Single-crystal Nanostructures Research Articles

Sm2Co17 nanoparticles synthesized by surfactant-assisted high energy ball milling

Synthesis of rare-earth-based magnetically hard single-crystal nanoparticles with significant magnetic properties and large quantities is highly challenging. Surfactant-assisted high energy ball milling (HEBM) is usually used for the preparation of separated Sm–Co-based hard nanoparticles. In this study, Sm2Co17 hard nanoparticles have been synthesized by the surfactant-assisted HEBM SmCo5 precursors. Phases, microstructure, particle sizes and magnetic properties of the synthesized Sm2Co17 nanoparticles have been investigated in detail. The results showed that the precursors had great effects on the microstructure of the synthesized Sm2Co17 nanoparticles. The Sm2Co17 nanoparticles prepared by one-step HEBM of ingot powders in heptane for 5h using oleic acid as surfactant had a single-crystal and a coercivity of 8.3kOe. The majority of the Sm2Co17 nanoparticles synthesized using oleylamine as a surfactant showed single-crystal, accompanied by the presence of a few of polycrystalline. In the case of two-step milling (initial low energy ball milling of ingot powders for 18h and then HEBM for 5h), the obtained nanoparticles were polycrystalline and showed a low coercivity. When the precursor was jet-milled SmCo5 powders, the synthesized Sm2Co17 nanoparticles had both single-crystal and polycrystalline nanostructures.

Defect-driven synthesis of self-assembled single crystal titanium nanowires via electrochemistry

One-dimensional single crystal nanostructures have garnered much attention, from their low-dimensional physics to their technological uses, due to their unique properties and potential applications, from sensors to interconnects. There is an increasing interest in metallic titanium nanowires, yet their single crystal form has not been actualized. Vapor–liquid–solid (VLS) and template-assisted top-down methods are common means for nanowire synthesis; however, each has limitations with respect to nanowire composition and crystallinity. Here we show a simple electrochemical method to generate single crystal titanium nanowires on monocrystalline NiTi substrates. This work is a significant advance in addressing the challenge of growing single crystal titanium nanowires, which had been precluded by titanium’s reactivity. Nanowires grew non-parallel to the surface and in a periodic arrangement along specific substrate directions; this behavior is attributed to a defect-driven mechanism. This synthesis technique ushers in new and rapid routes for single crystal metallic nanostructures, which have considerable implications for nanoscale electronics.

Preparation and investigation of the formation mechanism of organic single crystal nanostructures of PTCDA

Different types of nanostructures of an organic dye compound, perylene-3,4,9,10-tetracarboxylic-dianhydride (PTCDA), are prepared on anodic alumina oxide (AAO) at different values of substrate temperature (Ts) by a facile physical vapor deposition (PVD) method in a molecular beam epitaxy (MBE) system. Scanning electron microscopy (SEM), transmission electron microscopy (TEM), high resolution transmission electron microscopy (HRTEM) and selected area electron diffraction (SAED) techniques are applied to the systematical characterization of the nanostructures. It is found that the PTCDA nanofibers, nanoneedles, nanobelts, and nanorods are produced at 330 ℃Ts; Only nanorods are formed at 280 ℃, 230 ℃, and 180 ℃, and their lengths become short asTs decreases; the continuous films are obtained on 50 ℃ AAOs substrates. HRTEM and SAED results show that the nanoneedle and nanorods are of single crystal. According to SEM results, the formation of PTCDA nanostructures should be mainly affected by surface curvature andTs.

