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Real-time breath isoprene sensing provides noninvasive methods for monitoring human metabolism and early diagnosis of cardiovascular diseases. Nonetheless, the stable alkene structure and high humidity of the breath hinder sensitive and selective isoprene detection. In this work, we derived well-defined Co3O4@polyoxometalate yolk–shell structures using a metal–organic framework template. The inner space, including highly catalytic Co3O4yolks surrounded by a semipermeable polyoxometalate shell, enables stable isoprene to be reformed to reactive intermediate species by increasing the gas residence time and the reaction with the inner catalyst. This sensor exhibited selective isoprene detection with an extremely high chemiresistive response (180.6) and low detection limit (0.58 ppb). The high sensing performance can be attributed to electronic sensitization and catalytic promotion effects. In addition, the reforming reaction of isoprene is further confirmed by the proton transfer reaction–quadrupole mass spectrometry analysis. The practical feasibility of this sensor in smart healthcare applications is exhibited by monitoring muscle activity during the workout.

Precise detection of breath isoprene can provide valuable information for monitoring the physical and physiological status of human beings or for the early diagnosis of cardiovascular diseases. However, the extremely low concentration and low chemical reactivity of breath isoprene hamper the selective and sensitive detection of isoprene using oxide semiconductor chemiresistors. Herein, we report that macroporous WO3microspheres whose inner macropores are surrounded by Au nanoparticles exhibit a high response (resistance ratio = 11.3) to 0.1 ppm isoprene under highly humid conditions at 275 °C and an extremely low detection limit (0.2 ppb). Furthermore, the sensor showed excellent selectivity to isoprene over five interferants that could be exhaled by humans. Notably, the selectivity to isoprene is critically dependent on the location of Au nanocatalysts and macroporosity. The mechanism underlying the selective isoprene detection is investigated in relation to the reforming of less reactive isoprene into more reactive intermediate species promoted by macroporous catalytic reactors, which is confirmed by the analysis using a proton transfer reaction quadrupole mass spectrometer. The sensor for breath analysis has high potential for simple physical and physiological monitoring as well as disease diagnosis.

The grain growth behavior of La-doped BaTiO3specimens was investigated at 1350 °C under DC external electric field. In air atmosphere, grain growth was enhanced at the positive-biased region for the 0.15 mol% La-doped and 0.3 mol% La-doped specimens, while it was enhanced at the negative-biased region for the 1.0 mol% La-doped specimen. For the 0.6 mol% La-doped specimen, on the other hand, both positive- and negative-biased regions showed the same grain size. The demarcation donor composition (0.6 mol% La) shifted to a higher donor concentration when the specimen was heat-treated in nitrogen. The results were explained in terms of the grain boundary potential and its variation with donor concentration, oxygen partial pressure, and defect polarization.

Metal–organic frameworks (MOFs) with high surface area, tunable porosity, and diverse structures are promising platforms for chemiresistors; however, they often exhibit low sensitivity, poor selectivity, and irreversibility in gas sensing, hindering their practical applications. Herein, we report that hybrids of Cu3(HHTP)2(HHTP = 2,3,6,7,10,11-hexahydroxytriphenylene) nanoflakes and Fe2O3nanoparticles exhibit highly sensitive, selective, and reversible detection of NO2at 20 °C. The key parameters to determine their response, selectivity, and recovery are discussed in terms of the size of the Cu3(HHTP)2nanoflakes, the interaction between the MOFs and NO2, and an increase in the concentration and lifetime of holes facilitated by visible-light photoactivation and charge-separating energy band alignment of the hybrids. These photoactivated MOF–oxide hybrids suggest a new strategy for designing high-performance MOF-based gas sensors.

