Frontiers in Inorganic Nanoscience: Catching Up with the Milliron Research Group
Dr. Delia Milliron is passionate about clean energy and the enormous potential of nanoscience to address and solve energy challenges. Milliron, the T. Brockett Hudson Professor in Chemical Engineering at the McKetta Department of Chemical Engineering at UT, has been tracked as a rising star in nanoscience since her early work pioneering electrochromic “smart window” coating technology, solar photovoltaic cells, and self-assembly of nanocrystals.
“If we are going to solve the problems of clean energy and make the massive shift to a clean energy economy, we need to improve technologies for energy generation, storage, and efficient utilization,” Milliron told us on a recent tour of her lab space in the NHB building on the UT campus. And the Milliron Research Group is taking on those challenges on multiple fronts by advancing our knowledge of nanomaterials and how to harness their vast potential.
Milliron was presented with the American Chemical Society Division of Inorganic Chemistry’s 2019 Nanoscience Award for her ongoing innovations in the field at the ACS Fall National Meeting in San Diego, California, on August 26. We recently caught up with her and her lab to talk about the fundamentals and next big thing on the horizon for nanoscience.
On any given day, researchers in the Milliron Lab are hard at work at different laboratory stations, each focused on a different step in the process of studying the nanoscale world. Some are painstakingly synthesizing nanocrystals, developing recipes that take hours to generate less than halfa gram of product. Some are testing a variety of metal oxides and doped, or altered, metal oxides in their nanocrystal form or creating nanocrystal films – a process that seems more art than science. Others measure the properties of the resulting materials with highly specialized equipment. Ultimately and ambitiously, Milliron and her team are building a new, systematic science around the complex interface of materials at the nanoscale.
At the nanoscale, the properties of materials change because there is more surface or interfacial area. Take gold, for example. We understand gold to be a hard, vibrantly shiny, white-to-yellow metal. Reduce and concentrate the metal down to nanoparticles and the changed surface interactions of electrons cause light to be absorbed differently, creating a deep ruby red color. In a test tube, the nanocrystals themselves aren’t visible to the human eye (anything “nano” is 1/1000th the width of a human cell), but the rich ruby color tells us gold nanocrystals are present in the solution.
“When you take a material that has a very high electron density, such as metals, and you take them to the nanocrystal form, it changes their optical behavior completely,” explained Bharat Tandon, a post-doc working with the group this year. “In the last decade or so, we have observed that metal oxides will have altered electrical conductivity and new optical and plasmonic properties as well.”
The work of testing and studying these infinitesimal materials often leads to surprising discoveries. One current research project has revealed unexpected infrared energy spikes around different nanocrystal geometries. Infrared light, with longer wavelengths than the visible light spectrum, is known as low energy so the energy spikes, or hot spots, are intriguing.
“Think of it like a magnifying glass and frying an ant”, offered Stephen Gibbs, a 4th year graduate student who was measuring wavelength outputs in one corner of the lab. “The nanomaterial is not creating energy, but taking it and concentrating it into a small volume, increasing the density. The nanocrystal cube catches light from far away and concentrates it at the corners so you get this antenna effect that we can potentially take advantage of.”
Different nanocrystals form different shapes: spheres, cubes, squishy cubes and bumpy, protruding balls. The “antenna” effect they have for gathering far-field light into the near-field is enhanced in nano-shapes with sharp facets.
By studying shape and size control in nanocrystal creation and by refining the parameters around when these high energy spikes are generated in the typically low-energy infrared spectrum, Milliron and her team of researchers imagine future applications for energy technologies, electronic devices, signal enhancement for imaging, or advanced sensing and diagnostic tools.
“Energy devices are complex and not made of any one super-material,” Milliron explained. “The work of nanoscience over the last few decades is to deliberately reintroduce complexities into materials and combine interesting materials to derive targeted properties, like these infrared hot spots, so we can harness them in advanced technologies and applications.”
Milliron and the group always keep those possible future applications in mind as they engineer unique properties and unlock new uses for them.
“There’s an enormous space for unexplored potential in these designer nanomaterials,” said Milliron.
Image captions Top to Bottom: 1. Dr. Delia Milliron in her lab on the UT Austin campus. 2. Vials with nanocrystal dispersions, each demonstrating a unique optical property. 3. Nanocrystals with infrared “hot spots” around the corners. 4. SEM images of fluorine-doped indium oxide nanocrystals, revealing diverse geometries.
Scene in the Lab
Post-doc researcher Bharat Tandon makes minor adjustments to a fresh batch of nanocrystals – in this step, he is gently heating the solution so any water turns to steam and can be removed by evaporation. On the right, Tandon examines samples of small glass squares coated in a fine swath of plasmonic oxide nanocrystals as he studies how to optimize “smart window” technology.
Vikram Lakhanpal, a 3rd year graduate student, calls himself a “film maker.” That’s because he’s developed a special talent for creating nanocrystal films on the spin coater, a machine that uses rotation and centrifugal force to shake excess liquid from a substrate – in this case, a miniscule silicon wafer – and leave behind a thin, uniform layer of nanocrystal film. Think street fair spin art, but instead of a splatter paint canvas, the result is a tiny, perfectly unvarying square of film.
Graduate student Stephen Gibbs operates a tube furnace, a tool to uniformly heat film-coated silicon chips to further refine the product.Tags: laboratory, milliron, Milliron Research Group, nanocrystals, nanoscience