Perpendicular Orientation of Anisotropic Au-Tipped CdS Nanorods at the Air/Water Interface

Anisotropic CdS nanorods tipped by Au nanoparticles on one edge (Au-CdS-NRs) are perpendicularly oriented at the air/water interface, whereby all the Au tips are located in the subphase, using the Langmuir-Blodgett technique. Since these nano-objects reveal light-induced charge separation at the semiconductor/metal interface, it is of high interest to control their organization. The orientation of these assemblies is studied in situ while compressing the Langmuir-Blodgett trough using the π-A isotherm, Brewster angle microscopy, and horizontal touch voltammetry. All these analyses clearly confirm the induced organization of the amphiphilic Au-CdS-NRs by compression of the Langmuir layer. The compressed layers are successfully transferred by the Langmuir-Schaefer method onto transmission electron microscopy grids while maintaining the preferential orientation as analyzed by transmission, scanning and scanning trasmission electron microscopy, and X-ray photoelectron spectroscopy. As far as can be determined, the Langmuir-Blodgett technique has not been used so far for perpendicularly orienting anisotropic nano-objects. Moreover, these findings clearly demonstrate that anisotropic amphiphilic nano-objects can be treated with some similarity to the traditional amphiphilic molecular building blocks.