A new technique that measures the polarization at a surface is described. The polarization may or may not be induced by a modulated signal applied to the conducting probe used for detection. The polarization dipoles in the surface layers of the material generate an electrostatic attraction between the probe and the dielectric material. Using techniques common in non-contact force microscopy these forces can easily be sensed. Remarkably, this measurement technique can be extended to frequencies significantly greater than the mechanical resonant frequency of the probe cantilever by utilizing amplitude modulation heterodyning. By rastering the probe over the surface an image of the dielectric properties of the surface can be produced. We expect this technique to be useable up to frequencies of at least 20 GHz and time resolution of less than 100 ps. To demonstrate the capabilities of this technique we have obtained stroboscopic images of surface polarization associated with a surface acoustic wave. The surface polarization has been imaged as it travels across the exposed substrate of a surface acoustic wave filter operating at 434 MHz. We present calculations of the forces generated assuming simple probe geometries and also thermal noise that compare favourably with experimental results. The implications for future experiments involving components for and bonding mechanisms in molecular nanotechnology will be considered.
D R Oliver
Electrical & Computer Engineering, University of Manitoba
15 Gillson Street, Winnipeg, Manitoba R3T 5V6 CANADA
Phone: (204) 474 9563
Fax: (204) 261 4639