Today semiconducting metal oxide (SMOX) based gas sensors are used in a wide array of applications. Dopants, e.g., rhodium, are often used to change the sensor response of SMOXs. The adjustment of sensing characteristics with dopants is usually done empirically, and there is a knowledge gap surrounding how the presence of dopants alters the chemistry of sensing. Here using X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), dc resistance measurements, and operando diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy, it was understood how surface loading with Rh2O3changes sensing with WO3. As a result of uniform surface loading, reactions between the Rh2O3clusters and the analyte gas dominate the reception. Changes in the p–n heterojunction between Rh2O3and WO3are responsible for the transduction. These results in combination with existing literature indicate that, through controlled surface doping, it is possible to intentionally tune the sensor characteristics of SMOXs.

Noble metals or oxide catalysts have traditionally been loaded or doped to enhance the gas sensing properties of oxide semiconductor chemiresistors. However, the selective detection of various chemicals for a wide range of new applications remains a challenging problem. In this paper, we propose a novel bilayer design with an oxide chemiresistor sensing layer and nanoscale catalytic Au overlayer to provide high controllability for gas sensing characteristics. The Au nanocluster overlayer significantly enhances the methylbenzene response of a SnO2thick film sensor by reforming gases into more reactive species and suppresses the responses to reactive interference gases through oxidative filtering, leading to excellent selectivity to methylbenzene. Gas sensing characteristics can be tuned by controlling the morphology, amount, and number density of Au nanoclusters through the variation in the Au coating thickness (0.5–3 nm) and thermal annealing conditions (0.5–4 h at 550 °C). Furthermore, the general validity of the proposed Au-coated bilayer sensor design was confirmed through the enhancement of response and selectivity toward methylbenzenes by coating Au nanoclusters onto ZnO and Co3O4sensors. The sensing mechanism, advantages, and potential applications of bilayer sensors are discussed from the perspective of the separation of sensing and catalytic reactions, as well as the reforming and oxidation of analyte gases in association with the configuration of the sensing layer and Au catalytic overlayer.

Catalyst-loaded hollow spheres are effective at detecting ethanol with high chemical reactivity. However, this has limited the widespread use of catalyst-loaded hollow spheres in designing highly selective gas sensors to less-reactive gases such as aromatics (e.g., xylene). Herein, we report the preparation of xylene-selective Au–SnO2nanoreactors by loading Au nanoclusters on the inner surface of SnO2hollow shells using the layer-by-layer assembly technique. The results revealed that the sensor based on SnO2hollow spheres loaded with Au nanoclusters on the inner surface exhibited unprecedentedly high xylene selectivity and an ultrahigh xylene response, high enough to be used for indoor air quality monitoring, whereas the sensor based on SnO2hollow spheres loaded with Au nanoclusters on the outer surface exhibited the typical ethanol-sensitive sensing behaviors as frequently reported in the literature. In addition, the xylene selectivity and response were optimized when the hollow shell was sufficiently thin (∼25 nm) and semipermeable (pore size = ∼3.5 nm), while the selectivity and response decreased when the shell was thick or highly gas permeable with large mesopores (∼30 nm). Accordingly, the underlying mechanism responsible for the unprecedentedly high xylene sensing performance is discussed in relation to the configuration of the loaded Au nanoclusters and the morphological characteristics including shell thickness and pore size distribution. This novel nanoreactor concept can be widely used to design highly selective gas sensors especially to less-reactive gases such as aromatics, aldehydes, and ketones.

Graphene-based electronic textile (e-textile) gas sensors have been developed for detecting hazardous NO2gas. For the e-textile gas sensor, electrical conductivity is a critical factor because it directly affects its sensitivity. To obtain a highly conductive e-textile, biomolecules have been used for gluing the graphene to the textile surface, though there remain areas to improve, such as poor conductivity and flexibility. Herein, we have developed a dopamine–graphene hybrid electronic textile yarn (DGY) where the dopamine is used as a bio-inspired adhesive to attach graphene to the surface of yarns. The DGY shows improved electrical conductivity (∼40 times) compared to conventional graphene-based e-textile yarns with no glue. Moreover, it exhibited improved sensing performance in terms of short response time (∼2 min), high sensitivity (0.02 μA/ppm), and selectivity toward NO2. The mechanical flexibility and durability of the DGY were examined through a 1000-cycle bending test. For a practical application, the DGY was attempted to detect the NOxemitted from vehicles, including gasoline, diesel, and fuel cell electric vehicles. Our results demonstrated that the DGYs—as a graphene-based e-textile gas sensor for detecting NO2—are simple to fabricate, cheap, disposable, and mechanically stable.

