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Details of Grant 

EPSRC Reference: EP/I00713X/1
Title: Non-conservative dynamics: a new driver in molecular electronics
Principal Investigator: Dundas, Dr D
Other Investigators:
Paxton, Professor AT Todorov, Dr TN
Researcher Co-Investigators:
Project Partners:
Department: Sch of Mathematics and Physics
Organisation: Queen's University of Belfast
Scheme: Standard Research
Starts: 01 July 2011 Ends: 31 December 2015 Value (£): 524,779
EPSRC Research Topic Classifications:
Condensed Matter Physics Materials Characterisation
EPSRC Industrial Sector Classifications:
No relevance to Underpinning Sectors
Related Grants:
Panel History:
Panel DatePanel NameOutcome
08 Jul 2010 Physical Sciences - Physics Deferred
02 Sep 2010 Physical Sciences - Physics Announced
Summary on Grant Application Form
Electrical current flow interacts with the atoms in a conductor and causes a variety of effects. The most familiar is Joule heating: this is how a lightbulb and a toaster works. Another example is electromigration: current exerts forces on atoms, much like a river pushes rocks in its way. These current-induced forces can make atoms migrate, leading to the formation of defects in the conductor that can ultimately cause it to break down.In recent years experimentalists have been able to produce conductors of truly atomic dimensions - the smallest possible in nature - such as an atomic chain or a molecule between two electrodes. The excitement of these novel structures is the vision of molecular-scale electronics: electronic devices and circuit elements down on the size scale of individual atoms and molecules.But the current densities in these tiny wires can be very large - up to ten to the power of fifteen amps per square metre - many orders of magnitude larger than in an ordinary lightbulb for example. Under these huge current densities everything is big: both Joule heating and current-induced forces in nanowires can be very large, and can blow the conductor to pieces. We have worked for years on the theory and modelling of these effects in atomic-scale devices, and recently we have made a discovery: interatomic bonding forces in atomic wires under current are non-conservative, meaning that they can do net work on the atoms when they are taken on a closed path. We demonstrated the consequences for the simplest possible geometry: an atomic chain with a bend. There, the current drives and accelerates the bend atom in an expanding orbit, creating an elemental, single-atom waterwheel.This discovery found an immediate resonance within the science community through two News-and-Views articles in the Nature journals, and immediately opens up two new directions for research. (i) The non-conservative forces are a new mechanism for energy transfer from the current to the atoms, quite distinct from Joule heating. We have already given reasons, in our original Nature Nanotechnology paper, to believe that this mechanism can be more powerful than Joule heating. Therefore, it could be the new non-conservative effects, and not ordinary heating, that are the key factor limiting the stability and functionality of molecular electronic devices. (ii) Our atomic waterwheel shows that these forces can also be used constructively to drive atomic-scale engines.Our present project will develop new simulation tools to investigate these two possibilities from first principles and model the effects of the non-conservative forces in nanoscale conductors. We will model and understand how much effective heating these forces can produce, and whether they have the ability to destroy atomic wires. We will explore another novel idea: that the non-conservative waterwheel effect, and not Joule heating, could serve as the activation mechanism for electromigration of atoms on surfaces and in interfaces. Finally, together with experimentalists in Leiden, we will investigate a possible device that can act as a current-driven atomic-scale motor: a molecule on a current-carrying surface with a freely rotating side group, with the surface current driving the rotor like a watermill. In addition to the experimental group in Leiden we have joined forces also with a leading theory group in Denmark, who have taken up our discovery and have started their own long-term programme of research into it. Although the goal is shared, our theoretical approaches are mutually complementary and, together with our experimental friends, we aim not only to explore these new phenomena, but also to create a new direction of research in our dynamic field.
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