We present direct and linear measurements of the normal stiffness and damping of a confined, few molecule thick water layer. The measurements were obtained by use of a small amplitude (0.36 Å), off-resonance atomic force microscopy technique. We measured stiffness and damping oscillations revealing up to seven molecular layers separated by 2.526 ± 0.482 Å. Relaxation times could also be calculated and were found to indicate a significant slow-down of the dynamics of the system as the confining separation was reduced. We found that the dynamics of the system is determined not only by the interfacial pressure, but more significantly by solvation effects which depend on the exact separation of tip and surface. The dynamic forces reflect the layering of the water molecules close to the mica surface and are enhanced when the tip-surface spacing is equivalent to an integer multiple of the size of the water molecules. We were able to model these results by starting from the simple assumption that the relaxation time depends linearly on the film stiffness

Atomic scale dissipation is of great interest in nanomechanics and atomic manipulation. We present dissipation measurements with a linearized, ultra-small amplitude atomic force microscope which is capable of measuring dissipation at chosen, fixed separations. We show that the dynamic dissipation in the noncontact regime is of the order of a few 10-100 meV per cycle. This dissipation is likely due to the motion of a bistable atomic defect in the tip-surface region. In the contact regime we observe dc hysteresis associated with nanoscale plasticity. We find the hysteretic energy loss to be 1 order of magnitude higher for a silicon surface than for copper.

Interatomic force gradients between a W tip and a 7 × 7 reconstructed Si(111) surface were measured using an off-resonance, ultra-low-amplitude atomic force microscope (AFM) technique. The amplitudes used were less than 1 Å (peak-to-peak), which allowed direct measurement of the interaction force gradients as a function of separation. The force gradient curves are shown to consist of an attractive van der Waals part and short-range attractive and repulsive interactions. The van der Waals background can be subtracted, leaving a short-range interaction with an energy parameter of 1.9-3.4 eV and an interaction length-scale of 0.54-1.26 Å, characteristic of a single atomic bond. This correlates well with our observation of single-atom resolved force gradient images. In general, the interaction is reversible up to the zero intercept of the force gradient (inflection point of the energy). Beyond this point hysteresis tends to be observed and the onset of inelastic deformation can be clearly discerned. An analysis of the atomic scale contact gives reasonable values for the interfacial energy, yield strength, and the energy per atom needed to initiate plastic deformation

We describe a surface probe technique for measuring the electrical properties of thin films while simultaneously controlling the local mechanical stress. We have used this technique to measure the dielectric breakdown voltage of thin SiO2 films, and we present results which show that there exists a correlation between the dielectric breakdown strength and the mechanical stress applied to the oxide. We propose a model, in which the mechanical strength of the material provides the criterion for breakdown, which accounts well for this behavior. Apart from the possible importance in the breakdown mechanism, the results suggest that residual stresses in insulating films may influence their effectiveness as dielectrics.

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