Although several crystalline materials have been developed as Li-ion conductors for use as solid electrolytes in all-solid-state batteries (ASSBs), producing materials with high Li-ion conductivities is time-consuming and cost-intensive. Herein, we introduce a superionic halogen-rich Li-argyrodite (HRLA) and demonstrate its innovative synthesis using ultimate-energy mechanical alloying (UMA) and rapid thermal annealing (RTA). UMA with a 49 G-force milling energy provides a one-pot process that includes mixing, glassification, and crystallization, to produce as-milled HRLA powder that is ∼70% crystallized; subsequent RTA using an infrared lamp increases this crystallinity to ∼82% within 25 min. Surprisingly, this HRLA exhibits the highest Li-ion conductivity among Li-argyrodites (10.2 mS cm–1at 25 °C, cold-pressed powder compact) reported so far. Furthermore, we confirm that this superionic HRLA works well as a promising solid electrolyte without a decreased intrinsic electrochemical window in various electrode configurations and delivers impressive cell performance (114.2 mAh g–1at 0.5 C).

Pure and 3–12 at. % Pr-doped In2O3macroporous spheres were fabricated by ultrasonic spray pyrolysis and their acetone-sensing characteristics under dry and humid conditions were investigated to design humidity-independent gas sensors. The 12 at. % Pr-doped In2O3sensor exhibited approximately the same acetone responses and sensor resistances at 450 °C regardless of the humidity variation, whereas the pure In2O3exhibited significant deterioration in gas-sensing characteristics upon the change in the atmosphere, from dry to humid (relative humidity: 80%). Moreover, the 12 at. % Pr-doped In2O3sensor exhibited a high response to acetone with negligible cross responses to interfering gases (NH3, CO, benzene, toluene, NO2, and H2) under the highly humid atmosphere. The mechanism for the humidity-immune gas-sensing characteristics was investigated by X-ray photoelectron and diffuse reflectance infrared Fourier transform spectroscopies together with the phenomenological gas-sensing results and discussed in relation with Pr3+/Pr4+redox pairs, regenerative oxygen adsorption, and scavenging of hydroxyl groups.

Three PbTiO3nanostructures were synthesized using a one-step hydrothermal reaction with different TiO2powders as Ti sources, and their gas-sensing properties were investigated. The sensor comprising PbTiO3nanoplates (NPs) exhibited a high response (resistance ratio = 80.4) to 5 ppm ethanol at 300 °C and could detect trace concentrations of ethanol down to 100 ppb. Moreover, the sensor showed high ethanol selectivity and nearly the same sensing characteristics despite the wide range of humidity variation from 20 to 80% RH. The mechanism for humidity-independent gas sensing was elucidated using diffuse reflectance infrared Fourier transform spectra. PbTiO3NPs are new and promising sensing materials that can be used for detecting ethanol in a highly sensitive and selective manner with negligible interference from ambient humidity.

Ammonia (NH3) is an irritant gas with a unique pungent odor; sub-parts per million-level breath ammonia is a medical biomarker for kidney disorders and Helicobacter pyloribacteria-induced stomach infections. The humidity varies in both ambient environment and exhaled breath, and thus humidity dependence of gas-sensing characteristics is a great obstacle for real-time applications. Herein, flexible, humidity-independent, and room-temperature ammonia sensors are fabricated by the thermal evaporation of CuBr on a polyimide substrate and subsequent coating of a nanoscale moisture-blocking CeO2overlayer by electron-beam evaporation. CuBr sensors coated with a 100 nm-thick CeO2overlayer exhibits an ultrahigh response (resistance ratio) of 68 toward 5 ppm ammonia with excellent gas selectivity, rapid response, reversibility, and humidity-independent sensing characteristics at room temperature. In addition, the sensing performance remains stable after repetitive bending and long-term operation. Moreover, the sensors exhibit significant response to the simulated exhaled breath of patients with H. pyloriinfection; the simulated breath contains 50 ppb NH3. The sensors thus show promising potential in detecting sub-parts per million-level NH3, regardless of humidity fluctuations, which can open up new applications in wearable devices for in situ medical diagnosis and indoor/outdoor environment monitoring.

