A simple algorithm for measuring particle size distributions on an uneven background from TEM images.

Nanoparticles have a wide range of applications in science and technology. Their sizes are often measured using transmission electron microscopy (TEM) or X-ray diffraction. Here, we describe a simple computer algorithm for measuring particle size distributions from TEM images in the presence of an uneven background. The approach is based on adaptive thresholding, making use of local threshold values that change with spatial coordinate. The algorithm allows particles to be detected and characterized with greater accuracy than using more conventional methods, in which a global threshold is used. Its application to images of heterogeneous catalysts is presented.

Large-scale synthesis of single-crystalline iron oxide magnetic nanorings.

We present an innovative approach to the production of single-crystal iron oxide nanorings employing a solution-based route. Single-crystal hematite (alpha-Fe2O3) nanorings were synthesized using a double anion-assisted hydrothermal method (involving phosphate and sulfate ions), which can be divided into two stages: (1) formation of capsule-shaped alpha-Fe2O3 nanoparticles and (2) preferential dissolution along the long dimension of the elongated nanoparticles (the c axis of alpha-Fe2O3) to form nanorings. The shape of the nanorings is mainly regulated by the adsorption of phosphate ions on faces parallel to c axis of alpha-Fe2O3 during the nanocrystal growth, and the hollow structure is given by the preferential dissolution of the alpha-Fe2O3 along the c axis due to the strong coordination of the sulfate ions. By varying the ratios of phosphate and sulfate ions to ferric ions, we were able to control the size, morphology, and surface architecture to produce a variety of three-dimensional hollow nanostructures. These can then be converted to magnetite (Fe3O4) and maghemite (gamma-Fe2O3) by a reduction or reduction-oxidation process while preserving the same morphology. The structures and magnetic properties of these single-crystal alpha-Fe2O3, Fe3O4, and gamma-Fe2O3 nanorings were characterized by various analytical techniques. Employing off-axis electron holography, we observed the classical single-vortex magnetic state in the thin magnetite nanorings, while the thicker rings displayed an intriguing three-dimensional magnetic configuration. This work provides an easily scaled-up method for preparing tailor-made iron oxide nanorings that could meet the demands of a variety of applications ranging from medicine to magnetoelectronics.

Three-dimensional tomographic imaging and characterization of iron compounds within Alzheimer's plaque core material.

Although it has been known for over 50 years that abnormal concentrations of iron are associated with virtually all neurodegenerative diseases, including Alzheimer's disease, its origin, nature and role have remained a mystery. Here, we use high-resolution transmission electron microscopy (HR-TEM), energy dispersive X-ray (EDX) spectroscopy and electron energy-loss spectroscopy (EELS), electron tomography, and electron diffraction to image and characterize iron-rich plaque core material - a hallmark of Alzheimer's disease pathology - in three dimensions. In these cores, we unequivocally identify biogenic magnetite and/or maghemite as the dominant iron compound. Our results provide an indication that abnormal iron biomineralization processes are likely occurring within the plaque or the surrounding diseased tissue and may play a role in aberrant peptide aggregation. The size distribution of the magnetite cores implies formation from a ferritin precursor, implicating a malfunction of the primary iron storage protein in the brain.