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Interfacial water plays an essential role in natural phenomena and scientific applications despite causing many economic losses. Therefore, its real monitoring is no question mandatory; however, suitable techniques are quite rare and/or with limitations.Moisture Sensor (MS) was used to detect the galvanic response current arising from the stacked interfacial water molecules between two dissimilar electrodes under controlled relative humidity (RH). Simultaneously, the frequency response was detected using QCM sensor as a quantitative tool. Bare and Hydrophilic (HP) sensor surfaces were used to examine the surface wettability. Moreover, sum frequency generation (SFG) was used to investigate the qualitative formation and the nature of stacked interfacial water molecules on bare and HP modified surfaces of quartz prism.Results revealed that, response current and frequency change were increased as the number of stacked water molecules increased. Correlating response current and frequency gave a clear quantitative estimation of stacked water molecules on the sensors' surfaces. Interfacial water molecules possessed strong H-bonding nature at the bare prism surface whereas, strong and weak H-bonding were existing at the HP/prism surface. Such findings provide feasible evaluation for the galvanic current source due to stacked interfacial water molecules at different levels of RH.

Introduction Dew condensation might cause various phenomena like metal corrosion, crop disease, etc. They could be avoided properly if dew condensation is detected at early and initial stages or ideally in advance and followed by dehumidification. Conventional hygrometer cannot detect dew condensation accurately and quickly. Therefore, a new sensor to detect moisture has been developed. It has two interdigit structures made of different metal that intercalates each other. When water droplet connects the adjacent metals, galvanic current flows between these metals. Decreasing a gap between the adjacent metal lines enables smaller water droplet to be detected [1]. It was recently found that the sensor with 0.5 µm in metal gap showed possible detection of adsorbed water molecules as well as droplets under 100% in relative humidity [2]. In addition, temperature and wettability of this sensor could be controlled to imitate target where dew condensation occurs [3]. It means that this sensor might indicate moisture status on target surface. In order to quantify the moisture of the sensor surface, it is important to correlate the current response and the amount of water on the sensor surface. Especially the relationship around 100% in relative humidity was still unclear and studied by measuring the current and observing the sensor surface under stepwise increase and decrease in relative humidity. Experimental Arrays of Al and Au with 1 μm in width were alternately arranged with 0.5 μm in gap between the adjacent arrays on the insulating substrate and used as the electrodes. Electric current between the electrodes were measured by a precise amperemeter. Platinum wires was also placed on the substrate and their temperature was estimated from calibrated straight line of its electric resistance as a function of changing temperature. This sensor chip was attached with the measurement device and put inside a chamber, in which relative humidity was kept constant at 50% by using humidifier and hygrometer. The temperature of chip surface was changed by 1°C every 20 minutes with a Peltier device. The chip surface was observed by an optical microscope while the response current was measured. Result and Discussion Relative humidity (RH) on the sensor surface and response current with experimental time are shown in Fig. 1. The microscopic images at certain times are indicated as the inset of the figure. This RH was calculated from both vapor pressure in the chamber and the temperature of the chip surface. RH more than 100% in this study was nominal and the excess over 100% corresponds to condensed water on the sensor surface. When the current increased stepwise with RH at 100% or below while liquid water could not be observed on the sensor surface below 100% and it started to appear at 100%, as indicated in Fig. 1a. This behaviour was determined by equilibrium of water molecules between vapor in the chamber and adsorbed state on the sensor surface. When RH exceeded 100%, the current increased continuously. Simultaneously, water droplets appeared and became large to cross over the gaps between the arrays, as seen from Fig. 1b. Thereafter, while RH was lowered stepwise to 100%, the response current decreased slightly and kept almost the same level. During this period, the obvious area and the number of droplets on the sensor surface were reduced and most of liquid water seemed to exist between the electrodes, as seen in Fig. 1c. Above 100%, liquid water continued to be formed on the sensor surface and droplet on the gaps turn to infiltrate it by a kinetic reason. When RH fell below 100%, the current decreased continuously and was comparatively higher than that observed during the increasing RH instead of its stepwise change. In this region, liquid water became thin film in the gap, as shown in Fig. 1d. The liquid water tended to remain in the gap kinetically. Conclusion The relation between water status on micro/nano gap between the galvanic arrays around 100% in relative humidity (RH) and flowing current was clarified in this study. When RH increases up to 100%, the response current depended on RH owing to equilibrium of water molecules between vapor and adsorbed state on the sensor surface. Once liquid water was formed on the sensor surface, current depended on presence of water determined kinetically. References [1] J. Kawakita et al., ECS Trans. 75 (2017) 51. [2] Y. Kubota et al., Sensors and Actuators A: Physical 303 (2020) 111838. [3] R.G. Shrestha et al., Sensors 19 (2019) 4500. Figure 1

