Energy level alignment at Alq/metal interfaces

Lee, Shuit‐Tong; Hou, X. Y.; Mason, M. G.; Tang, Ching Wan

doi:10.1063/1.121125

Cited by 180 publications

(106 citation statements)

References 15 publications

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“…This is attributed to the formation of an interface dipole. 20 However, as more SubPc was deposited, Φ decreases by 0.2 eV, due to downward band bending (see below). Subsequent deposition of C 60 resulted in a shift of the interface dipole between C 60 and SubPc of 0.5 eV to higher energy.…”

Section: Resultsmentioning

confidence: 99%

“…Therefore, the shift of this E cutoff indicates the magnitude of the interfacial dipole, which is equal to increasing or decreasing the work function. 20,21 Similarly, the ionization potential (IP) can be obtained from E cutoff and the HOMO onset (E HOMO ) Figure 4 presents valence band photoemission spectra collected within 5 eV of E F , recorded from ITO, the ClAlPc film grown on ITO, and then the C 60 /ClAlPc/ITO bilayer [spectra from the 0.5 Å/s ClAlPc deposition rate films are presented in Figure 4a and from the 1.5 Å/s ClAlPc deposition rate films in Figure 4b]. The valence band spectra from the different ClAlPc films are clearly different.…”

Section: Resultsmentioning

confidence: 99%

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Electronic Structure of C₆₀/Phthalocyanine/ITO Interfaces Studied using Soft X-ray Spectroscopies

Cho¹,

Piper²,

DeMasi³

et al. 2010

J. Phys. Chem. C

100

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The interface electronic structure of a bilayer heterojunction of C 60 and three different phthalocyanines grown on indium tin oxide (ITO) has been studied using synchrotron radiation-excited photoelectron spectroscopy. The energy difference between the highest occupied molecular orbital level of the phthalocyanine (donor) layer and the lowest unoccupied molecular orbital level of the C 60 (acceptor) layer (E HOMOof a heterojunction with boron subphthalocyanine chloride (SubPc) was found to be much larger than those of copper phthalocyanine (CuPc) and chloro-aluminum phthalocyanine (ClAlPc). This observation is discussed in terms of the difference of the ionization energy of each donor material. Additionally, we have studied the molecular orientation of the phthalocyanine films on ITO using angle-dependent X-ray absorption spectroscopy. We found that the SubPc films showed significant disorder compared to the CuPc and ClAlPc films and also found that E HOMO D -E LUMO A varied with the orientation of the ClAlPc molecules relative to the ITO substrate. This orientation could be controlled by varying the ClAlPc deposition rate.

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Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

Electronic Structure of C₆₀/Phthalocyanine/ITO Interfaces Studied using Soft X-ray Spectroscopies

Cho¹,

Piper²,

DeMasi³

et al. 2010

J. Phys. Chem. C

100

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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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“…Since the onset of Alq 3 HOMO is 2.0 eV below the Fermi level and the secondary electron cutoff is 3.7 eV below the vacuum level, the ionization potential can be deduced as 5.7 eV, which is consistent with previous values. 6,13 The work function of Co is 5.0 eV, so the vacuum level offset at the interface between Alq 3 and Co is 1.3 eV, obtained by subtracting the work function of the inverted sample Alq 3 / Al 2 O 3 / Co ͑3.7 eV͒ from that of Co. This offset, caused by a strong interface dipole, rigidly shifts the valence features of Alq 3 toward higher binding energy, increasing the hole-injection barrier and decreasing the electron-injection barrier compared to the case of vacuum level alignment to a 5.0 eV work function electrode.…”

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confidence: 99%

The role of aluminum oxide buffer layer in organic spin-valves performance

Zhan

Liu

Carlegrim

et al. 2009

Applied Physics Letters

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The electronic structures of the 8-hydroxyquinoline-aluminum (Alq(3))/Al2O3/Co interfaces were studied by photoelectron spectroscopy. A strong interface dipole was observed, which leads to a reduction in the electron injection barrier. The x-ray photoelectron spectroscopy spectra further indicate that the Al2O3 buffer layer prevents the chemical interaction between Alq(3) molecules and Co atoms. X-ray magnetic circular dichroism results demonstrate that a Co layer deposited on an Al2O3 buffered Alq(3) layer shows better magnetic ordering in the interface region than directly deposited Co, which suggests a better performance of spin valves with such a buffer layer. This is consistent with the recent results from [Dediu , Phys. Rev. B 78, 115203 (2008)].

Original Publication:Yiqiang Zhan, Xianjie Liu, Elin Carlegrim, Fenghong Li, I Bergenti, P Graziosi, V Dediu and Mats Fahlman, The role of aluminum oxide buffer layer in organic spin-valves performance, 2009, APPLIED PHYSICS LETTERS, (94), 5, 053301.http://dx.doi.org/10.1063/1.3078274Copyright: American Institute of Physicshttp://www.aip.org/

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Energy level alignment at Alq/metal interfaces

Cited by 180 publications

References 15 publications

Electronic Structure of C₆₀/Phthalocyanine/ITO Interfaces Studied using Soft X-ray Spectroscopies

Electronic Structure of C₆₀/Phthalocyanine/ITO Interfaces Studied using Soft X-ray Spectroscopies

First-principles molecular dynamics study of Al/Alq₃interfaces

The role of aluminum oxide buffer layer in organic spin-valves performance

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Energy level alignment at Alq/metal interfaces

Cited by 180 publications

References 15 publications

Electronic Structure of C60/Phthalocyanine/ITO Interfaces Studied using Soft X-ray Spectroscopies

Electronic Structure of C60/Phthalocyanine/ITO Interfaces Studied using Soft X-ray Spectroscopies

First-principles molecular dynamics study of Al/Alq3interfaces

The role of aluminum oxide buffer layer in organic spin-valves performance

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Product

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Electronic Structure of C₆₀/Phthalocyanine/ITO Interfaces Studied using Soft X-ray Spectroscopies

Electronic Structure of C₆₀/Phthalocyanine/ITO Interfaces Studied using Soft X-ray Spectroscopies

First-principles molecular dynamics study of Al/Alq₃interfaces