Development of sub-nm roughness evaluation method using electron diffraction on HOPG

Precise control of sub-nanometer (sub-nm) surface roughness is vital for semiconductor fabrication, thin-film growth, and nanoscale engineering. While AFM is widely used, it faces limitations for complex 3D structures. Our previous studies demonstrated the potential of reflection high-energy electron diffraction (RHEED) to probe surface structures with different orientations  [1-3]. We hypothesized that electron diffraction inherently contains information related to sub-nm roughness correlated with surface ordering. 

Here, we systematically investigated the relationship between RHEED diffraction spot profiles and surface roughness. Flat HOPG was used as a model system, with roughness varied by Ar sputtering and independently measured by AFM. Intensity distributions of the HOPG 006 RHEED reflection were decomposed into sharp (I_ord) and broad (I<font size="1">dis) components, corresponding to ordered and disordered regions. The ratio (I_dis/(I_ord+I_dis)) showed a clear positive correlation with AFM-measured roughness, indicating that RHEED can serve as a quantitative tool for sub-nm roughness evaluation. This approach enables localized, directional analysis of arbitrarily oriented 3D surfaces, and, when combined with beam scanning, could establish a microscopy-based method for advanced surface characterization.

References:

[1] A. N. Hattori, K. Hattori, et al., Surf. Sci. 644 (2016) 86.

[2] A. N. Hattori, K. Hattori, et al., Appl. Phys. Exp. 9 (2016) 085501.

[3] S. Takemoto, K. Hattori, et al., Jap. J. Appl. Phys. 57 (2018) 090303.