Chemical and Mechanical Properties of Surfaces,
Interfaces and Nanostructures
Funded by DOE-BES-MSED
Miquel
Salmeron, Program Leader
Gabor
Somorjai, Peidong
Yang, Co-P.I.s
The purpose of this program is to carry out atomic level studies
of surfaces and nanomaterials, focusing on chemical, mechanical
and physical properties: structure, diffusion, reactions, catalysis,
friction and wear. The molecular level knowledge generated
by the proposed studies will speed the development of novel catalysts
with higher activity and selectivity and the discovery of novel
materials of nanometer dimensions with unique mechanical, chemical
and optical properties, and of materials with improved mechanical
properties of adhesion, friction, and wear. The results of
this project benefit many energy based industries, including chemical,
petroleum, mechanical, electronics, solar energy, etc. To
accomplish these goals, we utilize materials in the form of single
crystals, biointerfaces and nanoparticles. We develop methods
for making nanocrystals with narrow particle size distribution
and well-defined shape. We develop new instrumentation for
the characterization of our materials under the widest possible
range of operating conditions: under vacuum, at ambient pressure
and at the solid-liquid interface. This includes sum frequency
generation (SFG) surface vibrational spectroscopy, high pressure
scanning tunneling microscopy (HPSTM) and ambient pressure X-ray
photoelectron spectroscopy (APXPS).
This program benefits from the strong and synergistic collaboration
of three investigators with expertise in catalysis, surface science,
friction and lubrication, and synthesis of nanomaterials. The expertise
of these investigators is complementary and their interests overlap
in many areas, resulting in joint experiments and the sharing of
students and postdocs. Gabor Somorjai focuses on surface
structure, chemical bonding, reaction studies, and biomolecule
adsorption on surfaces. Peidong Yang designs and synthesizes
nanoparticle catalysts with control of parameters such as size,
shape, and composition. He develops strategies for assembling metallic
and bimetallic nanocrystals on surfaces. Miquel Salmeron focuses
on surface characterization using scanning probe techniques that
resolve single atoms and molecules and their dynamics, in conjunction
with theoretical studies using DFT and image simulations, single
molecule manipulation, and reactions via excitation of vibrations
and electronic transitions. He also investigates the structure
of liquid thin and organic films using atomic force microscopy
and electron spectroscopy to study friction and lubrication phenomena
at the molecular level. Instrument development for surface and
nanoparticle characterization is an important component of the
research of the team to expand the application to practical situations
under ambient gas pressures and temperatures with the goal of discovering
new phenomena. This program is in line with the DOE grand
challenges of control of matter at the single atom level, energy
conservation and efficiency by providing the scientific foundation
for the development of new catalysts, and an understanding of the
elementary mechanisms of energy dissipation in friction.
PROJECTS
- Studies of reactivity and selectivity as a function of size,
shape and composition of metal nanoparticles.
- High pressure STM studies will be carried out on stepped and
kinked metal surfaces and nanoparticles to determine structural
changes driven by high adsorbate coverage
- The study of the molecular scale origin of energy dissipation
in friction will continue using model lubricant films, in the
form of self-assembled monolayers. Particular attention will
be paid to the effect of the chemical nature of the molecular
ends. We will use alkylamines, alcohols and fatty acids self-assembled
on gold, mica and silica films on silicon wafers.
- Studies of water structure on metals (Pd, Ru and Cu) for catalysis
and tribology (lubrication) and to determine growth structure
and possible dissociation in the first monolayer.
- We will study the interaction of water with organic films with
different end group chemistry (CH3, CH2OH, COOH, NH2) and its
effect on friction.
- Application of non-contact AFM (completed last year) to studies
of force spectroscopy of single molecules completed. The aim
is to study the forces of interaction between individual adsorbed
molecules at the surface and at the AFM tip decorated with other
molecules.
- Vibrational spectroscopy on individual molecules using liquid
He cooled STM will be conducted to map reactive species and sites
on model single crystal catalyst surfaces. Reactants to
be studied include H2O, CHx, O2, H2, N2, NH3.
- Coadsorption studies of small molecules and water to understand
solvation and dissolution.
