PNNL-13501 - Pacific Northwest National Laboratory

Study Control Number: PN97048/1189
Nanoscale Fabrication for Enhanced Properties (a)
Don R. Baer, Yong Liang
This project focuses on development of functional nanometer components that can be integrated with smart microtechnology
for chemical processes.
Project Description
This research project investigated the formation and
properties of nanoscale functional structures with the
ultimate objective of integrating active nanometer-sized
components into smart microtechnology. The specific
research effort has been focused on establishing the
ability to create arrays of uniform-sized metal clusters on
oxide surfaces with possible catalytic application. The
ability to control and stabilize particle size provides the
opportunity to influence catalytic properties such as
selectivity and efficiency and may provide ways to deal
with poisoning. Two of the challenges in our research
have been preparing suitable oxide substrate surfaces for
control and measurement of particles and adequately
stabilizing nanodimensional particles on these surfaces.
Having established methods of preparing well-defined
and stable platinum clusters on titanium oxide surfaces,
the current efforts have focused on examining the
chemical properties of these particles.
Results and Accomplishments
This research on nanoscale component development uses
a range of new experimental tools recently made available
in the Environmental Molecular Sciences Laboratory.
These tools enhance our ability to work in the nanometer
sizes. We have demonstrated the general ability to create
the desired types of surfaces and to form organized strings
of platinum nanoclusters on these surfaces using selfassembled
processes. By controlling the nature of the
surface, the size, distribution, and stability of the clusters
can be altered. Scanning tunneling microscopy and
temperature-programmed desorption studies show that the
physical and chemical properties of the platinum clusters
(a) Project was formerly called “High Functionality Surfaces and Structures in Microchannels.”
are altered with size, offering the possibility of greater
control of reactivity and catalytic behavior.
Platinum Cluster Sizes and Stability
Titanium oxide (anatase or TiO2) is an important catalyst
support material. A flat, well-defined surface is needed to
enable detailed characterization of the properties of metal
clusters attached to this surface. It is well established that
the TiO2 (110) surface can form two different structures,
i.e., (1x1) and (1x2). However, recent work using the
scanning tunneling microscopy has shown that these
structures can exist in different domains on a single
surface. Because of their different geometric and
electronic structures, one would expect that these two
domains exhibit different interactions with metal clusters
(supported metal catalysts) and thus result in different
catalyst formations. The ability to control the surface
structure of TiO2 surfaces was established in previous
years. This work is the subject of a recent publication and
provides the basis for the current work.
The different sizes and distributions of platinum clusters
formed when platinum was evaporated onto three
different TiO2 surfaces are demonstrated in Figures 1, 2,
and 3. The number and size distribution of the clusters
depends upon the amount of platinum, the temperature,
and the structure of the substrate. Figures 1, 2, and 3
show platinum clusters on a rutile (110) 1x1 surface, a
rutile (110) 1x2 (reconstructed) surface, and an anatase
(001) surface, respectively.
Table 1 shows the cluster size and distribution for 0.5 mL
or less of platinum deposited on each surface. Based on
the observed size and growth, clusters on the
reconstructed rutile 1x2 surface are most stable and those
Micro/Nano Technology 347