Microstructure evolution and advanced performance of Mn3O4 nanomorphologies

Mn(3)O(4) morphologies with tetragonal single-crystal nanostructures including nanoparticles, nanorods and nanofractals were successfully prepared by a widely applicable chemical reaction route. The morphologies were synthesized using the reactants MnCl(2)·4H(2)O, H(2)O(2), and NaOH in a suitable surfactant and alkaline solution. The dripping speed of the NaOH solution plays an important role in the microstructure evolution of Mn(3)O(4) morphologies. The difference in the dripping speed of NaOH solutions leads to different Mn(3)O(4) nanomorphologies, which are called nanoparticles, nanorods and nanofractals. The average grain size of the Mn(3)O(4) nanoparticles ranged from a few to several tens of nanometers. The Mn(3)O(4) nanorods were smooth, straight, and the geometrical shape was structurally perfect. Their lengths ranged from several hundred nanometers to a few micrometers, and their diameters ranged from 10 nm to 30 nm. The fractal branches of the Mn(3)O(4) nanofractals were a few micrometers in length and several hundred nanometers in width. The catalytic properties of these Mn(3)O(4) nanomorphologies for the degradation of phenol were evaluated in detail. The results indicated that the Mn(3)O(4) nanofractals possess remarkable catalytic activity for the degradation of phenol in water treatment.

Synthesis and integration of tin oxide nanowires into an electronic nose

Single crystal nanostructures of semiconducting tin oxides have been fabricated and characterized as sensing materials for implementation in an electronic nose. The nanowires exhibit exceptional crystalline quality and a very high length-to-width ratio, resulting in enhanced sensing capability as well as long-term material stability for prolonged operation. A sensing device based on SnO 2 nanowires has been fabricated and comparatively tested in an array of chemical sensor with conventional thin film sensing device. Preliminary measurements ethanol/water mixtures demonstrate that nanowire-based sensors can be favourably implemented in the electronic nose and that they perform comparably with the conventional thin film layers.

Effects of experimental conditions on one-dimensional single-crystal nanostructure of β-FeOOH

A facile and friendly environmental route has been developed to prepare one-dimensional β-FeOOH nanorods without any template at low temperature. In the present reaction system, FeCl 3 6H 2O was used as a single iron precursor. Effects of different experimental conditions on morphology and polymorph of the as-prepared samples were studied. Compared with the urea, the concentration of FeCl 3 influenced evidently the length of the as-formed β-FeOOH nanorods. The aspect ratio of the sample was adjusted from 6 to 24 by changing the concentration of FeCl 3. When the experimental temperature increased from 70 to 80 °C, the morphology of the resulting β-FeOOH changed from spindle to rod. The influences of different kinds of electrolytes on the final products were also studied. The results demonstrated that different electrolytes (KCl, KSCN, NaNO 3 and NH 4Cl) can strongly influence the sizes and structures of the as-prepared samples. Compared with various surfactants, the anionic surfactant, sodium dodecyl sulfate (SDS), affected significantly the morphology and size of the as-prepared samples. Nanoribbon-shaped β-FeOOH was synthesized in the presence of SDS for the first time.

Edge and finite size effects in polycrystalline ferroelectrics

This paper proposes a method to engineer the effects of mesa aspect ratio on polarization switching for single-crystal and polycrystalline PZT nanostructures. The out-of-plane polarization switching of single-crystal and polycrystalline structures as a function of crystallographic orientation, epitaxial strain and mesa aspect ratio are explored. The results are summarized in terms of the mesa geometrical parameters, crystallographic orientation and expitaxial strain. The results demonstrate a strong correlation of single-crystal properties to the polarization hysteresis behavior of a central representative grain in a polycrystalline film. The average remnant polarization and its reliability are controlled through the aspect ratio of the mesa. Calculations demonstrate that the stresses at the edges are relaxed for film height, h f , to mesa width, w, ratios h f / w ⩽ 1 × 10 −4. For h f / w ⩾ 1 × 10 −2, the effective in-plane stress is relaxed throughout the deposited film. Moreover, the effective stresses at the center of the mesa are 15% of the stresses of an infinite film.

Two-dimensional hexagonal SnS2 nanoflakes: fabrication, characterization, and growth mechanism

Two-dimensional layered hexagonal SnS2 nanoflakes were synthesized by a mild hydrothermal method at 145°C for 48 h and then characterized in depth. The result shows that the SnS2 nanoflakes are very uniform and have a single-crystal layered nanostructure. These nanoflakes have an average size of about 300 nm and a thickness of about 50 nm. Based on time-dependent experimental results and other parallel experiments, we ascribe the self-repair–epitaxial growth mechanism to the growth of the SnS2 nanostructures. Furthermore, this growth mechanism is also discussed in detail from two aspects: the Bravais rule and the surface energy theories.

