Charge Transfer and Orbital Level Alignment at Inorganic/Organic Interfaces: The Role of Dielectric Interlayers

Hollerer, Michael; Lüftner, Diana; Hurdax, Philipp; Ules, Thomas; Soubatch, Serguei; Tautz, F. Stefan; Koller, Georg; Puschnig, Peter; Sterrer, Martin; Ramsey, Michael G.

doi:10.1021/acsnano.7b02449

Cited by 88 publications

(133 citation statements)

References 60 publications

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“…Reference experiments with pentacene. Previous studies of pentacene on Ag(001) have shown the energy-level alignment to be such that the LUMO is aligned with the Fermi energy and consequently partially occupied with an estimated charge of 0.7 electrons 35 . Any charge transfer-related magnetism is hindered by the substrate: the LUMO is substantially broadened by hybridization with the metal, and the high level of screening reduces electron correlations 36,37 .…”

Section: Resultsmentioning

confidence: 96%

“…The presence of this Kondo resonance is further proof of the decoupling effect that the "pentacene functionalization" at C-2 and C-3 with sp 3 carbon atoms brings about. If that were not the case, a broader LUMO level and reduced electron correlations would cause an equal population of spin up and spin down LUMO orbitals 36,37 , resulting in no net spin and no Kondo peak, as occurs with pristine pentacene 35 . On the other hand, the Kondo resonance still implies a minor molecule-substrate coupling, since it relates to the screening of the molecular spin by the substrate electrons and would thus be absent for a more efficient decoupling as observed for pentacene on an insulating MgO buffer layer.…”

Section: Resultsmentioning

confidence: 99%

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Electronic decoupling of polyacenes from the underlying metal substrate by sp3 carbon atoms

et al. 2020

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On-surface synthesis is becoming an increasingly popular approach to obtain new organic materials. In this context, metallic surfaces are the most commonly used substrates. However, their hybridization with the adsorbates often hinder a proper characterization of the molecule’s intrinsic electronic and magnetic properties. Here we report a route to electronically decouple molecules from their supporting substrates. In particular, we have used a Ag(001) substrate and hydrogenated heptacene molecules, in which the longest conjugated segment determining its frontier molecular orbitals amounts to five consecutive rings. The non-planarity that sp3 atoms impose on the carbon backbone results in electronically decoupled molecules, as demonstrated by scanning tunneling spectroscopy measurements. The charging resonances of the latter imply the presence of double tunneling barriers. We further explain the existing relation between the charging resonance energy and their contrast, as well as with the presence or absence of additional Kondo resonances.

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Section: Resultsmentioning

confidence: 96%

Section: Resultsmentioning

confidence: 99%

Electronic decoupling of polyacenes from the underlying metal substrate by sp3 carbon atoms

et al. 2020

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“…It should be noted that the theoretical momentum maps for 5A have already been experimentally confirmed by analyzing the photoelectron angular distribution within ARPES experiments. 52 , 53 , 56 − 58 Using the technique of photoemission tomography, 59 such measurements are being planned also for DHTA n in future.…”

Section: Resultsmentioning

confidence: 99%

Synthesis and Combined Experimental and Theoretical Characterization of Dihydro-tetraaza-acenes

et al. 2018

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We present a combined experimental and theoretical study of electronic and optical properties of dihydro-tetraaza-acenes (DHTAn). Using solvent-free condensation, we are able to synthesize not only DHTA5 but also the longer DHTA6 and DHTA7 molecules. We then investigate their gas-phase electronic structures by means of ab initio density functional calculations employing an optimally tuned range-separated hybrid functional. By comparing with the parent linear oligoacenes (nA) and based on computed ionization potentials and electron affinities, we predict DHTAn molecules to be more stable than acenes of the same length, where we expect DHTAn molecules to be persistent at least up to n = 7 rings. We further exploit the analogy with nA by analyzing the entire intramolecular π-band structure of the DHTAn molecules. This clearly reveals that the additional two electrons donated by the dihydropyrazine group are delocalized over the entire molecule and contribute to its π-electron system. As a consequence, the symmetry of the frontier orbitals of DHTAn differs from that of the parent nA molecule. This also affects the UV–vis absorption spectra which have been measured for DHTA5, 6, and 7 dissolved in dimethyl sulfoxide and analyzed by means of excited state calculations within a time-dependent density functional theory framework.

