Publications

47 Results
Skip to search filters

Deciphering Adsorption Structure on Insulators at the Atomic Scale

Thurmer, Konrad T.; Feibelman, Peter J.

We applied Scanning Probe Microscopy and Density Functional Theory (DFT) to discover the basics of how adsorbates wet insulating substrates, addressing a key question in geochemistry. To allow experiments on insulating samples we added Atomic Force Microscopy (AFM) capability to our existing UHV Scanning Tunneling Microscope (STM). This was accomplished by integrating and debugging a commercial qPlus AFM upgrade. Examining up-to-40-nm-thick water films grown in vacuum we found that the exact nature of the growth spirals forming around dislocations determines what structure of ice, cubic or hexagonal, is formed at low temperature. DFT revealed that wetting of mica is controlled by how exactly a water layer wraps around (hydrates) the K+ ions that protrude from the mica surface. DFT also sheds light on the experimentally observed extreme sensitivity of the mica surface to preparation conditions: K atoms can easily be rinsed off by water flowing past the mica surface.

More Details

K+-hydration in a low-energy two-dimensional wetting layer on the basal surface of muscovite

Journal of Chemical Physics

Feibelman, Peter J.

Density Functional Theory points to a key role of K+ solvation in the low-energy two-dimensional arrangement of water molecules on the basal surface of muscovite. At a coverage of 9 water molecules per 2 surface potassium ions, there is room to accommodate the ions into wetting layers wherein half of them are hydrated by 3 and the other half by 4 water molecules, with no broken H-bonds, or wherein all are hydrated by 4. Relative to the “fully connected network of H-bonded water molecules” that Odelius et al. found to form “a cage around the potassium ions,” the hydrating arrangements are several tens of meV/H2O better bound. Thus, low-temperature wetting on muscovite is not driven towards “ice-like” hexagonal coordination. Instead, solvation forces dominate.

More Details

Studies of the viscoelastic properties of water confined between surfaces of specified chemical nature

Moore, Nathan W.; Feibelman, Peter J.; Grest, Gary S.

This report summarizes the work completed under the Laboratory Directed Research and Development (LDRD) project 10-0973 of the same title. Understanding the molecular origin of the no-slip boundary condition remains vitally important for understanding molecular transport in biological, environmental and energy-related processes, with broad technological implications. Moreover, the viscoelastic properties of fluids in nanoconfinement or near surfaces are not well-understood. We have critically reviewed progress in this area, evaluated key experimental and theoretical methods, and made unique and important discoveries addressing these and related scientific questions. Thematically, the discoveries include insight into the orientation of water molecules on metal surfaces, the premelting of ice, the nucleation of water and alcohol vapors between surface asperities and the lubricity of these molecules when confined inside nanopores, the influence of water nucleation on adhesion to salts and silicates, and the growth and superplasticity of NaCl nanowires.

More Details

Erratum : two-dimensional Ir cluster-lattice on a graphene moire on Ir(111)

Proposed for publication in Physical Review Letters.

Feibelman, Peter J.

The reported theoretical 'average binding of 0.20 eV per C atom, relative to a free graphene sheet and a clean metal slab' was an artifact of faulty evaluation of the energy of the free graphene sheet. Escaping our notice, the error occurred in the electron-density update algorithm, where two of six nearly degenerate eigenvectors were dropped [1]. With the error corrected, the computed binding energy of the graphene layer to Ir(111), is much smaller, just 0.18 eV per moire unit cell, or 0.9 meV per C atom. With a finer, 3 x 3 sample of the 10 x 10 graphene supercell's surface Brillouin zone, it increases to 2 meV/C atom. The cost of having to stretch the graphene sheet by {approx}0.3 linear percent to make it epitaxial on an underlying 9 x 9 Ir(111) supercell is incorporated in these values.

More Details

Exploiting interfacial water properties for desalination and purification applications

Cygan, Randall T.; Jiang, Ying B.; Alam, Todd M.; Brinker, C.J.; Bunker, B.C.; Leung, Kevin L.; Nenoff, T.M.; Nyman, M.; Ockwig, Nathan O.; Orendorff, Christopher O.; Rempe, Susan R.; Singh, Seema S.; Criscenti, Louise C.; Stevens, Mark J.; Thurmer, Konrad T.; Van Swol, Frank; Varma, Sameer V.; Crozier, Paul C.; Feibelman, Peter J.; Houston, Jack E.; Huber, Dale L.

A molecular-scale interpretation of interfacial processes is often downplayed in the analysis of traditional water treatment methods. However, such an approach is critical for the development of enhanced performance in traditional desalination and water treatments. Water confined between surfaces, within channels, or in pores is ubiquitous in technology and nature. Its physical and chemical properties in such environments are unpredictably different from bulk water. As a result, advances in water desalination and purification methods may be accomplished through an improved analysis of water behavior in these challenging environments using state-of-the-art microscopy, spectroscopy, experimental, and computational methods.

