A5010279761- Force Microscopy Techniques and Applications
- Metal and Thin Film Mechanics
- Molecular Junctions and Nanostructures
- Lubricants and Their Additives
- Adhesion, Friction, and Surface Interactions
- High Entropy Alloys Studies
- Microstructure and mechanical properties
- Organic Electronics and Photovoltaics
- Aluminum Alloys Composites Properties
- Tribology and Wear Analysis
- nanoparticles nucleation surface interactions
- Additive Manufacturing Materials and Processes
- High-Temperature Coating Behaviors
- Conducting polymers and applications
- Metallic Glasses and Amorphous Alloys
- Metal Alloys Wear and Properties
- Diamond and Carbon-based Materials Research
- Additive Manufacturing and 3D Printing Technologies
- Advanced materials and composites
- Advanced Materials Characterization Techniques
- Intermetallics and Advanced Alloy Properties
- Advanced ceramic materials synthesis
- MXene and MAX Phase Materials
- Advanced Surface Polishing Techniques
- Mechanical stress and fatigue analysis
Sandia National Laboratories
2016-2025
Sandia National Laboratories California
2010-2024
Materials Science & Engineering
2011
Office of Scientific and Technical Information
2005-2011
National Technical Information Service
2011
University of New Mexico
2011
Computational Physics (United States)
2011
Integrated Nano-Technologies (United States)
2009
Center for Integrated Nanotechnologies
2009
Materials Research Group (United States)
2008
As the size of electronic and mechanical devices shrinks to nanometre regime, performance begins be dominated by surface forces. For example, friction, wear adhesion are known central challenges in design reliable micro- nano-electromechanical systems (MEMS/NEMS). Because complexity physical chemical mechanisms underlying atomic-level tribology, it is still not possible accurately reliably predict response when two surfaces come into contact at nanoscale. Fundamental scientific studies means...
We show that one-electron band theory fails to describe optical absorption in PPV and the spectrum can be described only within a Coulomb-correlated model. The lowest state is an exciton, whose binding energy estimated theoretically 0.90\ifmmode\pm\else\textpm\fi{}0.15 eV. Measurements of photoconductivity quantum efficiency poly[2-methoxy,5-(${2}^{\mathcal{'}}$-ethyl-hexyloxy)-1,4 phenylenevinylene] reveal good agreement with theoretical value.
Recent work suggests that thermally stable nanocrystallinity in metals is achievable several binary alloys by modifying grain boundary energies via solute segregation. The remarkable thermal stability of these has been demonstrated recent reports, with many exhibiting negligible growth during prolonged exposure to near-melting temperatures. Pt-Au, a proposed alloy consisting two noble metals, shown exhibit extraordinary resistance wear. Ultralow wear rates, less than monolayer material...
This work demonstrates the role of microstructure in friction and oxidation behavior lamellar solid lubricant molybdenum disulfide (MoS2). We report on systematic investigations for two MoS2 films with distinctively different microstructures—amorphous planar/highly-ordered—before after exposure to atomic oxygen (AO) high-temperature (250 °C) molecular oxygen. A combination experimental tribology, dynamics simulations, X-ray photoelectron spectroscopy (XPS), high-sensitivity low-energy ion...
Diamond-like carbon (DLC) films were tribochemically formed from ambient hydrocarbons on the surface of a highly stable nanocrystalline Pt-Au alloy. A sliding contact between an alumina sphere and coated steel exhibited friction coefficients as low μ = 0.01 after dry in environments containing trace (ppb) organics. Ex situ analysis indicated that change coefficient was due to formation amorphous films, Raman spectroscopy elastic recoil showed these consist sp2/sp3 with much 20% hydrogen....
Exhaled breath contains trace levels of volatile organic compounds (VOCs) that can reveal information about metabolic processes or pathogens in the body. These molecules be used for medical diagnosis, but capturing and accurately measuring them is a significant challenge chemical separations. A highly selective nanoporous sorbent to capture target from sample preconcentrate use detector. In this work, we present combined predictive modeling–experimental validation study which five Zr-based...
Within a model Hamiltonian with variable on-site and long-range Coulomb interactions between the \ensuremath{\pi} electrons for poly(para-phenylenevinylene), we conduct thorough search in parameter space to determine magnitudes of effective interaction parameters necessary fit all four absorption bands that are seen experimental spectra this material. We find best agreement calculated slightly smaller than standard Pariser-Parr-Pople parameters. For these values parameters, primary...
