Creation of submicron-scale metal oxide speckle patterns on single carbon fibers by a thermodynamically and kinetically controlled nonequilibrium process

Understanding the submicron scale deformation and failure mechanisms of fibers is essential for advancing carbon fiber-reinforced composites with superior strength-to-weight and stiffness-to-weight ratios for various structural applications. Recent advances in scanning electron microscopy (SEM) combined with digital image correlation (DIC) provide a powerful means to assess full-field deformations at submicron scales during in-situ mechanical loading. However, achieving precise and reliable measurements remains challenging due to the need for speckle patterns that are distinct, unique, non-periodic, and stable at the micro/nanoscale. To address these challenges, pulsed laser deposition (PLD) is utilized to create submicron-scale speckle patterns of metal oxide Nb-doped SrTiO₃ on individual carbon fibers with a nominal diameter of 5.2 µm. The influence of thermodynamic and kinetic parameters on the speckle pattern formation is systematically investigated by precisely controlling the deposition temperature and background gas pressure. Adatom mobility and nucleation rates are identified as key factors influencing the quality of speckle patterns. Numerical experiments confirm the optimal PLD conditions for creating speckle patterns that are suitable for in-situ SEM-DIC analysis. This work introduces a novel strategy for creating high-quality metal oxide speckle patterns and provides valuable insights into the precise control of speckle patterns on carbon fibers.