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Condensed Matter & Materials Physics

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David Gao

About me

I obtained my Bachelor's degree in Chemical Biology at the University of California at Berkeley in 2007. Immediately following graduation I began working in the fields of analytical chemistry and crude oil processing as part of the Process Technology Unit of the Chevron Energy Technology Company. In 2008 I transferred to the Components group of Chevron Oronite LLC where I worked to design novel dispersants, friction modifiers, and wear inhibitors. During my time researching lubricating oil additives, I began to explore using computational methods to investigate and screen new compounds and mechanisms. In 2011, I made the decision to move from California to London and join the Condensed Matter and Materials Physics group here at UCL. I am currently working as a consultant for Chevron Oronite, and my interests include friction, wear, polymer chemistry, molecular electronics, and surface interactions in general.

Research

My research is primarily focused on modelling the interaction between atoms and molecules and surfaces. I am interested in studying energy dissipation, formation of various structures, diffusion, and other properties of molecules adsorbed onto various surfaces. In order to understand these interactions I employ a range of theoretical and computational techniques to study both model and experimental systems. I begin by studying atoms, followed by molecules on surfaces, and finally examine layer and structure formation. Each step along the way provides insight into interactions at surfaces and interfaces as well as the mechanisms of friction and wear.

Atoms: Transient Mobility Mechanisms: Pd on MgO

Journal of Physical Chemistry

The adsorption of atoms, molecules, and clusters on surfaces and the processes that follow play an important role in many fields. Atoms may be able to diffuse to step edges, form islands, or travel to vacancies on the surface and influence the final structure of coatings and other deposited features. One interesting aspect of this event is the translation of incident and adsorption energy into "transient mobility".

Molecular dynamics simulations of a single Pd atom adsorbing and diffusing (shown on the right) on MgO can be studied as a model system. I am investigating the mechanisms of energy dissipation and adsorption involved in these processes in order to understand the physics of events such as scattering, surface diffusion, atomic friction, and make growth predictions.

Single Molecules: Imaging, Adsorption, and Diffusion of Organic Molecules

ACS NanoJournal of Physical Chemistry

Developments in imaging techniques including STM (Scanning Tunneling Microscope) and AFM (Atomic Force Microscope) have allowed experimentalists to image surfaces at the atomic level. With these techniques atoms and molecules adsorbed onto these surfaces can also be imaged and manipulated. Small molecules such as CO can be chemically resolved as shown to the left.

The rates at which molecules diffuse, the mechanisms by which dimers and other surface features are formed, and the differences between interactions with various surfaces can all be used in controlling surface features. Theory and computation can often aid in proposing explanations for interesting or unexpected results.

In order to study the rate at which diffusion and other similar processes occur various forms of accelerated molecular dynamics and Kinetic Monte Carlo can be used to lengthen the time scale of the simulations.

Layer Structures: Competing Interactions on the Surface

Advanced Materials Interfaces

The careful design, synthesis, and deposition of functionalized organic molecules allows us to fine tune the molecule-molecule and molecule-surface interactions within a surface that contribute to film structure.

Modular organic molecules can be engineered to create robust, self-assembly, self-healing, porous, monolayer structures as shown on the left. These materials can be used as friction modifiers, wear inhibitors, photovoltaics, catalysts, and coatings.

I am currently working on increasing the size and time scales of my simulations in order to study dynamic processes such as film growth and self healing.

The Macroscopic Level: Friction, Energy Dissipation, and Wear

SAE International

The focus of my previous work at Chevron Oronite involved the development of lubricating oil additives. Friction modifiers for example can help reduce fuel consumption and emissions. Each part of an engine will experience different operating conditions that coorespond to a various friction regimes. Inorganic friction modifiers have been shown to be effective in regimes where a large percentage of power is lost due to heat dissipation. One major concern in this area is that current inorganic friction modifiers use toxic starting materials.

The inorganic friction modifier we developed for this application works via the delivery of Molybdenum disulfide layers shown on the left to the surface. This material is then able to reduce friction as the surfaces slide against each other in a mechanism that can be related to sliding a deck of cards across a table illustrated below. In addition to using novel chemistry that allows replacement of toxic starting materials with elemental sulfur, this new compound has been shown to reduce friction in various bench and engine tests. For more information please see publications below. I received my first introduction into simulation here by employing various computational methods in order to screen candidates for synthesis and bench testing.

