Fine Nanostructure Research Articles

Interfacial structure and bonding mechanism of weld seams during porthole die extrusion of aluminum alloy profiles

Fine nanostructures of bonding interfaces of weld seams formed by porthole die extrusion in the absence/presence of a gas-pocket behind the bridge of the extrusion die were systematically studied to understand the underlying interfacial bonding mechanisms. Interfacial grain boundaries, nanoscale amorphous layers, and three kinds of new interfacial structures were found. Specifically, it was found that, in the absence of a gas-pocket behind the bridge, there are two distinctly different interfacial structures. For the first kind of bonding interface, interfacial grain boundaries exist in contact areas and micro-voids exist in non-contact areas. For the second kind of bonding interface, there are no interfacial grain boundaries in contact areas and only nanoscale micro-voids exist in non-contact areas. In the presence of a gas-pocket behind the bridge, nanoscale voids and amorphous layers exist at the bonding interface. It was also found that the formation of gas-pockets can be avoided by increasing the depth of the welding chamber, and the increase of the welding chamber's depth and extrusion speed also contributes to the volume reduction of micro-voids and the migration of grain boundaries at the bonding interface, so as to improve the welding quality of weld seams. Based on the experimental findings, two interfacial bonding mechanisms corresponding to the absence/presence of a gas-pocket are proposed. The specific behavior of micro-asperities contact, micro-voids closure, oxide films breaking and interfacial grain boundaries migration are described, and the solid-state bonding process during porthole die extrusion is revealed from the micro-nano scales.

Glass Forming Acceptor Alloys for Highly Efficient and Thermally Stable Ternary Organic Solar Cells

AbstractThe stability of donor:acceptor (D:A) semiconductor blends plays a key role in the development of solution‐processed organic solar cells. One essential condition for both high‐yield production and a long lifetime is excellent thermal stability. Recently, A1:A2 acceptor mixtures have received considerable attention and alloys of two miscible acceptors are singled out as a powerful tool for the design of efficient and durable organic solar cells. This progress report introduces a thermodynamic rationale for the superior thermal stability and reproducibility that is observed for some ternary blends. The increase in entropy upon mixing of several acceptors reduces the tendency for phase separation as well as crystallization, which facilitates the controlled formation of a fine blend nanostructure. Further, when combined with a high glass transition temperature many ternary blends can be readily quenched into a glassy state. Recent progress with regard to the thermal stability and efficiency of D:A1:A2 ternary blends is summarized in the light of the thermodynamic and kinetic arguments discussed in this article. Both, fullerene and fullerene‐free acceptor alloys now yield solar cell efficiencies in excess of 10%, which indicates that ternary blends are a promising avenue that is poised to considerably enhance the prospect of organic photovoltaics.

Hierarchically porous hexagonal microsheets constructed by well-interwoven MCo2S4 (M = Ni, Fe, Zn) nanotube networks via two-step anion-exchange for high-performance asymmetric supercapacitors

We report a significant advance in the design and fabrication of MCo2S4 (M = Ni, Fe, Zn) complex hierarchical structures with well-defined morphologies by achieving novel hierarchically porous hexagonal microsheets constructed by well-interwoven nanotube networks using a controllable two-step anion-exchange technique. Uniform and smooth hexagonal sheets are initially achieved for the first anion-exchange leading to nanowire-woven hexagons, followed by transformation of each nanowire to rough MCo2S4 nanotube via the second anion-exchange. The involved mechanism of this general top-down method allowing fine nanostructure control is clarified based on our proposed new insights into ion-induced anisotropic growth and time-dependent anion-exchange reaction kinetics. The merits of both maximized porosity and low resistance facilitate fast electron transfer/ion diffusion, thus NiCo2S4 electrode material exhibits a higher specific capacitance of 1780Fg−1 and superior rate capability than most reported NiCo2S4 nanostructures with different morphologies as well as excellent stability (92.4% capacity retention after 10,000 cycles at 10Ag−1). Furthermore, an asymmetric solid-state supercapacitor using such NiCo2S4 as positive and N-doped graphene film as negative electrodes achieves outstanding cycle ability (92.1% retention over 5000 cycles at 20Ag−1) and higher energy density of 67.2Whkg−1 (at 900Wkg−1) than that of similar devices. Such MCo2S4 electrode materials are promising for the future generation of high performance supercapacitors.

