How much does surface polymorphism influence the work function of organic/metal interfaces?

Jeindl, Andreas; Hörmann, Lukas; Hofmann, Oliver

doi:10.1016/j.apsusc.2021.151687

Cited by 5 publications

(18 citation statements)

References 33 publications

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“…This interface system is ideal for our study because its surface chemistry (in the absence of electric elds) is fairly well characterized, both experimentally [40][41][42] and through simulations. [42][43][44][45] Different polymorphs of TCNE on Cu(111) have been shown to exhibit substantially different properties such as the work function, which varies by up to 3 eV between polymorphs. 45 TCNE is known to bond to the surface through a Blyholder-like interaction, 46 comprising charge-donation from the metal into the molecular LUMO and back-donation from the molecular s-system to the surface.…”

Section: Resultsmentioning

confidence: 99%

“…[42][43][44][45] Different polymorphs of TCNE on Cu(111) have been shown to exhibit substantially different properties such as the work function, which varies by up to 3 eV between polymorphs. 45 TCNE is known to bond to the surface through a Blyholder-like interaction, 46 comprising charge-donation from the metal into the molecular LUMO and back-donation from the molecular s-system to the surface. 43 Importantly, the resulting molecule-substrate interaction is strongly different for different adsorption geometries.…”

Section: Resultsmentioning

confidence: 99%

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Polymorphism mediated by electric fields: a first principles study on organic/inorganic interfaces

et al. 2023

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Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

Polymorphism mediated by electric fields: a first principles study on organic/inorganic interfaces

et al. 2023

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“…68,[70][71][72]74 Conversely, the vibrations of the molecules on the substrate can differ substantially from the molecules in the gas phase, especially when charge-transfer at the interface occurs. 73 For the special case of TCNE/Cu(111), it was shown in previous work 43,44 the zero-point energy of the adsorption geometries differs only very little when there is no field applied.…”

Section: Temperature and Pressure Dependence: Electric Fields As Hand...mentioning

confidence: 87%

“…This interface system is ideal for our study because its surface chemistry is fairly well characterized (in absence of electric fields), both experimentally 39-41 and through simulations. [41][42][43][44] Different polymorphs of TCNE on Cu(111) have been shown to exhibit substantially different properties such as the work function, which varies by up to 3 eV between polymorphs. 44 TCNE is known to bond to the surface through a Blyholder-like interaction, 45 comprising charge-donation from the metal into the molecular LUMO and back-donation from the molecular system to the surface.…”

mentioning

confidence: 99%

“…[41][42][43][44] Different polymorphs of TCNE on Cu(111) have been shown to exhibit substantially different properties such as the work function, which varies by up to 3 eV between polymorphs. 44 TCNE is known to bond to the surface through a Blyholder-like interaction, 45 comprising charge-donation from the metal into the molecular LUMO and back-donation from the molecular system to the surface. 42 Importantly, the resulting molecule-substrate interaction is strongly different for different adsorption geometries.…”

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confidence: 99%

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Controlling the polymorphism of organic/inorganic interfaces with electric fields

Cartus

Jeindl

Werkovits

et al. 2022

Preprint

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Organic/inorganic interfaces are known to exhibit rich polymorphism, where different polymorphs often possess significantly different properties. Which polymorph forms during an experiment depends strongly on environmental parameters such as deposition temperature and partial pressure of the molecule to be adsorbed. To prepare desired polymorphs these parameters are varied. However, many polymorphs are difficult to access with the experimentally available temperature- pressure ranges. In this contribution, we investigate how electric fields can be used as an additional lever to make certain structures more readily accessible. On the example of tetracyanoethylene (TCNE) on Cu(111), we analyze how electric fields change the energy landscape of interface systems. TCNE on Cu(111) can form either lying or standing polymorphs, which exhibit significantly different work functions. We combine first-principles calculations with a machine-learning based structure search algorithm and ab-initio thermodynamics to demonstrate that electric fields can be exploited to shift the temperature of the phase transition between standing and lying polymorphs by up to 100 K.

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Interplay of Adsorption Geometry and Work Function Evolution at the TCNE/Cu(111) Interface

Niederreiter,

Cartus,

Werkovits

et al. 2023

J. Phys. Chem. C

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The adsorption of organic electron acceptors on metal surfaces is a powerful way to change the effective work function of the substrate through the formation of charge-transfer-induced dipoles. The work function of the interfaces is hence controlled by the redistribution of charges upon adsorption of the organic layer, which depends not only on the electron affinity of the organic material but also on the adsorption geometry. As shown in this work, the latter dependence controls the work function also in the case of adsorbate layers exhibiting a mixture of various adsorption geometries. Based on a combined experimental (core-level and infrared spectroscopy) and theoretical (density functional theory) study for tetracyanoethylene (TCNE) on Cu(111), we find that TCNE adsorbs in at least three different orientations, depending on TCNE coverage. At low coverage, flat lying TCNE dominates, as it possesses the highest adsorption energy. At a higher coverage, additionally, two different standing orientations are found. This is accompanied by a large increase in the work function of almost 3 eV at full monolayer coverage. Our results suggest that the large increase in work function is mainly due to the surface dipole of the free CN groups of the standing molecules and less dependent on the charge-transfer dipole of the differently oriented and charged molecules. This, in turn, opens new opportunities to control the work function of interfaces, e.g., by synthetic modification of the adsorbates, which may allow one to alter the adsorption geometries of the molecules as well as their contributions to the interface dipoles and, hence, the work function.

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How much does surface polymorphism influence the work function of organic/metal interfaces?

Cited by 5 publications

References 33 publications

Polymorphism mediated by electric fields: a first principles study on organic/inorganic interfaces

Polymorphism mediated by electric fields: a first principles study on organic/inorganic interfaces

Controlling the polymorphism of organic/inorganic interfaces with electric fields

Interplay of Adsorption Geometry and Work Function Evolution at the TCNE/Cu(111) Interface

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