title: Ligand-induced dependence of charge transfer in nanotube-quantum dot heterostructures.
abstract: As a model system to probe ligand-dependent charge transfer in complex composite heterostructures, we fabricated double-walled carbon nanotube (DWNT)-CdSe quantum dot (QD) composites. Whereas the average diameter of the QDs probed was kept fixed at ∼4.1 nm and the nanotubes analyzed were similarly oxidatively processed, by contrast, the ligands used to mediate the covalent attachment between the QDs and DWNTs were systematically varied to include p-phenylenediamine (PPD), 2-aminoethanethiol (AET), and 4-aminothiophenol (ATP). Herein, we have put forth a unique compilation of complementary data from experiment and theory, including results from transmission electron microscopy (TEM), near-edge X-ray absorption fine structure (NEXAFS) spectroscopy, Raman spectroscopy, electrical transport measurements, and theoretical modeling studies, in order to fundamentally assess the nature of the charge transfer between CdSe QDs and DWNTs, as a function of the structure of various, intervening bridging ligand molecules. Specifically, we correlated evidence of charge transfer as manifested by changes and shifts associated with NEXAFS intensities, Raman peak positions, and threshold voltages both before and after CdSe QD deposition onto the underlying DWNT surface. Importantly, for the first time ever in these types of nanoscale composite systems, we have sought to use theoretical modeling to justify and account for our experimental results. Our overall data suggest that (i) QD coverage density on the DWNTs varies, based upon the different ligand pendant groups used and that (ii) the presence of a π-conjugated carbon framework within the ligands themselves coupled with the electron affinity of their pendant groups collectively play important roles in the resulting charge transfer from QDs to the underlying CNTs.
authors.affiliation: Department of Chemistry, State University of New York at Stony Brook, Stony Brook, NY 11794-3400, USA. stanislaus.wong@stonybrook.edu sswong@bnl.gov.
authors.forename: Lei
authors.initials: L
authors.lastname: Wang
authors.affiliation: Condensed Matter Physics and Materials Sciences Division, Brookhaven National Laboratory, Building 480, Upton, NY 11973, USA.
authors.forename: Jinkyu
authors.initials: J
authors.lastname: Han
authors.affiliation: Institute of Advanced Computational Science, State University of New York at Stony Brook, Stony Brook, NY 11794, USA.
authors.forename: Bryan
authors.initials: B
authors.lastname: Sundahl
authors.affiliation: Institute of Advanced Computational Science, State University of New York at Stony Brook, Stony Brook, NY 11794, USA.
authors.forename: Scott
authors.initials: S
authors.lastname: Thornton
authors.affiliation: Department of Electrical and Computer Engineering and Birck Nanotechnology Center, Purdue University, West Lafayette, Indiana 47907, USA.
authors.forename: Yuqi
authors.initials: Y
authors.lastname: Zhu
authors.affiliation: Department of Electrical and Computer Engineering and Birck Nanotechnology Center, Purdue University, West Lafayette, Indiana 47907, USA.
authors.forename: Ruiping
authors.initials: R
authors.lastname: Zhou
authors.affiliation: Material Measurement Laboratory, National Institute of Standards and Technology, Gaithersburg, Maryland 20889, USA.
authors.forename: Cherno
authors.initials: C
authors.lastname: Jaye
authors.affiliation: Department of Chemistry, State University of New York at Stony Brook, Stony Brook, NY 11794-3400, USA. stanislaus.wong@stonybrook.edu sswong@bnl.gov.
authors.forename: Haiqing
authors.initials: H
authors.lastname: Liu
authors.affiliation: School of Marine and Atmospheric Sciences, State University of New York at Stony Brook, Stony Brook, NY 11794-5000, USA.
authors.forename: Zhuo-Qun
authors.initials: ZQ
authors.lastname: Li
authors.affiliation: School of Marine and Atmospheric Sciences, State University of New York at Stony Brook, Stony Brook, NY 11794-5000, USA.
authors.forename: Gordon T
authors.initials: GT
authors.lastname: Taylor
authors.affiliation: Material Measurement Laboratory, National Institute of Standards and Technology, Gaithersburg, Maryland 20889, USA.
authors.forename: Daniel A
authors.initials: DA
authors.lastname: Fischer
authors.affiliation: Department of Electrical and Computer Engineering and Birck Nanotechnology Center, Purdue University, West Lafayette, Indiana 47907, USA.
authors.forename: Joerg
authors.initials: J
authors.lastname: Appenzeller
authors.affiliation: Institute of Advanced Computational Science, State University of New York at Stony Brook, Stony Brook, NY 11794, USA and Computational Science Center, Brookhaven National Laboratory, Upton, NY 11973, USA.
authors.forename: Robert J
authors.initials: RJ
authors.lastname: Harrison
authors.affiliation: Department of Chemistry, State University of New York at Stony Brook, Stony Brook, NY 11794-3400, USA. stanislaus.wong@stonybrook.edu sswong@bnl.gov and Condensed Matter Physics and Materials Sciences Division, Brookhaven National Laboratory, Building 480, Upton, NY 11973, USA.
authors.forename: Stanislaus S
authors.initials: SS
authors.lastname: Wong