title: Systematic determination of absolute absorption cross-section of individual carbon nanotubes.
abstract: Optical absorption is the most fundamental optical property characterizing light-matter interactions in materials and can be most readily compared with theoretical predictions. However, determination of optical absorption cross-section of individual nanostructures is experimentally challenging due to the small extinction signal using conventional transmission measurements. Recently, dramatic increase of optical contrast from individual carbon nanotubes has been successfully achieved with a polarization-based homodyne microscope, where the scattered light wave from the nanostructure interferes with the optimized reference signal (the reflected/transmitted light). Here we demonstrate high-sensitivity absorption spectroscopy for individual single-walled carbon nanotubes by combining the polarization-based homodyne technique with broadband supercontinuum excitation in transmission configuration. To our knowledge, this is the first time that high-throughput and quantitative determination of nanotube absorption cross-section over broad spectral range at the single-tube level was performed for more than 50 individual chirality-defined single-walled nanotubes. Our data reveal chirality-dependent behaviors of exciton resonances in carbon nanotubes, where the exciton oscillator strength exhibits a universal scaling law with the nanotube diameter and the transition order. The exciton linewidth (characterizing the exciton lifetime) varies strongly in different nanotubes, and on average it increases linearly with the transition energy. In addition, we establish an empirical formula by extrapolating our data to predict the absorption cross-section spectrum for any given nanotube. The quantitative information of absorption cross-section in a broad spectral range and all nanotube species not only provides new insight into the unique photophysics in one-dimensional carbon nanotubes, but also enables absolute determination of optical quantum efficiencies in important photoluminescence and photovoltaic processes.
authors.affiliation: Department of Physics, University of California, Berkeley, CA 94720;State Key Laboratory for Mesoscopic Physics, School of Physics, Peking University, Beijing 100871, China;
authors.forename: Kaihui
authors.initials: K
authors.lastname: Liu
authors.affiliation: Department of Physics, University of California, Berkeley, CA 94720;
authors.forename: Xiaoping
authors.initials: X
authors.lastname: Hong
authors.affiliation: Department of Physics, University of California, Berkeley, CA 94720;Materials Science Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720;
authors.forename: Sangkook
authors.initials: S
authors.lastname: Choi
authors.affiliation: Department of Physics, University of California, Berkeley, CA 94720;
authors.forename: Chenhao
authors.initials: C
authors.lastname: Jin
authors.affiliation: Department of Physics, University of California, Berkeley, CA 94720;Instituto de Física, Universidade Federal do Rio de Janeiro, 21941-972, Rio de Janeiro, RJ, Brazil;
authors.forename: Rodrigo B
authors.initials: RB
authors.lastname: Capaz
authors.affiliation: Department of Physics, University of California, Berkeley, CA 94720;
authors.forename: Jihoon
authors.initials: J
authors.lastname: Kim
authors.affiliation: Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China;
authors.forename: Wenlong
authors.initials: W
authors.lastname: Wang
authors.affiliation: Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China;
authors.forename: Xuedong
authors.initials: X
authors.lastname: Bai
authors.affiliation: Department of Physics, University of California, Berkeley, CA 94720;Materials Science Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720;
authors.forename: Steven G
authors.initials: SG
authors.lastname: Louie
authors.affiliation: International Center for Quantum Materials and Collaborative Innovation Center of Quantum Matter, Peking University, Beijing 100871, China; and.
authors.forename: Enge
authors.initials: E
authors.lastname: Wang
authors.affiliation: Department of Physics, University of California, Berkeley, CA 94720;Materials Science Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720;Kavli Energy NanoSciences Institute at the University of California, Berkeley, and the Lawrence Berkeley National Laboratory, Berkeley, CA 94720 fengwang76@berkeley.edu.
authors.forename: Feng
authors.initials: F
authors.lastname: Wang
mesh_terms: D000042:Absorption; D008027:Light; D008956:Models, Chemical; D037742:Nanotubes, Carbon / Q000737:chemistry*; D055620:Optical Phenomena; D010825:Physics; D013057:Spectrum Analysis / Q000379:methods*
chemical_list: D037742:Nanotubes, Carbon
keywords: carbon nanotube optical spectroscopy; excitons in carbon nanotubes; homodyne detection; polarization microscope