Constructing a Quantum Twisting Microscope: Design Insights and Experimental Considerations

Abstract

We report the details of construction and testing of a Quantum Twisting Microscope, a recently developed scanning probe instrument that enables twist angle dependent electronic measurements on layered materials. Our implementation is based on a commercial atomic force microscope whose open geometry beneath the scan head allows integration of the rotation and translation stages required for QTM operation. We describe the complete fabrication process including tip preparation by focused ion beam deposition and graphite transfer, custom stage assembly with integrated rotation capability, and multistep alignment procedures. To validate the instrument, we perform conductance measurements between graphite layers as a function of twist angle, observing clear 60 degree periodicity consistent with the hexagonal lattice symmetry and conductance enhancements near the commensurate twist angles of 21.8 and 38.2 degrees. These results confirm the instruments ability to resolve crystallographic twist angle dependent transport features. By providing detailed construction and operational guidelines, we aim to make QTM technology accessible to research groups with standard AFM infrastructure, enabling investigations of twist angle dependent phenomena in van der Waals materials, complex oxide heterostructures and chiral systems.

Figures (6)

• Figure 1: Camera images of QTM setup: (a) Full instrument image showing the complete assembly. (b) Detailed view of different instrument components including the AFM head, translation stages, rotation stage, and sample mount.
• Figure 2: SEM images showing the QTM tip fabrication process: (a) Tipless cantilever after gold deposition showing the metallic coating. (b) Cantilever after FIB deposition of platinum pyramid with inset showing a magnified view of the pyramid structure. (c) Completed QTM tip after transfer of graphite layer onto the pyramid, creating the functional tip surface.
• Figure 3: Critical tip height considerations for QTM operation: (a) Schematic of conventional AFM tip touching the surface at the standard angle of $\theta \approx 9-12\degree$. (b) QTM tip with insufficient height causing cantilever apex to contact surface before tip engagement. (c) SEM image showing cantilever damage from apex contact when tilt angle is not properly optimized. (d) Optimized configuration with adjusted tilt angle ($\theta' < \theta$) ensuring only the tip contacts the surface.
• Figure 4: Stage alignment procedure for centering the area of interest at the rotation axis: (a) Initial configuration showing misalignment between tip, graphite area of interest, and rotation stage center (indicated by red dotted line). (b) After bottom XY stage adjustment, the tip is aligned with the rotation center. (c) Final configuration after top XY stage adjustment brings the graphite area to the rotation center, enabling twist-angle measurements without lateral displacement.
• Figure 5: Verification of rotation stage alignment: (a) AFM topography scans acquired at different rotation angles showing consistent feature positions. (b) Superposition of all rotation angles demonstrating that the rotation center is precisely located at the middle of the scan area, confirming successful alignment.