title: Confined Acoustic Phonons in Colloidal Nanorod Heterostructures Investigated by Nonresonant Raman Spectroscopy and Finite Elements Simulations.
abstract: Lattice vibrational modes in cadmium chalcogenide nanocrystals (NCs) have a strong impact on the carrier dynamics of excitons in such confined systems and on the optical properties of these nanomaterials. A prominent material for light emitting applications are CdSe/CdS core-shell dot-in-rods. Here we present a detailed investigation of the acoustic phonon modes in such dot-in-rods by nonresonant Raman spectroscopy with laser excitation energy lower than their bandgap. With high signal-to-noise ratio in the frequency range from 5-50 cm-1, we reveal distinct Raman bands that can be related to confined extensional and radial-breathing modes (RBM). Comparison of the experimental results with finite elements simulation and analytical analysis gives detailed insight into the localized nature of the acoustic vibration modes and their resonant frequencies. In particular, the RBM of dot-in-rods cannot be understood by an oscillation of a CdSe sphere embedded in a CdS rod matrix. Instead, the dot-in-rod architecture leads to a reduction of the sound velocity in the core region of the rod, which results in a redshift of the rod RBM frequency and localization of the phonon induced strain in vicinity of the core where optical transitions occur. Such localized effects potentially can be exploited as a tool to tune exciton-phonon coupling in nanocrystal heterostructures.
authors.affiliation: Nanochemistry Department, Istituto Italiano di Tecnologia , Via Morego 30, 16163 Genova, Italy.|Dipartimento di Chimica e Chimica Industriale, Università di Genova , Via Dodecaneso 31, 16146 Genova, Italy.
authors.forename: Mario
authors.initials: M
authors.lastname: Miscuglio
authors.affiliation: State Key Laboratory of Superlattices and Microstructures, Institute of Semiconductors, Chinese Academy of Sciences , Beijing 100083, China.
authors.forename: Miao-Ling
authors.initials: ML
authors.lastname: Lin
authors.affiliation: Nanochemistry Department, Istituto Italiano di Tecnologia , Via Morego 30, 16163 Genova, Italy.
authors.forename: Francesco
authors.initials: F
authors.lastname: Di Stasio
authors.affiliation: State Key Laboratory of Superlattices and Microstructures, Institute of Semiconductors, Chinese Academy of Sciences , Beijing 100083, China.
authors.forename: Ping-Heng
authors.initials: PH
authors.lastname: Tan
authors.affiliation: Nanochemistry Department, Istituto Italiano di Tecnologia , Via Morego 30, 16163 Genova, Italy.
authors.forename: Roman
authors.initials: R
authors.lastname: Krahne
keywords: Confined acoustic phonons; colloidal nanorod heterostructures; finite elements simulations; nonresonant Raman spectroscopy