Publications

  • Journal Publications
  • J. N. Tracey, F. Federici Canova, D. Z. Gao, P. Spijker, A. S. Foster, "Flexible and Modular Virtual Scanning Probe Microscope", Computer Physics Communications, 2015
  • D. Z. Gao, F. Federici Canova, M. B. Watkins, A. L. Shluger, "Efficient Parameterization of Complex Molecule-Surface Force Fields", Journal of Computational Chemistry, 2015
  • A. Amrous, F. Bocquet, L. Nony, F. Para, C. Loppacher, S. Lamare, F. Palmino, F. Cherioux, D. Z. Gao, F. Federici Canova, M. B. Watkins, A. L. Shluger, "Molecular Design and Control Over the Morphology of Self-Assembled Films on Ionic Substrates", Advanced Materials Interfaces, 2014
  • D. Z. Gao, J. Grenz, M. B. Watkins, F. Federici Canova, A. Schwarz, R. Wiesendanger, A. Shluger, "Using Metallic Noncontact Atomic Force Microscope Tips for Imaging Insulators and Polar Molecules: Tip Characterization and Imaging Mechanisms", ACS Nano,2014
  • A. Schwarz, D. Z. Gao, K. Lammle, J. Grenz, M. B. Watkins, A. L. Shluger, R. Wiesendanger, "Determining Adsorption Geometry, Bonding, and Translational Pathways of a Metal-Organic Complex on an Oxide Surface: Co-Salen on NiO(001)", Journal of Physical Chemistry C, 2013117, 1105-1112
  • D. Z. Gao, M. B. Watkins, A. L. Shluger, "Transient Mobility Mechanisms of Deposited Metal Atoms on Insulating Surfaces: Pd on MgO (100)", Journal of Physical Chemistry C, 2012116, 14471-14479.
  • G. Bhalla, M. H. Tsang, D. Gao, Q. Chen. W. Ruhe, N. Ushioda, "Frictional Properties of Molybdenum-Based Lubricating Oil Additives Using Green Chemistry", SAE International Journal of Fuels and Lubricants 20125, 496-503.
  • Book Chapters
  • D. Z. Gao, A. Schwarz, A. L. Shluger, Imaging Molecules on Bulk Insulators Using Metallic Tips, in S. Morita (ed) Noncontact Atomic Force Microscopy Volume 3 (Ch. 17). New York, NY: Springer.
  • Oral Presentations
  • D. Z. Gao, M. B. Watkins, A. L. Shluger, QM/MM Applications and Tutorial, CP2K User Group Meeting London (2015)
  • D. Z. Gao, M. B. Watkins, F. Federici Canova, A. L. Shluger, Multi-Scale Studies of Organic Molecules on Insulating Surfaces, Helmholtz-Zentrum Institute Invited Seminar (2014)
  • D. Z. Gao, M. B. Watkins, A. L. Shluger, Theoretical Studies of Organic Molecules: Designing Novel Lubricants, TYC Postgraduate Student Day (2014)
  • D. Z. Gao, M. B. Watkins, A. L. Shluger, A Point Dipole Model for Metallic Tips, 21st International Colloquium on Scanning Probe Microscopy (2013)
  • D. Z. Gao, M. B. Watkins, A. L. Shluger, Theoretical Studies of Film Formation of Organic Molecules on Bulk Insulators, Chevron Oronite Invited Seminar and Workshop (2013)
  • D. Z. Gao, M. B. Watkins, A. L. Shluger, A Point Dipole Model for Metallic AFM Tips, International Conference on non-contact Atomic Force Microscopy (2013)
  • D. Z. Gao, M. B. Watkins, A. L. Shluger, Adsorption, Mobility, and Growth of Organic Molecules on Insulators, WPI-AIMR Tohoku University Seminar (2013)
  • D. Z. Gao, M. B. Watkins, A. L. Shluger, Adsorption, Growth, Tip-Induced Motion, and Imaging Mechanisms of Individual Molecules on Bulk Insulators, University of Hamburg Invited Seminar (2013)
  • D. Z. Gao, M. B. Watkins, A. L. Shluger, Adsorption, Mobility, and Growth of Co-Salen on Bulk Insulators, ARTIST Winter Workshop (2013)
  • D. Z. Gao, M. B. Watkins, A. L. Shluger, Adsorption Geometry and Mobility of Co-Salen molecules on NiO (100), International Conference on Nanoscience + Technology (2012)
