Electronic structure of tris(8-hydroxyquinoline) aluminum thin films in the pristine and reduced states

Johansson, Nils; Osada, Takenori; Stafström, Sven; Salaneck, W. R.; Parenté, V.; Santos, D. A. dos; Crispin, Xavier; Brédas, Jean‐Luc

doi:10.1063/1.479486

Cited by 141 publications

(105 citation statements)

References 31 publications

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“…For small p-conjugated molecules, there is the additional effect of electron-electron repulsion, which can lead to the formation of a Coulomb gap, further shifting the integer charge-transfer states away from the LUMO/HOMO of the neutral molecule. [66,67] Note also that the hole or electron donated by the molecule or polymer at the interface is transferred to the nearby substrate surface enabling (significant) Coulomb interaction, which is not the case in, for example, photoemission or electron-absorption measurements. Hence, for all cases except highly crystalline molecular films showing band-like transport, the position of the HOMO and LUMO relative to the vacuum level are not the relevant energies to determine the energy-level alignment at this type of weakly interacting interfaces.…”

Section: Basics Of the Modelmentioning

confidence: 97%

Energy‐Level Alignment at Organic/Metal and Organic/Organic Interfaces

2009

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In this Review, we summarize recent work on modeling of organic/metal and organic/organic interfaces. Some of the models discussed have a semiempirical approach, that is, experimentally derived values are used in combination with theory, and others rely completely of calculations. The models are categorized according to the types of interfaces they apply to, and the strength of the interaction at the interface has been used as the main factor. We explain the basics of the models, their use, and give examples on how the models correlate with experimental results. We stress that given the complexity of organic/metal and organic/organic interface formation, it is crucial to know the exact way in which the interface was formed before choosing the model that is applicable, as none of the models presented covers the whole range of interface interaction strengths (weak physisorption to strong chemisorption).

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Section: Basics Of the Modelmentioning

confidence: 97%

Energy‐Level Alignment at Organic/Metal and Organic/Organic Interfaces

2009

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“…The interaction of organic semiconductor molecules with highly reactive alkali, alkaline earth and other metals has been investigated in the past; for example, tris(8-hydroxyquinoline)aluminium (Alq 3 ) with highly reactive elements such as Ca, K, Li, Mg and Al. [17][18][19] Herein, we report on the size-dependent interaction between organic semiconductors commonly used in organic optoelectronics-the electron-transport material Alq 3 and the hole-transport material 4,4-bis[N-(1-naphthyl)-N-phenylamino]-diphenyl (a-NPD)-with the coinage metal gold, which is generally considered to be inert with respect to the above-mentioned organic compounds. Although bulk gold is generally regarded as marginally reactive (e.g.…”

Section: Introductionmentioning

confidence: 99%

Organic Semiconductor/Gold Interface Interactions: From Physisorption on Planar Surfaces to Chemical Reactions with Metal Nanoparticles

2015

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The interaction of gold nanoparticles (AuNPs) with prototypical organic semiconductors used in optoelectronics, namely, tris(8-hydroxyquinoline)aluminium (Alq3 ) and 4,4-bis[N-(1-naphthyl)-N-phenylamino]diphenyl (α-NPD), is investigated in situ by X-ray photoelectron spectroscopy (XPS). These AuNPs-on-molecule experiments are compared with the reversed molecule-on-Au cases. The molecules-on-Au systems show only weak interactions, and the evolution of the XP spectra is dominated by final-state effects. In contrast, in the AuNPs-on-molecules cases, both initial-state effects and final-state effects occur. Spectral features arising for both molecules and metal indicate charge transfer and the formation of organometallic complexes (initial-state effects). The energy shift in the metal emission underlines the size-induced nanometric nature of the molecule/Au interaction (final-state effects). Consequently, the chemical interaction between metals and organic semiconductors likely depends strongly on the deposition sequence in general.

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“…Tris (8-hydroxyquinoline) aluminum ðAlq 3 Þ is the most famous electron transport and emission materials of OLEDs [1][2][3] and the Alq 3 /metal interfaces have been intensively studied experimentally [4][5][6][7][8][9][10][11][12][13][14][15][16][17] and theoretically [18][19][20][21][22][23][24]. By using ultraviolet photoemission spectroscopy (UPS) and metastable atom electron spectroscopy (MAES), interfacial gap states were observed at Al=Alq 3 interfaces [10,15].…”

Section: Introductionmentioning

confidence: 99%

First-principles molecular dynamics study of Al/Alq₃interfaces

Takeuchi

Yanagisawa

Morikawa

2007

Science and Technology of Advanced Materials

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We have carried out first-principles molecular dynamics simulations of Al deposition on tris (8-hydroxyquinoline) aluminum ðAlq 3 Þ layers to investigate atomic geometries and electronic properties of Al=Alq 3 interfaces. Al atoms were ejected to Alq 3 one by one with the kinetic energy of 37.4 kJ/mol, which approximately corresponds to the average kinetic energy of Al at the boiling temperature of metal Al. The first Al atom interacts with two of the three O atoms of meridional Alq 3 . Following Al atoms interact with Alq 3 rather weakly and they tend to aggregate each other to form Al clusters. During the deposition process, Alq 3 was not broken and its molecular structure remained essentially intact. At the interface, weak bonds between deposited Al atoms and N and C atoms were formed. The projected density of states (PDOS) onto the Alq 3 molecular orbitals shows gap states in between the highest occupied molecular orbitals (HOMOs) and the lowest unoccupied molecular orbitals (LUMOs), which were experimentally observed by ultraviolet photoelectron spectroscopy (UPS) and metastable atom electron spectroscopy (MAES). Our results show that even though the Alq 3 molecular structure is retained, weak N-Al and C-Al bonds induce gap states. r

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Electronic structure of tris(8-hydroxyquinoline) aluminum thin films in the pristine and reduced states

Cited by 141 publications

References 31 publications

Energy‐Level Alignment at Organic/Metal and Organic/Organic Interfaces

Energy‐Level Alignment at Organic/Metal and Organic/Organic Interfaces

Organic Semiconductor/Gold Interface Interactions: From Physisorption on Planar Surfaces to Chemical Reactions with Metal Nanoparticles

First-principles molecular dynamics study of Al/Alq₃interfaces

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Electronic structure of tris(8-hydroxyquinoline) aluminum thin films in the pristine and reduced states

Cited by 141 publications

References 31 publications

Energy‐Level Alignment at Organic/Metal and Organic/Organic Interfaces

Energy‐Level Alignment at Organic/Metal and Organic/Organic Interfaces

Organic Semiconductor/Gold Interface Interactions: From Physisorption on Planar Surfaces to Chemical Reactions with Metal Nanoparticles

First-principles molecular dynamics study of Al/Alq3interfaces

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First-principles molecular dynamics study of Al/Alq₃interfaces