We investigate theoretically and experimentally the effects of (2,5) chemical substitution on optical absorption in phenylene-based conjugated polymers. Theoretically, destroys both charge-conjugation symmetry spatial that characterize unsubstituted materials. Within Coulomb-correlated theoretical models, effect broken alone underlying electronic structure spectrum is rather weak. When are taken into account, a strong polyphenylene derivatives found. In spite symmetries structure,...
We have developed force fields for the calculation of adsorption NH3, CO2, and H2O on zeolite 4A by performing Gibbs ensemble Monte Carlo simulations to fit experimental isotherms at 298 K. The calculated NH3 CO2 are in excellent agreement with data over a wide range temperatures several orders magnitude pressure. using two different models found that saturates even pressures as low 0.01 kPa studied. studied geometry sites their dependence loading. At pressures, molecules adsorb longitudinal...
We present the results of massively parallel molecular dynamics simulations aimed at understanding nanotribological properties alkylsilane self-assembled monolayers (SAMs) on amorphous silica. In contrast to studies with opposing flat plates, as found in bulk simulation literature, we use a model system realistic AFM tip (radius curvature ranging from 3 30 nm) contact SAM-coated silica substrate. compare differences response between systems which chains are fully physisorbed, chemisorbed,...
The adhesion and friction between two ordered self-assembled monolayers of alkylsilane chains on a silicon dioxide surface are studied using molecular dynamics simulations. These simulations focus the alkylsilanes, which coating commonly used in microelectromechanical systems. We have investigated chain lengths 6−18 carbon atoms for systems with 100−1600 molecules each surface. force at given tail atom separation is found to increase monotonically decreasing length. For length were performed...
We apply density functional theory (DFT) and the DFT+U technique to study adsorption of transition metal porphine molecules on atomistically flat Au(111) surfaces. DFT calculations using Perdew-Burke-Ernzerhof exchange correlation correctly predict palladium (PdP) low-spin ground state. PdP is found adsorb preferentially gold in a geometry, not an edgewise qualitative agreement with experiments substituted porphyrins. It exhibits no covalent bonding Au(111), binding energy small fraction...
We present a theoretical model that predicts the peak strength of polycrystalline metals based on activation energy (or stress) required to cause deformation via amorphization. Building extensive earlier work, this is purely materials properties, requires no adjustable parameters, and shown accurately predict four exemplar (fcc, bcc, hcp, an alloy). This framework reveals new routes for design more complex high-strength systems, such as compositionally alloys, multiphase nonmetals, composite...
Heterojunctions of semiconductors and metals are the fundamental building blocks modern electronics. Coherent heterostructures between dissimilar materials can be achieved by composition, doping, or heteroepitaxy chemically different elements. Here, we report formation coherent single-layer 1H-1T MoS2 mechanical exfoliation on Au(111), which homogeneous with matched lattices but show electronically distinct semiconducting (1H phase) metallic (1T character, these heterojunctions attributed to...
Compositionally complex alloys, also known as high entropy or multiple principle component can exhibit greatly improved mechanical properties. Researchers often ascribe this to sluggish diffusion that is thought result from having constituents. Here, the authors present a systematic investigation of in multielement alloys with molecular dynamics simulations. Only small minority studied show diffusion, whereas large majority faster even vigorous. The find diffusivities do not correlate number...
Snapshot of a simulation showing water molecules adsorbing on sheet molybdenum disulfide (MoS 2 ).
The adhesion and friction between pairs of ordered disordered self-assembled monolayers on SiO2 are studied using molecular dynamics. disorder is introduced by randomly removing chains from a well crystalline substrate attaching to an amorphous substrate. force at given separation increases monotonically with chain length full coverage for fixed length. Friction simulations performed shear velocities 0.02-2 m/s constant applied pressures 200 600 MPa. Stick-slip motion observed but disappears...
To prevent the flocculation and phase separation of nanoparticles in solution, are often functionalized with short chain surfactants. Here we present fully-atomistic molecular dynamics simulations which characterize how these functional coatings affect interactions between surrounding solvent. For 5 nm diameter silica coated poly(ethylene oxide) (PEO) oligomers water, determined hydrodynamic drag on two approaching moving through solvent a single nanoparticle as it approaches planar surface....