Subcategory: Materials Science
Rajeh Alsaadi - Pennsylvania State University
Co-Author(s): Kayla A. Cooley, The Pennsylvania State University, PA ; Suzanne E. Mohney,The Pennsylvania State University, PA
Tungsten diselenide is one of many emerging 2D materials that show great promise for optoelectronics, solar arrays and flexible electronics. The potential for these applications is made possible by this material’s unique electronic properties and layered structure, where W and Se atoms are covalently bonded to each other within layers and the layers themselves are bound together by van der Waals forces. To successfully implement WSe2 and other 2D materials into current technology, we must first understand how they interact with other materials commonly found in devices, like metals. The literature reveals that some FCC metals, including Cu, Au and Ag, show epitaxy when deposited at room temperature on WSe2.  In some cases, metal epitaxy can affect electrical transport at contact interfaces.
In this study, we investigate the epitaxial relationship of additional metals (Ni, Pd, Co, and Al) on WSe2 in order to discover what factors control this unique growth. Samples were made by sputtering 30 nm of metal onto exfoliated WSe2 flakes at room temperature. Some flakes were then annealed at 400 °C for at least 4 hours to determine the effects of annealing on epitaxy. Each sample was analyzed by transmission electron microscopy and selected area electron diffraction to determine what metals and conditions demonstrated van der Waals epitaxy.
We observed that group 10 FCC metals, Ni and Pd, demonstrate an epitaxial relationship with WSe2 with the following orientation: (111)Metal || (001)WSe2 and <110>Metal || <110>WSe2. This result is in line with previous studies of Group 11 FCC metals . However, unlike previous studies, Pd was epitaxial only after annealing. In addition, HCP Co and FCC Al did not demonstrate epitaxy with WSe2. Further study is needed to understand the reasons for the differences among the metals.
 W. Jaegermann, et al. Phys. Rev. B 42, 7487 (1990).Epitaxy on WSe2-Abstarct.docx
Funder Acknowledgement(s): The first author acknowledges King Abdullah University of Science and Technology (KAUST) for providing a scholarship for this research project. The other authors acknowledge the National Science Foundation for supporting this work on grant number NSF DMR-1410334. The authors also express gratitude to Anna Domask and Chavez Lawrence for providing assistance during the period of this research.
Faculty Advisor: Suzanne E. Mohney, email@example.com
Role: I did search for literature. I did the experiments and analyzing data.