Large Spatially Resolved Rectification in a Donor–Acceptor Molecular Heterojunction

Smerdon, J. A.; Giebink, Noel C.; Guisinger, Nathan P.; Darancet, Pierre; Guest, Jeffrey R.

doi:10.1021/acs.nanolett.6b00171

Cited by 22 publications

(26 citation statements)

References 37 publications

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“…This behavior was inferred to a Fermi level pinning effect implying that the hybridization of the orbitals at the interface pinpoints the energy of the HOMO level; this pinning is induced by the appearance of an increased charge transfer (and hence increased interface dipole) from the metal to the molecule in the junction when the HOMO level in the isolated molecule gets increasingly deeper. Such pinning effects have also been recently exploited to design model molecular rectifiers with high rectification ratios both theoretically, and experimentally . A similar HOMO alignment was also calculated for biphenyl derivatives chemisorbed via sulfur on gold when introducing an electron accepting (nitrile) or electron donating (amino) substituent on the terminal carbon atom, although the pinning mechanism is different here; indeed, when considering an infinite layer of neutral and asymmetric molecules, a different ionization potential is computed in the left side versus right side of the system because the vacuum level shifts are different on the two sides.…”

Section: Introductionmentioning

confidence: 89%

Energy Level Alignment at Interfaces Between Au (111) and Thiolated Oligophenylenes of Increasing Chain Size: Theoretical Evidence of Pinning Effects

Diez‐Cabanes

Rodríguez‐González

Osella

et al. 2018

Advcd Theory and Sims

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We present a detailed theoretical characterization of the energetic alignment between the HOMO level of a series of thiolated oligophenylenes of increasing chain size, and the Fermi level of gold electrodes, using density functional theory (DFT) calculations for molecular self-assembled monolayers (SAMs) chemisorbed on an Au (111) surface, and the nonequilibrium Green's function (NEGF) formalism coupled to DFT for single molecule junctions. The additional role of the dynamic electronic polarization effects neglected in standard DFT calculations is also discussed. Interestingly, whereas the HOMO energy varies significantly among the unsubstituted oligomers in the gas phase, their alignment with respect to the Fermi level of the electrode is almost insensitive to chain size upon chemisorption, thus pointing to a strong pinning effect. The energy at which the HOMO is pinned strongly depends on the degree of interfacial hybridization, and hence on the contact geometry, as well as on the degree of surface coverage although a different mechanism enters into play.anchoring unit. Over the years, a large body of knowledge has been accumulated on the morphologies of such SAMs and on structure-property relationships for the work function shifts [3,4] ; in molecular electronics, many theoretical and experimental studies have focused on the changes in the transmission spectra and I/V characteristics when elongating the size of conjugated oligomers. [5][6][7] In contrast, less attention has been paid to structure-property relationships driving the alignment of the frontier electronic levels with respect to the Fermi level of the metallic electrodes; this energy offset can be deduced by ultraviolet photoelectron spectroscopy (UPS) measurements, [8,9] estimated from I/V characteristics of molecular junctions by using simple analytical models, [8,[10][11][12] or measured photocurrent spectra. [13] The alignment of the HOMO is clearly a key quantity in SAMs, providing electronic levels that favor charge injection in organic layers or in molecular junctions.Theory can prove useful in this context to shed light on this issue, even though it remains extremely challenging to predict the Fermi level alignment quantitatively via first-principles calculations, typically based on density functional theory (DFT). [14][15][16][17][18] This is due to the fact that the ionization potential/electron affinity (IP/EA) of SAM-forming molecules attached to metallic electrodes is governed by several effects not present for the isolated molecules: (i) the electronic polarization of the metal (i.e., image effects) and of the neighboring molecules in presence of a net charge, that both lower the IP and increase the EA of the molecules (i.e., stabilize the formation of a positive charge or negative charge on the molecules); these effects are neglected when performing standard DFT calculations on neutral systems; (ii) the hybridization of the orbitals of the anchoring group with the orbitals of the metallic atoms and the resulting charge reorganization ...

