Haiyang Xu

Superhydrophobic and Ultraviolet-Blocking Cotton Textiles

Cotton textile was coated with ZnO@SiO(2) nanorods in order to obtain superhydrophobic and ultraviolet (UV)-blocking properties. The coating process was conducted in mild conditions, which involved the low-temperature preparation of ZnO seeds, hydrothermal growth of ZnO nanorods, bioinspired layer-by-layer deposition of a SiO(2) shell on the surface of ZnO nanorods, and hydrophobic modification of ZnO@SiO(2) nanorods with octadecyltrimethoxysilane. Despite the highly curved morphology of cotton fibers, the ZnO@SiO(2) nanorods coated the textile densely and uniformly. The treated cotton textile was found to have a large UV protection factor (UPF = 101.51) together with UV-durable superhydrophobicity, as determined by contact-angle measurement under long-term UV irradiation. The good UV-blocking property can be ascribed to the high UV absorbance and scattering properties of ZnO nanorods, and the UV-durable superhydrophobicity is a result of suppression of the photoactivity of ZnO nanorods by a SiO(2) shell.

Localized surface plasmon-enhanced ultraviolet electroluminescence from n-ZnO/i-ZnO/p-GaN heterojunction light-emitting diodes via optimizing the thickness of MgO spacer layer

Localized surface plasmon (LSP)-enhanced ultraviolet light-emitting diodes were manufactured by introducing Ag nanoparticles and MgO spacer layer into n-ZnO/i-ZnO/p-GaN heterostructures. By optimizing the MgO thickness, which can suppress the undesired charge transfer and nonradiative Forster resonant energy transfer between Ag and ZnO, a 7-fold electroluminescence enhancement was achieved. Time-resolved and temperature-dependent photoluminescence measurements reveal that both spontaneous emission rate and internal quantum efficiency are increased as a result of coupling between ZnO excitons and Ag LSPs, and simple calculations, based on experimental data, also indicate that most of LSPs energy can be converted into the photon energy.

Enhanced ultraviolet emission and improved spatial distribution uniformity of ZnO nanorod array light-emitting diodes via Ag nanoparticles decoration

Localized surface plasmon (LSP) enhanced ultraviolet (UV) light-emitting diodes (LEDs) were fabricated by embedding a ZnO nanorod array/p-GaN film heterostructure into a Ag-nanoparticles/PMMA composite. By optimizing the concentration of Ag nanoparticles in PMMA, two distinct changes in electroluminescence (EL) spectra were observed: (1) the UV EL component from ZnO excitons was selectively enhanced more than 13-fold and the entire spectral lineshape was changed and (2) the spatial uniformity of the output photon intensity was improved and the linewidth of an angular distribution curve was increased by ∼2 times. These observations can be attributed to near-field optical coupling between Ag LSPs and ZnO excitons. Time-resolved luminescence measurements and a model calculation reveal that the optical coupling results in the increase of the spontaneous emission rate and internal quantum efficiency of Ag-nanoparticles-decorated ZnO nanorod arrays. Moreover, the LSP-exciton interaction allows the devices EL to be coupled out of the nanorod waveguide and to be isotropically scattered into every direction, thus broadening the angular distribution of the EL intensity.

Highly stable copper wire/alumina/polyimide composite films for stretchable and transparent heaters

Transparent heaters, which are capable of withstanding a high dynamic strain, in contrast with those made of brittle indium tin oxide films, are increasingly needed for heating of next-generation flexible and stretchable electronics, such as artificial skins, touch screens, displays, and sensors. This work provides a new approach for the fabrication of a transparent heater that is made of a Cu wire/alumina/polyimide composite film. The advantages of this film include a high transparency, low operating voltage, unprecedented stability against harsh environmental conditions, and repeated bending or stretching. A highly conductive Cu wire network was prepared via thermal evaporation of low-cost Cu on electrospun polymer nanofibers. Atomic layer deposition was used to conformably deposit an alumina film on the Cu wire network to suppress the diffusion and oxidation of Cu. The solution casted polyimide film that was introduced acts as a binder and can successfully improve the adhesion strength between the Cu wire and its substrate. After delicate optimization of the layered structure, we fabricated a transparent heater that exhibits a low sheet resistance of 8 Ω sq−1 and a high visible light transmittance of up to 91.4%, and it demonstrated an unprecedented ability to resist temperatures as high as 300 °C. Furthermore, the Cu wire/alumina/polyimide-based transparent heater can endure 100 cycles of stretching–releasing at a strain of 30% with an exceptionally high stability and reversibility. Thus, these copper wire/alumina/polyimide composite films have extremely high potential for applications in heating of future wearable optoelectronic devices.

