Journal
JOURNAL OF THE AMERICAN CHEMICAL SOCIETY
Volume 143, Issue 4, Pages 2156-2163Publisher
AMER CHEMICAL SOC
DOI: 10.1021/jacs.0c12641
Keywords
-
Categories
Funding
- National Science Foundation (NSF) [CHE-18083681]
- Materials Research and Engineering Center (MRSEC) at Harvard University [DMR-1420570]
- National Science Foundation [ECS-0335765]
- Basic Science Research Program through the National Research Foundation of Korea (NRF)
- Ministry of Education of Korea [2018R1A6A3A03013079]
- NRF of Korea [NRF-2019R1-A2C2011003, NRF-2019R1A6A1A11044070]
- Future Research Grant (FRG) of Korea University
- National Research Foundation of Korea [2018R1A6A3A03013079, 2019R1A2C2011003] Funding Source: Korea Institute of Science & Technology Information (KISTI), National Science & Technology Information Service (NTIS)
Ask authors/readers for more resources
This paper investigates the rectification mechanism in molecular tunneling junctions based on alkanethiolates terminated by a bipyridine group complexed with different metal ions. The study shows that the rectification behavior is determined by the accessibility of molecular orbitals at different bias voltages. The difference in tunneling mechanism at negative bias causes the variation in rectification ratio between the two types of junctions.
This paper addresses the mechanism for rectification in molecular tunneling junctions based on alkanethiolates terminated by a bipyridine roup complexed with a metal ion, that , is, having the structure Au-TS-S(CH2)(11)BIPY-MCl2 (where M = Co or Cu) with a eutectic indium-gallium alloy top contact (EGaIn, 75.5% Ga 24.5% In). Here, Au-TS-S(CH2)(11)BIPY is a self-assembled monolayer (SAM) of an alkanethiolate with 4-methyl-2,2'-bipyridine (BIPY) head groups, on template-stripped gold (Au-TS). When the SAM is exposed to cobalt(II) chloride, SAMs of the form Au-TS-S(CH2)(11)BIPY-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) Au-TS-S(CH2)(11)BIPY-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) Au-TS-S(CH2)(11)BIPY-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.
Authors
I am an author on this paper
Click your name to claim this paper and add it to your profile.
Reviews
Recommended
No Data Available