Single-crystalline Nanowires Research Articles

On the kinetics of phase transformations of dried porous vaterite particles immersed in deionized and tap water

Calcium carbonate exists in three allotropic forms: vaterite, aragonite and calcite. Metastable vaterite can be easily transformed into calcite and/or aragonite via different routes. We report how dry vaterite particles transform into aragonite and calcite when they are immersed into DeIonized water (DI) or tap water without additives at different temperature (22, 40 and 60 °C) with and without stirring. We show that the transformation rate of vaterite into more stable crystallographic forms is influenced not only by temperature but also by stirring and water purity. Low temperature, absence of stirring and absence of ions in water significantly slow down the kinetics of transformation of vaterite. Additionally, water purity influences the nature of the allotropic phase obtained after transformation. High temperatures and DI water favor the transformation of vaterite into single crystalline nanowires of aragonite, while tap water yields the transformation of vaterite into calcite. The absence of aragonite in tap water at high temperature can be explained by the presence of sulfate ions, which inhibit the formation of this phase. On the contrary, Mg2+ ions tend to stabilize vaterite.

Polar Solvent Induced Lattice Distortion of Cubic CsPbI3 Nanocubes and Hierarchical Self-Assembly into Orthorhombic Single-Crystalline Nanowires.

Despite the recent surge of interest in inorganic lead halide perovskite nanocrystals, there are still significant gaps in their stability disturbance and the understanding of their destabilization, assembly, and growth processes. Here, we discover that polar solvent molecules can induce the lattice distortion of ligand-stabilized cubic CsPbI3, leading to the phase transition into orthorhombic phase, which is unfavorable for photovoltaic applications. Such lattice distortion triggers the dipole moment on CsPbI3 nanocubes, which subsequently initiates the hierarchical self-assembly of CsPbI3 nanocubes into single-crystalline nanowires. The systematic investigations and in situ monitoring on the kinetics of the self-assembly process disclose that the more amount or the stronger polarity of solvent can induce the more rapid self-assembly and phase transition. These results not only elucidate the destabilization mechanism of cubic CsPbI3 nanocrystals, but also open up opportunities to synthesize and store cubic CsPbI3 for their practical applications in photovoltaics and optoelectronics.

Single-crystalline layered metal-halide perovskite nanowires for ultrasensitive photodetectors

Metal-halide perovskites have long carrier diffusion lengths, low trap densities and high carrier mobilities, and are therefore of value in the development of photovoltaics and light-emitting diodes. However, the presence of thermally activated carriers in the materials leads to high noise levels, which limits their photodetection capabilities. Here, we show that ultrasensitive photodetectors can be created from single-crystalline nanowire arrays of layered metal-halide perovskites. A series of nanowires was fabricated in which layer-by-layer self-organization of insulating organic cations and conductive inorganic frameworks, along the nanowire length, creates high resistance in the interior of the crystals and high conductivity at the edges of the crystals. Using these structures, high-performance photodetection was achieved with responsivities exceeding 1.5 × 104 A W−1 and detectivities exceeding 7 × 1015 jones. Our state-of-the-art device performance originates from a combination of efficient free-carrier edge conduction and resistive hopping barriers in the layered perovskites. Photodetectors made from single-crystalline nanowire arrays of layered metal-halide perovskites exhibit detectivities of more than 7 × 1015 jones, due to a nanowire structure that combines high resistance in the interior of the crystals and high conductivity at the edges of the crystals.

Atomic study of effects of crystal structure and temperature on structural evolution of Au nanowires under torsion

The effect of temperature on the structural evolution of nanocrystalline (NC) and single-crystalline (SC) Au nanowires (NWs) under torsional deformation is studied using molecular dynamics simulations based on the many-body embedded-atom potential. The effect is investigated using common neighbor analysis and discussed in terms of shear strain distribution and atomic flow field. The simulation results show that deformation for NC NWs is mainly driven by the nucleation and propagation of dislocations and the gliding of grain boundaries (GBs) and that for SC NWs is mainly driven by dislocations and the formation of disordered structures. Dislocations for NC and SC NWs easily nucleate at GBs and free surfaces, respectively. For NC NWs, torsional buckling occurs easily at GBs with large gliding. SC NWs have a more uniform and larger elastic deformation under torsion compared to that for NC NWs due to the former's lack of grains. SC NWs have a long period of elastic deformation transforming into plastic deformation. Increasing temperature facilitates stress transmission throughout NWs.

