Piezo‐Phototronic Matrix via a Nanowire Array

Piezoelectric semiconductors, such as ZnO and GaN, demonstrate multiproperty coupling effects toward various aspects of mechanical, electrical, and optical excitation. In particular, the three‐way coupling among semiconducting, photoexcitation, and piezoelectric characteristics in wurtzite‐structured semiconductors is established as a new field, which was first coined as piezo‐phototronics by Wang in 2010. The piezo‐phototronic effect can controllably modulate the charge‐carrier generation, separation, transport, and/or recombination in optical‐electronic processes by modifying the band structure at the metal–semiconductor or semiconductor–semiconductor heterojunction/interface. Here, the progress made in using the piezo‐phototronic effect for enhancing photodetectors, pressure sensors, light‐emitting diodes, and solar cells is reviewed. In comparison with previous works on a single piezoelectric semiconducting nanowire, piezo‐phototronic nanodevices built using nanowire arrays provide a promising platform for fabricating integrated optoelectronics with the realization of high‐spatial‐resolution imaging and fast responsivity.     

Graphene–Mesoporous Si Nanocomposite as a Compliant Substrate for Heteroepitaxy

The ultimate performance of a solid state device is limited by the restricted number of crystalline substrates that are available for epitaxial growth. As a result, only a small fraction of semiconductors are usable. This study describes a novel concept for a tunable compliant substrate for epitaxy, based on a graphene–porous silicon nanocomposite, which extends the range of available lattice constants for epitaxial semiconductor alloys. The presence of graphene and its effect on the strain of the porous layer lattice parameter are discussed in detail and new remarkable properties are demonstrated. These include thermal stability up to 900 °C, lattice tuning up to 0.9 % mismatch, and compliance under stress for virtual substrate thicknesses of several micrometers. A theoretical model is proposed to define the compliant substrate design rules. These advances lay the foundation for the fabrication of a compliant substrate that could unlock the lattice constant restrictions for defect‐free new epitaxial semiconductor alloys and devices.     

On the Mechanism of the BCC-HCP Transformations in Small Lennard-Jones Crystals

The structure relaxation of the initially body-centered cubic clusters to the most favorable configurations has shown that the transition to the hexagonal close-packed structure starts at the cluster surface and propagates to the cluster center. The intermediate orthorhombic structure was found and forms in application to helium the regions with delocalized atoms, which are presumably important in connection with the phenomenon of ‘supersolidity’. The time to complete the transition depends on the cluster size and shape.      

Controllable synthesis of pentagonal silver nanowires via a simple alcohol-thermal method

Pentagonal silver nanowires with diameters in range of 20-40 nm, and lengths up to ~ 10 µm were successfully synthesized via a simple and effective alcohol-thermal route. These nanowires were prepared by reducing silver nitrate in ethanol solution with dodecylamine which acted as complexing, reducing and capping agent. The molar ratio of dodecylamine to AgNO₃ played an important role in controlling aspect ratio of the products. Samples were characterized in detail by X-ray diffraction (XRD), field-emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM) and high-resolution transmission electron microscopy (HRTEM) technologies. UV-vis absorption spectrum of the nanowires in solution has been taken to study their optical properties. Based on the analysis of the experimental results, the possible formation mechanism of nanowires was proposed as well.     

Preparation of silver nanoparticles via a non-template method

Silver nanoparticles have been prepared by a non-template method. Silver nitrate can be easily decomposed into silver nanosized materials. Small nanoparticles (less than 2 nm) can be formed in aqueous solution. Larger silver particles of about 100 nm can be formed in ethanol solution. By rationally adjusting the experimental conditions we finally obtain silver particles of about 20 nm with a relatively narrow distribution in ethanol solution. Differing from the previous reports, we find that silver nanoparticles can be formed by direct decomposition of AgNO₃ under UV light irradiation. No catalyst like TiO₂ is needed at all. We believe that it is a further step to precede the preparation of silver nanometer sized materials.     

Synthesis of cup-like ZnO microcrystals via a CTAB-assisted hydrothermal route

Cup-like ZnO microcrystals were successfully synthesized by using a CTAB-assisted hydrothermal route. Zn(CH₃COO)₂·2H₂O was used as the only precursor to generate cup-like ZnO microcrystals. The morphologies and structures of the samples were characterized by XRD and SEM. The XRD pattern shows that the cup-like ZnO microcrystals are hexagonal. The SEM investigation reveals that the as-prepared ZnO product has cup-like morphology. CTAB was found to play a crucial role in determining the cup-like morphologies. A possible formation process of the cup-like ZnO microcrystals was proposed. Optical property of the product was also investigated by fluorophotometer at room temperature.     

Precise Patterning of Organic Single Crystals via Capillary‐Assisted Alternating‐Electric Field

Owing to the extraordinary properties, organic micro/nanocrystals are important building blocks for future low‐cost and high‐performance organic electronic devices. However, integrated device application of the organic micro/nanocrystals is hampered by the difficulty in high‐throughput, high‐precision patterning of the micro/nanocrystals. In this study, the authors demonstrate, for the first time, a facile capillary‐assisted alternating‐electric field method for the large‐scale assembling and patterning of both 0D and 1D organic crystals. These crystals can be precisely patterned at the photolithography defined holes/channels at the substrate with the yield up to 95% in 1 mm². The mechanism of assembly kinetics is systematically studied by the electric field distribution simulation and experimental investigations. By using the strategy, various organic micro/nanocrystal patterns are obtained by simply altering the geometries of the photoresist patterns on substrates. Moreover, ultraviolet photodetectors based on the patterned Alq3 micro/nanocrystals exhibit visible–blind photoresponse with high sensitivity as well as excellent stability and reproducibility. This work paves the way toward high‐integration, high‐performance organic electronic, and optoelectronic devices from the organic micro/nanocrystals.