Mechanical and Civil Engineering Seminar

Thursday February 17, 2022 11:00 AM

Graphene: from point defects to tunable twins

Speaker: Pilar Ariza, Head of the Doctoral on Program Mechanical Engineering and Industrial Organization, University of Seville (Spain)
Location: Gates-Thomas 135

Mechanical and Civil Engineering Seminar Series

Title: Graphene: from point defects to tunable twins

I will begin with a brief account of the computational methodology used in calculations. We divide calculations into three main steps: a first harmonic step aimed at building a pattern of defects into the lattice followed by a fully-nonlinear relaxation, and as a final step we investigate charge-carrier transmission across the structures that spontaneously arise in the graphene layer. Then, I will evaluate a number of point defect configurations in monolayer graphene and document different accommodation mechanisms. Finally, I will show that the transport gap of twinned graphene can be tuned through the application of a uniaxial strain in the direction normal to the twin band. Remarkably, we find that the transport gap Egap bears a square-root dependence on the control parameter εx −εc, where εx is the applied uniaxial strain and εc ∼ 19% is a critical strain. We interpret this dependence as evidence of criticality underlying a continuous phase transition, with εx−εc playing the role of control parameter and the transport gap Egap playing the role of order parameter. For εx < εc, the transport gap is non-zero and the material is semiconductor, whereas for εx > εc the transport gap closes to zero and the material becomes conductor, which evinces a semiconductor-to-conductor phase transition. The computed critical exponent of 1/2 places the transition in the meanfield universality class, which enables far-reaching analogies with other systems in the same class.

Bio: Pilar Ariza is professor of Solid Mechanics and Structures and head of the Doctoral on Program Mechanical Engineering and Industrial Organization at the University of Seville (Spain). After her PhD in 2002, she did postdoctoral research for the period of one year at the California Institute of Technology, where she worked as visiting associate for a second year. Since 2005, she holds a position as Visiting Associate in Aeronautics at the Graduate Aerospace Laboratories of the California Institute Technology (USA).

Her main research fields are modeling and simulation of advanced materials and multiphysics phenomena at different scales, with applications including sustainable energy, hydrogen storage, electronic devices and others. She organized an IUTAM symposium in 2014 and a Euromech colloquium in 2018. She also regularly serves on the scientific boards and organizing committees of international conferences in the area of Solid Mechanics.

Since 2014, Pilar Ariza is member of the IUTAM General Assembly and representative of Spain in IUTAM. She also serves as a member of the IUTAM Congress Committee. In 2018 she founded the Spanish scientific society SEMTA, which is adhered to IUTAM and Euromech, and has served as its president ever since. She also chaired the IUTAM diversity working group created in 2021. She has recently been elected as Treasurer of IUTAM and Officer of the IUTAM Bureau until 2024, and member of the EUROMECH Council for a six-year term (2022 – 2027).

Pilar Ariza has been a member of the general council of IACM for the period 2017-2021 and a member of the executive committee of the SEMNI for the period 2011-2018. She is a member of three editorial boards: International Journal of Fracture, International Journal of Mechanical Sciences and International Journal of Numerical Methods for Calculation and Design in Engineering.

NOTE: At this time, in-person Mechanical and Civil Engineering Lectures are open to all Caltech students/staff/faculty/visitors with a valid Caltech ID. Outside community members are welcome to join our online webinar.

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Series Mechanical and Civil Engineering Seminar Series

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