1,721,024 research outputs found
Ultrathin Nanowires - A Materials Chemistry Perspective
No full textThe recent years have seen an explosive interest in one-dimensional nanostructures,([1]) as testified by the number of citations this field has accured; as customary, its blossoming was enabled by chemical breakthrough that allowed the reproducible and affordable synthesis of such structures. ([2,3]) The limitations of those syntheses was in the diameter of the nanowires that it could produce (hardly < 10 nm), and in the use of expensive and low-yield techniques, such as chemical vapor deposition (CVD). This paper attempts to summarize the very recent chemical breakthroughs that have allowed the production of ultrathin nanowires, often in solution, and often in gram-scale quantities. By no means is this a comprehensive coverage of the field, which can in part be found in other excellent reviews,([1,2,4-6]) but a selection of those contributions that we feel would most help put this emerging field in perspective. We will review the various synthetic strategies, their pros and cons, and we will give our best guesses as to the future directions of the field and what we can expect from it
Emerging strategies for the synthesis of highly monodisperse colloidal nanostructures
No full textThis short perspective describes recent developments in the synthesis of nanoscale colloids from sparingly soluble precursors. These strategies, which we dubbed 'heterogeneous nanocrystal syntheses' owing to the presence of a precursor in a non-colloidal solid state, have demonstrated the ability to generate new colloidal shapes, a superior monodispersity and a remarkable ability to delay the onset of Ostwald ripening, when compared with more traditional and purely colloidal strategies. We review the key contributions to this emerging area of research and discuss in detail the remarkable number of differences between these syntheses and the widely used homogeneous organometallic syntheses for making nanoscale colloids
Nanocrystal Plasma Polymerization: From Colloidal Nanocrystals to Inorganic Architectures
No full textNanocrystal superstructures are increasingly becoming a subject of intense study. Such materials could constitute a new class of nanocomposites of designed structure, of homogeneous composition, and with unique properties. New phenomena are observed in these materials because of the interaction at such diminutive length scales. A common problem in the development of devices relying on colloidal nanocrystal assemblies is that the individual nanocrystal building blocks require organic molecules to control their size. These ligands are responsible for the colloidal stability of the individual nanocrystal building blocks and are thus necessary for their solution processibility. Because of the ligands incompatibility with many solid state applications, it is important to develop post-processing techniques that mildly remove them from these nanocomposites, while maintaining the size-dependent properties of the building blocks. This Account highlights a new strategy, nanocrystal plasma polymerization (NPP), for processing colloidal nanocrystal assemblies. This technique exposes the nanocomposite to a mild air plasma and allows for the removal of the nanocrystals' capping ligands while preserving their size-dependent and material properties. As a result, the process yields a nearly all-inorganic flexible solid-state material with unprecedented characteristics. We describe early experiments, in which NPP was used to create arbitrarily complex ID, 2D, and 3D inorganic freestanding architectures entirely composed of nanocrystals, as well as future directions and challenges. We expect this platform will be useful for the design of new materials and will be a valuable new addition to the nanoscientist's toolbox
C-60-PMO: Periodic mesoporous buckyballsilica
No full textHere we report the first documented synthesis of a periodic mesoporous organosilica (PMO), that contains a multiply bonded C-60 moiety integrated into the silica channel walls of the material, dubbed C-60-PMO. This is accomplished through the acid-catalyzed co-assembly, Of C-60(NHCH2CH2CH2Si(OEt)(3))(x) and tetraethylorthosilicate (TEOS) with a polyethyleneoxide-polylpropyleneoxide-polyethyleneoxide triblock copolymer template. The percentage Of C-60 in the final material was estimated to be a minimum of 63 vol %, but potentially as high as 91 vol %. The effects of the synthesis conditions on the mesostructure of the resulting materials are examined. In particular, we demonstrate that the C-60 is uniformly distributed throughout the entire sample by the use of energy dispersive X-ray fluorescence (EDX) analysis and an OsO4 label bonded to the C-60
Plasma within templates: Molding flexible nanocrystal solids into multifunctional architectures
