Atomically Thin Gold - Synthesis and Application

The first part of this project addresses our understanding and morphological control of the production of AuNS. The AuNS are produced in aqueous solution, at room temperature, via the reduction of gold salt in the presence of low concentrations of methyl orange (MO). The method requires good vibrational and temperature stability and the growth is slow (up to 12 h). A characteristic property of MO is its combination of amphiphilic nature and rigid aromatic core - such lyotropic 'chromonic phase' materials are known to self-assemble into 2D sheets and 3D stacks/columns, often with no critical concentration required for assembly.We propose to explore the growth more systematically, we will construct a temperature-controlled and vibrationally isolated chamber to allow investigations to be made for extended periods, up to 24 hr, under well-defined conditions.
The combination of factors affecting LC assembly as well as the parameters for AuNS synthesis provides a large phase-space of conditions to be explored to help better understand the formation mechanism and to develop control over morphology. For example, we will look at the importance of the different functional groups (head, tail, and aromatic core) in controlling AuNS growth, eg Methyl Red Fenaminosulf and 4-Dodecylbenzenesulfonic). Further, different mesogens assemble into different structures, eg CI RED acid 266, forms hollow chimney structures opening the intriguing possibility of templating large-diameter atomically thin Au nanotubes (which are predicted by theory to be stable. In addition to the different lyotropic mesogen type, the concentration, temperature, presence of salts and pH are all known to play a role in their assembly. Where known behaviour will be mapped on to existing phase-diagrams (or will be complemented with NMR / UV-vis studies of the chromonic systems formed). We will additionally investigate, independently, the role of Au salt and citrate reductant concentration on the number of nucleation centres and reaction rates. Through the combination of these studies, we aim to achieve morphological control over the NS produced.
The surface-modified AuNS will be characterised using XPS, UPS, AFM, Scanning Kelvin Probe, surface-enhanced Raman (SERS), and correlative TEM (fluorescence and TEM).

In the second part of the project, we will investigate one potential application of such materials - towards the development of electronic skin. Firstly, the electrical properties of single AuNS will be determined using 4-probe STM. This allows either 2- or 4- independently controlled STM tips to be brought into contact on an object under SEM guidance and has been extensively used in our labs for the characterisation of nanomaterials.[2] Finally, we will build the AuNS into polymeric matrices to create polymer-based conductive materials and investigate their conductivity as a function of stretch - this is an important factor for the development of new materials such as electronic skin.[3]