Reconfigurable Nanorod Films: An in Situ Study of the Relationship between the Tunable Nanorod Orientation and the Optical Properties of Their Self-Assembled Thin Films

Abstract

Understanding and controlling the self-assembly of colloidal nanostructures into ordered superstructures present scientifically interesting and technologically important research challenges. Here, we investigated the self-assembly, disordering, and reassembly of colloidal CdSe/CdS dot/rod nanorod (NR) films. We monitored the structural evolution of the NR films in real time using in situ grazing incidence small-angle and wide-angle X-ray scattering. In dry films, self-assembled from colloidal suspensions, NRs are oriented with the long axis normal to the substrate, but the preferred NR orientation is lost when dichlorobenzene vapor is introduced. Multiprobe optical and structural experiments allowed us to directly correlate the NR superlattice structure and optical absorption. We found that the optical absorption of the NR films is significantly enhanced in disordered NR films compared to NR arrays in which the rods are oriented normal to the plane of the substrate and parallel to the optical axis. Basic processing–structure–property relationships of NR thin films demonstrate that their structure and optical properties can be reconfigured through the adjustment of solvent vapor concentration. The phase behavior and optical properties of NRs present an interesting inorganic analogue to organic liquid crystals with potential applications in emerging optoelectronic technologies.