FORCE MODULATION ATOMIC-FORCE MICROSCOPY - BACKGROUND, DEVELOPMENT AND APPLICATION TO ELECTRODEPOSITED CERIUM OXIDE-FILMS

In force modulation atomic force microscopy (FMAFM), vertical oscillat ion of the scanning tip of the AFM is added purposely and the deflecti on of the tip, which is influenced by surface features of the sample, is used as the z dimension to construct images. FMAFM represents a pow erful technique for scientific research, but its merit has not been re alized adequately to date. In this paper, the basic principles and par ticular features, as well as potential drawbacks of the technique, an presented and demonstrated systematically, through its application to electrochemically deposited cerium oxide films. Comparisons are also m ade with the more familiar contact mode AFM (CMAFM) and tapping mode A FM (TMAFM). It is shown that FMAFM reveals the major topographic featu res of CMAFM, but affords (i) greater resolution for sample features t hat are difficult in CMAFM, and (ii) continuous two-dimensional mappin g of local mechanical properties on a scale of nanometres that the CMA FM, TMAFM and any other techniques, an not capable of sensing. This in formation can be used to elucidate other properties of the investigate d surface, such as crystallinity variation, phase separation and distr ibution, and mechanisms of formation of deposited films. Major artifac ts associated with the technique include 'wedge cavity effect' and 'ti p slip effect', for which a geometric model is proposed to elucidate t heir origins. The cerium oxide films are shown to be composed of relat ively hard crystalline grains, of well-defined individual geometry and comparatively regular packing, alongside relatively soft amorphous pa tches, devoid of distinct geometry and assembled disorderly. These fea tures are consistent with a nucleation and growth mechanism of the dep osition, in which crystalline nuclei arise and flow from an intermedia te cerium gel mass, produced in the interfacial region during depositi on. (C) 1998 Elsevier Science B.V.