Interfacial shear force microscopy

We present an experimental investigation of lossy and reactive shear forces at the nanometer scale using quartz-crystal tuning-fork shear-force micros copy. We show that this technique allows us not only to quantitatively meas ure viscous friction and elastic shear stress with a combination of high sp atial and force resolution (better than 10 nm, and less than 1 pN, respecti vely), but also to obtain such quantities with the tip positioned at any ar bitrary distance away from direct electrical tunnel contact with the sample surface. We are proposing that, even under vacuum conditions, the measured viscous and elastic shear stress (i.e., velocity dependent) are directly a ttributable to a third body filling the tip-sample gap A simple model is gi ven that allows us to obtain its local viscosity and shear modulus as a fun ction of the tip-sample distance, showing that tuning-fork shear-force micr oscopy can be applied to quantitative analysis in nanotribology.