Can nanometer-scale surface stress embrittle metal surfaces?

Controlling environmental effects in surface plasticity/fracture of metals is of interest for areas as diverse as structural safety and manufacturing processes. The key to controlling these effects is understanding effect of adsorbates on surface energy (γ) and surface stress (f). While γ has been well studied, the role of surface stress has received much less attention. We characterize surface stress induced in metals by adsorption of organic monolayers using in situ measurement of macroscopic cantilever deflection. We find that the adsorbates induce large surface stress of -4 to 30 N/m on Al substrates, the stress varying with the molecule chain length. The stress data explain embrittlement of metal surfaces by organic adsorbates in bending, cutting and comminution processes; and point to a critical role, hitherto ignored, for f in environment assisted cracking phenomena. Our results also suggest opportunities for utilizing controlled environment-assisted fracture as an aid to enhance material removal processes.