Nucleation and crystallization have been proven to be the key steps for early stage formation of metal-organic framework nanoparticles. However, the growth mechanisms attributed to size and topology control at the later stages require more research. In this study, we provide new insight into an aggregative growth pattern observed for zeolitic imidazolate framework-8 (ZIF-8). Nanoscaled ZIF-8 was synthesized with an excess of organic ligands. After reaching a size limitation, ZIF-8 particles undergo an oriented attachment (OA) growth pathway to form clusters. Additional imidazole ligands as bridging agents facilitate the OA process by cross-linking smaller ZIF-8 particles. Adding a cationic surfactant disturbs the interfacial electrostatic interactions among those nanoparticles and reduced the growth rate of {100} faces. We envision that the work presented here will inspire the mechanism studies for other nanoporous crystals.

This article reports the preparation of gold plasmonic transducers using a nanoparticle self-assembly/heating method and the characterization of the films using scattering-type scanning near-field optical microscopy (s-SNOM). Nanoparticle-polymer multilayer films were prepared by the layer-by-layer assembly on glass slides by alternating exposures to monodisperse Au(25) nanoparticles and ionic polymer linkers. Thermal evaporation of organic matters from the nanoparticle-polymer multilayer films at 600 °C allowed the nanoparticles to coalescence and form nanostructured films. Characterization of the nanostructured films generated from Au(25) nanoparticles using atomic force microscopy (AFM) showed that the films have rounded, small, island-like morphologies (d: 30-50 nm) with a pit in the center of many islands. However, further characterizations with s-SNOM revealed that the produced nanoislands contain a single gold cluster in a pit surrounded by donut-shaped dielectric species. Formation of such a structure is thought to be resulted from the embedding of gold clusters under the reorganized polysiloxane binder coatings and glass surfaces during heat treatment of the Au(25) nanoparticle multilayer films. The nanostructured films displayed strong surface plasmon resonance bands in UV-vis spectra with a peak absorbance occurring at ~545-550 nm. The optical sensing capability of the films was examined using D-glucose-functionalized gold island films with the interaction of Concanavalin A (ConA). The result showed that the adsorption of ConA on island films causes a large change in the LSPR band intensity.

This article introduces a facile nanoparticle self-assembly/annealing method for the preparation of nanoisland films. First, nanoparticle-polymer multilayer films are prepared with layer-by-layer assembly. Nanoparticle multilayer films are then annealed at similar to 500 degrees C in air to evaporate organic matters from the films. During the annealing process, the nanoparticles oil the solid surface undergo nucleation and coalescence, resulting in the formation of nanostructured gold island arrays. By controlling the overall thickness (number of layers) of nanoparticle multilayer films, nanoisland films with various island density and different average sizes are obtained. The surface property of gold nanoisland films is further controlled by the self-assembly of alkanethiols, which results in all increased surface hydrophobicity of the films. The structure and characteristics of these nanoisland film arrays are found to be quite comparable to those of nanoisland films prepared by vacuum evaporation method. However, this self-assembly/annealing protocol is simple and requires only common laboratory supplies and equipment for the entire preparation process.

This article presents a concise review of preparation methods for transparent nanostructured films, with an emphasis on their current applications in transmission-localized surface plasmon resonance (T-LSPR) sensing. One of the first methods used for the fabrication of transparent nanostructured metal films is a direct vacuum evaporation of thin gold films. Self-induced formations of small gold islands result in transparent nanostructured gold arrays. The most well-established method is a nanosphere lithography developed by Van Duyne. Nanotriangular island arrays with controlled size and optical properties can be fabricated by this protocol. A different nanolithography method known as focused ion beam milling is reported and used for the fabrication of nanohole arrays. Simple assembly of solution-phase synthesized nanoparticles has also been utilized for the preparation of nanoparticle arrays capable of T-LSPR sensing. Lastly, this article also describes a new preparation strategy, in which self-assembly/thermolysis of nanoparticle multilayers is employed to obtain transparent nanoisland architectures on glass substrates.