White-light upconversion emission of lanthanide double-doped oxide nanoparticles via defect state luminescence of ZnO

The white upconversion luminescence (UCL) of upconversion nanoparticles (UCNPs) is mainly made up of the color red, green and blue. Interestingly, the white-light-emitting UCNPs can be obtained via a complex method of tridoping lanthanide ions such as Yb3+, Er3+, and Tm3+. We herein report that an excellent white UCL can be obtained from Yb/Tm double-doped ZnO. In this system, the blue and red UCL-emissions around 475 and 652 nm originate from 1G4→3H6 and 1G4→3F4 transition of Tm3+, respectively, and the green one can be attributed to the defect states (oxygen vacancies) luminescence (DSL) of the ZnO host. Meanwhile, the fine nanostructure of ZnO:Yb/Tm is prepared by adjusting the concentration of OH−. Particularly, the one dimentional pencil-shaped nanorods with high aspect ratio achieve a strong green DSL emission due to the high concentration of oxygen vacancy. The oxygen vacancy defects play an irreplaceable role in affecting the intensities of blue and red UCL by acting as the intermediate state in the energy transfer process. More importantly, we demonstrate that the DSL and UCL can be combined into systems, paving a new road for obtaining the white UCL emission.

Novel development of nanocrystalline kesterite Cu2ZnSnS4 thin film with high photocatalytic activity under visible light illumination

Cu2ZnSnS4 (CZTS) represents a promising p-type direct band gap semiconductor with large absorption coefficient in the visible region of solar light. In the present study, a kesterite CZTS nanocrystalline film, with high purity, was successfully synthesized via the combination of successive ionic layer adsorption and reaction (SILAR) and chemical bath deposition (CBD) technique. The morphology and structural properties of the CZTS films were characterized by FE-SEM microscopy, porosimetry in terms of Brunauer-Emmett-Teller (BET) technique, X-ray diffraction and Raman spectroscopy. The as-prepared films under mild heat treatment at 250 °C in the presence of sulfur atmosphere exhibited fine nanostructure with 35 nm average particle size, high specific surface area of 53 m2/g and 9 nm pore diameter. The photocatalytic activity of the films was examined to the degradation of Basic Blue 41 (BB-41) and Acid Orange 8 (AO-8) organic azo dyes under visible light irradiation, demonstrating 97.5% and 70% discoloration for BB-41 and AO-8 respectively. Reusability of the CZTS films was also tested proving good stability over several repetitions. The reduction of photocatalyst's efficiency after three successive repetitions didn't exceed 5.6% and 8.5% for BB-41 and AO-8 respectively.

Atomic Force Microscopy Reveals the Dynamic Morphology of Fenestrations in Live Liver Sinusoidal Endothelial Cells

Here, we report an atomic force microscopy (AFM)-based imaging method for resolving the fine nanostructures (e.g., fenestrations) in the membranes of live primary murine liver sinusoidal endothelial cells (LSECs). From data on topographical and nanomechanical properties of the selected cell areas collected within 1 min, we traced the dynamic rearrangement of the cell actin cytoskeleton connected with the formation or closing of cell fenestrations, both in non-stimulated LSECs as well as in response to cytochalasin B and antimycin A. In conclusion, AFM-based imaging permitted the near real-time measurements of dynamic changes in fenestrations in live LSECs.

