Formation and grain analysis of spin-cast magnetic nanoparticle monolayers

Shape-Selective Mesoscale Nanoarchitectures: Preparation and Photocatalytic Performance

We create ordered arrays of shape-selective gold-titania composite nanomaterials at the mesoscale (100 µm to 5 mm) by a combination of both bottom-up and top-down approaches for exquisite control of the size, shape, and arrangement of nanomaterials. Lithographic techniques along with wet chemical synthetic methods were combined to create these composite nanomaterials. The photocatalytic activity of these TiO2, TiO2-Au and SiO2-TiO2-Au nano-composite mesoscale materials was monitored by the photodegradation of a model analyte, methyl orange, under UV and visible (Vis) illumination. Bare TiO2- and SiO2-TiO2-coated pillar arrays showed significant activity toward methyl orange in UV light with degradation rates on the order of 10−4–10−3 min−1. The photocatalytic activity of these arrays was also found to depend on the nanoparticle shape, in which particles with more edges and corners were found to be more reactive than spherical particles (i.e., the photocatalytic activity decreased as follows: diamonds > squares > triangles > spheres). SiO2-TiO2-Au nano-composite pillar arrays were tested in both UV and Vis light and showed increased activity in Vis light but decreased activity in UV light as compared to the bare semiconductor arrays. Additionally, the Au nanorod-functionalized nanoarrays exhibit a strong shape-dependence in their photocatalytic activity toward methyl orange degradation in Vis light.

Controlled Deposition of Nanosize and Microsize Particles by Spin-Casting

The deposition of nanosize and microsize spherical particles on planar solid substrates by hydrodynamic-evaporative spin-casting is studied. The particles are dispersed in a volatile liquid, which evaporates during the process, and the particles are finally deposited on the substrate. Their coverage, Γ, depends on the processing parameters (concentration by weight, particles size, etc.). The behavior of the particles during the spin-casting process and their final Γ values are investigated. It is found that for up to particle diameters of a few micrometers, particle deposition can be described by a theoretical approach developed for the spin-casting of polymer solutions (Karpitschka, S.; Weber, C. M.; Riegler, H. Chem. Eng. Sci. 2015, 129, 243-248. Danglad-Flores, J.; Eickelmann, S.; Riegler, H. Chem. Eng. Sci. 2018, 179, 257-264). For large particles, this basic theory fails. The causes of this failure are analyzed, and a corrected, more general theoretical approach is presented. It takes into account particle size effects as well as particle sedimentation. In summary, we present new insights into the spin-cast process of particle dispersions, analyze the contributions affecting the final particle coverage, and present a theoretical approach which describes and explains the experimental findings.

Quantifying the structural integrity of nanorod arrays

Arrays of aligned nanorods oriented perpendicular to a support, which are accessible by top-down lithography or by means of shape-defining hard templates, have received increasing interest as sensor components, components for nanophotonics and nanoelectronics, substrates for tissue engineering, surfaces having specific adhesive or antiadhesive properties and as surfaces with customized wettability. Agglomeration of the nanorods deteriorates the performance of components based on nanorod arrays. A comprehensive body of literature deals with mechanical failure mechanisms of nanorods and design criteria for mechanically stable nanorod arrays. However, the structural integrity of nanorod arrays is commonly evaluated only visually and qualitatively. We use real-space analysis of microscopic images to quantify the fraction of condensed nanorods in nanorod arrays. We suggest the number of array elements apparent in the micrographs divided by the number of array elements a defect-free array would contain in the same area, referred to as integrity fraction, as a measure of structural array integrity. Reproducible procedures to determine the imaged number of array elements are introduced. Thus, quantitative comparisons of different nanorod arrays, or of one nanorod array at different stages of its use, are possible. Structural integrities of identical nanorod arrays differing only in the length of the nanorods are exemplarily analysed.

Origin of order in bionanostructures

Analysis of corneal nanocoatings across insect species provides clues to the origin of order in the bionanoworld.

Tuning deposition of magnetic metallic nanoparticles from periodic pattern to thin film entrainment by dip coating method

In this work, we report on the self-assembly of bimetallic CoFe carbide magnetic nanoparticles (MNPs) stabilized by a mixture of long chain surfactants. A dedicated setup, coupling dip coating and sputtering chamber, enables control of the self-assembly of MNPs from regular stripe to continuous thin films under inert atmosphere. The effects of experimental parameters, MNP concentration, withdrawal speed, amount, and nature of surfactants, as well as the surface state of the substrates are discussed. Magnetic measurements revealed that the assembled particles were not oxidized, confirming the high potentiality of our approach for the controlled deposition of highly sensitive MNPs.

