High-quality ZnO films have been grown on Zn-polar ZnO substrates by plasma-assisted molecular beam epitaxy. With increasing O/Zn ratio from the stoichiometric to the O-rich flux condition, the growth mode and the surface morphology changed from three-dimensional growth with a rough surface to two-dimensional growth with a smooth surface. The minimum linewidth from the (10 1 10) !-rocking curve was 100 arcsec, and the n ¼ 2 state of A-exciton was clearly observed in the photoluminescence at 4.2 K. Due to the reduction in the edge-type threading dislocation density, the residual carrier concentration in these homoepitaxial ZnO films was as low as 2:2 Â 10 16 cm À3 , which is one order of magnitude lower than that previously reported for heteroepitaxial ZnO films.
Nanoantenna-like properties of sea-urchin shaped ZnO as a nanolight filter Appl. Phys. Lett. 101, 133101 (2012) Leaky mode analysis of luminescent thin films: The case of ZnO on sapphire J. Appl. Phys. 112, 063112 (2012) ZnO/ZnSxSe1−x core/shell nanowire arrays as photoelectrodes with efficient visible light absorption Appl. Phys. Lett. 101, 073105 (2012) Study of the photoluminescence emission line at 3.33eV in ZnO films
Polarity-controlled ZnO films with an MgO buffer layer were grown on c-plane sapphire by plasma-assisted molecular-beam epitaxy. Convergent beam electron diffraction results showed that Zn-polarity (+c) growth occurred when the MgO layer was thicker than 3 nm, whereas O-polarity (−c) growth occurred when the layer was less than 2 nm. Reflection high-energy electron diffraction results revealed that MgO growth was Stranski–Krastanov mode, and that the growth mode transition from two- to three-dimensional occurred when the layer was thicker than 1 nm. In conclusion, polarity conversion apparently occurs due to the different atomic structure between the wetting layer and islands of MgO.
We introduce ThreeDWorld (TDW), a platform for interactive multi-modal physical simulation. With TDW, users can simulate high-fidelity sensory data and physical interactions between mobile agents and objects in a wide variety of rich 3D environments. TDW has several unique properties: 1) realtime near photo-realistic image rendering quality; 2) a library of objects and environments with materials for high-quality rendering, and routines enabling user customization of the asset library; 3) generative procedures for efficiently building classes of new environments 4) high-fidelity audio rendering; 5) believable and realistic physical interactions for a wide variety of material types, including cloths, liquid, and deformable objects; 6) a range of avatar types that serve as embodiments of AI agents, with the option for user avatar customization; and 7) support for human interactions with VR devices. TDW also provides a rich API enabling multiple agents to interact within a simulation and return a range of sensor and physics data representing the state of the world. We present initial experiments enabled by the platform around emerging research directions in computer vision, machine learning, and cognitive science, including multi-modal physical scene understanding, multi-agent interactions, models that learn like a child, and attention studies in humans and neural networks. The simulation platform will be made publicly available.Preprint. Under review.
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