Gradient in defect density of ZnO nanorods grown by cathodic delamination, a corrosion process, leads to end-specific luminescence

Frequency stable dielectric constant with reduced dielectric loss of one-dimensional ZnO-ZnS heterostructures

The synthesis of one-dimensional heterostructures having high dielectric constant and low dielectric loss has remained a great challenge. Until now, the dielectric performance of ZnO-ZnS heterostructures was scarcely investigated. In this work, large-scale ZnO-ZnS heterostructures were synthesized by employing the chemical vapor deposition method. High resolution transmission electron microscopy (HRTEM) confirms the formation of heterostructures. X-ray photoelectron spectroscopy (XPS) shows that S atoms fill up the oxygen vacancy (V_O) in ZnO, leading to the suppression of charge carrier's movement from ZnO to ZnS; instead there is charge transfer from ZnS to ZnO. Conductivity mismatch between adjacent ZnO and ZnS materials leads to the accumulation of free charges at the interface of the heterostructure and can be considered as a capacitor-like structure. The electrical behaviors of the potential phases of ZnO, ZnS and the ZnO-ZnS heterostructure are well interpreted by a best fitted equivalent circuit model. Each heterostructure acts as a polarization node with a specific flip-flop frequency and all such nodes form continuous transmission of polarization, which jointly increase the dielectric energy-storage performance. The orientational polarization of the polarons and Zn²⁺-V_O dipoles present at the heterostructure interface contributes to the frequency stable dielectric constant at ≥10³ Hz. Our findings provide a systematic approach to tailor the electronic transport and dielectric properties at the interface of the heterostructure. We suggest that this approach can be extended for improving the energy harvesting, transformation and storage capabilities of the nanostructures for the development of high-performance energy-storage devices.

Glowing gold nanoparticle coating: restoring the lost property from bulk gold

The unique electronic, optical, and catalytic properties of AuNPs caused by localized surface plasmon resonance (LSPR) have attracted many scientists, but the LSPR diminishes the captivating luster of bulk gold. An exciting challenge is the fabrication of golden-colored AuNPs, but a decisive factor for controlling the absorption/reflection of AuNPs remains elusive. We now propose a simple and versatile method for the fabrication of glowing AuNPs to restore the "lost golden color" of AuNPs in combination with the deposition of AuNPs on a cellulose filter or a PET/cotton fabric by the successive ionic layer adsorption and reaction (SILAR) method and simple pencil drawing. The obtained materials exhibited the glowing golden-color on the pencil-drawn surface and common red and blue colors on the other parts. Surprisingly, the golden-colored AuNPs still maintain a catalytic activity different from that of bulk gold and could be used as a catalyst for the reduction of p-nitrophenol, pendimethalin or 2,4-dinitrophenol in the presence of NaBH₄. We believe that the re-endowment of such a property characteristic of bulk gold into gold nanomaterials would lead to further advancement in the arts and culture as well as electronics, optics, and catalysis.

Low-cost writing method for self-powered paper-based UV photodetectors utilizing Te/TiO2 and Te/ZnO heterojunctions

It has always been a challenge to prepare self-powered ultraviolet photodetectors (UV PDs) utilizing a green, facile and low-cost method. Here, we provide such an approach for fabricating self-powered photodetectors based on Te nanowire/TiO₂ nanoparticle (NP) and Te nanowire/ZnO nanoparticle (NP) heterojunctions. It is noteworthy that such devices were prepared via simply brushing non-toxic solution-processed Te nanowires and commercial TiO₂ and ZnO nanoparticles onto paper. The as-obtained UV PDs can work under zero bias due to photovoltaic effects from the Te/TiO₂ and Te/ZnO heterojunctions. This study not only presents high-performance UV PDs, but also provides a general and effective method for developing environmentally-friendly and energy-efficient optoelectronic devices for practical applications. The concept of employing daily-use brushes and recyclable paper provides a facile way to fabricate green low-cost PDs.