‘V6’-POM
‘V18’-POM
‘P2V3W15’-POM
“More than Moore” the interface between synthetic inorganic chemistry and condensed matter physics Molecular electronics is attracting a lot of attention as a means of enabling continued reductions in feature size in data storage and processing devices. Dr Kirill Monakhov and his colleagues synthesise stimuli-responsive molecules, characterise them, and apply them on substrate surfaces, work which could open up new possibilities in highly sought after ‘More than Moore’ information technology. The microelectronics industry developed rapidly over the second half of the twentieth century and beyond, as continued down-scaling of CMOS devices opened up wider commercial opportunities. However, further miniaturisation down to the sub-10 nm regime (so-called ‘quantum limit’) and below is growing ever more challenging, prompting researchers to explore other avenues; Dr Kirill Monakhov and his colleagues (Prof Rainer Waser in Jülich and Prof Bernd Abel in Leipzig) are investigating the field of molecular electronics. “We produce coordination compounds suitable for molecular deposition experiments and nanoscale imaging on surfaces. We try to design and then synthesise molecules that are likely to exhibit many discrete and thermodynamically stable oxidation states,” he explains. Among these molecules are biocompatible vanadium-oxo clusters (polyoxovanadates) and their heteropoly derivatives from a class of polyoxometalates (hereinafter referred to as POMs), which have beneficial structure–property characteristics. “For example, usually negatively charged polyoxovanadates (charged balanced by e.g. quaternary ammonium cations or alkali
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metal cations) feature a striking interplay of molecular charge, redox states and spin states,” says Dr Monakhov. “These can be manipulated by micro-spectroscopic means to address specific goals, not only in the domain of IT devices, but also in molecular biochemistry and biophysics.”
Molecular synthesis and surface studies Researchers at Dr Monakhov’s laboratory carry out multiple tasks, from preparing and characterising molecules to immobilising and electrically accessing them on substrate surfaces, work which could hold important implications for the future development of molecule-based computer memory cells in the electronics industry. The first step here is to produce the markedly different molecular structural motifs, including the development of conceptually new metal complexes and their supramolecular assemblies. “The molecules are designed to have a level of stability against air and moisture, solubility and a specific functionality. The latter could be a low molecular charge or the charge neutrality of a POM building block for example, or you might have organic ligation growth, that
provides a source of stabilisation on surfaces,” outlines Dr Monakhov. The next step after synthesis of these coordination compounds is to investigate their suitability for adsorption as intact molecules on surfaces, which is one of the crucial prerequisites for their applicability. “We usually explore deposition of our nonvolatile molecules in solution on different substrate surfaces under ultra-high vacuum – the surfaces can be conductive. Gold substrates are basically the first choice, due to the ease of handling,” continues Dr Monakhov. The team is also investigating molecular deposition and charge transport characteristics on semi-conductive surfaces, as they aim to demonstrate compatibility with CMOS devices. Different surface-sensitive methods are used here to elucidate the structure and properties of molecular adsorbates in the electrode environment. “We employ various different techniques for sub-molecular resolution imaging and the analysis of molecule–surface interfaces, from scanning tunnelling microscopy (STM) to Grazing-incidence small-angle X-ray scattering (GISAXS),” explains Dr Monakhov. “First, we want to determine the adsorption type, the agglomeration tendency, the distribution and the oxidation state of deposited molecules.”
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