Synthesis of metal nanoparticles and nanowires with controlled size and aspect ratio is well developed,1-4 but the creation of ordered nanostructures comprising these is much more challenging, presenting a barrier to further development of electronic and photonic devices based on these materials. Current fabrication methods rely either on top-down approaches with limited resolution (e.g., electron-beam or nanoimprint lithography), or involve assembly methods (e.g., fluidic or electric field-driven assembly) that cannot fully overcome local potential energy variations. These obstacles make structural order difficult to control. In contrast, bottom-up self-assembly methods hold the potential for much greater control over both material properties and architecture. Here, we demonstrate a method in which nanoporous metal-organic frameworks (MOFs) loaded with silver serve as templates for ordered silver nanostructures. Exposure to an electron beam breaks down the template, leading to rapid silver coalescence. The geometric and chemical structure of the MOF, as well as the extent of metal loading, determine whether nanoparticles or nanowires are formed and define their size and orientation. Nanowires with diameters as small as 4 nm and aspect ratios > 125 can be formed, opening a path to self-assembled nanostructure design and synthesis that overcomes the limitations of existing templating methods. This method is relatively simple, compatible with many materials, and proceeds by a distinct template-directed growth mechanism. Since MOFs offer an unprecedented level of synthetic flexibility combined with highly uniform porosity as a result of their crystalline structure, this approach opens a promising new field for synthesis of self-assembled, ordered inorganic nanostructures.
Pub Type: Journals
metal-organic-framework, MOF, template, nanostructure, assembly, silver, nanowire