MEASUREMENT OF THE LOCALIZED VISCOSITY OF MOLECULAR ASSEMBLIES USING NANOSCOPIC DEFECTS INDUCED WITH THE SCANNING TUNNELING MICROSCOPE

The scanning tunneling microscope (STM) has been employed to induce de fects, having dimensions of 100-200 Angstrom, in bilayers of stearic a cid or cadmium stearate supported on a graphite surface. Defect format ion followed the application of a bias pulse between the STM tip and s urface. Cylindrical voids or ''pores'', formed by this process, gradua lly refilled the approximate to 10 min following formation. From STM i mages of pore refilling, a hydrodynamic momentum equation-derived here -enabled the calculation of a viscosity of 2.6 Pa s m for a cadmium st earate bilayer. This measurement suggests that the STM provides a mean s for measuring the viscosity of nanometer-scale regions of supported molecular assemblies.