It may be true that seeing is believing, but sometimes hearing can be better.
Case in point: Two brothers in a lab at Rice University heard something unusual while making graphene. Ultimately, they determined that the sound itself could provide them with valuable product data.
The brothers, John Li, a former Rice student who is currently 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 article that describes the real-time analysis of laser-induced graphene (LIG) production through sound.
The brothers were working in the lab of Rice chemist James Tour when they formulated their hypothesis and presented it in a group meeting.
“Professor Tour said, ‘It’s interesting’ and told us to pursue it as a potential project,” recalls John Li.
The results, which appear in Advanced functional materials, describe a simple acoustic signal processing scheme that analyzes LIG in real time to determine its shape and quality.
LIG, introduced by the Tour lab in 2014, makes layers of interconnected graphene sheets by heating the top of a thin sheet of polymer to 2,500 degrees Celsius (4,532 degrees Fahrenheit), leaving only carbon atoms behind. The technique has since been applied to making graphene from other raw materials, even food.
“Under different conditions, we hear different sounds because different processes are happening,” John said. “So if we hear variations during synthesis, we would be able to detect different materials being formed.”
He said audio analysis enables “far superior 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 consistently process,” John said. “What we have here allows us to efficiently match the throughput of our analytical capabilities to the total amount of material we are trying to robustly synthesize.”
John invited his younger brother to Houston, knowing his expertise would be a plus in the lab. “We have complementary skill sets almost by design, where I avoid specializing in things that he knows very well, and likewise he avoids areas that I know very well,” he said. . “So we are a very strong team.
“Basically, I made the connection that the right sounds matched the right product, and he made the connection that different sounds matched different products,” he said. “Furthermore, he is much stronger than me in certain computational techniques, whereas I am first and foremost an experimenter.”
A small $31 microphone from Amazon taped to the laser head and attached to a cell phone inside the laser cabinet picks up audio for analysis.
“The brothers converted the sound pattern through a mathematical technique called Fast Fourier Transform, so they could get numerical data from the sound data,” Tour said. “Through certain mathematical calculations, this data can be an almost instantaneous analytical tool for assessing product type and purity.”
John Li said that the sounds emitted “provide information about the relaxation of energy input as the laser hits the sample and is absorbed, transmitted, scattered, reflected, or just converted into different types of energy. This allows us to obtain local information about the properties of graphene microstructure, morphology and nanoscale features.
Tour remains impressed with their ingenuity.
“What these brothers have found is amazing,” he said. “They hear the sounds of the synthesis as it runs, and from there they can determine the type and quality of the product almost instantly. This could be an important approach during synthesis to guide manufacturing parameters.
He said sound analysis could contribute to a number of manufacturing processes, including Joule flash heating from his own lab, a method to make graphene and other materials from waste, as well as sintering , phase engineering, strain engineering, chemical vapor deposition, combustion, annealing, laser cutting, gassing, distillation and more.
“Between John’s experimental expertise and Victor’s mathematical talent, the family team is great,” Tour said. “My greatest joy is providing an atmosphere where young minds can create and flourish, and in this case they have demonstrated expertise well beyond their years, John being only 19 and Victor 17 at the time. time of their discovery.
The paper’s co-authors are Rice graduate students Jacob Beckham and Weiyin Chen, postdoctoral researcher Bing Deng, alumnus Duy Luong, and researcher Carter Kittrell. Tour holds the TT and WF Chao Chair in Chemistry as well as a professor of computer science, materials science and nano-engineering.
The Air Force Office of Scientific Research (FA9550-19-1-0296) supported the research.