Creating New Opportunities From Nanoscale Materials

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Little Drinking Straws

“Sometimes you know more or less what you are going to see during a growth experiment, but very often there’s something that you don’t expect,” Ross says. She shows an example of zinc oxide nanowires that were grown using a germanium catalyst. Some of the long crystals have a hole through their centers, creating structures which are like little drinking straws, circular outside but with a hexagonally shaped interior. “This is a single crystal of zinc oxide, and the interesting question for us is why do the experimental conditions create these facets inside, while the outside is smooth?” Ross asks. “Metal oxide nanostructures have so many different applications, and each new structure can show different properties. In particular, by going to the nanoscale you get access to a diverse set of properties.” 

“Ultimately, we’d like to develop techniques for growing well-defined structures out of metal oxides, especially if we can control the composition at each location on the structure,” Ross says. A key to this approach is self-assembly, where the material builds itself into the structure you want without having to individually tweak each component. “Self-assembly works very well for certain materials but the problem is that there’s always some uncertainty, some randomness or fluctuations. There’s poor control over the exact structures that you get. So the idea is to try to understand self-assembly well enough to be able to control it and get the properties that you want,” Ross says.

“We have to understand how the atoms end up where they are, then use that self-assembly ability of atoms to make a structure we want. The way to understand how things self-assemble is to watch them do it, and that requires movies with high spatial resolution and good time resolution,” Ross explains. Electron microscopy can be used to acquire structural and compositional information and can even measure strain fields or electric and magnetic fields.

“Imagine recording all of these things, but in a movie where you are also controlling how materials grow within the microscope. Once you have made a movie of something happening, you analyze all the steps of the growth process and use that to understand which physical principles were the key ones that determined how the structure nucleated and evolved and ended up the way it does.” 

Future Directions

Ross hopes to bring in a unique high-resolution, high vacuum TEM with capabilities to image materials growth and other dynamic processes. She intends to develop new capabilities for both water-based and gas-based environments. This custom microscope is still in the planning stages but will be situated in one of the rooms in the Imaging Suite in MIT.nano.

“Professor Ross is a pioneer in this field,” Osherov says. “The majority of TEM studies to-date have been static, rather than dynamic. With static measurements you are observing a sample at one particular snapshot in time, so you don’t gain any information about how it was formed. Using dynamic measurements, you can look at the atoms hopping from state to state until they find the final position. The ability to observe self-assembling processes and growth in real time provides valuable mechanistic insights. We’re looking forward to bringing these advanced capabilities to MIT.nano.” she says. 

“Once a certain technique is disseminated to the public, it brings attention,” Osherov says. “When results are published, researchers expand their vision of experimental design based on available state-of-the-art capabilities, leading to many new experiments that will be focused on dynamic applications.”

Rooms in MIT.nano feature the quietest space on the MIT campus, designed to reduce vibrations and electromagnetic interference to as low a level as possible. “There is space available for Professor Ross to continue her research and to develop it further,” Osherov says. “The ability of in situ monitoring the formation of matter and interfaces will find applications in multiple fields across campus, and lead to a further push of the conventional electron microscopy limits.”



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