You missed us!
Here are some abstracts of talks that we have given.

Society of Analytical Chemists of Pittsburgh, Pittsburgh, PA.

Measurements of Single Molecules in Chemistry and Biology
Paul S. Weiss, Department of Chemistry, The Pennsylvania State University, University Park, PA 16802-6300

Scanning probe microscopies allow unprecedented views of the site-specific interactions and dynamics of atoms and molecules on surfaces. We are able to manipulate these adsorbates chemically or with our microscopes to form structures which we can in turn probe. We are able to measure directly the dramatic chemical changes and the origins of these changes due to surface features such as steps, defects, and other molecules. We discuss the chemical consequences of these changes and how they may be exploited to enhance reactivity and film growth with atomic-scale precision.

While biological systems are more complex, single molecules and particles can also be measured. We have entered a new era in which measurements of properties and manipulation at the single molecule level are possible. We will discuss current and future measurements, identification, separations, and manipulation in real and model biological systems.

University of Pittsburgh, Department of Chemistry Colloquium, Pittsburgh, PA.

Atomic-Scale Views of Interactions and Dynamics of Molecules on Surfaces
Paul S. Weiss, Department of Chemistry, The Pennsylvania State University, University Park, PA 16802-6300

Scanning probe microscopies work at the natural scale of molecular electronics and photonics. We anticipate that these will continue to be used throughout the development and use of functioning devices. We discuss how specific measurements can be used to guide synthesis and assembly of devices. Using our abilities to manipulate molecules and assemblies relative to macro-scale contacts and to probe, we can circumvent much design, synthetic, and assembly work in optimizing structures. This will allow a more direct route to functioning components and devices. We also discuss new tools for measuring environment-dependent electronic structure, photon emission, and conductivity.

Los Alamos National Laboratory, Los Alamos, NM.

Measurements of Single and Bundled Molecules Organized or Isolated in Monolayers
Paul S. Weiss, Department of Chemistry, The Pennsylvania State University, University Park, PA 16802-6300

The Pennsylvania State University, Department of Chemical Engineering, University Park, PA.

Atomic-Scale Views of Catalysis.
Paul S. Weiss, Department of Chemistry, The Pennsylvania State University, University Park, PA 16802-6300

University of Washington, Department of Chemistry, Seattle, WA.

Electrons In, Around, and Through Adsorbed Molecules
Paul S. Weiss, Department of Chemistry, The Pennsylvania State University, University Park, PA 16802-6300

Twelfth Annual Graduate Research Exhibition, Pennsylvania State University, University Park, PA, USA.

Atomic-Scale Insight into the Catalytic Properties of Ni Promoted MoS₂
J. G. Kushmerick and Paul S. Weiss, Department of Chemistry, The Pennsylvania State University, University Park, PA 16802-6300

Molybdenum disulfide (MoS₂) is an important catalyst for removing sulfur in order to increase the environmental compatibility of petroleum-based fuels. While this catalyst is of great industrial importance, the locations and structures of the active sites remain unknown. Nickel (Ni) is known to promote this reaction, but once again by an unknown mechanism. The scanning tunneling microscope provides atomic-scale spatial resolution and the ability to acquire local electronic spectra, making it an ideal tool to investigate such a system. We imaged the MoS₂ surface bare and with adsorbed Ni atoms from room temperature down to 4K using a low temperature ultrahigh vacuum scanning tunneling microscope. Ni atoms freely diffuse across the surface down to temperatures below 80K. At 4K, isolated atoms and small clusters of Ni are stable and can be imaged. Even at 4K, Ni atoms can easily be manipulated with the microscope tip. The sulfur-containing molecules do not stick well to the MoS₂ surface. Our observations suggest that the Ni promoter atoms may act to catch and to transport sulfur-containing hydrocarbons as organometallic complexes to the active sites for reaction. Neither of these roles has been previously suggested, and it is only through our initial measurements that we were able to propose these mechanisms.

Symposium on Electron Transfer Reactions: Fundamentals and Advances,
American Chemical Society Meeting, Dallas, TX, USA, Sunday 29 March - Thursday 3 April 1998.

Measuring and Understanding of Electron Transport Through Organic Molecules Isolated or Organized in Monomolecular Films
Paul S. Weiss, L. A. Bumm, L. F. Charles, T. D. Dunbar, J. J. Jackiw, J. A. Johnson, and D. L. Allara, Department of Chemistry, The Pennsylvania State University, University Park, PA 16802-6300

We measure electron transport through the lengths of single and bundled molecules. We compare organic molecules which are fully conjugated and those with saturated alkyl chains. We also study the effects of chemical substitution on electron transfer. By processing self-assembled monolayers we use film defects to insert single molecules, to insert bundles of molecules, or to graft new molecular terraces onto existing domains. We connect our scanning tunneling microscopy measurements to ubiquitous electron transfer phenomena in such areas as biochemistry and electrochemistry by separating the transconductance into components arising from transport through the molecule vs. the tunneling gap outside the film. We show how these components can be measured independently.

Scanning probe microscopes allow unprecedented views of surfaces. We discuss our efforts to identify and to characterize atoms and molecules on surfaces and how it is that the scanning tunneling microscope images these adsorbates. We are able to measure directly the dramatic changes in the dynamics due to surface features such as steps, defects, and co-adsorbates. In the case of dilute coverage, we can observe the origins of these local changes by observing the perturbations in the surface electronic structure using low temperature ultrahigh vacuum scanning tunneling microscopes. We are currently attempting to extend the spectroscopic capabilities of scanning probe microscopes in several ways. For example, recent advances in tunable microwave frequency AC scanning tunneling microscopy allow differentiation of some surface features and interrogation of single and bundled molecules. We are also able to map the emission of photons induced by tunneling electrons with nanometer resolution. We are developing these and other local spectroscopic tools to determine the chemical identity and modifications of surface features and adsorbates given their measured chemical environment.

