Controllable self-assembly of PbS nanostars into ordered structures: close-packed arrays and patterned arrays.

Controllable self-assembly of uniform star-shaped PbS nanocrystals with six symmetric 100-oriented horns into highly ordered structures including close-packed arrays and patterned arrays was realized by evaporation-induced assembly routes. First, large-area three-dimensional (3D) and two-dimensional (2D) hexagonal close-packed (hcp) arrays of PbS nanostars were assembled on clean Si substrate by drop coating and vertical deposition, respectively. Then, by using monolayer colloidal crystals (MCC) and inverted MCC (IMCC) as the template, a variety of non-close-packed (ncp) arrays of PbS nanostars with controllable patterns were fabricated through the vertical deposition method. With the MCC template, an ncp array of [111]-oriented PbS nanostars with three horns stably standing on the template plane was prepared, leading to the formation of novel star-sphere binary colloidal crystals with a stoichiometric star/sphere ratio of 1. The reflectance spectrum of the resultant MCC-PbS composite array was measured, which exhibited a considerable red shift in the reflectance peak compared with the original MCC template. Alternatively, with the IMCC template, an ncp array of [001]-oriented PbS nanostars with a single horn stretched vertically upward was obtained. Furthermore, some novel patterns for PbS ncp arrays were readily fabricated using MCC/IMCC templates with larger periodic spacings. For the template-assisted assembly of PbS nanostars, the obtained PbS ncp arrays generally inherited the long-range hexagonal order from the initial MCC template. This assembly strategy is a versatile approach and may open a new route for the controlled assembly of anisotropic nanostructured materials into large-scale ordered arrays with desirable patterns.