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Optical tweezers are a powerful platform for nano- and micro-assembly, as they provide a non-contact and biologically friendly method for the three-dimensional manipulation of objects over a range of sizes and of varying material properties. Three-dimensional micro- and nano-scale structures that are composed of multiple materials often achieve improved performance over single-material designs. In the case of optical devices, the inclusion of both metallic and dielectric media allows for the possibility of achieving functionality which is otherwise inaccessible. Although there are many methods for fabricating small-scale three-dimensional optical devices, the majority of these approaches only deal with a single material or type of material. Thus, in order to create structures that consist of multiple materials, it is typically necessary to use a combination of methods over the course of several steps. Here we show that optical tweezers are a promising technology for the assembly of heterogeneous optical structures in a single process. We demonstrate our approach by fabricating structures using core-shell nanoparticles with metallic shells and dielectric cores as building blocks. To the best of our knowledge, these structures represent the first nanoscale, multi-material devices built using the optical tweezer platform. Furthermore, we discuss several relevant metrics regarding the assembly process such as object translation speeds, placement accuracy, and overall rates of fabrication. Currently, we have achieved lateral speeds up to 0.2 mm/s and placement repeatability down to 50 nm. We suggest future applications of this fabrication method and discuss the next steps in its evolution.
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