  Recent advances in mechanical-diode based ultrasonic force microscopy
techniques are reviewed. The potential of Ultrasonic Force Microscopy (UFM) for
the study of material elastic properties is explained in detail. Advantages of
the application of UFM in nanofabrication are discussed. Mechanical-Diode
Ultrasonic Friction Force Microscopy (MD-UFFM) is introduced, and compared with
Lateral Acoustic Force Microscopy (LAFM) and Torsional Resonance (TR) - Atomic
Force Microscopy (AFM). MD-UFFM provides a new method for the study of shear
elasticity, viscoelasticity and tribological properties on the nanoscale. The
excitation of beats at nanocontacs and the implementation of Heterodyne Force
Microscopy (HFM) are described. HFM introduces a very interesting procedure to
take advantage of the time resolution inherent in high-frequency actuation.
