title: Gigahertz Acoustic Vibrations of Elastically Anisotropic Indium-Tin-Oxide Nanorod Arrays.
abstract: Active control of light is important for photonic integrated circuits, optical switches, and telecommunications. Coupling light with acoustic vibrations in nanoscale optical resonators offers optical modulation capabilities with high bandwidth and small footprint. Instead of using noble metals, here we introduce indium-tin-oxide nanorod arrays (ITO-NRAs) as the operating media and demonstrate optical modulation covering the visible spectral range (from 360 to 700 nm) with ∼20 GHz bandwidth through the excitation of coherent acoustic vibrations in ITO-NRAs. This broadband modulation results from the collective optical diffraction by the dielectric ITO-NRAs, and a high differential transmission modulation up to 10% is achieved through efficient near-infrared, on-plasmon-resonance pumping. By combining the frequency signatures of the vibrational modes with finite-element simulations, we further determine the anisotropic elastic constants for single-crystalline ITO, which are not known for the bulk phase. This technique to determine elastic constants using coherent acoustic vibrations of uniform nanostructures can be generalized to the study of other inorganic materials.
authors.affiliation: Department of Materials Science and Engineering, Northwestern University , 2220 Campus Drive, Evanston, Illinois 60208, United States.
authors.forename: Peijun
authors.initials: P
authors.lastname: Guo
authors.affiliation: Center for Nanoscale Materials, Argonne National Laboratory , 9700 South Cass Avenue, Building 440, Lemont, Illinois 60439, United States.|Department of Chemistry, Northwestern University , 2145 Sheridan Road, Evanston, Illinois 60208, United States.
authors.forename: Richard D
authors.initials: RD
authors.lastname: Schaller
authors.affiliation: Center for Nanoscale Materials, Argonne National Laboratory , 9700 South Cass Avenue, Building 440, Lemont, Illinois 60439, United States.
authors.forename: Leonidas E
authors.initials: LE
authors.lastname: Ocola
authors.affiliation: Department of Physics and Astronomy, Northwestern University , 2145 Sheridan Road, Evanston, Illinois 60208, United States.
authors.forename: John B
authors.initials: JB
authors.lastname: Ketterson
authors.affiliation: Department of Materials Science and Engineering, Northwestern University , 2220 Campus Drive, Evanston, Illinois 60208, United States.
authors.forename: Robert P H
authors.initials: RP
authors.lastname: Chang
keywords: Indium−tin-oxide; acoustic phonon; elasticity; nanorod; single crystalline; ultrafast spectroscopy