DYNAMIC FORCE MICROSCOPY BY MEANS OF THE PHASE-CONTROLLED OSCILLATOR METHOD

Dynamic force microscopy, a technique also known as non-contact force microscopy, has proved to be a powerful tool for atomic resolution ima ging. A number of schemes have been developed, but recently the oscill ator method has become the preferred operating mode. Here, the force s ensor acts as resonator in an active feedback circuit. A practical imp lementation of the method is described and the underlying key concepts are discussed. It is shown that a tracking oscillator excitation sche me is superior to the more standard direct feedback method for cases i n which the force sensor exhibits only a weak resonance enhancement. F urthermore, the simultaneous measurement of dissipative interaction ch annels is an important extension of dynamic force microscopy. It allow s one to differentiate between sample materials via their plasto-mecha nical response. As an example, a Cr test grating has been imaged in th e constant force gradient mode. The dissipation measured on Cr-covered areas is significantly lower than that on the bare quartz glass subst rate, which enables one to distinguish between the two materials with a lateral resolution comparable to that of the topographic image. (C) 1997 American Institute of Physics.