1. Introduction Dew condensation causes plant disease, metal corrosion, glass fogging and so on. In order to prevent dew condensation, its detection in early stages and preferably in advance should be followed by lowering relative humidity on the target. However, it is difficult to realize early and advanced detection of dew condensation accurately and in a short time by using current technologies such as hygrometer. Therefore, we have developed a sensor to detect fine water molecules directly. It has different metal arrays which are alternately arranged at fixed intervals (minimum distance: 100 nm). When water droplet or molecules cross over the adjacent arrays of the sensor, electric current flows spontaneously by the galvanic effect [1,2]. In addition, wettability of this sensor’s surface was changed [3]. Furthermore, the surface condition of the sensor could be made closer to that of the target for dew condensation if its surface temperature was controlled. So far, the temperature of the sensor surface was able to be changed from the back of silicon chip by using a Peltier device [2]. Taking into account actual application of this sensor, however, such Peltier device should not be adopted because the electric circuit for measurement and control becomes more complicated and the power consumption increases. Instead, it is suggested that heat capacity of the sensor can be close to the target by attaching a heat sink on the back of the silicon chip. Therefore, the purpose of this study was to clarify the influence of the material and weight of the heat sink on changing behaviour of the temperature of the sensor surface. 2. Experimental method Silicon wafer covered with a silica layer was used as the substrate of a sensor chip. Arrays of Al and Au were alternately arranged with 1 μm in width and 0.2 μm in thickness on the substrate to form an opposing interdigit structure and used as the electrodes. After fabrication of the electrodes, the wafer was cut into a 5mm square chip after Pt wires was also placed on the chip surface near the edge of the chip. The sensor chip was adhered on an aluminum lead frame. Except areas for the arrays, the rest surface of the chip was covered with the resin to make a sensor package. Electric current between two electrodes of Al and Au were measured by the hand-made device with precise amperemeter. The temperature of the sensor chip was estimated from after calibrated straight line of electric resistance of Pt as a function of changing temperature. Heat capacity of the sensor was varied by attaching a heat sink directly to the backside of a sensor package through a window which was open in the resin of the package. In this study, aluminum and copper were used as the heat sink and their volume was varied; 109 (cylindrical), 378 and 818 (cylindrical with rectangular) mm3. Temperature of a sensor was changed by putting it into a chamber and its internal temperature and water vapor pressure were controlled for 840 sec at 1 kPa from 25℃, respectively. 3. Results and discussion Temperature changing rate of the sensor was calculated from the slope of temperature with the square root of time. It was plotted as a function of additional heat capacity of the sensor with and without heat sink and results at cooling process were shown in Fig. 1. The temperature changing rate of the sensor was decreased by adding heat sinks to the sensor and it seems to be related almost linearly with the additional heat capacity. This means that it is possible to make temperature change of the sensor with close to that of the target when it becomes important on application such as dew condensation detection. 4. Conclusion This study clarified that the heat capacity of moisture sensor could be controlled by attaching heat sink of metals directly on a part of the sensor. Since the wettability of the sensor had been already controlled successfully, the surface status of the sensor could be made closer to the target on application that this sensor is needed even when the temperature of the target is changed. 5. Reference [1] J Kawakita et al., ECS trans., 75 (2017) 51. [2] Y. Kubota et al., Sensors and Actuators A: Phys., 303 (2020) 111838. [3] R.G. Shrestha et al., Sensors, 19 (2019) 4500. Figure 1

We examined a working hypothesis of sticky thermoelectric (TE) materials, which is inversely designed to mass-produce flexible TE sheets with lamination or roll-to-roll processes without electric conductive adhesives. Herein, we prepared p-type and n-type sticky TE materials via mixing antimony and bismuth powders with low-volatilizable organic solvents to achieve a low thermal conductivity. Since the sticky TE materials are additionally injected into punched polymer sheets to contact with the upper and bottom electrodes in the fabrication process, the sticky TE modules of ca. 2.4 mm in thickness maintained temperature differences of ca. 10°C and 40°C on a hot plate of 40 °C and 120°C under a natural-air cooling condition with a fin. In the single-cell resistance analysis, we found that 75~150-μm bismuth powder shows lower resistance than the smaller-sized one due to the fewer number of particle-particle interfaces in the electric pass between the upper and bottom electrodes. After adjusting the printed wiring pattern for the upper and bottom electrodes, we achieved 42 mV on a hot plate (120°C) with the 6 × 6 module having 212 Ω in the total resistance. In addition to the possibility of mass production at a reasonable cost, the sticky TE materials provide a low thermal conductivity for flexible TE modules to capture low-temperature waste heat under natural-air cooling conditions with fins for the purpose of energy harvesting.

Evaluating the presence of a slight amount of water plays a crucial role in practical applications such as the advanced detection of dew condensation and the microdetermination of perspiration and transpiration. For this purpose, we have developed a configuration for the moisture sensor that consists of a microgalvanic cell composed of narrow metal arrays. It is inferred that the output response current arising from this sensor should depend on the geometric parameters (e.g., number, area, volume, etc.) of water droplets attaching on the sensor surface. In this study, the output current was recorded, while the microscopic images of the sensor surface were captured. The droplets on the sensor surface were analyzed manually and by computational image processing with deep learning and ImageJ. The deep learning technique shortened the processing time to 1/1000 of the manual one and was able to match 90-100% of the manual count. The results revealed that the response current increased with the total projected area of droplets bridging the galvanic-coupled arrays on the sensor surface. In addition, a straight line with relatively strong positive correlation was obtained between the response current and the total volume of the bridging droplets. These findings suggested that our sensor can be practically used to estimate the presence of a slight amount of water.

Sensor surfaces with micron- and nano-gap scales possess high surface-to-volume ratio which greatly affects their contribution towards water adsorption and condensation. However, the quantitative relationship between adsorbed water molecules and condensed water droplets remains unclear. In this study, we used the humidity-based detected galvanic current within the micron gaps of our newly developed moisture sensor chip (MSC) to emphasize the quantitative relationship between adsorbed water molecules and condensed water droplets. The mass of adsorbed water molecules was detected using a quartz-crystal-microbalance electrode (QCM) whereas the mass of condensed water droplets was estimated microscopically based on their occupying volumes at MSC surface. Experimental results demonstrated that the minimum detection limit of MSC under these experimental conditions was ~150 ng/cm2 for adsorbed water molecules and ~700 ng/ cm2 for condensed water droplets. The detected-response galvanic current arises when a water bridges between two adjacent arrays is found to be linearly correlated to the adsorbed and/or the condensed water’s mass. Such correlation is believed to provide a feasible long-range sensor that can distinguish the status of its surface-existing water either in adsorbed molecular or condensed droplet-wise regimes.

