Molecular switches from benzene derivatives adsorbed on metal surfaces

Liu, Wei; Filimonov, Sergey N.; Carrasco, Javier; Tkatchenko, Alexandre

doi:10.1038/ncomms3569

Cited by 84 publications

(119 citation statements)

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“…In agreement with the experimental findings, this model captures the complex kinetics of the pattern formation for different light intensities, including the transition from a linear to a nonlinear regime and the direct coupling of the polarization to the dipole moment of the azopolymer. Beyond the new insight on the underlying physics that control the pattern formation, our work has an immediate impact on the efforts to gain full control over the pattern formation on azopolymer thin films (42,43) and their application in molecular electronic devices (44)(45)(46).…”

Section: Resultsmentioning

confidence: 99%

Instability-induced pattern formation of photoactivated functional polymers

Galinski

Ambrosio

Maddalena

et al. 2014

Proc. Natl. Acad. Sci. U.S.A.

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Since the pioneering work of Turing on the formation principles of animal coat patterns [Turing AM (1952) Phil Trans R Soc Lond B 237(641):37-72], such as the stripes of a tiger, great effort has been made to understand and explain various phenomena of selfassembly and pattern formation. Prominent examples are the spontaneous demixing in emulsions, such as mixtures of water and oil [Herzig EM, et al. (2007) Nat Mater 6:966-971]; the distribution of matter in the universe [Kibble TWB (1976 A zobenzenes, which belong to photochromic materials, are switchable two-state systems with distinct optical, electronic, magnetic, and/or electrochemical properties that can be reversibly converted by irradiation. Since the discovery of the unique photochemical properties of azobenzene in 1937 (1), azobenzenes have been mainly used in the chemical industry. Only recently, after studies of the molecular physics of the photoisomerization of azo dyes have revealed that the photoisomerization reaction occurs on the timescale of a few picoseconds (2, 3), azobenzenes came back into focus as potential photoswitchable materials (4, 5). Azobenzenes have been investigated in terms of ultrafast spectroscopy (4, 6, 7), mechanoisomerization (8), the effect of slow photons (9), two-photon absorption (10) and laser-induced periodic surface structuring (11-17). The latter describes the phenomenon of Turing pattern formation on the surface of an azopolymer film upon exposure to UV or visible light. The outstanding feature of this photoactivated pattern formation is its dependence on both the light's intensity and polarization, which allows for the formation of a large variety of Turing patterns, such as hexagonal cells, parallel stripes, or turbulent structures. Several attempts have been made to understand the underlying physics that controls these various forms of pattern formation (18-23), but a sound picture is still lacking.In this paper, we demonstrate that the photoactivated pattern formation on azopolymer films can be entirely explained by the physical concept of phase separation of two coexistent immiscible phases in the polymer. A phase separation can be briefly characterized as follows: A (meta)stable configuration subjected to an external perturbation (temperature, light) becomes unstable. The unstable system tends to equilibrate by the formation of two immiscible phases. These two phases tend to separate leading to a spatial reorganization of the system.In the case of azopolymers, the instability is caused by the random optical excitation of the isomers in the polymer film. Excited by a photon of suitable energy (λ = 200-550 nm), the azobenzene isomer undergoes a structural transition by inversion or rotation (3), called photoisomerization, and relaxes either in the trans or cis ground state. The symmetry of the system is broken. The principle of the photoisomerization reaction for one azobenzene isomer is illustrated in Fig. 1A. The ground-state energy is characterized by an asymmetric double-well potential (Fig. 1A), containing...

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Section: Resultsmentioning

confidence: 99%

Instability-induced pattern formation of photoactivated functional polymers

Galinski

Ambrosio

Maddalena

et al. 2014

Proc. Natl. Acad. Sci. U.S.A.

