Influence of van der Waals interfaces on electrical and optical properties of two-dimensional materials

The interactions between two-dimensional (2D) materials and surrounding surfaces are critical for electronic devices. Interfacial effects become increasingly important as electronic devices continue to shrink in size. This thesis investigates the influence of van der Waals (vdW) interfaces on electrical and optical properties of 2D materials. I began by studying the nucleation and growth of indium and gold metal films on 2D materials such as molybdenum disulfide (MoS2) and graphene. Indium and gold metal films were chosen because previous research in the group has demonstrated that indium forms vdW interfaces with 2D materials while gold forms defective non-vdW interfaces. Atomic force microscopy (AFM) and scanning electron microscopy (SEM) results show that indium metal deposition on MoS2 and graphene follows a 2D growth mechanism to form large grains. The layer-dependent study of MoS2 and graphene shows that increasing the number of layers reduces the influence of SiO2 substrate roughness so that the diffusivity and diffusion length of indium atoms increase and the activation energy for indium atom diffusion decreases - as reflected in the fivefold decrease in nucleation density (~12 μm-2 ). The influence of vdW interface between graphene and ferroelectric CuInP2S6 (CIPS) was also explored. Graphene field effect transistors (FETs) with CIPS as the top gate were studied. Polarisation-induced hysteresis in CIPS-gated graphene FETs was observed – indicating the realisation of ferroelectric FETs (FeFETs). We show that interfacial remote doping influences the macroscopic polarisation and performance of CIPS-based graphene FeFETs. Finally, Raman and photoluminescence (PL) measurements on MoS2 with indium metal film of thicknesses ranging from 2 to 25 nm were performed. The results suggest that the vdW gap between indium and MoS2 leads to a strong enhancement of Raman and PL signals. Strong Raman enhancement was also observed in graphene. In the absence of vdW gap with gold film, the plasmon-mediated enhancement of Raman and PL signals was not observed.

Name dc:type.qualificationname

Doctor of Philosophy (PhD)

Level dc:type.qualificationlevel

Doctoral

Grantor dc:publisher.institution

University of Cambridge

Year dc:date.issued

2025

Author dc:creator

• Ghani, Maheera Abdul

Advisor dc:contributor.advisor

• Chhowalla, Manish

• materials
• electronic devices
• Two-dimensional (2D) materials
• van der Waals
• Interfaces
• Optical properties
• Electrical properties
• metal films

Licence

• https://www.repository.cam.ac.uk/bitstreams/d98ab32a-14e4-45de-906d-322cad3643d1/download
• http://purl.org/NET/rdflicense/allrightsreserved

Language dc:language

eng

DOI dc:identifier.doi

https://doi.org/10.17863/CAM.121354

OAI identifier oai:identifier

oai:www.repository.cam.ac.uk:1810/389492