Optical and electronic interaction at metal–organic and organic–organic interfaces of ultra-thin layers of PTCDA and SnPc on noble metal surfaces

Gruenewald, Marco; Wachter, Kristin; Meißner, Matthias; Kozlik, Michael; Forker, Roman; Fritz, Torsten

doi:10.1016/j.orgel.2013.05.010

Cited by 29 publications

(56 citation statements)

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“…R(E,0) denotes the reflectance of the bare substrate at photon energy E, while R(E,d) is the reflectance recorded during film growth at a nominal adsorbate thickness d.T h e setup has been detailed previously [21,33]. For the spectral analysis the following substrates are used: h-BN/Rh(111) (this work), h-BN/Pt(111) (this work), Au(111) [22], Au(100) [23], Ag(111) [24], and bilayer graphene on 6H -SiC(0001) [25]. On graphene and h-BN the electronic coupling of the first PTCDA ML to the respective substrate is rather weak, as evidenced by an absorption behavior reminiscent of dissolved molecules [34][35][36].…”

Section: Methodsmentioning

confidence: 99%

“…(1)] to assess the optical absorption behavior of PTCDA films adsorbed on sp 2 -bonded layers, such as graphene on silicon carbide and metals covered by a hexagonal boron nitride (h-BN) or by a passivating molecular monolayer. For this purpose, measurements of PTCDA on h-BN/Rh(111) and h-BN/Pt(111) are compared to previous studies on various other substrates [22][23][24][25]. Surprisingly, only two distinct sets of S 0 → S 1 transition energies (hereafter called PTCDA HE and PTCDA LE for high and low energy, respectively) are observed, although the dielectric properties of the substrates vary considerably.…”

Section: Introductionmentioning

confidence: 96%

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Optical transition energies of isolated molecular monomers and weakly interacting two-dimensional aggregates

et al. 2016

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The optical excitation energies of organic dye molecules are often said to depend sensitively on the polarizability of the utilized substrate. To this end, we employ differential reflectance spectroscopy (DRS) to analyze the S 0 → S 1 fundamental transition energies observed for 3,4,9,10-perylene tetracarboxylic dianhydride (PTCDA) as a function of coverage on various surfaces, such as sp 2-bonded insulating layers [graphene and hexagonal boron nitride (h-BN)], and noble metals pre-covered by a molecular wetting layer which prevents hybridization of the second-layer molecules with the metal states. We elucidate the optical absorbance behavior of PTCDA layers grown on h-BN/Rh(111) and on h-BN/Pt(111) and characterize their structures by means of scanning tunneling microscopy. Surprisingly, although the dielectric properties of the employed substrates differ substantially, only two main transition energies are observed: (i) PTCDA HE essentially mimics the behavior of isolated monomers on surfaces (particularly at submonolayer coverage), while (ii) PTCDA LE , red-shifted by ≈ 70 meV (≈ 560 cm −1), is attributed to two-dimensional densely packed aggregates. This red-shift is in remarkable accordance with previous investigations for PTCDA on NaCl(100) and, therefore, likely arises from the same physical effects, namely the formation of two-dimensional excitonic bands and the polarizability of neighboring molecules within the monolayer. In distinction from earlier studies, we conclude that the polarizabilities of the employed substrates do not constitute the dominant contribution to the molecular S 0 → S 1 transition energies observed here.

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Section: Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 96%

Optical transition energies of isolated molecular monomers and weakly interacting two-dimensional aggregates

et al. 2016

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“…where ܴሺ‫,ܧ‬ ݀ሻ denotes in our case the reflectivity of the sample stack consisting of the quartz 1 MLE of PTCDA partially potassium-doped providing pronounced new features of PTCDA radical anions at low photon energies (investigated in detail previously 32 ), polycrystalline (pc) PTCDA 33 and the dramatically broadened spectra of 1 MLE of PTCDA on Au(111) and Ag(111) 34,35 are shown in the bottom panel. b) Δ‫ܴܵܦ‬ of PTCDA on quartz glass for nominal thicknesses ranging from submonolayers up to 1 MLE.…”