More Details

The effect of embedded Pb on Cu diffusion on Pb/Cu(111) surface alloys

Proposed for publication in Surface Science.

Dyck, Meredith L.; Bartelt, Norman C.; Feibelman, Peter J.; Swartzentruber, Brian S.; Kellogg, Gary L.

We have used scanning tunneling microscopy and low-energy electron microscopy to measure the thermal decay of two-dimensional Cu, Pb-overlayer, and Pb-Cu alloy islands on Pb-Cu(1 1 1) surface alloys. Decay rates covering 6-7 orders of magnitude are accessible by applying the two techniques to the same system. We find that Cu adatom diffusion across the surface alloy is rate-limiting for the decay of both Pb and Pb-Cu islands on the surface alloy and that this rate decreases monotonically with increasing Pb concentration in the alloy. The decrease is attributed to repulsive interactions between Cu adatoms and embedded Pb atoms in the surface alloy. The measured temperature dependences of island decay rates are consistent with first-principles calculations of the Cu binding and diffusion energies related to this 'site-blocking' effect.

More Details

Effect of high-viscosity interphases on drainage between hydrophilic surfaces

Feibelman, Peter J.

Drainage of water from the region between an advancing probe tip and a flat sample is reconsidered under the assumption that the tip and sample surfaces are both coated by a thin water 'interphase' (of width {approx}a few nm) whose viscosity is much higher than the bulk liquid's. A formula derived by solving the Navier-Stokes equations allows one to extract an interphase viscosity of {approx}59 KPa-sec (or {approx}6.6x10{sup 7} times the viscosity of bulk water at 25C) from Interfacial Force Microscope measurements with both tip and sample functionalized hydrophilic by OH-terminated tri(ethylene glycol) undecylthiol, self-assembled monolayers.

More Details

Relationship between domain boundary free energy and the temperature dependence of stress-domain patterns of Pb on Cu(111)

Proposed for publication in Physical Review B.

Bartelt, Norman C.; Feibelman, Peter J.; Leonard, Francois L.; Kellogg, Gary L.

Pb deposition on Cu(111) causes the surface to self-assemble into periodically arranged domains of a Pb-rich phase and a Pb-poor phase. Using low-energy electron microscopy (LEEM) we provide evidence that the observed temperature-dependent periodicity of these self-assembled domain patterns is the result of changing domain-boundary free energy. We determine the free energy of boundaries at different temperatures from a capillary wave analysis of the thermal fluctuations of the boundaries and find that it varies from 22 meV/nm at 600 K to 8 meV/nm at 650 K. Combining this result with previous measurements of the surface stress difference between the two phases we find that the theory of surface-stress-induced domain formation can quantitatively account for the observed periodicities.

More Details

Oscillatory interaction between O impurities and Al adatoms on Al(111) and its effect on nucleation and growth

Proposed for publication in Physical Review B.

Feibelman, Peter J.; Feibelman, Peter J.

We present a combined experimental and theoretical study of submonolayer growth in the presence of predeposited immobile impurities. Scanning tunneling microscopy measurements of Al/Al(1 1 1) epitaxy in the presence of oxygen adsorbates show that immobile O impurities influence all aspects of the early stages of homoepitaxial growth on Al(1 1 1). Possible scenarios for modified growth are investigated using kinetic Monte Carlo simulations. Dependences of island density on temperature, impurity concentration and strength and type of adatom-impurity interaction are compared. The comparison shows that the morphology of the growing Al film cannot result from only one interaction type: attractive or repulsive. An oscillatory interaction, suggested by ab initio calculations, is proposed to explain the behavior of the system.

More Details

Effect of high-viscosity interphases on drainage between hydrophilic surfaces

Proposed for publication in Langmuir Journal.

Feibelman, Peter J.; Feibelman, Peter J.

Drainage of water from the region between an advancing probe tip and a flat sample is reconsidered under the assumption that the tip and sample surfaces are both coated by a thin water 'interphase' (of width {approx} a few nm) whose viscosity is much higher than the bulk liquid's. A formula derived by solving the Navier-Stokes equations allows one to extract an interphase viscosity of {approx}59 KPa-sec (or {approx}6.6 x 10{sup 7} times the viscosity of bulk water at 25C) from Interfacial Force Microscope measurements with both tip and sample functionalized hydrophilic by OH-terminated tri(ethylene glycol) undecylthiol, self-assambled monolayers.