Atomic-Scale Views of Interactions and Dynamics of Molecules on Surfaces.
Paul S. Weiss, Department of Chemistry, The Pennsylvania State University, University Park, PA 16802-6300

Scanning probe microscopes allow unprecedented views of surfaces and the site-specific interactions and dynamics of adsorbates. We discuss our efforts to identify and to characterize atoms and molecules on surfaces and how it is that the scanning tunneling microscope images these adsorbates. We are able to measure directly the dramatic changes in the dynamics due to surface features such as steps, defects, and co-adsorbates. In the case of dilute coverage, we can observe the origins of these local changes by observing the perturbations in the surface electronic structure using low temperature ultrahigh vacuum scanning tunneling microscopes. We are currently attempting to extend the capabilities of scanning probe microscopes in several ways. For example, recent advances in tunable microwave frequency AC scanning tunneling microscopy allow differentiation of some surface features and interrogation of single and bundled molecules. We are also able to map the emission of photons induced by tunneling electrons with nanometer resolution. We are attempting to develop these and other local spectroscopic tools to determine the chemical identity and modifications of surface features and adsorbates given their measured chemical environment.
________________
This work is supported by NSF, ONR, PRF, the Exxon Education Foundation, Hewlett-Packard, the Alfred P. Sloan Foundation, and the John Simon Guggenheim Memorial Foundation.

Electron Transport through Single Molecules and Organic Films.
Paul S. Weiss, Department of Chemistry, The Pennsylvania State University, University Park, PA 16802-6300

University of Wisconsin, Department of Chemistry, Madison, WI.

Atomic-Scale Views of Interactions and Dynamics of Molecules on Surfaces.
Paul S. Weiss, Department of Chemistry, The Pennsylvania State University, University Park, PA 16802-6300

University of Wisconsin, Department of Materials Science and Engineering, Madison, WI.

Manipulating Adaptive Materials and Measuring Interactions.
Paul S. Weiss, Department of Chemistry, The Pennsylvania State University, University Park, PA 16802-6300

We have learned to measure and to control the structures of crystalline monomolecular films strongly bound to solid substrates. This typically involves self-assembling and processing the films so as to stay far from equilibrium. I show how we use these capabilities to tailor film properties and to measure isolated or bundled molecules inserted into these films.

In a new series of experiments we attempt to make analogous measurements on fluid interfaces -- vesicle and cell walls. Staying far away from equilibrium in these systems is no longer possible. Instead, we apply steady driving forces in order to affect local composition. I will discuss how we are trying to do this, how we measure our success (or lack thereof), and the resultant local film properties.

Electrons In, Around, and Through Adsorbed Molecules
Paul S. Weiss, Department of Chemistry, The Pennsylvania State University, University Park, PA 16802-6300

We measure electron transport through the lengths of single and bundled molecules. We compare organic molecules which are fully conjugated and those with saturated alkyl chains. We also study the effects of chemical substitution on electron transfer. By processing self-assembled monolayers we use film defects to insert single molecules, to insert bundles of molecules, or to graft new molecular terraces onto existing domains. We connect our scanning tunneling microscopy measurements to ubiquitous electron transfer phenomena in such areas as biochemistry and electrochemistry by separating the transconductance into components arising from transport through the molecule vs. the tunneling gap outside the film. We show how these components can be measured independently.

Atomic-Scale Insight into Catalytic Promoters
J. G. Kushmerick, and P. S. Weiss, Department of Chemistry, The Pennsylvania State University, University Park, PA 16802-6300

Two new roles for catalytic promoters are suggested based on scanning tunneling microscopy and spectroscopy measurements. Ni promoted molybdenum disulfide (MoS₂) is an important catalyst for removing sulfur from petroleum feedstock. We imaged the MoS₂ basal plane bare and with adsorbed Ni atoms at 298K, 77K and 4K using a low temperature ultrahigh vacuum scanning tunneling microscope. Ni atoms freely diffuse across the surface down to temperatures below 80K. At 4K, isolated atoms and small clusters of Ni are stable and can be imaged. Even at 4K, Ni atoms can easily be manipulated with the microscope tip. Spectroscopic measurements reveal that Ni promoters create favorable electronic structures for binding sulfur-containing reactants. Our observations suggest two new roles for the Ni promoter atoms: 1) they increase the sticking probability of sulfur-containing hydrocarbons by binding them to the unreactive basal planes of MoS₂ and 2) they transport these hydrocarbons as organometallic complexes to the active sites for reaction.

Control of Self-Assembled Monolayer Film Structure and Properties
L. F. Charles, L. A. Bumm, J. J. Jackiw, J. A. Johnson, E. H. Muth, T. D. Dunbar, D. L. Allara, and P. S. Weiss, Department of Chemistry, The Pennsylvania State University, University Park, PA 16802-6300

Scanning tunneling microscopy (STM) has been used to investigate self-assembled film formation of molecules in single and varied compositions of thiols and selenols on Au{111}. While the average surface composition of these films typically reflects that of the deposition solution, STM is used to determine the position and motion of these molecules on the surface. We also use STM to measure electron transport through these molecules to ascertain the roles of chain length and chemical contact with the substrate.

We discuss how spacer molecules such as adamantanethiol (C₁₀H₁₅SH) can be used to isolate other molecules for such studies. We show that ordered films can be produced from such molecules for this purpose. Unlike alkanethiolate films, this produces structural domain boundaries and other defects that do not involve significant conformation relaxation. These spacer molecules can also be mixed with alkanethiolate films.

We modify self-assembled surfaces to tailor the films to our needs. Our growing abilities to control the placement of molecules within these films are presented.

Electron Transport through Organic Molecules
Lloyd A. Bumm, J. J. Arnold, L. F. Charles, T. D. Dunbar, D. L. Allara, and P. S. Weiss, Department of Chemistry, The Pennsylvania State University, University Park, PA 16802-6300

Electron transport through molecular frameworks is central to a wide range of chemical, physical, and biological processes. We demonstrate a means to measure electronically and to quantify electron transport through organic molecules and films. We show quantitative agreement with universal values of electron transport inferred in biological, electrochemical, photochemical, and related systems. Scanning tunneling microscopy (STM) was used to image adjacent chains and molecular terraces of different length alkanethiolates in an ordered self-assembled monolayer lattice on Au{111}. The differences between the measured topography in STM and the physical heights of these molecules can be understood in terms of the transconductance through individual chains using a two-layer tunnel junction model.

