Ternary Heterostructures Based on BaTiO3/MoO3/Ag for Highly Efficient and Reusable Photocatalytic Applications

Abstract This work shows the fabrication of an efficient ternary heterostructure photocatalyst by integrating ferroelectric BaTiO3 (BTO) as the bottom layer, semiconductor MoO3 as the middle layer and plasmonic silver nanoparticles (Ag NPs) as the top layer, respectively. The BaTiO3/MoO3/Ag (BMA) heterostructure exhibits a higher photodegradation and photocatalytic efficiency of 100% for rhodamine B (RhB) dye under a UV–Visible light illumination of 60 min when compared with its binary heterostructure counterparts BaTiO3/Ag (BA) and MoO3/Ag (MA). The increased photocatalytic activity in BMA heterostructure is attributed to its enhanced interfacial electric field due to the electric double layer formation at BTO‐MoO3 and MoO3‐Ag interfaces. The higher blueshift in the surface plasmon resonance (SPR) peak observed for the BMA heterostructure clearly indicates an increased electron transfer toward the top Ag NPs layer under optical illumination. The higher resistive switching (RS) ratio, the increased difference in voltage minima, and the improved photocurrent generation, as evident from the I–V characteristics, illustrate the enhanced charge carrier generation and separation in BMA heterostructure. A smaller arc radius observed for the Nyquist plot of BMA heterostructure clearly showcases its increased interfacial charge transfer (CT). The CT mechanism and reusability of the BMA heterostructure are also studied

Pyroelectric nanogenerators in energy technology

[Excerpt] International crisis such as global warming, environmental pollution, and e-waste significantly increased the demand of electronic devices powered by renewable and sustainable energy sources [1, 2]. It is known that batteries are key renewable energy sources for powering electronic systems, which suffer from drawbacks like environmental issues, limited life-time, weight, and periodic maintenance or replacement [3]. Therefore, energy harvesting from the most reliable sources such as green energy (solar, wind, biomass, and hydrogen) and mechanical energy (water flow, mechani cal vibrations, and human motions) are inevitable. In our daily life, different forms of energies like thermal, mechanical, and photovoltaic are scattered around or wasted. Thus, commercialization of wasted energy into electrical energy has become imperative to build a clean and sustainable world [4, 5]. Moreover, thermal energy exists everywhere in the form of sun light, wind, human body, etc. [6–8]. For instance, our human body is an indispensable source of thermal energy, and we are simply wasting it without knowing the importance. However, harvesting of electrical energy from thermal energy requires a thermal fluctuation or temperature gradient. For instance, the human respiration and locomotion create fluctuations in the thermal energy and can be converted into electrical energy [7, 8]. The process of generating electrical energy using the temperature gradient is known as pyroelectric effect or pyroelectricity [8]. Besides, the pyroelectric materials can gener ate electrical energy from the temperature fluctuations induced due to small-scale physical changes. These pyroelectric materials that can generate electrical energy using small physical-change induced thermal fluctuation are known as pyroelectric nanogenerators (PENGs). Converting such a feasible energy source to electrical energy using PENGs under ambient conditions is of great impor tance for long-term self-powered energy systems. Figure 9.1 illustrates the schematic representation of various applications of PENGs. [...

Robust resistive switching performance of pulsed laser deposited SiC/Ag/SiC tri-layer thin films deposited on a glass substrate

In this work, the authors developed SiC(10 nm)/Ag/SiC(10 nm) thin films showing an electroforming-free resistive switching (RS) effect with a switching ratio of 102. The observed RS effect is attributed to charging and discharging of Ag nanoparticles in the film layer. Further, SiC/Ag/SiC film shows an excellent endurance and retention as well as a good thermal stability of RS characteristics. It is also identified that the switching ratio is invariant but the switching voltage of the device greatly depends on the Ag nanoparticles concentration and the operation temperature of the device. Therefore, SiC/Ag/SiC thin films are attractive for next-generation memory devices with enhanced durabilityDST-SERB, Government of India through Grants ECR/2017/002537 (KK) and ECR/2017/000068 (KCS) and Portuguese Foundation for Science and Technology (FCT) in the framework of the Strategic Funding UIDB/04650/2020 (JPBS and MP

Effect of annealing temperature on photoluminescence and resistive switching characteristics of ZnO/Al2O3 multilayer nanostructures