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Section: Introductionmentioning

confidence: 89%

Energy Level Alignment at Interfaces Between Au (111) and Thiolated Oligophenylenes of Increasing Chain Size: Theoretical Evidence of Pinning Effects

Diez‐Cabanes

Rodríguez‐González

Osella

et al. 2018

Advcd Theory and Sims

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“…11,12 While the behavior of heterojunctions in macroscopic semiconductor crystals has been extensively studied, 13 heterojunction behavior in molecular nanostructures is not as well understood. [14][15][16][17] Bottom-up GNR heterojunctions have previously been fabricated by an approach that combines two different molecular precursor types, thus yielding either impurity-modulated 18 or widthmodulated 19 GNR heterojunctions. This fabrication method, however, depends on the random process of precursor self-assembly and does not allow heterojunction fabrication or modification after a GNR has been synthesized.…”

Section: Introductionmentioning

confidence: 99%

Atomically precise graphene nanoribbon heterojunctions from a single molecular precursor

et al. 2017

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TitleAtomically precise graphene nanoribbon heterojunctions from a single molecular precursor AbstractThe rational bottom-up synthesis of atomically defined graphene nanoribbon (GNR)heterojunctions represents a key enabling technology for the design of nanoscale electronic devices. Synthetic strategies have thus far relied on the random copolymerization of two electronically distinctive molecular precursors to yield a segmented band structure within a GNR. Here we report the fabrication and electronic characterization of atomically precise GNR heterojunctions prepared through a late-stage functionalization of chevron GNRs obtained from a single precursor that features fluorenone substituents along the convex edges. Excitation of the GNR induces cleavage of sacrificial carbonyl groups at the GNR edge, thus giving rise to atomically well-defined heterojunctions comprised of segments of fluorenone GNR and unfunctionalized chevron GNR. The structure of fluorenone/unfunctionalized GNR heterojunctions was characterized using bond-resolved STM (BRSTM) which enables chemical bonds to be imaged via STM at T = 4.5 K. Scanning tunneling spectroscopy (STS) reveals that the band alignment across the interface yields a staggered gap Type II heterojunction and is consistent with first-principles calculations. Detailed spectroscopic and theoretical studies reveal that the band realignment at the interface between fluorenone and unfunctionalized chevron GNRs proceeds over a distance less than 1nm, leading to extremely large effective fields.

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“…1 Such low rectification is probably better termed asymmetry (of the I-V curve). A very few molecular junctions have reached RR ≥ 1000, using a donor-acceptor,381 ferrocene redox center,382 , or with a C60 monolayer 383. There are a few different possible mechanisms that explain rectification, which involves either specific donor / acceptor levels in the molecule or just the built-in field within the film (see Ref.1 for a detailed explanation).…”

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confidence: 99%

Large-Area, Ensemble Molecular Electronics: Motivation and Challenges

2017

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We review charge transport across molecular monolayers, which is central to molecular electronics (MolEl), using large-area junctions (NmJ). We strive to provide a wide conceptual overview of three main subtopics. First, a broad introduction places NmJ in perspective to related fields of research and to single-molecule junctions (1mJ) in addition to a brief historical account. As charge transport presents an ultrasensitive probe for the electronic perfection of interfaces, in the second part ways to form both the monolayer and the contacts are described to construct reliable, defect-free interfaces. The last part is dedicated to understanding and analyses of current-voltage (I-V) traces across molecular junctions. Notwithstanding the original motivation of MolEl, I-V traces are often not very sensitive to molecular details and then provide a poor probe for chemical information. Instead, we focus on how to analyze the net electrical performance of molecular junctions, from a functional device perspective. Finally, we point to creation of a built-in electric field as a key to achieve functionality, including nonlinear current-voltage characteristics that originate in the molecules or their contacts to the electrodes. This review is complemented by a another review that covers metal-molecule-semiconductor junctions and their unique hybrid effects.

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Large Spatially Resolved Rectification in a Donor–Acceptor Molecular Heterojunction

Cited by 22 publications

References 37 publications

Energy Level Alignment at Interfaces Between Au (111) and Thiolated Oligophenylenes of Increasing Chain Size: Theoretical Evidence of Pinning Effects

Energy Level Alignment at Interfaces Between Au (111) and Thiolated Oligophenylenes of Increasing Chain Size: Theoretical Evidence of Pinning Effects

Atomically precise graphene nanoribbon heterojunctions from a single molecular precursor

Large-Area, Ensemble Molecular Electronics: Motivation and Challenges

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