The role of initial and final states in molecular spectroscopies

Kirchhuebel, Tino; Monti, Oliver L. A.; Munakata, Toshiaki; Kera, Satoshi; Forker, Roman; Fritz, Torsten

doi:10.1039/c8cp07318j

Cited by 16 publications

(50 citation statements)

References 61 publications

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“…The ultraviolet photoelectron spectroscopy (UPS) measurements of the DBP films on Ni(111) and h-BN/Ni(111) are depicted in Figure 4. We use the notation proposed by Kirchhuebel et al to assign spectroscopic features to the underlying molecular orbitals, taking into consideration the probing process [37]. Within this notation, each feature is ascribed to the involved molecular orbital with the probing process being characterized by the initial state as subscript and the final state as a superscript.…”

Section: Valence Band Structure and Work Function Changementioning

confidence: 99%

Hybridization vs decoupling: influence of an h-BN interlayer on the physical properties of a lander-type molecule on Ni(111)

Schaal¹,

Aihara²,

Gruenewald³

et al. 2020

Beilstein J. Nanotechnol.

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2D materials such as hexagonal boron nitride (h-BN) are widely used to decouple organic molecules from metal substrates. Nevertheless, there are also indications in the literature for a significant hybridization, which results in a perturbation of the intrinsic molecular properties. In this work we study the electronic and optical properties as well as the lateral structure of tetraphenyldibenzoperiflanthene (DBP) on Ni(111) with and without an atomically thin h-BN interlayer to investigate its possible decoupling effect. To this end, we use in situ differential reflectance spectroscopy as an established method to distinguish between hybridized and decoupled molecules. By inserting an h-BN interlayer we fabricate a buried interface and show that the DBP molecules are well decoupled from the Ni(111) surface. Furthermore, a highly ordered DBP monolayer is obtained on h-BN/Ni(111) by depositing the molecules at a substrate temperature of 170 °C. The structural results are obtained by quantitative low-energy electron diffraction and low-temperature scanning tunneling microscopy. Finally, the investigation of the valence band structure by ultraviolet photoelectron spectroscopy shows that the low work function of h-BN/Ni(111) further decreases after the DBP deposition. For this reason, the h-BN-passivated Ni(111) surface may serve as potential n-type contact for future molecular electronic devices.

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Section: Valence Band Structure and Work Function Changementioning

confidence: 99%

Hybridization vs decoupling: influence of an h-BN interlayer on the physical properties of a lander-type molecule on Ni(111)

Schaal¹,

Aihara²,

Gruenewald³

et al. 2020

Beilstein J. Nanotechnol.

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“…6 ) revealed that the optical gap seemed to be smaller than the electronic gap. This was expected due to the intrinsic differences in the measurement process of these gaps [ 85 ]. However, studies comparing orbital-resolved STM/STS data to optical gaps are scarce [ 86 ].…”

Section: Discussionmentioning

confidence: 99%

“…A comparison between the values of the HOMO-LUMO gaps and the excitation energy obtained by STS and UV-vis absorption (see Figure 6) revealed that the optical gap seemed to be smaller than the electronic gap. This was expected due to the intrinsic differences in the measurement process of these gaps [85]. However, studies comparing orbital-resolved STM/STS data to optical gaps are scarce [86].…”

Section: Spectroscopic Investigations and Determination Of The Molecumentioning

confidence: 99%

Self-assembly and spectroscopic fingerprints of photoactive pyrenyl tectons on hBN/Cu(111)

Zimmermann¹,

Seufert²,

Đorđević³

et al. 2020

Beilstein J. Nanotechnol.

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The controlled modification of electronic and photophysical properties of polycyclic aromatic hydrocarbons by chemical functionalization, adsorption on solid supports, and supramolecular organization is the key to optimize the application of these compounds in (opto)electronic devices. Here, we present a multimethod study comprehensively characterizing a family of pyridin-4-ylethynyl-functionalized pyrene derivatives in different environments. UV–vis measurements in toluene solutions revealed absorption at wavelengths consistent with density functional theory (DFT) calculations, while emission experiments showed a high fluorescence quantum yield. Scanning tunneling microscopy (STM) and spectroscopy (STS) measurements of the pyrene derivatives adsorbed on a Cu(111)-supported hexagonal boron nitride (hBN) decoupling layer provided access to spatially and energetically resolved molecular electronic states. We demonstrate that the pyrene electronic gap is reduced with an increasing number of substituents. Furthermore, we discuss the influence of template-induced gating and supramolecular organization on the energies of distinct molecular orbitals. The selection of the number and positioning of the pyridyl termini in tetrasubstituted, trans- and cis-like-disubstituted derivatives governed the self-assembly of the pyrenyl core on the nanostructured hBN support, affording dense-packed arrays and intricate porous networks featuring a kagome lattice.

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“…Another complication when employing the initial-state approach is that (in contrast to final-state approaches) [68,[109][110][111] it does not account for core-hole screening effects. Unfortunately, final-state approaches are not applicable to systems like the ones considered here, as in conjunction with periodic boundary conditions one would need unit cells comprising thousands of atoms in order to avoid spurious collective electrostatic effects due to periodic replicas of the core holes (and the compensation charges).…”

Section: Computational Methodologymentioning

confidence: 99%

“…[70][71][72][73][74][75][76][77][78][79][80][81] In this paper we will argue that the electrostatic core-level shifts make XPS an ideally suited tool for probing interface dipoles. For supporting that claim, we will use state of the art quantum-mechanical simulations to determine core-level shifts encountered biphenyl-based SAMs attached to a Au (111) substrate by a variety of chemically different docking groups. To the best of our knowledge, a corresponding set of experimental XPS data with systematically varied docking groups and consistent film structures and morphologies does not exist yet.…”

Section: Introductionmentioning

confidence: 99%

X-Ray Photoelectron Spectroscopy for Determining Interface Dipoles of Self-Assembled Monolayers

Taucher¹,

Zojer²

2020

Preprint

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In the current manuscript we assess to what extent X-ray photoelectron spectroscopy is a suitable tool for probing the dipoles formed at interfaces between self-assembled monolayers and metal substrates. To that aim, we perform dispersion-corrected, slab-type band-structure calculations on a number of biphenyl-based systems bonded to a Au(111) surface via different docking groups. In addition to changing the docking chemistry (and the associated interface dipoles), also the impacts of polar tail-group substituents and varying dipole densities are investigated. We find that for densely-packed monolayers the shifts of the peak positions of the simulated XP-spectra are a direct measure for the interface dipoles. In the absence of polar tail-group substituents they also directly correlate with adsorption-induced work-function changes. At reduced dipole-densities this correlation deteriorates, as work function measurements probe the difference between the Fermi-level of the substrate and the electrostatic energy far above the interface, while core level shifts are determined by the local electrostatic energy in the region of the atom from which the photoelectron is excited.

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The role of initial and final states in molecular spectroscopies

Abstract: Interpreting experimental spectra of thin films of organic semiconductors is challenging, and understanding the relationship between experimental data obtained by different spectroscopic techniques requires a careful consideration of the initial and final states for each process.

Cited by 16 publications

References 61 publications

Hybridization vs decoupling: influence of an h-BN interlayer on the physical properties of a lander-type molecule on Ni(111)

Hybridization vs decoupling: influence of an h-BN interlayer on the physical properties of a lander-type molecule on Ni(111)

Self-assembly and spectroscopic fingerprints of photoactive pyrenyl tectons on hBN/Cu(111)

X-Ray Photoelectron Spectroscopy for Determining Interface Dipoles of Self-Assembled Monolayers

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