Correlation between surface nanomorphology and charge density waves in 1T-TaS₂

Abstract

This study investigates the structural and electronic properties of 1T-TaS₂ using scanning tunneling microscopy (STM) and complementary Fourier analysis. The objective was to correlate surface morphology with the emergence of commensurate charge density wave (CDW) order and to quantify the periodicities governing its modulation. High-resolution STM imaging revealed both the atomic lattice and the superimposed CDW, with measured lattice constant of 0.343 ± 0.02 nm and CDW periodicities of 1.1 ± 0.05 nm and 2.0 ± 0.05 nm. Fourier transforms confirmed reciprocal vectors of 2.9 ± 0.1 nm⁻¹ for the lattice and 0.5–0.9 ± 0.1 nm⁻¹ for the CDW, rotated by approximately 30° with respect to the atomic lattice, consistent with a commensurate  ×  reconstruction. Surface roughness characterization showed root-mean-square variations of 3.5 ± 0.2 nm and terrace widths of only 25–40 nm, reflecting the brittle nature of the crystal and highlighting constraints for achieving atomically stable imaging. Bias-dependent measurements demonstrated contrast inversion between filled and empty states, providing direct evidence of the electronic origin of the CDW. These results confirm the robustness of CDW ordering in 1T-TaS₂, address the research objective of linking morphology with electronic superstructures, and highlight both the opportunities and challenges of using this material as a platform for studying correlated electron phenomena in low-dimensional solids.