric contrast model and is consistent across the investigated periodicity range of the NW arrays. Furthermore, the effect of this anisotropy on the NW carrier dynamics is explored through power-dependence and transient PL measurements. We have observed a faster carrier lifetime for light polarized parallel to the NWs than the perpendicular polarization. Finally, we demonstrate a translation of this polarization dependence to the technologically significant erbium-induced 1540 nm emission from the erbium centers in the NW arrays. The ability to engineer emission polarization and placement of these centers in the NW array offers a promising platform for emission enhancement of telecom emitters through effective coupling to optical nanocavities for applications in chip-scale photonics and quantum photonics.

A simulation study of polarization characteristics of ultrathin CsPbBr3 nanowires with different cross-section shapes and sizes

The polarization characteristics of ultrathin CsPbBr3 nanowires are investigated. Especially, for the height of cross-section of nanowires between 2 nm and 25 nm, the normalized intensity and polarization ratio ρ of CsPbBr3 nanowires with triangular, square and hexagonal cross-section shapes are compared. The results show that, along with the increase of the height of cross-section, the polarization ratios of these three nanowires decrease until T = 15 nm, and increase afterwards. Also, along with the increase of the cross-section area up to 100 nm2, the polarization ratios of these three nanowires increase too. In general, for the same height or area, the polarization ratio ρ of these nanowires follows ρ hexagon > ρ square > ρ triangle. Therefore, the nanowire with the hexagonal cross-section should be chosen, where for a cross-section height of 2 nm and a length-height ratio of 20:1, the maximal polarization ratio is 0.951 at the longitudinal center of the NW. Further, for the hexagonal NW with a cross-section height of 10 nm, the hexagonal NW with a length-height ratio of 45:1 exhibits the maximal polarization ratio at the longitudinal center of the NW. These simulation results predict the feasible size and shape of CsPbBr3 nanowire devices with high polarization ratios.

Facile Surface Modification of Ultrathin Gold Nanowires Film with Hydrogen Sulfide for Improvement of Stability

Ultrathin gold nanowires (AuNWs) have an important role and promising applications in areas of wearable sensors, matter detection, and flexible transparent electronic materials. But oleylamine (OAm) ligand on the ultrathin AuNWs surface leads to high junction resistance and the inherent Rayleigh instability leads to decomposition into gold spheres within a few days. To eliminate these two disadvantages, herein, the implementation of one facile H2S gas treatment method to improve the conductivity and stability of ultrathin AuNWs is tried. The conductivity of AuNWs on the interdigital electrode can be improved by 4 × 107 times because the AuNWs became bent and cross‐linked, due to the H2S exchange of the ligand OAm. In addition, the conductivity of the three‐layer ultrathin AuNW film on polyethylene terephthalate (PET) can be improved by at least 2000 times. The ultrafine structure of AuNWs can be maintained for more than 1 week at room temperature, which attributes to H2S that can protect the surface structure of AuNWs. The findings highlight a new method of the ultrathin AuNWs for exceeding improvement in electronic conduction and stability.

Ultrathin Sb2Se3 Nanowires for Polarimetric Imaging Photodetectors with a High Signal/Noise Ratio

AbstractThis work presents a study on the optical applications of chemical vapor deposition‐grown Sb2Se3 nanowires in polarized single nanowire photodetectors. High‐quality Sb2Se3 nanowires are obtained with diameters as small as ≈15 nm, which is the first report for ultrathin Sb2Se3 nanowires. The fabricated Sb2Se3 nanowire‐based photodetector presents a low shot noise of ≈ 9 × 10–16 A Hz–1/2, a large signal/noise ratio of 1436.55, a high responsivity of 3.61 A W–1, and a high specific detectivity of 2.36 × 1011 Jones, which can be attributed to the high‐quality crystalline nanowires obtained. More interestingly, the Sb2Se3 nanowire‐based photodetectors exhibit broadband polarized photoresponse to incident light with wavelengths ranging from visible to near‐infrared (532 – 830 nm). A linearly dichroic ratio of 1.71 is obtained for the 830 nm light illumination. The Sb2Se3 nanowire detectors also present appropriate polarimetric imaging quality, revealing the potential of Sb2Se3 nanowires for polarimetric imaging applications.

