AVS 61st International Symposium & Exhibition
    2D Materials Focus Topic Wednesday Sessions
       Session 2D+EM+NS+SS+TF-WeM

Paper 2D+EM+NS+SS+TF-WeM4
Growth, Structure, and Properties of 2D SiO2 Polymorphs

Wednesday, November 12, 2014, 9:00 am, Room 310

Session: Novel 2D Materials 
Presenter: Eric Altman, Yale University
Authors: E.I. Altman, Yale University
J. Götzen, Yale University
X. Zhu, Yale University
A. Sonnenfeld, Yale University
U.D. Schwarz, Yale University
Correspondent: Click to Email
Recently it has been shown that SiO2 can form closed 2D bilayers; because the layers have no dangling bonds they are expected to interact solely through van der Waals interactions. Despite the expected weak interactions, hexagonal crystalline bilayers on Pd(100) are stretched 4% to match the lattice constant of the substrate. Both electron diffraction and STM reveal that the size of the crystalline domains is limited along Pd[011] and one of the other bilayer close-packed directions but was long along the third one. The formation of regular domain boundaries on the square Pd substrate is attributed to stress relief in the crystalline layer. Ab initio calculations indicate that much of the remaining strain energy can be relieved by allowing the film to relax along the incommensurate direction. In this way the square substrate actually aids the templating of the overlayer despite the severe geometric mismatch. The calculations also indicate that the bilayer is surprisingly compliant, explaining the lattice matching despite the weak interaction and poor match. Amorphous bilayers could also be prepared on Pd(100). Atomic-scale features in STM images of the amorphous film could be associated with 4-9 membered rings of corner-sharing SiO4 tetrahedra. In addition to the structural heterogeneity, spectroscopic STM imaging revealed electronic heterogeneity with oxygen sites joining larger rings of corner-sharing SiO4 tetrahedra fading at low bias; spectra revealed two distinct electronic states responsible for this phenomenon. MBE growth of silica bilayers on graphene layers grown on epitaxial Ru on sapphire will also be discussed.