- Multilayer growth of water to determine the transition form
surface-structured water to bulk water.
- Continue the development of a high surface area, monodispersed
metal nanocatalyst for application in heterogeneous catalysis. Studies
of structure-activity and more importantly structure-selectivity
relationships using multi-path catalyzed reactions such as alkane
(n-hexane, n-heptane) reforming.
- Apply nanocrystal shape control chemistry to bimetallic system,
to generate metal nanocrystals of desired shape such as cube
with (001) surface exposed, tetrahedron/octahedron/icosahedron
with (111) surface exposed, in particular, focus will be placed
on monodispersity, uniformity and purity control.
- Size- and shape controlled nanocrystals will be embedded into
mesoporous oxide matrices (e.g. SBA-15), to model 3-dimensional
metal-nanocrystal/oxide-matrix catalysts with well-defined surface
area, controlled surface type (i.e. (111) vs. (100), and controlled
nanocrystal size and metal-oxide interface.
- We will apply the co-assembly concept to a metal-oxide heterostructured
composite system to create metal-oxide hybrid nanocrystals with
high interfacial area as well as specific crystallographic interface. We
will use CeO2 (or TiO2) and Pt (or Pd) as our model system for
this proposed study. The different electronic property of nanoparticles
from that of bulk metal oxide may modify the interaction with
the metal nanoparticle in a different manner and could lead to
better catalysis.
- EXAFS and Treshold XPS spectroscopies will be
developed at high pressures (~ 1 atm) to determine composition,
coordination and oxidation states of bimetallic nanoparticles
under reaction conditions.
- Continue studies of particle size and
shape dependence of metal nanoparticles in surface reactivity.
- High
pressure SFG and STM studies will be carried out on stepped and
kinked platinum and other metal crystal surfaces and nanoparticles
in the presence of gases, CO, O2 and H2.
- Amino acids and peptides
on hydrophobic (polymer) and hydrophilic surfaces will be studied
by SFG and QCM techniques to measure their surface structures
and adsorption isotherms.
Nanoscience and Nanoparticles for 100% Selective Catalytic Reactions
Funded by DOE-BES-CSG&B
Gabor
Somorjai, Program Leader
Miquel
Salmeron, Heinz
Frei, Dean Toste, Co-P.I.s
Heterogeneous catalysts are nanoparticles. They are utilized in
most industrial chemical processes in the form of metal clusters
dispersed on high surface area oxide supports. Recent breakthroughs
in nanotechnology have created the ability to control material
structures on scales that are relevant for catalyst design (e.g.,
the diffusion length of molecular intermediates in a bifunctional
catalyst, ca. 5 nm). The goal of this project is to explore the
molecular and nanoscale variables, structure, composition and dynamic
properties of catalysts to achieve 100% selectivity in multipath
surface catalyzed reactions. The three main areas of emphasis that
are combined in this program:
• to fabricate 3-dimensional or 2-dimensional catalyst systems
with complete control of catalyst nanoparticle location, structure,
thermal and chemical stability;
• to characterize these nanoscale systems by a combination
of steady-state and time-resolved and spectroscopic techniques
that identifies their size, location, electronic structure and
composition during and after fabrication and under reaction conditions;
• to carry out multipath chemical reactions and correlate
reaction selectivity with the physical-chemical variables of
nanoparticle catalyst fabrication with in-situ probes of the
catalyst surface, if possible.
The Structure of Water on Metal and Oxide Surfaces
Funded by DOE-BER-Environmental Remediation Sciences Program
Miquel
Salmeron, Principal Investigator
Studies of water adsorption on environmental mineral surfaces,
concentrating on the growth and wetting properties of oxide surfaces
and on the dissolution and ionic exchange of alkali halide and
rock mineral surfaces.
The Influence of Electron Flow at Oxide-Metal Interface on the
Selectivity and Turnover Rates of Catalytic Reactions
Funded by DOE-BES-CSG&B
Gabor
Somorjai, Principal Investigator
Fabrication of catalytic nanodiodes and mechanism of hot electron
production by exothermic catalytic reactions.
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