ABSTRACT
Since the introduction of the Scanning Tunneling Microscope in the early 1980’s, scanning-probe microscopies have developed very rapidly and are presently widely used in remarkably diverse applications ranging from research into fundamental material-science problems, through nanoscale fabrication and characterization to advanced metrology at the nanometer scale. The scanning force microscopies (notably the Atomic Force Microscope--AFM), because of their applicability to nearly all materials, are presently the most widely used of the scanning-probe techniques. However, the AFM uses a deflection sensor to measure sample/probe forces which suffers from an inherent mechanical instability that occurs when the rate of change of the force with respect to the interfacial separation becomes equal to the spring constant of the deflecting member. This instability dramatically limits the breadth of applicability of AFM-type techniques to materials problems. The instability problem has been overcome by the development of the Interfacial Force Microscope (IFM) [1], which utilizes a differential capacitor in a self balancing, force-feedback sensor concept. Forces are sensed by the change in capacitance and an electrostatic force is applied to balance the probe-tip force. This sensor eliminates the instability problem and greatly enhances the applicability of the scanning force-probe technique to a broader range of materials and materials parameters. It permits quantitative measurements of the interaction force vs. relative tip/sample separation and extraordinary control over the system parameters.
