The modification of graphene band structure by periodic potential perturbation

Monolayer graphene has been under the spotlight of research since its discovery in 2004, due to its unusual properties such as massless Dirac fermions, exceptional tensile strength, ultrahigh thermal conductivity, superior charge carrier mobility, remarkable optical properties etc. Graphene-based devices are expected to be promising building blocks in nanotechnology for a range of applications. However, it has no intrinsic band gap which means that graphene FETs will have a very low on/off ratio. Several groups have tried to introduce a band gap in graphene artificially, such as etching graphene into nanoribbons. This thesis suggests the possibility to modify graphene’s band structure from appropriately engineered periodic potential patterns. Ferroelectrics is widely applied in everyday technologies, such as non-volatile memories and medical imaging, due to the presence of spontaneous polarisation in the material and that being reversible by an externally applied electric field. A ferroelectric material PZT (PbZrxTi1−xO3), is utilised in this work to produce 1D periodic potentials. A piece of single crystal thin film PZT undergoes domain engineering to create periodic potentials. With single layer graphene transferred on top, this structure qualifies as an 1D electrostatic graphene superlattice (EGSL), whose effect is measurable as a broadening of the current valley near the CNP point and variations in conductance on the gate sweep curve. A PZT-graphene device is designed, fabricated, and electrically characterised at different temperatures. The device size is kept around 300∼400nm to ensure coherence transport of electrons in the device. A unique room temperature fabrication process is developed and put in use. Evidence of a bandgap is observed, and the measurements prove to match theoretical predictions on the 1D electrostatic graphene superlattice effect.

Name dc:type.qualificationname

Doctor of Philosophy (PhD)

Level dc:type.qualificationlevel

Doctoral

Grantor dc:publisher.institution

University of Cambridge

Year dc:date.issued

2021

Author dc:creator

• Wan, Qifang

Advisor dc:contributor.advisor

• Durkan, Colm

• Graphene Ferrotronics
• Hybrid graphene/ferroelectric device
• Band structure
• Electrostatic graphene superlattice
• Domain engineering
• Graphene FET
• Piezoresponse Force Microscopy
• Kelvin Probe
• Nano-fabrication
• Low temperature measurements

Licence

• https://www.repository.cam.ac.uk/bitstreams/395d4863-3a60-4a0a-953c-934abc105567/download
• https://www.rioxx.net/licenses/all-rights-reserved/

Language dc:language

eng

DOI dc:identifier.doi

https://doi.org/10.17863/CAM.72294

OAI identifier oai:identifier

oai:www.repository.cam.ac.uk:1810/324841