Brothers discover the sound of graphene

Two brothers in a Rice University laboratory noticed a fascinating result during the production of the miracle material graphene that could potentially change the way it is manufactured – by listening to the sound it makes.

The brothers, John Li, a Rice alumnus now studying at Stanford University, and Victor Li, then a high school student in New York and now a freshman at the Massachusetts Institute of Technology, are co-lead authors of a paper that describes real-time analysis of laser-induced graphene production through sound.

Working in the lab of Rice chemist James Tour when they came up with their hypothesis, the brothers presented it at a group meeting.

"Professor Tour said, 'It is interesting,' and told us to pursue it as a potential project," John recalled.

The results, which appear in "Advanced Functional Materials," describe the simple acoustic signal processing method that analyzes laser-induced graphene production in real-time to determine its form and quality.

LIG, introduced by the Tour lab in 2014, makes layers of interconnected graphene sheets by heating the top of a thin polymer sheet to 4,532 degrees Fahrenheit (2,500 degrees Celsius), leaving only the carbon atoms behind.

The technique has since been applied to making graphene from other feedstock, including food.

"Under different conditions, we hear different sounds because different processes are occurring," said John. "So, if we hear variations during the synthesis, we'd be able to detect different materials being formed."

He added that audio analysis allows for "far greater quality control capabilities that are orders of magnitude faster than characterization of laser-induced graphene by microscopy techniques."

"In materials analysis, there are often tradeoffs between cost, speed, scalability, accuracy and precision, especially in terms of how much material you can systematically process," John continued. "What we have here allows us to efficiently scale the throughput of our analytical capabilities to the entire amount of material we're trying to synthesize in a robust manner."

John invited his younger brother, Victor, to Houston, Texas – where Rice University is located – knowing his expertise would be a vital component in the lab.

"We have complementary skill sets almost by design, where I avoid specializing in the things that he knows very well, and likewise, he avoids areas that I know very well," John said. "So, we form a very solid team.

"Basically, I made the connection that the right sounds correspond to the right product, and he made the connection that the different sounds corresponded to different products," he added. "Also, he is much stronger than I am at certain computational techniques, whereas I'm primarily an experimentalist."

A small $31 microphone from Amazon taped to a laser head and attached to a cellphone inside the equipment cabinet was all that was used to pick up the audio for analysis.

"The brothers converted the sound pattern through a mathematical technique called a Fast Fourier transform, so they could get numerical data from the sound data," said James Tour. "Through some mathematical computations, that data can be a near-instant analytical tool to assess the product type and purity."

John added that the sounds emitted "provide information on the relaxation of the energy input when the laser hits the sample and gets absorbed, transmitted, scattered, reflected or just in general converted to different types of energy. That allows us to get local information on properties of the graphene's microstructure, morphology and nanoscale characteristics."

Tour has remained impressed by their ingenuity.

"What these brothers came up with is amazing," he said. "They are hearing the sounds of synthesis as it is performed, and from that they can determine the product type and quality near-instantaneously. This could be an important approach during synthesis to guide manufacturing parameters."

Furthermore, he added that sound analysis could contribute to a number of manufacturing processes, including his own lab's flash Joule heating, a method to make graphene and other materials from waste products, as well as sintering, phase engineering, strain engineering, chemical vapor deposition, combustion, annealing, laser-cutting, gas evolution, distillation, and more.

"Between John's experimental expertise and Victor's mathematical talent, the family team is formidable," Tour said. "My greatest joy is to provide an atmosphere where young minds can create and flourish, and in this case, they demonstrated expertise way beyond their years, John being only 19 and Victor 17 at the time of their discovery."

With such a discovery that not only could flip the manufacturing world on its head but could be a solution to systematic production of upscaled graphene production, the two brothers have marked a significant accolade in their careers.

But if it can be done once, it can be done again. As materials sciences continue to explode at exponential rates due to the ongoing renewable energy transition, we should all look forward to more innovations by the Li brothers.