Emergent and artificial conductive mesoscale patterns in a polar Mott insulator

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• Publisher: Cuvillier Verlag
• Year: 2024
• eBook ISBN:
  9783689520786
• Print ISBN:
  9783689520007
• Edition: 1

The global demand for increased computational power is fuelled by the miniaturisation of electronic components. Next to this more Moore approach, more than Moore and beyond CMOS expand on existing technologies and on devices with fundamentally different principles of operation. Mott based devices are introduced under the scope of beyond CMOS, with a potentially reduced energy consumption during operation in comparison to semiconductor-based devices. In such devices quantum properties are utilised to control the current flow. Mott insulators are especially intriguing as they fulfil all conditions to be metallic but show properties of insulating materials. Up to now the properties in Mott-insulators have typically been controlled at the macroscopic length scale, which leaves room for miniaturisation. It is apparent that such a versatile material class has untapped potential with regards to utilisation of its quantum properties.This work investigates a novel class of materials, beyond CMOS, the lacunar spinels, where the electrons are localised on molecular clusters instead of atomic sites. The target system of this thesis, GaV4S8, is such a lacunar spinel and shows a structural transition, which gives rise to ferroelectric domain walls that could be used as nanoscale functional objects. Here, potential 2D conducting pathways are investigated to push Mott science to the nanoscale. These pseudo 2D properties are characterised using a range of surface sensitive techniques to understand their origin, a critical first step for functionalisation. Transferring the knowledge gained on these structures allowed for an in-situ control of the current flow at the nanoscale, pushing the boundaries of research in this quantum material.

Table of contents

• 1. Introduction: Surfaces and interfaces in potential applications
• 2. Ferroelectric materials and theirnanoscopic features
• 2.1. Symmetry in solids and phase transitions
• 2.2. Ferroics
• 2.3. Nanoscopic features
• 2.4. Spontaneous strain
• 2.5. Mott insulators
• 3. Nanoscale characterisationtechniques
• 3.1. Scanning probe microscopy
• 3.2. Piezoresponse force microscopy
• 3.3. Conductive atomic force microscopy
• 3.4. Scanning electron microscopy and the focusedion beam
• 3.5. Experimental equipment
• 3.6. Samples
• 4. Multiferroic, Mott insulator GaV4S8
• 5. Emergent mesoscale conductive patterns in GaV4S8
• 5.1. Strain driven conductivity of polar domain walls
• 5.2. Strain-induced conductivity of nano-cracks
• 6. Artificial mesoscale conductive patterns in GaV4S8
• 6.1. Brute force approach
• 6.2. In-situ written conducting features
• 7. Outlook: Nanoscopic control ofelectronic conductivity in the future of nanotechnology
• A. Further contributions to GaV4S8
• A.1. FIB written features
• A.2. GaV4S8 lamella
• A.3. Machine learning approaches to disentangle electric contributions in GaV4S8
• Bibliography
• Postface
• Acknowledgements