Despite the rapid growth of microfabrication technologies over the past decades, many desirable microstructures remain difficult or even impossible to create, especially when the structures are composed of multiple components that feature different materials that must be arranged in a highly specific, 3-D pattern. We have developed aqueous photoresists that can be used in combination with different techniques for nanomanipulation to create such structures. Multiphoton absorption polymerization can be used to create unsupported polymeric microstructures that can be nanomanipulated to place them in any desired position and orientation. Nanomanipulation techniques can also be used to place micro- or nanoscale components in desired locations in three dimensions, after which they can be immobilized photochemically. This toolbox of techniques offers the capability of creating a broad range of new structures and devices featuring polymeric, inorganic, metallic and biomolecular components.
Controlled manipulation of quantum dots with nanometer precision is an essential capability for basic science as well as
for scalable engineering of nanophotonic and quantum optical devices. The most common methods for manipulation of
particles use optical or dielectric trapping forces which scale poorly with particle size, making it difficult to manipulate
single quantum dots. Here we demonstrate a particle manipulation technique that achieves nanometer positioning by
controlling the flow of the surrounding liquid. This approach scales much more favorable with particle size, enabling
the position of colloidal quantum dots with better precision. Using this approach we demonstrate the capture, quantum
optical characterization, and manipulation of individually selected single quantum dots with up to 45.5 nm precision for
times exceeding one hour. This technique can be used to place pre-selected single photon sources in nanophotonic
structures such as cavities and waveguides for engineering of integrated quantum optical devices.
Considerable effort has gone into the development of techniques for three-dimensional fabrication. A particularly
promising class of techniques for creating 3D structures relies upon the use of multiphoton absorption. In multiphoton
absorption polymerization (MAP), 3D structures are created on a point-by-point basis by hardening a prepolymer resin
with a tightly focused laser beam. While MAP offers the capability of creating arbitrarily complex 3D structures with
feature sizes on the order of 100 nm, it is inherently a serial technique. In order to scale this technique up for mass
production of microstructures, it will be necessary to develop a means for parallelizing the creation of structures on the
wafer scale. One promising avenue for attaining this goal is the use of soft lithography, in the form of microtransfer
molding (&mgr;TM). However, in the past &mgr;TM has been limited to the reproduction of "2.5D" structures, i.e. those without
closed loops. We have developed a new technique called membrane-assisted microtransfer molding (MA-&mgr;TM) that can
circumvent the closed-loop issue, allowing for the replication of truly 3D structures.