Hydrothermal growth of iron oxide NPs with a uniform size distribution for magnetically induced hyperthermia: Structural, colloidal and magnetic properties

Magnetic iron oxide nanoparticles with a narrow size distribution were synthesized by hydrothermally treating suspensions of iron oxide nanoparticles. Ricinoleic-acid-coated magnetic nanoparticles were co precipitated at room temperature from an aqueous solution of Fe2+/Fe3+ cations by the addition of a base. The presence of the ricinoleic acid on the nanoparticles' surfaces strongly suppressed their growth under the hydrothermal conditions. Because of the strong dependency of the rate of particle growth on their size, the size distribution significantly narrowed during the hydrothermal treatment. The size of the nanoparticles was successfully controlled by the temperature of the synthesis and the amount of ricinoleic acid present in the reaction mixture to between 9 and 30 nm. The presence of the ricinoleic acid on nanoparticles' surfaces enabled the preparation of colloidal suspensions in even moderately polar organic liquids. Measurements of the magnetic properties revealed that the nanoparticles smaller than 14 nm exhibited superparamagnetic behavior and nanoparticles larger than 15 nm displayed single domain ferrimagnetic behavior. The nanoparticles exhibited large values of saturation magnetization of up to 90 emu/g. The strong dependence of the nanoparticles' specific power losses when subjected to an alternating magnetic field on their average size and frequency was demonstrated. The ferrimagnetic nanoparticles showed much higher power losses than the superparamagnetic nanoparticles. (C) 2016 Elsevier B.V. All rights reserved.

Surface-bound nanostructures

Kyumin Lee

This thesis looks at surface-bound nanowires and nanoparticles, the mechanical and the metrological properties of which are of practical importance in the realization of nanometer-scale electronics. Atomic force microscope (AFM) was the main instrument of research. By bending suspended carbon nanotube structures with the AFM, the Young's modulus of carbon nanotubes has been measured. An efficient new technique that involves an ac-dielectrophoresis preparation of carbon nanotubes on v-groove GaAs substrates and a force-curve measurement of the stiffness has been devised. The Young's modulus of a batch of multiwall carbon nanotubes grown by a single chemical vapor deposition (CVD) process shows a strong diameter dependence, indicating that the small catalyst particles produce crystalline tubes, while the thicker particles produce low-quality tubes with an abundance of structural defects. The experimental result is a strong evidence for the metastable-catalyst growth model of carbon nanotubes in CVD — the growth kinetics of carbon nanotubes is determined by the catalyst's liquid skin, which is more stable for smaller catalysts. As the nanotube study highlighted the importance of the size of catalyst nanoparticles, the topic of accurate nanoparticle sizing by dynamic AFM was then investigated. The measured size of a surface-bound nanoparticle was found to vary with imaging parameters, and a theoretical modeling showed that the non-contact — intermittent-contact mode switching can lead to discrepancies. Experimental results confirmed that the mode switching indeed causes the largest error in size measurements. A discrepancy also exists between the all-non-contact-mode and all-intermittent-contact-mode cases, and this anomaly could be explained by the effects of particle-substrate deformation and capillary forces. Nanoparticles were prepared on surfaces by boiling colloid drops on hot surfaces, a new technique developed for the uniformly dispersed deposition of colloidal nanoparticles and nanowires. Our experiments suggest that the actual deposition occurs through the smooth dewetting of liquid microdrops at elevated temperatures. The method is applicable on a wide range of surfaces and materials. Finally, a general haptic interface for the AFM was realized. The interface can be implemented on different AFM models with little effort, and it supports both the contact- and dynamic-AFM operations. Manipulation of gold nanoparticles has been carried out by raster scanning at different dynamic AFM setpoints, a promising approach for a quantitative study of the nanoparticle-substrate friction.

EPFL2008

Experimental observation of thermal fluctuations in single superconducting Pb nanoparticles through tunneling measurements

Klaus Kern

An important question in the physics of superconducting nanostructures is the role of thermal fluctuations (TFs) on superconductivity in the zero-dimensional limit. Here, we probe the evolution of superconductivity as a function of temperature and particle size in single, isolated Pb nanoparticles. Accurate determination of the size and shape of each nanoparticle makes our system a good model to quantitatively compare the experimental findings with theoretical predictions. In particular we study the role of TFs on the tunneling density of states (DOS) and the superconducting energy gap (Delta) in these nanoparticles. For the smallest particles h

2011

Enhanced precipitate growth at reduced temperatures during chemical ordering in deformed red gold alloys

Nadine Baluc, Marina Garcia Gonzalez, Samy Hocine, Steven Van Petegem, Helena Van Swygenhoven

Manufacturing of red gold components relies widely on controlling the formation of ordered precipitates during thermo-mechanical processing. The ordered phase hardens the material, makes it less workable and introduces residual stresses. We show that an industrial wire straightening process on chemically disordered wires enhances the formation of ordered precipitates in the near surface region during natural ageing. To address the role of plastic deformation during artificial ageing, in situ X-ray experiments are carried out on deformed and undeformed samples. It is shown that pre-deformation decreases the onset temperature for ordering and enhances precipitation growth at the early stages of the transformation. (C) 2019 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

PERGAMON-ELSEVIER SCIENCE LTD2019

Surface-bound nanostructures

Kyumin Lee

EPFL2008