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 transfered 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 completed my PhD in 2015 and continued to work as a research associate until 2017. My generals interests include friction, wear, polymer chemistry, molecular electronics, and surface interactions. I am now the director and founder of Nanolayers Research Computing, a materials design company focused on developing novel catalysts and lubricating oil additives.
My current research at UCL is primarily focused on modelling amorphous silicon dioxide (a-SiO2) as a prototypical disordered wide band gap oxide which can be used in novel resistive random-access memory (RRAM) devices. So far, point defects in these materials have both been linked to detrimental effects and implicated in critical processes including the formation of conductive filaments.
Defect Generation Mechanisms: An Electron Injection Facilitated Process
Electrically biasing thin films of amorphous silicon oxide results in surprisingly large structural changes which can be observed as density variations, oxygen movement, and the emission of superoxide ions. These structural changes can be exploited to switch between high and low resistance states by incorporating the amorphous oxide layer in a metal-insulator-metal stack as shown on the left and simply electrically biasing the material. Such properties are useful for a wide range of technologies including resistance switching memory devices.
We used density functional theory (DFT) calculations to examine the formation of point defects under bias application. Our results indicated that many intrinsic sites in a-SiO2 are capable of trapping up to two electrons. When the second electron localizes at these sites, it greatly weakens one of the corresponding SiO bonds, resulting in a mechanism that creates a neutral O vacancy and interstitial O(2-) ion which can migrate rapidly through the oxide layer.
I am also interested in 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 and 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.
Single Molecules: Imaging, Adsorption, and Diffusion of Organic Molecules
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
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. We can then work towards creating a database of results which can be combined with machine learning techniques to identify important structure-property relationships. This allows us to tailor our functional molecules for specific industrial applications.
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.
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