The ongoing trend of increasing the performance of microelectronics devices, while simultaneously reducing their size, has greatly increased the thermal demand in modern systems. Excess heat, that has its genesis at the level of nanoscale components, builds up and leads to increased running temperatures that can act as roadblocks to making faster, more efficient devices. Despite many decades of research into thermal transport and management, approaches to actively control heat flow at the nanoscale in solids is still at the level of fundamental research [1,2].
One promising approach is to use materials with reconfigurable microstructure in order to control heat flow by affecting how easily thermal vibrations can propagate. Ferroelectric materials are exciting candidates in this regard, since they support intrinsically nanostructured features called ‘domain walls’ that can both affect thermal transport and can be reproducibly created or erased with applied voltage signals. This offers the possibility to manipulate the effective thermal properties of the ferroelectric material with a control voltage and therefore to control how easily heat flows through the material.
This PhD research project aims to investigate the extent to which the thermal conductivity of ferroic crystals can be altered by controlled scattering of thermal vibrations (phonons) from both ferroelectric and ferroelastic domain walls [2-4]. Early macroscopic heat flow experiments suggest that domain walls are active in phonon scattering , but we wish to perform a systematic set of experiments to see the extent to which variations in domain wall type, density and orientation cause resulting changes in thermal conduction. This will involve careful steady-state heat flow measurements on bulk crystals in our newly installed cryostat system, down to temperatures as low as 3K. Building on this, we wish to use Focused Ion Beam machining to make cutting-edge prototype nanostructured thermal devices that incorporate ferroelectric material. Importantly, as domain walls can be created and erased using voltages, this would allow for electrical control of heat flow in a nanostructured device. As part of the research, these experiments will be supported by nanoscale heat-flow experiments using the newly commissioned Scanning Thermal Microscope (SThM) capability within CNM.
The PhD project is core to the lead investigator’s £950k UKRI Future Leaders Fellowship award  and will mainly comprise of fundamental research with a heavy experimental focus. The broader ferroelectrics activity at CNM is internationally renowned and the research features in high-impact journals and at international conferences. The student will work with Dr Ray McQuaid (as the primary supervisor) and with a vibrant and enthusiastic team of established PhD students and post-doctoral researchers.
Eligibility and How to Apply:
Informal discussions with Dr Ray McQuaid ([Email Address Removed]) are encouraged. The envisaged start date for the PhD is October 2022.