Section: Resultsmentioning

confidence: 99%

“…Note that the apparent spectral width depends on the strength of molecule-metal interaction and is therefore a fingerprint of the degree of chemisorption vs. physisorption. 35 Yet another general consequence of strong hybridization is the effect of charge backdonation from the molecule toward the substrate, frequently observed in strong hybridization at metal / organic interfaces: Due to broadening of the molecular states, certain deep lying orbitals extend energetically above the Fermi level, such that the charge density on the molecule is lowered, as was explicitly shown for the case of PTCDA on Ag(111). 46 All these effects (spatial extension of the molecular wave function into the substrate, charge back-donation, formation of two-dimensional bands at the interface due to the substrate-mediated intermolecular interaction) result in a fractional net charge transfer, usually well below 1 electron charge and e.g., in the case of PTCDA on Ag(111) as low as 0.3 e.…”

Section: Acs Paragon Plus Environmentmentioning

confidence: 94%

“…1(a)), characteristic of strong hybridization with delocalized states as delineated above. 35 Therefore, the slight broadening of the anion peaks in the DRS spectra in Figure 1 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 molecules on ZnO. On the scale of electronic interaction strength, the adsorption regime can be however clearly regarded as physisorption, comparable to PTCDA on top of 1 ML PTCDA / Ag(111), where a slight broadening of the optical spectra is also observed.…”

Section: Acs Paragon Plus Environmentmentioning

confidence: 99%

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Integer Charge Transfer and Hybridization at an Organic Semiconductor/Conductive Oxide Interface

et al. 2015

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We investigate the prototypical hybrid interface formed between PTCDA and conductive ndoped ZnO films by means of complementary optical and electronic spectroscopic techniques.We demonstrate that shallow donors in the vicinity of the ZnO surface cause an integer charge transfer to PTCDA, which is clearly restricted to the first monolayer. By means of DFT calculations, we show that the experimental signatures of the anionic PTCDA species can be understood in terms of strong hybridization with localized states (the shallow donors) in the substrate and charge back-donation, resulting in an effectively integer charge transfer across the interface. Charge transfer is thus not merely a question of locating the Fermi level above the PTCDA electron-transport level, but requires rather an atomistic understanding of the interfacial interactions. The study reveals that defect sites and dopants can have a significant influence on the specifics of interfacial coupling and thus on carrier injection or extraction.

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Recent Progress in the Consistent Interpretation of Complementary Spectroscopic Results Obtained on Molecular Systems

Forker

Gruenewald

Kirchhuebel

et al. 2021

Advanced Optical Materials

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Research on organic thin films is largely driven by potential (opto‐)electronic applications and turns out to be no less intriguing from a fundamental point of view. Numerous studies make it clear that the understanding of device‐relevant molecular thin film architectures is quite challenging—often hampered by insufficient spectroscopic data and the lack of a consistent interpretation of the available datasets. Consequently, speculative aspects prevail in the discussion of energy levels in conjunction with the optical properties of organic thin films. Adequate spectroscopic techniques applicable to thin films of organic molecules (typical thicknesses required for devices are in the nanometer range) with the necessary sensitivities are rather demanding. Some of those methods were developed or significantly improved in the recent past. Here, the now available complementary spectroscopies are briefly surveyed with particular emphasis on some techniques that have not yet become widespread standards, and a non‐exhaustive set of examples of acquired experimental results are provided. For a consistent interpretation of the latter, the concepts brought forward in the literature considering the role of initial and final states of spectroscopic processes are outlined, with important consequences for quantitatively correct energy diagrams.

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Optical and electronic interaction at metal–organic and organic–organic interfaces of ultra-thin layers of PTCDA and SnPc on noble metal surfaces

Cited by 29 publications

References 39 publications

Optical transition energies of isolated molecular monomers and weakly interacting two-dimensional aggregates

Optical transition energies of isolated molecular monomers and weakly interacting two-dimensional aggregates

Integer Charge Transfer and Hybridization at an Organic Semiconductor/Conductive Oxide Interface

Recent Progress in the Consistent Interpretation of Complementary Spectroscopic Results Obtained on Molecular Systems

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