The chemiresistive sensing characteristics of metal oxide gas sensors depend closely on ambient humidity. Herein, we report that gas sensors using Tb-doped SnO2yolk–shell spheres can be used for reliable acetone detection, regardless of the variations in humidity. Pure SnO2and Tb-doped SnO2yolk–shell spheres were prepared via ultrasonic spray pyrolysis and their chemiresistive sensing characteristics were studied. The sensor resistance and gas response of the pure SnO2yolk–shell spheres significantly changed and deteriorated upon exposure to moisture. In stark contrast, the Tb-doped SnO2yolk–shell spheres exhibited similar gas responses and sensor resistances in both dry and humid [relative humidity (RH) 80%] atmospheres. In addition, the Tb-doped SnO2yolk–shell sensors showed a high gas response (resistance ratio) of 1.21 to the sub-ppm-levels (50 ppb) of acetone with low responses to the other interference gases. The effects of Tb oxide and the chemical interactions among the Tb oxide, SnO2, and water vapor on this humidity-independent gas sensing behavior of the Tb-doped SnO2yolk–shell sensors were investigated. This strategy can provide a new road to achieve highly sensitive, selective, and humidity-independent sensing of acetone, which will facilitate miniaturized and real-time exhaled breath analysis for diagnosing diabetes.

Sn-doped NiO multiroom spheres with unique microreactor morphology were prepared by facile ultrasonic spray pyrolysis of a solution containing tin oxalate, nickel nitrate, and dextrin and subsequent heat treatment. The multiroom structure was formed by phase segregation between the molten metal source and liquidlike dextrin and sequent decomposition of dextrin during spray pyrolysis, which played the dual roles of enhancing gas response and selectivity. The response (resistance ratio) of the Sn-doped NiO multiroom spheres to 1 ppm p-xylene was as high as 65.4 at 300 °C, which was 50.3 and 9.0 times higher than those of pure NiO multiroom spheres and Sn-doped NiO dense spheres, respectively. In addition, the Sn-doped NiO multiroom sensors showed a high selectivity to xylene. The unprecedented high response that enables the sensing of sub-ppm xylene was explained by the high gas accessibility of the multiroom structures and the Sn-doping-induced change in oxygen adsorption as well as the charge carrier concentration, whereas the high xylene selectivity was attributed to the decomposition/re-forming of xylene into smaller or more active species within the unique multiroom structure of Sn-doped NiO microreactors characterized by high catalytic activities. The multiroom oxide spheres can be used as a new and generalized platform to design high-performance gas sensors.

Nearly monodisperse hollow hierarchical Co3O4nanocages of four different sizes (∼0.3, 1.0, 2.0, and 4.0 μm) consisting of nanosheets were prepared by controlled precipitation of zeolitic imidazolate framework-67 (ZIF-67) rhombic dodecahedra, followed by solvothermal synthesis of Co3O4nanocages using ZIF-67 self-sacrificial templates, and subsequent heat treatment for the development of high-performance methylbenzene sensors. The sensor based on hollow hierarchical Co3O4nanocages with the size of ∼1.0 μm exhibited not only ultrahigh responses (resistance ratios) to 5 ppm p-xylene (78.6) and toluene (43.8) but also a remarkably high selectivity to methylbenzene over the interference of ubiquitous ethanol at 225 °C. The unprecedented and high response and selectivity to methylbenzenes are attributed to the highly gas-accessible hollow hierarchical morphology with thin shells, abundant mesopores, and high surface area per unit volume as well as the high catalytic activity of Co3O4. Moreover, the size, shell thickness, mesopores, and hollow/hierarchical morphology of the nanocages, the key parameters determining the gas response and selectivity, could be well-controlled by tuning the precipitation of ZIF-67 rhombic dodecahedra and solvothermal reaction. This method can pave a new pathway for the design of high-performance methylbenzene sensors for monitoring the quality of indoor air.