Soft magnetic Fe-Si-B-Cu nanocrystalline alloys with high Cu concentrations

High saturation magnetic flux density (Bs) soft magnetic nanocrystalline alloys with good manufacturability were developed in a simple Fe-Si-B-Cu alloy system with high Cu concentrations. The nanocrystalline alloys with high Bs of ∼1.77 T and low coercivity of ∼7.1 A/m were obtained by annealing the melt-spun Fe-Si-B-Cu alloys containing 1.7–2.0 at% Cu. The high content of Cu facilitates the formation of high-number-density α-Fe nuclei with an average grain size of ∼6 nm pre-existing in the amorphous matrix, which inhibits the excessive growth of the α-Fe grains by their competitive growth even during the low-heating-rate annealing, resulting in a fine nanostructure and excellent soft magnetic properties.

Tuning Unique Peapod‐Like Co(SxSe1–x)2 Nanoparticles for Efficient Overall Water Splitting

The development of efficient electrocatalysts with low cost and earth abundance for overall water splitting is very important in energy conversion. Although many electrocatalysts based on transition metal dichalcogenides have been developed, rational design and controllable synthesis of fine nanostructures with subtle morphologies and sequential chemical compositions related to these materials remains a challenge. This study reports a series of peapod‐like composites with component‐controllable Co(SxSe1–x)2 nanoparticles encapsulated in carbon fibers, which are obtained by using Co(CO3)0.5(OH)·0.11H2O nanowires as a precursor followed by coating carbon fiber and an adjustable sulfuration/selenylation process. Due to its increased exposure of active sites and improved charge and mass transport capability derived from the unique structure and morphology, the Co(SxSe1–x)2 samples display favorable catalytic activities. It is found that Co(S0.71Se0.29)2 exhibits the best hydrogen evolution reaction (HER) performance and Co(S0.22Se0.78)2 shows the highest activity for the oxygen evolution reaction (OER). When using Co(S0.71Se0.29)2 as a cathode and Co(S0.22Se0.78)2 as an anode, it demonstrates a durable activity for overall water splitting to deliver 10 mA cm−2 at a cell voltage of 1.63 V, thus offering an attractive cost‐effective earth abundant material system toward water splitting.

Development of optimized nanogap plasmonic substrate for improved SERS enhancement

SERS enhancement factor (EF) of planar substrates depends on the size and shape of the fine nanostructure forming a defect free, well-arranged matrix. Nano-lithographic process is considered to be the most advanced methods employed for the fabrication SERS substrates. Nanostructured plasmonic substrates with nanogap (NG) pattern often results in stable, efficient and reproducible SERS enhancement. For such substrates, NG and their diagonal length (DL) need to be optimized. Theoretically smaller NGs (∼30-40 nm or smaller) results in higher SERS enhancement. However, fabrication of NG substrates below such limit is a challenge even for the most advanced lithography process. In this context, herein, we report the optimization of fabrication process, where higher SERS enhancement can be realized from larger NGs substrates by optimizing their DL of nanostructures between the NGs. Based on simulation we could demonstrate that, by optimizing the DL, SERS enhancement from larger NG substrate such as 60 and 80 nm could be comparable to that of smaller (40nm) NG substrates. We envision that this concept will open up new regime in the nanofabrication of practically feasible NG based plasmonic substrates with higher SERS enhancement. Initial results of our experiments are in close agreement with our simulated study.

Development of Optimized Nanogap Plasmonic Substrate for ImprovedSERS Enhancement

SERS enhancement factor (EF) of planar substrates depends on the size and shape of the fine nanostructure forming a defect free, well-arranged matrix. Nano-lithographic process is considered to be the most advanced methods employed for the fabrication SERS substrates. Nanostructured plasmonic substrates with nanogap (NGs) pattern are often results in stable, efficient and reproducible SERS enhancement. For such substrates, NG and their diagonal length (DL) need to be optimized. Theoretically smaller NGs (~30-40 nm or smaller) results in higher SERS enhancement. However, fabrication of NG substrates below such limit is a challenge even for the most advanced lithography process, In this context, herein, we report the optimization of fabrication process, where higher SERS enhancement can be realized from larger NGs substrates by optimizing their DL of nanostructures between the NGs. Based on simulation we could demonstrate that, by optimizing the DL, SERS enhancement from larger NG substrate such as 60 and 80 nm could be comparable to that of smaller (40 nm) NG substrates. We envision that this concept will open up new regime in the nanofabrication of practically feasible NG based plasmonic substrates with higher SERS enhancement. Initial results of our experiments are in close agreement with our simulated study.