More Details

Electric field effects on surface dynamics: Si ad-dimer diffusion and rotation on Si(001)

Surface Science

Mattsson, Thomas M.; Mattsson, Thomas M.; Swartzentruber, Brian S.; Stumpf, Roland R.; Feibelman, Peter J.

Density functional calculations show that the electric field effect on Si ad-dimer diffusion on Si(0 0 1) is largely a reflection of the position dependence of the ad-dimer’s dipole moment. We can use surface diffusion barriers’ dependence on perpendicular electric fields to discriminate between diffusion mechanisms. Since the previously accepted mechanism for ad-dimer diffusion on Si(0 0 1) has the opposite field dependence to what is observed, it cannot be the one that dominates mass-transport. Here, we identify an alternate process, with a similar barrier at zero electric field and field dependence in agreement with measurements. For rotation, calculations to date show linear field dependence, in contrast to experiments.

More Details

Ab-Initio Step- and Kink-Formation Energies on Pb(111)

Physical Review B

Feibelman, Peter J.

Ab-initio formation energies for (100)- and (111)-microfacet steps on Pb(111) are in satisfactory agreement with measured values, given that these values are known only as well as the Pb(111) surface energy; the calculated step-energy ratio, 1.29, is within {approximately}8% of experiment. In contrast, calculated kink-formation energies, 41 and 60 meV for the two step types, are 40--50% below published experimental values derived from STM images. The discrepancy results from interpreting the images with a step-stiffness vs. kink-energy relation appropriate to (100) but not (111) surfaces. Good agreement is found when the step-stiffness data are reinterpreted, taking proper account of the trigonal symmetry of Pb(111).

More Details

Thermal Fluctuations in the Structure of Naturally Chiral Pt Surfaces

Topics in Catalysis

Feibelman, Peter J.; Feibelman, Peter J.

The intrinsic chirality of metal surfaces with kinked steps (e.g. Pt(643)) endows them with enantiospecific adsorption properties (D. S. Shell, Langmuir, 14, 1998, 862). To understand these properties quantitatively the impact of thermally-driven step wandering must be assessed. The authors derive a lattice-gas model of step motion on Pt(111) surfaces using diffusion barriers from Density Functional Theory. This model is used to examine thermal fluctuations of straight and kinked steps.

More Details

Formation and diffusion of S-decorated Cu clusters on Cu(111)

Physical Review Letters

Feibelman, Peter J.

S-decorated Cu trimers are investigated as likely agents of S-enhanced Cu transport between clusters on Cu(111). It is shown what Cu3S3 clusters form more readily on Cu(111) than a Cu adatom and what diffuse easily to determine how S acts. Using a systematic ab initio search, results show that the smallest of such cluster is ad-Cu3S3. approximately 0.5 ev formation energy, lower than that of a Cu adatom, and ≤0.35 eV diffusion barrier, corresponding to tight internal bonding, are obtained.

More Details

The CO/Pt(111) Puzzle

Journal of Physical Chemistry

Feibelman, Peter J.

Notwithstanding half a dozen theoretical publications, well-converged density-functional calculations, whether based on a local or generalized-gradient exchange-correlation potential, whether all-electron or employing pseudopotentials underestimate CO's preference for low-coordination binding sites on Pt(111) and vicinals to it. For example, they imply that CO should prefer hollow- to atop-site adsorption on Pt(111), in apparent contradiction to a host of low temperature experimental studies.

More Details

Step- vs. kink-formation energies on Pt(111)

Surface Science Letters

Feibelman, Peter J.

Ab-initio kink-formation energies are about 0.25 and 0.18 eV on the (100)- and (111)-microfacet steps of Pt(111), while the sum of the step-formation energies is 0.75 eV/atom. These results imply a specific ratio of formation energies for the two step types, namely 1.14, in excellent agreement with experiment. If kink-formation costs the same energy on the two step types, an inference recently drawn from scanning probe observations of step wandering, this ratio ought to be 1.

More Details

Surfactant-modified diffusion on transition-metal surfaces (reprinted with the addition of the appendices)

Feibelman, Peter J.; Kellogg, Gary L.

Wanting to convert surface impurities from a nuisance to a systematically applicable nano-fabrication tool, the authors have sought to understand how such impurities affect self-diffusion on transition-metal surfaces. Their field-ion microscope experiments reveal that in the presence of surface hydrogen, self-diffusion on Rh(100) is promoted, while on Pt(100), not only is it inhibited, but its mechanism changes. First-principles calculations aimed at learning how oxygen fosters perfect layerwise growth on a growing Pt(111) crystal contradict the idea in the literature that it does so by directly promoting transport over Pt island boundaries. The discovery that its real effect is to burn off adventitious adsorbed carbon monoxide demonstrates the predictive value of state-of-the-art calculation methods.

More Details
47 Results
47 Results