R&D Profile: Achieving both nanopatterning and desired upright orientation with alkanedithiol self-assembled monolayers on gold
The capability of design and fabrication of nanometer-sized functional materials are highly desired in nanotechnology due to their potential use as building blocks in nanodevices.
Due to the high affinity of SH functionalities to metals, thiol-terminated self-assembled monolayers (SAMs) have attracted tremendous attention for potential applications such as anchoring metal atoms to organic thin films or construction of molecular electronic devices [1]. Organodithiols on gold are promising candidates to generate layers exhibiting free SH groups if molecules attach to the substrate through only one end and adopt a standing-up configuration as in the case of alkanethiols. However, the dithiols usually yield lying-down or looped alkanedithiolates on gold via the binding of both SH groups when adsorbed layers are prepared from the widely used natural growth approach. Here, a new approach to circumvent that obstacle and achieve high-quality thiol-terminated assemblies is developed [2]. It applies an atomic force microscopy (AFM)-based lithography method known as nanografting performed in a dithiol solution. The spatially constrained reaction environment in nanografting sterically favors the adoption of a standing-up configuration for the initially adsorbed dithiol molecules. In addition, nanografting enables the fabrication of thiol-terminated layers on gold with nanometer-scale precision in geometry, size and location. These thiol-terminated nanostructures can be served as templates to direct subsequent metal binding on surfaces.
(a) Mechanism of AFM-based nanolithography method known as nanografting. (b) A fabricated "AFM" logo with the line width less than 10 nm. (c) An example of nanopatterning of closely packed thiol-terminated SAMs using nanografting.
