Ni-oxide-based thin films, prepared by sputtering, are investigated by electrochemical impedance spectroscopy in a KOH electrolyte. The films are electrochromic, and an increase of the applied potential leads to a variation from a bleached to a colored state as a result of proton (H+) extraction together with extraction of electrons from the valence band. The complex frequency-dependent impedance displays different features in different potential ranges. At low potentials, where coloration is weak, the spectra give evidence for a constant-phase element in parallel with a leak resistance. At intermediate and high potentials, the impedance spectra indicate the presence of a diffusion process, and a model for anomalous diffusion gives excellent fits to the spectra except in a crossover region. The applicability of this model in a significant part of the studied potential range suggests the presence of a multiple-trapping process for the ions. The potential dependence of the chemical capacitance, as well as the diffusion coefficient of un-trapped ions, are analyzed. The electrochemical density-of-states of the charge-compensating electrons gives indications of the top of the valence band and of a band tail extending into the band gap. Diffusion coefficients are found to increase steeply in the crossover potential region to very high values at high potentials. These features are discussed and related to the electrochromic behavior of Ni-oxide-based thin films.

Tungsten oxide and titanium doped tungsten oxide thin films, deposited by sputtering, were immersed in a viscous electrolyte comprised of LiClO4 in propylene carbonate and 2.0 wt% of polyethylene oxide (PEO). Electrochromic properties of the films were investigated by electrochemical techniques and in situ transmittance measurements. Cyclic voltammetry data were taken in the voltage ranges 2.0-4.0 and 1.5-4.0 V vs Li/Li+ for up to 500 cycles. A potentiostatic rejuvenation treatment was then performed on the degraded electrochromic films, at 6.0 V for 20 h, which was subsequently followed by another cyclic voltammetry measurement. Titanium incorporation into tungsten oxide resulted in a small cyclic stability improvement in the 2.0-4.0-V range, whereas less pronounced effects were observed for cycling in the 1.5-4.0-V range. Combining the results of the present study with our previous work, we are able to assess the relative merits of titanium incorporation and PEO addition to the electrolyte for the durability of electrochromic tungsten oxide thin films. Titanium addition was found advantageous for electrochemical durability in the 2.0-4.0-V range, but no clear benefits of PEO in the electrolyte were seen. On the other hand, in the wider 1.5-4.0-V range, tungsten oxide exhibited better durability than titanium-containing films, and this was especially so after rejuvenation in the PEO-containing electrolyte.

Electrochromic (EC) technology allows control of the transmission of visible light and solar radiation through thin-film devices. When applied to "smart" windows, EC technology can significantly diminish energy use for cooling and air conditioning of buildings and simultaneously provide good indoor comfort for the buildings' occupants through reduced glare. EC "smart" windows are available on the market, but it is nevertheless important that their degradation under operating conditions be better understood and, ideally, prevented. In the present work, we investigated EC properties, voltammetric cycling durability, and potentiostatic rejuvenation of sputter-deposited WO3 thin films immersed in LiClO4-propylene carbonate electrolytes containing up to 3.0 wt% of-7-nm-diameter SiO2 nanoparticles. Adding about 1 wt% SiO2 led to a significant improvement in cycling durability in the commonly used potential range of 2.0-4.0 V vs. Li/Li+. Furthermore, X-ray photoemission spectroscopy indicated that O-Si bonds were associated with enhanced durability in the presence of SiO2 nanoparticles.

Tungsten oxide is a widely used electrochromic material with important applications in variable-transmittance smart windows as well as in other optoelectronic devices. Here we report on electrochemical impedance spectroscopy applied to hydrous electrochromic tungsten oxide films in a wide range of applied potentials. The films were able to reversibly bleach and color upon electrochemical cycling. Interestingly, the bleaching potential was found to be significantly higher than in conventional non-hydrous tungsten oxide films. Impedance spectra at low potentials showed good agreement with anomalous diffusion models for ion transport in the films. At high potentials, where little ion intercalation takes place, it seems that parasitic side reactions influence the spectra. The potential dependence of the chemical capacitance, as well as the ion diffusion coefficient, were analyzed. The chemical capacitance is discussed in terms of the electron density of states in the films and evidence was found for a band tail extending below the conduction band edge.

