Thanks to a series of spectroscopic, physical and chemical advances; the Nanoscience field has moved forward and continuing to do so at an incredible rate. But with these advances, we are also encountering lots of different challenges. One of the main problems is, that when delving into the Nano-realm we HAVE to acknowledge that there is a whole new set of rules that we have to understand and play-by if we want to develop « functional » materials at this scale.
In 2000, the concept of Nanoarchitectonics was proposed (Ariga et al. , Adv. Mater. 2016) to offer a new approach/vision towards the development of NANOTECHNOLOGY; and to make a clear differentiation that this is NOT JUST a refinement of micro-technology. They summarise this more or less in a few key points:
First off, that the blueprint design at the nanoscale is NOT RELIABLE, given the thermal & statistical fluctuations that become present at this scale. The properties vary greatly between the molecular, nano and bulk scale (they are not translatable). Sometimes, new and unexpected properties can arise as the interactions between the individual molecular components affect the system as a whole. And finally, they insist that we should consider using a nanoscale structural unit vs molecular or atomic components to allow for a hierarchical and rational approach to develop functional nanomaterials.
So… what is a nanostructural unit and how can we make one?..
If we think about it, supramolecular self-assembly (SA) is an ideal approach to develop nanostructural units. We have molecular components, that self-assemble to form complex, integrated systems. If we then confine this system on a surface we are then in possession of a multicomponent system that we can manipulate and transfer as a whole. There is already a well-established expertise on surface self-assembly that allows for a wide range of patterns, from simple to increasingly complex systems on a variety of substrates. SO ultimately, if we incorporate a functionality atop of these 2D assemblies; we can then increase the complexity of the systems, and thus we obtain a FUNCTIONALISED SURFACE or NANOSTRUCTURE UNIT.
My research focuses on the fabrication/assembly of Nanostructures (functional surfaces), and for this we need to think of suitable molecular precursors. In this case these molecular building blocks can be imagined as a ‘smart’ unit composed of several parts/components. On the one hand, a ‘functional motif’ which will be located at an appropriate distance from a second component that will drive the self-assembly on the surface. This will help us control and prevent any ‘interfering’ interactions between the functionality and the substrate (in our case, we are mostly interested in energy and charge transfer processes).
Of course, this 3D building block must have the ability to form long-range, well-ordered SAs in a controllable and reproducible manner. And, from a chemist’s point of view we are looking for a versatile design; that will allow for a relatively quick/easy synthesis of components that we can mix ‘n match according to our needs.
From molecular devices…
Together with G. Schull, we developed and fabricated molecular wires based on polythiophenes and porphyrins to study them as single molecule junctions and light-emitting devices. The molecular wires were polymerised in-situ under high vaccum conditions, and manipulated & studied by cryogenic STM.
Once the molecular wires were formed, they were ‘plucked’ by one end by the STM tip and raised from the surface. These experiments demonstrated that as the porphyrin is lifted further away from the surface by the STM tip (in this case Au) a narrow-line emission signal could be detected as a result of the tunelling electrons that flow through the SINGLE MOLECULE. Modification of the molecular structure of the porphyrin (fluorophore) allowed us to tune the colour emitted by the device.
The challenge is now to study the photonic properties in the NANOSCALE of functional NANOSTRUCTURES.
We would like to see how these energy and charge transfer processes change with small differences in the molecular structure of the components, their 2D-arrangement and if the molecular properties are translatable into the nanoscale and beyond.
KEEP WATCHING THIS SPACE!
PUBLICATIONS on this TOPIC:
Ordinary and Hot Electroluminescence from Single-Molecule Devices: Controlling the Emission Color by Chemical Engineering, M. C. Chong, L. Sosa-Vargas, H. Bulou, A. Boeglin, F. Scheurer, F. Mathevet, G. Schull, Nano Lett., 2016, 16 (10), pp 6480–6484.
Beyond “decorative” 2D-supramolecular self assembly; a new strategy towards functional surfaces for nanomaterials, L. Sosa-Vargas, E. Kim, A.-J. Attias, Mater. Horiz, 2017, 4, 570-583.
Probing the in-air growth of large area of 3D functional structures into a 2D supramolecular nanoporous network, R. Brisse, D. Guianvarc’h, C. Mansuy, S. Sagan, D. Kreher, L. Sosa-Vargas, L. Hamitouche, V. Humblot, I. Arfaoui, V. Labet, C. Paris, C. Petit, A.-J. Attias, Chem. Comm. 2018, 10068-10071.