X-ray scattering as a liquid and solid phase probe of ordering within sub-monolayers of iron oxide nanoparticles fabricated by electrophoretic deposition

Order within sub-monolayers of nanoparticles, fabricated by electrophoretic deposition, was assessed during nanoparticle deposition in a liquid suspension and after the films had dried by grazing-incidence small-angle X-ray scattering. Experiments were performed in a custom-made, liquid-phase cell. The results indicated that ordering occurred during the drying event.

Co-assembled thin films of Ag nanowires and functional nanoparticles at the liquid-liquid interface by shaking

In this paper, we report the fabrication of co-assembled thin films composed of silver nanowires (NWs) and Au nanoparticles (NPs) at the liquid-liquid interface (water-chloroform) by vigorous shaking. The composition of co-assembled thin films can be controlled by adjusting the concentration of the nanosized building blocks. As a versatile interfacial assembly method, other nanoparticles such as Ag2S and Fe3O4 NPs can also be co-assembled with Ag NWs using the same procedure. Meanwhile, the co-assembly state of the obtained Au NPs and Ag NWs makes a significant contribution to the high sensitivity of surface-enhanced Raman scattering (SERS) to model the molecule 3,3'-diethylthiatricarbocyanine iodide (DTTCI). The SERS intensities show high dependence on the molar ratio of Au NPs and Ag NWs and the layer number of the co-assembled thin films. This shaking-assisted liquid-liquid assembly system has been proved to be a facile way for co-assembling nanowires and nanoparticles, and will pave a way for further applications of the macroscopic co-assemblies with novel functionalities.

Hybridization of inorganic nanoparticles and polymers to create regular and reversible self-assembly architectures

Inorganic nanoparticles (NPs) with diversified functionalities are promising candidates in future optoelectronic and biomedical applications, which greatly depend on the capability to arrange NPs into higher-order architectures in a controllable way. This issue is considered to be solved by means of self-assembly. NPs can participate in self-assembly in different manners, such as smart self-organization with blended molecules, as the carriers of host molecules for assembly and disassembly with guest molecules, as netpoints to endow the architectures specific functionalities, and so forth. To enhance the structural stability of the as-prepared assembly architectures, polymers have been utilized to create NP-polymer composites. Meanwhile, such a strategy also demonstrates the possibility of integrating the functionalities of NPs and/or polymers by forming regular architectures. The emerging interest in the current optoelectronic and biological areas strongly demands intelligent nanocomposites, which are produced by combination of the excellent functionalities of NPs and the responsiveness of polymers. On the basis of the recent progress in fabricating NP-polymer composites, this critical review summarizes the development of new methods for fabricating regular self-assembly architectures, highlights the reversible assembly and disassembly behavior, and indicates the potential applications.

Coating alumina on catalytic iron oxide nanoparticles for synthesizing vertically aligned carbon nanotube arrays

To synthesize long and uniform vertically aligned carbon nanotube (VACNT) arrays, it is essential to use catalytic nanoparticles (NPs) with monodisperse sizes and to avoid NP agglomeration at the growth temperature. In this work, VACNT arrays were grown on chemically synthesized Fe(3)O(4) NPs of diameter 6 nm by chemical vapor deposition. Coating the NPs with a thin layer of Al(2)O(3) prior to CNT growth preserves the monodisperse sizes, resulting in uniform, thick and dense VACNT arrays. Comparison with uncoated NPs shows that the Al(2)O(3) coating effectively prevents the catalyst NPs from sintering and coalescing, resulting in improved control over VACNT growth.

Sinter-free phase conversion and scanning transmission electron microscopy of FePt nanoparticle monolayers

Thermally robust monolayers of 4-6 nm diameter FePt nanoparticles (NPs) were fabricated by combining chemical synthesis and atomic layer deposition. Spin-cast monolayers of FePt NPs were coated with thin, 11 nm-thick layers of amorphous Al(2)O(3), followed by annealing to convert the FePt NPs from an alloy (A1) into intermetallic FePt (L1(0)) and FePt(3) (L1(2)) phases. The Al(2)O(3) layer serves as a barrier that prevents sintering between NPs during annealing at temperatures up to 730 °C. Electron and X-ray diffraction in conjunction with high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) show that as-synthesized A1 FePt NPs convert into L1(0) and L1(2) phase NPs through annealing. HAADF-STEM measurements of individual NPs reveal imperfect ordering and show that the NP composition determines which intermetallic phase is obtained. Mixed-phase NPs with L1(0) cores and FePt(3) L1(2) shells were also observed, as well as a smaller number of unconverted A1 NPs. These results highlight the need for improved control over the compositional uniformity of FePt NPs for their use in bit-patterned magnetic recording.