Thin films of W oxide were prepared by reactive DC magnetron sputtering (5 cm-diameter W target), and their electrochromic (EC) properties were investigated in an electrolyte of LiClO4 in propylene carbonate. The purpose of the study was to elucidate the role of critical deposition parameters-oxygen/argon gas flow ratio for the sputter plasma Gamma, total pressure in the sputter plasma p(tot) , and sputtering power P-s - on the EC performance with foci on electrochemical cycling durability and optical modulation range Delta T. Specifically, we used 0.15 <= Gamma <= 0.90, 5 <= p(tot) <= 30 mTorr, and 200 <= P-s <= 400 W and studied cycling durability for up to 500 voltammetric cycles in the range 2.0-4.0 V vs. Li/Li+ together with optical properties at a wavelength of 528 nm. Most significantly, we discovered that a judicious choice of deposition parameters could yield films with superior cycling durability. Thus a similar to 300 nm-thick film prepared at Gamma = 0.90, p(tot) = 10 mTorr, and P-s = 200 W showed Delta T approximate to 65% after an initial "training" during similar to 100 voltammetric cycles; higher values of p(tot), on the other hand, yielded films whose Delta Ts degraded by similar to 10% during the cycling, and a lower value of p(tot) led to dark films with only marginal electrochromism. Hence our work delineates a pathway towards W oxide films with excellent durability of the EC properties. (C) 2020 The Author(s). Published by Elsevier Ltd.

We present experimental results of fluctuation-enhanced gas sensing by low-cost resistive sensors made of a mixture of graphene flakes and TiO2 nanoparticles. Both components are photocatalytic and activated by UV light. Two UV LEDs of different wavelengths (362 and 394 nm) were applied to modulate the gas sensing of the layers. Resistance noise was recorded at low frequencies, between 8 Hz and 10 kHz. The sensors’ response was observed in an ambient atmosphere of synthetic air and toxic NO2 at selected concentrations (5, 10, and 15 ppm). We observed that flicker noise changed its frequency dependence at different UV light wavelengths, thereby providing additional information about the ambient atmosphere. The power spectral density changed by a few times as a result of UV light irradiation. The sensors were operated at 60 and 120°C, and the effect of UV light on gas sensing was most apparent at low operating temperature. We conclude that UV light activates the gas-sensing layer and improves gas detection at low concentrations of NO2. This result is desirable for the detection of the components of gas mixtures, and the modulated sensor can replace an array of independent resistive sensors which would consume much more energy for heating. We also suggest that a more advanced technology for preparing the gas-sensing layer, by use of spin coating, will produce corresponding layers with thickness of about a few μm, which is about ten times less than that for the tested samples. The effects induced by the applied UV light, having a penetration depth of only a few μm, would then be amplified.

Tungsten-oxide-based thin films were prepared by reactive DC magnetron sputtering in the presence of oxygen and nitrogen. Nitrogen contents up to 12 at.% were documented by Rutherford backscattering spectrometry and time-of-flight elastic recoil detection analysis. Optical and electrochemical measurements showed that films with up to 4 at.% of nitrogen were as transparent as undoped tungsten oxide films and displayed enhanced electrochromic properties manifested in an increase in the coloration efficiency by as much as 20%.

Electrochromic W oxide and W-In oxide thin films were prepared by dual-target reactive DC magnetron sputtering and were cycled voltammetrically in an electrolyte of lithium perchlorate in propylene carbonate. Film degradation was investigated for up to 500 cycles in the voltage ranges 1.5-4.0, 1.7-4.0 and 2.0-4.0 V vs. Li/Li+, and optical transmittance was recorded concurrently. Indium doping was found to be unambiguously detrimental to electrochromic cycling durability, which resolves an outstanding issue related to recently discovered unprecedented durability of potentiostatically pretreated W oxide films backed by In2O3:Sn and gives strong support in favor of beneficial effects of solid-electrolyte interfacial layers.

Thin films of electrochromic (EC) W oxide were prepared by reactive DC magnetron sputtering and were immersed in electrolytes of LiClO4 in propylene carbonate with 0.5-3.0 wt% of added polyethylene oxide (PEO). Charge density and optical modulation range were found to diminish monotonically upon prolonged voltammetric cycling with concurrent optical transmittance measurements for up to 500 and 200 cycles in the voltage ranges 2.0-4.0 and 1.5-4.0 V vs. Li/Li+, respectively. Rejuvenation of the degraded EC films was then accomplished by potentiostatic treatment at 6.0 V vs. Li/Li+ for 20 h and has been ascribed to expulsion of trapped Li ions. Importantly, degradation subsequent to rejuvenation was found to progress at a significantly lowered pace than for as-deposited films in proportion with the amount of PEO especially for harsh voltammetric cycling in the voltage range 1.5-4.0 V vs. Li/Li+. The results of this explorative study are of considerable value for the development of highly durable EC devices such as polymer-laminated smart glazing for energy efficient buildings with excellent indoor comfort.

