Single crystalline nanostructures of giant dielectric calcium copper titanate: a convenient route toward materialization of hard to realize multi-component perovskite nanostructures

Single-crystalline nanostructures of calcium copper titanate, an important giant dielectric quaternary oxide is disclosed for the first time through a convenient molten salt synthesis technique. The technique is not only blessed with high yield but also can readily generate a wide range of morphologies from nanoparticles, nanocubes to nanorods in reproducible way. Most importantly, the as-synthesized nanostructures, irrespective of their shapes, maintain single-crystalline character as it is evident from high-resolution transmission electron microscopic investigation. The present study will pave the way for the development of single-crystalline multi-component perovskite nanostructures which were seem to be extremely hard to realize to date. The possible mechanism on morphological evolution of the as-prepared nanostructures in molten salt is also discussed.     

Plasma‐Induced Hetero‐Nanostructures on a Polymer with Selective Metal Co‐Deposition

Plasma‐induced pattern formation is explored on polyethylene terephthalate (PET) using an oxygen plasma glow discharge. The nanostructures on PET are formed through preferential etching directed by the co‐deposition of metallic elements, such as Cr or Fe, sputtered from a stainless‐steel cathode. The local islands formed by metal co‐deposition have significantly slower etching rates than those of the pristine regions on PET, generating anisotropic nanostructures in pillar‐ or hair‐like form during plasma etching. By covering the cathode with the appropriate material, the desired metallic or polymeric elements can be co‐deposited onto the target surfaces. When the cathode is covered by a relatively soft material composed of only carbon and hydrogen, such as polystyrene, nanostructures typically induced by preferential etching are not observed on the PET surface, and the surfaces are uniformly etched. A variety of metals, such as Ag, Cu, Pt, or Si, can be successfully co‐deposited onto the PET surfaces by simply using a cathode covered in the desired metal; high‐aspect‐ratio nanostructures coated with the co‐deposited metal are subsequently formed. Therefore this simple single‐step method for forming hetero‐nanostructures—that is, nanoscale hair‐like polymer structures decorated with metals—can be used to produce nanostructures for various applications, such as catalysts, sensors, or energy devices.     

Morphological syntheses of ZnO nanostructures under microwave irradiation

ZnO nanostructures with flower-, rod-, and flake-like morphologies have been controllably synthesized using Zn(acac)₂·H₂O (acac = acetylacetonate) as a single-source precursor through a facile and fast microwave-assisted method. The morphologies of ZnO nanostructures can be systematically adjusted by using various surfactants. The ZnO products are characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and selected area electron diffraction. The results show that all ZnO nanostructures are of single-crystalline nature with hexagonal wurtzite structure. The possible formation mechanism for these ZnO nanostructures is proposed and their photoluminescence properties are also investigated.     

Sub-threshold signal processing in arrays of non-identical nanostructures

Weak input signals are routinely processed by molecular-scaled biological networks composed of non-identical units that operate correctly in a noisy environment. In order to show that artificial nanostructures can mimic this behavior, we explore theoretically noise-assisted signal processing in arrays of metallic nanoparticles functionalized with organic ligands that act as tunneling junctions connecting the nanoparticle to the external electrodes. The electronic transfer through the nanostructure is based on the Coulomb blockade and tunneling effects. Because of the fabrication uncertainties, these nanostructures are expected to show a high variability in their physical characteristics and a diversity-induced static noise should be considered together with the dynamic noise caused by thermal fluctuations. This static noise originates from the hardware variability and produces fluctuations in the threshold potential of the individual nanoparticles arranged in a parallel array. The correlation between different input (potential) and output (current) signals in the array is analyzed as a function of temperature, applied voltage, and the variability in the electrical properties of the nanostructures. Extensive kinetic Monte Carlo simulations with nanostructures whose basic properties have been demonstrated experimentally show that variability can enhance the correlation, even for the case of weak signals and high variability, provided that the signal is processed by a sufficiently high number of nanostructures. Moderate redundancy permits us not only to minimize the adverse effects of the hardware variability but also to take advantage of the nanoparticles' threshold fluctuations to increase the detection range at low temperatures. This conclusion holds for the average behavior of a moderately large statistical ensemble of non-identical nanostructures processing different types of input signals and suggests that variability could be beneficial for signal processing. We demonstrate also that circuits composed of coupled non-identical nanoparticles can act as elementary nano-oscillators that show synchronization properties for sub-threshold stimuli. The results obtained should be of conceptual interest for the design of reliable signal processing schemes with non-identical nanostructures.     