No full textRecently, there has been a great deal of progress in the synthesis of colloidal nanocrystals with tailored physical and chemical properties through control of size and shape, chemical composition, and surface functionalization (Alivisatos, A. P. Science 1996, 271 (5251), 933-937; Burda, C.; Chen, X. B.; Narayanan, R.; El-Sayed, M. A. Chem. Rev. 2005, 105 (4), 1025-1102). Nanocrystals are thus ideal building blocks for hierarchical self-assembly of topologically complex, multifunctional architectures with properties tuneable at each level of the hierarchy. Here, we present a method, which combines template-assisted self-assembly of nanocrystals with plasma polymerization (Cademartiri, L.; von Freymann, G.; Arsenault, A. C.; Bertolotti, J.; Wiersma, D. S.; Kitaev, V.; Ozin, G. A. Small 2005, 1 (12), 1184-1187) to realize hierarchical architectures that both retain the properties of the nanocrystals and offer multifunctionality. As examples, we describe CoFe2O4-PbS mixed nanocrystal nanorods, which photoluminesce, and align and move in unison with an applied magnetic field and PbS nanocrystal inverse opals, which emit and Bragg diffract near-infrared light. Such hierarchical nanocrystal architectures can be envisioned to spawn new nanotechnologies that integrate multiple functionalities into a single construct
Polymer-like Conformation and Growth Kinetics of Bi2S3 Nanowires
No full textOne-dimensional inorganic crystals (i.e., crystalline nanowires) are one of the most intensely investigated classes of materials of the past two decades. Despite this intense effort, an important question has yet to be answered: do nanowires display some of the unique characteristics of polymers as their diameter is progressively decreased? This work addresses this question with three remarkable findings on I the growth and form of ultrathin Bi2S3 nanowires. (i) Their crystallization in solution is quantitatively describable as a form of living step-growth polymerization: an apparently exclusive combination of addition of "monomer" to the ends of the nanowires and coupling of fully formed nanowires "end-to-end", with negligible termination and initiation. (ii) The rate constants of these two main processes are comparable to those of analogous processes found in polymerization. (iii) The conformation of these nanowires is quantitatively described as a worm-like conformation analytically analogous to that of semiflexible polymers and characterized by a persistence length of 17.5 nm (shorter than that of double-stranded DNA) and contour lengths of hundreds of micrometers (longer than those of most synthetic polymers). These findings do not prove a chemical analogy between crystals and polymers (it is unclear if the monomer is a molecular entity tout court) but demonstrate a physical analogy between crystallization and polymerization. Specifically, they (i) show that the crystallization of ensembles of nanoscale inorganic crystals can be conceptually analogous to polymerization and can be described quantitatively with the same experimental and mathematical tools, (ii) demonstrate that one-dimensional nanocrystals can display topological characteristics of polymers (e.g., worm-like conformation in solution), (iii) establish a unique experimental model system for the investigation of polymer-like topological properties in inorganic crystals, and (iv) provide new heuristic guidelines for the synthesis of polymer-like nanowires
Using shape for self-assembly
No full textA 1980 poem by Alan Mackay outlines his aspiration 'to see what all have seen but think what none have thought': a daunting task, which he accomplished not once, but several times. A 'truly myriadminded, manysided man-a veritable triacontahedron' in the words of his colleagues and friends, Alan Mackay pursued a lifelong interest in the problems of morphogenesis and form, a comprehension of which necessitated him crisscrossing the borders of the inanimate and animate world of soft and hard materials, through the integration of concepts and methods of chemistry, physics, mathematics and biology. In other words, he realized in his time a genuinely interdisciplinary approach to complex problems that still to this day remains beyond much of the academic community. Being invited to contribute a paper on the theme 'beyond crystals', we naturally wondered how Alan Mackay would think about the world of nanoscale self-assembly where so much depends on shape and form
Ultrathin Sb2S3 nanowires and nanoplatelets
No full textUltrathin (thickness < 2.2 nm) colloidal Sb2S3 nanowires and nanoplatelets were synthesized via a simple solution synthesis. The nanowires and platelets were stable in solution for months and were characterized via SAED, XRD, UV-VIS spectroscopy, SAXS, XPS and EDAX
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