Probing Excitonic Resonances of Metal Films on Suspended 2D Membranes Using Electron Energy Loss Spectroscopy

We characterize Oriented Porous mEtallic Networks (OPEN) using aberration-corrected scanning transmission electron microscopy (STEM) and electron energy loss spectroscopy (EELS). These OPEN films are synthesized by annealing metal films on 2D layers, which causes lattice registry between the metal layer and the 2D materials, and we will examine the morphological influence that MoS₂ monolayers have on relatively thick (13-25nm) gold thin films during annealing. Ex-situ annealing experiments of MoS₂/Au on SiO₂ substrates shows that the Au films can become textured (oriented), as revealed through electron beam scattering diffraction, and that the Au film can locally dewet beneath the MoS₂ layer to form a porous metal layer with suspended MoS₂ membranes. Further, using both STEM and EELS at 60 kV, we show the metal ordering is aligned with the 2D lattice and find EELS resonances at ~ 2 eV, which is associated with the so-called A and B excitons, as well as at several other energies. We will discuss the origin of these resonances, and how both the metal overlayer and disordered carbon contamination affect them.
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