Optimization of YBCO surfaces of tunnel junctions

It is established that in YBa₂Cu₃O₇ films prepared by annealing amorphous oxide deposits, Ba segregation in the amorphous phase and YBCO decomposition after recrystallization are the major causes of surface degradation. The authors have grown films by entirely in-situ processing in which these effects are minimized. The films were epitaxially grown on (100) SrTiO ₃ substrates with the a-axis normal to the film plane. Both structural and chemical analyses indicated that they are homogeneous and have proper stoichiometry up to their surfaces. At 4.2 K, contact resistivities below 4×10^-10 ohm-cm² were obtained with gold overlayers. Junctions have been formed by depositing thin Au proximity layers over the YBCO films followed by MgO barriers and Nb counterelectrodes. In some of the junctions weak-link shorts were observed, providing unambiguous evidence that the growth procedures used can produce films that are superconducting up to their surfaces     

Combined electrochromic and plasmonic optical responses in conducting polymer/metal nanoparticle films

Poly(3,4-ethylenedioxithiophene)/poly(styrene sulphonate) (PEDOT/PSS) aqueous dispersions were mixed with aqueous gold nanoparticle and aqueous silver nanoparticle colloids. PEDOT/gold nanoparticles (Au NP) and PEDOT/silver nanoparticles (Ag NP) films were obtained by solvent casting the corresponding aqueous solutions. The nanocomposite films showed the optical characteristics associated with both the surface plasmon absorption resonance of the metal nanoparticles and the excitation of the bipolaron band of the conducting polymer. As an interesting application we demonstrate the use of metal nanoparticles to tune the color of PEDOT based electrochromic films from blue to violet in the case of Au NP or green in the case of Ag NP.     

Synthesis and characterizations of three-dimensional ordered gold- nanoparticle-doped titanium dioxide photonic crystals

We developed a simple method to prepare gold-nanoparticle-doped titanium dioxide (GTD) sol-gel solution. The optimized GTD sol-gel solutions were a mixture of TEA, titanium (IV) butoxide, HAuCl₄, and deionized water in 0.3:1:0.5:3 volume ratios at room temperature. Using this sol-gel solution, we fabricated the GTD photonic crystal structure by infiltrating this solution by dip-coating into a polystyrene (PS) template. It was found that high quality of thin films was obtained by infiltrating twice the PS templates with the synthesized GTD sol-gel solutions. Energy dispersive X-ray spectroscopy and X-ray photoelectron spectra revealed the doping of TiO₂ and Au in the GTD photonic crystals. X-ray diffraction showed that TiO₂ and Au existed as anatase phase and metallic Au phase, respectively, in the GTD photonic crystals. The results indicated that the gold nanoparticles were doped into the framework of the photonic crystals.     

Growth of two-dimensional arrays of uncapped gold nanoparticles on silicon substrates

A method of preparing large area patterned 2D arrays of uncapped gold (Au) nanoparticles has been developed. The pattern has been formed using self-assembly of uncapped Au nanoparticles. The Au nanoparticles were synthesized via toluene/water two phase systems using a reducing agent and colloidal solution of Au nanoparticles was produced. These nanoparticles have been prepared without using any kind of capping agent. Analysis by TEM showed discrete Au nanoparticles of 4 nm average diameter. AFM analysis also showed similar result. The TEM studies showed that these nanoparticles formed self-assembled coherent patterns with dimensions exceeding 500 nm. Spin coating on silicon substrate by suitably adjusting the speed can self-assemble these nanoparticles to lengths exceeding 1 μm.     

Biosynthesis of gold and silver nanoparticles using Emblica Officinalis fruit extract, their phase transfer and transmetallation in an organic solution

The design, synthesis and characterization of biologically synthesized nanomaterials have become an area of significant interest. In this paper, we report the extracellular synthesis of gold and silver nanoparticles using Emblica Officinalis (amla, Indian Gooseberry) fruit extract as the reducing agent to synthesize Ag and Au nanoparticles, their subsequent phase transfer to an organic solution and the transmetallation reaction of hydrophobized silver nanoparticles with hydrophobized chloroaurate ions. On treating aqueous silver sulfate and chloroauric acid solutions with Emblica Officinalis fruit extract, rapid reduction of the silver and chloroaurate ions is observed leading to the formation of highly stable silver and gold nanoparticles in solution. Transmission Electron Microscopy analysis of the silver and gold nanoparticles indicated that they ranged in size from 10 to 20 nm and 15 to 25 nm respectively. Ag and Au nanoparticles thus synthesized were then phase transferred into an organic solution using a cationic surfactant octadecylamine. Transmetallation reaction between hydrophobized silver nanoparticles and hydrophobized chloroaurate ions in chloroform resulted in the formation of gold nanoparticles.     