Piezoelectrically Enhanced Photocatalysis with BiFeO3 Nanostructures for Efficient Water Remediation

SummaryDesigning new catalysts that can efficiently utilize multiple energy sources can contribute to solving the current challenges of environmental remediation and increasing energy demands. In this work, we fabricated single-crystalline BiFeO3 (BFO) nanosheets and nanowires that can successfully harness visible light and mechanical vibrations and utilize them for degradation of organic pollutants. Under visible light both BFO nanostructures displayed a relatively slow reaction rate. However, under piezocatalysis both nanosheets and nanowires exhibited higher reaction rates in comparison with photocatalytic degradation. When both solar light and mechanical vibrations were used simultaneously, the reaction rates were elevated even further, with the BFO nanowires degrading 97% of RhB dye within 1 hr (k-value 0.058 min−1). The enhanced degradation under mechanical vibrations can be attributed to the promotion of charge separation caused by the internal piezoelectric field of BFO. BFO nanowires also exhibited good reusability and versatility toward degrading four different organic pollutants.

High‐Performance Triphase Bio‐Photoelectrochemical Assay System Based on Superhydrophobic Substrate‐Supported TiO2 Nanowire Arrays

AbstractThe design and fabrication of bio‐photoelectrodes that simultaneously possess rapid charge and gas‐phase mass transport abilities are highly desirable for the development of high‐performance bio‐photoelectrochemical assay systems. Here, a solid–liquid–air triphase bio‐photoelectrode is demonstrated by immobilizing glucose oxidase, a model redox active enzyme, onto 1D single crystalline TiO2 nanowire arrays grown upon a superhydrophobic carbon textile substrate. Based on this triphase bio‐photoelectrode system, oxygen can be directly and constantly supplied from the air phase to sustain enzymatic reactions, leading to much enhanced oxidase kinetics. Further, the photogenerated electrons can transport rapidly and be efficiently collected along the nanowire arrays. The bio‐photoelectrochemical assay system demonstrates a significant wide detection range, high sensitivity, and selectivity as well as a low detection limit. The design principle is generally applicable to the fabrication of other triphase bio‐photoelectrodes, which offers an excellent opportunity for significant advances in environmental analysis and clinical diagnosis.

Investigation of trapping levels in p-type Zn3P2 nanowires using transport and optical properties

Here, we report the synthesis and structural characterization of high-quality Zn3P2 nanowires via chemical vapour deposition. Structural and morphological characterization studies revealed a reliable growth process of long, uniform, and single-crystalline nanowires. From temperature dependent transport and photoluminescence measurements, we have observed the contribution of different acceptor levels (15, 50, 70, 90, and 197 meV) to the conduction mechanisms. These levels were associated with zinc vacancies and phosphorous interstitial atoms which assigned a p-type character to this semiconductor. From time resolved photoluminescence experiments, a 91 ps lifetime decay was found. Such a fast lifetime decay is in agreement with the exciton transition along the bulk emission from high quality crystalline nanowires.

Synthesis and photoluminescence of doped Si3N4 nanowires with various valence electron configurations

In this work, Y-, Ce- and Tb-doped Si3N4 nanowires have been successfully synthesized by directly nitriding-doped nanocrystalline silicon powders obtained by cryomilling. The obtained single-crystalline α-Si3N4 nanowires are nearly 20–50 nm in diameter and up to several micrometers in length. The photoluminescence properties of doped Si3N4 nanowires have also been investigated. The Y-doped Si3N4 nanowires exhibit the main peak at 425 nm, Ce-doped Si3N4 nanowires show a narrow emission peak at 450 nm, and Tb-doped Si3N4 nanowires present a strong and sharp emission peak at 545 nm. Combining with our previous works on Al-, La- and Eu-doped Si3N4 nanowires, the effects of dopants with different valence electron configurations on the photoluminescence properties have been explored. The present study provides a guide to fabricate Si3N4-based nanomaterials for different photonic applications.

Metal-Organic Framework (MOF) Nanorods, Nanotubes, and Nanowires.

New mechanisms for the controlled growth of one-dimensional (1D) metal-organic framework (MOF) nano- and superstructures under size-confinement and surface-directing effects have been discovered. Through applying interfacial synthesis templated by track-etched polycarbonate (PCTE) membranes, congruent polycrystalline zeolitic imidazolate framework-8 (ZIF-8) solid nanorods and hollow nanotubes were found to form within 100 nm membrane pores, while single crystalline ZIF-8 nanowires grew inside 30 nm pores, all of which possess large aspect ratios up to 60 and show preferential crystal orientation with the {100} planes aligned parallel to the long axis of the pore. Our findings provide a generalizable method for controlling size, morphology, and lattice orientation of MOF nanomaterials.

Single crystalline SmB6 nanowires for self-powered, broadband photodetectors covering mid-infrared

Self-powered photodetectors with a broadband response have attracted great attention due to their potential applications in sensing, imaging, communication, and spectroscopy. Specifically, those with the detection wavelength range covering mid-infrared at room temperature are very challenging and highly desired. Here, the photoresponse of self-powered SmB6 photodetectors is demonstrated through the spatially resolved photocurrent mapping. The photocurrent originates from the interface between the SmB6 and Au electrodes due to the charge separation by built-in electric fields at the interface. It exhibits a stable photoresponse over broadband wavelengths ranging from 488 nm to 10.6 μm at room-temperature. Our results suggest that the chemical vapor deposition grown SmB6 nanowires could be promising candidates for future broadband self-powered detectors and pave the way toward SmB6-based optoelectronic applications.

