Research Interests

Helium nanobubbles in metals

Helium can accumulate in metals in radiation environments. It is generally very insoluble, and can precipitate to form nanometer-scale helium bubbles. We are interested in understanding how the bubbles form and evolve, and how they affect macroscopic material properties.

Moving helium bubbles in Pd

Motion of helium nanobubbles in palladium, formed by helium ion implantation, at elevated temperature in a transmission electron microscope.

Hydrogen storage and transport in nanoporous palladium alloys

Palladium is a high-performance storage material for hydrogen isotopes, and enhanced properties are being discovered when the material has nanoscale structure. If all of the hydrogen is within a few nanometers of an interface, we expect charge and discharge rates to be faster and hysteresis to be lower. When tritium is used, it should be easy for decay products to escape without damaging the material. We are making nanoporous palladium powders and using them to test these hypotheses.

More research on hydrogen storage in nanoporous palladium alloys
Transmission electron micrograph of nanoporous rhodium particle

Transmission electron micrograph of nanoporous rhodium particle.

Ion transport and storage in nanoporous metal electrodes

When a nanoporous metal is soaked in a salty liquid, there can be enough surface area to remove bulk amounts of salt from the liquid through electrostatic and chemical adsorption. This can change how quickly ions move through pores. We have found ways to study and manipulate this effect, and are using it to design and build energy storage devices that can charge and discharge at rates near physical limits. In collaboration with Prof. Roger Narayan and his students at the joint biomedical engineering departments of North Carolina State University and the University of North Carolina, we have used these electrodes to controllably store and deliver high-value cargo such as therapeutic agents.

More research on Ion transport and storage in nanoporous metal electrodes
Nanoporous gold opals with porosity on two length scales

Nanoporous gold opals with porosity on two length scales. Cover design by Sandia’s Vicente Garcia. Adapted with permission from ACS Applied Materials and Interfaces. © 2012 American Chemical Society.

Solution-phase deposition of multilayer films

We are expanding the capabilities of electrochemical atomic layer deposition (PDF, 586 KB) and similar techniques to create high-performance materials for hydrogen storage, as well as thermoelectric cooling and power generation.

More research on solution-phase deposition of multilayer films
February 2013 Langmuir journal cover article
Palladium films are grown one atomic layer at a time by alternately depositing copper (which deposits a monolayer onto Pd more easily than it deposits onto other copper atoms) and then soaking in a solution of Pd salt that exchanges for the copper. Adapted with permission from Langmuir. © 2013 American Chemical Society.

Porous materials for diverse energy applications

We have applied our skills developed in the above projects to benefit other energy materials projects at Sandia.

Electron transfer kinetics at electrodes

In graduate school, I used well defined organic monolayers to study how charge crosses the boundary between an ion-conducting phase (like salty water) and an electron- or hole-conducting phase such as a metal. The process involves rearrangement of atoms into a favorable configuration, and then tunneling of a charge carrier through the monolayer. We are able to measure and control both of these steps.

Organic monolayer on gold with tethered redox-active molecule
Organic monolayer on gold with tethered redox-active molecule.

Charge transport through metal-organic-metal structures

Organic material is normally thought of as insulating, but on a scale of nanometers, appreciable amounts of charge can travel through it, and the process is strongly dependent on the structure of the material. The phenomenon is crucial to the use of energy by living things, and is of technological interest for energy harvesting and information processing. With various collaborators, I have made contributions to the box of tools and techniques necessary to take advantage of this.

Gold electrodes bridged by organic molecule with low tunneling barrier
Gold electrodes bridged by organic molecule with low tunneling barrier.

Single- or several-molecule biological binding assays using nanoparticles

In postdoctoral work before Sandia, I synthesized magnetic nanoparticles that are stable in biological environments, and attached DNA segments to them. I also worked to stabilize and functionalize microfabricated spin valve sensors that can detect small numbers of them. At Sandia, in collaboration with Lawrence Berkeley Lab’s Molecular Foundry, we have developed new small molecules for stabilizing nanoparticles in the salty conditions typically found in biology.

More research on single- or several-molecule biological binding assays using nanoparticles
DNA binding event detected by spin valve detector
DNA binding event detected by spin valve detector.

Strong biomimetic shell materials

Sandia’s interest in biofuels led us to study how diatoms (algae) grow the glass capsules that serve as their skeletons. For Sandia’s efforts to make compact bioanalytical instruments, we made tough polymer skeletons that helped with handling of organic capsules used to shuttle materials in microfluidic devices.

Polymer-reinforced lipid vesicles, candidates for cargo containers in microfluidic devices
Polymer-reinforced lipid vesicles, candidates for cargo containers in microfluidic devices.

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