Co3O4sensors with a nanoscale TiO2or SnO2catalytic overlayer were prepared by screen-printing of Co3O4yolk–shell spheres and subsequent e-beam evaporation of TiO2and SnO2. The Co3O4sensors with 5 nm thick TiO2and SnO2overlayers showed high responses (resistance ratios) to 5 ppm xylene (14.5 and 28.8) and toluene (11.7 and 16.2) at 250 °C with negligible responses to interference gases such as ethanol, HCHO, CO, and benzene. In contrast, the pure Co3O4sensor did not show remarkable selectivity toward any specific gas. The response and selectivity to methylbenzenes and ethanol could be systematically controlled by selecting the catalytic overlayer material, varying the overlayer thickness, and tuning the sensing temperature. The significant enhancement of the selectivity for xylene and toluene was attributed to the reforming of less reactive methylbenzenes into more reactive and smaller species and oxidative filtering of other interference gases, including ubiquitous ethanol. The concurrent control of the gas reforming and oxidative filtering processes using a nanoscale overlayer of catalytic oxides provides a new, general, and powerful tool for designing highly selective and sensitive oxide semiconductor gas sensors.

NiO/NiWO4composite yolk–shell spheres with a nanoscale NiO outer layer were prepared using one-pot ultrasonic spray pyrolysis and their gas sensing characteristics were studied. The NiO/NiWO4yolk–shell spheres exhibited an extremely high response to 5 ppm p-xylene (ratio of resistance to gas and air = 343.5) and negligible cross-responses to 5 ppm ethanol, ammonia, carbon monoxide, hydrogen, and benzene, whereas pure NiO yolk–shell spheres showed very low responses and selectivity to all the analyte gases. The detection limit for p-xylene was as low as 22.7 ppb. This ultrasensitive and selective detection of p-xylene is attributed to a synergistic catalytic effect between NiO and NiWO4, high gas accessibility with large specific surface area, and increased chemiresistive variation due to the formation of a heterojunction. The NiO/NiWO4yolk–shell spheres with a thin NiO outer layer can be used to detect subppm-level p-xylene in a highly sensitive and selective manner for monitoring indoor air pollution.

Xylene is a hazardous volatile organic compound, which should be measured precisely for monitoring of indoor air quality. The selective detection of ppm-level xylene using oxide semiconductor chemiresistors, however, remains a challenging issue. In this study, NiO/NiMoO4nanocomposite hierarchical spheres assembled from nanosheets were prepared by hydrothermal reaction, and the potential of sensors composed of these nanocomposites to selectively detect xylene gas was investigated. The sensors based on the NiO/NiMoO4nanocomposite hierarchical spheres exhibited high responses (maximum resistance ratio =101.5) to 5 ppm p-xylene with low cross-responses (resistance ratios <30) to 5 ppm toluene, benzene, C2H5OH, CH3COCH3, HCHO, CO, trimethylamine, and NH3. In contrast, a sensor based on pure NiO hierarchical spheres exhibited negligibly low responses to all 9 analyte gases. The gas-sensing mechanism underlying the high selectivity and response to xylene in the NiO/NiMoO4nanocomposite hierarchical spheres is discussed in relation to the catalytic promotion of the xylene-sensing reaction by synergistic combination between NiO and NiMoO4, gas-accessible hierarchical morphology, and electronic sensitization by Mo addition. Highly selective detection of xylene can pave the road toward a new solution for precise monitoring of indoor air pollution.