Accurate detection and quantitative evaluation of environmental water in vapor and liquids state expressed as humidity and precipitation play key roles in industrial and scientific applications. However, the development of supporting tools and techniques remains a challenge. Although optical methods such as IR and LASER could detect environmental water in the air, their apparatus is relatively huge. Alternatively, solid detection field systems (SDFSs) could recently lead to a revolution in device downsizing and sensing abilities via advanced research, mainly for materials technology. Herein, we present an overview of several SDFS based sensing categories and their core materials mainly used to detect water in atmosphere, either in the vapor or liquid phase. We considered the governing mechanism in the detection process, such as adsorption/desorption, condensation/evaporation for the vapor phase, and surface attach/detach for the liquid phase. Sensing categories such as optical, chilled mirror, resistive, capacitive, gravimetric sensors were reviewed together with their designated tools such as acoustic wave, quartz crystal microbalance, IDT, and many others, giving typical examples of daily based real scientific applications.

Sticky thermoelectric (TE) materials have been inversely designed to enable the mass production of flexible TE sheets through lamination or roll-to-roll processes without using electrically conductive adhesives. They have also been demonstrated as inorganic/organic hybrid materials consisting of TE inorganic particles and low-volatilizable organic solvents to exhibit Seebeck coefficients based on the TE particles and low thermal conductivities based on the organic matrix. To achieve energy harvesting of 250 µW for driving various electric devices using voltage boosters, herein, we employ p- and n-type Bi2Te3 particles due to their high Seebeck coefficients, and cover the Bi2Te3 bodies with Au skins because the interfacial electrical resistance depends on the electrical resistance of opposing substances at the interface. After controlling the plating amount to cover the Bi2Te3 particles with Au skins, we achieve a TE power generation two orders of magnitude greater than the previous study, i.e., 255 µW on a hot plate of 110 °C with a 6 × 6 module. Overall, with input from other organic devices, like organic light-emitting diodes and dye-sensitized solar cells, this study presents a hierarchical design for TE hybrid materials that suppresses the thermal conduction by hybridizing TE particles with the organic matrix at the microscale. This reduces the electrical resistance by modifying the interfaces of the TE particles at the nanoscale and optimizes the Seebeck coefficient of TE particles at the atomic scale. To compete with solid-state TE modules with regards to power generation capacity, the hierarchical design towards a possible further two orders of magnitude improvement is also discussed.

A stable, sensitive, and accurate moisture chip with long life time is always desired in practical applications. Therefore, it is very important to investigate several factors that affect these properties. In this context, an enhancement in the sensitivity and life time of galvanic array moisture chip used for dew condensation detection has been reported. The chip is capable of early prediction of dew condensation promptly and precisely. The sensing aptitude of the chip with the smallest electrode gap ~500 nm is very fast and can detect water molecules, even much before actual dew condensation occurs. Furthermore, through modification of the surface of the chip using modified superhydrophilic polymer coating, the output could be enhanced by ~2 orders than that of moisture chip without coating. The wettability was promoted by the coating and hence adsorption of water on the surface between the electrodes, generating galvanic current. It could increase the number and area of bridging water droplets between the electrodes, leading to an enhanced output. Interestingly, with the modified superhydrophilic polymer coating used in this study, a wide thin film of water was observed covering the whole surface of moisture chip, not easily observed otherwise. Optical images, contact angle measurement and output current results supported the fact that a moisture chip showed long term stability and excellent capacity towards detection of dew condensation. The life time of moisture chip with superhydrophilic surface is also comparatively long (time period for this study ~20 months).

The chemical bonding state of Mn film on SiO 2 , which is expected to be applied as a bonding material for Si wafer, was investigated by x-ray photoelectron spectroscopy (XPS). The as deposited Mn film had unintentionally oxidized surface and interface layer, caused by an air exposure and a redox reaction with SiO x at the SiO 2 surface, respectively. Post deposition anneal (PDA) enhanced the redox reaction between MnO x and SiO 2 . The N 2 plasma treatment eliminates the redox reaction, and enhances the Si-Mn-O bonding formation, which should improve the tensile strength of wafer bonding.

Behavior of water droplets at around 100%RH (relative humidity) was examined using developed galvanic arrays with micro/nano gap. Experimental results showed that the response current detected while observing arrays and gap surfaces depended on the variation of RH according to the adsorption behavior of water droplets. At 100%RH, response current showed a steady value determined by the equilibrium between the condensation of liquid phase and the evaporation of vapor phase. These results indicated that, once the liquid water was formed on the sensor surface above 100%RH, the response current that depended on the water droplet’s size could be estimated kinetically.

This paper describes the adhesive interface between a conducting polymer/metal composite and a polytetrafluoroethylene (PTFE) substrate. Strong adhesion was observed from using a Ag/polypyrrole (Ag/PPy) composite on a fluoropolymer substrate, which in most cases has a very low adhesion to different materials. To clarify the adhesion mechanism between the Ag/PPy composite and the PTFE substrate, the interfacial structure was studied by the use of transmission electron microscope (TEM) and X-ray photoelectron spectroscopy (XPS). Our results show that Ag/PPy composite is absorbed inside the nano-sized pores of PTFE and the composite mechanically interlocks after solidifying, which causes the nanocomposite to stick strongly to the substrate. The use of Ag/PPy coating could be a novel technique for developing electrodes, antennae or other high performance applications as this metal/conductive polymer composite has excellent adhesion properties on various plastics.