Enhanced ultraviolet emission from Au/Ag-nanoparticles@MgO/ZnO heterostructure light-emitting diodes: A combined effect of exciton- and photon- localized surface plasmon couplings

Localized surface plasmon (LSP)-enhanced ultraviolet light-emitting diodes (LEDs) based on a Au/MgO/ZnO metal/insulator/semi- conductor heterostructure were fabricated by embedding Ag nanoparticles (Ag-NPs) into MgO dielectric layer. A ~6-fold electroluminescence (EL) enhancement was achieved from the Ag-NPs decorated device. Time-resolved spectroscopy studies, as well as analogue simulation and theoretical estimation based on experimental data, reveal that the internal quantum efficiency and light extraction efficiency of the heterojunction LED are increased ~3-fold and ~2-fold, respectively, as a result of the introduction of Ag LSPs. This result indicates that the observed EL enhancement originates from a combined effect of both exciton-LSP coupling and photon-LSP coupling.

Enhanced near-UV electroluminescence from p-GaN/i-Al2O3/n-ZnO heterojunction LEDs by optimizing the insulator thickness and introducing surface plasmons of Ag nanowires

p-GaN/i-Al2O3/n-ZnO (PIN) heterojunction LEDs with different dielectric Al2O3 thicknesses were fabricated via an atomic layer deposition technique. By optimizing the i-Al2O3 layer thickness to be ∼12 nm, the effective electron accumulation and hole injection are simultaneously achieved in the n-ZnO active layer, resulting in a greatly improved near-UV electroluminescence intensity of this PIN type LED. Moreover, by introducing Ag nanowires, whose surface plasmon (SP) resonant energy is closer to the ZnO UV emission energy, into the LED structure, the electroluminescence intensity was further increased ∼2.8 times. Time-resolved and temperature-dependent spectroscopy analyses reveal that both the spontaneous radiation rate and internal quantum efficiency of the ZnO active layer are increased as a result of resonant couplings between ZnO excitons and Ag nanowire SPs, which gives rise to the observed near-UV electroluminescence enhancement.

The Western Region

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Understanding the role of lithium sulfide clusters in lithium–sulfur batteries

Lithium sulfide (Li2S) as an electrode material not only has high capacity but also overcomes many problems caused by pure sulfur electrodes. In particular, the battery performance of nanoscale (Li2S)n clusters is much better than that of bulk sized Li2S. However, the structures, stability, and properties of (Li2S)n clusters, which are very important to improve the performance of Li–S batteries, are still unexplored. Herein, the most stable structures of (Li2S)n (n = 1–10) are reliably determined using the advanced swarm-intelligence structure prediction method. The (Li2S)n (n ≥ 4) clusters exhibit intriguing cage-like structures, which are favorable for eliminating dangling bonds and enhancing structural stability. Compared to the Li2S monomer, each sulfur atom in the clusters is coordinated with more lithium atoms, thus lengthening the Li–S bond length and decreasing the Li–S bond activation energy. Notably, the adsorption energy gradually increases on the considered anchoring materials (AMs) as the cluster size increases. Moreover, B-doped graphene is a good AM in comparison with graphene or N-doped graphene. The predicted characteristic peaks of infrared, Raman, and electronic absorption spectra provide useful information for in situ experimental investigation. Our work represents a significant step towards understanding (Li2S)n clusters and improving the performance of Li–S batteries.

Anisotropic strained cubic MgZnO/MgO multiple-quantum-well nanorods: Growths and optical properties

In present study, [110]-oriented cubic phase Mg0.21Zn0.79O/MgO biaxial strained multiple-quantum-well (MQW) nanorods were grown on Al2O3 (101¯0) substrates by pulsed laser deposition technique. In spite of the large lattice mismatch between Mg0.21Zn0.79O and MgO layers, coherent epitaxial growths of cubic Mg0.21Zn0.79O /MgO MQWs have been realized in each nanorod structure, which has been confirmed by high resolution transmission electron microscopy and X-ray diffraction spectroscopy. A quasi-Stranski-Krastanov (SK) growth mode was exploited to describe the growth of the MQW nanorods. Experimental and theoretical results demonstrate that in-plane compressive stress not only converts low Mg-content MgZnO alloys in an anomalous rocksalt (RS) phase but also broadens the band gaps of RS-MgZnO/MgO MQWs into the deep-ultraviolet (DUV) range. Our results indicate that RS-MgZnO/MgO MQW structures have potential applications in UV and DUV optoelectronic devices.

Sp2 clustering-induced improvement of resistive switching uniformity in Cu/amorphous carbon/Pt electrochemical metallization memory

We studied the influence of sp2 clustering on resistive switching uniformity in Cu/amorphous carbon/Pt electrochemical metallization memory. Herein, a simple method was utilized to adjust the degree of sp2 clustering by changing compliance currents (CCs). The small sp2 clusters within the a-C layer were found to condense into larger clusters with increasing CCs because of the CC-dependent Joule heating effect. Raman spectra experimentally verified the increase of sp2 cluster diameter with increasing CCs. Importantly, a switching uniformity improvement can be obtained by increasing the degree of sp2 clustering. The enhanced local electric field around sp2 clusters can account for the reduction of the Cu conductive filament randomness and corresponding improvement of memory performance.