Vertically ordered hematite nanotubes are considered to be promising photoactive materials for high-performance water-splitting photoanodes. However, the synthesis of hematite nanotubes directly on conducting substrates such as fluorine-doped tin oxide (FTO)/glass is difficult to be achieved because of the poor adhesion between hematite nanotubes and FTO/glass. Here, we report the synthesis of hematite nanotubes directly on FTO/glass substrate and high-performance photoelectrochemical properties of the nanotubes with NiFe cocatalysts. The hematite nanotubes are synthesized by a simple electrochemical anodization method. The adhesion of the hematite nanotubes to the FTO/glass substrate is drastically improved by dipping them in nonpolar cyclohexane prior to postannealing. Bare hematite nanotubes show a photocurrent density of 1.3 mA/cm2at 1.23 V vs a reversible hydrogen electrode, while hematite nanotubes with electrodeposited NiFe cocatalysts exhibit 2.1 mA/cm2at 1.23 V which is the highest photocurrent density reported for hematite nanotubes-based photoanodes for solar water splitting. Our work provides an efficient platform to obtain high-performance water-splitting photoanodes utilizing earth-abundant hematite and noble-metal-free cocatalysts.

Co3O4hollow spheres prepared by ultrasonic spray pyrolysis were converted into Co3O4–SnO2core–shell hollow spheres by galvanic replacement with subsequent calcination at 450 °C for 2 h for gas sensor applications. Gas selectivity of the obtained spheres can be controlled by varying the amount of SnO2shells (14.6, 24.3, and 43.3 at. %) and sensor temperatures. Co3O4sensors possess an ability to selectively detect ethanol at 275 °C. When the amount of SnO2shells was increased to 14.6 and 24.3 at. %, highly selective detection of xylene and methylbenzenes (xylene + toluene) was achieved at 275 and 300 °C, respectively. Good selectivity of Co3O4hollow spheres to ethanol can be explained by a catalytic activity of Co3O4; whereas high selectivity of Co3O4–SnO2core–shell hollow spheres to methylbenzenes is attributed to a synergistic effect of catalytic SnO2and Co3O4and promotion of gas sensing reactions by a pore-size control of microreactors.

The chemical vapor deposition (CVD) of silicon carbide (SiC) on carbon has been widely used as a general method to suppress dust generation on carbon surfaces. For a CH3SiCl3(MTS) and hydrogen system, computational fluid dynamic simulations to predict the growth rate of the silicon carbide are performed. The results of the simulations are consistent with the experimental results where the deposition rate depends highly on the H/Si composition and the specimen’s location. This simulation can provide guidance in optimizing the CVD process and improving the apparatus for CVD of SiC.

Metal oxide–carbon nanotube (CNT) composite microspheres with a novel structure were fabricated using a one-step spray pyrolysis process. Metal oxide–CNT composite microspheres with a uniform distribution of void nanospheres were prepared from a colloidal spray solution containing CNTs, metal salts, and polystyrene (PS) nanobeads. Perforated SnO2–CNT composite microspheres with a uniform distribution of void nanospheres showed excellent lithium storage properties as anode materials for lithium-ion batteries. Bare SnO2microspheres and SnO2–CNT composite microspheres with perforated and filled structures had a discharge capacity of 450, 1108, and 590 mA h g–1for the 250th cycle at a current density of 1.5 A g–1, and the corresponding capacity retention compared to the second cycle was 41, 98, and 55%, respectively. The synergetic combination of void nanospheres and flexible CNTs improved the electrochemical properties of SnO2. This effective and innovative strategy could be used for the preparation of perforated metal oxide–CNT composites with complex elemental compositions for many applications.