Galvanic current flows when water bridges over the adjacent arrays of Au and Al intercalated with each other with micro/nano gap in a microgalvanic cell. This cell is capable of sensing small water droplet and condensed water molecules and enables it to apply in the detection of dew condensation at an early stage. Enhancing galvanic current, i.e. electrochemical reaction rate of this system, improves its sensitivity as a sensor. This study clarified that cathodic reaction in the galvanic action between the Au and Al arrays in contact with condensed water molecules under the atmospheric condition should be reduction of oxygen gas on the Au array. Galvanic current could be enhanced by coating Pt on Au electrode, by enhancing the oxygen reduction reaction, increasing the sensitivity of microgalvanic cell as a sensor.

Introduction Prediction of dew condensation at an early stage is very important to control its side-effects like, metal corrosion, molding, crop disease, glass flogging etc. Conventional techniques such as commercial hygrometer are not appropriate for this purpose in terms of accuracy and response time. In this context, we have developed a small and portable sensing device termed as Moisture Sensor that can detect invisibly small water droplet and distinguish its size with high accuracy and high speed. The sensor has two interdigit structures made of two different metals as electrodes, intercalating each other with gaps of 0.5 to 10 μm. The working principle of this sensor is based on the generation of galvanic current when aggregation of water molecules connects adjacent electrodes. If structure of electrodes and the environment are modified, it is likely that the output current from the sensor can be improved. The output must be enhanced for employing it in wide areas of applications. The purpose of this study was to clarify the effects of cathode metal and oxygen content surrounding the sensor on its output response. Experimental Silica layer covered Si - wafer was used as the substrate. Arrays of Al and Au/Pt were alternately arranged on the substrate to form an opposing interdigit structure and used as the electrodes. The thickness of Pt on Au was varied; 10 - 90 nm. The gaps between the adjacent arrays were 0.5 and 10 μm and the number of each electrode was 50. The wafer was cut into a 5mm square chip. Electric current between two electrodes of Al and Au were measured by the hand-made device with precise amperemeter. Surface of the sensor was observed by scanning electron microscopy. The sensor was placed in a humidity controlled chamber, maintained by a dew generator (50±1%). The sensor surface was cooled with a Peltier device. This controlled the relative humidity on sensor’s surface and generated water molecules and droplets on the sensor surface. The response current from Moisture Sensor was measured simultaneously, by changing the thickness of Pt coating on Au electrode and under different O2 concentrations by using nitrogen, air and oxygen as carrier gas for dew generator. Result and Discussion As the relative humidity on the sensor surface exceeded 60%, the output current of the sensor started increasing gradually by water molecules adsorption and stacking on the sensor surface, between the electrodes. When it reaches 100 %, dew condensation should occur on the sensor surface while vaporization should make water molecules leave the sensor surface thermodynamically. Therefore, steady response current was obtained theoretically and actually in this study. Fig. 1 shows response current of the sensor with the electrode gap of 0.5 μm at 100% RH when the thickness of Pt was varied for the cathode. The response current was increased from 10 to 60 nm thickness and further increase showed almost same or decreased response current. SEM images of the sensor surface showed that particles of Pt became smaller with the increase of Pt thickness, (deposition time). From these results, it can be said that response current was enhanced by acceleration of electrochemical reaction on the cathode; O2 + 2H2O + 4e− → 4OH− on Pt due to the better catalytic action than on Au. It was further enhanced by the increase in surface area of Pt with decreasing its particle size. As the Pt thickness was increased, however, the thickness of Au was decreased, leading to increase in actual electrical resistance of the cathode. Therefore, the whole response current got saturated or decreased. In addition, an increase in the content of oxygen in the chamber increased the output response. Conclusion This study showed that the output current between water and micro/nano galvanic arrays of the moisture sensor was enhanced by coating Au electrode with a thin layer of Pt and increasing the oxygen pressure around the electrode. These modification actuall accelerated electrochemical reaction rate on the cathode. This improved the sensitivity of this sensor. The outcome of this study will contribute to predict dew condensation more accurately and to widen the area of its application where highly sensitive and accurate moisture detection is desired. References: J. Kawakita, et al., ECS Trans. 2017, 75, 51. R.G. Shrestha, et al., Sensors, 2019, 19, 4500. Y. Kubota et al., Sensors and Actuators A: Physical, 2020, 303, 111838. Figure 1

Dew condensation is ubiquitous but its consequences are mostly catastrophic for building, crops, electrical devices, aviation industry, air conditioning and pharmaceuticals, therefore detection and it’s monitoring at early or initial stage are critically required for its prevention which cannot be realized by current technologies. Moisture Sensor can detect a small water droplet and distinguish its size with high accuracy and quick response by the galvanic action upon water getting attached and bridging adjacent arrays composed of different metals. In this study, it was applied to detect dew condensation. The experimental results showed that Moisture Sensor could detect occurrence of dew condensation in initial and early stage with high accuracy in terms of dew point. Moreover, a stage prior to dew condensation, presumably adsorption of water molecules, was detected and distinguished quantitatively and accurately depending on the relative humidity below 100 % around the arrays. Moisture Sensor also takes advantage of modifying its surface status such as wettability and temperature. It suggests that this sensing method can be an alternative to conventional hygrometer, especially in a high relative humidity region and expect prediction or premonition of dew condensation, which occurs on the actual target.

