Homogeneous Nanostructures Research Articles

Optically Active AuNR@Ag Core-Shell Nanoparticles and Hierarchical Assembly via DNA-Mediated Surface Chemistry.

To manipulate the chiroptical activity of plasmonic metal nanoparticles (MNPs) and control their hierarchical self-assembly are of great fundamental and technological significance; however, they remain a big challenge. Here, we in situ fabricated anisotropic bimetallic AuNR@Ag core-shell nanoparticles (AuNR@Ag NPs) capped with designed DNA molecules and systematically studied the plasmonic chiroptical properties of the individual AuNR@Ag NPs and their assemblies. The AuNR@Ag NPs were facilely prepared by employing DNA-capped Au nanorods (AuNRs) as seeds to grow Ag shells, and it was found that the as-prepared AuNR@Ag NP surfaces were encoded by the original DNA molecules through an in situ DNA "desorption and re-adsorption" dynamic process during shell overgrowth. This observation is distinctly different from the previous results that DNA molecules were embedded in the Ag shell. Interestingly, with this in situ DNA-mediated surface chemistry, plasmonic chiroptical activities were observed from individual AuNR@Ag NPs, and the chiroptical responses were conveniently manipulated over a broad optical window by simply modifying the shape anisotropy of the building blocks. Furthermore, the DNA molecules capped on the AuNR@Ag NP surface facilitate the hierarchical assembly of homogeneous and heterogeneous nanostructures with distinct chiral optical responses.

Combined effect of carbon nanotubes and polypyrrole on the electrical properties of cellulose-nanopaper

In the present study, 2,2,6,6,-tetramethylpiperidine-1-oxyl (TEMPO)-oxidized cellulose nanofibers (CNF) were combined with multi-walled carbon nanotubes (MWCNTs) and with hybrid MWCNT/polypyrrole to produce a variety of binary and ternary formulations of conductive nanopapers. By following a simple mixing/sonication/filtering process, a homogeneous and well-distributed CNF-MWCNT nanostructure was formed, resulting in a nanopaper of strong mechanical properties (141 MPa tensile strength and 9.41 GPa Young’s modulus) and good electrical conductivity (0.78 S cm−1), for the formulation with 50 wt% of MWCNT. The subsequent in situ polymerization of pyrrole in CNF-MWCNT mixtures produced ternary multiphase CNF-MWCNT-PPy nanopapers with much improved electrical conductivity (2.41 S cm−1) and electrochemical properties (113 F g−1 specific capacitance), even using little amounts of MWCNTs. With these materials, improved hybrid capacitors can be designed. The article presents a trend for the application of cellulose nanofibers in the field of green and flexible electronics.

Molecular Engineering of Somatostatin Analogue with Minimal Dipeptide Motif Induces the Formation of Functional Nanoparticles

AbstractFunctionalized nanoparticles decorated with functional biological entities serve as preferred vehicles for numerous theranostic applications. Here we offer an alternative strategy in which the targeting moieties also act as building blocks for the formation of functional nanoassemblies. Diphenylalanine, a small, highly potent self‐assembling module, was incorporated with a somatostatin analogue, a modified hormone which preferentially binds to cancer cells. The co‐assembly of the engineered hormone together with the structurally diverse diphenylalanine derivative allowed the formation of bioactive homogenous spherical nanostructures. Significant internalization capacity of the loaded co‐assembled nanospheres into cancer cells in vitro, as well as selective in vivo accumulation in tumors, were demonstrated. These findings present a new method for the molecular engineering of bioactive peptide molecules by minor modifications with a remarkably potent association motif.

Pre-texturing multi-crystalline silicon wafer via a two-step alkali etching method to achieve efficient nanostructured solar cells

Alkali solutions are not suitable for texturing multi-crystalline silicon (mc-Si) wafer due to the anisotropic etching. In this study, a two-step alkali-etch process is developed to form a flat surface on the wafer, which can be quickly and nearly isotropically etched by immersion in a sodium hydroxide solution, followed by a sodium hydroxide-sodium hypochlorite solution. The etching process leads to the formation of homogenous nanostructure, thereby improving the cell's repeatability and performance by simultaneously increasing its short-circuit current and open-circuit voltage.