Synthesis and formation mechanism of α-Si3N4 single-crystalline nanowires via direct nitridation of H2-treated SiC fibres

Silicon nitride (Si3N4) nanowires were synthesised using H2-treated SiC fibres as raw materials and a graphite cylinder as the substrate at 1500 °C in N2 atmosphere. The nanowires were characterised by X-ray photoelectron spectroscopy, chemical analysis, X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy, and high-resolution transmission electron microscopy. The results showed that the Si3N4 nanowires have diameters ranging from a few tens to hundreds of nanometres and lengths of several hundred micrometres. The preferred growth direction of the nanowires was (010), and the nanowires comprised single-crystalline α-Si3N4. In addition, the formation mechanism of Si3N4 nanowires was discussed. The free silicon in the H2-treated SiC fibres was found to react with N2 to form Si3N4 nanowires, leading us to speculate that the growth mechanism involves a vapour-solid process.

Fast, green microwave-assisted synthesis of single crystalline Sb2Se3 nanowires towards promising lithium storage

Abstract In this work, a fast (0.5 h), green microwave-assisted synthesis of single crystalline Sb2Se3 nanowires was developed. For the first time we demonstrated a facile solvent-mediated process, whereby intriguing nanostructures including antimony selenide (Sb2Se3) nanowires and selenium (Se) microrods can be achieved by merely varying the volume ratio of ethylene glycol (EG) and H2O free from expensive chemical and additional surfactant. The achieved uniform Sb2Se3 nanowire is single crystalline along [001] growth direction with a diameter of 100 nm and a length up to tens of micrometers. When evaluated as an anode of lithium-ion battery, Sb2Se3 nanowire can deliver a high reversible capacity of 650.2 mAh g−1 at 100 mA g−1 and a capacity retention of 63.8% after long-term 1000 cycles at 1000 mA g−1, as well as superior rate capability (389.5 mAh g−1 at 2000 mA g−1). This easy solvent-mediated microwave synthesis approach exhibits its great universe and importance towards the fabrication of high-performance metal chalcogenide electrode materials for future low-cost, large-scale energy storage systems.

In situ TEM study of the sodiation/desodiation mechanism of MnO2 nanowire with gel-electrolytes

In this work, in situ transmission electron microscopy study of the electrochemical sodiation and desodiation processes was performed in a nanobattery which consisted of a single MnO2 nanowire and different kinds of gel-electrolyte. It is found that after full sodiation, single crystalline MnO2 nanowire is transformed to a mixed nanocrystalline phases of Na2O and MnO, and the following cycles are controlled by the reversible conversion reaction between NaMnO2 and MnO. Both in situ electrochemical test and ex situ battery test show that the glyme-based gel-electrolyte is more suitable for the MnO2 nanowires anode materials. It is also revealed that the MnO2 nanowire expansion ratio strongly depends on the diameter of the nanowires. This work provides a new insight on the sodiation/desodiation mechanism in MnO2 nanowire and gel-electrolyte, and may pave the path for the development of practical sodium-ion batteries with gel-electrolyte.

Carbon-coated single-crystalline LiMn2O4 nanowires synthesized by high-temperature solid-state reaction with high capacity for Li-ion battery

It is a challenge to synthesize highly crystalline nanomorphologies under high-temperature environments. Here, we report that carbon-coated single-crystal LiMn2O4 nanowires were obtained via a high-temperature solid-state method under air environment using carbon-coated MnO2 as the precursor. Without the coated layer of carbon, the obtained LiMn2O4 is bulk. The carbon layer coating on MnO2 acts as a space-limiting layer to maintain the nanowire morphology of the final product of LiMn2O4 during the reaction. Owing to the merits of the highly crystalline, 1D nanowire morphology and the close-coated thin carbon layer, the produced LiMn2O4@C nanowires deliver large capacity and long-term cycling stability. In addition, the space-limiting role of the carbon layer was also found to function for LiMn2O4@C sphere. It is a general strategy to obtain ternary nanomaterials with high crystallinity.

Space selective crystal growth induced single crystalline metal oxide nanowires and their nanodevice applications

Space selective crystal growth induced single crystalline metal oxide nanowires and their nanodevice applications

Controlled synthesis of organic single-crystalline nanowires via the synergy approach of the bottom-up/top-down processes.