This work demonstrates the role of defects generated during rapid thermal annealing of pulsed laser deposited ZnO/Al2O3 multilayer nanostructures in presence of vacuum at different temperatures (Ta) (500–900 C) on their electrical conductance and optical characteristics. Photoluminescence (PL) emissions show the stronger green emission at Ta 600 C and violet–blue emission at TaP800 C, and are attributed to oxygen vacancies and zinc related defects (zinc vacancies and interstitials) respectively. Current–voltage (I–V) characteristics of nanostructures with rich oxygen vacancies and zinc related defects display the electroforming free resistive switching (RS) characteristics. Nanostructures with rich oxygen vacancies exhibit conventional and stable RS behavior with high and low resistance states (HRS/LRS) ratio 104 during the retention test. Besides, the dominant conduction mechanism of HRS and LRS is explained by trap-controlled-space-charge limited conduction mechanism, where the oxygen vacancies act as traps. On the other hand, nanostructures with rich zinc related defects show a diode-like RS behavior. The rectifying ratio is found to be sensitive on the zinc interstitials concentration. It is assumed that the rectifying behavior is due to the electrically formed interface layer ZnAl2O4 at the Zn defects rich ZnO crystals – Al2O3 x interface and the switching behavior is attributed to the electron trapping/de-trapping process at zinc vacancies.This study has been partially funded by: (i) Portuguese Foundation for Science and Technology (FCT) under the Project PTDC/FIS/ 098943/2008 and strategic Project PEST-C/FIS/UI0607/2011; (ii) European COST Actions MP0901-NanoTP and MP0903-NanoAlloy. The authors K.C.S. and K.K. are grateful for financial support through the FCT Grants SFRH/BPD/68489/2010 and SFRH/BPD/ 87215/2012 respectively. The authors would also like to thank Engineer José Santos for technical support at Thin Film Laboratory

Effect of rapid thermal annealing on texture and properties of pulsed laser deposited zinc oxide thin films

A comparative study on the properties of pulsed laser deposited ZnO thin films as a function of rapid thermal annealing temperature (Ta) is presented. Grazing incidence x-ray diffraction pattern reveals that preferred orientation of the films changes from (002) to (103) as Ta varies from 500 to 800 1C. A clear correlation between grain morphology and texture formation is noticed. Photoluminescence spectra of all films show a strong near-band-edge ultraviolet (UV) emission and the UV emission intensity increases with Ta. Simultaneously, a weak and broad green emission centered at 505 nm corresponds to oxygen vacancies also emerged in the films annealed at TaZ600 1C. A significant hysteresis behavior is observed in current–voltage characteristics and attributed to trapping/ de-trapping driven effect. It is shown that high resistance state is dominated by space charge limited currents and low resistance state is governed by both Pool–Frenkel (2–5 V) and Schottky emission (0–2 V).This study has been partially funded by: (i) FEDER through the COMPETE Program and by the Portuguese Foundation for Science and Technology (FCT) under the projects PTDC/FIS/098943/2008 and PEST-C/FIS/UI607/2011; (ii) European COST Actions MP0901-NanoTP and MP0903-NanoAlloy. We acknowledge the Synchrotron Light Source ANKA for provision of beamtime at the PDIFF beamline and financial support for our participation at the experiments under proposal MNT-123. The authors K.C.S. and K.K. are grateful for financial support through the FCT grants SFRH/BPD/68489/2010 and SFRH/BPD/87215/2012 respectively. The authors would also like to thank Engineer Jose Santos for technical support at Thin Film Laboratory

Semiconductor layer thickness impact on optical and resistive switching behavior of pulsed laser deposited BaTiO3/ZnO heterostructures

This work reports the impact of ZnO layer thickness on optical and resistive switching behavior of BaTiO3/ZnO heterostructures grown by pulsed laser deposition. The interface polarization coupling becomes more efficient and causes a remarkable change in heterostructure properties with decrease in ZnO layer thickness. The heterostructure with ZnO thickness of 25 nm displays the enhanced resistive switching characteristics with switching ratio ≈106 and good stability in low and high resistance states. Moreover, the photoluminescence spectrum exhibits two additional blue emissions when ZnO thickness is ≤50 nm and their mechanism is highlighted based on interface band offset and interface polarization coupling effect.This study has been partially funded by: (i) FEDER through the COMPETE Program and by the Portuguese Foundation for Science and Technology (FCT) under the projects PTDC/FIS/098943/2008 and PEST-C/FIS/UI607/2011; (ii) European COST Actions MP0901-NanoTP and MP0903-NanoAlloy. The authors K. C. S., J.P.B.S., and K. K. are grateful for financial support through the FCT Grant Nos. SFRH/BPD/68489/2010, SFRH/BD/44861/2008, and SFRH/BPD/87215/2012, respectively. The authors would also like to thank Engineer Jose Santos for technical support at Thin Film Laboratory

Tuning the surface plasmon resonance and surface-enhanced Raman scattering of pulsed laser deposited silver nanoparticle films by ambience and deposition temperature

