Towards Scalable High-Resolution Characterization of Confined 2D Metals

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Synopsis

Two-dimensional gallium (2D Ga) is recently realized through the confinement heteroepitaxy (CHet) technique. In this technique, Ga is intercalated at the interface between a bilayer epitaxial graphene (EG) and silicon carbide (SiC) substrate. 2D Ga exhibits optical and electronic properties such as huge nonlinear optical response, superconductivity, and near-zero index. However, the thickness, uniformity, and area coverage of this heterostructure have not been previously studied with high spatial resolution techniques.

In this work, we resolved and measured the 2D Ga thicknesses from scanning electron microscopy (SEM). Secondary electron emission in SEM is sensitive to the local surface potential, which is controlled by the layer thicknesses. This thickness variation is correlated with the contrast in SEM image by multiple correlative methods of the same specific site. Then, SEM contrast is quantified to indicate the location of the intercalated Ga, which facilities the measurement of the Ga coverage over a few millimeters square area.

Helium ion microscopy (HIM) is a potential future alternative for tracking intercalants or determining CHet layer thicknesses. SEM and HIM provide high-spatial-resolution compatible with the SiC surface features.

This work leverages the advantages of electron (or ion) microscopy in spectroscopic imaging for characterizing 2D materials compared to other spectroscopic techniques (ellipsometry or XPS) with several micrometer probe size.