Scanning force microscope observations of particle detachment from substrates: The role of water vapor in tribological debonding

The tip of a scanning force microscope was used to detach nanometer-scale, single crystal NaCl particles from a glass substrate under controlled atmos pheres of known humidity. After characterizing a particle at low contact fo rce, a single line scan at high contact force was used to apply stresses to the attached particle. The lateral force during the line scan showed a sha rp discontinuity associated with detachment of the particle from the substr ate. The peak lateral force during this procedure is a strong function of p article contact area and humidity. As the relative humidity is raised from low values, the strength of the particle-substrate bond decreases dramatica lly. We interpret these results in terms of detachment by chemically assist ed crack growth along the NaCl-glass interface. (C) 1999 American Institute of Physics. [S0021-8979(99)04521-1].