Monitoring Galvanic Replacement Through Three-Dimensional Morphological and Chemical Mapping

Galvanic replacement reactions on metal nanoparticles are often used for the preparation of hollow nanostructures with tunable porosity and chemical composition, leading to tailored optical and catalytic properties. However, the precise interplay between the three-dimensional (3D) morphology and chemical composition of nanostructures during Galvanic replacement is not always well understood as the 3D chemical imaging of nanoscale materials is still challenging. It is especially far from straightforward to obtain detailed information from the inside of hollow nanostructures using electron microscopy techniques such as SEM or TEM. We demonstrate here that a combination of state-of-the-art EDX mapping with electron tomography results in the unambiguous determination of both morphology transformation and elemental composition of nanostructures in 3D, during Galvanic replacement of Ag nanocubes. This work provides direct and unambiguous experimental evidence leading to new insights in the understanding of the galvanic replacement reaction. In addition, the powerful approach presented here can be applied to a wide range of nanoscale transformation processes, which will undoubtedly guide the development of novel nanostructures

Superconductivity induced by spark erosion in ZrZn2

We show that the superconductivity observed recently in the weak itinerant ferromagnet ZrZn2 [C. Pfleiderer et al., Nature (London) 412, 58 (2001)] is due to remnants of a superconducting layer induced by spark erosion. Results of resistivity, susceptibility, specific heat and surface analysis measurements on high-quality ZrZn2 crystals show that cutting by spark erosion leaves a superconducting surface layer. The resistive superconducting transition is destroyed by chemically etching a layer of 5 microns from the sample. No signature of superconductivity is observed in rho(T) of etched samples at the lowest current density measured, J=675 Am-2, and at T < 45 mK. EDX analysis shows that spark-eroded surfaces are strongly Zn depleted. The simplest explanation of our results is that the superconductivity results from an alloy with higher Zr content than ZrZn2.Comment: Final published versio

Reliable irogane alloys and niiro patination—further study of production and application to jewelry

Japanese metalworkers use a wide range of irogane alloys (shakudo, shibuichi), which are colored with a single patination solution (niiro eki). This approach allows different alloys to be combined in one piece and patinated, producing a multi-colored piece of metalwork. At present the niiro patination process is unreliable. In this study we develop a deeper understanding of the effect of patination solution ingredients on color. We have tested a synthetic niiro solution, comparing the color results with traditional niiro solution patination. Surface products have been analyzed to determine how they are influenced by both the niiro solution and cleaning procedures during patination. A large range of shibuichi and shakudo alloys have been produced to determine the full color pallette. This work also explores the use of alternative processes for the patination of irogane alloys, examining the effect of laser marking and anodizing on irogane alloys

Effects of Acid Treatment on the SEM-EDX Characteristics of Kaolin Clay

Raw kaolin was refluxed by sulphuric acid in variable concentrations of 2 M, 4 M, 6 M and 8 M. The morphology and elemental compositions of the acid-leached kaolin were analyse by Field Scanning Electron Microscopy (FESEM) and Energy Dispersive X-ray analysis (EDX) respectively. The disintegration and leaching of Al3+ ions of the clay are determined by FESEM studies. The acid treatment increases the silicon content and decreases aluminium content as revealed by EDX analysis. The leaching of Al3+ ions increases with gradual increase in concentration of the acid. Therefore, kaolin reflux with acid at lower strength (2 M and 4 M) are more dispersed and more industrially useful than that which is treated at higher acid strength

Complex Pt/Al2O3 materials for small catalytic systems

This paper reports on the preparation of catalytic materials composed of a porous metallic preform containing winding microchannels whose surface is coated by a complex catalytic film. Al2O3 is deposited inside the pores by means of wet impregnation in a first step, in order to increase the surface and to serve as an intermediate layer on which Pt nanoparticles are deposited in a second step. The latter deposition takes place by means of forced metalorganic chemical vapour infiltration (F-MOCVI). Pt(acac)2, is used in appropriate low pressure operating conditions, to allow for a process with low thermal budget, compatible with the geometrical and physical characteristics of the porous substrate. The results are evaluated by means of BET, SIMS, SEM/EDX and FEG/SEM. The catalytic material is finally being tested following the oxidation of carbon monoxide, a model reaction with high industrial interest

Tunable magnetism on the lateral mesoscale by post-processing of Co/Pt heterostructures

Controlling magnetic properties on the nm-scale is essential for basic research in micro-magnetism and spin-dependent transport, as well as for various applications such as magnetic recording, imaging and sensing. This has been accomplished to a very high degree by means of layered heterostructures in the vertical dimension. Here we present a complementary approach that allows for a controlled tuning of the magnetic properties of Co/Pt heterostructures on the lateral mesoscale. By means of in-situ post-processing of Pt- and Co-based nano-stripes prepared by focused electron beam induced deposition (FEBID) we are able to locally tune their coercive field and remanent magnetization. Whereas single Co-FEBID nano-stripes show no hysteresis, we find hard-magnetic behavior for post-processed Co/Pt nano-stripes with coercive fields up to 850 Oe. We attribute the observed effects to the locally controlled formation of the CoPt L1$_{0}$ phase, whose presence has been revealed by transmission electron microscopy.Comment: Accepted for publication in Beilstein J. Nanotechno

Synthesis of tripodal catecholates and their immobilization on zinc oxide nanoparticles

A common approach to generate tailored materials and nanoparticles (NPs) is the formation of molecular monolayers by chemisorption of bifunctional anchor molecules. This approach depends critically on the choice of a suitable anchor group. Recently, bifunctional catecholates, inspired by mussel-adhesive proteins (MAPs) and bacterial siderophores, have received considerable interest as anchor groups for biomedically relevant metal surfaces and nanoparticles. We report here the synthesis of new tripodal catecholates as multivalent anchor molecules for immobilization on metal surfaces and nanoparticles. The tripodal catecholates have been conjugated to various effector molecules such as PEG, a sulfobetaine and an adamantyl group. The potential of these conjugates has been demonstrated with the immobilization of tripodal catecholates on ZnO NPs. The results confirmed a high loading of tripodal PEG-catecholates on the particles and the formation of stable PEG layers in aqueous solution

Synthesis of NiO nanowalls by thermal treatment of Ni film deposited onto a stainless steel substrate

Two-dimensional nanostructures have a variety of applications due to their large surface areas. In this study, the authors present a simple and convenient method to realize two-dimensional NiO nanowalls by thermal treatment of a Ni thin film deposited by sputtering onto a stainless steel substrate. The substrate surface area is supposed to be significantly increased by creating nanowalls. The effects on the nanowall morphology of the thermal treatment temperature and duration are investigated. A mechanism based on the surface diffusion of Ni2+ ions from the Ni base film is then proposed for the growth of the NiO nanowalls. The as-synthesized NiO nanowalls are characterized by scanning electron microscopy, energy-dispersive x-ray analysis, x-ray diffraction, transmission electron microscopy and high resolution transmission electron microscopy