Implementing Structural Defects As a New Direction to Improve the Durability of Pt-Based/C Nanoparticles

Due to strain and ligand effects, the simultaneous presence of concave and convex surfaces and their highly-defective nanostructure (atomic vacancies, grain boundaries), hollow Pt-rich/C electrocatalysts have proven to enhance remarkably the oxygen reduction reaction (ORR) kinetics. However, a technologically-relevant proton-exchange membrane fuel cell (PEMFC) cathode catalyst should be able to maintain its initial catalytic activity on the long-term. This is hardly feasible on nanocatalysts based on platinum alloyed with transition metals (PtM alloys, M being a transition metal) or M-rich core@Pt-rich shell nanoparticles due to the dissolution of the transition metal in the harsh operating conditions of a PEMFC cathode but the question remains open for nanocatalysts in which catalytic activity is not solely due to alloying effects. Herein, the ORR activity of solid or hollow PtNi/C nanoparticles with identical chemical composition but different fine nanostructure was evaluated before and after accelerated stress tests (ASTs) under simulated PEMFC operating conditions (5,000 potential cycles between 0.6 and 1.0 V vs. RHE at T = 80°C). Independently on the nanostructure, the combined physical, chemical and electrochemical results show that the losses in ORR activity are related to weakening of strain and ligand effects associated with the dissolution of Ni atoms. However, the catalytic advantage of hollow over solid PtNi/C nanoparticles was maintained during the ASTs. Hence, implementing structural disorder in PEMFC cathode electrocatalysts represents a new direction to look at to improve sustainably the ORR kinetics. Figure 1

PEGylated Perylenemonoimide-Dithienylethene for Super-Resolution Imaging of Liposomes.

We have designed and synthesized an amphiphilic photoswitchable fluorophore, PEGylated perylenemonoimide-dithienylethene (PEG-PMI-DTE), which exhibits evident bistable photochromism, fluorescence switching, and fatigue resistance. The fine nanostructures of liposomes can be observed directly under super-resolution fluorescent microscopy by aid of the amphiphilic photoswitchable fluorophore as a staining agent, with an optical resolution of 30 nm.

Third-harmonic generation from gold nanowires of rough surface considering classical nonlocal effect.

We demonstrate that the nonlocal dielectric response of metal, comparing with the traditional local model, will significantly boost the third-order harmonic generation (THG) from gold nanowires of rough surface by a factor of several orders of magnitude. The enhancement is probably due to the penetrated field into the fine nanostructures on the metal surface in nonlocal model. The anisotropy THG efficiency versus the angle of incidence is also demonstrated due to the inhomogeneous surface morphology. The possible ways to verify the nonlocal effect to the THG are demonstrated. The results have a general significance in explaining the experimental observations.

Indolo[3,2-b]indole-Containing Donor–Acceptor Copolymers for High-Efficiency Organic Solar Cells

