A hierarchical nano- and microstructured morphology for visible-blind UV photo-detectors is developed, which provides record-high milliampere photocurrents, nanoampere dark currents, and excellent selectivity to ultralow UV light intensities. This is a significant step toward the integration of high-performance UV photodetectors in wearable devices.

We report the growth of stacking-fault-free and taper-free wurtzite InP nanowires with diameters ranging from 80 to 600 nm using selective-area metal-organic vapor-phase epitaxy and experimentally determine a quantum efficiency of ∼50%, which is on par with InP epilayers. We also demonstrate room-temperature, photonic mode lasing from these nanowires. Their excellent structural and optical quality opens up new possibilities for both fundamental quantum optics and optoelectronic devices.

The recent rise of metamaterials opens new opportunities for absorbers due to their designed electrodynamic properties and effects, allowing the creation of materials with effective values of permittivity and permeability that are not available in naturally occurring materials. Since their first experimental demonstration in 2008, recent literature has offered great advances in metamaterial This article is protected by copyright. All rights reserved. 2 perfect absorber (MMPA) operating at frequencies from radio to optical. Broadband absorbers are indispensable in thermophotovoltaics, photodetection, bolometry and manipulation of mechanical resonances. Although it is easy to obtain MMPA with single band or above, achieving broadband MMPA (BMMPA) remains a challenge due to the intrinsically narrow bandwidth of surface plasmon polaritons, localized surface plasmon resonances generated on metallic surfaces at nanoscale or high Q-factor in GHz region. To guide future development of BMMPA, recent progress is reviewed here: the methods to create broadband absorption and their potential applications. The four mainstream methods to achieve BMMPA are introduced, including planar and vertical element arrangements, their welding with lumped elements and the use of plasmonic nanocomposites, accompanied by the description of other, less common approaches. Following this, applications of BMMPA in solar photovoltaics, photodetection, bolometry and manipulation of mechanical resonances are reviewed. Finally, challenges and prospects are discussed.

Nb+Al) codoped rutile TiO 2 ceramics with nominal composition Ti 4+ 0.995 Nb 5+ 0.005y Al 3+ 0.005z O 2 , z = (4−5y)/3 and y = 0.4, 0.5, 0.6, 0.7, and Ti 4+ 0.90 Nb 5+ 0.05 Al 3+ 0.05 O 2 have been synthesized. The resultant samples in ceramic pellet form exhibit a colossal dielectric permittivity (>∼10 4 ) with an acceptably low dielectric loss (∼10 −1 ) after optimization of the processing conditions. It is found that a conventional surface barrier layer capacitor (SBLC) effect, while it contributes significantly to the observed colossal permittivity, is not the dominant effect. Rather, there exists a subtle chemical compositional gradient inward from the pellet surface, involving the concentration of Ti 3+ cations gradually increasing from zero at the surface without the introduction of any charge compensating oxygen vacancies. Instead, well-defined G r ± 1 / 3 [011]* satellite reflections with the modulation wave-vector q = 1 / 3 [011] r * and sharp diffuse streaking running along the G r ± ε[011]* direction from electron diffraction suggest that the induced additional metal ions appear to be digested by a locally intergrown, intermediate, metal ion rich structure. This gradient in local chemical composition exists on a scale up to ∼ submillimeters, significantly affecting the overall dielectric properties. This work suggests that such a controllable surface compositional gradient is an alternative method to tailor the desired dielectric performance.

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The anisotropic nature of the new two-dimensional (2D) material phosphorene 1-9 , in contrast to other 2D materials such as graphene 10 A neutral exciton is a bound quasi-particle state between one electron and one hole through a Coulomb interaction, similar to a neutral hydrogen atom. A trion is a charged exciton composed of two electrons and one hole (or two holes and one electron), analogous to H -(or H2 + ) 20 . Trions have been of considerable interest for the fundamental studies of many-body interactions, such as carrier multiplication and Wigner crystallization 21 . In contrast to the exciton, a trion has an extra charge with nonzero spin, which can be used for spin manipulation 22,23 . More importantly, the density of trions can be electrically tuned by the gate voltage, enabling remarkable optoelectronic applications [18][19][20]24,25 . For these purposes, a large trion binding energy is critical in order to overcome the room-temperature thermal fluctuations as well as to widen the spectral tuning range. The dimensional confinement is the dominating factor that determines the binding energy of trions. In quasi-2D quantum wells, the trion binding energy is only 1-5 meV, and trions are highly unstable, except at cryogenic temperatures 16,17 . The complete separation of the exciton and trion emission peaks was observed at room temperature 16,17 . However, the application of 1D carbon nanotubes for practical optoelectronic devices is intrinsically limited by their small cross-sections. The overall optical responses of such 1D lines are extremely weak. The diverse distribution of the chirality in carbon nanotubes also makes it impossible to assemble a large-size film with uniform optoelectronic responses.While the reduced dimensionality leads to far more attractive exciton and trion properties, the trade-off between the cross-section and the dimensional confinement has hindered the development of useful excitonic optoelectronic devices.Here, we show that phosphorene presents an intriguing platform to overcome the aforementioned trade-off. We observed quasi-1D trions with ultra-high binding energies up to This new type of material, few-layer phosphorene, is unstable and does not survive well in many standard nanofabrication processes. To overcome the challenge of the instability, we designed special fabrication and characterization techniques. We used mechanical exfoliation to drily transfer 26 a phosphorene flake onto a SiO2/Si substrate (275 nm thermal oxide on n + -doped silicon). The phosphorene was placed near a gold electrode that was pre-patterned on the substrate. Another thick graphite flake was similarly transferred to electrically bridge the phosphorene flake and the gold electrode, forming a MOS device (Figure 1). This fabrication procedure kept the phosphorenes free from chemical contaminations by minimizing the postprocesses after the phosphorene flake was transferred. In the measurement, the gold electrode is grounded, and the n + -doped Si substrate functions as a back gate providing uniform...

Controllable axial switching of polarity in GaAs nanowires with minimal tapering and perfect twin-free ZB structure based on the fundamental understanding of nanowire growth and kinking mechanism is presented. The polarity of the bottom segment is confirmed to be (111)A by atomically resolved scanning transmission electron microscopy.

Water droplets on rough hydrophobic surfaces are known to exist in two states; one in which the droplet is impaled on the surface asperities (Wenzel state) and the other, a superhydrophobic state in which air remains trapped beneath the droplet (Cassie state). Here, we demonstrate that water droplets can transit from the Wenzel-to-Cassie state even though the former is energetically favored. We find that two distinct superhydrophobic states are produced. One is a true Cassie state, whereas the other exhibits superhydrophobicity in the absence of a vapor phase being trapped in the surface roughness. Furthermore, we can selectively drive the motion of water droplets on tilted structured hydrophobic surfaces by exploiting Wenzel-to-Cassie transitions. This can be achieved by heating the substrate or by directly heating the droplet using a laser.