New materials inspired by nature could be key to future electronics
Self-assembled nanostructures have atomically-precise structure and tailored electronic properties.
Bio organisms are the most-complex machines we know, and are capable of achieving demanding functions with great efficiency.
A common theme in these bio-machines is that everything important happens at the level of single molecules – that is, at the nanoscale.
The functionality of these bio-systems relies on self-assembly – that is, molecules interacting precisely and selectively with each other to form well-defined structures. A well-known example of this phenomenon is the double-helix structure of DNA.
Now, inspired by self-assembling bio-systems, a group of international scientists led by Monash physicists has created a new, carbon-based, self-assembled nanomaterial, which could be key to new photovoltaic and catalysis technologies.
Using self-assembly the researchers were able to engineer, with atomic-scale precision, a new 1D nanostructure composed of organic (carbon-based) molecules and iron atoms.
The findings are described in two studies published this month in Nature Communications and ACS Nano.
Atomic-scale precision via self-assembly: a pathway to functionality
“Fabricating nanomaterials by controlling the position of single atoms and molecules one at a time is very tedious, if not impossible,” said lead scientist Dr Agustin Schiffrin, Senior Lecturer at the Monash School of Physics and Astronomy and FLEET Chief Investigator. “Instead, we can create atomically-precise structures via self-assembly, by choosing the right molecules, atoms and preparation conditions,” he said.
“This has the benefit that no external intervention is required.”
Such self-assembly capability comes from using organic (that is, carbon-based) molecules as building nano-units.
The shape, size and interacting functional groups of these organic molecules can be tuned in an almost infinite number of ways using organic synthetic chemistry.
Control of interactions between molecules leads to creation of the desired, well-defined nanostructure, similarly to the way interactions between nucleic acids in DNA give rise to the double-helix.
“We can thus build materials with a very precise, engineered structure, which results in the material having the desired electronic properties,” said study co-author Marina Castelli, a Monash School of Physics and Astronomy PhD student.
“Just as the functions of bio-organisms depend on nano-scale interactions, the physical and electronic properties of these new materials come from their structure at a single-molecule level,” said study collaborator Monash Research Fellow Dr Cornelius Krull.
Conventional methods for material nanofabrication, such as lithography, rely on ‘top-down’ approaches, with materials patterned by removal of matter. Such methods are limited to resolutions of the order of 1 nanometre at best.
Instead, ‘bottom-up’ methods can allow for sub-nanometre patterning resolution, with the potential for a higher level of control and efficiency of electronic properties.
Moreover, applying ‘bottom-up’ synthesis approaches with a surface as a substrate allows for nanostructures with properties that cannot be achieved via conventional synthetic methods.
Nanomaterials based on metal-organic molecular complexes allow for a vast range of useful functionalities, both technological and biological, from catalysis to photovoltaics to gas sensing and storage.
In these systems, the atomic-scale morphology and electronic configuration of the metal-organic coordination motif play a crucial role, dictating their overall electronic and chemical properties.
The two studies
Examining electronic properties, potential for optoelectronics. The paper Designing Optoelectronic Properties by On-Surface Synthesis: Formation and Electronic Structure of an Iron-Terpyridine Macromolecular Complex, published in ACS Nano, describes energy- and spatial-dependence of the electronic states (occupied and unoccupied) of the 1D iron-based metal-organic nanostructure, in an energy range near the Fermi level, which can be useful for optoelectronic applications such as photovoltaics, photo-catalysis and light-emitting devices.
Studying structure and chemistry at the single-atom level. The paper ‘Iron-based trinuclear metal-organic nanostructures on a surface with local charge accumulation’, published in Nature Communications, describes at an atomic-scale the intramolecular structure and charge distribution of the nontrivial iron-molecule coordination motif, useful for catalysis applications.
The studies represent a successful collaboration between Monash University researchers, FLEET and scientists from the University of British Colombia and the Czech Academy of Sciences (see the papers for full list of authors and affiliations).
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