Silver nanoparticle (AgNP) thin films were deposited by pulsed laser deposition onto glass substrates, at different fixed temperatures, under inert gas ambience and vacuum. Their morphology, surface plasmon resonance (SPR) and surfaceenhanced Raman scattering (SERS) activities were investigated. AFM analysis of the films showed the formation of densely packed nanoparticles of varying size and shape by changing the ambience and deposition temperature (Ts). A SPR peak is not evidently observed in the spectrum of films deposited at room temperature, in either high vacuum or neon ambience. The SPR frequency blue shifts from 569 to 470 nm and from 581 to 574 nm with increasing Ts for the films processed in high vacuum and in neon ambience, respectively, while the absorption band becomes narrower with increasing Ts. The SERS intensity of Rhodamine B (RhB) adsorbed on a AgNP substrate grown at 600 C in neon ambience exhibits a higher intensity compared with that of RhB adsorbed on the SERS active substrates at other values of Ts. Good correlation has been observed between the SPR and SERS activities and the morphology of the NPs.This study has been partially funded by (i) the Portuguese Foundation for Science and Technology (FCT) under the project PTDC/FIS/098943/2008 and the strategic project PESTC/ FIS/UI0607/2011, and (ii) European COST Actions MP0901NanoTP and MP0903NanoAlloy. The authors KK and KCS are grateful for financial support through the FCT grants SFRH/BPD/87215/2012 and SFRH/BPD/68489/2010 respectively. The authors would also like to thank Engineer José Santos for technical support at the Thin Film Laboratory

Barium‐doped zinc oxide thin films as highly efficient and reusable photocatalysts

In this study, the effect of Ba doping content on the photocatalytic activity of (Zn1‐xBaxO (ZBO); x=0 to 0.2) thin films is investigated. The efficiency of ZBO photocatalyst for the decolorization of Rhodamine B (RhB) is found to be optimum at x=0.1. The Zn0.9Ba0.1O film exhibits an efficiency of urn:x-wiley:23656549:media:slct201904943:slct201904943-math-0001 96% at an irradiation time of 60 min. The high photocatalytic activity of Ba doped ZnO films is attributed to the high efficient generation and separation of photo‐induced charge carriers as evident from photocurrent measurements. Further, the texture and the oxygen vacancies favor the photocatalytic activity as suggested by the x‐ray diffraction (XRD), scanning electron microscope (SEM), x‐ray photoelectron spectroscopy (XPS), Raman spectroscopy and photoluminescence (PL) analysis. Moreover, the reusability test reveals that the photocatalyst performance remains for at least six consecutive cycles without significant change. The higher efficiency and outstanding reusability of Zn0.9Ba0.1O make it a potential candidate for photocatalytic applications.DST-SERB, Govt. of India . Grant Numbers: ECR/2017/000068, ECR/2017/002537 UGC. Grant Number: F.4-5(59-FRP/ 2014(BSR) DST-SERB, Govt of India. Grant Number: ECR/2017/002537. Portuguese Foundation for Science and Technology (FCT) Strategic Funding. Grant Number: UIDB/FIS/04650/202

Advances in dielectric thin films for energy storage applications, revealing the promise of group IV binary oxides

Among currently available energy storage (ES) devices, dielectric capacitors are optimal systems owing to their having the highest power density, high operating voltages, and a long lifetime. Standard high performance ferroelectric-based ES devices are formed of complex composition perovskites and require precision, high-temperature thin film fabrication. The discovery of ferroelectricity in doped HfO2 in 2011 at the nanoscale was potentially game-changing for many modern technologies, such as field effect transistors, non-volatile memory, and ferroelectric tunnel junctions. This is because HfO2 is a well-established material in the semiconductor industry, where it is used as a gate dielectric. On the other hand, (pseudo)binary HfO2 and ZrO2-based materials have received much less attention for ES capacitors, even though antiferro-electric HfO2 and ZrO2-based thin films show strong promise. This Focus Review summarizes the current status of conventional polymer and perovskite ferroic-based ES. It then discusses recent developments in, and proposes new directions for, antiferroelectric and ferroelectric group IV oxides, namely HfO2 and ZrO2-based thin filmsThis work was supported by the Portuguese Foundation for Science and Technology (FCT) in the framework of the Strategic Funding Contract UIDB/04650/2020 and by DST-SERB, Govt. of India through Grant No. ECR/2017/00006. Part of this work was supported by the COST Action CA18203 − Optimizing Design for Inspection (ODIN). J.L.M.-D. thanks the Royal Academy of Engineering, grant CIET 1819 24. H.P. thanks the China Scholarship Council (No. 201806210299)