Fabrication of conducting polymer micro/nanostructures coated with Au nanoparticles for electrochemical sensors

Polypyrrole (PPy) micro/nanostructures coated with Au nanoparticles were prepared by electropolymerization and electro-deposition. Two types of PPy structures, micro-embossed and nanowire forest, were synthesized on patterned gold electrodes using different aqueous solutions, and Au nanoparticles were coated onto the PPy micro/nanostructure surface. The size of the Au nanoparticles ranged from 10 to 100 nm, and the maximum density of the nanoparticles was 73 particles/microm2. The small size and high density of the Au nanoparticles were achieved by optimizing the deposition time and chloroauric acid (HAuCl4) concentration. Cyclic voltammograms of ferrocyanide oxidation showed that the PPy micro/nanostructures coated with Au nanoparticles exhibit good electrochemical activity. These high-performance electrodes can be used in electrochemical sensors because the Au nanoparticles enhance electron transfer and provide a binding site for biomarker molecules, such as DNA, protein, and aptamers.     

Temperature distribution in SFCLs based on Au/YBCO films during quenches

We investigated temperature distribution in SFCLs based on Au/YBa₂Cu₃O₇ (YBCO). SFCLs were fabricated by patterning Au/YBCO thin films grown on sapphire substrates into meander lines by photolithography. A gold film grown on the back side of the substrate was patterned into a meander line, and used as a thermometer. The front meander line was subjected to simulated AC fault currents, and the back line to DC current. Resistance of the front and back meander lines were measured and analyzed. The SFCLs were immersed in liquid nitrogen during the experiment for effective cooling. The temperature at the back side was close to that at the front side, and was closer at lower temperatures. This was observed at all stripes. The oscillatory component of the resistance of the back meander line is smaller than, and out-of-phase with that of the front meander line, which was more pronounced at higher temperatures. These results were analyzed quantitatively with the concept of heat transfer within the SFCL and to surroundings. Solutions for a heat equation explained the temperature distribution in SFCLs quantitatively: data coincided well with the solutions. In addition, quench development near the quench start point could be understood better than before, using the results.     

Localized surface plasmon resonance sensing properties of photocatalytically prepared Au/TiO2 films

Photocatalytic deposition of Au nanoparticles from a mixed aqueous solution of HAuCl₄ and ethylene glycol onto TiO₂ films (Au/TiO₂ films) was carried out by using ultraviolet light irradiation at room temperature. In the optical absorption spectra of the Au/TiO₂ film, the localized surface plasmon resonance (LSPR) peak of Au nanoparticles was observed at 534.5 nm. When the film was immersed in various kinds of solutions, such as alcohols, NaCl and d-glucose aqueous solutions, a linear relation was clearly observed between the LSPR peak wavelength and the refractive index of the solutions, in the range of 1.0003–1.4181.     

Particle growth mechanisms in Ag-ZrO(2) and Au-ZrO(2) granular films obtained by pulsed laser deposition

Thin films consisting of Ag and Au nanoparticles embedded in amorphous ZrO(2) matrix were grown by pulsed laser deposition in a wide range of metal volume concentrations in the dielectric regime (0.08相似文献   

Optically active poly(dimethylsiloxane) elastomer films through doping with gold nanoparticles

Poly(dimethylsiloxane) (PDMS) elastomer films synthesized through a cross-linking reaction between hydroxyl-terminated or vinyl-terminated PDMS have been homogeneously doped with silica-coated Au nanoparticles. The nanocomposite synthesis involves mixing a preformed colloid of surface-modified metal nanoparticles with the elastomer film precursors. The homogeneous distribution of nanoparticles is demonstrated through the presence of well defined plasmon absorbance bands in the visible, which clearly show that the composites retain the characteristic optical properties of single Au nanoparticles. The metal particle concentration could be easily tailored either through the amount or the concentration of the nanoparticle colloid added. Since the Au nanoparticles are not cross-linked to the polymer and the concentration of particles is relatively low, we postulate that the presence of the nanoparticles does not affect the mechanical properties of the films, though this remains to be confirmed.     

Dispersion of gold dodecanethiolate in a silsesquioxane film with pendant dodecyl chains: from photoluminescent materials to gold nanocomposites

Photoluminescence of Au(I)-dodecane thiolate (Au(I)-DDT) and its thermal reduction to metallic gold have been extensively reported in the literature. However, the incorporation of this salt to a polymeric matrix to produce photoluminescent materials or gold nanocomposites by thermal reduction is a difficult task due to the insolubility of Au(I)-DDT. In this study it is shown that a silsesquioxane with pendant dodecyl chains can be a convenient host of Au(I)-DDT. The presence of dodecyl chains in both compounds and the in situ generation of the salt in the solution of the silsesquioxane precursor enabled to obtain a uniform dispersion of Au(I)-DDT in the silsesquioxane matrix. Flexible films were generated, exhibiting characteristic photoluminescent properties before thermal treatment and a uniform dispersion of gold nanoparticles after heating at 150 °C for different periods of time.     

