Observation of Coulomb staircase and negative differential resistance at room temperature by scanning tunneling microscopy

Nanometer-sized Au dots have been fabricated on p-type Si(lll) substrates by field-induced transfer of tip material in a scanning tunneling microscope, thus forming a nanometer Schottky contact. Positioning the scanning tunneling microscope tip on a very tiny dot (10-15 nm in diameter), equidistant steps with a spacing of several 100 mV and regions with negative differential resistance are observed in the current-voltage characteristic. Numerical simulations confirm that the determinant capacitance between tip and Au dot falls in the 10(-19) F range, implying that the origin of the monitored step structure can be interpreted to arise from single-electron tunnel effects (Coulomb staircase). As the nanometer Schottky contact forms a not well-insulating configuration, the development of negative differential resistance might be explained by a leaking of excess carriers from the dot to the immediate surroundings. (C) 1996 American Vacuum Society.