Fabrication of ultra-clean gate-tunable rhombohedral multilayer graphene devices for STM study (Part 2)

Rhombohedral multilayer graphene has recently arisen as a compelling platform where electron correlation and topology interplay, enabled by its highly tunable flat band structure. Transport measurements have discovered several quantum phases, including correlated insulators, Chern insulators, and, most significant, the fractional quantum anomalous Hall effect (FQAHE). Despite these advancements, the atomic-scale mechanisms underlying these novel quantum phenomena have not been investigated, possibly due to the difficulties in fabricating rhombohedral graphene devices compatible with scanning tunneling microscopy and spectroscopy (STM/S) in which the ultra-clean requirements for STM/S measurements conflict with the high likelihood of stacking order relaxation caused by thermal or mechanical perturbations. Here we demonstrate our exploration of developing an ultra-clean gate-tunable rhombohedral device while maintaining its rhombohedral stacking order. Our approach involves optimizing every stage of device preparation and cleaning, including electron beam evaporation, contact-mode atomic force microscopy (AFM) scratching, and high-temperature annealing, paving the way to facilitate high-resolution STM/S measurements and provide nano-scale insights into the novel quantum properties of rhombohedral multilayer graphene system.