Exploring the Atomic-Scale World
Paul S. Weiss

Kyoto University, Venture Business Laboratory, Department of Electronic Science and Engineering, Kyoto, Japan.

Exploring and Controlling the Atomic-Scale World
Paul S. Weiss, Department of Chemistry, The Pennsylvania State University, University Park, PA 16802-6300, USA

Electron Transport through Organic Molecules
L. A. Bumm,* L. F. Charles, J. J. Arnold, T. D. Dunbar, D. L. Allara, and Paul S. Weiss, Department of Chemistry, The Pennsylvania State University, University Park, PA 16802-6300, USA

We use high resolution scanning tunneling microscopy (STM) to investigate electron transport through organic molecules using multi-component self-assembled monolayers (SAMs) of thiolates adsorbed on Au{111}. Through a combination of deposition and processing techniques, we prepare well-ordered monolayers wherein the components are made to form a segregated mosaic of patches with molecularly sharp boundaries between the patches. These boundaries enable us to measure directly the differences in electron transport between the domains of each component. STM is ideally suited for these measurements because the STM probe tip interacts with the molecules via electron tunneling, i.e. the STM contrast mechanism is inexorably linked to the electron transport properties of the film. We interpret our results using a two-layer model of the STM tunnel junction.

MITRE/DARPA Nanosystems Review of Devices and Architectures, Reston, VA.

Current and Future Experimental Developments in Molecular Electronics
J. C. Love, G. S. McCarty, C. D. Keating, M. J. Natan, and Paul S. Weiss, Department of Chemistry, The Pennsylvania State University, University Park, PA 16802-6300, USA

Symposium on the Structure and Electronic Properties of Materials by Scanning Probe Microscopy, American Chemical Society Meeting, Boston, MA, USA, Sunday 23 August - Thursday 27 August 1998.

Atomic-Scale Insight Into the Catalytic Properties of Nickel Promoted Molybdenum Disulfide
J. G. Kushmerick and Paul S. Weiss, Department of Chemistry, The Pennsylvania State University, University Park, PA 16802-6300

Sci-Mix, American Chemical Society Meeting, Boston, MA, USA, Sunday 23 August - Thursday 27 August 1998.

Atomic-Scale Insight Into the Catalytic Properties of Nickel Promoted Molybdenum Disulfide
J. G. Kushmerick and Paul S. Weiss, Department of Chemistry, The Pennsylvania State University, University Park, PA 16802-6300

Symposium on the Structure and Electronic Properties of Materials by Scanning Probe Microscopy, American Chemical Society Meeting, Boston, MA, USA, Sunday 23 August - Thursday 27 August 1998.

Measuring and Understanding of Electron Transport Through Organic Molecules Isolated or Organized in Monomolecular Films
Paul S. Weiss, L. A. Bumm, L. F. Charles, T. D. Dunbar, J. J. Jackiw, J. A. Johnson, and D. L. Allara, Department of Chemistry, The Pennsylvania State University, University Park, PA 16802-6300

Electrons In, Around, and Through Adsorbed Molecules
Paul S. Weiss, Department of Chemistry, The Pennsylvania State University, University Park, PA 16802-6300, USA

Scanning probe microscopes allow unprecedented views of surfaces and the site-specific interactions and dynamics of adsorbates. We discuss our efforts to identify and to characterize atoms and molecules on surfaces and how it is that the scanning tunneling microscope images these adsorbates. We are able to measure directly the dramatic changes in the dynamics due to surface features such as steps, defects, and co-adsorbates. In the case of dilute coverage, we can observe the origins of these local changes by observing the perturbations in the surface electronic structure using low temperature ultrahigh vacuum scanning tunneling microscopes. We are able to use these effects and also film defects to control and to direct the placement of molecules on the surface or in and out of films.

We are currently extending the capabilities of scanning probe microscopes in several ways. For example, we map the emission of photons induced by tunneling electrons with nanometer resolution. We are developing these and other local spectroscopic tools to determine the chemical identity and modifications of surface features and adsorbates given their measured chemical environment.

Electrons In, Around, and Through Adsorbed Molecules
Paul S. Weiss, Department of Chemistry, The Pennsylvania State University, University Park, PA 16802-6300, USA

Exploring and Controlling the Atomic-Scale World
Paul S. Weiss, Department of Chemistry, The Pennsylvania State University, University Park, PA 16802-6300, USA

Scanning probe microscopes allow unprecedented views of the site-specific interactions and dynamics of adsorbates on surfaces. I will discuss our efforts to identify and to characterize atoms and molecules on surfaces and how it is that the scanning tunneling microscope images these adsorbates. We are able to measure directly the dramatic changes in the dynamics due to surface features such as steps, defects, and co-adsorbates. In the case of dilute coverage, we can also observe the origins of these local changes by measuring the perturbations in the local surface electronic structure using low temperature ultrahigh vacuum scanning tunneling microscopes. We are able to use these effects and also film defects to control and to direct the placement of molecules on the surface as well as in and out of monolayer films.

We are now trying to extend to biological interfaces our ability to probe and to control at the molecular scale. To do so, we can no longer stay far from equilibrium nor can we use scanning probe methods. Thus, we must develop new strategies and tools. I will briefly discuss our first primitive efforts along these lines -- to direct the placement of molecules and to measure the resulting properties of fluid lipid bilayers in vesicles and cell walls.