  • D. Z. Gao, M. B. Watkins, A. L. Shluger, Transient Mobility Mechanisms on Oxide Surfaces, International Conference on Nanoscience + Technology (2012)
  • D. Z. Gao, M. B. Watkins, A. L. Shluger, Theoretical Treatment of Metal-Organic Complexes on Oxide Surfaces: Co-Salen on NiO (100), Thomas Young Centre Lunchtime Get-Together (2012)
  • D. Z. Gao, M. B. Watkins, A. L. Shluger, Modelling Metal-Organic Complexes on Oxide Surfaces, Chevron Oronite Invited Seminar and Workshop (2012)
  • D. Z. Gao, M. B. Watkins, A. L. Shluger, Pd on MgO (001): Transient Mobility Mechanisms on Oxide Surfaces, MRS Spring Meeting (2012)
  • M. Watkins, D. Gao, A. Shluger, Adsorption of magnetic molecules on insulating surfaces, Materials Chemistry Consortium Meeting (2012)
  • D. Z. Gao, M. B. Watkins, A. L. Shluger, Transient Mobility Mechanisms : Pd on MgO, University of Hamburg Invited Seminar (2011)
  • D. Z. Gao, M. B. Watkins, A. L. Shluger, Adsorption and Friction Mechanisms, Chevron Oronite Invited Seminar (2011)
  • Poster Presentations
  • D. Z. Gao, M. B. Watkins, F. Federici Canova, A. L. Shluger, Multi-Scale Studies of Organic Molecules on Bulk Insulators, Towards Reality in Nanoscale Materials VIII (2014)
  • D. Z. Gao, M. B. Watkins, A. L. Shluger, Theoretical Treatment of Growth and Nucleation, 21st International Colloquium on Scanning Probe Microscopy (2013)
  • D. Z. Gao, M. B. Watkins, A. L. Shluger, Multiscale Modeling of NC-AFM experiments, CECAM/Psi-K: Multi-scale Modeling from First Principles (2013)
  • D. Z. Gao, M. B. Watkins, A. L. Shluger, Theoretical Treatment of NC-AFM experiments: Complex Materials, Large Organic Molecules, and Dynamic Processes, International Conference on non-contact Atomic Force Microscopy (2013)
  • D. Z. Gao, M. B. Watkins, A. L. Shluger, Antoine Hinaut, David Martrou, Adeline Pujol, Andre Gourdon, Vacancy Mediated Adsorption: Invisible Agents on Insulating Surfaces, 4th International Workshop on Advanced AFM Techniques(2013)
  • D. Z. Gao, M. B. Watkins, A. L. Shluger, Theoretical Treatment of Metal-Organic Complexes on Bulk Insulators, Functional Molecules on Surfaces: New Building Blocks for Nano-spintronics (2012)
  • D. Z. Gao, M. B. Watkins, A. L. Shluger, Observing Atomic Mobility on the Surface: Pd-MgO, International Conference on non-contact Atomic Force Microscopy (2012)
  • D. Z. Gao, M. B. Watkins, A. L. Shluger, Theoretical Treatment of NC-AFM Experiments : Co-salen NiO(100), International Conference on non-contact Atomic Force Microscopy (2012)
  • D. Z. Gao, M. B. Watkins, A. L. Shluger, Adsorption Geometry and Mobility of Co-Salen Molecules on NiO (100), RSC Graduate Student Meeting (2012)
  • D. Z. Gao, M. B. Watkins, A. L. Shluger, Transient Mobility Mechanisms : Pd on MgO, 8th International Workshop on Oxide Surfaces (2012)
  • D. Gao, M. H. Tsang, W. Ruhe Jr., Q. Chen, G. Bhalla, The Effect of Molecular Weight on the Frictional Properties of Molybdenum Based Lubricating Oil Additives Containing Elemental Sulfur, American Chemical Society National Meeting (2010)
  • M. H. Tsang, D. Gao, W. Ruhe Jr., Q. Chen, G. Bhalla, Synthesis of a Molybdenum Oxysulfide Complex Derived from Elemental Sulfur as a Lubricating Oil Additive to Improve Fuel Economy and Reduce Emissions, American Chemical Society National Meeting (2010)