Prof. Hayden Taylor
Assistant Professor, Department of Mechanical Engineering, UC Berkeley
April 28, 2015 | 12:30 to 01:30 | 540 Cory Hall
Host: Dorian Liepmann
There is increasing interest in using van der Waals solids (“2D materials”) to manufacture high-performance field-effect transistors, light-emitting diodes, sensors, and other devices. The creation of these structures involves the production or isolation of single- or few-atomic layers of the constituent material(s), followed either by adhesion to other 2D materials or by the vapor-phase deposition and patterning of, e.g., gate dielectric oxides and metallic electrodes. Progress is, however, being hampered by the absence of truly repeatable techniques for manipulating single atomic layers and integrating them with other materials. At the root of the problem is a lack of understanding of the mechanical interactions that occur between van der Waals material crystals and the substrates on which we wish to deposit them.
In this talk I will discuss numerical modeling work that we have done to understand two possible methods of mechanically manipulating graphene. In the first method, a special thinning phenomenon is observed through molecular dynamics, where compression of AB-stacked graphite flakes between two hydrogen-terminated silicon substrates leads to the exfoliation of graphene layers. We have studied how this thinning phenomenon is affected by parameters such as graphene flake size, the number of graphene layers, and the crystalline orientation of the substrate surface. It appears that the thinning phenomenon occurs through the activation of an inter-layer superlubricity regime, caused by torque-induced spontaneous rotations of the layers which are initiated by in-plane shear modes of graphite during compression. Secondly, I will describe finite-element modeling of a graphene contact-printing process which enables the formation of graphene folds with controlled size and position. These folds have been experimentally found by our collaborators to exhibit anisotropy of charge carrier mobility.
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