Controllable synthesis of undoped/Cd-doped ZnO nanostructures

Various undoped/Cd-doped ZnO nanostructures have been synthesized through a simple evaporating method. The gold particles-filled anodic aluminum oxide templates and catalyst-free graphite sheet were used as substrates. The morphologies of the products can be controlled by simply tuning the evaporation temperature of zinc and gases flow rates. Moreover, morphological difference between the undoped and Cd-doped ZnO nanostructures is presented. These as-grown ZnO nanostructures could be nanowires, nanobelts, nanoneedles, nanocombs, and saw-like structures, wherein in the saw-like ZnO structure was firstly found to originate nanowires on its rough lateral side. Room-temperature photoluminescence measurement shows strong green emissions from the ZnO nanostructures.     

Elucidating the role of surface hydrolysis in preparing organosilane nanostructures via particle lithography

A new method of particle lithography is described for preparing rings or nanoporous films of organosilanes. Millions of exquisitely uniform and precisely spaced nanostructures with designed surface chemistry can be rapidly produced using vapor deposition through mesoparticle masks. Nanoscopic amounts of water are essential for initiating surface hydrosilation. Thus, the key step for preparing covalently bonded nanostructures of organosilanes is to control drying parameters to spatially direct the placement of water on surfaces.     

Growth of one-dimensional zinc sulfide nanostructures through electrophoretic deposition

One-dimensional ZnS nanostructures were grown through EPD of ZnS nanoparticles prepared by a microwave assisted synthesis. The nanostructures were formed without using template membranes after 24 h of deposition on aluminum plates at direct current low voltage. Dimensions of the nanostructures can be varied by deposition time and electric field. AFM results show the polycrystalline character of the nanostructures. Lyosphere distortion and thinning and subsequent dipole–dipole interactions phenomena are proposed as a possible mechanism of the one dimensional nanostructures formation.     

Synthesis and properties of β-Ga2O3 nanostructures

A novel method was utilized to synthesize one-dimensional β-Ga₂O₃ nanostructures. In this method, β-Ga₂O₃ nanostructures have been successfully synthesized on Si(111) substrates through annealing sputtered Ga₂O₃/Mo films under flowing ammonia in a quartz tube. The as-obtained samples were analyzed in detail using the methods of X-ray diffraction (XRD), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM) and energy dispersive X-ray spectroscopy (EDX) attached to the HRTEM instrument. The results show that the formed nanostructures are single-crystalline Ga₂O₃. The annealing temperature has an evident influence on the morphology of the β-Ga₂O₃ nanostructures. The growth mechanism of the β-Ga₂O₃ nanostructures is also discussed by conventional vapor-solid (VS) mechanism.     

Engineering Single Nanopores on Gold Nanoplates by Tuning Crystal Screw Dislocation

Compared with the large variety of solid gold nanostructures, synthetic approaches for their hollow counterparts are limited, largely confined to chemical and irradiation‐based etching of preformed nanostructures. In particular, the preparation of through nanopore structures is extremely challenging. Here, a unique strategy for direct synthesis of gold nanopores in solution without the need for sacrificial templates or postsynthesis processing is reported. By controlling the degree of crystal screw dislocation, a single through pore with diameter ranging from sub‐nanometer to tens of nanometers, in the center of large gold nanoplates, can be engineered with precision. Ionic current rectification behaviors are observed using the gold nanopore, potentially enabling new capabilities in biosensing, sequencing, and imaging.     

Direct assembly of hydrophobic nanoparticles to multifunctional structures

We present a general process that allows convenient production of multifunctional composite particles by direct self-assembly of hydrophobic nanoparticles on host nanostructures containing high-density surface thiol groups. Hydrophobic nanoparticles of various compositions and combinations can be directly assembled onto the host surface through the strong coordination interactions between metal cations and thiol groups. The resulting structures can be further conveniently overcoated with a layer of normal silica to stabilize the assemblies and render them highly dispersible in water for biomedical applications. As the entire fabrication process does not involve complicated surface modification procedures, the hydrophobic ligands on the nanoparticles are not disturbed significantly so that they retain their original properties such as highly efficient luminescence. Many complex composite nanostructures with tailored functions can be efficiently produced by using this versatile approach. For example, multifunctional nonspherical nanostructures can be efficiently produced by using mercapto-silica coated nano-objects of arbitrary shapes as hosts for immobilizing functional nanoparticles. Multilayer structures can also be achieved by repeating the mercapto-silica coating and nanoparticle immobilization processes. Such assembly approach will provide the research community a highly versatile, configurable, scalable, and reproducible process for the preparation of various multifunctional structures.     

