Rectification in Molecular Tunneling Junctions Based on Alkanethiolates with Bipyridine-Metal Complexes

Junwoo Park; Lee Belding; Li Yuan; Maral P.S. Mousavi; Samuel E. Root; Hyo Jae Yoon; George M. Whitesides

doi:10.1021/jacs.0c12641

Rectification in Molecular Tunneling Junctions Based on Alkanethiolates with Bipyridine-Metal Complexes

Junwoo Park, Lee Belding, Li Yuan, Maral P.S. Mousavi, Samuel E. Root, Hyo Jae Yoon, George M. Whitesides

Department of Chemistry

Research output: Contribution to journal › Article › peer-review

34 Citations (Scopus)

Abstract

This paper addresses the mechanism for rectification in molecular tunneling junctions based on alkanethiolates terminated by a bipyridine group complexed with a metal ion, that is, having the structure AuTS-S(CH2)11BIPY-MCl2 (where M = Co or Cu) with a eutectic indium-gallium alloy top contact (EGaIn, 75.5% Ga 24.5% In). Here, AuTS-S(CH2)11BIPY is a self-assembled monolayer (SAM) of an alkanethiolate with 4-methyl-2,2′-bipyridine (BIPY) head groups, on template-stripped gold (AuTS). When the SAM is exposed to cobalt(II) chloride, SAMs of the form AuTS-S(CH2)11BIPY-CoCl2 rectify current with a rectification ratio of r+ = 82.0 at ±1.0 V. The rectification, however, disappears (r+ = 1.0) when the SAM is exposed to copper(II) chloride instead of cobalt. We draw the following conclusions from our experimental results: (i) AuTS-S(CH2)11BIPY-CoCl2 junctions rectify current because only at positive bias (+1.0 V) is there an accessible molecular orbital (the LUMO) on the BIPY-CoCl2 moiety, while at negative bias (-1.0 V), neither the energy level of the HOMO or the LUMO lies between the Fermi levels of the electrodes. (ii) AuTS-S(CH2)11BIPY-CuCl2 junctions do not rectify current because there is an accessible molecular orbital on the BIPY-CuCl2 moiety at both negative and positive bias (the HOMO is accessible at negative bias, and the LUMO is accessible at positive bias). The difference in accessibility of the HOMO levels at -1.0 V causes charge transfer - at negative bias - to take place via Fowler-Nordheim tunneling in BIPY-CoCl2 junctions, and via direct tunneling in BIPY-CuCl2 junctions. This difference in tunneling mechanism at negative bias is the origin of the difference in rectification ratio between BIPY-CoCl2 and BIPY-CuCl2 junctions.

Original language	English
Pages (from-to)	2156-2163
Number of pages	8
Journal	Journal of the American Chemical Society
Volume	143
Issue number	4
DOIs	https://doi.org/10.1021/jacs.0c12641
Publication status	Published - 2021 Feb 3

Bibliographical note

Funding Information:
This work was supported by the National Science Foundation (NSF, CHE-18083681). We acknowledge the Materials Research and Engineering Center (MRSEC, DMR-1420570) at Harvard University for supporting XPS and UPS measurements, and providing access to the clean-room facilities. Sample characterization was performed in part at the Center for Nanoscale Systems (CNS) at Harvard University, a member of the National Nanotechnology Infrastructure Network (NNIN), which is supported by the National Science Foundation (ECS-0335765). J.P. acknowledges fellowship support from the Basic Science Research Program through the National Research Foundation of Korea (NRF), funded by the Ministry of Education of Korea (2018R1A6A3A03013079). HJY acknowledges the support from the NRF of Korea (NRF-2019R1A2C2011003, NRF-2019R1A6A1A11044070) and the Future Research Grant (FRG) of Korea University. We thank Christian A. Nijhuis (Department of Chemistry, National University of Singapore), Victoria E. Campbell, and Philipp Rothemund for useful discussion and input. J.P. and G.M.W. conceived the research and designed the experiments. J.P., L.B., L.Y., M.P.S.M., S.E.R. and H.J.Y. performed the experiments and analyzed the data. L.B. performed the computational simulations. J.P., L.B., S.E.R., and G.M.W. wrote the manuscript.

Publisher Copyright:
© 2021 American Chemical Society.