Composite of metal and conducting polymer is expected for electrical application by the use of their advantages. For improvement of the composite’s characteristics, it is important to control formation rate and structure of the composites obtained by simultaneous metal deposition and polymerization under photo irradiation. The purpose of this research was to reveal the effects of UV irradiation and dopant type for conducting polymer on photo-electrochemical deposition of metal. Cathodic polarization curves for silver deposition on polypyrrole doped with different types of anion at different intensity of the UV light were compared. Deposited particles were evaluated by the statistical analysis. The experimental results showed that silver deposition on polypyrrole was enhanced by UV introduction and depended on the dopant type.

The interconnect of flexible electronics requires to be electronically conductive as well as mechanically flexible, adhesive to plastic substrate and productively efficient while conventional technologies to form the interconnect are difficult to attain all of these requirements. The conductive polymer/metal composite material synthesized by solution chemistry was developed to meet these requirements. This composite material is promising as the interconnect of flexible electronics.

This paper describes the interface reactions and diffusion between silver/polypyrrole (Ag/PPy) composite and silicon substrate. This composite material can be used as a novel technique for 3D-LSI (large-scale integration) by the fast infilling of through-silicon vias (TSV). By immersion of the silicon wafer with via holes into the dispersed solution of Ag/PPy composite, the holes are filled with the composite. It is important to develop a layer between the composite and the Si substrate with good diffusion barrier and adhesion characteristics. In this paper, SiOx and two types of SiOxNy barrier layers with various thicknesses were investigated. The interface structure between the Si substrate, the barrier, and the Ag/PPy composite was characterized by transmission electron microscopy. The adhesion and diffusion properties of the layers were established for Ag/PPy composite. Increasing thickness of SiOx proved to permit less Ag to transport into the Si substrate. SiOxNy barrier layers showed very good diffusion barrier characteristics; however, their adhesion depended strongly on their composition. A barrier layer composition with good adhesion and Ag barrier properties has been identified in this paper. These results are useful for filling conductive metal/polymer composites into TSV.

Employing electropolymerization route, a coulombic-controlled approach was adopted to polymerize the pyrrole monomers on the TiO2:SnO2 made nanocomposite working electrodes. The absorbance values of the composite electrodes in the UV region were found to improve the rate of formation of oligomeric products from the pyrrole monomers. The role of anionic dopant in the evolution of polymer structures has been discussed using bi-polaronic states. The polymer deposits were studied using FT-IR spectroscopy to elucidate their functional groups and their three-dimensional morphological arrangements were perceived using atomic force microscopy and scanning electron microscopy. A negative shift in the flat band potential was observed from the Mott–Schottky plots, as a function of Sn composition in the composite electrodes, which favours a faster rate of electron transfer, while the Sn sites minimizes the rate of electron–hole recombination.

One-dimensional Mn doped ZnO nanocrystallites were synthesized through a facile low temperature surfactant free chemical route. The crystallite structure and morphological evolution of the particles were revealed to be of wurtzite phase and rod like structures from the X-ray diffraction and transmission electron microscopic analysis, respectively. Using Raman spectroscopy the role of oxygen related defects and phase purity in the Mn substituted ZnO systems were studied systematically. A significant suppression in the sub-band edge emission was visualized in the room temperature emission spectra of the Mn doped systems. The intensity ratio in between the near-band edge and defect-level emissions was observed to increase, signifying the reduction in oxygen related defects and revealing their influence on the crystallinity on the Mn substituted ZnO species. These variations were correlated with the increasing number of Mn ions in the host lattice, which results with their passivating action on the surface defects.

Composite of metal and conducting polymer is expected for the electrical application by the use of their advantages. The purpose of this research was to reveal photo-electrochemical deposition behavior of metal, which is important to control the formation rate and the composite’s structure obtained by simultaneous metal deposition and polymerization under the photo-irradiation. Cathodic polarization curves for silver deposition on polypyrrole film with different substrates under UV irradiation were compared in addition to the electrical resistance of the polypyrrole and the substrate. Morphology of silver deposition on polypyrrole was characterized by microscopic observation. The experimental results showed that photo introduction to polypyrrole upon silver deposition enhanced the deposition rate to 24 times at maximum.

The interconnect of flexible electronics requires to be electronically conductive as well as mechanically flexible, adhesive to plastic substrate and productively efficient while conventional technologies to form the interconnect are difficult to attain all of these requirements. The conductive polymer/metal composite material synthesized by solution chemistry was developed to meet these requirements. This composite material is promising as the interconnect of flexible electronics.

With progressive downsizing of semiconductor devices, conducting polymers are a promising candidate for Ohmic contacts because of their variable size and work function. In order to optimize the polymer structure, it is important to evaluate the Fermi level of the polymer joined with semiconductor because that depends on the polymer structure and surface state of semiconductor. In this study, polypyrrole as a conducting polymer was formed through photo-electrochemical reaction on single crystal TiO 2 as the n-type semiconductor with a well-defined surface. Surface potential of the polypyrrole was measured by Kelvin probe force microscopy. The Fermi level estimated from the surface potential was homogeneous and independent on the morphology of polypyrrole, determined by the balance of the charge density between the polypyrrole layer and the TiO 2 substrate. The Fermi level was changed 0.25 eV with the amount of polypyrrole formed on TiO 2 .