Exploring and Controlling the Atomic-Scale World
Paul S. Weiss, Department of Chemistry, The Pennsylvania State University, University Park, PA 16802-6300, USA

Scanning probe microscopes allow unprecedented views of the site-specific interactions and dynamics of adsorbates on surfaces. I will discuss our efforts to identify and to characterize atoms and molecules on surfaces and how it is that the scanning tunneling microscope images these adsorbates. We are able to measure directly the dramatic changes in the dynamics due to surface features such as steps, defects, and co-adsorbates. In the case of dilute coverage, we can also observe the origins of these local changes by measuring the perturbations in the local surface electronic structure using low temperature ultrahigh vacuum scanning tunneling microscopes. We are able to use these effects and also film defects to control and to direct the placement of molecules on the surface as well as in and out of monolayer films.

We are now trying to extend to biological interfaces our ability to probe and to control at the molecular scale. To do so, we can no longer stay far from equilibrium nor can we use scanning probe methods. Thus, we must develop new strategies and tools. I will briefly discuss our first primitive efforts along these lines -- to direct the placement of molecules and to measure the resulting properties of fluid lipid bilayers in vesicles and cell walls.

Exploring the Atomic-Scale World: Research Opportunities in the Weiss Group
Paul S. Weiss, Department of Chemistry, The Pennsylvania State University, University Park, PA 16802-6300, USA

Electrons In, Around, and Through Adsorbed Molecules
Paul S. Weiss, L. A. Bumm, and G. S. McCarty, Department of Chemistry, The Pennsylvania State University, University Park, PA 16802-6300, USA

Scanning probe microscopes allow unprecedented views of surfaces. We discuss our efforts to identify and to characterize atoms and molecules on surfaces and how it is that the scanning tunneling microscope images these adsorbates. We are currently attempting to extend the spectroscopic capabilities of scanning probe microscopes in several ways. For example, recent advances in tunable microwave frequency AC scanning tunneling microscopy allow differentiation of some surface features and interrogation of single and bundled molecules. We are also able to map the emission of photons induced by tunneling electrons with nanometer resolution. We are developing these and other local spectroscopic tools to determine the chemical identity and modifications of surface features and adsorbates given their measured chemical environment.

Exploring and Controlling the Atomic-Scale World
Paul S. Weiss, Department of Chemistry, The Pennsylvania State University, University Park, PA 16802-6300, USA

Scanning probe microscopes allow unprecedented views of the site-specific interactions and dynamics of adsorbates on surfaces. I will discuss our efforts to identify and to characterize atoms and molecules on surfaces and how it is that the scanning tunneling microscope images these adsorbates. We are able to measure directly the dramatic changes in the dynamics due to surface features such as steps, defects, and co-adsorbates. In the case of dilute coverage, we can also observe the origins of these local changes by measuring the perturbations in the local surface electronic structure using low temperature ultrahigh vacuum scanning tunneling microscopes. We are able to use these effects and also film defects to control and to direct the placement of molecules on the surface as well as in and out of monolayer films.

We are now trying to extend to biological interfaces our ability to probe and to control at the molecular scale. To do so, we can no longer stay far from equilibrium nor can we use scanning probe methods. Thus, we must develop new strategies and tools. I will briefly discuss our first primitive efforts along these lines -- to direct the placement of molecules and to measure the resulting properties of fluid lipid bilayers in vesicles and cell walls.

Detecting Chemical Warfare Agents
Terrence G. J. D'Onofrio, Department of Chemistry, The Pennsylvania State University, University Park, PA 16802-6300, USA

Electrons In, Around, and Through Adsorbed Molecules
Paul S. Weiss, Department of Chemistry, The Pennsylvania State University, University Park, PA 16802-6300, USA

Phenyl-Containing Radicals on Cu{111}
G. S. McCarty,* M. M. Kamna and P. S. Weiss, Department of Chemistry, The Pennsylvania State University, University Park, PA 16802-6300, USA.
Poster presented by G. S. McCarty.

Surface features such as step edges, impurities, and adsorbates cause modification of the local electronic properties of a surface. We are taking advantage of this phenomenon to produce active sites for surface reactions. We explore the atomic scale electronic effects on reactions of phenyl containing species to understand the catalytic properties of copper. Copper catalyzes reactions of phenyl containing species through the Ullmann coupling reaction. A low temperature UHV STM was used to study Cu[111] dosed with iodobenzene, di-iodobenzene, and biphenyl. The dissociation of iodobenzene into iodine and phenyl was observed. The reaction can be driven to produce biphenyl. We observed the intermediate complex pairs responsible for the exquisite specificity of this reaction.

Curvature-Induced Domain Formation in Lipid Bilayer Membranes
C. D. Keating,* T. G. D'Onofrio, M. J. Natan, and P. S. Weiss, Department of Chemistry, The Pennsylvania State University, University Park, PA 16802-6300, USA.
Poster presented by C. D. Keating.

A number of studies have suggested the importance of domain formation in biological membranes. We describe recent results concerning the effect of lipid bilayer lateral heterogeneity on model membrane function in single unilamellar vesicles. Initial work has focused on preparation and imaging of lipid membranes of various curvatures, and manipulation of these membranes in flowing solution by optical trapping. Several methods have been applied to alter liposome morphology, from encapsulation of materials (both biological and nonbiological) to stretching vesicles using multiple optical traps. Fluorescence microscopic data on lateral domains as a function of membrane curvature will be discussed.

Control of Self-Assembled Monolayer Film Structure and Properties
P. S. Weiss, L. F. Charles,* L. A. Bumm, T. D. Dunbar, and D. L. Allara, Department of Chemistry, The Pennsylvania State University, University Park, PA 16802-6300, USA.
Presented by L. F. Charles.

Scanning tunneling microscopy (STM) has been used to investigate self-assembled film formation of molecules in single and varied compositions of alkanethiols on Au{111}. While the average surface composition of these films typically reflects that of the deposition solution, STM is used to determine the position and motion of these molecules on the surface. We also use STM to measure electron transport through these molecules to ascertain the roles of chain length and chemical contact with the substrate.