ASJC Scopus subject areas

Catalysis
Chemistry(all)
Biochemistry
Colloid and Surface Chemistry

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@article{d30689f4625d4ede8591e022d5861930,

title = "Rectification in Molecular Tunneling Junctions Based on Alkanethiolates with Bipyridine-Metal Complexes",

abstract = "This paper addresses the mechanism for rectification in molecular tunneling junctions based on alkanethiolates terminated by a bipyridine group complexed with a metal ion, that is, having the structure AuTS-S(CH2)11BIPY-MCl2 (where M = Co or Cu) with a eutectic indium-gallium alloy top contact (EGaIn, 75.5% Ga 24.5% In). Here, AuTS-S(CH2)11BIPY is a self-assembled monolayer (SAM) of an alkanethiolate with 4-methyl-2,2′-bipyridine (BIPY) head groups, on template-stripped gold (AuTS). When the SAM is exposed to cobalt(II) chloride, SAMs of the form AuTS-S(CH2)11BIPY-CoCl2 rectify current with a rectification ratio of r+ = 82.0 at ±1.0 V. The rectification, however, disappears (r+ = 1.0) when the SAM is exposed to copper(II) chloride instead of cobalt. We draw the following conclusions from our experimental results: (i) AuTS-S(CH2)11BIPY-CoCl2 junctions rectify current because only at positive bias (+1.0 V) is there an accessible molecular orbital (the LUMO) on the BIPY-CoCl2 moiety, while at negative bias (-1.0 V), neither the energy level of the HOMO or the LUMO lies between the Fermi levels of the electrodes. (ii) AuTS-S(CH2)11BIPY-CuCl2 junctions do not rectify current because there is an accessible molecular orbital on the BIPY-CuCl2 moiety at both negative and positive bias (the HOMO is accessible at negative bias, and the LUMO is accessible at positive bias). The difference in accessibility of the HOMO levels at -1.0 V causes charge transfer - at negative bias - to take place via Fowler-Nordheim tunneling in BIPY-CoCl2 junctions, and via direct tunneling in BIPY-CuCl2 junctions. This difference in tunneling mechanism at negative bias is the origin of the difference in rectification ratio between BIPY-CoCl2 and BIPY-CuCl2 junctions. ",

author = "Junwoo Park and Lee Belding and Li Yuan and Mousavi, {Maral P.S.} and Root, {Samuel E.} and Yoon, {Hyo Jae} and Whitesides, {George M.}",

note = "Funding Information: This work was supported by the National Science Foundation (NSF, CHE-18083681). We acknowledge the Materials Research and Engineering Center (MRSEC, DMR-1420570) at Harvard University for supporting XPS and UPS measurements, and providing access to the clean-room facilities. Sample characterization was performed in part at the Center for Nanoscale Systems (CNS) at Harvard University, a member of the National Nanotechnology Infrastructure Network (NNIN), which is supported by the National Science Foundation (ECS-0335765). J.P. acknowledges fellowship support from the Basic Science Research Program through the National Research Foundation of Korea (NRF), funded by the Ministry of Education of Korea (2018R1A6A3A03013079). HJY acknowledges the support from the NRF of Korea (NRF-2019R1A2C2011003, NRF-2019R1A6A1A11044070) and the Future Research Grant (FRG) of Korea University. We thank Christian A. Nijhuis (Department of Chemistry, National University of Singapore), Victoria E. Campbell, and Philipp Rothemund for useful discussion and input. J.P. and G.M.W. conceived the research and designed the experiments. J.P., L.B., L.Y., M.P.S.M., S.E.R. and H.J.Y. performed the experiments and analyzed the data. L.B. performed the computational simulations. J.P., L.B., S.E.R., and G.M.W. wrote the manuscript. Publisher Copyright: {\textcopyright} 2021 American Chemical Society.",

year = "2021",

month = feb,

day = "3",

doi = "10.1021/jacs.0c12641",

language = "English",

volume = "143",

pages = "2156--2163",

journal = "Journal of the American Chemical Society",

issn = "0002-7863",

publisher = "American Chemical Society",

number = "4",

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TY - JOUR

T1 - Rectification in Molecular Tunneling Junctions Based on Alkanethiolates with Bipyridine-Metal Complexes

AU - Park, Junwoo

AU - Belding, Lee

AU - Yuan, Li

AU - Mousavi, Maral P.S.

AU - Root, Samuel E.

AU - Yoon, Hyo Jae

AU - Whitesides, George M.

N1 - Funding Information: This work was supported by the National Science Foundation (NSF, CHE-18083681). We acknowledge the Materials Research and Engineering Center (MRSEC, DMR-1420570) at Harvard University for supporting XPS and UPS measurements, and providing access to the clean-room facilities. Sample characterization was performed in part at the Center for Nanoscale Systems (CNS) at Harvard University, a member of the National Nanotechnology Infrastructure Network (NNIN), which is supported by the National Science Foundation (ECS-0335765). J.P. acknowledges fellowship support from the Basic Science Research Program through the National Research Foundation of Korea (NRF), funded by the Ministry of Education of Korea (2018R1A6A3A03013079). HJY acknowledges the support from the NRF of Korea (NRF-2019R1A2C2011003, NRF-2019R1A6A1A11044070) and the Future Research Grant (FRG) of Korea University. We thank Christian A. Nijhuis (Department of Chemistry, National University of Singapore), Victoria E. Campbell, and Philipp Rothemund for useful discussion and input. J.P. and G.M.W. conceived the research and designed the experiments. J.P., L.B., L.Y., M.P.S.M., S.E.R. and H.J.Y. performed the experiments and analyzed the data. L.B. performed the computational simulations. J.P., L.B., S.E.R., and G.M.W. wrote the manuscript. Publisher Copyright: © 2021 American Chemical Society.

