Subcategory: Materials Science
Bennett Cromer - Pennsylvania State University
Co-Author(s): Yixuan Chen, Justin Rodriguez, and Ying Liu, Pennsylvania State University, PA
Bulk ZrSiSe has mechanically useful properties such as high carrier mobility and a large magnetoresistance. Previous studies have predicted that crystals with the ZrSiS-type structure, such as ZrSiS, ZrSiSe, and ZrSiTe may be topologically insulating, meaning insulating on the interior and conducting on the outer surface, two-dimensionally  . Some 3D Topological Insulators are used in the quantum computing field by creating qubits when paired with s-wave superconductors. This breakthrough paired with the increasing focus on thin electronics served as inspiration for this project. Investigation of these derivatives offer new pathways for investigation and study. This project serves to perform transport measurements on thin ZrSi- chalcogenide derivatives under Ionic Liquid Gating and to develop a reliable method to prepare derivatives prior to measurement. The process we’re working with involves mechanically exfoliating the derivatives from bulk crystals using the scotch tape method. Once a suitable crystal is obtained we apply a single layer of resist and prepare the surface with an Ion Mill. After this, we apply metal contacts and an ionic liquid to increase charge carrier density for our measurements. We’ve found single layer resist and Ion Milling to produce more consistent electrical contact than bilayer resist and other methods of surface cleaning such as Oxygen Plasma. Samples of ZrSiSe and ZrSiTe appear to degrade within a few hours in air, thus further research involves covering freshly exfoliated samples with a layer of Graphene or hexagonal Boron Nitride. These coverings should preserve the ZrSi- chalcogenide derivatives for us to reliably perform transport measurements on.
References:  Qiunan Xu, ‘Two-Dimensional Oxide Topological Insulator with Iron-Pnictide Superconductor LiFeAs Structure,’ Physical Review B, Volume 92, Issue 20, 2015.
 Jin Hu, ‘Topological nodal-line fermions in ZrSiSe and ZrSiTe,’ Physical Review Letters, Volume 117, Issue 1, 2016.
Funder Acknowledgement(s): This project is made through the EFRI 2D REM program which is supported by the National Science Foundation (EFMA 1433378 and EFMA 1433307) and the Penn State Department of Science and Engineering.
Faculty Advisor: Ying Liu, email@example.com
Role: I primarily exfoliate the crystals from bulk and am focusing on preparing the graphene overlay, although I have worked on each step of the process.