Theoretical Study on the Thermodynamics of Si(001) Surface

As one of the most widely used substrates in the integrated circuit industry, the surface structure of Si(001) is critical for the semiconductor manufacturing process. Due to the dimerization-related surface reconstruction and possible hydrogen saturation, the Si(001) surface exhibits structural diversity. However, the bonding mechanism and phase diagram of this surface have not been fully studied theoretically. Here, the thermodynamics of the Si(001) surface is systematically investigated using multiscale simulations based on density functional theory (DFT), grand canonical Monte Carlo (GCMC), and machine learning force fields (MLFF). A complete phase diagram of the Si(001) surface is obtained with respect to temperature and H₂ pressure, which reveals the isotropic premelting phenomenon on the Si(001) surface through MLFF-based molecular dynamics (MD) simulations. Finally, infrared (IR) adsorption spectra is presented of typical phases for comparison with experimental results. This study provides valuable insights into understanding surface bonding rules and contributes to elucidating the annealing mechanisms in silicon-based semiconductor fabrication.