Nanoscale strain engineering of graphene and graphene-based devices

Significance Statement

Graphene, a single layer of carbon atoms forming a honeycomb lattice structure, has been considered as a wonder material for both scientific research and technological applications because of its unique electronic, thermal, magnetic and mechanical properties and its super-functional capabilities. Among various novel properties, the existence of a nontrivial topological phase (also known as the Berry phase) associated with each of the two inequivalent valleys in graphene is deemed as a unique component suitable for applications to quantum information technology and dissipation-free field effect transistors (FETs). However, such valleytronic applications can only be realized by either breaking the time-reversal symmetry or the inversion symmetry of graphene. The former may be achieved by inducing finite ferromagnetism in graphene, whereas the latter may be realized by gingerly aligning the honeycomb lattice of a monolayer of graphene with atomic precision on top of a monolayer of hexagonal boron nitride. However, neither approach is easily manageable for scale-up applications because of the small energy gaps involved in the aforementioned perturbations, which imply the requirement of low-temperature operation. The complicated material processing also imposes additional challenges on device fabrication in large quantity.

A recently developed single-step process for room-temperature PECVD growth of large-area, high-mobility and nearly strain-free graphene opens up a new paradigm for realizing graphene-based valleytronics when combined with modern nanoscale fabrication technology. Specifically, properly strained graphene at nanoscales can result in giant pseudo-magnetic fields that couple to the two inequivalent valleys with opposite signs. Therefore, controlled strain on perfect graphene can be tailored to yield the desirable electronic properties for valleytronic applications, and the strength and spatial distributions of the required strain may be induced by designing and then fabricating nanostructures on the substrates for graphene. In particular, the energy scale of the giant pseudo-magnetic fields could be so high that even room temperature operation would be feasible. The notion of nanoscale “strain engineering” of the gauge potential of graphene is the primary motivation of this article published in Acta Mechanica Sinica, which describes the theoretical foundation for strain engineering the electronic properties of graphene, demonstrates preliminary theoretical simulations and nanofabrication approaches to implementing the nanoscale engineering, and then provides experimental evidences for the manifestation of strain-induced giant pseudo-magnetic fields. Exemplifying valleytronic devices based on nanoscale strain engineering of graphene are also discussed.

While this article focused on nanoscale strain engineering of graphene for valleytronic applications, it should be considered as an example of a new paradigm of research that exploits the interesting interplay of structural, electronic, and topological properties of nano- and meta-materials. This type of endeavor is likely to open up new frontiers in scientific and technological expeditions that have not been envisioned before. 

Nanoscale strain engineering of graphene and graphene-based devices- Advances in Engineering

About the author

 Nai-Chang Yeh is currently the Fletcher Jones Foundation Co-Director of the Kavli Nanoscience Institute and Professor of Physics at the California Institute of Technology (Caltech). She received her B.Sc. in Physics from the National Taiwan University in 1983 and Ph.D. in Physics from the Massachusetts Institute of Technology in January 1988. From January 1988 to August 1989, she was a visiting scientist at IBM, Thomas J. Watson Research Center in New York. She joined the physics faculty at the California Institute of Technology in 1989, and has remained there since.

Her principal research field is experimental condensed matter physics, with special emphasis on correlated electronic materials, topological matter, spintronics, low-dimensional systems, nanoscience and nanotechnology, and energy research. She is best known for her work on superconductors, magnetic materials, and superconductor/ferromagnet heterostructures. She is also interested in the physics of low-dimensional electronic systems such as graphene, two-dimensional transition-metal dichalcogenides, nanoribbons, nanotubes and quantum dots. Some of her experimental techniques include development of various types of cryogenic scanning probe microscopes for applications to nanoscience and technology, fabrication of nanostructures and nano-devices, as well as superconducting resonator technologies for high-resolution studies of superfluid phase transitions and Bose-Einstein condensation in helium gas.

Dr. Yeh is a fellow of the American Association for the Advancement of Science, the American Physical Society, as well as the Institute of Physics in the United Kingdom. Some of her other professional honors include the David and Lucile Packard Fellowship for Science and Engineering, Sloan Research Fellowship, Distinguished Alumni Award by the Physics Department of National Taiwan University, Wu Chien-Shiung Distinguished Lectureship by the National Central University in Taiwan, Achievement Awards by the Southern California Chinese-American Faculty Association, and Outstanding Young Researcher Award by the International Organization of Chinese Physicists and Astronomers.   

About the author

Chen-Chih Hsu is currently a Ph.D. candidate in the Physics Department at California Institute of Technology (Caltech), working in Professor Nai-Chang Yeh’s group. Mr. Hsu received his B.Sc. degree in physics and M.Sc. degree from the Graduate Institute of Photonics and Optoelectronics at the National Taiwan University (NTU). Before joining Caltech, he carried out research on quantum size effect of low-temperature growth of Pb islands under the supervision of Professor Chih-I Wu in the Electrical Engineering Department at NTU and Dr. Chia-Seng Chang in the Institute of Physics, Academia Sinica, Taiwan.