The incorporation of preformed metal nanoparticles in zinc oxide thin films using aerosol assisted chemical vapour deposition

The feasibility of Aerosol Assisted Chemical Vapour Deposition (AA-CVD) has been investigated for the growth of zinc oxide (ZnO) films containing preformed metal nanoparticles. The deposition parameters were first established for ZnO thin films, by varying the heating configuration, substrate temperature and deposition time. Films were characterised using Scanning Electron Microscopy and X-Ray Diffraction. As-deposited films, grown at 250 °C, were mostly amorphous and transformed to highly crystalline Wurtzite ZnO at higher substrate temperatures (400-450 °C). A change in the preferential orientation of the films was observed upon changing (i), the substrate temperature or (ii), the heating configuration. Following this, the applicability of the AA-CVD process for the incorporation of preformed nanoparticles (platinum and gold) in ZnO thin films was investigated. It was found that surface agglomeration occurred, such that the ZnO films were capped with an inhomogeneous coverage of the metal. These layers were characterised using Transmission Electron Microscopy and Electron Diffraction. A possible mechanism for the formation of these metal surface clusters is presented.     

Thermal Diffusivity Determination of Protoporphyrin IX Solution Mixed with Gold Metallic Nanoparticles

Nanoparticles appear to be ideally suited for applications in targeted thermal effects in medical therapies and photothermally activated drug delivery; all depend critically on the thermal transport between the nanoparticles and the surrounding liquid. In this work thermal lens spectroscopy (TLS) was used to determine the thermal diffusivity of protoporphyrin IX (PpIX) solutions mixed with gold metallic nanoparticles. PpIX disodium salt (DS) was used in a HCl solution at 25%. Fluids containing gold (Au) nanoparticles at different concentrations were prepared and added to the PpIX solutions. For each solution, UV–Vis spectroscopy was used to obtain the optical absorption spectrum, and transmission electron microscopy (TEM) was used to obtain the gold nanoparticle size. From the TLS signal intensity, it was possible to determine the characteristic time constant of the transient thermal by fitting the theoretical expression to the experimental data. From this characteristic time, the thermal diffusivity was obtained for each solution. The results show that the thermal diffusivity of PpIX mixed with gold nanoparticles increases with an increase of the nanoparticle metallic concentration.     

正负错配纳米颗粒掺杂对YBCO薄膜性能影响的研究

利用低氟MOD工艺制备了Ba₂YTaO₆(BYTO)单一纳米颗粒掺杂及BYTO和LaAlO₃(LAO)双纳米颗粒共掺杂的YBCO复合薄膜。研究表明BYTO在YBCO薄膜中的最优掺杂量为6mol%, 此时薄膜的自场J_c为1.25 MA/cm ², 在1.2 T下获得的最大钉扎力为3.02 GN/m ³。共掺杂试验中引入与YBCO具有正错配度的BYTO粒子和负错配度的LAO粒子, 两者相互作用使有效掺杂总量提高至10mol%。调整两种纳米粒子的配比发现6mol% BYTO+4mol% LAO掺杂的YBCO复合薄膜样品在外加磁场为2 T时, J_c值高达0.27 MA/cm ², 获得最大钉扎力时的磁场由纯YBCO薄膜的0.42 T提高至共掺杂的1.6 T, 此时最大钉扎力为5.6 GN/m ³。正负错配纳米颗粒共掺杂有效地提高了YBCO复合薄膜在外加磁场下的超导性能。     

Chiral Au₂₅ nanospheres and nanorods: synthesis and insight into the origin of chirality

Chirality in nanoparticles is an intriguing phenomenon. Herein, we have devised a well-defined gold nanoparticle system for investigating the origin of chirality in nanoparticles. We have designed chiral thiols (R- and S-isomers) and synthesized chiral gold nanoparticles composed of 25 gold atoms and 18 ligands, referred to as Au(25)(pet)(18), where pet represents chirally modified phenylethylthiolate -SCH(2)CH(CH(3))Ph at the 2-position. These optically active nanoparticles are close analogues of the optically nonactive phenylethylthioalte-capped Au(25)(pet)(18) nanoparticles, and the latter's crystal structure is known. On the basis of the atomic and electronic structures of these well-defined Au(25) nanoparticles, we have explicitly revealed that the ligands and surface gold atoms of Au(25)(pet)(18) play a critical role in effecting the circular dichroism responses from the nanoparticles. Similar effects are also observed in chiral Au(25) rods. The mixing of electronic states of ligands with those of surface gold atoms constitutes the fundamental origin of chirality in such nanoparticles.     