Mutations in the gene encoding Cu-Zn superoxide dismutase (SOD1) are one of the causes of familial amyotrophic lateral sclerosis (FALS). Fibrillar inclusions containing SOD1 and SOD1 inclusions that bind the amyloid-specific dye thioflavin S have been found in neurons of transgenic mice expressing mutant SOD1. Therefore, the formation of amyloid fibrils from human SOD1 was investigated. When agitated at acidic pH in the presence of low concentrations of guanidine or acetonitrile, metalated SOD1 formed fibrillar material which bound both thioflavin T and Congo red and had circular dichroism and infrared spectra characteristic of amyloid. While metalated SOD1 did not form amyloid-like aggregates at neutral pH, either removing metals from SOD1 with its intramolecular disulfide bond intact or reducing the intramolecular disulfide bond of metalated SOD1 was sufficient to promote formation of these aggregates. SOD1 formed amyloid-like aggregates both with and without intermolecular disulfide bonds, depending on the incubation conditions, and a mutant SOD1 lacking free sulfhydryl groups (AS-SOD1) formed amyloid-like aggregates at neutral pH under reducing conditions. ALS mutations enhanced the ability of disulfide-reduced SOD1 to form amyloid-like aggregates, and apo-AS-SOD1 formed amyloid-like aggregates at pH 7 only when an ALS mutation was also present. These results indicate that some mutations related to ALS promote formation of amyloid-like aggregates by facilitating the loss of metals and/or by making the intramolecular disulfide bond more susceptible to reduction, thus allowing the conversion of SOD1 to a form that aggregates to form resembling amyloid. Furthermore, the occurrence of amyloid-like aggregates per se does not depend on forming intermolecular disulfide bonds, and multiple forms of such aggregates can be produced from SOD1.

The optical properties of Nd0.7Sr0.3MnO3 thin films have been studied from 5 meV to 25 meV and from 0.25 eV to 3 eV, at temperatures from 15 K to 300 K and magnetic fields up to 8.9 T. A large transfer of spectral weight from high energy to low energy occurs as the temperature is decreased below 180 K, where the dc resistivity peaks, or as the magnetic field is increased. The optical data are found to be consistent with models that include both the double exchange interaction and the dynamic Jahn-Teller effect on the Mn3+ eg levels. PACS 75.70.P, 78.20.L, 78.3 Typeset using REVTEX

: The grant supported research effort to understand factors limiting current-carrying capabilities in coated conductors (CCs). Three new operating modes of scanning laser microscopy (SLM) were developed under this grant, and total of five SLM modes were utilized for the research. The research found that the increased local-current density (current-crowding) was the main cause for the dissipation and the limiting factor for the current-carrying capacity. It was found in striated CCs that the current-crowding was caused by scratches from sample-handling, localized damages during striation process, or current flow configuration due to specific striation patterns. The other aspect of the research was to understand superconducting dissipation from various YBCO-family films on bicrystal grain boundary (GB) junctions. The samples on 240 [100]-tilt GB showed that the dissipation appeared like along GB. There was no significant difference in the size and/or the pattern of hot-spots for different YBCO-family samples (regardless of nanoparticle additions, doping, and multi-layering) even though the current-carrying capability varied widely among the samples. The results implied that SLM features were determined by the GB angles not by the property of YBCO films when the dissipation began and the hot-spot appeared on GB.

Multifilamentary coated conductor (MFCC) samples with patterned links have been studied using transport and scanning laser microscopy (SLM) techniques. Striation patterns are fashioned to define multiple filaments with discretely placed superconducting (SC) links between the filaments for current sharing and redistribution. After initial measurements, an artificial incision is made on a filament to mimic a disabled filament. The changes in global and local current transport characteristics are noted for in terms of the redistribution of current flow and the modification of local dissipation. Our results show that the patterned links between filaments play a vital role in redistributing current and encouraging current sharing. We find that the main factors in limiting the current-carrying capability of MFCC samples are local current density increases, which we call “current crowding.” The susceptible areas for current crowding are several: (1) filaments adjacent to the disabled ones, since the intact filaments have to carry extra current, (2) the links where current redistribution occurs, and (3) the partially blocked filament.