Noncontact Atomic Force Microscopy - Yale School of Engineering ...

We-0940
Character of the short-range interaction between a silicon based tip and
the TiO2(110) surface: a DFT study
Cesar Gonzalez 1,2 , Pavel Jelínek 1 , and Ruben Pérez 3
1
Department of Thin Films, Institute of Physics of the ASCR, Prague, Czech Republic
2
Departamento de Superficies y Recubrimientos, Instituto de Ciencia de Materiales de Madrid del CSIC,
Spain
3 Departamento de Fisica Teorica de la Materia Condensada, Universidad Autonoma de Madrid, Spain
Non-contact atomic force microscopy (NC-AFM) provides a rich variety of atomic
contrasts on the rutile TiO2 (110) surface, imaging either the bridging oxygen atoms
(hole mode) or the titanium atoms (protrusion mode) [1]. These contrast modes have been
assigned to purely electrostatic interaction. Another contrast mode that does not ?t into
the scheme of purely electrostatic interaction, the so-called neutral mode, has also been
reported[]. Recently it has been demonstrated that NC-AFM is capable of imaging both,
the bridging oxygen atoms and the titanium rows simultaneously in a new “all inclusive”
mode [3]. Such diversity of contrast modes can be attributed to the complex character of
the short range interaction between tip and characteristic sites of the rutile TiO2 (110)
surface driven by (i) a weak short-range electrostatic interaction [4] depending on atomic
termination of tip and its polarization and (ii) the onset of chemical bond formed between
a tip and surface [5]. A proper characterization of the different regimes in the short-range
interaction regime Si-based tips and this oxide surface is crucial for the interpretation of
the experimental images and the design of protocols for single atom manipulation and
chemical identification.
Here we have employed density-functional theory (DFT) calculations to understand
the character of tip-sample interaction between clean and contaminated Si-based tips and
the TiO2 surface. We have performed a detailed analysis of electronic structure and the
charge transfer between tip and sample. Our calculations show that the relative
contribution of the weak short-range electrostatic interaction and the on-set of chemical
bonding between the closest tip and surface atoms is very sensitive to the tip-sample
distance, de?ning di? erent interaction regimes along the tip-sample distance. In
particular, we show the short-range electrostatic interaction in weak interaction regime
can provide a complex atomic contrast such as the experimentally reported neutral and
all-inclusive contrast modes.
[1] J.V. Lauritsen et al., Nanotechnology 17, 3436 (2006).
[2] G.H. Enevoldsen et al., Phys. Rev. B 78, 045416 (2008).
[3] R. Bechstein et al (submitted).
[4] A.S. Foster et al., Phys. Rev. B 68, 195420 (2003).
[5] R. Pérez et al., Phys, Rev. B 58, 10835 (1998).
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