Fabrication of Si 3N 4/SiC nanocomposites toughened by in-situ formed low-dimensional nanostructures

We report the fabrication of Si 3N 4/SiC nano/nano-composite reinforced by single-crystal low-dimensional nanostructures via spark plasma sintering of nanocomposite powders containing in-situ formed Si 3N 4 nanowires/nanobelts. The fabricated nanocomposite is analyzed by scanning electron microscopy, X-ray diffraction, transmission electron microscopy and selective area electron diffraction. The results show that the in-situ formed Si 3N 4 nanowires/nanobelts are uniformly distributed within the matrix. Such a nanocomposite could exhibit improved mechanical properties, due to the superior mechanical properties and uniform distribution of the nano-reinforcements.

Realization of aligned three-dimensional single-crystal chromium nanostructures by thermal evaporation

Aligned three-dimensional single-crystal chromium nanostructures are fabricated onto a silicon substrate by thermal evaporation in a conventional thermal evaporator, where the incident angle of Cr vapor flux with respect to the substrate surface normal is fixed at 88°. The effects of the deposition time and incident angle on the morphology of the resulting nanostructures are investigated. The achieved Cr nanostructures are characterized by scanning electron microscopy, energy dispersive X-ray analysis, X-ray diffraction, transmission electron microscopy, high-resolution transmission electron microscopy, and surface area measurement. This study provides a convenient way to fabricate three-dimensional single-crystal Cr nanostructures, which is suitable for batch fabrication and mass production. Finally, the same technique is employed to fabricate the nanostructures of other metals such as Ag, Au, Pd, and Ni.

Facile preparation of Co3O4 nanocrystals via a solvothermal process directly from common Co2O3 powder

Abstract A facile solvothermal process is successfully developed to prepare F-center cubic Co 3 O 4 nanocrystals in alcohol–water solvent at 160 °C for 6–24 h. The common Co 2 O 3 powder is originally directly used as precursors and alcohol performs as solvent, reducer, and modified agent in the system. The as-obtained samples are characterized by XRD, FTIR, SEM, TEM, SAED and VSM. The influence of reaction time is investigated. The type and concentration of alcohol are discussed. XRD and FTIR results indicate the Co 3 O 4 nanocrystals are effectively obtained with the average size around 40–25 nm. SEM and TEM images demonstrate the nanoparticles with narrow size distraction and high dispersivity. The SAED pattern shows the products with single-crystal nanostructure. The room-temperature antiferromagnetic properties of samples are detected. The formation mechanism of crystalline Co 3 O 4 is proposed.

Imaging domains in BaTiO3 single crystal nanostructures: comparing information from transmission electron microscopy and piezo-force microscopy

This article compares and contrasts information obtained, using transmission electron microscopy (TEM) and piezo-force microscopy (PFM), on domain configurations adopted in single crystal lamellae of BaTiO3, that had been cut directly from bulk using a focused ion beam microscope with top and bottom surfaces parallel to {100}pseudocubic. Both forms of imaging reveal domain walls parallel to {110}pseudocubic, consistent with sets of 90° domains with dipoles oriented parallel to the two pseudocubic directions in the plane of the lamellae. However, the domain width was observed to be dramatically larger using PFM than it was using TEM. This suggests significant differences in the surface energy densities that drive the domain formation in the first place, that could relate to differences in the boundary conditions in the two modes of imaging (TEM samples are imaged under high vacuum, whereas PFM imaging was performed in air). Attempts were made to map local dipole orientations directly, using a form of ‘vector’ PFM. However, information inferred was largely inconsistent with the known crystallography of the samples, raising concern about the levels of care needed for accurate interpretation of PFM images.

