Since the isolation of the first monolayer material, graphene, in 2004, the field of two-dimensional (2D) materials has evolved significantly. Semiconductors, metals, insulators and superconductors have now all been fabricated in the monolayer form. The weak van der Waals forces between the layers allows any 2D material to be stacked upon any other 2D material, creating a wide range of systems that can be studied for new emergent quantum phenomena that depend upon the interlayer coupling and the twist angle between the layers. Twist-dependent interlayer interactions, such as moir´e potentials, have been shown to give rise to novel physical properties such as moir´e excitons and electronic bands with a flat dispersion and a high density of states. These twist-dependent properties can be exploited to create new 2D twistronic devices, adding to the variety of 2D electronic, spintronic,
valleytronic and optoelectronic devices that have already been created.
In this thesis, angle-resolved photoemission spectroscopy with micrometre spatial resolution (µARPES) has been used to visualise interlayer interactions in 2D van der Waals heterostructures. We observe twist-dependent interlayer Umklapp scattering in heterostructures of graphene combined with monolayer and multi-layer
post transition metal chalcogenides, such as InSe and GaSe. Additionally, we combine µARPES measurements with in-situ electrostatic gating to study the conduction band in heterobilayers of transition metal dichalcogenides, a popular family of semiconducting 2D materials with chemical composition MX2, where M is a transition metal atom and X is a chalcogen atom. We determine band gaps and band alignments for the heterobilayers; MoSe2/WSe2, WS2/MoSe2
and WS2/WSe2. At high carrier concentrations, intralayer band gap renormalisation is observed within the layer which charge is injected, leaving the heterobilayer interlayer band gap unaltered. µARPES with in-situ electrostatic gating was used to study moir´e effects within the conduction band of WS2/WSe2 heterobilayers. Furthermore, we observe moir´e induced replica bands in graphene on WS2/WSe2, due to the moir´e potential in the heterobilayer. In this work, it is important to distinguish between replica bands observed in µARPES spectra due to initial state effects and those due to final state photoelectron diffraction. Overall, we show µARPES combined with in-situ electrostatic gating to be a powerful technique in characterising 2D materials and their interlayer interactions.