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“…The studies above included the vdW force in the calculations, but neglected the pronounced contributions of many-body electronic correlations, which arise from the collective electronic fluctuations in the combined molecule/ surface system [25]. The vdW interactions have been shown to strongly affect the stability and structure of hybrid systems [26][27][28][29][30]. However, the most widely employed vdW-inclusive methods simply add a correction to the density-functional theory (DFT) total energy in the form of a non-local interaction energy [31,32].…”

Section: Introductionmentioning

confidence: 99%

Tuning the work function of stepped metal surfaces by adsorption of organic molecules

Jiang

et al. 2017

J. Phys.: Condens. Matter

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Understanding the binding mechanisms for aromatic molecules on transition-metal surfaces, especially with defects such as vacancies, steps and kinks, is a major challenge in designing functional interfaces for organic devices. One important parameter in the performance of organic/inorganic devices is the barrier of charge carrier injection. In the case of a metallic electrode, tuning the electronic interface potential or the work function for electronic level alignment is crucial. Here, we use density-functional theory (DFT) calculations with van der Waals (vdW) interactions treated with both screened pairwise (vdW surf ) and many-body dispersion (MBD) methods, to systematically study the interactions of benzene with a variety of stepped surfaces. Our calculations confirm the physisorptive character of Ag(2 1 1), Ag(5 3 3), Ag(3 2 2), Ag(7 5 5) and Ag(5 4 4) surfaces upon the adsorption of benzene. The MBD effects reduce the adsorption energies by about 0.15 eV per molecule compared to the results from the DFT + vdW surf method. In addition, we find that the higher the step density, the larger the reduction of the work function upon the adsorption of benzene. We also study the effect of vdW interactions on the electronic structure using a fully selfconsistent implementation of the vdW surf method in the Kohn-Sham DFT framework. We find that the self-consistent vdW surf effects increase the work function due to the lowered Fermi level and the increased vacuum level. As a result, the benzene/Ag(2 1 1) system has the lowest work function (3.67 eV) among the five adsorption systems, significantly smaller than the work function of the clean Ag(1 1 1) surface (4.74 eV). Our results provide important insights into the stability and electronic properties of molecules adsorbed on stepped metal surfaces, which could help in designing more appropriate interfaces with low work functions for electron transfer.

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“…In particular, hybrid metal/organic systems (HMOS) are used as models for novel interfaces due to the high electrical conductivity of the metal and the tunable structural, electronic, and optical properties of organic molecules [1,2]. For example, HMOS composed of anode-cathode sandwiches or thin films of organic molecules on metal substrates show significant promise for applications as components for transistors, lightemitting diodes, switches, sensors, and photovoltaics [1,3,4].…”

Section: Introductionmentioning

confidence: 99%

Electronic charge rearrangement at metal/organic interfaces induced by weak van der Waals interactions

Ferri

Ambrosetti

Tkatchenko

2017

Phys. Rev. Materials

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Electronic charge rearrangements at interfaces between organic molecules and solid surfaces play a key role in a wide range of applications in catalysis, light-emitting diodes, single-molecule junctions, molecular sensors and switches, and photovoltaics. It is common to utilize electrostatics and Pauli pushback to control the interface electronic properties, while the ubiquitous van der Waals (vdW) interactions are often considered to have a negligible direct contribution (beyond the obvious structural relaxation). Here, we apply a fully self-consistent Tkatchenko-Scheffler vdW density functional to demonstrate that the weak vdW interactions can induce sizable charge rearrangements at hybrid metal/organic systems (HMOS). The complex vdW correlation potential smears out the interfacial electronic density, thereby reducing the charge transfer in HMOS, changes the interface work functions by up to 0.2 eV, and increases the interface dipole moment by up to 0.3 Debye. Our results suggest that vdW interactions should be considered as an additional control parameter in the design of hybrid interfaces with the desired electronic properties.

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Molecular switches from benzene derivatives adsorbed on metal surfaces

Cited by 84 publications

References 50 publications

Instability-induced pattern formation of photoactivated functional polymers

Instability-induced pattern formation of photoactivated functional polymers

Tuning the work function of stepped metal surfaces by adsorption of organic molecules

Electronic charge rearrangement at metal/organic interfaces induced by weak van der Waals interactions

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