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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 formore » our experimental results. Finally, 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 and the electron affinity of the pendant groups collectively play important roles in the resulting charge transfer from QDs to the underlying CNTs.« less

Authors:
 [1];  [2];  [3];  [3];  [4];  [4];  [5];  [1];  [6];  [6];  [5];  [4];  [7];  [8]
  1. Stony Brook Univ., NY (United States). Dept. of Chemistry
  2. Brookhaven National Lab. (BNL), Upton, NY (United States). Condensed Matter Physics and Materials Sciences Division
  3. State Univ. of New York (SUNY) at Stony Brook, Stony Brook, NY (United States). Inst. of Advanced Computational Science
  4. Purdue Univ., West Lafayette, IN (United States). Birck Nanotechnology Center, Dept. of Electrical and Computer Engineering
  5. National Inst. of Standards and Technology (NIST), Gaithersburg, MD (United States). Material Measurement Lab.
  6. State Univ. of New York (SUNY) at Stony Brook, Stony Brook, NY (United States). School of Marine and Atmospheric Sciences
  7. State Univ. of New York (SUNY) at Stony Brook, Stony Brook, NY (United States). Inst. of Advanced Computational Science; Brookhaven National Lab. (BNL), Upton, NY (United States). Computational Science Center
  8. Stony Brook Univ., NY (United States). Dept. of Chemistry; Brookhaven National Lab. (BNL), Upton, NY (United States). Condensed Matter Physics and Materials Sciences Division
Publication Date:
Research Org.:
Brookhaven National Laboratory (BNL), Upton, NY (United States)
Sponsoring Org.:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
OSTI Identifier:
1303000
Report Number(s):
BNL-112413-2016-JA
Journal ID: ISSN 2040-3364; NANOHL; R&D Project: PM037; KC0201030
Grant/Contract Number:
SC00112704; ACI-121664; OCE-1336724
Resource Type:
Journal Article: Accepted Manuscript
Journal Name:
Nanoscale
Additional Journal Information:
Journal Name: Nanoscale; Journal ID: ISSN 2040-3364
Publisher:
Royal Society of Chemistry
Country of Publication:
United States
Language:
English
Subject:
77 NANOSCIENCE AND NANOTECHNOLOGY; 36 MATERIALS SCIENCE; NEXAFS; theoretical modeling; charge transfer; CdSe QDs; DWNTs; ligands

Citation Formats

Wang, Lei, Han, Jinkyu, Sundahl, Bryan, Thornton, Scott, Zhu, Yuqi, Zhou, Ruiping, Jaye, Cherno, Liu, Haiqing, Li, Zhuo-Qun, Taylor, Gordon T., Fischer, Daniel A., Appenzeller, Joerg, Harrison, Robert J., and Wong, Stanislaus S. Ligand-induced dependence of charge transfer in nanotube–quantum dot heterostructures. United States: N. p., 2016. Web. doi:10.1039/C6NR03091B.
Wang, Lei, Han, Jinkyu, Sundahl, Bryan, Thornton, Scott, Zhu, Yuqi, Zhou, Ruiping, Jaye, Cherno, Liu, Haiqing, Li, Zhuo-Qun, Taylor, Gordon T., Fischer, Daniel A., Appenzeller, Joerg, Harrison, Robert J., & Wong, Stanislaus S. Ligand-induced dependence of charge transfer in nanotube–quantum dot heterostructures. United States. doi:10.1039/C6NR03091B.
Wang, Lei, Han, Jinkyu, Sundahl, Bryan, Thornton, Scott, Zhu, Yuqi, Zhou, Ruiping, Jaye, Cherno, Liu, Haiqing, Li, Zhuo-Qun, Taylor, Gordon T., Fischer, Daniel A., Appenzeller, Joerg, Harrison, Robert J., and Wong, Stanislaus S. Fri . "Ligand-induced dependence of charge transfer in nanotube–quantum dot heterostructures". United States. doi:10.1039/C6NR03091B. https://www.osti.gov/servlets/purl/1303000.
