Interfacial strain and defects in asymmetric Fe-Mn oxide hybrid nanoparticles.

Asymmetric Fe-Mn oxide hybrid nanoparticles have been obtained by a seed-mediated thermal decomposition-based synthesis route. The use of benzyl ether as the solvent was found to promote the orientational growth of Mn1-xO onto the iron oxide nanocube seeds yielding mainly dimers and trimers whereas 1-octadecene yields large nanoparticles. HRTEM imaging and HAADF-STEM tomography performed on dimers show that the growth of Mn1-xO occurs preferentially along the edges of iron oxide nanocubes where both oxides share a common crystallographic orientation. Fourier filtering and geometric phase analysis of dimers reveal a lattice mismatch of 5% and a large interfacial strain together with a significant concentration of defects. The saturation magnetization is lower and the coercivity is higher for the Fe-Mn oxide hybrid nanoparticles compared to the iron oxide nanocube seeds.

Controlling Orientational and Translational Order of Iron Oxide Nanocubes by Assembly in Nanofluidic Containers.

We demonstrate that spatial confinement can be used to control the orientational and translational order of cubic nanoparticles. For this purpose we have combined X-ray scattering and scanning electron microscopy to study the ordering of iron oxide nanocubes that have self-assembled from toluene-based dispersions in nanofluidic channels. An analysis of scattering vector components with directions parallel and perpendicular to the slit walls shows that the confining walls induce a preferential parallel alignment of the nanocube (100) faces. Moreover, slit wall separations that are commensurate with an integer multiple of the edge length of the oleic acid-capped nanocubes result in a more pronounced translational order of the self-assembled arrays compared to incommensurate confinement. These results show that the confined assembly of anisotropic nanocrystals is a promising route to nanoscale devices with tunable anisotropic properties.

Probing planar defects in nanoparticle superlattices by 3D small-angle electron diffraction tomography and real space imaging.

We demonstrate how the acquisition and processing of 3D electron diffraction data can be extended to characterize structural features on the mesoscale, and show how lattice distortions in superlattices of self-assembled spherical Pd nanoparticles can be quantified by three-dimensional small-angle electron diffraction tomography (3D SA-EDT). Transmission electron microscopy real space imaging and 3D SA-EDT reveal a high density of stacking faults that was related to a competition between fcc and hcp arrangements during assembly. Information on the orientation of the stacking faults was used to make analogies between planar defects in the superlattices and Shockley partial dislocations in metallic systems.

WO3 nanorods created by self-assembly of highly crystalline nanowires under hydrothermal conditions.

WO3 nanorods and wires were obtained via hydrothermal synthesis using sodium tungstate as a precursor and either oxalic acid, citric acid, or poly(methacrylic acid) as a stabilizing agent. Transmission electron microscopy images showed that the organic acids with different numbers of carboxylic groups per molecule influence the final sizes and stacking nanostructures of WO3 wires. Three-dimensional electron diffraction tomography of a single nanocrystal revealed a hexagonal WO3 structure with preferential growth along the c-axis, which was confirmed by high-resolution transmission electron microscopy. WO3 nanowires were also spin-coated onto an indium tin oxide/glass conducting substrate, resulting in the formation of a film that was characterized by scanning electron microscopy. Finally, cyclic voltammetry measurements performed on the WO3 thin film showed voltammograms typical for the WO3 redox process.

Phase identification and structure solution by three-dimensional electron diffraction tomography: Gd-phosphate nanorods.

Hydrothermal synthesis of GdPO4 in the presence of poly(methacrylic acid) yields nanorods with a diameter of 15 nm and an aspect ratio of 20. Powder X-ray diffraction patterns showed that the GdPO4 nanorods display peaks characteristics for both monoclinic and hexagonal structures. Three-dimensional electron diffraction tomography (3D EDT) was used to determine the structures ab initio on the basis of reciprocal volume reconstruction of electron diffraction data sets collected from single nanorods. The crystal structure of the monoclinic form was shown to be P21/n, corroborating previous work. We were able to solve the 3D structure of the hexagonal P6222 form, which has not been reported previously. Our work shows that 3D EDT is a powerful method that can be used for solving structures of single nanocrystals.

Precise control over shape and size of iron oxide nanocrystals suitable for assembly into ordered particle arrays.

Here we demonstrate how monodisperse iron oxide nanocubes and nanospheres with average sizes between 5 and 27 nm can be synthesized by thermal decomposition. The relative importance of the purity of the reactants, the ratio of oleic acid and sodium oleate, the maximum temperature, and the rate of temperature increase, on robust and reproducible size and shape-selective iron oxide nanoparticle synthesis are identified and discussed. The synthesis conditions that generate highly monodisperse iron oxide nanocubes suitable for producing large ordered arrays, or mesocrystals are described in detail.

Dimers of anthrathiophene and anthradithiophene derivatives: synthesis and characterization.

Synthesis, isolation, and characterization of derivatives of an anthrathiophene dimer (TOTBAT) and of anthradithiophene oligomers (ADTO), possessing octylthiophene units on their backbone, are described. These semiconductors are prepared through oxidative copper(II) chloride coupling. The spectroscopic properties and stability of these newly synthesized semiconductors were evaluated and supported by quantum-chemical calculations.