Films of electrochromic Ni oxide, with thickness in the similar to 100-1000-nm range, were prepared by reactive advanced gas deposition (AGD) and, for comparison, also by reactive DC magnetron sputtering (MS). Voltammetric cycling was performed in an electrolyte of lithium perchlorate in propylene carbonate in the voltage range 2.0-4.1 V vs Li/Li+, and concurrent optical transmittance modulation was studied at a wavelength of 530 nm. For the thickest films, the optical modulation range was as large as similar to 54% and the maximum transmittance was similar to 82% for deposition by AGD, whereas the corresponding numbers were similar to 45% and similar to 87% for MS. Rutherford backscattering spectrometry together with measurements of film thickness demonstrated that the porosity of 400-500-nm-thick films made by AGD and MS were similar to 84% and similar to 45%, respectively. The charge exchange per mass unit was as high as 48-67 C g(-1) for samples made by AGD. The corresponding number was much lower for MS, namely 13-18 C g(-1). These results lend convincing support to the view that the electrochromism of Ni-oxide-based films in Li-ion-conducting electrolytes is dominated by surface effects. (C) 2020 The Electrochemical Society ("ECS"). Published on behalf of ECS by IOP Publishing Limited.

Department of Engineering Sciences, The Å P.O. Box 534, SE-751 21 Uppsala, Sweden. E MIIT Key Laboratory of Critical Materials T Storage, School of Chemistry and Chem Technology, 150001 Harbin, China Department of Physics and Astronomy, The P.O. Box 516, SE-751 20 Uppsala, Sweden † Electronic supplementary informa 10.1039/c8ta09621j ‡ These authors contributed equally to th Cite this: J. Mater. Chem. A, 2019, 7, 2908

Recent work has shown that electrochromic WO3 films, backed by In2O3:Sn (ITO) and immersed in a lithium-ion-conducting electrolyte, can attain unprecedented electrochemical cycling durability after potentiostatic pretreatment at high voltage. Here we demonstrate that this intriguing feature is associated with changes in the properties of the ITO film. Specifically, we studied thin films of ITO and WO3/ITO immersed in an electrolyte of LiClO4 in propylene carbonate at potentials up to 6.0 V vs. Li/Li+ by cyclic voltammetry and impedance spectroscopy and present evidence that electrochemical reactions occur under these conditions. X-ray photoemission spectroscopy indicated that the ITO film was partly dissolved at high voltages and that the dissolution reaction promoted diffusion of In and Sn into the WO3 film.

Spectrally selective nanocoatings that exhibit synergistically enhanced solar light modulation, luminous transmittance and catalytic properties can be made by combining dielectric film stacks with ...

TiO2/VO2 bilayer coatings for glazing: Synergetically enhanced photocatalytic, thermochromic, and luminous properties

At the end of a rush lasting over half a century, in which CMOS technology has been experiencing a constant and breathtaking increase of device speed and density, Moore's law is approaching the insurmountable barrier given by the ultimate atomic nature of matter. A major challenge for 21st century scientists is finding novel strategies, concepts and materials for replacing silicon-based CMOS semiconductor technologies and guaranteeing a continued and steady technological progress in next decades. Among the materials classes candidate to contribute to this momentous challenge, oxide films and heterostructures are a particularly appealing hunting ground. The vastity, intended in pure chemical terms, of this class of compounds, the complexity of their correlated behaviour, and the wealth of functional properties they display, has already made these systems the subject of choice, worldwide, of a strongly networked, dynamic and interdisciplinary research community. Oxide science and technology has been the target of a wide four-year project, named Towards Oxide-Based Electronics (TO-BE), that has been recently running in Europe and has involved as participants several hundred scientists from 29 EU countries. In this review and perspective paper, published as a final deliverable of the TO-BE Action, the opportunities of oxides as future electronic materials for Information and Communication Technologies ICT and Energy are discussed. The paper is organized as a set of contributions, all selected and ordered as individual building blocks of a wider general scheme. After a brief preface by the editors and an introductory contribution, two sections follow. The first is mainly devoted to providing a perspective on the latest theoretical and experimental methods that are employed to investigate oxides and to produce oxide-based films, heterostructures and devices. In the second, all contributions are dedicated to different specific fields of applications of oxide thin films and heterostructures, in sectors as data storage and computing, optics and plasmonics, magnonics, energy conversion and harvesting, and power electronics.

