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Modification of TiO <sub/>2</sub> (1?1?0)/organic hole transport layer interface energy levels by a dipolar perylene derivative
摘要： Our photoemission study reveals that the work function of TiO2(1 1 0) decreases by up to 1.5 eV upon deposition of 9-(bis-(p-(tert-octyl)phenyl)amino)-perylene-3,4-dicarboxylic anhydride (BOPA-PDCA). This effect is attributed to a chemical reaction of TiO2(1 1 0) and the molecular anhydride group, as well as the molecular dipole. Analysis of the film thickness dependent photoemission and metastable atom electron spectroscopy data reveals that for low coverage the perylene backbone of BOPA-PDCA is almost parallel to the substrate surface and higher coverage leads to an orientational transition to essentially upright standing molecules. Comparing the energy-level alignment between TiO2(1 1 0) and the hole transport materials N,N′-bis(1-naphthyl)-N,N′-diphenyl-1,1′-biphenyl-4,4′-diamine (NPB) without and with the BOPA-PDCA interlayer, we find that the perylene derivative has a positive impact on the level alignment for dye-sensitized solar cells with high open-circuit voltages.
关键词： solid state dye-sensitized solar cell,titanium dioxide,energy-level alignment,ultraviolet photoelectron spectroscopy,metastable atom electron spectroscopy,perylene
更新于2025-09-23 15:23:52
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Properties of sputtered BaSi<sub>2</sub> thin films annealed in vacuum condition
摘要： Herein, BaSi2 films are deposited by the sputtering technique. A vacuum annealing process is subsequently carried out to crystallize sputtered BaSi2 films. Raman spectroscopy is used to study surface structures and crystalline quality. Elemental depth profile is measured by Auger Electron spectroscopy to understand the compositions of films. Optical and electrical properties are further investigated to reveal the effects of annealing condition. Applying vacuum annealing condition can effectively suppress diffusions of Ba and ensures a stochiometric BaSi2 layer. However, surface oxidation still occurs even in the vacuum environment owing to the high reactivity of Ba. Further attempts to prevent BaSi2 surface oxidation may focus on the combination of other methods, such as capping layer and reducing atmosphere, with vacuum (or low-pressure) annealing condition.
关键词： Auger Electron spectroscopy,vacuum annealing,BaSi2,surface oxidation,Raman spectroscopy,sputtering
更新于2025-09-12 10:27:22
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Field emission microscopy pattern of a single-crystal diamond needle under ultrafast laser illumination
摘要： We report herein on the spatial beam properties of a ?eld emission electron source based on a single-crystal diamond needle illuminated by ultrashort light pulses. We show that the increasing of the laser intensity strongly modi?es the emission pattern, leading to the emergence of a new emission region at high peak power. This region is situated on the opposite side of the diamond needle to the one irradiated by the laser. By spatially-resolved energy spectrometry, we prove that the electrons emitted from this region are governed by a multi-photon absorption process. The occurrence of this emission pattern can be explained by accounting for the inhomogeneous distribution of the optical ?eld enhancement and the laser absorption induced by light diffraction within the nanometric needle. The numerical simulations performed on a real sub-wavelength tip con?rm this localization of the optical ?eld enhancement and reveal that the electrons trajectories match the spatial beam distribution evidenced experimentally. This work underlines the need to closely monitor the surface roughness of the ?eld emitter as well as the laser illumination conditions to ?nely control its emission pattern.
关键词： ?eld emission,diamond,ultrafast laser,electron spectroscopy,nanoemitters
更新于2025-09-11 14:15:04
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The Influence of Moisture on the Energy Level Alignment at the MoO <sub/>3</sub> /Organic Interfaces
摘要： MoO3 is widely used in polymer-based organic solar cells as an anode buffer layer due to its high workfunction and formation of a strong dipole at the MoO3/polymer interface facilitating the charge transfer across the MoO3/polymer interface. In the present work we show that exposure of the MoO3/polymer interface to moisture attracts water molecules to the interface via diffusion. Due to their own strong dipole water molecules counter the dipole at the MoO3/polymer interface. As a consequence, the charge transfer across the MoO3/polymer will reduce and affect the charge transport across the interface. The outcome of this work thus suggest that it is critical to keep the MoO3/polymer interface moisture free which requires special precautions in device fabrications. The composition of the MoO3/P3HT:PC61BM interface is analyzed with X-ray photoelectron spectroscopy and the depth profiling technique neutral impact collision ion scattering spectroscopy. The results show that the concentration of oxygen increases upon exposure but leave the oxidation state of the Mo unchanged. Valence electron spectroscopy technique shows that the dipole across the MoO3/P3HT:PC61BM interface decreases even for short time exposure to atmosphere due to the diffusion of water molecules to the interface. The far-ranging consequences for organic electronic devices are discussed.
关键词： exposure to air,interface,dipole formation,electron spectroscopy,metal oxide,organic photovoltaic,conjugated polymer
更新于2025-09-11 14:15:04
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Silicide phase formation by Mg deposition on amorphous Si. Ab initio calculations, growth process and thermal stability
摘要： Formation of magnesium silicides on amorphous silicon by deposition of Mg at room temperature is studied by electron energy loss spectroscopy, differential reflectance spectroscopy and high resolution transmission electron microscopy. Optimal crystal structures of Mg silicides under high pressure are found by ab initio DFT calculations. These structures are related to the particular minima of enthalpy. Dielectric functions are calculated for these structures. The transitions from the cubic phase c-Mg2Si to orthorhombic o-Mg2Si at 5.6 GPa and then from o-Mg2Si to hexagonal h-Mg2Si at 22.3 GPa are predicted using the USPEX code. The experimental spectra and the data obtained from the calculated dielectric functions are mutually consistent. Optical reflectance is suitable for monitoring the growth and transformations of the phases during experiments. During Mg deposition onto amorphous Si, the o-Mg2Si phase forms first, then the c-Mg2Si phase grows upon it. The observed sequence of phase formation is related with the compression stress arising in the depth of the Mg-Si mixture.
关键词： optical reflection spectroscopy,electron energy loss spectroscopy,solid state reactions,thin films,high resolution transmission electron spectroscopy,ab initio calculations
更新于2025-09-09 09:28:46