His current research focuses on the plasma enhanced chemical vapor deposition (PECVD) growth of graphene and graphene nanoribbons, nano-scale strain engineering of graphene, and graphene valleytronics. His primary experimental technique involves PECVD, scanning tunneling microscopy, atomic force microscopy, scanning electron microscopy, and nanofabrication by means of electron-beam lithography and focused-ion-beam lithography.

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About the author

Marcus Teague is currently a staff scientist in the condensed matter physics research group of Professor Nai-Chang Yeh at the California Institute of Technology. Dr. Teague was born in the state of Texas in the United States and studied physics at the Texas A&M University for four years before he completed his B.Sc. degree in 2003. He then studied at the California Institute of Technology for eight years when he completed his Ph.D. in Physics under Professor Yeh.  He decided to remain at Caltech to continue his research.

His current research interests involve experimental studies and theoretical simulations of high-temperature superconductors and graphene as well as development of new experimental instrumentation. His experimental techniques involve cryogenic scanning tunneling microscopy with high magnetic field capabilities and scanning electron microscopy. While his theoretical simulations employ matlab and molecular dynamics calculations.

In addition to physics, Dr. Teague enjoys reading, political debate, hiking, running, and camping. He volunteers at local elementary schools to encourage young students to become interested in science and technology and pursue this passion as a vocation. His career goals are to teach physics at a four-year undergraduate institution and develop an undergraduate research program to help teach the next generation of budding physics the art of research.

About the author

Jiaqing Wang is currently a senior undergraduate student in physics at the Fudan University in China and is expected to receive his B.Sc. degree in July 2016. He will join Professor Nai-Chang Yeh’s condensed matter physics research group as a physics graduate student at the California Institute of Technology in the fall of 2016. His scientific interests encompass topics of correlated electronic systems, low dimensional materials and topological matter. Currently, his research focuses on the growth and characterization of two-dimensional materials (including graphene) and the design of nanoscale perturbations to induce desirable physical properties on graphene by means of theoretical simulations.

About the author

David A. Boyd is currently a staff scientist at the California Institute of Technology in the Division of Physics, Mathematics & Astronomy. He received his Ph.D. degree in Engineering Physics from University of Virginia in 1998, and B.Sc. degree in Physics from University of Alabama, Birmingham in 1990. His research interests include chemical vapor deposition (CVD), block copolymer lithography, plasmonics, and optical spectroscopy. His current research focuses include single-step deposition of large-area, high mobility graphene by plasma enhanced CVD and the application of plasmon heating to CVD, catalysis, and chemical separations.

About the author

Chien-Chang Chen is currently a physics Ph.D. graduate student at the California Institute of Technology, working in Professor Nai-Chang Yeh’s group. Mr. Chen was born in Taiwan, studied physics at the National Taiwan University for two years before he transferred to the Physics Department of University of Illinois, Urbana Champaign, where he completed his B.Sc. degree in 2011.

His current research focuses on experimental studies and theoretical simulations of high-temperature superconductors, topological insulators and graphene. His primary experimental technique involves cryogenic scanning tunneling microscopy with high magnetic field capabilities, and his theoretical simulations employ matlab and density functional theory.

Mr. Chen has always enjoyed nature and science since childhood. In high school he represented Taiwan for the International Physics Olympia competition and won a gold medal. In addition to physics, he is interested in biology, earth science, astronomy, programming, simulations, hiking and sports. His career aspiration is to explore interdisciplinary research among different fields in the future.

Journal Reference

Acta Mechanica Sinica, pp 1-13, February 2016.

N.-C. Yeh 1, C.-C. Hsu1, M. L. Teague1, J.-Q. Wan2, D. A. Boyd3, C.-C. Chen1 

Show Affiliations
  1. Department of Physics, Institute for Quantum Information and Matter, and Kavli Nanoscience Institute, California Institute of Technology, Pasadena, CA, 91125, USA
  2. Department of Physics, Fudan University, Shanghai, China
  3. Department of Physics, California Institute of Technology, Pasadena, CA, 91125, USA

Abstract

Structural distortions in nano-materials can induce dramatic changes in their electronic properties. This situation is well manifested in graphene, a two-dimensional honeycomb structure of carbon atoms with only one atomic layer thickness. In particular, strained graphene can result in both charging effects and pseudo-magnetic fields, so that controlled strain on a perfect graphene lattice can be tailored to yield desirable electronic properties. Here, we describe the theoretical foundation for strain engineering of the electronic properties of graphene, and then provide experimental evidence for strain-induced pseudo-magnetic fields and charging effects in monolayer graphene. We further demonstrate the feasibility of nano-scale strain engineering for graphene-based devices by means of theoretical simulations and nano-fabrication technology.

Go To Acta Mechanica Sinica

 

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