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3.1 AFM of fine grain titanium

AFM pictures of a titanium surface are shown in Fig. 1. Grains with lateral dimensions of 10-30 mm can be clearly distinguished, while the surface of a single grain ist flat with a

Fig. 1. (a) AFM-picture of a fine grain titanium surface covered with 20 am Ti02 (anodized up to 10 V), xy range: 70 pm, z^ = 68 nm; (b) LFM picture, same position; (c) dF/ds picture, same position; (d) AFM-picture of the same surface, zoom on a grain, xy range 586 nm, Zjx^i — 5 nm; (e) line profile (as indicated by the arrow in (a).

roughness of only 1-3 nm. Quantitative data can be obtained from the line profile in Fig. 1(e): the height differences between these grains are 5-20 nm. The grain boundaries have lateral dimensions of 100-200 nm therefore the dz/dx-gradient ranges from 5-10%. In Fig. 1(b) and (c) the corresponding (simultaneously recorded) LFM (lateral force) and dF/ds (stiffness) pictures are shown, respectively. The lateral forces are higher on the marked grains (with different crystal orientation, described in more detail in [17]), and meanwhile the relative stiffness is lower on these grains. This indicates that oxide films on grains with different orientation (within the grains a crystal structure is assumed) have significantly different mechanical properties. These two additional pieces of mechanical information are a fascinating new aspect in surface analysis. In [17] it is documented, that the electronic properties vary as well with the orientation. Figure 1(d) shows a zoom on one of the grains: Small structures can be seen with xy dimensions of 20-50 nm and heights of 1-5 nm. These structures were found on all titanium dioxide surfaces. Even on a Ti single crystal these substructures could be detected (after electrochemical polishing and anodizing with 20 nm oxide).

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