Role of the sample preparation and measurement conditions

Table 1 shows that many authors have conducted experiments on even more different surfaces. Most authors refer to TiC>2 surfaces, but the sample was either electrochemically polished covered with natural oxide, or was covered with thermal or anodically grown oxide. The tunnel current arises due to defects in the oxides. Some authors increase the conductivity with annealing, heating in hydrogen, water adsorption or nitrogen implantation. These modified surface films can no longer be described as T1O2. The chemical and physical state of this ‚Äěreduced oxide" is unclear. The measurements were carried out in vacuum, dry nitrogen or with water films due to wet air or electrolyte. Since the tunnel current arises from the outermost layer of the surface, the chemical state of this layer determines the STM picture. In vacuum or dry nitrogen the surface will be dehydrated, in wet air or in electrolyte the surface will be hydrated or covered with a water film. For AFM and LFM this water film will be important as well, since lateral forces will be induced by the motion of the tip over the surface (changing the entire picture). In AFM the force curve will be changed due to water films (not necessarily changing the picture at the applied force, but resulting in different pictures at different forces and a hysteresis between forward and backward scans).

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