We have developed a novel technique for the study of nanometer scale properties of materials, based on conductive atomic force microscopy (C-AFM), complemented with femtosecond (fs) laser irradiation. Illumination of the samples was achieved in the near field of a metal-coated microcantilever tip, placed in the beam of a fs pulsed laser that is incident at a grazing angle with respect to the sample surface. In this way, photoelectron current maps can be obtained during AFM scan by recording the non-linear photoelectric response to the enhanced optical field at the tip edge. We have successfully implemented this technique to probe surface and sub-surface electronic properties at the nanoscale. In particular, we have investigated the dielectric properties of Si nanowire (NW) oxide which acts as an insulator in transistor gates and compared them to that of planar silicon oxides. It is found that, the interface barrier to electron transit from the semiconductor to the dielectric and the threshold electric field for current flow in Si NWs are quite similar to those in the planar geometry. This is not true for the lowest currents measured which are not uniformly distributed, indicating variations of trap density in the gap of NW oxide. C-AFM combined with multiphoton probing of electronic transitions can reveal electrically active defects in the oxide and serve as a guide to both the clarification of the origin of these defects and to the optimization of growth and processing in order to avoid them. It also introduces a highly versatile tool for nanoscale characterization of single or stacked multiple dielectric structures and of future nanoelectronic devices.Collaborators
C. P. Grigoropoulos, Univ. Of California Berekeley, Dept. Of Mech. Eng.