The controlled synthesis of nanoparticles in the form of spheres, rods and wires has led to a variety of applications. A much wider spectrum of applications e.g. in integrated devices would be available if a precise placement and alignment relative to neighbouring particles or other functional structures on the substrate is achieved. A potential solution to this challenge is to use top-down methods to guide the placement and orientation of nanoparticles. Ideally, a precise orientation and placement is achieved for a wide range of particle shapes, a so far unresolved challenge.
Here we propose to generate a tunable electrostatic potential minimum by exploiting double-layer potentials between two confining surfaces in liquid. The shape of the potential is determined by the local three-dimensional topography of the confining surfaces. This topography can be precisely tailored using the patterning technology that has been developed in our research group. The potential shape can be adapted to fit to a wide range of particle shapes. The trapping energies exceed the thermal energies governing Brownian motion and trap and orient particles reliably. After trapping, the particles are transferred in a subsequent step onto the substrate by external manipulation.
The separation of the trapping and placement steps has several unique advantages over existing strategies. High aspect ratio structures or fragile pre-assembled structures like nanoparticles linked by DNA strands can be pre-aligned in the trapping field and placed in the desired geometry. For applications like the placement of quantum dots into high fidelity cavities, the trapped particles can be examined optically and repelled if the spectral properties do not match. In particular the precise positioning of nanowires is promising to build up complex circuits for (opto-)electronic applications. Additionally, the trapping and placement processes proceed in parallel and high throughput values can be achieved.
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Funding SchemeERC-SG - ERC Starting Grant
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