| AVS 62nd International Symposium & Exhibition | |
| 2D Materials Focus Topic | Thursday Sessions |
| Session 2D+EM+MG+NS+SE+SM+SS+TF-ThM |
| Session: | Emergent 2D Materials |
| Presenter: | Rafik Addou, University of Texas at Dallas |
| Authors: | R. Addou, University of Texas at Dallas H. Zhu, University of Texas at Dallas Y.-C. Lin, Penn State University S.M. Eichfeld, Penn State University J.A. Robinson, Penn State University R.M. Wallace, University of Texas at Dallas |
| Correspondent: | Click to Email |
Heterogeneous fabrication of semiconducting two-dimensional layered materials presents a promising opportunity to develop highly tunable electronic and optoelectronic materials.(1-2) An example of crystalline monolayer of WSe2 grown by chemical vapor deposition on epitaxial graphene (EG) grown from silicon carbide had been investigated at nanoscale level. The WSe2 surface was characterized using atomic force microscopy (AFM) scanning tunneling microscopy/spectroscopy (STM/STS) and X-ray photoelectron spectroscopy (XPS).(3,4) AFM and large STM images show high-quality WSe2 monolayers. The sharpness of the W 4f and Se 3d core levels confirms the absence of any measurable reaction at the interface and oxide formation. The photoemission measurements of WSe2-Graphene interface suggest p-type doping due to charge transfer (EG withdraws electrons from WSe2) at the interface and formation of Schottky-type contact,(5) suggesting possible applications of such heterostructures as diodes and photodetectors. High-resolution STM images reveal atomic-size imperfections induced by Se vacancies and impurities. Additionally, the investigation of bulk WSe2(0001) surface shows spatial variation attributed to the presence of two components in W 4f7/2 core level attributed to the presence of both n- and p-type behavior. STM images exhibit also various types of defect induced by vacancies and dopants. The STS spectra reveal two main characteristics i) expected p-type conductivity where the Fermi level located at the valence band edge, and ii) zero conductivity at negative bias explained by defect-induced band bending as reported on geological MoS2 crystal surfaces.(4) In conclusion, the spatial variation (topography and electronic structure) is more noticeable in bulk WSe2 grown by chemical vapor transport than in CVD thin films.
This work was supported in part by the Southwest Academy on Nanoelectronics sponsored by the Nanoelectronic Research Initiative and NIST and the Center for Low Energy Systems Technology, one of six centers supported by the STARnet phase of the Focus Center Research Program, a Semiconductor Research Corporation program sponsored by MARCO and DARPA.
(1) Yu-Chuan Lin et al., Nano Lett., 14 (2014) 6936-6941.
(2) Yu-Chuan Lin et al., Nature Comm. arXiv:1503.05592v1.
(3) Robert M. Wallace, ECS Trans. 64 (2014) 109-116.
(4) Rafik Addou, Luigi Colombo, and Robert M. Wallace, ACS Appl. Mater. Interfaces (Accepted, 2015).
(5) Horacio Coy Diaz, Rafik Addou, and Matthias Batzill, Nanosclae 6 (2014) 1071-1078.