Gradients of Rectification: Tuning Molecular Electronic Devices by the Controlled Use of Different‐Sized Diluents in Heterogeneous Self‐Assembled Monolayers

Kong, Gyu Don; Kim, Miso; Cho, Soo-Jin; Yoon, Ho‐Geun

doi:10.1002/anie.201604748

Cited by 81 publications

(74 citation statements)

References 31 publications

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“…35 The XPS and KPFM data show that the polarization of SAMs of S(CH 2 ) n CO 2 H·H 2 O translates into a lowering of frontier orbitals both from the increased electronegativity of the terminal CO 2 H groups and the increased work function, i.e., binding H 2 O lowers the absolute and relative energy of the LUMO. The direction of the rectification, J (+ V ) > J (− V ), implicates the LUMO as the dominant frontier orbital; 35,36 however, variable-temperature measurements reveal a lack of thermally activated processes (Figure 4e), thus we can exclude a tunneling-hopping mechanism. 37 Instead, we propose the mechanism shown in Figure 4, in which the binding of water to the carboxylic acid groups brings the LUMO sufficiently close to the Fermi level that its tail is brought into resonance with the bottom electrode at bias.…”

Section: Resultsmentioning

confidence: 87%

In-Place Modulation of Rectification in Tunneling Junctions Comprising Self-Assembled Monolayers

Kovalchuk

Qiu

et al. 2018

Nano Lett.

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This paper describes tunneling junctions comprising self-assembled monolayers that can be converted between resistor and diode functionality in-place. The rectification ratio is affected by the hydration of densely packed carboxylic acid groups at the interface between the top-contact and the monolayer. We studied this process by treatment with water and a water scavenger using three different top-contacts, eutectic Ga–In (EGaIn), conducting-probe atomic force microscopy (CP-AFM), and reduced graphene oxide (rGO), demonstrating that the phenomena is molecular in nature and is not platform-speciffc. We propose a mechanism in which the tunneling junctions convert to diode behavior through the lowering of the LUMO, which is suffcient to bring it close to resonance at positive bias, potentially assisted by a Stark shift. This shift in energy is supported by calculations and a change in polarization observed by X-ray photoelectron spectroscopy and Kelvin probe measurements. We demonstrate light-driven modulation using spiropyran as a photoacid, suggesting that any chemical process that is coupled to the release of small molecules that can tightly bind carboxylic acid groups can be used as an external stimulus to modulate rectification. The ability to convert a tunneling junction reversibly between a diode and a resistor via an effect that is intrinsic to the molecules in the junction extends the possible applications of Molecular Electronics to reconfigurable circuits and other new functionalities that do not have direct analogs in conventional semiconductor devices.

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Section: Resultsmentioning

confidence: 87%

In-Place Modulation of Rectification in Tunneling Junctions Comprising Self-Assembled Monolayers

Kovalchuk

Qiu

et al. 2018

Nano Lett.

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“…However, the room-temperature data are perfectly symmetric, and differential conductance plots ( Figure S10 ) are smooth and U-shaped, both of which strongly suggest nonresonant tunneling. Hopping processes arising from strong coupling to localized π-states and defects cause asymmetry 48 and negative curvature, 49 respectively.…”

Section: Resultsmentioning

confidence: 99%

Mixed Monolayers of Spiropyrans Maximize Tunneling Conductance Switching by Photoisomerization at the Molecule–Electrode Interface in EGaIn Junctions

et al. 2016

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This paper describes the photoinduced switching of conductance in tunneling junctions comprising self-assembled monolayers of a spiropyran moiety using eutectic Ga–In top contacts. Despite separation of the spiropyran unit from the electrode by a long alkyl ester chain, we observe an increase in the current density J of a factor of 35 at 1 V when the closed form is irradiated with UV light to induce the ring-opening reaction, one of the highest switching ratios reported for junctions incorporating self-assembled monolayers. The magnitude of switching of hexanethiol mixed monolayers was higher than that of pure spiropyran monolayers. The first switching event recovers 100% of the initial value of J and in the mixed-monolayers subsequent dampening is not the result of degradation of the monolayer. The observation of increased conductivity is supported by zero-bias DFT calculations showing a change in the localization of the density of states near the Fermi level as well as by simulated transmission spectra revealing positive resonances that broaden and shift toward the Fermi level in the open form.

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“…A clear correlation between breakdown voltage and the mechanical robustness of T4C4 would imply that mechanism 1 is dominant because the electrochemical window of T4C4 is much smaller than that of an alkanethiol. Extending the potential window in which a SAM can operate in a large-area junction is particularly relevant to molecule diodes 45 such as SAMs incorporating ferrocenyl, 46 , 47 bypyridyl, 48 , 49 pyrimydyl, 14 and fullerene 50 moieties because the degree of rectification tends to scale with bias and they function under bias in integrated circuits. 10 …”

Section: Resultsmentioning

confidence: 99%

Mechanically and Electrically Robust Self-Assembled Monolayers for Large-Area Tunneling Junctions

et al. 2017

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This paper examines the relationship between mechanical deformation and the electronic properties of self-assembled monolayers (SAMs) of the oligothiophene 4-([2,2′:5′,2″:5″,2‴-quaterthiophen]-5-yl)butane-1-thiol (T4C4) in tunneling junctions using conductive probe atomic force microscopy (CP-AFM) and eutectic Ga–In (EGaIn). We compared shifts in conductivity, transition voltages of T4C4 with increasing AFM tip loading force to alkanethiolates. While these shifts result from an increasing tilt angle from penetration of the SAM by the AFM tip for the latter, we ascribe them to distortions of the π system present in T4C4, which is more mechanically robust than alkanethiolates of comparable length; SAMs comprising T4C4 shows about five times higher Young’s modulus than alkanethiolates. Density functional theory calculations confirm that mechanical deformations shift the barrier height due to changes in the frontier orbitals caused by small rearrangements to the conformation of the quaterthiophene moiety. The mechanical robustness of T4C4 manifests as an increased tolerance to high bias in large-area EGaIn junctions suggesting that electrostatic pressure plays a significant role in the shorting of molecular junctions at high bias.

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Gradients of Rectification: Tuning Molecular Electronic Devices by the Controlled Use of Different‐Sized Diluents in Heterogeneous Self‐Assembled Monolayers

Cited by 81 publications

References 31 publications

In-Place Modulation of Rectification in Tunneling Junctions Comprising Self-Assembled Monolayers

In-Place Modulation of Rectification in Tunneling Junctions Comprising Self-Assembled Monolayers

Mixed Monolayers of Spiropyrans Maximize Tunneling Conductance Switching by Photoisomerization at the Molecule–Electrode Interface in EGaIn Junctions

Mechanically and Electrically Robust Self-Assembled Monolayers for Large-Area Tunneling Junctions

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