@article{osti_1303000,
title = {Ligand-induced dependence of charge transfer in nanotube–quantum dot heterostructures},
author = {Wang, Lei and Han, Jinkyu and Sundahl, Bryan and Thornton, Scott and Zhu, Yuqi and Zhou, Ruiping and Jaye, Cherno and Liu, Haiqing and Li, Zhuo-Qun and Taylor, Gordon T. and Fischer, Daniel A. and Appenzeller, Joerg and Harrison, Robert J. and Wong, Stanislaus S.},
abstractNote = {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. Finally, 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 and the electron affinity of the pendant groups collectively play important roles in the resulting charge transfer from QDs to the underlying CNTs.},
doi = {10.1039/C6NR03091B},
journal = {Nanoscale},
number = ,
volume = ,
place = {United States},
year = {Fri Jul 01 00:00:00 EDT 2016},
month = {Fri Jul 01 00:00:00 EDT 2016}
}

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Cited by: 6works
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  • As a model system for understanding charge transfer in novel architectural designs for solar cells, double-walled carbon nanotube (DWNT)–CdSe quantum dot (QD) (QDs with average diameters of 2.3, 3.0, and 4.1 nm) heterostructures have been fabricated. The individual nanoscale building blocks were successfully attached and combined using a hole-trapping thiol linker molecule, i.e., 4-mercaptophenol (MTH), through a facile, noncovalent π–π stacking attachment strategy. Transmission electron microscopy confirmed the attachment of QDs onto the external surfaces of the DWNTs. We herein demonstrate a meaningful and unique combination of near-edge X-ray absorption fine structure (NEXAFS) and Raman spectroscopies bolstered by complementary electricalmore » transport measurements in order to elucidate the synergistic interactions between CdSe QDs and DWNTs, which are facilitated by the bridging MTH molecules that can scavenge photoinduced holes and potentially mediate electron redistribution between the conduction bands in CdSe QDs and the C 2p-derived states of the DWNTs. Specifically, we correlated evidence of charge transfer as manifested by (i) changes in the NEXAFS intensities of π* resonance in the C K-edge and Cd M3-edge spectra, (ii) a perceptible outer tube G-band downshift in frequency in Raman spectra, as well as (iii) alterations in the threshold characteristics present in transport data as a function of CdSe QD deposition onto the DWNT surface. Furthermore, the separate effects of (i) varying QD sizes and (ii) QD coverage densities on the electron transfer were independently studied.« less
  • As a model system for understanding charge transfer in novel architectural designs for solar cells, double-walled carbon nanotube (DWNT)–CdSe quantum dot (QD) (QDs with average diameters of 2.3, 3.0, and 4.1 nm) heterostructures have been fabricated. The individual nanoscale building blocks were successfully attached and combined using a hole-trapping thiol linker molecule, i.e., 4-mercaptophenol (MTH), through a facile, noncovalent π–π stacking attachment strategy. Transmission electron microscopy confirmed the attachment of QDs onto the external surfaces of the DWNTs. We herein demonstrate a meaningful and unique combination of near-edge X-ray absorption fine structure (NEXAFS) and Raman spectroscopies bolstered by complementary electricalmore » transport measurements in order to elucidate the synergistic interactions between CdSe QDs and DWNTs, which are facilitated by the bridging MTH molecules that can scavenge photoinduced holes and potentially mediate electron redistribution between the conduction bands in CdSe QDs and the C 2p-derived states of the DWNTs. Specifically, we correlated evidence of charge transfer as manifested by (i) changes in the NEXAFS intensities of π* resonance in the C K-edge and Cd M3-edge spectra, (ii) a perceptible outer tube G-band downshift in frequency in Raman spectra, as well as (iii) alterations in the threshold characteristics present in transport data as a function of CdSe QD deposition onto the DWNT surface. Furthermore, the separate effects of (i) varying QD sizes and (ii) QD coverage densities on the electron transfer were independently studied.« less
    Cited by 6
