Nanoscale device engineering and plasmon-enhanced light – matter interactions for the characterization of 2D materials

Abstract

The PhD thesis introduces nanoscale tools for optoelectronic characterization of 2D materials, addressing limitations of existing techniques including destructiveness, imprecision, and vacuum requirements. Three novel characterization methods are proposed. They all employ gold nanoparticles as electrical contacts, offering both nano-sized electrodes and significant optical enhancement within the biased region, enabling the first precise, non invasive concurrent optical and electrical characterization of nanomaterials. The established methods are subsequently applied to evaluate the potential of 2D materials as nanoscale electrical switches by analysing the kinetics of their switching mechanism. First, the thesis presents a technique involving the drop-casting of gold nanoparticles onto 2D materials placed on gold substrates. Electrical contact is established by positioning an optically transparent and electrically conductive cantilever on a single nanoparticle. It is used to unveil morphological nano-processes occurring in MoS2 electrical nano-switches, known for their ultralow switching energies but poorly understood switching mechanism. Second, a novel scanning plasmonic microscopy technique is devised, utilizing a plasmonic nanoprobe with a single gold nanoparticle on an optically transparent and conductive cantilever. The nanoprobes enable precise electrode positioning on various material regions, offering user-friendliness, durability, reproducibility, and minimal material perturbation, as validated on WSe2 and MoS2 nanosheets, making them applicable to diverse materials. Third, the thesis introduces a configuration where a nanosheet is biased using patterned gold nano-discs located at the intersection of striped electrodes patterned using shadow masks. This layout eliminates the need for motorized cantilevers and the variability in the location of gold nanoparticles, as observed in the first approach. This configuration is employed to gain an understanding of the switching mechanism in nanoscale h-BN memristors, which are promising as foundational components for logic-in-memory computing systems. Therefore, this PhD thesis introduces nano-techniques for characterizing 2D materials, yielding insights into their electrical behaviour. These findings have implications for advancing and optimizing 2D electronic devices, opening new avenues for nanotechnology applications.