Deepa Kathiravan

Self-Assembled Hierarchical Interfaces of ZnO Nanotubes/Graphene Heterostructures for Efficient Room Temperature Hydrogen Sensors

Herein, we report the novel nanostructural interfaces of self-assembled hierarchical ZnO nanotubes/graphene (ZNT/G) with three different growing times of ZNTs on graphene substrates (namely, SH1, SH2, and SH3). Each sample was fabricated with interdigitated electrodes to form hydrogen sensors, and their hydrogen sensing properties were comprehensively studied. The systematic investigation revealed that SH1 sensor exhibits an ultrahigh sensor response even at a low detection level of 10 ppm (14.3%) to 100 ppm (28.1%) compared to those of the SH2 and SH3 sensors. The SH1 sensor was also found to be well-retained with repeatability, reliability, and long-term stability of 90 days under hydrogenation/dehydrogenation processes. This outstanding enhancement in sensing properties of SH1 is attributed to the formation of a strong metalized region in the ZNT/G interface due to the inner/outer surfaces of ZNTs, establishing a multiple depletion layer. Furthermore, the respective band models of each nanostructure were also purposed to describe their heterostructure, which illustrates the hydrogen sensing properties. Moreover, the long-term stability can be ascribed by the heterostructured combination of ZNTs and graphene via a spillover effect. The salient features of this self-assembled nanostructure are its reliability, simple synthesis method, and long-term stability, which makes it a promising candidate for new generation hydrogen sensors and hydrogen storage materials.

Multifunctional sustainable materials: the role of carbon existing protein in the enhanced gas and UV sensing performances of ZnO-based biofilms

Due to environmental problems such as global warming and ozone depletion, it is essential to detect harmful UV rays from sunlight and to commercialize a clean energy source (H2), and both issues require a reliable sensor. With these considerations, herein, multifunctional ZnO-based biofilms with innovative designs (needle-fibre and jute-fibre like) are prepared by a simple hydrothermal route with sericin protein (SP) for different growing times, and fabricated as sensors. The present combination of ZnO/SP forms carbon and nitrogen enriched ZnO-based biofilms, which exhibit superior H2 and UV sensing characteristics. Among them, a sample grown for 5 h (with a jute-fibre like architecture) shows excellent H2 sensing and remarkable UV detection performance. Thus, the novel architecture based H2 sensor exhibits an ultra-fast response of 31.24% at 100 ppm within 11 s to reach a stable-state and easily recovers within 7 s, while the UV sensor shows an ultra-high photo-responsivity of 650 A W−1 with a response time of 16 s and a recovery time of 12 s, especially at room temperature. In particular, the as-fabricated sensor also produces good sensitivity/responsivity, high reversibility and long-term stability. This striking enhancement in sensing performance is attributed to the adsorptive coating of SP among ZnO lattice planes, which also affects the adsorption of chemisorbed ions from the surface of biofilms when exposed to H2 and UV atmosphere. Moreover, the present ZnO–SP based sensor overcomes the current problems of state-of-the-art room temperature ZnO based H2 and UV sensors with a cost-effective, eco-friendly and simple synthesis with easy fabrication. Furthermore, the salient feature of tailoring this bio-waste SP into versatile ZnO is the development of a low cost semiconductor nanocomposite biomaterial for multi-functional applications.

Natural Biowaste-Cocoon-Derived Granular Activated Carbon-Coated ZnO Nanorods: A Simple Route To Synthesizing a Core–Shell Structure and Its Highly Enhanced UV and Hydrogen Sensing Properties

Granular activated carbon (GAC) materials were prepared via simple gas activation of silkworm cocoons and were coated on ZnO nanorods (ZNRs) by the facile hydrothermal method. The present combination of GAC and ZNRs shows a core-shell structure (where the GAC is coated on the surface of ZNRs) and is exposed by systematic material analysis. The as-prepared samples were then fabricated as dual-functional sensors and, most fascinatingly, the as-fabricated core-shell structure exhibits better UV and H2 sensing properties than those of as-fabricated ZNRs and GAC. Thus, the present core-shell structure-based H2 sensor exhibits fast responses of 11% (10 ppm) and 23.2% (200 ppm) with ultrafast response and recovery. However, the UV sensor offers an ultrahigh photoresponsivity of 57.9 A W-1, which is superior to that of as-grown ZNRs (0.6 A W-1). Besides this, switching photoresponse of GAC/ZNR core-shell structures exhibits a higher switching ratio (between dark and photocurrent) of 1585, with ultrafast response and recovery, than that of as-grown ZNRs (40). Because of the fast adsorption ability of GAC, it was observed that the finest distribution of GAC on ZNRs results in rapid electron transportation between the conduction bands of GAC and ZNRs while sensing H2 and UV. Furthermore, the present core-shell structure-based UV and H2 sensors also well-retained excellent sensitivity, repeatability, and long-term stability. Thus, the salient feature of this combination is that it provides a dual-functional sensor with biowaste cocoon and ZnO, which is ecological and inexpensive.

