Two Different Length-Dependent Regimes in Thermoelectric Large-Area Junctions of <i>n</i>-Alkanethiolates

Park, Sohyun; Cho, Nayoung; Yoon, Ho‐Geun

doi:10.1021/acs.chemmater.9b02461

Cited by 33 publications

(61 citation statements)

References 55 publications

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“…Using eq 3, we further examined the PF of one molecule thick organic films that have the conjugated or nonconjugated backbones: phenylene ( 1 , 2 (24)), n -alkane ( 3 , 4 ), 35 thiophene ( 5 – 6 , 50 7 , 51 9 52 ), and diketopyrrolopyrrole (DPP; 8 ) 53 in Figure 4a. β for these molecules has been experimentally determined in the literature, and we used these values for simulating PF values.…”

Section: Resultsmentioning

confidence: 99%

“…For the sake of simplicity, we also assumed that J 0 and S C for the molecules 2 – 9 are the same as those for molecules 1 ; that is, the PF is measured in the same junction platform, allowing direct comparison of PF values between the molecules. Because there is a difference in β S between short and long n -alkanethiolates, 35 short ( 3 ) and long ( 4 ) n -alkanethiolates were separately considered.…”

Section: Resultsmentioning

confidence: 99%

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Power Factor of One Molecule Thick Films and Length Dependence

2019

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There is a rapidly increasing interest in organic thin film thermoelectrics. However, the power factor of one molecule thick organic film, the self-assembled monolayer (SAM), has not yet been determined. This study describes the experimental determination of the power factor in SAMs and its length dependence at an atomic level. As a proof-of-concept, SAMs composed of n-alkanethiolates and oligophenylenethiolates of different lengths are focused. These SAMs were electrically and thermoelectrically characterized on an identical junction platform using a liquid metal top-electrode, allowing the straightforward estimation of the power factor of the monolayers. The results show that the power factor of the alkyl SAMs ranged from 2.0 × 10–8 to 8.0 × 10–12 μW m–1 K–2 and exhibited significant negative length dependence, whereas the conductivity and thermopower of the conjugated SAMs are the two opposing factors that balance the power factor upon an increase in molecular length, exhibiting a maximum power factor of 3.6 × 10–8 μW m–1 K–2. Once correction factors about the ratio of effective contact area to geometrical contact area are considered, the values of power factors can be increased by several orders of magnitude. With a newly derived parametric semiempirical model describing the length dependence of the power factor, it is investigated that one molecule thick films thinner than 10 nm composed of thiophene units can yield power factors rivaling those of famed organic thermoelectric materials based on poly(3,4-ethylenedioxythiophene)/polystyrenesulfonate (PEDOT/PSS) and polyaniline/graphene/double-walled carbon nanotube. Furthermore, how the transition of the transport regime from tunneling to hopping as molecules become long affects power factors is examined.

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Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

Power Factor of One Molecule Thick Films and Length Dependence

2019

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“…Such a transition in the slope was consistent with the trend of Au/SC n SAM. [5] 2. SLG on Cu foil exhibited WF of 4.5 eV, and, upon SAM formation, it decreased to 3.8 eV (see the Supporting Information for UPS spectra and analysis), which was consistent with previously reported WF of organic-doped graphene.…”

Section: Enhanced S and Its Length Dependencementioning

confidence: 99%

Enhanced Thermopower of Saturated Molecules by Noncovalent Anchor‐Induced Electron Doping of Single‐Layer Graphene Electrode

Park

Kim

et al. 2021

Advanced Materials

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Enhancing thermopower is a key goal in organic and molecular thermoelectrics. Herein, it is shown that introducing noncovalent contact with a single-layer graphene (SLG) electrode improves the thermopower of saturated molecules as compared to the traditional gold-thiolate covalent contact. Thermoelectric junction measurements with a liquid-metal technique reveal that the value of Seebeck coefficient in large-area junctions based on n-alkylamine self-assembled monolayers (SAMs) on SLG is increased up to fivefold compared to the analogous junction based on n-alkanethiolate SAMs on gold. Experiments with Raman spectroscopy and field-effect transistor analysis indicate that such enhancements benefit from the creation of new in-gap states and electron doping through noncovalent interaction between the amine anchor and the SLG electrode, which leads to a reduced energy offset between the Fermi level and the transport channel. This work demonstrates that control of interfacial bonding nature in molecular junctions improves the Seebeck effect in saturated molecules.

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“…The authors also investigated thermoelectric properties of the NHC SAMs in the identical junction 18,19 . As the temperature differential applied to the junction was increased (Δ T = 2, 4, 6 K), the thermoelectric voltage (Δ V ) was increased toward negative direction (Figure 9(e)).…”

Section: Molecular Electronicsmentioning

confidence: 99%

“…is an good example that demonstrates the advantage of NHC anchor for constructing a robust molecular device; the NHC‐based molecular device remained nearly undamaged even upon heating at 120°C. Fourth, thiol anchors have been widely used in molecular thermoelectrics, which aims to understand thermoelectric properties of individual molecules 18–20,28 . The delicate feature of thiol anchor limited the available temperature range for the study of molecular thermoelectrics 29 .…”

Section: Concluding Remarks and Perspectivesmentioning

confidence: 99%

N‐Heterocyclic Carbene Anchors in Electronics Applications

Kang

Byeon

Yoon

2021

Bulletin Korean Chem Soc

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Since the first demonstration of chemisorption of N-heterocyclic carbene (NHC) on a gold substrate by Weidner and Siemeling in 2011, NHCs for anchors to deposit molecules on metallic surfaces are gathering increasing attention in academic research. The covalent chemistry of divalent carbenic C atom in NHCs with coinage metal substates can overcome the limitations that traditional thiol anchors have encountered. This review covers recent advances on NHC anchor-based molecular devices for electronics applications through the following stepwise approach. (1) The background of covalent bonding of NHC with coinage metals is briefly introduced. (2) Next, a comprehensive summary about functions of NHC anchor-based molecular devices under electric fields is provided. (3) Last, we wrap up this review, discussing future challenges and perspectives.

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Two Different Length-Dependent Regimes in Thermoelectric Large-Area Junctions of n-Alkanethiolates

Cited by 33 publications

References 55 publications

Power Factor of One Molecule Thick Films and Length Dependence

Power Factor of One Molecule Thick Films and Length Dependence

Enhanced Thermopower of Saturated Molecules by Noncovalent Anchor‐Induced Electron Doping of Single‐Layer Graphene Electrode

N‐Heterocyclic Carbene Anchors in Electronics Applications

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