Frequency-modulation atomic force microscopy observation of 1T-TaS2 in the nearly commensurate charge density wave phase

Charge density wave (CDW) is an electron–phonon correlated phenomenon in which charge density modulation and atomic lattice distortion are entangled. Here, we investigate the nearly commensurate CDW phase of 1T-TaS2 using frequency modulation atomic force microscopy (AFM) at room temperature. In addition to atomic resolution, the CDW superlattice was observed in the AFM topography. With three-dimensional force spectroscopy, we demonstrate the local quantification of the atomic displacement contribution associated with the CDW ordering. Besides, Kelvin probe force microscopy and Hartree potentials calculated by the density functional theory show that the electronic contribution to the AFM images is negligibly small, thus disentangling the contributions of electronic density and atomic displacement.