Anodic deposition of colloidal iridium oxide thin films from hexahydroxyiridate(IV) solutions

A facile, in-situ deposition route to stable iridium oxide (IrO(x)·nH(2)O) nanoparticle thin films from [Ir(OH)(6)](2-) solutions is reported. The [Ir(OH)(6)](2-) solution, made by alkaline hydrolysis of [IrCl(6)](2-), is colorless and stable near neutral pH, and forms blue IrO(x)·nH(2)O nanoparticle suspensions once it is adjusted to acidic or basic conditions. IrO(x)·nH(2)O nanoparticle thin films are grown anodically on glassy carbon, fluorine-doped tin oxide, and gold electrodes by electrolyzing [Ir(OH)(6)](2-) solutions at +1.0-1.3 V versus Ag/AgCl. The thickness of the IrO(x)·nH(2)O films can be controlled by varying the concentration of [Ir(OH)(6)](2-) , the deposition potential, and/or the deposition time. These thin films are stable between pH 1 and 13 and have the lowest overpotential (η) for the oxygen evolution reaction (OER) of any yet reported. Near neutral pH, the Tafel slope for the OER at a IrO(x)·nH(2)O film/Au rotating disk electrode was 37-39 mV per decade. The exchange current density for the OER was 4-8 × 10(-10) A cm(-2) at a 4 mC cm(-2) coverage of electroactive Ir.     

Synthesis, characterization, and optical properties of AuSe nanoalloys

A solution phase approach to synthesize a new metal-semiconductor nanocomposite, AuSe nanoalloy has been reported. The synthesis has been achieved through UV-photoactivation of preformed Au and Se nanoparticles in micelle. Non-ionic surfactant Triton X-100 was exploited as a micellar medium for effective fusion of gold and selenium particles under UV. Both physical and chemical studies have been performed to characterize the composition and morphology of the particles. UV-visible, TEM, SEM, XPS and AFM analyses were done for characterization purpose. The optical properties of nanocomposites have been substantiated through their interaction with a fluorescent probe, eosin in aqueous solution. The spectroscopic investigation of dye-metal-semiconductor assembly has been examined critically. It has been found that the dye experiences J and H types of aggregation on the surfaces of gold and selenium nanoparticles respectively. Again, the composition dependent change of the emission profile of the probe on different nanocomposite surfaces has been rationalized in accordance with the molecular dimerization of the dye.     

Seeded growth of InP and InAs quantum rods using indium acetate and myristic acid

A synthesis of soluble III–V semiconductor quantum rods using gold nanoparticles to direct and catalyze one-dimensional growth is developed. The growth takes place via the solution–liquid–solid (SLS) mechanism where proper precursors are injected into a coordinating solvent. We report the synthesis of InP nanorods using indium acetate and myristic acid with gold nanoparticles as the catalysts in the SLS growth mode. A similar route was successfully developed for the growth of InAs nanorods. We find that the amount of Au catalyst in the reaction is an important parameter to achieve shape control. Transmission electron microscope (TEM) images of InP and InAs nanocrystals revealed that the crystals are mostly rod-shaped, and provide strong evidence for Au presence in one edge. The rods were characterized structurally using X-ray diffraction and high-resolution TEM and optically by absorption and photoluminescence.     

Surface plasma resonance spectra of Au nanoparticles formed from dewetted thin films

We investigated surface plasma resonance (SPR) properties of gold (Au) nanoparticles formed by step-by-step thermal annealing of Au films deposited onto substrates. We found that the averaged sizes of the Au particles formed in the annealing process depend on the initial thicknesses of the films. Using the geometric parameters extracted from the images of Au particles, the optical transmission spectra measured can be completely described in terms of SPR in the particles. The results suggest that annealing of Au films can be a simple and effective approach for producing Au nanoparticles with desired optical transmission properties, and the approach can be easily integrated into thin film fabrication processes.     

Au-MgF2复合纳米颗粒薄膜的制备和微结构

用射频磁控共溅射法制备了Au体积分数分别为6%、15%、25%、40%、50%和60%的Au-MgF2复合纳米颗粒薄膜.用X射线衍射、透射电镜、X射线光电子能谱对薄膜的微结构和组分进行了测试分析,分析结果表明:制备的Au-MgF2复合纳米颗粒薄膜由fcc-Au晶态纳米微粒镶嵌于主要为非晶态的MgF2陶瓷基体中构成,当Au体积百分含量由15%增至60%时,其平均晶粒尺寸由5.1nm增大到21.2 nm,晶格常数由0.399 84nm增大到0.407 43nm;随Au体积百分含量由6%增至50%,其颗粒平均粒径则由9.8nm增至21.4 nm.名义组分为vol.60%Au-MgF2样品中Au的体积百分含量约为62.6%,与设计值基本一致.