Direct visualization of field-driven valence band modulation in electrostatically reconfigured graphene devices

Graphene with ultrathin metal-oxide layers has emerged as a scalable platform for integrated electronic, spintronic, and neuromorphic devices. The in-plane electric fields in such devices are typically inferred indirectly from transport measurements, which do not provide microscopic details of the interface potential profile. Here, we use photoemission microscopy to uncover the precise electrostatic landscape of a complete device comprising diverse, heterogeneous ultrathin metal-oxide-covered graphene junctions. Using in operando x-ray photoelectron spectroscopy with submicron resolution, we directly image the real potential profile across an entire graphene device, including regions covered by AlO_xand TiO_xnanometer-thick overlayers. Tracking the valence band edge under current bias and gate voltage enables quantitative analysis of internal field evolution via a spectroscopic screening factor, revealing an up to more than 50% suppression of the electric field in graphene covered with oxides, in agreement with transport measurements. This demonstrates local reconfiguration of electric fields in graphene for advanced two-dimensional (2D) device engineering and circuitry, while our operando circuit spectroscopy measurements provide a generic means to uncover intricate potential landscapes and carrier redistribution in 2D electronic and spintronic circuits.