We discuss how spacer molecules such as adamantanethiol (C₁₀H₁₅SH) can be used to isolate other molecules for such studies. Our investigation of this system shows that ordered films can be produced from such molecules for this purpose. Unlike alkanethiolate films, this produces structural domain boundaries and other defects that do not involve significant conformation relaxation.

In our studies we focus on the modification of self-assembled surfaces to tailor the films to our needs. Our growing abilities to control the placement of molecules within these films are presented.

Growth, Modification, and Control of the Structures of Mixed Composition Organic Monolayers
T. D. Dunbar, T. P. Burgin, J. M. Tour, D. L. Allara, and L. A. Bumm, Department of Chemistry, The Pennsylvania State University, University Park, PA 16802-6300, USA.
Presented by L. A. Bumm.

Control of the molecular-scale structure of multi-component self-assembled of organic thiols on Au(111) can be achieved by selecting a combination of deposition and processing techniques. These include competitive adsorption (growth) and subsequent exchange (modification). The effects of this processing on the molecular-scale structure have been studied by conventional and AC scanning tunneling microscopy. Lateral epitaxy has been observed where a growing domain of one molecular species is grafted onto an existing crystalline lattice of a different molecular species with no lattice mismatch. In other examples, the limited substrate access afforded by structural defects in the films has been utilized to insert single molecules for further use or study. We also use these mixed composition monolayers to gain insight into the mechanism by which these films can be imaged and the extent to which organic molecules conduct. By analyzing images and local spectra of isolated and aggregated molecules, we can determine the extent to which neighboring molecules contribute to these processes. We believe that none of the structures we obtain are equilibrium structures. We discuss relevant considerations for stabilizing the nanometer-scale structures created.

Controlling Defects in Self-Assembled Monolayers
J. J. Jackiw, J. J. Arnold, J. A. Johnson, T. D. Dunbar, T. L. Spiva, D. L. Allara, and P. S. Weiss, Department of Chemistry, The Pennsylvania State University, University Park, PA 16802-6300, USA.
Presented by J. J. Jackiw.

Much is known about the formation, structure, stability, and properties of alkanethiolate monolayers on Au (111). We have begun to explore the effects of changing the molecule-surface linkage. In the cases of alkanethiolates and alkaneselenolates, monolayers can be made respectively from: thiols and selenols, disulfides and diselenides, and by deprotecting alkanethioacetates and alkaneselenoacetates, which are less prone to oxidation. Our experiments probe monolayer structures and defects resulting from the deposition of dodecanethiol, didodecane disulfide, didodecane diselenide, dodecaneselenol, and in situ deprotected dodecanethioacetate and dodecaneselenoacetate. We compare the structures and defects in the resulting monolayers. The defect identities and densities are important in determining the properties of the films, especially our ability to manipulate their structures and compositions.

Tunneling and Photon Emission of Colloidal Particles
G. S. McCarty,* C. D. Keating, P. S. Weiss, and M. J. Natan, Department of Chemistry, The Pennsylvania State University, University Park, PA 16802-6300, USA.
Poster presented by G. S. McCarty.

Binding of molecules of interest to colloidal particles allows the optical properties of the molecules to be studied using techniques such as surface enhanced Raman spectroscopy. By binding these colloidal particles to a conducting surface the electronic properties of the molecules can be probed using scanning tunneling microscopy. We have imaged gold and silver colloids bound to Au(111) coated with 2-mercaptoethylamine. The particles were then studied using photon emission scanning tunneling microscopy to probe the electronic and optical properties of single particles.

Anisotropic Electron Scattering from Point Defects on Graphite at Low Temperature
K. F. Kelly,* J. G. Kushmerick,* H. P. Rust, N. J. Halas, and P. S. Weiss, Department of Chemistry, The Pennsylvania State University, University Park, PA 16802-6300, USA and Department of Electrical and Computer Engineering, Rice University, Houston, TX, USA.
Poster presented by K. F. Kelly and J. G. Kushmerick.

A low temperature ultrahigh vacuum scanning tunneling microscope was used to image threefold symmetric electron scattering from point defects in the graphite surface. Such defects were theoretically predicted,¹ but had only previously been observed with C₆₀-functionalized tips at room temperature.² Cryogenic temperatures sharpen the Fermi distribution enabling the observation of electron scattering. The energy dependence of the scattering was mapped by spectroscopic imaging and acquiring complete current-voltage curves at specific positions with respect to the scattering center.

Exploring and Controlling the Atomic-Scale World
Paul S. Weiss, Department of Chemistry, The Pennsylvania State University, University Park, PA 16802-6300, USA

Scanning probe microscopes allow unprecedented views of the site-specific interactions and dynamics of adsorbates on surfaces. We are able to measure directly the dramatic changes in the dynamics due to surface features such as steps, defects, and co-adsorbates. In the case of dilute coverage, we can also observe the origins of these local changes by measuring the perturbations in the local surface electronic structure using low temperature ultrahigh vacuum scanning tunneling microscopes. We are able to use these effects and also film defects to control and to direct the placement of molecules on the surface as well as in and out of monolayer films. We measure electron transport through the lengths of single and bundled molecules. We connect our scanning tunneling microscopy measurements to ubiquitous electron transfer phenomena in such areas as biochemistry and electrochemistry.

We are now trying to extend to biological interfaces our ability to probe and to control at the molecular scale. To do so, we can no longer stay far from equilibrium nor can we use scanning probe methods. Thus, we must develop new strategies and tools. I will briefly discuss our first primitive efforts along these lines -- to direct the placement of molecules and to measure the resulting properties of fluid lipid bilayers in vesicles and cell walls.

