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A More Durable Smart Phone?

Published: July 10, 2017

When you drop your cellphone, and we all do, do you cringe at the all-too-real possibility of picking it up, only to find that dreaded cracked screen?

Physics and Astronomy’s Claudia Ojeda-Aristizabal recently worked on a project that, at long term, could help manufacturers find something more durable and cheaper to use in an effort to prevent such damage in the nearly 1.5 billion smart phones bought worldwide last year. It could replace expensive, fragile compounds like silicon that are vital ingredients in today’s smart phones.

Ojeda-Aristizabal is an expert in graphene, the first truly two-dimensional crystal observed in nature. Her expertise drew her to study an interesting combination of materials in collaboration with Elton Santos from the School of Mathematics and Physics at Queen’s University and top-notch scientists from Stanford, UC Berkeley and the National Institute for Materials Science in Japan. Their goal was to create and understand a versatile new hybrid material that brings all the benefits from graphene, a thin, strong, transparent and conductive material); hexagonal boron nitride, an insulator that can be atomically thin just like graphene; and C60, an organic molecule with fascinating properties and often used in organic solar cells.

Ojeda-Aristizabal and her team found that by combining semiconducting “buckyball” molecules of C60 with graphene and hexagonal boron nitride, interesting patterns of charge transfer between graphene and C60 would appear, something of great importance for the design of a wide variety of electronic applications. They observed that when molecules of C60 are nicely organized on top of graphene, one of the most remarkable properties of graphene is preserved—the mobility of its electrons. At room temperature, electrons move in graphene more easily than in any other semiconductor, like silicon. It is still the case for electrons traveling in this interesting combination of materials.

The team observed that the presence or absence of Boron nitride and the orientation of the C60 molecules on top of graphene modifies the charge transfer at the interface between graphene and C60. They concluded from experimental observations and numerical simulations that the C60 molecules normally spinning at room temperature are actually orientationally locked into position in this material. Finally, it was predicted through calculations that the charge transfer between graphene and C60 can actually be tuned using an external knob: a large vertical electric field.

The member of the university since 2015 knows the bad feeling that goes with seeing the spider web cracks across the screen of a dropped phone. Materials like the one investigated in this project could revolutionize touch screens. Not only is the material investigated crack-resistant—it is also efficient in conducting electricity. In addition, because of the presence of C60 molecules, the material could be integrated into an array of solar cells, collecting energy from the sun for the functioning of the touch screen. Ojeda-Aristizabal said the material investigated could lead to different applications. The results of their work appear in the journal ACS Nano.

Ojeda-Aristizabal is glad for the support that her current research on layered materials receives from the CSULB graduate and undergraduate students in her campus lab.

Claudia Ojeda-Aristizabal

“They are essential to the experiments,” she said. “CSULB is a good place for me to perform this kind of research because the students here are highly motivated. The department of physics and astronomy has a very good master’s program, one of the largest in the country, which attracts very good students.”

Ojeda-Aristizabal points with pride to the lab’s equipment that includes a dry closed cycle cryostat that allows measurements at temperatures as low as 300 mili Kelvin and magnetic fields as large as 12 Tesla, an electron beam evaporator to deposit metallic thin films and a system of nanolithography, to print circuits at the nano-scale.

She earned her BSc in physics from the Universidad de los Andes in Bogotá Colombia in 2004. She went on to earn her MSc in condensed matter physics from the École Normale Supérieure in Paris in 2007 before acquiring her Ph.D. in physics from the Université Paris-sud XI in Orsay France, in 2010. She was born and raised in Colombia and arrived to the U.S. in 2011 for postdoctoral trainings at the University of Maryland College Park and UC Berkeley before joining CSULB as an assistant professor in 2015.

Ojeda-Aristizabal feels her research on layered materials has the potential to revolutionize many technologies.

“I am interested in different materials that exhibit rich physics and exotic properties. To me, this project that studied the combination of different fascinating materials such as graphene and C60 represents a step toward a better understanding of the physics behind the interface of dissimilar materials,” she said.

Her current research on strongly correlated materials in the two-dimensional limit was recently funded by the U.S. Department of Energy with a three-year, $255,000 grant.