Critical thickness of phenolic resin-based carbon interfacial layer for improving long cycling stability of silicon nanoparticle anodes

Silicon has a high theoretical capacity, still limits its application on Si-based anodes due to the problems of low electric conductivity, large volume change, continuous formation of unstable solid electrolyte interphase layer, and easy fracture during lithiation and delithiation process. Despite various carbon coating approaches are developed to fabricate carbon coated silicon core-shell and yolk-shell nanocomposites with improved electrochemical performance, the challenges including poor long-term cyclability, low Si mass ratio, and scalability remains. To overcome these challenges, we design an interfacial microporous carbon coating strategy on silicon nanoparticles to form homogeneous coaxial core-shell nanostructures. This synthesis sol-gel approach is simple, easy to scale up, and direct growth phenolic resins on the surface with uniform and controllable thickness. Additionally, the fabricated carbon layers form the microporous structures and phenolic resin frameworks, thus enabling the fast lithium ion transport and formation of stable solid electrolyte interphase film. By finely controlling the thickness of this phenolic resin-based carbon of 10nm, excellent protection of silicon nanoparticles as well as high electrochemical performance are achieved, delivering a high capacity of 1006mAhg−1 and Coulombic efficiency of >99.5% after 500 times at a current density of 500mAg−1.

Efficient NiSe-Ni3Se2/Graphene Electrocatalyst in Dye-Sensitized Solar Cells: The Role of Hollow Hybrid Nanostructure.

Hollow and hybrid nanomaterials are excellent electrocatalysts on account of their novel electrocatalytic properties compared with homogeneous solid nanostructures. In this report, NiSe-Ni3Se2 hybrid nanostructure with morphology of hollow hexagonal nanodisk was synthesized in situ on graphene. A series of NiSe-Ni3Se2/RGO with different phase constitutions and nanostructures were obtained by controlling the durations of solvothermal treatment. Because of their unique hollow and hybrid structure, NiSe-Ni3Se2/RGO hollow nanodisks exhibited higher electrocatalytic performance than NiSe/RGO and solid NiSe-Ni3Se2/RGO nanostructure for reducing I3(-) as counter cell (CE) of dye-sensitized solar cells (DSSCs). Additionally, NiSe-Ni3Se2/RGO hollow nanodisks achieved much lower charge transfer resistance (Rct = 0.68 Ω) and higher power conversion efficiency (PCE) (7.87%) than those of Pt (Rct = 1.41 Ω, PCE = 7.28%).

Microstructural evolution and phase transformation in twinning-induced plasticity steel induced by high-pressure torsion

The microstructural evolution of twinning-induced plasticity steel during high-pressure torsion (HPT) processing at 573 K was systematically evaluated. Due to the high processing temperature, the formation of a homogeneous nanostructure was primarily dominated by complicated dislocation and grain boundary activities in lieu of deformation twinning. Apart from the grain refinement process, phase transformation took place at late stages of deformation, resulting in the microstructural fingerprint of equaxied nanograins with multiple phases in the steel. On account of remarkable elemental redistribution, the diffusion-controlled nature of the transformation was convincingly identified. During the transformation, although the cementite also initially formed, austenite eventually decomposed into ferrite and Mn-riched M23C6 carbide, implying that Mn is the pivotal alloying element for the transformation kinetics. Owing to the sluggish bulk diffusivity of Mn, it is proposed that a high density of defects, nanostructures and the HPT processing play a crucial role in promoting the elemental diffusion and segregation and in stimulating the phase transformation.

Study of uranium oxide milling in order to obtain nanostructured UCx target

A R&D program is developed at the ALTO facility to provide new beams of exotic neutron-rich nuclei, as intense as possible. In the framework of European projects, it has been shown that the use of refractory targets with nanometric structure allows us to obtain beams of nuclei unreachable until now. The first parameter to be controlled in the processing to obtain targets with a homogeneous nanostructure is the grinding of uranium dioxide, down to 100nm grain size. In this study, dry and wet grinding routes are studied and the powders are analyzed in terms of phase stabilization, specific surface area and grain morphology. It appears that the grinding, as well dry as wet, leads to the decrease of the particle size. The oxidation of UO2 is observed whatever the grinding. However, the dry grinding is the most efficient and leads to the oxidation of UO2 into U4O9 and U3O7 whose quantities increase with the grinding time while crystallite sizes decrease.