PY - 2021/2/3

Y1 - 2021/2/3

N2 - This paper addresses the mechanism for rectification in molecular tunneling junctions based on alkanethiolates terminated by a bipyridine group complexed with a metal ion, that is, having the structure AuTS-S(CH2)11BIPY-MCl2 (where M = Co or Cu) with a eutectic indium-gallium alloy top contact (EGaIn, 75.5% Ga 24.5% In). Here, AuTS-S(CH2)11BIPY is a self-assembled monolayer (SAM) of an alkanethiolate with 4-methyl-2,2′-bipyridine (BIPY) head groups, on template-stripped gold (AuTS). When the SAM is exposed to cobalt(II) chloride, SAMs of the form AuTS-S(CH2)11BIPY-CoCl2 rectify current with a rectification ratio of r+ = 82.0 at ±1.0 V. The rectification, however, disappears (r+ = 1.0) when the SAM is exposed to copper(II) chloride instead of cobalt. We draw the following conclusions from our experimental results: (i) AuTS-S(CH2)11BIPY-CoCl2 junctions rectify current because only at positive bias (+1.0 V) is there an accessible molecular orbital (the LUMO) on the BIPY-CoCl2 moiety, while at negative bias (-1.0 V), neither the energy level of the HOMO or the LUMO lies between the Fermi levels of the electrodes. (ii) AuTS-S(CH2)11BIPY-CuCl2 junctions do not rectify current because there is an accessible molecular orbital on the BIPY-CuCl2 moiety at both negative and positive bias (the HOMO is accessible at negative bias, and the LUMO is accessible at positive bias). The difference in accessibility of the HOMO levels at -1.0 V causes charge transfer - at negative bias - to take place via Fowler-Nordheim tunneling in BIPY-CoCl2 junctions, and via direct tunneling in BIPY-CuCl2 junctions. This difference in tunneling mechanism at negative bias is the origin of the difference in rectification ratio between BIPY-CoCl2 and BIPY-CuCl2 junctions.

AB - This paper addresses the mechanism for rectification in molecular tunneling junctions based on alkanethiolates terminated by a bipyridine group complexed with a metal ion, that is, having the structure AuTS-S(CH2)11BIPY-MCl2 (where M = Co or Cu) with a eutectic indium-gallium alloy top contact (EGaIn, 75.5% Ga 24.5% In). Here, AuTS-S(CH2)11BIPY is a self-assembled monolayer (SAM) of an alkanethiolate with 4-methyl-2,2′-bipyridine (BIPY) head groups, on template-stripped gold (AuTS). When the SAM is exposed to cobalt(II) chloride, SAMs of the form AuTS-S(CH2)11BIPY-CoCl2 rectify current with a rectification ratio of r+ = 82.0 at ±1.0 V. The rectification, however, disappears (r+ = 1.0) when the SAM is exposed to copper(II) chloride instead of cobalt. We draw the following conclusions from our experimental results: (i) AuTS-S(CH2)11BIPY-CoCl2 junctions rectify current because only at positive bias (+1.0 V) is there an accessible molecular orbital (the LUMO) on the BIPY-CoCl2 moiety, while at negative bias (-1.0 V), neither the energy level of the HOMO or the LUMO lies between the Fermi levels of the electrodes. (ii) AuTS-S(CH2)11BIPY-CuCl2 junctions do not rectify current because there is an accessible molecular orbital on the BIPY-CuCl2 moiety at both negative and positive bias (the HOMO is accessible at negative bias, and the LUMO is accessible at positive bias). The difference in accessibility of the HOMO levels at -1.0 V causes charge transfer - at negative bias - to take place via Fowler-Nordheim tunneling in BIPY-CoCl2 junctions, and via direct tunneling in BIPY-CuCl2 junctions. This difference in tunneling mechanism at negative bias is the origin of the difference in rectification ratio between BIPY-CoCl2 and BIPY-CuCl2 junctions.

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U2 - 10.1021/jacs.0c12641

DO - 10.1021/jacs.0c12641

M3 - Article

C2 - 33480255

AN - SCOPUS:85100193153

SN - 0002-7863

VL - 143

SP - 2156

EP - 2163

JO - Journal of the American Chemical Society

JF - Journal of the American Chemical Society

IS - 4

ER -

Rectification in Molecular Tunneling Junctions Based on Alkanethiolates with Bipyridine-Metal Complexes

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