Flexible Ceramic Film Sensors for Free-Form Devices.

Recent technological innovations, such as material printing techniques and surface functionalization, have significantly accelerated the development of new free-form sensors for next-generation flexible, wearable, and three-dimensional electronic devices. Ceramic film sensors, in particular, are in high demand for the production of reliable flexible devices. Various ceramic films can now be formed on plastic substrates through the development of low temperature fabrication processes for ceramic films, such as photocrystallization and transferring methods. Among flexible sensors, strain sensors for precise motion detection and photodetectors for biomonitoring have seen the most research development, but other fundamental sensors for temperature and humidity have also begun to grow. Recently, flexible gas and electrochemical sensors have attracted a lot of attention from a new real-time monitoring application that uses human breath and perspiration to accurately diagnose presymptomatic states. The development of a low-temperature fabrication process of ceramic film sensors and related components will complete the chemically stable and reliable free-form sensing devices by satisfying the demands that can only be addressed by flexible metal and organic components.

Flexible and Epitaxial Metal Oxide Thin Film Growth by Photoreaction Processing for Electrical and Optical Applications.

This review summarizes the use of photoreactions that replace conventional heating processes for growing oxide thin films from chemical solutions. In particular, this review outlines key variables in photoreactions that affect epitaxial and polycrystalline thin film growth, including precursor materials, laser wavelength, laser fluence, and carbon. In addition, the features of the photoreaction process that can be controlled at a low temperature by oxygen non-stoichiometry are examined. Likewise, functions that are neither achieved by developing a gradient structure nor controlled by a thermal equilibrium reaction are detailed. Two new concepts are presented, known as photoreaction of nanoparticles (PRNP) and photoreaction of a hybrid solutions (PRHS), in which crystal nuclei are pre-dispersed in a metal-organic compound film. This method has successfully produced flexible phosphor films used as resistor or thermistor electronic components. Finally, thin film growth using different light sources such as flash lamps and femtosecond lasers (fs) is explored.

UV-assisted nucleation and growth of oxide films from chemical solutions.

The fabrication of thin oxide films at low temperatures using simple processes has been a significant challenge associated with expanding the potential applications of these materials. Recent developments have demonstrated that the photo-assisted chemical solution deposition (PACSD) process offers a promising means of solving these difficulties, allowing high volume, on-demand production of variable sample sizes using an advantageous wet process. A better understanding of the crystal growth phenomena associated with this process, however, is required to enable various oxide thin films to be prepared using this new concept. Under pulsed ultraviolet (UV) laser irradiation, crystal growth has been confirmed to proceed by near-instantaneous photothermal heating and photochemical effects at the reaction interface. Vacuum UV lamp irradiation is also a useful means of generating oxide nuclei, since it results in effective chemical bond cleavage and simultaneously produces reactive oxidant (O3/O((1)D)) species. In this review, the nucleation and growth mechanisms which occur during the PACSD process are introduced and discussed and we examine the future possible applications of this process.

The significant effect of heterojunction quality on photoelectrochemical water splitting in bilayer photoelectrodes: Rb(x)WO3 thin films on RbLaNb2O7 layers.

We have prepared nearly perfect hexagonal m-plane-oriented RbxWO3 films on (010)-oriented RbLaNb2O7 layers. The prepared bilayer films showed Rb diffusion from the RbLaNb2O7 seed layers, and we obtained uniaxially oriented RbxWO3/Rb1-yLaNb2O7 photoanodes. The RbxWO3/Rb1-yLaNb2O7 bilayer photoanodes exhibited enhanced photoelectrochemical water splitting compared with the RbxWO3 and RbLaNb2O7 monolayer photoanodes. Furthermore, we clearly demonstrated that the high crystal quality of the heterojunction significantly enhanced water splitting. The photocurrent density of the nearly perfectly oriented RbxWO3/Rb1-yLaNb2O7 photoanode that we prepared was 9.4-fold that of an unoriented bilayer photoanode. This increase was attributed to the inhibition of photo-excited charge recombination and stimulated electron transfer derived from low grain-boundary resistance.

A universal value of effective annealing time for rapid oxide nucleation and growth under pulsed ultraviolet laser irradiation.

