The electronic structure of the interfaces formed after deposition of MoO3 hole‐injection layers on top of a polymer light‐emitting material, poly(dioctylfluorene‐alt‐benzothiadiazole) (F8BT), is studied by ultraviolet photoelectron spectroscopy (UPS), X‐ray photoelectron spectroscopy and metastable atom electron spectroscopy. Significant band bending is induced in the F8BT film by MoO3 “acceptors” that spontaneously diffuse into the F8BT “host” probably driven by kinetic energy of the deposited hot MoO3. Further deposition leads to the saturation of the band bending accompanied by the formation of MoO3 overlayers. Simultaneously, a new electronic state in the vicinity of the Fermi level appears on the UPS spectra. Since this peak does not appear in the bulk MoO3 film, it can be assigned as an interface state between the MoO3 overlayer and underlying F8BT film. Both band bending and the interface state should result from charge transfer from F8BT to MoO3, and they appear to be the origin of the hole‐injection enhancement by the insertion of MoO3 layers between the F8BT light‐emitting diodes and top anodes.

This paper reports that structural imperfection in an organic thin film modulates the electronic structure to result in a serious band bending and change in the energy-level alignment (ELA) at the organic-conductor interface. Ultraviolet photoelectron spectroscopy (UPS) and metastable atom electron spectroscopy (MAES) were adopted to investigate thickness dependences of the electronic structure of polar phthalocyanine (chlorogallium phthalocyanine) thin films grown on graphite with respect to the film structure. We observed a large bandbending-like shift of occupied molecular-orbital bands toward the Fermi level and a continuous increase in the vacuum level for the as-grown film, whereas these phenomena were considerably suppressed by annealing the film. Both the as-grown and annealed films were characterized as essentially the same stacked bilayer film structure; however, high-resolution UPS and MAES measurements evidenced that there are structural defects in the as-grown film but not clearly in the annealed film, indicating that the defects are the origin of the modulation of the ELA and the band bending. Controlling the structural imperfections is a key issue for the desired ELA in organic devices.

Atomically flat terraced ZnO surfaces were prepared with thermal annealing in air. CdO dots were successfully formed on the ZnO substrate surfaces with in-situ post-growth thermal annealing of CdO layers grown by metalorganic molecular-beam epitaxy. Well-organized alignment of the CdO dots along surface atomic-step edges on the terraced surfaces is demonstrated.1 Introduction ZnO and related oxide materials have large exciton binding energies and the corresponding large oscillator strengths [1]. Further enhancement of excitonic properties is expected in oxide quantum structures such as quantum dots and wires, and higher-performance lasers and/or single-photonbased quantum information processing devices are expected with these distinguished features in oxidebased quantum nanostructures. Especially enhanced oscillator strengths in oxide-based nanostructures are expected to open the high possibility to realize strong coupling regime between excitons and photonic fields [2]. That has been difficult with widely used III-V semiconductors with some exceptions [3,4].Researches on oxide-based nanostructures therefore have been activated recently, and open-shaped ZnO dots [5,6] and nanowires [7][8][9] or nanorods [10] have been mainly studied. These ZnO-based nanostructures cover the ultraviolet wavelength range shorter than 350 nm. The other oxide material candidates which will cover visible wavelength range will be CdO or CdZnO. However, growth of single-crystalline CdO or CdZnO has been difficult. The growth of CdZnO faced a phase separation problem and a reproducible growth of CdZnO alloy semiconductors was difficult [11]. Very recently a growth of wurtzite (WZ) CdZnO was reported with plasma-assisted metaloragnic vapor-phase epitaxy [12]. The growth of single-crystalline rocksalt (RS) CdO was also reported with metalorganic molecularbeam epitaxy (MOMBE) [13].Following the above background, trials to grow CdO-based nanostructures are a challenging issue to open a new possibility of oxide nanostructures in visible regions. In this paper, a first successful formation of CdO dots is reported on atomically flat ZnO substrate surfaces with in-situ post-growth thermal annealing. Well-organized alignment of the CdO dots along the surface atomic step edges on terraced surfaces is also demonstrated and its formation mechanism is discussed.

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