Synthesis and characterization of In 2O 3 nanocube via a solvothermal-calcination route

In 2O 3 nanocubes have been generated by a two-step process, a simple solvothermal technique for In(OH) 3 nanocubes and subsequent reaction with O 2 to form the In 2O 3 nanocubes, which exhibit morphologies identical to the original In(OH) 3 nanocube. The In(OH) 3 nanocubes and the In 2O 3 nanocubes are well-crystallized single-crystal nanostructure. Under optimal conversion conditions, the final geometry features of In 2O 3 are predetermined by the size and morphology of the In(OH) 3 nanocubes. The size of In(OH) 3 nanocubes is effected by pH value of solution.

Self-organized vertically aligned single-crystal silicon nanostructures with controlled shape and aspect ratio by reactive plasma etching

The formation of vertically aligned single-crystalline silicon nanostructures via “self-organized” maskless etching in Ar+H2 plasmas is studied. The shape and aspect ratio can be effectively controlled by the reactive plasma composition. In the optimum parameter space, single-crystalline pyramid-like nanostructures are produced; otherwise, nanocones and nanodots are formed. This generic nanostructure formation approach does not involve any external material deposition. It is based on a concurrent sputtering, etching, hydrogen termination, and atom/radical redeposition and can be applied to other nanomaterials.

Microwave-assisted synthesis of flower-like and leaf-like CuO nanostructures via room-temperature ionic liquids

Flower-like and leaf-like cupric oxide (CuO) single-crystal nanostructures have been successfully synthesized using ionic liquid 1-octyl-3-methylimidazolium trifluoroacetate ([Omim]TA) under the microwave-assisted approach. By controlling the concentration of [Omim]TA and reaction temperature, shape transformation of CuO nanostructures could be achieved in a short period of time. The results indicate that ionic liquid [Omim]TA plays an important role in the formation of different morphologies of CuO crystals. The crystal structure and morphology of products were characterized by X-ray powder diffraction (XRD), infrared spectrum (IR), scanning electron microscope (SEM), transmission electron microscopy (TEM), and selected-area electron diffraction (SAED). A possible mechanism for CuO nanostructure was proposed. In addition, UV–vis spectroscopy was employed to estimate the band gap energies of CuO crystals.

Use of the Carbothermal Route to Prepare Anisotropic Single-Crystal Platinum Nanostructures with Low Resistivity

We have used a carbothermal process in the absence of a catalyst or template to prepare two-dimensional (2D) platinum (Pt) nanoplatelets and one-dimensional (1D) Pt nanobelts on sapphire surfaces. This paper describes the first examples of the growth of Pt nanobelts and mesobelts. It appears that the presence of adequate quantities of diamond and Y2O3 powder at a molar ratio was a critical factor controlling the Pt gas species to form nanobelts at a relative low level of supersaturation. When the growth time was 15 h, we obtained ultralong (0.5 mm) mesobelts and microsheets. Electrical measurements indicated that the single-crystal Pt nanobelt had an extremely low resistivity of 16.8 μΩ cm and a failure current density of greater than 1 × 107 A cm−2. These unique Pt nanobelts are potentially attractive nanoscale building blocks for use as interconnects in nanoelectronic devices.

Synthesis of two-dimensional single-crystal berzelianite nanosheets and nanoplates with near-infrared optical absorption

