B. Pittenger, M. Ye, P. De Wolf
Bruker Corporation,
United States
Keywords: torsional resonance, AFM, SPM, 2D materials, Van der Waals materials
Summary:
Atomic Force Microscopy (AFM) was among the first techniques applied to the study of two-dimensional (2D) crystals such as graphene, and it remains a cornerstone of 2D material research. Identifying and characterizing single layers and multilayers is now routine, and with the appropriate choice of mode and probe, crystal orientation can often be determined. Because the AFM probe can function as a nanoscale electrode, it enables direct measurement of electrical properties with sub-nanometer resolution—making AFM uniquely suited for simultaneous structural and functional characterization. Torsional resonance (TR) modes in AFM have recently gained renewed attention for their utility in this domain. TR dynamic friction microscopy (TR-DFM), which operates at the torsional contact resonance frequency, allows atomic-scale imaging under ambient conditions—resolving component lattices, moiré superlattices, twist angles, and lattice strain. Phase-locked loop (PLL) tracking further enhances contrast by distinguishing local variations in shear stiffness and damping. Complementary to TR-DFM, conductive AFM (C-AFM) has proven effective in mapping local conductivity with atomic resolution. Given the central importance of electronic properties in 2D systems, C-AFM provides critical insight into charge transport and heterogeneity, enriching the structural data obtained from TR-based modes. Together, these techniques establish torsional resonance and conductive AFM as complementary, high-resolution platforms for multidimensional characterization of 2D materials—advancing the design and understanding of next-generation electronic, optoelectronic, and quantum devices.