The controlled fabrication of organic single-crystalline nanowires (OSCNWs) with a uniform diameter in the nanoscale via the bottom-up approach, which is just based on weak intermolecular interaction, is a great challenge. Herein, we utilize the synergy approach of the bottom-up and the top-down processes to fabricate OSCNWs with diameters of 120 ± 10 nm through stepwise evolution processes. Specifically, the evolution processes vary from the self-assembled organic micro-rods with a quadrangular pyramid-like end-structure bounded with {111}s and {11-1}s crystal planes to the "top-down" synthesized organic micro-rods with the flat cross-sectional {002}s plane, to the organic micro-tubes with a wall thickness of ∼115 nm, and finally to the organic nanowires. Notably, the anisotropic etching process caused by the protic solvent molecules (such as ethanol) is crucial for the evolution of the morphology throughout the whole top-down process. Therefore, our demonstration opens a new avenue for the controlled-fabrication of organic nanowires, and also contributes to the development of nanowire-based organic optoelectronics such as organic nanowire lasers.

Gate-tunable transport characteristics of Bi2S3 nanowire transistors

Electrical transport and resistance noise spectroscopy measurements are performed on individual, single crystalline Bi2S3 nanowires in the field-effect geometry. The nanowires exhibit n-type conduction and device characteristics such as activation energy, ON/OFF ratio, and mobility are calculated over a temperature range of 120–320 K and at several bias values. The noise magnitude is measured between 0.01 and 5 Hz at several gate voltages as the device turns from it's OFF to ON state. The presence of mid-gap states which act as charge traps within the band gap can potentially explain the observed transport characteristics. Sulfur vacancies are the likely origin of these mid-gap states which makes Bi2S3 nanowires appealing for defect engineering as a means to enhance its optoelectronic properties and also to better understand the important role of defects in nanoscale semiconductors.

1D Wires of 2D Layered Materials: Germanium Sulfide Nanowires as Efficient Light Emitters

We considered the formation of one-dimensional (1D) nanowires from the two-dimensional (2D) layered material GeS. Growth by a low-temperature vapor–liquid–solid process over a Au catalyst gives rise to single-crystalline nanowires with typical diameters of ∼100 nm and length exceeding 10 μm that consist of a crystalline GeS core with layering along the nanowire axis, surrounded by an ultrathin, sulfur-rich GeSx shell with larger bandgap that provides chemical and electronic passivation of the nanowires. Combined variable-temperature in situ electron microscopy, chemical mapping, and single-nanowire cathodoluminescence spectroscopy are used to uncover key elements of the growth process and to identify the optoelectronic properties of the GeS/GeSx core–shell nanowires. Our results suggest that vapor–liquid–solid processes can readily be extended from conventional three-dimensional crystals to the growth of 1D wires from 2D layered crystals and may provide novel low-dimensional materials for electronic, opto...

In-situ TEM and XRD analysis of microstructures changes in solution-grown copper silicide nanowires array for field emitters

Pristine polycrystalline copper silicide nanowires were synthesized via facile semi-batch solution reaction on Cu foil at low temperature, 400 °C. Comparing with as-grown products, the annealed (800 °C) Cu3Si nanowires array exhibits excellent field emission properties, the turn-on field was reduced from 1.16 V/μm to 0.40 V/μm and the field enhancement factor (β) was improved from 1400 to 4637. Field emission properties of the annealed copper silicide nanowires show the performance of field emission could be enhanced through the annealing process. In-situ TEM annealing of copper silicide nanowires array was used to investigate the thermal effect on microstructure of copper silicide nanowires. In-situ XRD annealing results provide the phase transformation information at varied temperature and show that the transition phase Cu15Si4 existed to assist in growing single crystalline Cu3Si nanowire. Systemic study can help to realize the solution-phase metal silicide reaction growth mechanism; furthermore, the effect of annealing temperature on nanowires shows the potential towards fabrication of high performance field emission devices.

An atomistic study of the deformation behavior of tungsten nanowires

Large-scale atomistic simulations are performed to study tensile and compressive \(\langle 112\rangle\) loading of single-crystalline nanowires in body-centered cubic tungsten (W). Effects of loading mode, wire cross-sectional shape, wire size, strain rate, and crystallographic orientations of the lateral surfaces are explored. Uniaxial deformation of a W bulk single crystal is also investigated for reference. Our results reveal a strong tension–compression asymmetry in both the stress–strain response and the deformation behavior due to different yielding/failure modes: while the nanowires fail by brittle fracture under tensile loading, they yield by nucleation of dislocations from the wire surface under compressive loading. It is found that (1) nanowires have a higher strength than the bulk single crystal; (2) with a cross-sectional size larger than 10 nm, there exists a weak dependence of strength on wire size; (3) when the wire size is equal to or smaller than 10 nm, nanowires buckle under compressive loading; (4) the cross-sectional shape, strain rate, and crystallographic orientations of the lateral surfaces affect the strength and the site of defect initiation but not the overall deformation behavior.