Flash welding of conducting polymer nanofibres

The absorption of light by a material generates heat through non-radiative energy dissipation and exothermic photochemical reactions. In nanostructured materials, the heat generated through photothermal processes will be confined within the individual nanostructures when heat transfer to neighbouring nanostructures and the environment is slow. This leads to unprecedented photothermal effects that cannot be observed in bulk materials, especially when a strong, pulsed light source is used. Here we demonstrate an enhanced photothermal phenomenon with conducting polymer nanofibres in which a camera flash causes instantaneous welding. Under flash irradiation, polyaniline nanofibres 'melt' to form a smooth and continuous film from an originally random network of nanofibres. This photothermal effect can be used to form asymmetric nanofibre films, to melt-blend polymer-polymer nanocomposites rapidly and to photo-pattern polymer nanofibre films.     

Fabrication and photoluminescence of high-quality ternary CdSSe nanowires and nanoribbons

Ternary alloy CdSSe nanowires and nanoribbons were successfully grown through a one-step thermal evaporation route using Au as a catalyst. The nanostructures obtained are uniform in diameter, and have smooth surfaces. High-resolution transmission electron microscopy, energy dispersive x-ray spectra and x-ray diffraction showed that both the nanowires and the nanoribbons have high-quality single-crystalline nature, and their compositions can be determined as CdS(0.6)Se(0.4) and CdS(0.3)Se(0.7), respectively. The mechanisms of formation of these two different nanostructures were discussed. The photoluminescence measurements showed very strong band-edge emission for both samples, which further demonstrates the single-crystal nature of the as-obtained CdSSe alloys. This finding may be extended for fabricating other composition-tunable 1D?ternary alloy nanostructures.     

Nanostenciling of Functional Materials by Room Temperature Pulsed Laser Deposition

We present how various features drawn in a miniature shadow mask (nanostencil) can be efficiently transferred to a surface in the form of three-dimensional nanostructures of metals (Pt, Cr), semiconductors (Ge), and complex oxides (e.g.,$hboxBaTiO_3$) by room temperature pulsed laser deposition. Selective deposition is obtained by interposing a sieve with apertures down to 100 nm between source and substrate. Nanostenciling allows for the organization of structures in predefined architectures with high accuracy. The patterning process is simple and rapid, since it does not imply additional processing steps. It is also parallel, resistless, and does not interfere with the structures' growth dynamics. The material deposited through the stencil mask conserves the desired functionality even at the level of the individual nanostructures. Nanostenciling can be performed in high or ultrahigh vacuum and is suitable for parallel prototyping of fragile or functionalized surfaces.     

Reconfigurable Chiral Self‐Assembly of Peptides through Control of Terminal Charges

Self‐assembly of chiral nanostructures is of considerable interest, since the ability to control the chirality of these structures has direct ramifications in biology and materials science. A new approach to design chiral nanostructures from self‐assembly of N‐(9‐fluorenylmethoxycarbonyl)‐protected phenylalanine‐tryptophan‐lysine tripeptides is reported. The terminal charges can induce helical twisting of the assembled β‐sheets, enabling the formation of well‐defined chiral nanostructures. The degree and direction of twisting in the β‐sheets can be precisely tailored through in situ pH and temperature modulations. This enables the assembly of reconfigurable chiral nanomaterials with easily adjustable size and handedness. These results offer new insight into the mechanism of helical twist formation, which may enable the precise assembly of highly dynamical materials with potential applications in biomedicine, chiroptics, and chiral sensing.     

Maskless multiple-beam laser lithography for large-area nanostructure/microstructure fabrication

This paper reports a maskless multiple-beam laser lithography technique for large-area nanostructure/microstructure fabrication. This lithography technique can flexibly generate arbitrary nanostructures/microstructures over a large area at a high speed. The feature size of the nanostructures/microstructures can be controlled by exposure time and moving speed of the nanostage. Functional predesigned patterns, including split-ring resonator metamaterials for terahertz waves, can be obtained. More complicated structures can be made by single- and double-exposure schemes to make hybrid nanostructures/microstructures and tune surface plasmonic resonance properties. Meanwhile, microstructures with large height to lateral dimension ratios (2.5D microstructures) fabricated on silicon substrates can be used as mold tools for soft lithography. This technology shows its unique capacity to create various nanostructures/microstructures for extensive applications.     