The effective annealing times (t(eff)) for nucleating various oxides from an amorphous matrix under nanosecond pulsed laser irradiation have been determined. The oxides, which had perovskite, bixbyite, anatase, and pyrochlore structures, showed similar t(eff) values for crystal nucleation of around 60 ns. This indicates that the effective annealing time is a good universal value for evaluating pulsed laser-induced oxide nucleation. Time-resolved resistance measurements of tin-doped In2O3 thin films under pulsed laser irradiation showed that crystal nucleation and rapid growth proceeded spontaneously with an instantaneous temperature rise.

Acid-Resistant BiVO4 Photoanodes: Insolubility Control by Solvents and Weak W Diffusion in the Lattice.

We have revealed for the first time that BiVO4 photoanodes can be used even in strong acid media by mixing organic solvents into the electrolyte and depositing multilayers with a WO3 bottom layer. In general, the BiVO4 photoanodes are photocorrosive, especially in acid solutions. However, this shortcoming has been overcome using a combination of the two aforementioned modifications. We deduced that the contribution of each mixing organic solvent for the anti-photocorrosion of BiVO4 in sulfuric acid solutions can be evaluated on the basis of a new empirical indicator that incorporates molecular density, the Hansen solubility parameter, and molecular polarizability. Acetone and tert-butyl alcohol were especially promising solvents for stabilizing BiVO4 in acid media. We confirmed that the mixed organic solvents stabilized surface-emergent Bi oxide species as a passivation layer, which was generated via multilayering with a WO3 bottom layer. During heat treatment in the fabrication process, W weakly diffused into the BiVO4 layer and a Bi oxide layer was formed on the outermost surface because of the Bi segregation that arose from the charge compensation between W6+ and V5+ in the BiVO4 lattice. The surface Bi oxide layer, which was protected by the mixed organic solvents, steadily served as a passivation layer for anti-photocorrosion of the underlying BiVO4 layer. We have confirmed that the BiVO4/WO3 photoanodes in acetone-mixed aqueous sulfuric acid solution reliably functioned for a photoelectrochemical reaction under simulated sunlight illumination, and photoelectrochemical production of S2O82- ions was confirmed under light irradiation at λ > 480 nm. These results suggest that the BiVO4-based photoanodes have significant potential for use in acid media in conjunction with very straightforward modifications.

Solar-to-Pharmaceutical Raw Material Production: Photoelectrochemical Naphthoquinone Formation Using Stabilized BiVO4 Photoanodes in Acid Media.

In the quest for efficient use of solar energy to produce high-value-added chemicals, we first achieved the photoelectrochemical (PEC) diketonization of naphthalene, using a BiVO4/WO3 photoanode, to obtain naphthoquinone, an important pharmaceutical raw material with excellent efficiency by solar energy conversion. In the electrochemical (EC) reaction using F-doped SnO2 (FTO) substrates and a 0.5 M H2SO4 H2O-acetone (60 vol %) mixed solution containing 5 mM naphthalene, we produced a small amount of naphthoquinone evolution in the dark. However, naphthoquinone (ηNQ)'s Faradic efficiency and its evolution rate at 1.7 VAg/AgCl were only 28.5% and 0.48 µmol·cm-2·h-1, respectively. The PEC reaction using a WO3 photoanode had very low efficiency for naphthalene diketonization, with low ηNQ and evolution rate values at 1.1 VAg/AgCl of 0.3% and 0.039 µmol·cm-2·h-1, respectively. In contrast, the BiVO4/WO3 photoanode strongly enhanced the PEC reaction, and the ηNQ and evolution rates at 1.1 VAg/AgCl were boosted up to 37.5% and 4.7 µmol·cm-2·h-1, respectively. The evolution rate of the PEC reaction in the BiVO4/WO3 photoanode was 10 times higher than that of the EC reaction with the FTO substrate regardless of the very low bias voltage. This result suggests that the BiVO4-based photoanode was very efficient for the selective oxidation of naphthalene even in acid media because of the acetone-mixed electrolyte's anti-photocorrosion effect and the multilayering of WO3 and BiVO4. At a naphthalene concentration of 20 mM, the naphthoquinone evolution rate reached its maximum value of 7.1 µmol·cm-2·h-1. Although ηNQ tended to decrease with the increase in the electric charge, it reached 100% at a low bias voltage of 0.7 VAg/AgCl. An intensity-modulated photocurrent spectroscopy analysis indicated the rate constant of charge transfer at the photoanode surface to the naphthalene molecules was strongly enhanced at a low bias voltage of 0.7-1.1 VAg/AgCl, resulting in the high ηNQ value. The acid-resistant BiVO4/WO3 photoanode functioned in acetone-mixed electrolytes enabled the realization of a new PEC oxidation reaction driven by solar energy to produce high-value-added pharmaceutical raw materials.

