03/30/2021
By Matthew Gage

The Kennedy College of Science, Department of Chemistry, invites you to attend a master’s thesis defense by Enic Quero-Mieres entitled “Investigation of the Surface Chemistry of Lithium Oxides and Their Affinity for Self-Assembled Thiol and Silane Monolayers.” The defense will be held on April 22 at 7 p.m. via Zoom.

Please contact Matthew Gage for meeting information if you are interested in attending. The committee will be composed of James Whitten (chair), Marina Ruths, Yuyu Sun, and Mingdi Yan. A brief abstract is provided below.

Abstract: The surface chemistry of oxidized lithium species (Li2O, Li2CO3, LiOH) was studied by XPS and UPS, as well as their chemical affinity for thiol and silane molecular groups. This study is a building block in the path to understanding the reactivity of the surface of lithium anodes and how to protect them from unwanted side reactions that occur on bare lithium anodes. These side reactions may ultimately shorten the cycling life of rechargeable lithium batteries. The first part of this project comprises studies of the surface chemistry of industrial-grade samples of vapor-deposited lithium substrates, passivated with two different gasses (N2O and CO2). Their chemical affinity to several alkoxysilanes, mercaptosilanes, chlorosilanes and silanes that contain amino groups, and an alkylthiol, were all deposited from solution. XPS measurements showed an unexpected low affinity to certain silanes, and this was attributed to the likely low presence of -OH groups in these surfaces that were only exposed to dry air during their preparation. In the second part of this project, XPS and UPS measurements were carried out on clean lithium surfaces that were vapor deposited onto clean Si (111) wafers in ultra-high vacuum conditions. However, both XPS and UPS results showed some degree of oxidation on the Li surface. Li2O was obtained by O2 dosing of the lithium, and LiOH was obtained by dosing pure H2O vapor on lithium. The LiOH surface was exposed to methanethiol vapor, and XPS unexpectedly showed adsorption with 2.5% of sulfur after dosing. Li2O was exposed to (3-mercaptopropyl) trimethoxysilane, and angle-resolved XPS showed possible adsorption through both alkoxy and thiol groups.

All interested students and faculty members are invited to attend.