title: Infrared fingerprints of few-layer black phosphorus.
abstract: Black phosphorus is an infrared layered material. Its bandgap complements other widely studied two-dimensional materials: zero-gap graphene and visible/near-infrared gap transition metal dichalcogenides. Although highly desirable, a comprehensive infrared characterization is still lacking. Here we report a systematic infrared study of mechanically exfoliated few-layer black phosphorus, with thickness ranging from 2 to 15 layers and photon energy spanning from 0.25 to 1.36 eV. Each few-layer black phosphorus exhibits a thickness-dependent unique infrared spectrum with a series of absorption resonances, which reveals the underlying electronic structure evolution and serves as its infrared fingerprints. Surprisingly, unexpected absorption features, which are associated with the forbidden optical transitions, have been observed. Furthermore, we unambiguously demonstrate that controllable uniaxial strain can be used as a convenient and effective approach to tune the electronic structure of few-layer black phosphorus. Our study paves the way for black phosphorus applications in infrared photonics and optoelectronics.
authors.affiliation: State Key Laboratory of Surface Physics and Key Laboratory of Micro and Nano Photonic Structures (Ministry of Education), Department of Physics, Fudan University, Shanghai 200433, China.|Collaborative Innovation Center of Advanced Microstructures, Nanjing 210093, China.
authors.forename: Guowei
authors.initials: G
authors.lastname: Zhang
authors.affiliation: State Key Laboratory of Surface Physics and Key Laboratory of Micro and Nano Photonic Structures (Ministry of Education), Department of Physics, Fudan University, Shanghai 200433, China.|Collaborative Innovation Center of Advanced Microstructures, Nanjing 210093, China.
authors.forename: Shenyang
authors.initials: S
authors.lastname: Huang
authors.affiliation: Departamento de Física, Universidade Federal do Ceará, Caixa Postal 6030, Campus do Pici, Fortaleza, Ceará 60455-900, Brazil.|Department of Chemistry, Columbia University, New York, New York 10027, USA.
authors.forename: Andrey
authors.initials: A
authors.lastname: Chaves
authors.affiliation: State Key Laboratory of Surface Physics and Key Laboratory of Micro and Nano Photonic Structures (Ministry of Education), Department of Physics, Fudan University, Shanghai 200433, China.|Collaborative Innovation Center of Advanced Microstructures, Nanjing 210093, China.
authors.forename: Chaoyu
authors.initials: C
authors.lastname: Song
authors.affiliation: Andlinger Center for Energy and the Environment, Princeton University, Princeton, New Jersey 08544, USA.
authors.forename: V Ongun
authors.initials: VO
authors.lastname: Özçelik
authors.affiliation: Department of Electrical and Computer Engineering, University of Minnesota, Minneapolis, Minnesota 55455, USA.
authors.forename: Tony
authors.initials: T
authors.lastname: Low
authors.affiliation: State Key Laboratory of Surface Physics and Key Laboratory of Micro and Nano Photonic Structures (Ministry of Education), Department of Physics, Fudan University, Shanghai 200433, China.|Collaborative Innovation Center of Advanced Microstructures, Nanjing 210093, China.
authors.forename: Hugen
authors.initials: H
authors.lastname: Yan