Investigating the Passivity and Dissolution of a Corrosion Resistant Mg-33at.%Li Alloy in Aqueous Chloride Using Online ICP-MS

The corrosion and dissolution of a new magnesium-lithium (Mg-Li) alloy was studied using an electrochemical flow cell coupled with inductively coupled plasma - mass spectroscopy (ICP-MS) allowing real-time spectroelectrochemical analysis. The alloy studied is a corrosion resistant Mg-33at. % Li alloy, which possesses a body centered cubic matrix and a homogenous nanostructure. A detailed investigation of the dissolution kinetics of this alloy is important for understanding the origins of its apparently high corrosion resistance. Whilst the alloy composition ratio of Mg:Li is ∼2, it was revealed that the dissolution ratio of metallic Mg:Li in 0.01 M NaCl was ∼3.4 via downstream detection of ions. The deficiency of Li detected in the downstream electrolyte via ICP-MS was attributed to the development of a persistent Li-rich surface film that forms dynamically in the open circuit condition and for applied potentials below ∼−1050 mVAg/AgCl. For potentials positive to ∼−1050 mVAg/AgCl, significant Li ion detection in solution was observed, commensurate with the alloy compositional ratio.

Structural and optical control of DNA-mediated Janus plasmonic nanostructures.

The broken symmetry of Janus nanostructures (JNs) provides a distinctive means to express drastically different chemical and physical characters within a single particle and acquire emergent properties usually inconceivable for homogeneous or symmetric nanostructures. In spite of their tremendous application potential, considerable challenges are encountered in identifying pathways to synthesize or assemble JNs with a controllable geometry and morphology. Here, we exploit the reverse process of growth, i.e. silver etching, to quantitatively control the structural and optical properties of the DNA-mediated Au-Ag JNs. The transmission electron microscopy and optical measurements, along with numerical simulations, present a comprehensive view of the etching dynamics and a detailed analysis of the influencing factors that provide handles for regulating the silver etching rate and progress. In addition, a novel type of composite JN is proposed and a model system is designed and engineered through dynamical control of the etching and DNA-hybridization processes.

Development of anode mixture composition from processing products of coal to produce carbon nanostructures by the plasma-arc method

It is discussed the use of coal processing products as a part of the anode mixture and their effect on the production of homogeneous carbon nanostructures by the plasma-arc method. The main aim of this research is to develop a theoretical basis and anode mixture composition, allowing to obtain morphologically uniform carbon nanostructures. It was used arc evaporation method for synthesis of nanostructures. Identification of carbon nanostructures and sizes was carried out by electron microscopy. Carbon nanoparticles, carbon filamentary structure and carbon fiber were obtained using the proposed components that make up the anode mixture, pitch coke, coal tar and coal medium temperature pitch. The carbon content in pitch coke and in the form of aromatics in the coal medium temperature pitch may allow to obtain more homogeneous morphologically carbon nanostructure. The research results can be used to improve the strength and corrosion resistance of metals. We propose to use the processing products of coal as part of the anode mixture to produce morphologically uniform carbon nanostructures by the plasma-arc method.

Nitrided 08Kh17T steel after high-pressure torsion

The effect of severe plastic deformation by high-pressure torsion (HPT) on the microstructure, the phase composition, the microhardness, and the thermal stability of 08Kh17T steel preliminarily subjected to high-temperature bulk nitriding followed by annealing is studied. Nitriding is performed in a pure nitrogen atmosphere at 1075°C. HPT is found to cause the formation of a homogeneous nanostructure with a grain size of 55–85 nm. The microhardness of the steel after HPT increases by a factor of 2.2–2.7, to HV 780–860 depending on nitriding conditions. Hardening is retained when the material is heated to 450°C.

Flexible solid-state supercapacitors based on freestanding electrodes of electrospun polyacrylonitrile@polyaniline core-shell nanofibers

Three-dimensional porous polyacrylonitrile/polyaniline core-shell (PAN@PANI) nanofibers are fabricated by electrospinning technique combining in situ chemical polymerization of aniline monomers. The obtained PAN@PANI nanofibers possess unique continuous and homogeneous core-shell nanostructures and high mass loading of PANI (∼60wt%) as active materials, which have greatly improved the electrochemical performance with a specific capacitance up to 577F/g at a scan rate of 5mV/s. Moreover, the porous networks of randomly arrayed PAN@PANI nanofibers provide binder-free and freestanding electrodes for flexible solid-state supercapacitors. The obtained devices based on PAN@PANI networks present excellent electrochemical properties with an energy density of 12.6Wh/kg at a power density of 2.3kW/kg and good cycling stability with retaining more than 98% of the initial capacitance after 1000 charge/discharge cycles, showing the possibility for practical applications in flexible electronics.

