Characterizing Exfoliation Variability in Flake Dimensions and Structural Quality of NbSe₂

Abstract

Niobium diselenide (NbSe₂) is a layered transition-metal dichalcogenide with thickness-dependent superconducting and charge-density-wave (CDW) properties. Near the monolayer limit, these properties make NbSe₂ a promising 2D quantum material. Mechanical exfoliation is the standard method for producing thin NbSe₂ flakes for these studies, yet exfoliation parameters like peel angle and fold count remain relatively unexplored. This imposes a challenge in isolating process-induced disorders from any intrinsic thickness-dependent properties. In this work, NbSe₂ flakes were exfoliated under a controlled two-angle, four-fold-count design (45°/90°; 4, 6, 8, 10 folds). Flake in-plane dimensions were measured using an optical microscope across 80 flakes total. Additionally, one representative flake per condition was mapped via Raman spectroscopy to extract both the position and linewidth of characteristic peaks. Two-way ANOVA showed fold count had a significant effect on a flake area (η² = 0.255). Higher fold counts produced smaller flakes, while peel angle had no significant effect, with the two factors not interacting. Raman spectroscopy revealed that specific peel-angle and fold-count combinations produced significantly more disordered flakes than others. Disorder was unrelated to variations in the flake size, suggesting independent sources of variations. Together, these results indicate the fold count controls the flake size, while exfoliation conditions can independently affect structural quality. Standardizing and reporting these parameters would ensure reproducible superconducting and CDW measurements in NbSe₂