CMSS Coloquium: STM Studies of Surface Electronic Structure & Local Hydrogenation of Graphene Islands on Cu(111), Oct. 16

Shawna Hollen

The Condensed Matter & Surface Sciences Colloquium Series presents Shawna Hollen on “STM studies of the surface electronic structure and local hydrogenation of graphene islands on Cu(111)” on Thursday, Oct. 2, at 4:10 p.m. in Walter Lecture Hall 245.

Abstract: The innate sensitivity of 2D material surfaces to their environment presents a challenge for applications that aim to employ the properties of the pristine materials, and at the same time an opportunity to design devices that exploit the surface sensitivity to tune electronic structure by functionalization.  For example, hydrogen functionalization of graphene to open a band gap is being widely researched because of its potential for use in lateral patterning of 2D devices. It is increasingly important to understand and characterize surface functionalization and interactions with environmental elements, such as substrate, metallic contacts, and adatoms.

In this talk, I will describe STM experiments that probe the effects of the local environment on the electronic structure of graphene, and present our most recent work on metal-coupled and hydrogenated graphene. We developed a method for reproducible, epitaxial growth of pristine graphene islands on Cu(111) in ultra-high vacuum and performed local spectroscopy that shows a modification of surface electronic structure due to the graphene. Measured shifts in the local work function and changes to the Shockley surface state indicate significant interaction with the Cu substrate and confirm expectations for graphene doping by metallic contacts. We then use a novel tip-induced field electron dissociation technique to locally hydrogenate the graphene. This technique produces crystalline hydrogenated graphene, which has not been achieved using conventional methods.  Additionally, this process is reversible, and we have shown we are able to remove the hydrogen with a high tip-sample bias. The hydrogenation and its reversibility represent significant progress towards writing lateral 2D devices. To this end, we are developing the capability to repeat the hydrogenation on working graphene devices.