Electrochromic windows and glass facades are able to impart energy efficiency jointly with indoor comfort and convenience. Long-term durability is essential for practical implementation of this technology and has recently attracted broad interest. Here we show that a simple potentiostatic pretreatment of sputter-deposited thin films of amorphous WO3-the most widely studied electrochromic material-can yield unprecedented durability for charge exchange and optical modulation under harsh electrochemical cycling in a Li-ion-conducting electrolyte and effectively evades harmful trapping of Li. The pretreatment consisted of applying a voltage of 6.0 V vs. Li/Li+ for several hours to a film backed by a transparent conducting In2O3:Sn layer. Associated compositional and structural modifications were probed by several techniques, and improved durability was associated with elemental intermixing at the WO3/ITO and ITO/glass boundaries as well as with carbonaceous solid-electrolyte interfacial layers on the WO3 films. Our work provides important new insights into long-term durability of ion-exchange-based devices.

Nanocrystalline-nanoporous Ni oxide is of much interest for gas sensors and other applications. Reactive advanced gas deposition (AGD) stands out as a particularly promising technique for making thin films of this material owing to the techniques ability to separate between the growth of individual nanoparticles and their subsequent deposition to create a consolidated material on a substrate. Here we report on the characterization of Ni oxide films, made by reactive AGD, by several methods. X-ray diffractometry showed that the films had a face centered cubic NiO structure, and scanning electron microscopy indicated a compact nanoparticulate composition. X-ray photoelectron spectroscopy showed the presence of Ni3+ and demonstrated that these states became less prominent upon heat treatment in air. Extended x-ray absorption fine structure analysis elucidated the local atomic structure; in particular, data on interatomic distances and effects of annealing on local disorder showed that the Ni oxide nanoparticles crystallize upon annealing while maintaining their nanoparticle morphology, which is a crucial feature for reproducible fabrication of Ni oxide thin films for gas sensors. Importantly, several techniques demonstrated that grain growth remained modest for annealing temperatures as high as 400 degrees C for 1700-nm-thick films. The present article is a sequel to an earlier one [U. Cindemir et al., Sensors and Actuators B 242 (2017) 132-139] in which we reported on fluctuation-enhanced and conductometric gas sensing with Ni oxide films prepared by AGD.

Most electrochromic (EC) devices must have a service lifetime of many years, and this is particularly so for "smart windows" in buildings with good energy efficiency and indoor comfort.The central part of oxide-based EC devices contains thin films based on W oxide and Ni oxide together with an interposed electrolyte.Depending on operating conditions, these films may show degradation at a slower or faster pace, and means to prevent or reverse this phenomenon, or as a minimum allow reliable lifetime prediction, have been sought ever since the beginnings of EC technology.Here we survey recent endeavors related to EC films of W oxide and Ni oxide and show that (i) electrochemical pretreatment of films in a liquid electrolyte can significantly improve durability, (ii) electrochemical posttreatment in a liquid electrolyte can rejuvenate degraded films, (iii) mixed oxides can have better durability and optical performance than corresponding pure oxides, and (iv) lifetime prediction is possible.

Thin films of electrochromic W oxide and W-Ti oxide were prepared by reactive DC magnetron sputtering and were cycled voltammetrically in an electrolyte of lithium perchlorate in propylene carbonate. Film degradation was studied for up to 500 voltammetric cycles in voltage ranges between 1.5-4.0 and 2.0-4.0 V vs. Li/Li+. Optically and electrochemically degraded films were subjected to potentiostatic posttreatment at 6.0 V vs. Li/Li+ to achieve ion de-trapping and rejuvenation so that the films partly regained their original properties. Ti incorporation and potentiostatic posttreatment jointly yielded superior electrochromic properties provided the lower limit of the voltage range was above 1.6-1.7 V vs. Li/Li+. Degradation dynamics for as-deposited and rejuvenated thin films was modeled successfully by power-law kinetics; this analysis indicated coexistence of two degradation mechanisms, one based on dispersive chemical kinetics and operating universally and another, of unknown origin, rendered inactive by rejuvenation. The results of the present study are of large interest for the development of electrochromic devices with exceptional durability. (C) 2019 The Electrochemical Society.