Characterization of ultrathin superconducting FeSe nanowires on SrTiO3 substrates

Superconducting quantum devices, due to their ultra-low power consumption, high sensitivity and high speed, have attracted great attention in recent years and put forward higher requirements for fabrication technology. Here, we report on the first superconducting ultrathin FeSe nanowires on SrTiO3 substrates successfully fabricated by electron beam lithography and Ar plasma ion beam etching. As the superconductivity of the molecular beam epitaxial ultrathin FeSe film is highly susceptible by moisture and oxygen, FeTe layers were deposited for protection. We synthesized a superconducting ∼300 nm wide, ∼1.1 nm thick ultrathin FeSe nanowire with (the critical temperature of zero resistance), as revealed by electrical transport measurements. The proper synthesis conditions of the high-quality ultrathin superconducting FeSe nanowires on SrTiO3 substrates are evaluated by analyzing the morphology and physical properties of the ∼300 nm width ultrathin FeSe nanowire. Our work may pave the way for future applications of air-sensitive iron-based superconducting films.

Boosting the Photocatalytic H2 Evolution and Benzylamine Oxidation using 2D/1D g-C3N4/TiO2 Nanoheterojunction.

The present research aims at the elevation of solar-to-chemical energy conversion with extortionate performance and sustainability. The nanostructured materials are revolutionizing the water splitting technology into decoupled hydrogen with simultaneous value-added organic chemical production. Yet, the bottleneck in semiconductor photocatalysis is rapid charge recombination and sluggish reaction kinetics. Herein, we demonstrate an efficient and non-noble metal-based catalyst for successful redox reaction with a theoretical modeling through density functional theory (DFT) study. Implementing this robust approach on 2D/1D ultrathin g-C3N4 nanosheets and TiO2 nanowires heterojunction, we achieved H2 production of 5.1 mmol g-1 h-1 with apparent quantum efficiency of 7.8% under visible light illumination and 93% of benzylamine conversion to N-benzylidene benzylamine in situ. The interface of 2D g-C3N4 nanosheets and 1D nanowires provide ample active sites and extends the visible light absorption with requisite band edge position for the separation of photoinduced charge carriers with superior stability. The electronic properties, band structure, and stability of the heterojunction are further investigated via DFT calculations which corroborate the experimental results and in good agreement for the enhanced activity of the heterojunction.

Electronic state tuning over Mo-doped W18O49 ultrathin nanowires with enhanced molecular oxygen activation for desulfurization

Developing catalyst with abundant surface active sites is the core issue to achieve efficient catalytic oxidative desulfurization performance. In this work, Mo doped W18O49 ultrathin nanowires is fabricated through solvothermal method to provide plentiful low coordinated metal atoms around oxygen vacancies to trigger oxidative desulfurization reaction. As a non-stoichiometric oxide, the discorded lattice microstructure in W18O49 endows the formation of O vacancies neighboring low-valence W atoms, while the ultrathin structure ensure the fully exposure of surface atoms. Moreover, the doped Mo atoms will tune the surface atomic structure and electronic state of W18O49 nanowires, leading to the higher oxygen vacancy concentration and strengthened interaction with target sulfide molecules. Benefiting from these features, the higher molecular oxygen activation capacity can be realized over Mo-W18O49 nanowires to yield more superoxide radicals, making it with greatly improved oxidative desulfurization performance. The optimized 2 %Mo-W18O49 catalyst shows nearly 100% removal of dibenzothiophene within 5 h and maintain the good cycle stability. This work supply new insights for the design of catalytic sites towards selective catalytic oxidative desulfurization.