Target lesion thin-cap fibroatheroma defined by virtual histology intravascular ultrasound affects microvascular injury during percutaneous coronary intervention in patients with angina pectoris.

BACKGROUND: Several reports suggest that virtual histology intravascular ultrasound (VH-IVUS) assessment could predict microvascular damage during percutaneous coronary intervention (PCI). A novel index of microcirculatory resistance (IMR) has been developed as a reproducible and less hemodynamic-dependent index. The purpose of this study was to investigate the relationship between thin-cap fibroatheroma (TCFA) defined by VH-IVUS and a change in the IMR during PCI in patients with angina pectoris (AP). METHODS AND RESULTS: The study investigated 30 lesions from 28 AP patients. VH-IVUS imaging was performed before PCI. TCFA was defined as the presence of confluent necrotic core (>10%) without detectable overlying fibrous cap segment. Patients were divided into 2 groups according to the presence of TCFA. Using a pressure guidewire, IMR were measured before and after PCI. After successful PCI, patients were prospectively followed up clinically. TCFA was detected in 9 lesions (30%). IMR tended to improve after PCI in the non-TCFA group, but tended to worsen in the TCFA group. DeltaIMR (=IMR after PCI-IMR before PCI) was significantly higher in the TCFA group compared with the non-TCFA group (13.2+/-29.9 vs -4.4+/-16.0, P=0.04). During follow-up (mean 20 months), survival free of major adverse cardiac events was significantly less in the TCFA group than in the non-TCFA group. CONCLUSIONS: Target lesion TCFA may be related to both microvascular injury and the long-term clinical outcome after successful PCI in patients with AP.

Ultrathin Highly Flexible Featherweight Ceramic Temperature Sensor Arrays.

We fabricated highly flexible Sr- and Ni-doped perovskite SmMnO3 thermistor film sensor arrays on an ultrathin (5 µm thick) and lightweight (21 mg) polyimide sheet for healthcare monitoring devices. The Ag nanowire and nanoparticle-impregnated carbon microcone array, which was prepared by precisely controlled surface laser carbonization of polyimide, showed sufficiently low resistance as a bottom electrode and good stability against sharp bending angles. The dot-shaped (diameter: 900 µm) perovskite thermistor film with a thickness of 900 nm was crystallized by pulsed ultraviolet laser irradiation of a precursor film printed with perovskite nanoparticle dispersion ink, and the film functioned well as the thermistor with a thermistor constant of 2820 K. The thermistor sensor sheet exhibited rapid responses to temperature variation and high stability in the temperature cycle tests over 1000 cycles between room temperature and 80 °C. The bending durability for a bending angle of 60° with a small bending radius (500 µm) was also high. During the bending test over 1000 cycles, the monitoring temperature variation was suppressed only within 0.1 °C. This ultrathin sensor array sheet can be mounted on surfaces with shape variations, and we used the sensor for real-time monitoring in healthcare to detect precise temperature variations on the human skin during physical exercise.

Direct fabrication of metavanadate phosphor films on organic substrates for white-light-emitting devices.

White-light-emitting materials have attracted considerable attention because of their applications, such as large-surface emitting devices. Inorganic phosphor films are expected to be applied to these devices because of good chemical stability; however, a substantial reduction of fabrication temperature is required for future industrial uses such as lighting materials fabricated onto flexible organic substrates. Here we show the optical properties of white-light-emitting metavanadate phosphors, AVO3 (A: K, Rb and Cs), and we report a new direct fabrication process for RbVO3 films onto flexible polyethylene terephthalate (PET) substrates by means of a vacuum ultraviolet irradiation using an excimer lamp. In addition, the (Ca,Sr,Pr)TiO3/a-Al2O3/RbVO3/PET heterostructure prepared by an excimer-laser-assisted metal-organic deposition process has demonstrated the possibility of colour modification for RbVO3 films on PET. Our findings suggest new possibilities for further development of large-surface emitting lighting devices.

Improvement of the Properties of Direct-Current Magnetron-Sputtered Al-Doped ZnO Polycrystalline Films Containing Retained Ar Atoms Using 10-nm-Thick Buffer Layers.

