Abstract
We have used noncontact atomic force microscopy (NC-AFM) and Kelvin probe force microscopy (KPFM) to directly visualize the presence of charged subsurface impurities on rutile TiO2(110). The subsurface charges add an additional electrostatic force between the sample and tip so that they appear as hillocks in the NC-AFM topography. Analysis of several subsurface defects in the same NC-AFM image reveals that the hillocks have discrete heights, which means that defects at different subsurface levels can be detected and distinguished. H adatoms, which are positively charged at the TiO2(110) surface, were found to be repelled by the buried positive charge, so that they form a ∼80–120 Å wide hydrogen-free zone around the charge. Thus, there is an opportunity to deliberately add dopants in order to exclude or perhaps even to confine certain adsorbates to a local region at the surface.
Highlights
TiO2 has been investigated intensely since the 1970s when it was discovered that it is an active photocatalyst.[1]
In noncontact atomic force microscopy (NC-AFM) images, depending on the exact nature of can point the tip apex, defects (i.e., Ti5c rows Ob-vacs can appear bright or or H adatoms).[27−32] dark as In the image shown in Figure 2a, the Ob rows are imaged bright and the H adatoms appear as dark depressions on those rows
We have unambiguously identified the presence of charged subsurface defects using Kelvin probe force microscopy (KPFM)
Summary
TiO2 has been investigated intensely since the 1970s when it was discovered that it is an active photocatalyst.[1]. TiO2(110) face,[3,4] and naturally, this examine the role that dopants play in surface has catalysis.[5−8]. It is becoming more and more apparent that both extrinsic subsurface dopants and intrinsic subsurface defects can dramatically modify the behavior at the surface.[9−14] For instance, exposing the rutile TiO2(110) surface to O2 and annealing in ultrahigh vacuum (UHV) or annealing. Nb-doped TiO2(110) has received particular attention in part because it can be used to introduce conductivity to TiO2(110) in a partial pressure of O2 leads to the creation of TiOx (x < 2) islands because of segregation and subsequent reaction of interstitial Ti with oxygen.[9,12,13] On the other hand, when TiO2(110) is doped with niobium, Nb can occupy interstitial sites and thereby suppress the formation of TiOx.[12]
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