Exploring and Controlling the Atomic-Scale World
Paul S. Weiss, Department of Chemistry, The Pennsylvania State University, University Park, PA 16802-6300, USA

Scanning probe microscopes allow unprecedented views of the site-specific interactions and dynamics of adsorbates on surfaces. We are able to measure directly the dramatic changes in the dynamics due to surface features such as steps, defects, and co-adsorbates. In the case of dilute coverage, we can also observe the origins of these local changes by measuring the perturbations in the local surface electronic structure using low temperature ultrahigh vacuum scanning tunneling microscopes. We are able to use these effects and also film defects to control and to direct the placement of molecules on the surface as well as in and out of monolayer films. We measure electron transport through the lengths of single and bundled molecules. We connect our scanning tunneling microscopy measurements to ubiquitous electron transfer phenomena in such areas as biochemistry and electrochemistry.

We are now trying to extend to biological interfaces our ability to probe and to control at the molecular scale. To do so, we can no longer stay far from equilibrium nor can we use scanning probe methods. Thus, we must develop new strategies and tools. I will briefly discuss our first primitive efforts along these lines -- to direct the placement of molecules and to measure the resulting properties of fluid lipid bilayers in vesicles and cell walls.

Exploring and Controlling the Atomic-Scale World
Paul S. Weiss, Department of Chemistry, The Pennsylvania State University, University Park, PA 16802-6300, USA

We measure electron transport through the lengths of single and bundled molecules. We compare organic molecules that are fully conjugated and those with saturated alkyl chains. We also study the effects of chemical substitution on electron transfer. By processing self-assembled monolayers we use film defects to insert single molecules, to insert bundles of molecules, or to graft new molecular terraces onto existing domains. We use intermolecular interactions mediated by the substrate to direct and to enhance chemical reactions. We connect our scanning tunneling microscopy measurements to ubiquitous electron transfer phenomena in such areas as biochemistry and electrochemistry by separating the transconductance into components arising from transport through the molecule vs. the tunneling gap outside the film. We show how these components can be measured independently.

Attempts to Manipulate and to Probe Local Composition and Resultant Properties in Lipid Bilayers
Paul S. Weiss, Department of Chemistry, The Pennsylvania State University, University Park, PA 16802-6300, USA

Probing the Atomic-Scale Chemistry and Physics of Anisotropic Surfaces
Jim Kushmerick, Department of Chemistry, The Pennsylvania State University, University Park, PA 16802-6300, USA

The anisotropic nature of surfaces can lead to interesting and important chemical and physical effects. We have studied two anisotropic systems -- Ni on MoS₂ and point defects in graphite. I discuss the local electronic effects in these systems and their implications. I also discuss the new atomic-scale roles in binding and transport of reactants on anisotropic catalysts that our experiments have revealed.

Electrons In, Around, and Through Adsorbed Molecules
Paul S. Weiss, Department of Chemistry, The Pennsylvania State University, University Park, PA 16802-6300, USA

We measure electron transport through the lengths of single and bundled molecules. We compare organic molecules which are fully conjugated and those with saturated alkyl chains. We also study the effects of chemical substitution on electron transfer. By processing self-assembled monolayers we use film defects to insert single molecules, to insert bundles of molecules, or to graft new molecular terraces onto existing domains. We connect our scanning tunneling microscopy measurements to ubiquitous electron transfer phenomena in such areas as biochemistry and electrochemistry by separating the transconductance into components arising from transport through the molecule vs. the tunneling gap outside the film. We show how these components can be measured independently.

Directing Assembly and Probing Single and Bundled Molecules Isolated in 2D Molecular Matrices
Paul S. Weiss, Department of Chemistry, The Pennsylvania State University, University Park, PA 16802-6300, USA

We process self-assembled monolayers to insert single molecules, to insert bundles of molecules, or to graft new molecular terraces onto existing domains by using film defects to advantage. These inserted molecules can serve as the anchor points for polymerization so that we are able to choose to produce single polymer dots or isolated polymer brushes. We connect our scanning tunneling microscopy measurements to ubiquitous electron transfer phenomena in such areas as biochemistry and electrochemistry by separating the transconductance into components arising from transport through the molecule vs. the tunneling gap outside the film. We show how these components can be measured independently.

Mobile Promoters on Anisotropic Catalysts
Jim Kushmerick, Department of Chemistry, The Pennsylvania State University, University Park, PA 16802-6300, USA

Molecular Measurements with Scanning Tunneling Microscopy
Lloyd A. Bumm, Department of Chemistry, The Pennsylvania State University, University Park, PA 16802-6300, USA

Exploring and Controlling the Atomic-Scale World
Paul S. Weiss, Department of Chemistry, The Pennsylvania State University, University Park, PA 16802-6300, USA

Exploring and Controlling the Atomic-Scale World
Paul S. Weiss, Department of Chemistry, The Pennsylvania State University, University Park, PA 16802-6300, USA

Exploring and Controlling the Atomic-Scale World
Paul S. Weiss, Department of Chemistry, The Pennsylvania State University, University Park, PA 16802-6300, USA

Electron Transport Through Organic Molecules
Lloyd A. Bumm, Lyndon F. Charles, Jamie J. Arnold, Timothy D. Dunbar, David L. Allara, Paul S. Weiss, Department of Chemistry, The Pennsylvania State University, University Park, PA 16802-6300, USA

Electron transport through molecular frameworks is central to a wide range of chemical, physical, and biological processes. We demonstrate a means to measure electronically and to quantify electron transport through organic molecules and films. We show quantitative agreement with universal values of electron transport inferred in biological, electrochemical, photochemical, and related systems. Scanning tunneling microscopy (STM) was used to image adjacent chains and molecular terraces of different length alkanethiolates in an ordered self-assembled monolayer lattice on Au(111). The differences between the measured topography in STM and the physical heights of these molecules can be understood in terms of the transconductance through individual chains using a two-layer tunnel junction model.

The anisotropic nature of surfaces can lead to interesting and important chemical and physical effects. We have studied two anisotropic systems -- Ni on MoS₂ and point defects in graphite. I discuss the local electronic effects in these systems and their implications. I also discuss the new atomic-scale roles in binding and transport of reactants on anisotropic catalysts that our experiments have revealed.

