Transparent, Flexible, and Low-Operating-Voltage Resistive Switching Memory Based on Al2O3/IZO Multilayer.

In this study, a different number of indium zinc oxide (IZO) interlayers are fabricated into Al2O3-based transparent resistive switching memory on a transparent indium tin oxide (ITO)/glass substrate at room temperature. Al2O3/IZO multilayer transparent memory has a transmittance of at least 65% in the wavelength range of 400-900 nm. In addition, the Al2O3/IZO multilayer transparent memory can achieve an electroforming voltage that is 35.7% lower than that of ITO/pure-Al2O3/IZO transparent memory. The fabricated Al2O3/IZO multilayer transparent memory exhibits typical bipolar resistive switching behavior, regardless of the number of IZO interlayers. Also, the fabricated Al2O3/IZO multilayer transparent memory has a low operating voltage within ±1.5 V. In addition, a flexible Al2O3/IZO multilayer transparent memory is fabricated using the same process on ITO-coated polyethylene terephthalate. The fabricated flexible transparent memory also maintains the resistive switching characteristics during the bending state.

High thermoelectric figure of merit of porous Si nanowires from 300 to 700 K.

Thermoelectrics operating at high temperature can cost-effectively convert waste heat and compete with other zero-carbon technologies. Among different high-temperature thermoelectrics materials, silicon nanowires possess the combined attributes of cost effectiveness and mature manufacturing infrastructures. Despite significant breakthroughs in silicon nanowires based thermoelectrics for waste heat conversion, the figure of merit (ZT) or operating temperature has remained low. Here, we report the synthesis of large-area, wafer-scale arrays of porous silicon nanowires with ultra-thin Si crystallite size of ~4 nm. Concurrent measurements of thermal conductivity (κ), electrical conductivity (σ), and Seebeck coefficient (S) on the same nanowire show a ZT of 0.71 at 700 K, which is more than ~18 times higher than bulk Si. This ZT value is more than two times higher than any nanostructured Si-based thermoelectrics reported in the literature at 700 K. Experimental data and theoretical modeling demonstrate that this work has the potential to achieve a ZT of ~1 at 1000 K.

Single-step manufacturing of hierarchical dielectric metalens in the visible.

Metalenses have shown a number of promising functionalities that are comparable with conventional refractive lenses. However, current metalenses are still far from commercialization due to the formidable fabrication costs. Here, we demonstrate a low-cost dielectric metalens that works in the visible spectrum. The material of the metalens consists of a matrix-inclusion composite in which a hierarchy satisfies two requirements for the single-step fabrication; a high refractive index and a pattern-transfer capability. We use a UV-curable resin as a matrix to enable direct pattern replication by the composite, and titanium dioxide nanoparticles as inclusions to increase the refractive index of the composite. Therefore, such a dielectric metalens can be fabricated with a single step of UV nanoimprint lithography. An experimental demonstration of the nanoparticle composite-based metalens validates the feasibility of our approach and capability for future applications. Our method allows rapid replication of metalenses repeatedly and thereby provides an advance toward the use of metalenses on a commercial scale.

Enhancing light conversion efficiency of YAG:Ce phosphor substrate using nanoimprinted functional structures.

A phosphor substrate converts a moderate amount of blue light to green light to produce white light. In this study, we have successfully demonstrated the enhancement of the light extraction efficiency of YAG:Ce phosphor substrate using a simple imprint process. Spin-on-glass materials were used to fabricate a pattern on the surface of a phosphor substrate, and nano- and micro-scale patterns were formed to test the performance according to the size of pattern. The light extraction efficiency of the phosphor substrate with a micro-cone pattern increased by 33.2% compared with the flat phosphor substrate.

The optimization of surface morphology of Au nanoparticles on WO3 nanoflakes for plasmonic photoanode.