The solar cell industry requires convenient and inexpensive fabrication of semiconductor nanostructures as highly efficient absorptive layers with low-cost, environmentally benign, heavy-metal-free (i.e., free from Hg, Cd, and Pb) and suitable band gap near 1 eV features. In this paper, we demonstrate the synthesis of two-dimensional single-crystal berzelianite (Cu2−xSe) nanosheets (in-plane diameter-to-thickness ratio ∼100) and nanoplates (in-plane diameter-to-thickness ratio ∼10) via a simple, “green” and environmentally benign method of injecting Cu(I)-complex precursor into Se-solution in paraffin liquid. Unlike the previous syntheses of binary chalcogenide nanostructures such as CdSe, the current strategy for berzelianite synthesis does not use expensive and toxic phosphine ligands such as trioctylphosphine (TOP). The products were characterized by a range of methods, such as X-ray powder diffraction, scanning electron microscopy, energy-dispersive X-ray spectroscopy, transmission electron microscopy, and selected area electron diffraction, revealing that the products have the cubic phase and high-quality single-crystal two-dimensional nanostructure. UV-Vis-NIR absorption spectroscopy reveals that the nanosheets and nanoplates show obvious absorption onsets at 0.89 eV and 0.80 eV, respectively, and strong optical absorption peak at 1.70 eV and 1.62 eV, covering the whole red range of the solar spectrum. The present study opens a new avenue to “green” and low-cost controllable synthesis of binary chalcogenides with technological applications in solar energy conversion and also in a wide range of photonic devices operating in the near-infrared.

Defect-pit-assisted growth of GaN nanostructures: nanowires, nanorods and nanobelts

A new method using defect-pit-assisted growth technology to successfully synthesize the high-quality single crystalline GaN nanostructures by ammoniating Ga(2)O(3) films was proposed in this paper. During the ammoniating process, the amorphous middle buffer layer may unavoidably produce some defects and dislocations. Some defect pits come out, which have the lowest surface energy and can subsequently be used as a mask/template or act as potential nucleation sites to fabricate the GaN actinomorphic nanostructures. The as-prepared products are characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM) and high-resolution transmission electron microscopy (HRTEM). The results indicate that all the reflections of the samples can be indexed to the hexagonal GaN phase and the clear lattice fringes in HRTEM further confirm the growth of high-quality single-crystal GaN nanostructures. The SEM images show that the nanostructures have been realized under different experimental conditions exhibiting different shapes: nanowires, nanorods, and nanobelts. No particles or other nanostructures are found in the SEM study, demonstrating that the product possesses pure nanostructures. These nanostructures show a very good emission peak at 366 nm, which will have a good advantage for applications in laser devices using one-dimensional structures. Finally, the growth mechanism is also briefly discussed.

Facile Solution Route to Vertically Aligned, Selective Growth of ZnO Nanostructure Arrays

For any future cost-effective applications of inorganic nanostructures, in particular, hybrid photovoltaic cells, it is essential that these inorganic nanomaterials be solution processable and selectively printable. This letter reports the selective growth of single-crystal ZnO nanostructures based on the microcontact printing of an inorganic nanocrystal seeding film. The pattern-transfer quality is dependent on the concentration of the inking solution. Variable yet controllable anisotropic growth of ZnO nanowires has been demonstrated on the transferred patterns of ZnO nanocrystal films. The patterning and growth of these highly ordered arrays of ZnO nanostructures employ a simple soft lithography technique and mild reaction conditions at low temperature and in the absence of harmful organic additives.

Chelation‐Mediated Aqueous Synthesis of Metal Oxyhydroxide and Oxide Nanostructures: Combination of Ligand‐Controlled Oxidation and Ligand‐Cooperative Morphogenesis

We have synthesized nanostructures of iron and cobalt oxyhydroxides and manganese oxides in aqueous solution containing a chelating agent. Nanosheets of FeOOH and NaxMnO2 and nanoflakes of CoOOH were generated from the corresponding divalent metal salts and ethylenediaminetetraacetate (EDTA) by one-pot synthesis under ambient conditions. The chelating agent fulfilled multiple roles in the reaction process and morphogenesis leading to two-dimensional nanostructures. Coordination to the divalent metal ions inhibited rapid precipitation of metal hydroxides and mediated oxidation to tri- and tetravalent species by dissolved oxygen. Along with the deposition, the two-dimensional and single-crystal nanostructures were also associated with interactions of the chelating agent. Therefore, this approach can be regarded as a combination of ligand-controlled oxidation and ligand-cooperative morphogenesis. Parallel control of the reaction and the morphology was achieved by a simple approach. The model cases suggest that tailoring chelation can facilitate the design of other metal oxide nanomaterials.