David A. Muller
School of Applied and Engineering Physics, Cornell University

The structure of Two-Dimensional Glasses and Crystals

Location: EB1 Room 1011

Friday, March 22nd 2013 - 11:00 am

Graphene films a single atom thick can be produced by chemical vapor deposition on copper substrates on up to meter scales, large enough that its polycrystallinity is unavoidable. Using transmission electron microscopy, we image graphene grains and grain boundaries across six orders of magnitude, from atomic-resolution images of graphene grain boundaries, to the shape, orientation and stacking of grains and multilayers [1]. These images reveal an intricate patchwork of grains with structural details depending strongly on growth conditions so that large grains do not always offer the highest mobility films. We find the structure of boundaries are qualitatively different between graphene and polar 2D materials such as MoS2.

Large-area graphene substrates also provide a promising lab bench for synthesizing, manipulating, and characterizing low-dimensional materials, opening the door to high-resolution analyses of novel structures, such as 2D glasses, that cannot be exfoliated and may not occur naturally. The accidental discovery of a 2D silica glass supported on graphene enabled the first atomic resolution transmission electron microscopy of a glass, producing images that strikingly resemble Zachariasen's original 1932 cartoon models of 2D continuous random network glasses[2]. From these images, we directly obtain ring statistics and pair distribution functions that span short-, medium-, and long-range order and test these against long-standing theoretical predictions of glass structure and dynamics.

North Carolina State University