PNNL-13501 - Pacific Northwest National Laboratory

identified low energy step structures that have not been
investigated theoretically or experimentally. Much of the
chemistry that occurs on surfaces may be tied to step
edges due to the under-coordination of the ions.
Interaction with Water
Both the anatase (001) and (101) surfaces are under
investigation to better understand their respective
interaction with water. The (001) surface was found to
dissociate water using high-resolution electron energy
loss spectroscopy. Characteristic vibrational states for
dissociated water are observed for the water desorption
state at 305 K. Essentially, four desorption states are
observed for water, and three of those states are indicated
in Figure 3. They correspond to multilayer water (not
shown at 160 K), water hydrogen bound to anion sites
(185 K), water bound to cation sites (255 K), and
dissociated water (305 K). Currently we are studying the
interaction of water with the (101) surface as well. We
find that there is no dissociation of water on this surface,
and that the desorption state related to water bound to
anions and cations at the surface is very similar to that
observed for the (001) surface.
m/e = 18 QMS signal (x 10 5 cps)
4
2
0
100
185
200
255
305
300 400
Temperature (K)
Figure 3. TPD spectra for water obtained from the anatase
(001) – (1x4) surface. The desorption temperatures are
indicated.
Summary and Conclusions
Our ability to grow epitaxial thin films of anatase has
provided a unique opportunity to investigate the role of
electronic and geometric structure effects in regards to
TiO2 photocatalysts. To date, these studies have provided
new and unique information that will help clarify the
500
600
structural sensitivity of the photocatalytic production of
hydrogen from water. Both the geometric and electronic
structure has been investigated in detail. Furthermore, we
are initiating the first studies that investigate the
interaction of water with well-characterized anatase single
crystalline surfaces. We have found that the (001) and
(101) surfaces behave differently with respect to water,
where the (001) surface dissociates water and the (101)
surfaces do not.
Publications and Presentations
Gan S, Y Liang, DR Baer, MR Sievers, GS Herman, and
CHF Peden. “The effect of Pt nanocluster size and
surface structure upon CO desorption chemistry on Pt
supported TiO2(110).” Journal of Physical Chemistry B
(submitted).
Hebenstreit W, N Ruzycki, GS Herman, Y Gao, and
U Diebold. “Scanning tunneling microscopy
investigation of the TiO2 anatase (101) surface.” Physical
Review Letters (submitted).
Herman GS and Y Gao. “Growth of epitaxial anatase
(001) and (101) films.” Thin Solid Films (submitted).
Herman GS, Y Gao, TT Tran, and J Osterwalder. 2000.
“X-ray photoelectron diffraction study of an anatase thin
film: TiO2(001).” Surface Science 447:201-211.
Herman GS, MR Sievers, and Y Gao. 2000. “Structure
determination of the two-domain (1x4) anatase TiO2(001)
surface.” Physical Review Letters 84:3354-3357.
Perkins CL, MA Henderson, DE McCready, and
GS Herman. “Comment to electron source in
photoinduced hydrogen production on Pt-supported TiO2
particles.” Journal of Physical Chemistry B (submitted).
Henderson MA, GS Herman, and U Diebold. September
2000. “Measurement of the surface bandgaps of TiO2
polymorphs using electron energy loss spectroscopy.”
Pacific Northwest American Vacuum Society
Symposium, Forest Grove, Oregon.
Herman GS. January 2000. “Structural characterization
of the anatase TiO2(001) surface.” Stanford University,
Stanford, California (invited).
Herman GS. May 2000. “Structural characterization of
the anatase TiO2(001) surface.” University of
Washington, Seattle, Washington (invited).
Micro/Nano Technology 337