Two-dimensional (2D) materials such as graphene, transition metal dichalcogenides (TMDs), and hexagonal boron nitride (hBN) have attracted a large amount of interests due to their extraordinary electrical, optical, and mechanical properties comparing with their bulk counterparts. Recently, black phosphorus (BP) has emerged as a new 2D material with demonstrated high hole mobility, showing great potential in electronic applications such as field-effect transistors (FETs). In this talk we will first review our recent works on the electric, photo-electrical, mechanical, and thermal behaviors of few-layer black phosphorus [1-4]. We will then discuss the photonics applications of black phosphorus. 2D black phosphorus is an excellent candidate for use in photodetection devices due to its direct and thickness-dependent bandgap . However, light absorptions in these 2D materials are often very low due to its ultra- thin nature. For example, the visible light absorption in single layer graphene is only 2.3%. Making plasmonic structures, such as nano disks and rods, on top of the 2D material can be a possible way to enhance the absorption. In our work, a new bowtie-like plasmonic structure was proposed, and numerical simulations were used to design and optimize the plasmonic structures that are used to enhance both absorption and polarization selectivity in black phosphorus photodetection devices. The optimized structure devices were then fabricated on black phosphorus on transparent substrate. Photocurrent measurements showed strong light polarization dependence/selectivity in the fabricated device as well as much stronger photo responsivity compared with devices without plasmonic enhancement. Our study demonstrated the potentials of black phosphorus for photodetection and other light harvesting applications.
 Liu, H., Neal, A., Zhu, Z., Luo, Z., Xu, X., Tomanek, D., Ye, P.D., 2014, “Phosphorene: An Unexplored 2D Semiconductor with a High Hole Mobility,” ACS Nano, 8(4), pp. 4033–4041.
 Deng, Y., Luo, Z., Conrad, N. J., Liu, H., Gon,g Y., Najmaei, S., Ajayan, P. M., Lou, J., Xu, X., and Ye, P. D., 2014, “Black Phosphorus-Monolayer MoS2 van der Waals Heterojunction P-N Diode.,” ACS Nano, 8(8), pp. 8292–8299.
 Luo, Z., Maassen, J., Deng, Y., Du, Y., Garrelts, R. P., Lundstrom, M. S., Ye, P. D., and Xu, X., 2015, "Anisotropic in-plane thermal conductivity observed in few-layer black phosphorus", Nat. Commun. 6:8572, pp. 9572-1-8.
 Du, Y., Maassen, J., Wu, W., Luo, Z., Xu, X., and Ye, P., 2016, "Auxetic Black Phosphorus: A 2D Material with Negative Poisson’s Ratio", Nano Lett., DOI: 10.1021/acs.nanolett.6b03607.
Xianfan Xu, "Black phosphorus: a novel 2D material and its photonics applications (Conference Presentation)," Proc. SPIE 10521, Synthesis and Photonics of Nanoscale Materials XV, 1052106 (Presented at SPIE LASE: January 29, 2018; Published: 14 March 2018); https://doi.org/10.1117/12.2286329.5751466761001.
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