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Journal of Applied Linguistics 08/2012;
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ABSTRACT: We demonstrate that the interfacial hole injection barrier D h between p-type organic materials (i.e., CuPc and pentacene) and Co substrate can be tuned by the insertion of a MoO 3 buffer layer. Using ultraviolet photoemission spectroscopy, it was found that the introduction of MoO 3 buffer layer effectively reduces the hole injection barrier from 0.8 eV to 0.4 eV for the CuPc/Co interface, and from 1.0 eV to 0.4 eV for the pentacene/Co interface, respectively. In addition, by varying the thickness of the buffer, the tuning effect of D h is shown to be independent of the thickness of MoO 3 interlayer at both CuPc/Co and pentacene/Co interfaces. This Fermi level pinning effect can be explained by the integer charge-transfer model. Therefore, the MoO 3 buffer layer has the potential to be applied in p-type organic spin valve devices to improve the device performance via reducing the interfacial hole injection barrier. V C 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4740455]
Journal of Applied Physics 08/2012; 112:033704. · 2.17 Impact Factor
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ABSTRACT: In this paper, we successfully demonstrated the fabrication of highly ordered and large-scale P3HT:PCBM nanowires via a slow-drying method, which allows for the convenient and cost-effective preparation of well-defined P3HT:PCBM nanostructures with large domains. The formation of the organic nanowires can be explained by the self-organization of polymer chains under favorable thermodynamic conditions in the slow-drying process. Furthermore, the C-V measurements revealed that the P3HT:PCBM nanowires possess high capacitance. This supercapacitive behavior of the nanowires is related to their large surface area and open structure, which can facilitate ion transport and accumulation. Owing to their extremely easy preparation and excellent capacitance performance, the P3HT:PCBM nanowires offer a promising electrode material for supercapacitor devices.
Nanoscale 05/2012; 4(12):3725-8. · 5.91 Impact Factor
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Liang Cao, Yu-Zhan Wang,
Tie-Xin Chen,
Wen-Hua Zhang,
Xiao-Jiang Yu,
Kurash Ibrahim,
Jia-Ou Wang,
Hai-Jie Qian,
Fa-Qiang Xu,
Dong-Chen Qi,
Andrew T S Wee
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ABSTRACT: Charge transfer dynamics across the lying-down 3,4,9,10-perylene-tetracarboxylic-dianhydride (PTCDA) organic semiconductor molecules on Au(111) interface has been investigated using the core-hole clock implementation of resonant photoemission spectroscopy. It is found that the charge transfer time scale at the PTCDA∕Au(111) interface is much larger than the C 1s core-hole lifetime of 6 fs, indicating weak electronic coupling between PTCDA and the gold substrate due to the absence of chemical reaction and∕or bonding.
The Journal of chemical physics 11/2011; 135(17):174701. · 3.09 Impact Factor
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ABSTRACT: The electronic structures at the MoO(3)∕Co interface were investigated using synchrotron-based ultraviolet and x-ray photoelectron spectroscopy. It was found that interfacial chemical reactions lead to the reduction of Mo oxidation states and the formation of Co-O bonds. These interfacial chemical reactions also induce a large interface dipole, which significantly increases the work function of the cobalt substrate. In addition, two interface states located at 1.0 and 2.0 eV below the Fermi level are identified. These two states overlap at film thickness of between 2-4 nm, which suggests the MoO(3) intermediate layer may facilitate ohmic charge transport.
The Journal of chemical physics 01/2011; 134(3):034706. · 3.09 Impact Factor
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ABSTRACT: The interface electronic structure of C60/CuPc and C60 heterojunctions on SiO2 and highly oriented pyrolytic graphite has been studied using ultraviolet photoelectron spectroscopy, x-ray photoelectron spectroscopy, and synchrotron based photoelectron spectroscopy. Fermi level pinned to the negative integer charge transfer state of C60 molecules on the standing CuPc film has been observed, while nearly vacuum-level alignment is observed for C60 on the lying CuPc film. We also found small vacuum-level shifts for C60 on both standing and lying F16CuPc films, which can be attributed to the rearrangement of underlying F16CuPc molecules. With the use of orientation-controlled CuPc and F16CuPc thin films, C60 highest occupied molecular orbital energy levels relative to the substrate Fermi level can be tuned from 1.9 eV for C60 on the standing CuPc film to 1.0 eV on the standing F16CuPc film.
Journal of Applied Physics 09/2010; 108(5):053706-053706-6. · 2.17 Impact Factor
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Zhenyu Chen,
Iman Santoso,
Rui Wang,
Lan Fei Xie,
Hong Ying Mao,
Han Huang, Yu Zhan Wang,
Xing Yu Gao,
Zhi Kuan Chen,
Dongge Ma,
Andrew Thye Shen Wee,
Wei Chen
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ABSTRACT: Synchrotron-based in situ photoelectron spectroscopy investigations demonstrate effective surface transfer p-type doping of epitaxial graphene (EG) thermally grown on 4H–SiC(0001) via the deposition of MoO3 thin film on top. The large work function difference between EG and MoO3 facilitates electron transfer from EG to the MoO3 thin film. This leads to hole accumulation in the EG layer with an areal hole density of about 1.0×1013 cm−2, and places the Fermi level 0.38 eV below the graphene Dirac point.
Applied Physics Letters 05/2010; 96(21):213104-213104-3. · 3.84 Impact Factor
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Journal of Applied Physics 01/2010; · 2.17 Impact Factor
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ABSTRACT: Molecular orientation dependent energy level alignments at organic−organic heterojunction (OOH) interfaces have been investigated with synchrotron based high-resolution photoemission spectroscopy and near-edge X-ray absorption fine structure (NEXAFS) measurements. Model systems of the lying-down 3,4,9,10-perylene-tetracarboxylic-dianhydride (PTCDA) films on both standing-up and lying-down copper hexadecafluorophthalocyanine (F16CuPc) and copper(II) phthalocyanine (CuPc) thin films have been used to illustrate the molecular orientation dependent interface properties. The formation of different interface dipoles at the heterojunction interfaces is strongly influenced by the orientation dependent ionization potentials of the underlying F16CuPc or CuPc thin films. This is attributed to the intrinsic surface dipoles induced in the standing-up F16CuPc (CuPc) film due to the polar intermolecular C−F (C−H) bonds formed at the interface. In situ NEXAFS measurements reveal that the room-temperature deposition of PTCDA layers does not alter the molecular orientation of the underlying lying-down or standing-up F16CuPc thin films. We also demonstrate that the binding energies of both the C 1s core level and the highest-occupied-molecular-orbital (HOMO) of PTCDA on the lying-down F16CuPc thin film is 0.3 eV higher than those on the standing-up F16CuPc thin film. This shows that it is possible to manipulate the energy level alignment at OOH interfaces by choosing the appropriate molecular orientation. In contrast, the HOMO positions of PTCDA on both lying-down and standing-up CuPc films are almost identical. This suggests that an orientation independent Fermi-level pinning occurs at the PTCDA/CuPc interfaces involving interfacial charge transfer.
07/2009;