The organic solar cell (OSC) performance of a series of new donor–acceptor copolymers containing indolo[3,2-b]indole as a key donor block and benzothiadiazole (BT) units with various degrees of fluorination as acceptors is reported. Compared with the simple carbazole unit, the strategically developed indolo[3,2-b]indole unit is found to significantly extend π-conjugation and thus increase the intermolecular interactions of the resulting copolymer, as probed by density functional theory calculations, photophysical studies, and structural/morphological analyses. In addition, fluorination of BT can facilitate nanostructuring of the copolymers, mainly due to further planarization of the backbone, which leads to apparently higher hole/electron charge carrier mobilities. The OSC properties of this series of new copolymers blended with fullerene show a strong dependence on the fine and continuous fibrous nanostructure of the blend film. The indolo[3,2-b]indole-based copolymer with singly fluorinated BT units possesses optimal intermolecular interactions and achieves the highest power conversion efficiency of 8.84% under AM 1.5G illumination. This result shows the potential of π-extended carbazole moieties for achieving high-performance OSCs with many of the favorable properties induced by large heteroacene blocks.

Rapid fabrication of bio-inspired nanostructure with hydrophobicity and antireflectivity on polystyrene surface replicating from cicada wings.

The fine nanostructure on the cicada wing of Cryptotympana atrata fabricius, which exhibits hydrophobicity and antireflectivity, is carefully examined. A promising strategy is proposed for facilely and successively replicating the natural functional nanostructure of the cicada wing onto polystyrene (PS) surfaces. First, a nickel replica with tapered nanopores is fabricated by combining electroless plating and subsequent electroplating with the natural cicada wing as an original template. Then, using microinjection compression molding, with the nickel replica as a template, the tapered nanopores are transcribed onto the PS surface, resulting in orderly and densely arranged nanopillars with a mean diameter of about 156 nm and a mean pitch of about 180 nm. The natural cicada wing and fabricated nickel replica are reusable. Interestingly, the PS replica surface exhibits a water contact angle of 143° ± 2° and a reflectance of about 4% in the wavelength range of 400-1000 nm. These results mean that the bionic PS replica not only inherits the nanostructure of the natural wing, but also its hydrophobic and antireflective properties. The mechanisms for the hydrophobic and antireflective properties are revealed via composite wetting interface and effective medium layer on the replica surface, respectively. The proposed fast and efficient replication strategy can be an excellent candidate for mimicking bio-inspired functional micro/nanostructures without complicated procedures and expensive materials.

Beyond Strain and Ligand Effects: Microstrain-Induced Enhancement of the Oxygen Reduction Reaction Kinetics on Various PtNi/C Nanostructures

The electrical performance of a proton exchange membrane fuel cell is limited by the slow oxygen reduction reaction (ORR) kinetics. Catalytic improvements for the ORR have been obtained on alloyed PtM/C or M-rich-core@Pt-rich-shell/C catalysts (where M is an early or late transition metal) in comparison to pure Pt/C, due to a combination of strain and ligand effects. However, the effect of the fine nanostructure of the nanomaterials on the ORR kinetics remains underinvestigated. Here, nanometer-sized PtNi/C electrocatalysts with low Ni content (∼15 atom %) but different nanostructures and different densities of grain boundary were synthesized: solid, hollow, or “sea sponge” PtNi/C nanoalloys, and solid Ni-core@Pt-shell/C nanoparticles. These nanostructures were characterized by transmission and scanning transmission electron microscopy, X-ray energy dispersive spectroscopy, synchrotron wide-angle X-ray scattering (WAXS), atomic absorption spectroscopy, and electrochemical techniques. Their electrocatalyti...

Propylene glycol-assisted seed layer-free hydrothermal synthesis of nanostructured WO3 thin films for electrochromic applications

This research article presents an overview of the hydrothermal synthesis of nanostructured tungsten oxide (WO3) and its electrochromic (EC) performance. A remarkable evolution in the past few years of producing pure and fine WO3 nanostructures using mild hydrothermal synthesis has received great attention. The hydrothermal process is highly suited for producing monodispersed nanoparticles with control over size and morphology, low processing temperature, and easy synthesis. In this article, we developed a facile seed layer-free hydrothermal approach for preparing WO3 thin films with improved EC performance. Structural and morphological properties were studied using X-ray diffraction, Fourier transform infrared spectroscopy, and scanning electron microscopy. The electrochemical stability of the propylene glycol-assisted nanostructured WO3 film was examined in lithium per chlorate-propylene carbonate (LiClO4-PC) electrolyte for prolonged color/bleach cycles. The results showed an improvement in electrochemical stability with fast response time.

