Symposium X—MRS/The Kavli Foundation Frontiers of Materials

Deji Akinwande, University of Texas at Austin

Unconventional Applications of Atomic Materials from Nonvolatile Electronics to Wearable Health and Ion Transport

Written by Sophia Chen

So-called two-dimensional (2D) materials, which consist of a single layer of atoms, offer many desirable properties for use in electronics, according to Deji Akinwande of the University of Texas at Austin. Akinwande made the case for this emerging category of materials during his Symposium X talk on Monday, December 2, titled “Unconventional Applications of Atomic Materials from Nonvolatile Electronics to Wearable Health and Ion Transport.” He presented research on the use of these materials in applications ranging from nanoelectronics to bioelectronics to energy.

To give the audience an intuitive conception of these materials, Akinwande likened 2D materials to a single sheet of paper in a stack. “In the x-y plane, they're very strongly bonded…But out of the plane, they're very weak,” he explained. These materials, removed from a stack one sheet at a time, have already proven useful in commercial applications. Examples of 2D materials include graphene, found in pencil lead, hexagonal boron nitride, found in makeup, and molybdenum disulfide, which is used as a dry lubricant in vehicles.

Akinwande first discussed the application of 2D molybdenum disulfide (MoS₂) for building a new type of computer known as a neuromorphic computer. The architecture of a neuromorphic computer emulates the human brain, where information is encoded and transported by “neurons” that connect to each other via “synapses” in imitation of human brain biology. This is in contrast to typical computers used today, which store its memory separately from where it computes, known as von Neumann architecture. Proponents of neuromorphic computers say that these machines offer higher energy efficiency than conventional computers, which could help solve the growing energy footprint of information technology.

Akinwande’s research involved developing the MoS₂ as a material for a memristor, which is a component of a neuromorphic computer for storing and computing data. The memristor cycles between two different resistances like a fast switch. As a thin crystalline material, MoS₂ tends to have fewer defects than metal oxides, which are the currently most popular material for memristors. Akinwande also said that the engineering of MoS₂ memristors has increased the number of times they can cycle from hundreds to millions. (See also: https://www.nature.com/articles/s41565-020-00789-w and https://onlinelibrary.wiley.com/doi/full/10.1002/advs.202406703 )

He also discussed projects involving using 2D materials for electrodes in wearable health technology. These technologies make use of the fact that the human body is full of ions, which means you can measure voltages and currents and resistances in the human body correlated with human health.

These graphene electrodes, known as electronic tattoos, are thinner than other materials for wearable electrodes, such as thin metal: electronic tattoos. This makes it conform better to the skin, improving the signal-to-noise ratio. In addition, they designed the tattoos so that the wearer does not feel their presence. They performed a demonstration where they placed the graphene tattoo on a person’s eyelids to measure EOG, the electrical signal that emanates from your eyes. From their studies, “we can conclude that the graphene gives comparable signal fidelity and in some cases even superior signal fidelity to the commercial standard,” he said. They have also used these electrodes to measure blood pressure. Unlike the standard cuff, their wearable device can measure blood pressure with “every beat of the heart,” he says, leading to about 100,000 data points per day.

Akinwande ended his talk discussing the use of 2D materials in fuel cells. Strategies include mixing the 2D materials to create semi-permeable membranes in the cells which allow for proton conduction inside the cell while blocking undesired reactants.

Symposium X—MRS/The Kavli Foundation Frontiers of Materials features lectures aimed at a broad audience to provide meeting attendees with an overview of leading-edge topics.