Impact of shock waves on the physical and chemical properties of aligned zinc oxide structures grown over metal-sheets

Zinc oxide (ZnO) nanorods were developed on stainless steel (SS) sheets as well as glass substrates in two steps by adopting well-established two different chemical methods namely, spray pyrolysis and chemical bath deposition techniques. Then, the structures were exposed to dynamically generated shock waves in a home-built shock tunnel. All the as-grown and shock waves exposed structures were characterized with advanced analytical techniques. Surface morphology and structural studies reveal that the as-grown nanostructured films over the both SS and glass substrates possess nanorods-like surface morphology; however, they exhibited (101) and (001) orientations as predominant orientations, respectively. From micro Raman analysis, it is noticed that the nanorod structures grown on both surfaces have good phase purity and crystalline quality. On the other hand, the cathodoluminescence studies show that these hydrothermally grown ZnO nanorods possess a large number of native defects. Finally, the ZnO nanorods exposed to shock waves generated with a temperature and pressure of ca. ∼20,000 K and ∼6 MPa for a short duration of 2–3 ms exhibited superb sustainability in terms of surface morphology as well as crystalline quality, which is mainly attributed to the slantly overlapped morphology as well as the high melting temperature of ZnO nanorods. © 2022 Elsevier Ltd1

Passivation layer-dependent catalysis of zinc oxide nanostructures

Electrochemical and photoelectrochemical catalysis of surface-passivated zinc oxide (ZnO) nano structures with three different metal oxides were investigated. Initially, vertically aligned ZnO nanorods structures were developed over conductive substrates by a two-step approach and then passivated with an ultrathin zinc hydroxide, that is, Zn(OH)(2), cobalt oxide, that is, CoO, and Zn(OH)(2)/CoO as bilayer, by electrochemical deposition. Compared with the pristine ZnO structures, the surface-passivated nano structures possess slightly rough surfaces, whereas their crystal structure remains unchanged. From electrochemical catalysis studies under dark and illumination, it is noticed that vertically aligned ZnO nanostructures passivated with narrow band-gap CoO layers have a predominant water oxidation performance than that of the structures passivated with other oxide materials. It is mainly attributed to the eradication of surface states present on ZnO nanorods. Interestingly, the structures passivated with bilayers, that is, Zn(OH)(2)/CoO, showed significant stability and durability (similar to 103% retention in current density@60th min) with a continuous oxygen evolution reaction process for long durations. (C) 2021 Elsevier Ltd. All rights reserved.1

Larger, flexible, and skin-mountable energy devices with graphene single layers for integratable, wearable, and health monitoring systems

In recent years, the development of weightless, ultrathin, and non-toxic devices has received tremendous interest owing to their potential applications as building blocks for various flexible, wearable, and skin-mountable systems. In this view, we explored the exceptional performances of flexible energy harvesters and storage devices along with wearable optoelectronic devices by adopting high-quality graphene monolayers and a user-friendly transfer methodology. Flexible and transparent energy generators with an active layer (AL) thickness of ∼20 μm and storage devices (AL≤ 1 μm) were developed by sandwiching the piezoelectric and solid electrolyte materials between two graphene monolayers, respectively. Wearable photosensors, with an AL thickness of ∼30 μm, were designed by integrating an ultrathin zinc oxide layer with a graphene monolayer. Under nominal mechanical movements, typical graphene monolayers-based piezoelectric energy generators exhibited very stable peak voltage and current density of 5.5 V and 0.2 nA/cm2, respectively. Whereas the skin-mountable micro-supercapacitor (mSC) showed slightly lower areal and volumetric capacitances (6.3 μF/cm2 and 91 mF/cm3@100 mV/s scan rate) than that of the flexible mSCs. Interestingly, these mSC devices also showed significant mechanical flexibility, stability, and durability. Further, the as-fabricated photosensors exhibited a strong response to visible light with an On/Off current density ratio of 1.8 and excellent wearability. Based on these demonstrated outcomes, we emphasize that the devices fabricated on different substrates by using graphene single layers could be adopted for various wearable, biocompatible, and skin-mountable devices that are widely being used in various health monitoring systems. © 2021 Elsevier Ltd1

User-friendly methodology for chemical vapor deposition -grown graphene-layers transfer: Design and implementation

An ecofriendly wet-chemical methodology for the transfer of chemical vapor deposition-grown, two-dimensional (2D) graphene layers onto desired surfaces is proposed and demonstrated by transferring the graphene monolayers (GMLs) onto Si/SiO2 substrates. The quality and purity of transferred graphene layers along with their uniformity and electrical characteristics were examined. Furthermore, the areal uniformity of the transferred layers is explored by fabricating the devices with a configuration of graphene/insulator/metal (GIM). The transferred GMLs over Si/SiO2 substrates exhibited good uniformity with high chemical purity along with excellent electrical characteristics. The GIM-based devices fabricated over planar substrates showed high conductivity and low leakage current density. Based on these demonstrated outcomes, it is emphasized that the proposed methodology can be adopted for the transfer of any 2D materials irrespective of their size by avoiding chemical exposure and failure of the fabrication process that are the major hurdles in the conventional approach. (C) 2021 Elsevier Ltd. All rights reserved.1