Nanoconfined Atomic Layer Deposition of TiO2/Pt Nanotubes: Toward Ultrasmall Highly Efficient Catalytic Nanorockets.

Small machines are highly promising for future medicine and new materials. Recent advances in functional nanomaterials have driven the development of synthetic inorganic micromachines that are capable of efficient propulsion and complex operation. Miniaturization and large-scale manufacturing of these tiny machines with true nanometer dimension are crucial for compatibility with subcellular components and molecular machines in operation. Here, block copolymer lithography is combined with atomic layer deposition for wafer-scale fabrication of ultrasmall coaxial TiO2/Pt nanotubes as catalytic rocket engines with length below 150 nm and a tubular reactor size of only 20 nm, leading to the smallest man-made rocket engine reported to date. The movement of the nanorockets is examined using dark-field microscopy particle tracking and dynamic light scattering. The high catalytic activity of the Pt inner layer and the reaction confined within the extremely small nanoreactor enable highly efficient propulsion, achieving speeds over 35 μm s-1 at a low Reynolds number of <10-5. The collective movements of these nanorockets are able to efficiently power the directional transport of significantly larger passive cargo. [ABSTRACT FROM AUTHOR]