Among many candidates for photoanode materials of photoelectrochemical (PEC) cell, nanostructured tungsten trioxide (WO3) is regarded as one of the most promising materials due to its superior electrical properties and adequate bandgap (∼2.8 eV) and band edge position. WO3 nanoflakes (WO3 NFs), which have merits on its high surface area and crystallinity, have been actively studied for this manner but solar-to-hydrogen efficiency of WO3 NFs based photoanode is still not sufficient both in light absorption and charge separation. Plasmon-induced enhancement using Au nanoparticles is excellent approach for both the efficiency of light absorption and charge separation of WO3. However, it still needs optimization on its amount, shape, coverage, and etc. Here, we synthesized WO3 NFs by solvothermal growth and decorated gold nanoparticles on these nanoflakes by e-beam evaporation and rapid thermal annealing process in a row. By this process, a large-area AuNPs/WO3 nanocomposite structure with various size, interparticle distance, and coverage of AuNPs were fabricated. These AuNPs/WO3 NFs type photoanode achieve high light absorption both in UV and visible range and consequently higher photocurrent density. The optimized AuNPs/WO3 nanocomposite photoanode exhibits 1.01 mA cm-2 of photocurrent density, which is increased to 19.8% compared with bare WO3 nanoflakes. Field emission-scanning electron microscope, x-ray diffraction, UV-vis spectrometer analysis were measured to analyze the morphology and crystallinity and relationship between structure and PEC performance.

Customizable 3D-printed architecture with ZnO-based hierarchical structures for enhanced photocatalytic performance.

ZnO-based hierarchical structures including nanoparticles (NPs), nanorods (NRs) and nanoflowers (NFs) on a 3D-printed backbone were effectively fabricated via the combination of the fused deposition modelling (FDM) 3D-printing technique and hydrothermal reaction. The photocatalytic performance of the ZnO-based hierarchical structures on the 3D-backbone was verified via the degradation of the organic pollutant methylene blue, which was monitored by UV-vis spectroscopy. The new photocatalytic architectures used in this investigation give an effective approach and wide applicability to overcome the limitation of photocatalysts such as secondary removal photocatalyst processes.

Spontaneous Registration of Sub-10 nm Features Based on Subzero Celsius Spin-Casting of Self-Assembling Building Blocks Directed by Chemically Encoded Surfaces.

For low-cost and facile fabrication of innovative nanoscale devices with outstanding functionality and performance, it is critical to develop more practical patterning solutions that are applicable to a wide range of materials and feature sizes while minimizing detrimental effects by processing conditions. In this study, we report that area-selective sub-10 nm pattern formation can be realized by temperature-controlled spin-casting of block copolymers (BCPs) combined with submicron-scale-patterned chemical surfaces. Compared to conventional room-temperature spin-casting, the low temperature ( e.g., -5 °C) casting of the BCP solution on the patterned self-assembled monolayer achieved substantially improved area selectivity and uniformity, which can be explained by optimized solvent evaporation kinetics during the last stage of film formation. Moreover, the application of cold spin-casting can also provide high-yield in situ patterning of light-emitting CdSe/ZnS quantum dot thin films, indicating that this temperature-optimized spin-casting strategy would be highly effective for tailored patterning of diverse organic and hybrid materials in solution phase.

Metal-Organic Framework-Templated PdO-Co3O4 Nanocubes Functionalized by SWCNTs: Improved NO2 Reaction Kinetics on Flexible Heating Film.

Detection and control of air quality are major concerns in recent years for environmental monitoring and healthcare. In this work, we developed an integrated sensor architecture comprised of nanostructured composite sensing layers and a flexible heating substrate for portable and real-time detection of nitrogen dioxide (NO2). As sensing layers, PdO-infiltrated Co3O4 hollow nanocubes (PdO-Co3O4 HNCs) were prepared by calcination of Pd-embedded Co-based metal-organic framework polyhedron particles. Single-walled carbon nanotubes (SWCNTs) were functionalized with PdO-Co3O4 HNCs to control conductivity of sensing layers. As a flexible heating substrate, the Ni mesh electrode covered with a 40 nm thick Au layer (i.e., Ni(core)/Au(shell) mesh) was embedded in a colorless polyimide (cPI) film. As a result, SWCNT-functionalized PdO-Co3O4 HNCs sensor exhibited improved NO2 detection property at 100 °C, with high sensitivity (S) of 44.11% at 20 ppm and a low detection limit of 1 ppm. The accelerated reaction and recovery kinetics toward NO2 of SWCNT-functionalized PdO-Co3O4 HNCs were achieved by generating heat on the Ni(core)/Au(shell) mesh-embedded cPI substrate. The SWCNT-functionalized porous metal oxide sensing layers integrated on the mechanically stable Ni(core)/Au(shell) mesh heating substrate can be envisioned as an essential sensing platform for realization of low-temperature operation wearable chemical sensor.