  • For solar energy conversion, not only must a semiconductor absorb incident solar radiation efficiently but also its photoexcited electron—hole pairs must further be separated and transported across interfaces. Charge transfer across interfaces requires consideration of both thermodynamic driving forces as well as the competing kinetics of multiple possible transfer, cooling, and recombination pathways. In this work, we demonstrate a novel strategy for extracting holes from photoexcited CdSe quantum dots (QDs) based on interfacing with β-Pb 0.33V 2O 5 nanowires that have strategically positioned midgap states derived from the intercalating Pb 2+ ions. Unlike midgap states derived from defects or dopants,more » the states utilized here are derived from the intrinsic crystal structure and are thus homogeneously distributed across the material. CdSe/β-Pb 0.33V 2O 5 heterostructures were assembled using two distinct methods: successive ionic layer adsorption and reaction (SILAR) and linker-assisted assembly (LAA). Transient absorption spectroscopy measurements indicate that, for both types of heterostructures, photoexcitation of CdSe QDs was followed by the transfer of electrons to the conduction band of β-Pb 0.33V 2O 5 nanowires and holes to the midgap states of β-Pb 0.33V 2O 5 nanowires. Holes were transferred on time scales less than 1 ps, whereas electrons were transferred more slowly on time scales of ~2 ps. In contrast, for analogous heterostructures consisting of CdSe QDs interfaced with V 2O 5 nanowires (wherein midgap states are absent), only electron transfer was observed. Interestingly, electron transfer was readily achieved for CdSe QDs interfaced with V 2O 5 nanowires by the SILAR method; however, for interfaces incorporating molecular linkers, electron transfer was observed only upon excitation at energies substantially greater than the bandgap absorption threshold of CdSe. Furthermore, transient absorbance decay traces reveal longer excited-state lifetimes (1–3 μs) for CdSe/β-Pb 0.33V 2O 5 heterostructures relative to bare β-Pb 0.33V 2O 5 nanowires (0.2 to 0.6 μs); the difference is attributed to surface passivation of intrinsic surface defects in β-Pb 0.33V 2O 5 upon interfacing with CdSe.« less
  • Here, semiconductor heterostructures for solar energy conversion interface light-harvesting semiconductor nanoparticles with wide-band-gap semiconductors that serve as charge acceptors. In such heterostructures, the kinetics of charge separation depend on the thermodynamic driving force, which is dictated by energetic offsets across the interface. A recently developed promising platform interfaces semiconductor quantum dots (QDs) with ternary vanadium oxides that have characteristic midgap states situated between the valence and conduction bands. In this work, we have prepared CdS/β-Pb 0.33V 2O 5 heterostructures by both linker-assisted assembly and surface precipitation and contrasted these materials with CdSe/β-Pb 0.33V 2O 5 heterostructures prepared by the samemore » methods. Increased valence-band (VB) edge onsets in X-ray photoelectron spectra for CdS/β-Pb 0.33V 2O 5 heterostructures relative to CdSe/β-Pb 0.33V 2O 5 heterostructures suggest a positive shift in the VB edge potential and, therefore, an increased driving force for the photoinduced transfer of holes to the midgap state of β-Pb 0.33V 2O 5. This approach facilitates a ca. 0.40 eV decrease in the thermodynamic barrier for hole injection from the VB edge of QDs suggesting an important design parameter. Transient absorption spectroscopy experiments provide direct evidence of hole transfer from photoexcited CdS QDs to the midgap states of β-Pb 0.33V 2O 5 NWs, along with electron transfer into the conduction band of the β-Pb 0.33V 2O 5 NWs. Hole transfer is substantially faster and occurs at <1-ps time scales, whereas completion of electron transfer requires 5—30 ps depending on the nature of the interface. The differentiated time scales of electron and hole transfer, which are furthermore tunable as a function of the mode of attachment of QDs to NWs, provide a vital design tool for designing architectures for solar energy conversion. More generally, the approach developed here suggests that interfacing semiconductor QDs with transition-metal oxide NWs exhibiting intercalative midgap states yields a versatile platform wherein the thermodynamics and kinetics of charge transfer can be systematically modulated to improve the efficiency of charge separation across interfaces.« less