The progress in studying the interfacial electronic structures of the developing new class of hybrid organic/inorganic material systems have envisaged a new dimension into the field of photovoltaics, which could be of great help in understanding the nature of charge transfer in them. In this regard, electropolymerization of pyrrole monomers have been carried out at room temperature on the surface of TiO2 working electrodes (assisted by UV radiations) and their interfacial electronic structure has been studied as a function of the applied photo anodic potentials. The formation of polypyrrole deposits has been ensured using FT-IR and Raman spectroscopy. Surface analysis of the hybrid matrix revealed the tendency of polymer molecules to cover up the spherical surface of TiO2 nanoparticles that could help in improving the light absorption rate. Signals (bands) corresponding to pyrrole molecules observed in the ultraviolet photoelectron spectroscopy measurements have been correlated with the polaronic states formed and identified to shift as a function of the applied photo anodic potentials, revealing the decrease in work function of the hybrid system to take place (confirmed using cyclic voltammetry measurements). The decreasing trend in the work function elucidates the adjustment in electronic structure of the system (hybrid materials possessing smaller work functions are generally preferred for photovoltaic studies). The aforementioned behavioural aspects have been reasoned with the increase in overpotential values for polarization, from the decrease in up-take rate of the anionic dopant, which increases the current density values, thereby modifying the conductivity of the systems.

Hybrid materials of the organic and inorganic semiconductors have a potential to show the better performance in the charge separation at the junction upon the photovoltaic action by the presence of the space charge layer in the inorganic semiconductor. In this study, the photo-anodic polymerization was selected as a fabrication method for the hybrid materials composed of TiO2 and polypyrrole on the basis of some advantages of this method. For the process control of the photo-anodic polymerization, it is important to elucidate the formation and growth mechanisms of the organic polymer. In this study, a flat sheet of single-crystal TiO2 was used as a well-defined surface for preparation of the organic polymer of pyrrole. Photo-anodic polarization behaviour was clarified and polypyrrole was prepared on TiO2. The formation process, especially the initial step was revealed by observation of polypyrrole with atomic force microscope (AFM) and statistical interpretation of the morphology of polypyrrole in the nano-scopic level. The formation process of polypyrrole on the TiO2 surface was summarized; (1) adsorption of precursors, (2) localized formation and growth of polypyrrole under the photo-illumination, and (3) homogenous growth of polypyrrole with the external current application under the photo-illumination.

防食コーティングに対する様々な要求事項に応えるプロセスの開発が必要である．そこで，超音速粒子の衝突・堆積現象の解明に基づいて，粒子の温度・速度制御機構を考案することにより，優れた防食性能を有しているが大気開放下では成膜することが困難とされてきた各種材料（チタンや金属ガラス，酸化チタン，プラスチックなど）のコーティング技術（ウォームスプレー）の開発に成功した．

The theoretical calculation of a two-stage high-velocity oxy-fuel thermal spray gun was conducted for the purpose of predicting the stagnant pressure in the mixing chamber (MC). The theoretical results were compared with the experimental ones obtained by the cold flow and actual spray gun tests. The effect of the diffuser shape installed between the combustion chamber (CC) and the MC was also investigated in the cold flow test. It was clarified in this study that 1) the theoretical calculation shows that in order to obtain a larger pressure in the MC the diameter rations of d3t/d1t and d1e/d1t should be chosen to satisfy Eq.(11), to keep the diffuser throat unchoked, 2) the theoretical results of p03/p01 agree with the results of cold flow test within an accuracy of 6%, 3) the theoretical results of p01 agree with the results of actual two-stage HVOF gun test within an accuracy of 4%, demonstrating the validity of the present theoretical calculation.

Effective design of a dye-sensitized solar cell (DSSC) requires a clear understanding of the reaction mechanisms of the constituent cell materials. The relationship between structural and photo-electrochemical properties of the photo-anodic materials is of the first priority for such investigations. Highly oriented aggregates of anatase phase TiO2 nanoparticles were deposited on Indium Tin oxide (ITO) glass substrates; over which N719 dyes were adsorbed through electrophoretic deposition under a strong magnetic field. The properties were evaluated by electrochemical measurements, UV–VIS spectroscopy, and electrical resistance measurements. The results showed that the absorbed photon number in the TiO2 aggregates with adsorbed dye and their resistivity showed different dependences on the orientation of the crystal plane in the TiO2 particle. The dependence of the photocurrent on the plane orientation of aggregates of dye-sensitized TiO2 nanoparticles has been determined from a combination of the electrical conductivity of TiO2 aggregate and the amount of dye adsorbed on the surface of TiO2.

In order to evaluate the characteristics of photocatalysts such as TiO2, it is important to separately estimate the oxidation and reduction reaction rates, since the overall reaction rate is limited by the rate-determining step. In this study, photoelectrochemical techniques were applied to thin films of crystalline oriented anatase TiO2 with polycrystalline aggregations deposited on the transparent conductive oxide (TCO) glass substrate, fabricated by the electrophoretic deposition (EPD) in a strong magnetic field. The influence of the plane orientation on the photocatalytic reaction rates was discovered for both oxidation and reduction with respect to current through the electrochemical measurements. The maximum photocurrent for the (001) plane orientation is three times higher than that for the (100) plane orientation, and is comparable with that of the random orientation. The rate of the anodic reaction determines the rate of the overall photocatalytic reaction, therefore affecting the photopotential.

In high-velocity oxy-fuel (HVOF) spraying of WC-Co coatings, the decomposition and decarburization of WC during deposition are responsible for their much lower toughness compared with a sintered bulk WC-Co. In a previous study, Warm Spray (WS) process, which is capable to control the flame temperature used to propel powder particles, was successfully applied in an attempt to suppress such detrimental reactions by keeping particles’ temperature lower than their melting point. The coatings deposited by WS process showed no or little formation of W2C and η phases and demonstrated moderately improved fracture properties. However, there is still a gap in fracture toughness between WS coatings and the corresponding sintered bulk. In order to optimize the properties of the WS coatings, the effect of original powder sizes were investigated. Microstructural characterization and phase analysis were carried out on deposited coatings by SEM and XRD. The results show that the feedstock powder size has substantial effects on the properties of the coatings, i.e., the smaller powder showed improved properties.

