Synthesis, Structure, and Electronic Properties of Germanane and Layered Materials DISSERTATION Presented in Partial Fulfillment of the Requirements for the Degree Doctor of Philosophy in the Graduate School of The Ohio State University By Nicholas David Cultrara Graduate Program in Chemistry The Ohio State University 2018 Professor Joshua E. Goldberger, Advisor Professor Shiyu Zhang Professor Yiying Wu Copyrighted by Nicholas David Cultrara 2018 Abstract In the past decade, since the isolation of a single layer of graphene, materials research has been dominated by exploration and characterization of layered materials with an interesting range of electronic, optical, spintronic and spin-orbit coupling properties. Herein, we present research into the exploration and advancement in research of two-dimensional materials, focusing on the layered germanium structure, germanane and transport properties of other exfoliatable layered Zintl phase materials. Chapter 2 focuses on the ability to add external dopants to the layered 6R structure of the germanane family. Gallium and arsenic were successfully introduced to the precursor Zintl phase CaGe2 and 2.3% Ga and 1.1% As were retained through the topotactic deintercalation process. Single flake transport measurements show a reduction of 3-orders of magnitude in H2O containing atmosphere for the As doped samples and >4-orders of magnitude in the highest doped Ga samples in inert atmospheres. These structures were also found to be relatively stable over 1-day exposure to ambient conditions, while showing signs of oxidation between 1-4 days in ambient atmosphere. Chapter 3 focuses on the ability to selectively grow 3 different polymorphs of layered germanium Zintl phases which can be used as precursors in the topotactic deintercalation reaction to form the corresponding hydrogen terminated layered germanane structures. Both the 6R and 1T structures are obtained from annealing elements in quartz but the 2H structure must be obtained from a synthesis using an indium flux. A ii small portion of indium is retained by the germanane following deintercalation, which causes the formation of the two layered structure. Both the 6R and 1T show remarkable similar properties, while the 2H shows a shrinking of the band gap and shifting of Raman and FTIR peaks, associated with the retention of the heavier indium on the germanium lattice. Finally the thermal expansion of the 6R phase was investigated and found to negative in the in-plane direction while the out-of-plane direction was positive. Chapter 4 focuses on the device fabrication and electronic measurements of layered materials. The role of contact resistance and contact size on highly resistive germanane was optimized to allow to electronic characterization. Bulk resistivity measurements of both the NaSn2As2 and EuSn2As2 were conducted using indium and silver epoxy contacts respectively. Both were found to behave as metals with phonon mediated resistivity, while the EuSn2As2 shows an increase of resistivity around the magnetic transition temperature, associated with the spin-scattering of conduction electrons by Eu2+ f-electrons. iii Acknowledgments Firstly, my journey though graduate school would have been possible without the years of mentorship, especially by Prof. Joshua E. Goldberger. As a young chemist, I would never have been able to accomplish what I have accomplished in my Ohio State career without the hands on work and with the countless hours spend conceptualizing experiments and analyzing data. I would also like to thank Professor Yiying Wu and Professor Shiyu Zhang for their scientific input to my dissertation. Secondly, I would like to acknowledge the members of the Goldberger group and collaborators who mentored me in the finer points of being a research scientist. Dr. Shishi Jiang, Dr. Maxx Arguilla, Mr. Chuanchuan Sun and Dr. Basant Chitara of the Goldberger groups, Dr. Justin Young of the Johnson-Halperin group, and Mr. Bin He of the Heremans group, along with countless others in chemistry, physics, and mechanical engineering at The Ohio State. To the present and former members of the Goldberger group, thank you for the support, entertainment, and scientific conversations, especially Mr. Tianyang Li, Mr. Zachary Baum, Mr. Rick Morasse, Dr. Ashley Wallace, Ms. Elisabeth Bianco, Mr. Michael Scudder, Mr. Dom Ross, Mr. Fan Fan, and Mr. Ben Redemann. Lastly, I would like to thank the friends and family who were always there to support me through my time as a graduate student. iv Vita 2008................................................................Kenmore West Senior High School 2012................................................................B.S. Chemistry, State University of New York at Buffalo 2012 to Present ..............................................Graduate