New storage technology keeps nano surfaces clean

Rice University engineers have developed containers that prevent volatile organic compounds (VOCs) from accumulating on the surface of stored nanomaterials.

The portable and inexpensive storage technology addresses a ubiquitous problem in nanofabrication and materials science laboratories and is described in a paper published July 11. Nano letters.

„VOCs are in the air around us every day,” said study corresponding author Daniel Preston, assistant professor in Rice’s Department of Mechanical Engineering. „They stick to surfaces, forming coatings primarily of carbon. You can’t see these layers with the naked eye, but they form within minutes on any surface exposed to air.”

VOCs are carbon-based molecules that are emitted from many common materials, including liquids, paints, and office and craft supplies. They accumulate in particularly high concentrations indoors, and the thin layers of carbon dioxide they deposit on surfaces can hinder industrial nanofabrication processes, limit the accuracy of microfluidic testing equipment, and confound scientists doing basic research on surfaces.

To solve the problem, Ph.D. student and lead author of the study Jen Liu, along with Preston and others from his lab, developed a new type of storage container that keeps things clean. Tests show that his approach effectively prevents surface contamination for at least six weeks and can even clean VOC-deposited layers from previously contaminated surfaces.

The technology relies on an ultraclean wall in the container. The surface of the inner wall has small bumps and is enhanced in sizes ranging from a few millionths to a few billionths of a meter. Microscopic and nanoscopic defects increase the surface area of ​​the wall and make its metal atoms available to the air for VOCs, which remain inside the containers when they are sealed.

„The system allows the inner container wall to act as a 'sacrificial’ material,” Liu said. „VOCs are drawn to the surface of the container wall, allowing other items stored inside to remain clean.”

The idea of ​​using a large pre-cleaned surface to concentrate pollutants was proposed more than 50 years ago, but was largely overlooked, he said. She and her colleagues advanced the idea with modern methods of surface cleaning and nanotexturing. Through a series of experiments, they showed that their approach did a better job of preventing VOCs from coating the surface of stored materials than other approaches, including sealed Petri dishes and sophisticated vacuum desiccators.

Preston’s team built on its experiments to create a theoretical model that accurately characterized what was happening inside the containers. Preston said the model will allow them to refine their designs and improve system performance in the future.