Face-selective electrostatic control of hydrothermal zinc oxide nanowire synthesis

Rational control over the morphology and the functional properties of inorganic nanostructures has been a long-standing goal in the development of bottom-up device fabrication processes. We report that the geometry of hydrothermally grown zinc oxide nanowires can be tuned from platelets to needles, covering more than three orders of magnitude in aspect ratio (~0.1–100). We introduce a classical thermodynamics-based model to explain the underlying growth inhibition mechanism by means of the competitive and face-selective electrostatic adsorption of non-zinc complex ions at alkaline conditions. The performance of these nanowires rivals that of vapour-phase-grown nanostructures and their low-temperature synthesis (<60 °C) is favourable to the integration and in situ fabrication of complex and polymer-supported devices. We illustrate this capability by fabricating an all-inorganic light-emitting diode in a polymeric microfluidic manifold. Our findings indicate that electrostatic interactions in aqueous crystal growth may be systematically manipulated to synthesize nanostructures and devices with enhanced structural control.National Science Foundation (U.S.) (MIT Center for Bits and Atoms (NSF CCR0122419))Massachusetts Institute of Technology. Media LaboratoryKorea Foundation for Advanced StudiesSamsung Electronics Co. (research internship)Harvard University. Society of FellowsWallace H. Coulter Foundation (Early Career Award)Brain & Behavior Research Foundation (Young Investigator Award)National Science Foundation (U.S.)National Institutes of Health (U.S.) (Director’s New Innovator Award

Solvothermal reactions: an original route for the synthesis of novel materials

Twenty years after the first development of solvothermal reactions, it appears important through the last research activities to trace the future trends taking into account their potentialities and the different economical constraints. During these last 20 years solvothermal reactions have been mainly used from preparing micro- or nanoparticles with different morphologies. Due to the importance to dispose of new materials for developing either basic research or industrial applications, such a presentation will be only focussed on the potentialities of solvothermal reactions in materials synthesis. Solvothermal reactions are mainly characterized by different chemical parameters (nature of the reagents and of the solvent) and thermodynamical parameters (in particular temperature, pressure). (a) The selection of the composition of the solvent opens new research areas for stabilizing materials belonging to different classes of materials (alloys, oxides, nitrides, sulphides...). (b) The mild temperature conditions generally used are able to improve chemical diffusion and reactivity in order to help the preparation of specific materials at the frontier between either different classes of inorganic materials (oxides-nitrides, nitrides-halides...) or inorganic/organic, inorganic/biologic frameworks. (c) The high pressure conditions, due to the small conveyed energy compared to temperature, allow also to stabilize metastable frontier materials (geo-inspired or bio-inspired materials). (d) In the future, taking into account, from one side: the economical and the environmental constraints, and from the other: the industrial demand of materials characterized by specific physical, chemical and biological properties, the potential developments of solvothermal processes will be analyzed