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Dopant atoms are used to tailor the properties of materials. However, whether the desired effect is achieved through selective doping depends on the dopant distribution within the host material. The clustering of dopant atoms can have a deleterious effect on the achievable properties because a two-phase material is obtained instead of a homogeneous material. Thus, the examination of dopant fluctuations in nanodevices requires a reliable method to chemically probe individual atoms within the host material. This is particularly challenging in the case of functionalized nanoparticles where the characteristic length scale of the particles demands the use of a high-spatial-resolution and high-sensitivity technique. Here we demonstrate a chemically sensitive atomic resolution imaging technique which delivers direct site-specific information on the dopant distribution in nanoparticles. We employ electron energy-loss spectroscopy imaging in a scanning transmission electron microscope combined with multivariate statistical analysis to map the distribution of Ba dopant atoms in SrTiO(3) nanoparticles. Our results provide direct evidence for clustering of the Ba dopants in the SrTiO(3) nanoparticles outlining a possible explanation for the presence of polar nanoregions in the Ba:SrTiO(3) system. The results we present constitute the first example of site-specific atomic resolution spectroscopy of foreign atoms in doped nanoparticles and suggest a general strategy to ascertain the spatial distribution of impurity atoms in nanocrystals and hence improve the performance of nanoparticle-based devices.

Zinc oxide nanostructures are known to exist in a great variety of morphologies. However, the underlying mechanisms leading to these architectures are far from being fully understood. Here, we present a time dependent study of the generation of zinc oxide nanorods, which arrange into bundles with a fan- or bouquet-like structure, using the benzyl alcohol route. The structural evolution of the nanoparticles was monitored by electron microscopy techniques, whereas the progress of the chemical reaction was followed by quantification of the organic by-products using gas chromatography. With this study we give a detailed insight into the formation of the zinc oxide structures, which involves a complex pathway based on many in parallel occurring processes such as crystallization of primary particles, their oriented attachment and surface reconstruction inside the nanoparticulate agglomerates. However, in spite of such an intricate growth behavior, the ZnO nanostructures are surprisingly uniform in size and shape., (This journal is © The Royal Society of Chemistry 2012)

This Feature Article gives an overview of microwave-assisted liquid phase routes to inorganic nanomaterials. Whereas microwave chemistry is a well-established technique in organic synthesis, its use in inorganic nanomaterials' synthesis is still at the beginning and far away from having reached its full potential. However, the rapidly growing number of publications in this field suggests that microwave chemistry will play an outstanding role in the broad field of Nanoscience and Nanotechnology. This article is not meant to give an exhaustive overview of all nanomaterials synthesized by the microwave technique, but to discuss the new opportunities that arise as a result of the unique features of microwave chemistry. Principles, advantages and limitations of microwave chemistry are introduced, its application in the synthesis of different classes of functional nanomaterials is discussed, and finally expected benefits for nanomaterials' synthesis are elaborated.

We present a multigram scale, one-step nonaqueous synthesis route to monodisperse, highly crystalline ZrO(2) nanoparticles. The nanoparticles can be stabilized in nonpolar solvents via a simple functionalization procedure using only minute amounts of organic stabilizers. Their great potential in materials applications is demonstrated by the fabrication of organic-inorganic nanocomposites that can be selectively photopolymerized to inscribe extremely effective and volume holographic gratings with the highest refractive index contrast (n(1) of up to 0.024) achieved so far.

The crystallization pathway of indium tin oxide nanoparticles during solvothermal synthesis in benzyl alcohol was investigated. The synthesis was stopped after different reaction times in the range of 1-24 h, and the structural and morphological characteristics of the products were analyzed by powder X-ray diffraction, electron microscopy, and UV/Vis spectroscopy. Interestingly, the crystallization mechanism does not proceed along a simple nucleation and growth pathway, but involves a two-step process. In the first 12 h an intermediate phase is formed, which consists of nanocrystallites 3-6 nm in size stabilized by an organic matrix. In this organic-inorganic network the nanoparticles are aligned into superstructures, but without any crystallographic orientation. After 12 h the intermediate phase is abruptly transformed into indium tin oxide nanoparticles with the bixbyite structure and with crystallite sizes of about 10-12 nm. This step is accompanied by the disappearance of the organic phase and the loss of the superstructure.

In this review, we highlight particle based crystallization pathways leading to single crystals via mesoscopic transformation. In contrast to the classical mechanism of atom/molecule mediated growth of a single crystal, the particle mediated growth and assembly mechanisms are summarized as "non-classical crystallization", including exiting processes like oriented attachment and mesocrystal formation. Detailed investigations of non-classical crystallization mechanisms are a recent development, but evidence for these pathways is rapidly increasing in the literature. A major driving force for these investigations originates from biomineralization, because it seems that these crystallization routes are frequently applied by natural organisms. We give a non-exhaustive literature survey on these two mechanisms with a focus on recent examples and studies, which are dedicated to a mechanistic understanding. Furthermore, conditions are introduced for which these non-classical crystallization mechanisms can be expected, as they are always an alternative reaction pathway to classical crystallization.

Nanoparticle powders composed of surface-functionalized anatase crystals with diameters of about 3 nm self-organize into different structures upon redispersion in water. The assembly is directed by a small amount of a low-molecular-weight functional ligand (the "assembler") adsorbed on the surface of the nanoparticles. The ligand functionality determines the anisotropy of the resulting structures. Multidentate ligands, such as trizma ((HOCH(2))(3)CNH(2)) and serinol ((HOCH(2))(2)CNH(2)), with a chargeable terminal group preferentially induce the formation of anisotropic nanostructures several hundreds of nanometers in total length, whereas all the other investigated ligands (ethanolamine H(2)N(CH(2))(2)OH, glycine hydroxamate H(2)NCH(2)CONHOH, dopamine (OH)(2)C(6)H(3)(CH(2))(2)NH(3)Cl, tris (HOCH(2))(3)CCH(3)) mainly lead to uncontrolled agglomeration. Experimental data suggests that the anisotropic assembly is a consequence of the water-promoted desorption of the organic ligands from the {001} faces of the crystalline building blocks together with the dissociative adsorption of water on these crystal faces. Both processes induce the preferred attachment of the titania nanoparticles along the [001] direction. The use of polydentate and charged ligands to functionalize the surface of nanoparticles thus provides a versatile tool to control their arrangement on the nanoscale.

A nonaqueous synthetic route for the preparation of a regular crystalline yttria mesostructure is presented. The reaction between yttrium alkoxides and benzyl alcohol results in the formation of a highly ordered lamellar nanocomposite consisting of yttria layers with a confined thickness of about 0.6 nm, separated from each other by organic layers of intercalated benzoate molecules. Doping with europium leads to strong red luminescence. The nanostructure formation proceeds via two reactions. A C--C bond formation occurs between benzyl alcohol and the isopropanolate ligand. At the same time, yttrium oxide catalyzes two low-temperature hydride-transfer reactions to form benzoic acid and toluene from benzyl alcohol via benzaldehyde, thus limiting the growth of the thickness of the lamellae.