Engineered design and fabrication of long lifetime multifunctional devices based on electrically conductive diamond ultrananowire multifinger integrated cathodes

Multi-functional vacuum electron field emission (VEFE) devices were developed using a laterally arranged multi-finger configuration with negative biased ultrananocrystalline-diamond graphite (NBG-UNDG) cathode/anode materials. The NBG-UNDG based multifinger lateral electron field emitter (ML-EFE) devices were fabricated using micropatterning and a simple lift-off process. The fabrication process of ML-EFE devices is observed to markedly enhance the electron field emission (EFE) properties of NBG-UNDG materials. The EFE investigations of ML-EFE devices revealed a low turn-on field for EFE at a voltage as low as 2.02 V μm−1 with a high current density of 1.51 mA at an electric field of 2.6 V μm−1. The presence of multi-layer nanographite (ng) in NBG-UNDG diamond nanowires and a Au interlayer at the film-to-substrate interface are presumed to be the main factors, which result in superior EFE properties for NBG-UNDG ML-EFE devices. The enhanced properties of NBG-UNDG based multifinger integrated cathodes have noteworthy potential for the generation of new display panel applications. Using NBG-UNDG ML-EFE devices as cathodes, a microplasma device was fabricated that can generate plasma at a low voltage of 260 V. Also, a photodetector, which provides an excellent photoresponsivity of 1.7 A W−1, was demonstrated using NBG-UNDG ML-EFE devices as sensing materials. Moreover, a NBG-UNDG based self-aligned cathode and gate VEFE transistor was fabricated, which exhibits enhanced transistor characteristics with a low turn-on gate voltage of 320 V. The fabrication of these NBG-UNDG devices, which can be operated at high power and under various vacuum conditions with long lifetime, demonstrates a practical approach in diamond based vacuum microelectronics and integrated circuits.

Concurrent enhancement in the H2 and UV sensing properties of ZnO nanostructures through discontinuous lattice coating of La3+via partial p–n junction formation

The development of multifunctional sensors with surface-modified one-dimensional ZnO nanostructures has attracted significant scientific interest due to their versatility. Herein, we present a simple hydrothermal route to coat lanthanum (La3+) ions onto the surface lattice of ZnO nanorods (La-coated ZNRs). The as-prepared ZnO nanorods (ZNRs) without La3+ ion coating were also synthesized under the same conditions for comparison. Each sample was then fabricated as a multisensor with interdigitated electrodes, and their H2 gas and UV sensing properties were systematically studied. Thus, the La-coated ZNR-based multisensor exhibited remarkable H2 sensing and efficient UV detection properties when compared to that of the as-prepared ZNRs. An ultra-high H2 response of 63.8% was achieved even at a low detection level (ppm) with an ultra-fast response (15 s) and recovery time (9 s). Also, excellent UV sensing properties were observed with a high switch ratio (Iphoto/Idark) of 256.3. Moreover, the present multisensor was also revealed to exhibit superb sensitivity, stability, repeatability and selectivity towards H2 gas and UV light. This outstanding enhancement in the multisensing measurements of La-coated ZNR-based multisensors can be ascribed to their high oxygen vacancies, and the formation of partial p–n junctions on their discontinuous surface lattices. Furthermore, this sensor was also utilized for the simultaneous detection of UV light and H2 gas in a single measurement. The prominent feature of the incorporation of La3+ ions into ZNRs is the improvement in efficient multisensors, but, in addition, this combination can be highly useful for H2 storage materials.

Bio-industrial Waste Silk Fibroin Protein and Carbon Nanotube-Induced Carbonized Growth of One-Dimensional ZnO-based Bio-nanosheets and their Enhanced Optoelectronic Properties

High performance UV/Visible photodetectors are successfully fabricated from ZnO/fibroin protein-carbon nanotube (ZFPCNT ) composites using a simple hydrothermal method. The as-fabricated ZnO nanorods (ZnO NRs) and ZFPCNT nanostructures were measured under different light illuminations. The measurements showed the UV-light photoresponse of the as-fabricated ZFPCNT nanostructures (55,555) to be approximately 26454 % higher than that of the as-prepared ZnO NRs (210). This photodetector can sense photons with energies considerably smaller (2.75 eV) than the band gap of ZnO (3.22 eV). It was observed that the finest distribution of fibroin and CNT into 1D ZnO resulted in rapid electron transportation and hole recombination via carbon/nitrogen dopants from the ZFPCNT . Carbon dopants create new energy levels on the conduction band of the ZFPCNT , which reduces the barrier height to allow for charge carrier transportation under light illumination. Moreover, the nitrogen dopants increase the adsorptivity and amount of oxygen vacancies in the ZFPCNT so that it exhibits fast response/recovery times both in the dark and under light illumination. The selectivity of UV light among the other types of illumination can be ascribed to the deep-level energy traps (ET ) of the ZFPCNT . These significant features of ZFPCNT lead to the excellent optical properties and creation of new pathways for the production of low-cost semiconductors and bio-waste protein based UV/Visible photodetectors.