The anisotropic nature of surfaces can lead to interesting and important chemical and physical effects. We have studied two anisotropic systems -- Ni on MoS₂ and point defects in graphite. I discuss the local electronic effects in these systems and their implications. I also discuss the new atomic-scale roles in binding and transport of reactants on anisotropic catalysts that our experiments have revealed.

Controlling and Probing Local Composition in Membranes
Paul S. Weiss, Department of Chemistry, The Pennsylvania State University, University Park, PA 16802-6300, USA

Exploring and Controlling the Atomic-Scale World
Paul S. Weiss, Department of Chemistry, The Pennsylvania State University, University Park, PA 16802-6300, USA

Scanning probe microscopes allow unprecedented views of the site-specific interactions and dynamics of adsorbates on surfaces. I will discuss our efforts to identify and to characterize atoms and molecules on surfaces and how it is that the scanning tunneling microscope images these adsorbates. We are able to measure directly the dramatic changes in the dynamics due to surface features such as steps, defects, and co-adsorbates. In the case of dilute coverage, we can also observe the origins of these local changes by measuring the perturbations in the local surface electronic structure using low temperature ultrahigh vacuum scanning tunneling microscopes. We are able to use these effects and also film defects to control and to direct the placement of molecules on the surface as well as in and out of monolayer films.

We are now trying to extend to biological interfaces our ability to probe and to control at the molecular scale. To do so, we can no longer stay far from equilibrium nor can we use scanning probe methods. Thus, we must develop new strategies and tools. I will briefly discuss our first primitive efforts along these lines -- to direct the placement of molecules and to measure the resulting properties of fluid lipid bilayers in vesicles and cell walls.

Exploring and Controlling the Atomic-Scale World
Paul S. Weiss, Department of Chemistry, The Pennsylvania State University, University Park, PA 16802-6300, USA

Scanning probe microscopes allow unprecedented views of the site-specific interactions and dynamics of adsorbates on surfaces. I will discuss our efforts to identify and to characterize atoms and molecules on surfaces and how it is that the scanning tunneling microscope images these adsorbates. We are able to measure directly the dramatic changes in the dynamics due to surface features such as steps, defects, and co-adsorbates. We are able to use these effects and also film defects to control and to direct the placement of molecules on the surface as well as in and out of monolayer films.

We are now trying to extend to biological interfaces our ability to probe and to control at the molecular scale. To do so, we can no longer stay far from equilibrium nor can we use scanning probe methods. Thus, we must develop new strategies and tools. I will briefly discuss our first primitive efforts along these lines -- to direct the placement of molecules and to measure the resulting properties of fluid lipid bilayers in vesicles and cell walls.

Exploring and Controlling the Atomic-Scale World
Paul S. Weiss, Department of Chemistry, The Pennsylvania State University, University Park, PA 16802-6300, USA

Scanning probe microscopes allow unprecedented views of the site-specific interactions and dynamics of adsorbates on surfaces. I will discuss our efforts to identify and to characterize atoms and molecules on surfaces and how it is that the scanning tunneling microscope images these adsorbates. We are able to measure directly the dramatic changes in the dynamics due to surface features such as steps, defects, and co-adsorbates. In the case of dilute coverage, we can also observe the origins of these local changes by measuring the perturbations in the local surface electronic structure using low temperature ultrahigh vacuum scanning tunneling microscopes. We are able to use these effects and also film defects to control and to direct the placement of molecules on the surface as well as in and out of monolayer films.

We are now trying to extend to biological interfaces our ability to probe and to control at the molecular scale. To do so, we can no longer stay far from equilibrium nor can we use scanning probe methods. Thus, we must develop new strategies and tools. I will briefly discuss our first primitive efforts along these lines -- to direct the placement of molecules and to measure the resulting properties of fluid lipid bilayers in vesicles and cell walls.

Probing the Atomic-Scale Chemistry and Physics of Surfaces
James G. Kushmerick, Department of Chemistry, The Pennsylvania State University, University Park, PA 16802-6300, USA

Molecular-Scale Measurement and Control in Molecular Monolayers and Molecular Electronics
Paul S. Weiss, Department of Chemistry, The Pennsylvania State University, University Park, PA 16802-6300, USA

Identifying and Locating Functional Groups by Selective Reactions: Staining for Scanning Probe Microscopy
G. S. McCarty and P. S. Weiss, Department of Chemistry, The Pennsylvania State University, University Park, PA 16802-6300, USA

Our goal is to develop scanning probe analogues to the stains used in conventional optical microscopy. We employ chemical reactions for the selective decoration of surface chemical features. In place of the dyes that are used in optical measurements, we decorate with species identifiable with scanning probe spectroscopy. This is both for confirmation of identification and also so that multiple stains may be used on the same sample.

In our initial work, we use metallic nanoparticles to highlight surface functional groups. We then use the well developed surface functionalization chemistry to determine which metal will react with which functional group. For example, Au nanoparticles can be utilized as a "stain" for exposed thiols and disulfides. Nanoparticles appear as prominent features in images and are thus easy to locate. We have shown that we can use photon emission scanning tunneling microscopy to distinguish between different nanoparticle compositions. This gives us the ability to have multiple simultaneous stains.

We discuss these stains and others being developed for organic and biological samples.

Controlling the Placement of Molecules in the Self-Assembly and Directed Assembly of Organic Monolayers
Paul S. Weiss, Department of Chemistry, The Pennsylvania State University, University Park, PA 16802-6300, USA

Probing Single Molecular Electronics and Chemistry at the Atomic Scale Using Scanning Tunneling Microscopy and Spectroscopy
Paul S. Weiss, Department of Chemistry, The Pennsylvania State University, University Park, PA 16802-6300, USA

Scanning probe microscopes enable unprecedented views of the site-specific interactions and dynamics of atoms and molecules on surfaces. We are able to manipulate these adsorbates chemically or with our microscopes to form structures which we can in turn probe. We are able to measure directly the dramatic chemical changes and the origins of these changes due to surface features such as steps, defects, and other molecules. We discuss the chemical consequences of these changes and how they may be exploited to enhance reactivity and film growth with atomic-scale precision. Scanning probe microscopes work at the natural scale of molecular electronics. We anticipate that these probes will continue to be used throughout the development and use of functioning molecular electronic devices. We discuss new tools for measuring environment-dependent electronic structure, bonding, photon emission, conductivity, and other properties.

