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

Noncontact Atomic Force Microscope Observation
of TiO2(110) Surface in Pure Water
Akira Sasahara 1 , Yonkil Jeong 1 , and Masahiko Tomitori 1
1 School of Materials Science, Japan Advanced Institute of Science and Technology, Ishikawa, Japan
P.II-14
Titanum dioxide (TiO2) has a wide range of industrial applications such as pigments,
optical devices, catalyst supports, photocatalysts, and photoelectrodes. A rutile
TiO2(110) surface, which exhibits a simple truncation of the bulk structure (Fig. 1(a)) by
simple cleaning procedures, has been most frequently employed in ultra high vacuum
(UHV) studies to understand the origin of its properties. In many of the applications,
TiO2 demonstrates the excellent properties in the presence of aqueous media. Nanoscale
investigation of a well-defined rutile TiO2(110) surface in a liquid possibly provides
further insight into the surface chemical properties of TiO2. We attempted noncontact
atomic force microscope (NC-AFM) observation of TiO2(110) surface in pure water.
The experiments were performed by using an intermittent contact mode atomic force
microscope (5500 AFM/SPM, Agilent Technologies). The microscope was operated as
an NC-AFM by using a phase locked loop detector (easy PLL plus, Nanosurf AG). The
microscope was placed in a glass chamber, and imaging was performed under a flow of
Ar. The TiO2(110) surface was cleaned by cycles of Ar + sputtering and annealing in
UHV, removed from the vacuum chamber, and immersed in Ar-purged Milli-Q water.
Figure 1(b) shows an NC-AFM image of the surface in water. Strings elongated to the
[001] direction were observed. Along cross section 1 in Fig. 1(c), subnanometer
corrugation was observed perpendicular to the rows. The distance between the lowest
rows, indicated by arrowheads, was approximately 0.65 nm. On some of the rows,
periodic corrugation was observed as shown in the cross sections 2 and 3. We attributed
the lowest rows to the oxygen atom rows, and the corrugation along the rows to H2O
clusters.
Figure 1: (a) Ball model of a rutile TiO2(110)-(1×1) surface. Size of the unit cell is 0.65
nm×0.30 nm. (b) NC-AFM image of the TiO2(110) surface in pure water (15×15 nm 2 ).
Frequency shift = +150 Hz, sample bias voltage = 0 V, peak-to-peak amplitude of the cantilever
oscillation = 2 nm. (c) Cross sections obtained along the lines in the image.
142