Evidence for directed self-assembly of quantum dots in a nematic liquid crystal

Assembling quantum dots (QDs) into nanoscale configurations over macroscopic dimensions is an important goal to realizing their electro-optical potential. In this Rapid Communication, we present a detailed study of a pentylcyanobiphenyl liquid crystal (LC) and a CdS QD colloidal dispersion by probing the dielectric property (epsilon) over bar and relaxation as a function of an applied ac electric field E-ac. In principle, dispersing QDs in a nematic LC medium can direct the dots to align in nearly one-dimensional chainlike structures along the nematic director and these assemblies of QDs can be directed by external electric fields. In a uniform planar aligned cell, the Freedericksz switching of the LC+QDs appears as a two-step process with the same initial switching field as the bulk but with the final (epsilon) over bar value larger than that for an aligned bulk LC. The relaxation of (epsilon) over bar immediately following the removal of E-ac follows a single-exponential decay to its original value that is slower than the bulk but becomes progressively faster with increasing E-ac, eventually saturating. These results suggest that the arrangement of the QDs is mediated by the LC.