A. L. Bross,^* A. Hooper, D. L. Allara, and Paul S. Weiss, Department of Chemistry, The Pennsylvania State University, University Park, PA 16802-6300, USA

G. S. McCarty, C.D. Keating, D.J. Fuchs, and Paul S. Weiss, Department of Chemistry, The Pennsylvania State University, University Park, PA 16802-6300, USA

We are developing general means to differentiate between molecular structures using scanning tunneling microscopy. It remains difficult to do this in general using only tunneling spectroscopy. We are investigating several routes to enable identification and differentiation of molecules. Photons emitted from Au and Ag nanoparticles in the tunneling junction allow us to differentiate between them. We can use these and other methods to develop "stains" for scanning probe microscopy in analogy to those used in conventional optical microscopy. Functionalized nanoparticles are bound selectively to parts of molecules to decorate moieties of interest. Different nanoparticles are used to differentiate the function groups on a molecule. These labels are then imaged and resolved using the local photon emission spectra induced by the scanning tunneling microscope tip.

How Low Can You Go with Scanning Probe Microscopy?
P. S. Weiss, Department of Chemistry, The Pennsylvania State University, University Park, PA 16802-6300, USA

Controlling the Placement of Molecules in the Self Assembly and Directed Assembly of Organic Monolayers
P. S. Weiss, D. L. Allara, L. A. Bumm, and J. J. Jackiw, Department of Chemistry, The Pennsylvania State University, University Park, PA 16802-6300, USA

We manipulate and measure the structures of monolayer films in order to tune their properties. This is accomplished by controlling the defect type and density in the films. We then process the films to insert single molecules, to insert bundles of molecules, or to graft new molecular terraces onto existing domains by using these defects to advantage. The inserted molecules can serve as the anchor points for polymerization; this allows us to choose to produce single polymer dots or isolated polymer brushes. We connect our scanning tunneling microscopy measurements to electron transfer phenomena which are ubiquitous in such areas as biochemistry and electrochemistry by separating the transconductance into components arising from transport through the molecule vs. the tunneling gap outside the film. We show how these components can be measured independently. We prepare films predicted to have many equivalent defect sites so as to provide identical matrix isolation environments for single molecular wire candidates. We also prepare films with well defined interfaces between separated components so that insertion, deposition, or reaction can be directed to these molecularly sharp boundaries.

Local Control of Composition and Curvature in Lipid Bialyer Membranes
P. S. Weiss, T. G. D'Onofrio, A. Hatzor, C. D. Keating, E. H. Muth, and R. K. Smith, Department of Chemistry, The Pennsylvania State University, University Park, PA 16802-6300, USA.

Vibrational Spectroscopy of Single Molecules with the Scanning Tunneling Microscope
S. A. Kandel, Department of Chemistry, The Pennsylvania State University, University Park, PA 16802-6300, USA.

Progress in Molecular Electronics
P. S. Weiss, Department of Chemistry, The Pennsylvania State University, University Park, PA 16802-6300, USA.

Local Surface Electronic and Chemical Changes in Molecular Adsorption
S. A. Kandel and P. S. Weiss, Department of Chemistry, The Pennsylvania State University, University Park, PA 16802-6300, USA

We measure local perturbations of the surface electronic structure and correlate these with changes in adsorption strength, chemistry, dynamics, and structure. Scanning tunneling microscopy and spectroscopy allow us to measure the relevant energy and spatially resolved local densities of states on surfaces. We observe the changes in residence times and intermolecular interactions due to the locally enhanced and depleted electronic structure.

We attempt to exploit these electronic changes to enhance surface reactions and to target creation of atomically precise structures. We have induced pairing and higher complexes of reaction intermediates in the reaction of haloaromatics to produce coupled aromatic structures on the Cu{111} surface. Even in unreactive systems, we find that adsorbate structures nucleate at step edges where the electronic perturbations are strongest, and grow out based on molecule-induced perturbations of the nearby electronic structure. We can predict where molecular adsorption is enhanced based on the electronic character of the adsorbate. While we cannot yet predict the strengths of these enhancements, we plan and describe experiments to make these correlations.

Tunable Microwave Frequency AC Scanning Tunneling Microscopy for Dopant Profiling
P. S. Weiss,^1,2 G. S. McCarty,^1,2 L. A. Bumm,¹Z. J. Donhauser,¹ and B. A. Mantooth^1
1Department of Chemistry, The Pennsylvania State University, University Park, PA 16802-6300, USA
²Atolytics, Inc., State College, PA, USA.

Controlling the Placement of Molecules in the Self Assembly and Directed Assembly of Organic Monolayers
P. S. Weiss, D. L. Allara, L. A. Bumm, and J. J. Jackiw, Department of Chemistry, The Pennsylvania State University, University Park, PA 16802-6300, USA We manipulate and measure the structures of monolayer films in order to tune their properties. This is accomplished by controlling the defect type and density in the films. We then process the films to insert single molecules, to insert bundles of molecules, or to graft new molecular terraces onto existing domains by using these defects to advantage. The inserted molecules can serve as the anchor points for polymerization; this allows us to choose to produce single polymer dots or isolated polymer brushes. We connect our scanning tunneling microscopy measurements to electron transfer phenomena which are ubiquitous in such areas as biochemistry and electrochemistry by separating the transconductance into components arising from transport through the molecule vs. the tunneling gap outside the film. We show how these components can be measured independently. We prepare films predicted to have many equivalent defect sites so as to provide identical matrix isolation environments for single molecular wire candidates. We also prepare films with well defined interfaces between separated components so that insertion, deposition, or reaction can be directed to these molecularly sharp boundaries.

Total since November 1999

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10 February 2000
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