Crystal-oriented and crack-free thin TiO2 films with a good interfacial adhesion on indium-tin oxide (ITO) glass substrates for photoelectrodes were fabricated by the electrophoretic deposition (EPD) method in a 12 T strong magnetic field. A binder-free suspension for the EPD was prepared by dispersing TiO2 in the mixture of 2-propanol and 2,4-pentanedione. The electrophoretic mobility and the sedimentation rate were measured at various ratios of the mixed solution. The optimized state of the suspension exhibiting the highest surface charge potential and producing deposits with the highest green density was obtained at the 50:50 mixing ratio. The TiO2 films were characterized by XRD and SEM analyses. The photo-current measurement was also conducted to investigate the relation between the photo-anode characteristics of a dye-sensitized solar cell and the plane orientation of the TiO2 films

Crystal-oriented and crack-free thin TiO2 films with a good interfacial adhesion on indium–tin oxide glass substrates for photoelectrodes of dye-sensitized solar cells were fabricated by the constant voltage electrophoretic deposition (EPD) method in a strong magnetic field of 12 T generated by a superconducting magnet. A binder-free suspension for the EPD was prepared by dispersing TiO2 in a mixture of 2-propanol and 2,4-pentanedione (acetylacetone). The electrical conductivity, sedimentation rate, and the electrophoretic mobility were measured at varying ratios of the mixed solution. The optimized state of the suspension exhibiting the highest surface charge potential and producing deposits with the highest green density was obtained at the 50:50 mixing ratio. The TiO2 films were characterized by X-ray diffraction and scanning electron microscopic analyses.

The influence of the crystalline orientation of the TiO2 photoanode on the photo-electrochemical characteristics was investigated to reveal the primary factors responsible for improving the photoelectric conversion efficiency of a dye-sensitized solar cell. It was observed that the photocurrent depended on the plane orientation, whereas the dependence of the photopotential on the open circuit was almost constant. The rate of the photoanodic reaction was attributed to the dye adsorption, depending on the surface energy of each oriented plane of the TiO2. The cathodic reaction on TiO2 during open circuit is likely to determine the rate of the entire electrochemical reaction.

Micron-sized titanium particles were deposited on steel substrates by the warm spraying, which is a modified high velocity oxy-fuel (HVOF) spraying technique. In the process, nitrogen gas is mixed with the HVOF flame jet to lower the temperature of injected powder particles. Detailed observations of splats formed on polished substrates by using scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were conducted to investigate the effects of particle temperature on the bonding of splats with the substrate and the microstructure within the splats. At lower nitrogen flow rates, the particles observed were heavily deformed and exhibited diverse splat morphologies and microstructures. At higher nitrogen flow rates, most of the particles were impacted in the solid state and the oxidation of particles was remarkably less. The TEM observation revealed distinctively different microstructures within the splats as well as the splat/substrate interfaces depending on whether the particle was molten or solid before the impact.

The high-velocity oxy-fuel (HVOF) process is commonly used to deposit WC-Co coatings. There are some problems with this process, especially the decomposition and decarburization of WC during the spraying. To eliminate these degradation, the warm-spray (WS) process originally developed by our group, which provides a possibility to control the flame temperature and the fabrication of WC-Co coatings can be made at lower temperature ranges that those of HVOF process, was applied to deposit WC-Co coatings. Microstructural characterization and phase analysis were carried out on deposited coatings by SEM and XRD. The mechanical properties such as hardness, fracture toughness, and wear properties were investigated. The results showed that WS coatings did not contain any detrimental phase such as W2C and W, which are usually observed in HVOF coatings. The hardness of WS coatings were lower than those of HVOF coatings, however, the relation of hardness-Co content of WS coatings showed the similar trend as that of the sintered WC-Co. The improvement of wear behavior was also observed in WS coatings.

Titanium powder particles were deposited at high velocity on a steel substrate by a process called warm spraying. Extremely fine grains, several tens of nanometers in size, were observed along the interfacial boundary of the deposited particles known as splats and the substrate, where the most severe deformation had taken place. A schematic model to explain the mechanism of grain refinement of titanium powder is presented, in which dynamic recrystallization caused by adiabatic shear instability plays the major role.

Warm Spray is an atmospheric coating process through continuous impact and deposition of solid particles heated and accelerated by a supersonic jet controlled between 800~1900 K and 900~1600 m s − 1 . This paper introduces successful fabrication of dense and less-oxidized metallic titanium (Ti) coatings by Warm Spray and clarification of phenomena occurring upon the spray process. Temperature and velocity of an in-flight Ti particle were compared between measurement by the diagnostic instrument and calculation based on the fluid dynamics simulation. Deformation behaviour of particle from impact to deposition was analyzed through the finite element method (FEM). Densification of stacking particles was attained by applying bi-modal size distribution to the feedstock Ti powder. Qualitative restriction of changes in chemical composition of Ti coating obtained was demonstrated by elemental analysis and by calculation based on the oxidation model. Warm Spray enables various materials to fabricate coatings without thermal deterioration of the original characteristics such as purity and crystallographic phase.

Titanium dioxide TiO 2 can be used as a photo-anode to give generated electrons to the metal substrate under illumination. The transition metal oxide such as iron oxide Fe 2 O 3 can be used to store electrons generated by the photo-electric conversion function of TiO 2 under the illuminated situation while the electrons are discharged from the transition metal oxide to the metal substrate in the dark. In this paper, coatings of nano-sized composite of TiO 2 and Fe 2 O 3 were fabricated by the Warm Spray process, in which the feedstock powder is accelerated by a supersonic gas jet with speed above 1.0 km s - 1 and temperature between 800 and 2500 K, and then impacted onto the target substrate continuously to form coatings. The coatings of TiO 2 and Fe 2 O 3 nano-composite fabricated by Warm Spray showed no thermal deterioration such as phase transformation and particle growth of the feedstock during the spray process. The coatings fabricated by the Warm Spray had larger photo-current and the electron charge/discharge capacity than that by a conventional HVOF process. In addition, these characteristics were improved by decreasing the primary particle size of TiO 2 and Fe 2 O 3 .