Research Assistant, Department of Chemistry and Biochemistry, The Ohio State University Publications 1. N. D. Cultrara, M. Q. Arguilla, S. Jiang, C. Sun, M. R. Scudder, R. D. Ross, J. E. Goldberger, (2017) “Group 13 and 15 Doping of Germanane.” Beilstein Journal of Nanothechnology 8(1), 1642-1648 2. M. Q. Arguilla, N. D. Cultrara, M. R. Scudder, S. Jiang, R. D. Ross, J. E. Goldberger, (2017) “Optical Properties and Raman-Active Phonon Modes in Two-Dimensional Honeycomb Zintl Phases.” Journal of Materials Chemistry C, 2017 v 3. M. Q. Arguilla, N. D. Cultrara, Z. J. Baum, S. Jiang, R. D. Ross, J. E. Goldberger (2017). "EuSn2As2: An Exfoliatable Magnetic Layered Zintl–Klemm Phase." Inorganic Chemistry Frontiers, 4, 378-386 4. M. Q. Arguilla, J. Katoch, K. Krymowski, N. D. Cultrara, J. Xu, X. Xi, A. Hanks, S. Jiang, R. D. Ross, R. J. Koch, S. Ulstrup, A. Bostwick, C. Jozwiak, E. Rotenberg, D. McComb, J. Shan, W. Windl, R. K. Kawakami and J. E. Goldberger (2016). "NaSn2As2: An Exfoliatable Layered van der Waals Zintl Phase." ACS Nano 10(10): 9500-9508. 5. G. Coloyan, N. D. Cultrara, A. Katre, J. Carrete, M. Heine, E. Ou, J. Kin, S. Jiang, L. Lindsay, N. Mingo, D. Broido, J. P. Heremans, J. E. Goldberger, L. Shi, (2016). "Basal-plane Thermal Conductivity of Nanocrystalline and Amorphized Thin Germanane." Applied physics letters 109(13): 131907. 6. S. Jiang, M. Q. Arguilla, N. D. Cultrara, J. Goldberger (2016). "Improved Topotactic Reactions for Maximizing Organic Coverage of Methyl Germanane." Chemistry of Materials 28(13): 4735-4740. vi 7. S. Jiang, K. Krymowski, T. Asel, M.Q. Arguilla, N. D. Cultrara, E. Yanchenko, X. Yang, L. Brillson, W. Windl, J. E. Goldberger, (2016). "Tailoring the Electronic Structure of Covalently Functionalized Germanane via the Interplay of Ligand Strain and Electronegativity." Chemistry of Materials 28(21): 8071-8077. 8. J. R. Young, B. Chitara, N. D. Cultrara, S. Jiang, F. Fan, E. Johnston-Halperin, J. E. Goldberger, (2015). "Water Activated Doping and Transport in Multilayered Germanane Crystals." Journal of Physics: Condensed Matter 28(3): 034001. 9. S. Jiang,* M. Q. Arguilla,* N. D. Cultrara,* J. E. Goldberger, (2014). "Covalently-controlled Properties by Design in Group IV Graphane Analogues." Accounts of Chemical Research 48(1): 144-151. (*equal contribution) Fields of Study Major Field: Chemistry vii Table of Contents Abstract ............................................................................................................................... ii Acknowledgments.............................................................................................................. iv Vita ...................................................................................................................................... v Publications ......................................................................................................................... v Fields of Study .................................................................................................................. vii Table of Contents ............................................................................................................. viii List of Tables ..................................................................................................................... xi List of Figures ................................................................................................................... xii Chapter 1: Introduction ....................................................................................................... 1 1.1 Introduction ............................................................................................................... 1 1.2 Topotactic Synthesis ................................................................................................. 6 1.3 Single and Few-Layer Thick Materials ................................................................... 13 1.4 Covalently Modifiable Building Blocks ................................................................. 16 1.5 Tuning the Electronic Structure .............................................................................. 21 1.6 Thermal and Air Stability ........................................................................................ 30 viii 1.7 Conclusion and Outlook .......................................................................................... 34 1.8 References ............................................................................................................... 34 Chapter 2: Group 13 and 15 Doping of Germanane ......................................................... 41 2.1 Introduction ............................................................................................................