Epitaxial Growth of Atomically Smooth Aluminum on Silicon and Its Intrinsic Optical Properties.

Aluminum (Al) provides an excellent material platform for plasmonic applications in the ultraviolet (UV) regime due to its low loss coefficient at UV wavelengths. To fully realize the potential of this material, it is imperative to create nanostructures with minimal defects in order to prevent light scattering and better support plasmonic resonances. In this work, we report the successful development of atomically smooth epitaxial Al films on silicon. These epitaxial Al thin films facilitate the creation of fine plasmonic nanostructures and demonstrate considerable loss reduction in the UV frequency range, in comparison to the polycrystalline Al films based on spectroscopic ellipsometry measurements. Remarkably, our measurements on the epitaxial Al film grown using the two-step method suggest that the intrinsic loss in Al is significantly lower, by up to a factor of 2 in the UV range, with respect to current widely quoted Palik's values extracted from polycrystalline films. These high-quality epitaxial Al films provide an ideal platform for UV plasmonics. In addition, the availability of intrinsic optical constants will enable more accurate theoretical predictions to guide the device design.

Improvements in nanoscale zero-valent iron production by milling through the addition of alumina

A new milling procedure for a cost-effective production of nanoscale zero-valent iron for environmental remediation is presented. Conventional ball milling of iron in an organic solvent as Mono Ethylene Glycol produces flattened iron particles that are unlikely to break even after very long milling times. With the aim of breaking down these iron flakes, in this new procedure, further milling is carried out by adding an amount of fine alumina powder to the previously milled solution. As the amount of added alumina increases from 9 to 54 g l-1, a progressive decrease of the presence of flakes is observed. In the latter case, the appearance of the particles formed by fragments of former flakes is rather homogeneous, with most of the final nanoparticles having an equivalent diameter well below 1 µm and with an average particle size in solution of around 400 nm. An additional increase of alumina content results in a highly viscous solution showing worse particle size distribution. Milled particles, in the case of alumina concentrations of 54 g l-1, have a fairly large specific surface area and high Fe(0) content. These new particles show a very good Cr(VI) removal efficiency compared with other commercial products available. This good reactivity is related to the absence of an oxide layer, the large amount of superficial irregularities generated by the repetitive fracture process during milling and the presence of a fine nanostructure within the iron nanoparticles.

Capacitive characteristics of nanocomposites of conducting polypyrrole and functionalized carbon nanotubes: pulse current synthesis and tailoring

Conducting polypyrrole (PPy) is an attractive material for supercapacitors with a high specific capacitance and environmental friendliness feature, but it suffers from the limited power density and short cycling life due to the low ionic mobility and mechanic stress resulting from ions in/out solid phase, respectively. Here, we present PPy–p-toluenesulfonate (TOS) and functionalized single-walled carbon nanotube (FSWNT) nanorod-like composites deposited by pulse current method in TOS and FSWNT dispersive solutions, with a diameter of less than 20 nm due to the improved FSWNT concentration near the polymerization interface during pulse-off time. The reduced ion diffusion length and the high diffusion coefficient of PPy–TOS synthesized by pulse current method lead to the nanocomposites with a high specific capacitance of 360 F g−1 at a current loading of 20 A g−1 and an ultrafast charging/discharging capability with a value of 280 F g−1 at even 0.1 s. Moreover, the fine nanostructure, which can accommodate the mechanical stress during charging/discharging process, significantly prolongs the cycling life of the nanocomposites, with its capacitance well maintained of 80 % after 100,000 continuous cycles at a current load of 400 A g−1. All of these enable the nanocomposites to be excellent active materials for high-performance supercapacitors.