By putting photo-electric conversion materials and electron storage materials together on one device, full-time cathodic protection system was expected to function and its coating technique is required to realize the system. So far, Warm Spray, impact deposition of supersonic particle with temperature controllable in a wide range, enabled nano-sized TiO2 and Fe2O3 to be deposited controlling thermal degradation of the particles and it was revealed that each of photo-electric conversion and electron storage were functioned. The rest potential of the coatings as an indicator of overall system performance was not negative sufficiently, which might be related to the less conductive nature. Therefore, metallic Zn was introduced in this paper for shifting the rest potential to more negative direction and increase of the conductivity. The coatings were successfully fabrication with control of thermal degradation of Zn, which worked as a binder to connect the oxide particles. Photo-cathodic protection behaviour indicated that the steady rest potential of the Warm Sprayed coatings of the TiO2-Fe2O3 system was not influenced on the introduction of metallic Zn, implying that it might not be limited by the conductive property of the coatings.

Metallic glasses are highly attractive because of their superior strength, relatively low Young’s modulus and superb corrosion resistance[S1], etc. By combining a metallic glass with different materials, synergy effect can be expected in the mechanical properties and corrosion resistance, for example. Fabricating a thick metallic glass layer on a substrate material by thermal spray process is one way to bond these materials. In such practice, however, the temperature of the sprayed metallic glass and that of the substrate must be kept relatively low in order to avoid crystallization and/or oxidation of the amorphous deposits. Warm Spray is a modified version of HVOF spraying developed by National Institute for Materials Science (NIMS) suited for spraying of heat sensitive feedstock materials. In the process, high-velocity solid particles heated to the temperatures below its melting point are projected on to the substrate. A Zr-base metallic glass powder was warm sprayed onto cylindrical substrates of 316L stainless steel to various thicknesses. Negligible crystallization and oxidation were observed in the deposited layer of the glass alloy. The linear relationship between the thickness of the glass alloy layer and the Young’s modulus of the composite bar demonstrated that the mechanical property of such composite structures can be controlled. [doi:10.2320/matertrans.T-MRA2007882]

WC–20 mass%Cr3C2–7 mass%Ni powder was sprayed onto low-carbon steel substrates by a commercial high velocity oxygen-fuel (HVOF) spray process as well as by an improved HVOF process equipped with a gas shroud attachment. The latter process utilizes a nitrogen gas flow to shield the region between the spray gun and the substrate in order to suppress the material's degradation caused by reaction with air such as oxidation and decarburization. Some coatings were further heat-treated in air at 773 K for 30 h to form a thin oxide film on the surface. The sliding wear properties of these coatings against an iron pin were evaluated by using a pin-on-disk wear tester. The specific wear rate of the as-sprayed cermet coatings prepared under the conventional spray condition was about three times higher than that of the chrome plating but by using the gas shroud, the wear rate was reduced to the same level with the chrome plating. The specific wear rate could be further decreased by the oxidation heat-treatment. It was found that a proper amount of oxides existing on the surface or within the coatings have a great beneficial effects on the wear properties such as to promote the transition from severe wear to mild wear and thus to reduce the wear rate remarkably. XPS analysis of the transfer particles collected from the wear track revealed a shift in the oxidation state of iron depending on the wear condition.

Toward fast formation of TSV for 3D-IC or 3D-LSI, a composite with polypyrrole as a conducting polymer and metal silver prepared through the solution photo chemistry was studied with respect to filling status of vertical holes in silicon chip, electrical characteristics and interfacial structures between the filling composite and silicon substrate. Based on the experimental results, the composite was capable of filling within 10 minutes, evaluation procedures of electrical resistance was established and excellent barrier layer was found.

A modification of high-velocity oxy-fuel (HVOF) thermal spray process named as warm spray (WS) has been developed. By injecting room-temperature inert gas into the combustion gas jet of HVOF, the temperature of the propellant gas can be controlled in a range approximately from 2300 to 1000 K so that many powder materials can be deposited in thermally softened state at high impact velocity. In this chapter, the characteristics of WS process were analyzed using gas dynamic simulation of the flow field and heating/acceleration of powder particles in comparison with HVOF, cold spray (CS), and high-velocity air-fuel spray. Transmission electron microscopy of WS and CS titanium splats revealed marked differences in the microstructures stemming from the different impact temperatures. Mechanical properties of several metallic coatings formed under different WS and CS conditions were compared. The characteristics of WC-Co coatings made by WS were demonstrated for wear-resistant applications.

In this article, air and steam oxidation resistance of bare and nanoceria coated 9Cr–1Mo ferritic steel at 650 °C for 500 h is reported. The kinetics of the oxidation process and the changes in the morphology and the chemistry for both the specimens were analyzed by backscattered electron and EPMA mapping. The nanoceria coated 9Cr–1Mo ferritic steel showed better oxidation resistance than uncoated steel under similar conditions. The thickness of the oxide scales formed on the coated samples was significantly reduced as compared to the uncoated substrates. The effectiveness of such a thin and simple nanocoating to improve the oxidation resistance of 9Cr–1Mo ferritic steel compared to the pristine is attributed to the change in the migration of cations from outward to inward diffusion of oxygen as the major mechanism.