The use of a 10-nm-thick buffer layer enabled tailoring of the characteristics, such as film deposition and structural and electrical properties, of magnetron-sputtered Al-doped ZnO (AZO) films containing unintentionally retained Ar atoms. The AZO films were deposited on glass substrates coated with the buffer layer via direct-current magnetron sputtering using Ar gas, a substrate temperature of 200 °C, and sintered AZO targets with an Al2O3 content of 2.0 wt %. The use of a Ga-doped ZnO film possessing a texture with a specific well-defined orientation as the buffer layer was very effective for improving the crystallographic orientation, reducing the residual stress, and improving the carrier transport of the AZO films. The residual compressive stress and in-grain carrier mobility were responsible for the retention of Ar atoms by the films, as observed using an electron probe microanalyzer.

Plant Habitat-Conscious White Light Emission of Dy(3+) in Whitlockite-like Phosphates: Reduced Photosynthesis and Inhibition of Bloom Impediment.

It has been pointed out that agricultural crops and other natural plants may be damaged by outdoor lighting systems. Therefore, lighting that does not affect plant growth is needed. To address this problem, we have prepared a new whitlockite-like phosphate Dy-phosphor Ca8MgY1-x-yLaxDyy(PO4)7, which exhibits a yellow-white Dy(3+) luminescence that has a maximum internal quantum efficiency of 65.6% under a 387 nm excitation light for x = 0.10 and y = 0.05. The x dependence of IQE showed two maxima at x = 0.10-0.15 and 0.80-0.85, which could be due to the partial allowance of f-f forbidden transitions by local lattice distortion around the Dy(3+) ions originating from the La incorporation at near end members of Ca8MgY1-x-yLaxDyy(PO4)7. Concentration quenching occurred for x > 0.05. A white light-emitting diode (LED) was fabricated from a UV LED emitting at 385 nm and a Ca8MgY1-x-yLaxDyy(PO4)7 phosphor (Dy-WLED) for which the CIE color coordinates and correlated color temperature were CIE(0.350,0.378) and 4919 K, respectively. Plant cultivation experiments on Chlorella photosynthetic growth and blooming of the short-day plant Cosmos were carried out using the prepared Dy-WLED and reference commercial LEDs. We found that the Dy-WLED substantially reduced the photosynthesis of Chlorella and inhibited bloom impediment in Cosmos. These effects originated especially from the reduction of red-near-IR emissions. Thus, we conclude that the Dy-WLED is a very promising candidate for plant habitat-conscious white LEDs for outdoor lights that can protect both natural plant habitats and crop yields.

Relationship between arterial and fibrous cap remodeling: a serial three-vessel intravascular ultrasound and optical coherence tomography study.

BACKGROUND: Positive arterial remodeling and thin fibrous cap are characteristics of rupture-prone or vulnerable plaque. The natural course of the fibrous cap thickness and the relationship between serial arterial remodeling and changes in fibrous cap thickness are unknown. Therefore, the purpose of this study was to evaluate the relationship between changes in fibrous cap thickness and arterial remodeling by using optical coherence tomography (OCT) and intravascular ultrasound (IVUS) during 6-month follow-up. METHODS AND RESULTS: Both IVUS and OCT examinations were performed on 108 vessels from 36 patients with ischemic heart disease who underwent percutaneous coronary intervention. Fifty-eight fibroatheromas were selected from 82 nonsignificant, nonculprit lesions (angiographic diameter stenosis, 25% to 75%; plaque burden, >40% by IVUS). Fibroatheroma was defined by OCT as lipid-rich plaque in >1 quadrant that has lipid. Thickness of the fibrous cap was measured by OCT. IVUS and OCT examinations were repeated at 6-month follow-up. Serial changes and relationships between IVUS indices and fibrous cap thickness were investigated. Overall, fibrous cap thickness (98.1±38.9 to 96.9±44.5 µm) as well as IVUS indices did not change significantly within 6 months. The percent changes in fibrous cap thickness correlated negatively and significantly (r=-0.54; P<0.0001; generalized estimating equation adjusted, r=-0.42; P=0.001) with the percent changes in external elastic membrane cross-sectional area. CONCLUSIONS: Arterial remodeling is related to changes in fibrous cap thickness. Positive arterial remodeling is not only an adaptive process, but also related to thinning of the fibrous cap.