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An internal quantum efficiency (IQE) as high as 39% was achieved with the nonpolar a-plane AlGaN-based multiple quantum wells (MQWs) grown on the r-plane sapphire substrate with metal organic chemical vapor deposition technology. Evident fourth order X-ray diffraction satellite peak and intense MQW-related exciton emission peak at a wavelength of 279.2 nm were observed, implying the successful growth of high quality nonpolar aplane AlGaN-based MQWs. It was found that the employment of the trimethyl-aluminum (TMAl) flow duty-ratio modulation method played a crucial role in the epitaxial growth of the nonpolar a-plane AlGaN MQWs with sharp heterointerfaces and high IQE. Moreover, the unambiguous absence of the blue-shift in the MQWs-related exciton emission peak was verified in spite of the increase in the excitation power during the measurement of the excitation power-modulated photoluminescence spectra, indicating a complete elimination of the quantum confined Stark effect in the nonpolar AlGaN-based MQWs.

Nonpolar a-plane AlGaN epi-layers were grown on a semi-polar r-plane sapphire substrate with an innovative two-way pulsed-flows metal organic chemical vapor deposition growth technology. A root-mean-square value of 1.79 nm was achieved, and the relative light transmittance of the a-plane AlGaN epi-layer was enhanced by 36.9%. These results reveal that the innovative growth method is able to improve the surface morphology and reduce the defect density in nonpolar a-plane Al x Ga1– x N epi-layers, particularly those with an Al composition greater than 0.5, which are key materials for the fabrication of nonpolar AlGaN-based high light emission efficiency deep-ultraviolet light-emitting diodes.

Monolayer and multilayer films with morphology-controllable structures are promising for applications in building novel sensor devices, light-emitting diodes, biomedical coatings, and in creating organically based nonlinear optical materials. [1] Various approaches, including spin-coating, the Langmuir± Blodgett technique, electrostatic adsorption of oppositely charged polyelectrolytes, and covalent attachment of polymers using conventional coupling chemistry, have been used to produce complex nanostructures and have been developed for preparing different hybrids with diversified morphologies.[2] The general utility of these methods has been further extended by incorporating nanocrystals into polymer matrices.[3] The versatility and complexity of these polymeric composites provide new opportunities in the semiconductor, photovoltaic, and molecular electronic fields. [4] However, it is still important to study thin-film preparation in various media and with a variety of modification agents.[5]Incorporating metal nanocrystals in biological systems is a widespread, yet incompletely understood, procedure, involving complex interactions at the biomacromolecule±metal nucleus interface.[6] Studying this process may help us to understand and control the formation of metal nanocrystals in a generalized peptide±amphiphile chain system. Two major approaches have been developed to organize metal nanoparticles into polymer substrates.[7±12] The first method involves the self-coding of nanoparticle building blocks that can be coupled via interparticle connectors with specific recognition properties based on, for example, DNA duplex formation, [7] antibody±antigen specificity, [8] streptavidin±biotin coupling, [9] electrostatic matching, [10] or shape-directed hydrophobic forces.[11]Another method, the template-directed approach, [12] utilizes porous solid substrates or discrete liquid droplets as patterned or shaped interfaces for the assembly of preformed nanoparticles. In this process capillary, drying, and swelling forces, or other chemical interactions, are used to implant, position, and immobilize nanoparticles irreversibly within the template or around the surface of individual latex beads pre-coated with a layer-by-layer shell of oppositely charged polyelectrolyte macromolecules. However, to the best of our knowledge, there has been no previous example of incorporating bimetal solid solutions into a biological system in order to form a well-defined morphology without using any template or specific recognition interparticle connectors.Herein, we present a versatile procedure, based on the selfassembly process, for preparing a large-area nanoscale ªsand-wichº layer array of tailored composition, with a controllable crystalline phase and defined morphology. The idea for creating this composite film was stimulated by Yang and Rubner, [13] who developed a novel assembly method by using hydrogen-bonding interactions to fabricate a polyelectrolyte multilayer film. Differing from their work, we employed a protein with a unique...

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A three-dimensional lightweight metamaterial (MM) with ultra-wideband microwave absorption is proposed in this paper. Based on the concept of MMs, periodically arranged resistive films are introduced into the standing frame to form a standing lossy structure, which can introduce electric resonances in the gap between adjacent sub-wavelength unit cells at lower frequencies. Several standing wave modes are also excited in the standing lossy structure at higher frequencies, resulting in an ultra-wideband absorption for electromagnetic waves. The full-wave simulation demonstrates that the MM can absorb over 90% of the incident wave energy in the range 1.46-40 GHz, with a relative bandwidth of 185.9%. The experimentally measured results correspond to the simulated results across the entire frequency range. In addition, the proposed MM is lightweight, easy to fabricate.

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