Cu2S nanostructures prepared by Cu-cysteine precursor templated route

A facile Cu-cysteine precursor templated route for the synthesis of Cu₂S nanowires, dendritic-like and flowerlike nanostructures is reported. The Cu-cysteine precursors are prepared through the reaction between Cu²⁺, l-cysteine and ethanolamine at room temperature, and the morphologies of Cu-cysteine precursors can be controlled by adjusting the molar ratio of l-cysteine to Cu²⁺. The Cu-cysteine precursors are used as both templates and source materials for the subsequent preparation of polycrystalline Cu₂S nanostructures by thermal treatment, and the morphologies of the precursors can be well preserved after the thermal transformation to Cu₂S nanostructures. The samples are characterized using X-ray powder diffraction, scanning electron microscopy, transmission electron microscopy, energy dispersive spectroscopy and Fourier transform infrared spectroscopy.     

Vertically aligned one-dimensional AlN nanostructures on conductive substrates: Synthesis and field emission

Herein we report the synthesis of vertically aligned AlN nanostructures on conductive substrates through the chemical reaction between AlCl₃ and NH₃ in the temperature range of 650-850 °C. The morphologies of the AlN nanostructures could be controllably modulated from cone-like to rod-like geometries by increasing the reaction temperature. The formation mechanism of the AlN nanostructures on the nitrified Ti substrates has been discussed based on the analysis of the intermediate products. The field emission (FE) property of AlN nanocones grown on the nitrified Ti substrate is better than that for AlN nanocones on Si substrate. The improvement of FE property can be attributed to the lower resistance between AlN nanocones and the nitrified Ti substrate because the conductive titanium nitride film can directly contact with AlN emitters while a high-resistive silica layer would easily form between Si substrate and AlN nanocones. These results indicate that the deposition of nanoscale filed emitters on conductive substrates is an effective way to improve the FE behavior, and may find potential applications in FE devices.     

Vapor growth and photoconductivity of single-crystal nickel-phthalocyanine nanorods

Nickel-phthalocyanines (NiPc) with planar aromatic structures are ideal building blocks for organic nanostructures. They can self-assemble into stacks through π-π interaction, exhibit high thermal and chemical stabilities, and possess outstanding electrical and optical properties. Herein, single-crystal NiPc nanorods were synthesized by a facile vapor transfer deposition method. Their nanostructures and compositions were investigated by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), and Fourier-transform infrared (FTIR) in detail. The deposited NiPc nanorods were found to be the β-phase single crystals. Moreover, the NiPc nanorod-based devices were fabricated and exhibited high photocurrent upon white-light illumination. This indicates that the NiPc nanorods can be considered as a candidate material for fabricating photoelectric devices.     

Engineering Bulk,Layered, Multicomponent Nanostructures with High Energy Density

The precise control of individual components in multicomponent nanostructures is crucial to realizing their fascinating functionalities for applications in electronics, energy‐conversion devices, and biotechnologies. However, this control remains particularly challenging for bulk, multicomponent nanomaterials because the desired structures of the constitute components often conflict. Herein, a strategy is reported for simultaneously controlling the structural properties of the constituent components in bulk multicomponent nanostructures through layered structural design. The power of this approach is illustrated by generating the desired structures of each constituent in a bulk multicomponent nanomaterial (SmCo + FeCo)/NdFeB, which cannot be attained with existing methods. The resulting nanostructure exhibits a record high energy density (31 MGOe) for this class of bulk nanocomposites composed of both hard and soft magnetic materials, with the soft magnetic fraction exceeding 20 wt%. It is anticipated that other properties beyond magnetism, such as the thermoelectric and mechanical properties, can also be tuned by engineering such layered architectures.     

Chiral metamaterial composed of three-dimensional plasmonic nanostructures

We introduce a top-down fabricated metamaterial composed of three-dimensional, chiral, plasmonic nanostructures for visible and near-infrared wavelengths. Based on a combined spectroscopic and interferometric characterization, the entire complex transmission response in terms of a Jones matrix is disclosed. Particularly, the polarization output state of light after propagation through the nanostructures can be decoded from the measurements for any excitation configuration. We experimentally found a rotation of the polarization azimuth of linearly polarized light exceeding 50° at wavelengths around 1.08 μm. This corresponds to a specific rotation which is significantly larger than that of any linear, passive, and reciprocal medium reported to date.