Pulsed ultra-violet laser interactions with ultra-low-density porous carbon nanotube sponges

In order to improve the understanding of laser interactions of materials with homogeneous nano-structures, pulsed laser induced plasma from a low density, high-porosity multiwall carbon nanotube (CNT) sponge and a dense graphite block have been investigated by combinational spectroscopy approaches. We observe distinct differences in the laser-induced light emission of the CNT sponge and graphite block which we attribute to the occurrence of a phase explosion caused by the lower thermal conductivity and weaker mechanical strength of the CNT sponge. Furthermore, spectroscopy plasma analysis reveals that differences in the surface of the two systems play a key role in the generation of negative carbon ions. We observe a more effective production of negative ions for the CNT sponge as compared to the graphite block due to the greater number of surface defects of the CNT sponge.

Facile Carbothermal Reduction Synthesis of ZrB2 Nanoparticles: The Effect of Starting Precursors

Zirconium diboride (ZrB2) ceramic nanoparticles were synthesized by using zirconium (IV) complexes as new precursors. The citrate sol–gel process, which included the mixing of ions at the atomic scale, affected hydrolysis reactions and finally led to the formation of the pure phase of the sample. Results showed that the different sizes of ZrB2 nanocrystals were produced by adjusting four potential chelating agents of bi- and tetra-dentate (N2O2 donor set) ligands by the sol-gel process during carbothermal reduction. The samples were characterized by thermal gravimetric analysis (TGA), X-ray diffraction, fourier transform infrared (FTIR) spectroscopy, field emission scanning electron microscopy (FESEM), and transmission electron microscopy (TEM). The results obtained from microscopic observations indicated that pure and homogeneous ZrB2 nanostructures have been formed by using 2-hydroxyacetophenone (hap).

Sound barrier properties of sustainable waste rubber/geopolymer concretes

Noise is one of the most important environment pollutants, especially in our modern everyday life. Concrete panels can be used as sound barriers to eliminate or, at least, to reduce the noise pollution. Conventional concrete is produced using ordinary Portland cement (OPC) as a binder, a highly energy intensive product which releases carbon dioxide (CO2) during hydration. Therefore, conventional concrete cannot be considered sustainable, as far as energy consumption and greenhouse gases emissions are concerned. In this work, due to its high mechanical performance and environmental advantages, we used a nanostructured geopolymeric binder as an alternative to OPC. Geopolymeric binders offer a significantly lower CO2 footprint compared with that associated with the production of OPC. Besides it, we used waste rubber (WR) in preparation of noise barriers to combat the existing problems of both waste disposal and noise pollution, simultaneously. Hereby, a new concrete was developed based on metakaolin-geopolymer incorporating WR, targeted as base for designing and construction of noise screens. For producing high strength geopolymer concrete, the optimum molar ratios of SiO2/Al2O3, Na2O/SiO2 and H2O/Na2O were adjusted as 3.7, 0.22 and 18, respectively, at an NaOH concentration of 15 M. SEM micrographs showed a homogeneous nanostructure for corresponding metakaolin-geopolymer. Crumbed WR was used to replace total aggregate at ratios of 2, 6, 10 and 14 wt%. The results indicated that waste rubber geopolymer concrete exhibited higher sound transmission loss, better sound absorption property and noise reduction coefficient compared to conventional concrete.

Preparation of Homogeneous Nanostructures in 5 Minutes for Cancer Cells Capture

Grafting aptamers on nanostructured substrates has shown ultrasensitivity in isolation of circulating tumor cells (CTCs). Here, we report that over 80 cm2 of homogenous nanostructured surface on glass substrates can be prepared in 5 min after one‐step dry etching. The surface area was doubled; the average diameter of nanostructures is approximately 374 nm, which is more close to the nanostructures of natural extracellular matrix. Antiepithelial cell adhesion molecule aptamers grafted nanostructured glass substrates captured over 76% of PC3 cells compared to 30% of planar substrates. Bispecific aptamers cofunctionalized nanostructured substrates, however, fail to capture cancer cells probably due to the formation of heterodimers. This limitation reveals that multispecific aptamers, when applied to cell isolation, must be analyzed to exclude any potential formation of heterodimers due to complementary sequence matching.

