We have measured pre-sliding tangential deflections (PSTD) between micromachined surfaces of up to 200 nanometers in length before the static friction event using a polysilicon nanotractor actuator [1,2]. The detailed PSTD structure is resolved by a one-nanometer-resolution in-plane optical metrology we have developed, and may be a manifestation of discrete asperity-asperity interactions leading to an effective spatial distribution of friction coefficients. Results indicate a dependence on surface treatment, with a perfluorinated eight-carbon chain monolayer coating showing substantially different PSTD than an eighteen-carbon chain hydrocrabon monolayer. This behavior may qualitatively be related to variations in dynamic versus static friction. We present a simple phenomenological model that captures some of the behavior of PSTD, and suggest some possible microscopic interpretations.

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