The International Technological Roadmap for Semiconductors (ITRS) predicts that the exponential downscaling of silicon integrated circuits (Moore’s Law) will continue at least for the coming decade, reaching 10 nm feature sizes. What will happen beyond the 10 nm horizon is an open and very intriguing question. It is very likely that alternative electron device concepts and architectures will be necessary to push Moore’s Law any further. One of the developments beyond, but also very much besides mainstream silicon electronics, is hybrid nanoelectronics.
Where conventional electronics makes use mainly of top-down fabrication technology, the introduction of molecular materials paves the way for bottom-up fabrication as well (self-assembly). Hybrid electronic devices benefit from the strong aspects of both fabrication methods. In this research line we take advantage of all these characteristics of hybrid electronic devices to carry out experiments in a largely unexplored area of fundamental and broad scientific interest.
The conduction mechanism in organic (molecular) materials often differs drastically from that in their inorganic (crystalline) counterparts, and still many aspects remain to be understood. A very important and critical issue is the understanding of electronic phenomena at the interface between inorganic and molecular materials, as they usually play a dominant role in the overall properties.
The research addresses magnetic interactions, quantum coherence and electronic characterization of single nanostructures, topics lying at the very heart of solid-state physics, with many fascinating and important questions to be answered. The combination of expertise in nanoelectronics, magnetism, (supramolecular) chemistry and bottom-up fabrication puts us in a unique, internationally competitive, position. An interdisciplinary approach as in our NanoElectronics Group at MESA+, is being followed in an increasing number of institutes around the world. We aim to experimentally investigate fundamental concepts that are attracting a lot of theoretical and experimental attention, in such areas as correlated condensed matter physics, molecular electronics, spintronics and quantum information science.
Tunable doping of a metal with molecular spins
The mutual interaction of localized magnetic moments and their interplay with itinerant conduction electrons is a key topic in solid-state physics. To enable systematic study of a given magnetic impurity-host system, straightforward tuning of the impurity density is highly desirable, as this sets its physical properties. We have developed a novel, facile molecular fabrication method for inserting isolated localized magnetic moments in a gold film with tunable density. Our results show excellent agreement with Kondo- and weak localization theory. We show that the impurity concentration can be systematically varied up to ~800 ppm without any sign of inter-impurity interaction, or undesired clustering from which alternative methods often suffer.
Metal–ligand complexes used for the tunable spin doping. The Co complex (left) has spin half, whereas the Zn complex (right) has spin zero.
Temperature dependence of the metal film resistivity for different Co:Zn complex ratios. The upturn at low temperature is due to the Kondo effect.
Tunable doping of a metal with molecular spins
T. Gang et al., Nature Nanotechnology, DOI: 10.1038/NNANO.2012.1 (2012).
Coherent transport properties of organic molecules
Although coherent electron transport in inorganic systems is experimentally well studied by now, the coherence of electron transport through organic molecules is experimentally much less explored. It is a fascinating question to ask to what extent transport through organic molecules is coherent and how the coherence depends on the molecule’s characteristics (e.g. length, chemical composition, side groups, chemical bonding, electron-lattice coupling), as well as on external parameters (e.g. temperature, electrostatic potential, magnetic field, electronic coupling of the molecules to their environment). Our objective is a systematic study of charge coherence in molecular systems.
Electronic characterization of single nanostructures and molecules
Connecting single nanostructures to electric circuitry has proven to be an extremely difficult task. Our objective is to develop an unconventional bottom-up nanocontacting scheme for addressing single nanostructures – quantum dots and potentially molecules – for the ultimate goal of single-electron/photon control. The nanostructures are attached by self-assembly to highly-conductive leads, bridging the gap between the nano- and microscale. An important and unique advantage compared to conventional (top-down) nanocontacting schemes is the high control and reproducibility afforded by molecular recognition, enabling a wide range of unprecedented experiments. We will study low-temperature electron transport through single semiconductor QDs and single molecules.
The added value of integrating top-down and bottom-up (self-assembly) techniques to open up unexplored areas of physics, forms a key unifying element of this project. It will thereby strongly benefit from existing collaborations with leading chemistry groups at Twente, Münster and Bologna.
These projects are financed by the European Research Council (ERC)