Molecular Electronics: Novel Materials for Room Temperature Spintronics in Thin Films
Who: Prof Nicholas M Harrison (Director, Institute of Molecular Science and Engineering, Imperial College London, London, UK)
When: Tue, 4-Feb-2020, 11am
Where: S16 Level 6 – Theory Common Conference Room
Host: Prof Andrew Wee
Current electronic devices are the product of a top-down approach involving the miniaturization of their components. We are now entering an era in which the unavoidable limits imposed by quantum mechanics prevent further reductions in scale. The prospect of a bottom-up approach with electronic and spintronic devices assembled from molecular components is an intriguing alternative that is now being very actively explored. This introduces a class of versatile, sustainable and highly processable materials that could facilitate sustainable production of low energy, flexible and efficient devices. Spintronics is however based on the manipulation of electronic spin; there is unfortunately only one known example of a magnetic molecular semiconductor operating at room temperature.
In this talk we present an overview of how a combination of theoretical modelling and experimental characterisation has been used to design, synthesise and grow molecular thin films and nanostructures with tuneable magnetic coupling, charge transport and light absorption properties that are approaching the requirements for practical applications. A recent example of a film based on cobalt phthalocyanine reaching 100K and a theoretical prediction of a film with room temperature magnetism will be highlighted.
About the speaker:
Professor Harrison is co-Director of the Institute for Molecular Science and Engineering at Imperial College London. He is the developer of multiple widely used theoretical and computational methods for the discovery and optimisation of advanced materials. His contributions include the introduction of hybrid exchange methods to solid state physics and chemistry, the computational discovery of the hardest known oxide, advances in first principles thermodynamics and the discovery of near room temperature organic ferromagnets. He has been the Professor of Computational Materials Science at Imperial College since 2000, is a Fellow of the Institute of Physics and of the Royal Society of Chemistry.
Engineering Strain and Symmetry in Semiconductor Nanostructures
Who: Prof Edward T. Yu, The University of Texas at Austin, USA
When: Wed, 5-Feb-2020, 11am
Where: CQT Level 3 Seminar Room, S15-03-15
Host: Professor Berthold-Georg Englert
Mechanical deformation, or strain, is a well-established tool for engineering electronic and optical behavior in semiconductors. In crystalline semiconductor nanostructures, the spatial distribution of strain, and its corresponding consequences, can be considerably more complex than in conventional epitaxial thin-film materials. We will describe studies from our laboratory in which strain and its consequences are characterized and explored in two types of semiconductor nanostructures – Ge/SiGe core-shell nanowires, and atomically thin transition metal dichalcogenide (TMD) materials. In Ge/SiGe core-shell nanowires, we show that tip-enhanced Raman spectroscopy (TERS) can be used to determine local, diameter-dependent strain levels in nanowires via strain-dependent phonon shifts, and that phonon-carrier interactions at the two-dimensional hole gas formed at the Ge/SiGe interface lead to phonon energy renormalization that depends on carrier density. In atomically thin TMD semiconductors, strain becomes an even more powerful tool for controlling material properties due to the high levels of elastic strain that can be accommodated and the possibility of achieving precise, highly inhomogeneous strain distributions at the nanoscale. Furthermore, reductions in crystal symmetry that can arise in the atomically thin limit can give rise to behaviors that are absent or unobservable in the corresponding bulk materials. Particularly intriguing is the phenomenon of electromechanical coupling – the interplay between strain and dielectric polarization in materials – in the form of piezoelectricity and flexoelectricity. We will describe various studies in which proximal probe microscopy has been used to characterize strain and electromechanical coupling behaviors, including the first observation of flexoelectricity, in monolayer TMD materials. We will also discuss some of the likely implications of strain, electromechanical coupling, and the corresponding electrostatic charge distributions that arise in electronic, photonic, and quantum device structures fabricated from atomically thin TMD materials.
About the speaker:
Edward Yu is Professor of Electrical & Computer Engineering and holds the Judson S. Swearingen Regents Chair in Engineering at the University of Texas at Austin. He received his A.B. (summa cum laude) and A.M. degrees in Physics from Harvard University in 1986, and his Ph.D. degree in Applied Physics from the California Institute of Technology in 1991. He was a postdoctoral fellow at the IBM Thomas J. Watson Research Center from 1991 until 1992, and a faculty member at the University of California, San Diego from 1992 until 2009, when he assumed his current position at the University of Texas. Professor Yu has been the recipient of an NSF CAREER Award, ONR Young Investigator Award, Alfred P. Sloan Research Fellowship, UCSD ECE Graduate Teaching Award, and UT Austin Lepley Memorial Teaching Award, and is an AVS and IEEE Fellow. He has served as a member and Chair of the DARPA Defense Sciences Research Council (DSRC), and currently serves at UT Austin as founding Director of the Center for Dynamics and Control of Materials: an NSF MRSEC. Current research interests in his laboratory include photovoltaics and other technologies for energy harvesting and generation; nanoscale imaging and characterization techniques; and solid-state nanoscience and nanotechnology generally. The results of his research have been reported in over 190 archival journal publications.
There will be lunchtime refreshments after the talk, courtesy of the Julian Schwinger Foundation. For catering purpose, please register here if you would like to attend the seminar.