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“…[1][2][3][4][5] Despite the potential impact of this approach, only af ew molecules have been shown to efficiently donate (or accept) significant charge,t his quality being related to the presence of donor (acceptor) moieties in their structures.…”

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confidence: 99%

On‐Surface Bottom‐Up Synthesis of Azine Derivatives Displaying Strong Acceptor Behavior

et al. 2018

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On-surface synthesis is an emerging approach to obtain, in asingle step,precisely defined chemical species that cannot be obtained by other synthetic routes.The control of the electronic structure of organic/metal interfaces is crucial for defining the performance of many optoelectronic devices.A facile on-surface chemistry route has now been used to synthesize the strong electron-acceptor organic molecule quinoneazine directly on aC u(110) surface,v ia thermally activated covalent coupling of para-aminophenol precursors. The mechanism is described using ac ombination of in situ surface characterization techniques and theoretical methods. Owing to astrong surface-molecule interaction, the quinoneazine molecule accommodates 1.2 electrons at its carbonyl ends, inducing an intramolecular charge redistribution and leading to partial conjugation of the rings,conferring azo-character at the nitrogen sites.Organicheterostructuresbasedonelectronacceptor-donor organic molecules on surfaces have become strategic materials owing to their huge technological impact in fields such as organic light-emitting diodes (OLEDs), organic field effect transistors (OFETs), or solar cell devices,amongst others.In electronic devices,o rganic layers are placed on metallic surfaces for electrical contact, and the structure of the metalorganic interface enormously affects the performance.[1] In particular,s ome molecules promote charge transfer at the interface with metal electrodes owing to their donor (acceptor) nature,which may induce energy level realignment that can be exploited to tune the transport properties of the system. [1][2][3][4][5] Despite the potential impact of this approach, only af ew molecules have been shown to efficiently donate (or accept) significant charge,t his quality being related to the presence of donor (acceptor) moieties in their structures.[6] A typical example is tetracyano-p-quinodimethane (TCNQ), as trong acceptor molecule that when deposited on Cu(100) accommodates around 1.6 electrons whereby almost one electron aromatizes the central hexagonal ring and the remaining fraction of the charge is accommodated in one of the peripheral nitrogen atoms of the cyano groups.[3]On the other hand, on-surface synthesis can generate unique molecules or extended molecular architectures that have been rationally formed via alternative synthetic routes to those available through solution-based chemistry. [7,8] These surface-stabilized species can lead to compounds that are difficult or impossible to obtain via conventional synthetic procedures. [9][10][11][12] Herein, we combine both of the aforementioned features. We show that the on-surface coupling reaction of two simple and inexpensive para-aminophenol (p-Ap) molecules can be employed to form aq uinonoid-like derivative,q uinoneazine (QAz). This molecule has been theoretically proposed for organic electrodes owing to their extreme redox voltages,and it can also be employed as an intermediate in the preparation of several chemically and biologically active ...

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Charge Transfer and Orbital Level Alignment at Inorganic/Organic Interfaces: The Role of Dielectric Interlayers

Cited by 88 publications

References 60 publications

Electronic decoupling of polyacenes from the underlying metal substrate by sp3 carbon atoms

Electronic decoupling of polyacenes from the underlying metal substrate by sp3 carbon atoms

Synthesis and Combined Experimental and Theoretical Characterization of Dihydro-tetraaza-acenes

On‐Surface Bottom‐Up Synthesis of Azine Derivatives Displaying Strong Acceptor Behavior

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