Surface-enhanced Raman imaging of cell membrane by a highly homogeneous and isotropic silver nanostructure.

Label-free chemical imaging of live cell membranes can shed light on the molecular basis of cell membrane functionalities and their alterations under membrane-related diseases. In principle, this can be done by surface-enhanced Raman scattering (SERS) in confocal microscopy, but requires engineering plasmonic architectures with a spatially invariant SERS enhancement factor G(x, y) = G. To this end, we exploit a self-assembled isotropic nanostructure with characteristics of homogeneity typical of the so-called near-hyperuniform disorder. The resulting highly dense, homogeneous and isotropic random pattern consists of clusters of silver nanoparticles with limited size dispersion. This nanostructure brings together several advantages: very large hot spot density (∼10(4) μm(-2)), superior spatial reproducibility (SD < 1% over 2500 μm(2)) and single-molecule sensitivity (Gav ∼ 10(9)), all on a centimeter scale transparent active area. We are able to reconstruct the label-free SERS-based chemical map of live cell membranes with confocal resolution. In particular, SERS imaging is here demonstrated on red blood cells in vitro in order to use the Raman-resonant heme of the cell as a contrast medium to prove spectroscopic detection of membrane molecules. Numerical simulations also clarify the SERS characteristics of the substrate in terms of electromagnetic enhancement and distance sensitivity range consistently with the experiments. The large SERS-active area is intended for multi-cellular imaging on the same substrate, which is important for spectroscopic comparative analysis of complex organisms like cells. This opens new routes for in situ quantitative surface analysis and dynamic probing of living cells exposed to membrane-targeting drugs.

Impact of Ultrasonic Waves in Direct Electrodeposition of Nanostructured AuPt Alloy Catalyst on Carbon Substrate: Structural Characterization and Its Superior Electrocatalytic Activity for Methanol Oxidation Reaction

We have successfully developed a facile, fast, and efficient synthetic methodology for direct fabrication of stable AuPt alloy nanostructure catalyst on Toray carbon (TC) as well as glassy carbon substrates without involving any additional stabilizer or surfactant through ultrasonic-wave-assisted electrodeposition (USA-ED) using simple Au and Pt metal salt precursors in electrolyte solution. To know the real effect of ultrasonic waves on deposited particles, the same experimental methods also followed without ultrasonic waves. Size, morphology, surface composition, and surface structure of AuPt alloy nanostructures were investigated by field emission scanning electron microscopy (FE-SEM), energy-dispersive X-ray analysis (EDAX), X-ray diffraction (XRD), inductively coupled plasma mass spectrometry (ICP-MS), and cyclic voltammetric techniques. The observed results clearly reveal that the USA-ED method yields densely packed Pt-rich AuPt alloy nanostructure, which is a more active electrocatalyst for methanol oxidation, whereas the normal (i.e., without ultrasonic wave) ED method shows loosely packed homogeneous alloy AuPt nanostructure, which is very poor for methanol oxidation. More significantly, USA-ED of Pt-rich AuPt alloy nanostructured surface showed profound enhancement of both electrocatalytic activity and long-term stability of methanol oxidation when compared to ED of Pt nanoparticles, USA-ED of Pt nanoparticle surfaces, and also state-of-the-art commercial electrocatalysts with 30 wt % loading of Pt/C (E-TEK). These obtained results confirm that our synthetic methodology of USA-ED is effective for preparing Pt-rich AuPt alloy nanostructured electrocatalyst with excellent activity and stability in methanol oxidation reaction.

Hetero- and homogeneous three-dimensional hierarchical tungsten oxide nanostructures by hot-wire chemical vapor deposition

We present the synthesis of three-dimensional tungsten oxide (WO3−x) nanostructures, called nanocacti, using hot-wire chemical vapor deposition. The growth of the nanocacti is controlled through a succession of oxidation, reduction and re-oxidation processes. By using only a resistively heated W filament, a flow of ambient air and hydrogen at subatmospheric pressure, and a substrate heated to about 700°C, branched nanostructures are deposited. We report three varieties of simple synthesis approaches to obtain hierarchical homo- and heterogeneous nanocacti. Furthermore, by using catalyst nanoparticles site-selection for the growth is demonstrated. The atomic, morphological and crystallographic compositions of the nanocacti are determined using a combination of electron microscopy techniques, energy-dispersive X-ray spectroscopy and electron diffraction.