Co-doped branched ZnO nanowires were prepared by multistep vapor-phase reactions for the ultraselective and sensitive detection of p-xylene. Highly crystalline ZnO NWs were transformed into CoO NWs by thermal evaporation of CoCl2powder at 700 °C. The Co-doped ZnO branches were grown subsequently by thermal evaporation of Zn metal powder at 500 °C using CoO NWs as catalyst. The response (resistance ratio) of the Co-doped branched ZnO NW network sensor to 5 ppm p-xylene at 400 °C was 19.55, which was significantly higher than those to 5 ppm toluene, C2H5OH, and other interference gases. The sensitive and selective detection of p-xylene, particularly distinguishing among benzene, toluene, and xylene with lower cross-responses to C2H5OH, can be attributed to the tuned catalytic activity of Co components, which induces preferential dissociation of p-xylene into more active species, as well as the increase of chemiresistive variation due to the abundant formation of Schottky barriers between the branches.

In this work, we report a dramatic enhancement in ethanol sensing characteristics of NiO hollow nanostructures via decoration with In2O3nanoclusters. The pure NiO and 1.64–4.41 atom % In-doped NiO and In2O3-decorated NiO hollow spheres were prepared by ultrasonic spray pyrolysis, and their gas sensing characteristics were investigated. The response (the ratio between the resistance in gas and air) of the In2O3-decorated NiO hollow spheres to 5 ppm ethanol (C2H5OH) was 9.76 at 350 °C, which represents a significant improvement over the In-doped NiO and pure NiO hollow spheres (3.37 and 2.18, respectively). Furthermore, the 90% recovery time was drastically reduced from 1880 to 23 s, and a selective detection of ethanol with negligible cross-response to other gases was achieved. The enhanced gas response and fast recovery kinetics were explained in relation to the thinning of the near-surface hole accumulation layer of p-type NiO underneath n-type In2O3, the change of charge carrier concentration, and the variation of oxygen adsorption.

The use of composite materials and polynary compounds is a promising strategy to promote conductometric sensor performances. The perovskite oxides provide various compositional combinations between different oxides for tuning gas-sensing reaction and endowing rich oxygen deficiencies for preferable gas adsorption. Herein, a sacrificial colloidal template approach is exploited to fabricate crystalline ternary LaFeO3perovskite porous thin films, by transferring a La3+–Fe3+hybrid solution-dipped template onto a substrate and sequent heat treatment. The honeycomb-like LaFeO3film consisted of monolayer periodic pore (size: ∼ 500 nm) array can be successfully in situ synthesized in a homogeneous layout with a single phase of perovskite. This periodic porous LaFeO3film with p-type semiconductivity exhibits a high gas response, fast response (∼4 s), trace detection capacity (50 ppb), and favorable ethanol selectivity from similar acetone. It exhibits enhanced sensing performances compared to those of a binary n-type Fe2O3film and a nontemplated dense LaFeO3film. In addition, a five-axe spiderweb diagram is introduced to make a feasible evaluation of the optimal practical work condition, comprehensively regarding the response/recovery rate, gas response, selectivity and operating temperature. The enhanced ethanol sensing mechanism of honeycomb-like LaFeO3periodic porous film is also addressed. This novel and facile route to fabricate well-ordered porous LaFeO3thin film can also be applied to many fields to obtain special performances, such as solar cells, ion conductors, gas separation, piezoelectricity, and self-powered sensing device system.

Vertically ordered nanotube array is a desirable configuration to improve gas sensing properties of the hematite which is the most abundant and cheapest metal oxide semiconductor on earth but has low and sluggish chemiresistive responses. We have synthesized a vertically aligned, highly ordered hematite nanotube array directly on a patterned SiO2/Si substrate and then it used as a gas sensor without additional processing. The nanotube array sensor shows unprecedentedly ultrahigh and selective responses to acetone with detection limits down to a few parts per billion and response time shorter than 3 s.

Diagnostic sensing device using exhaled breath of human have critical advantages due to the noninvasive diagnosis and high potential for portable device with simple analysis process. Here, we report ultrafast as well as highly sensitive bumpy WO3hemitube nanostructure assisted by O2plasma surface modification with functionalization of graphene-based material for the detection of acetone (CH3COCH3) and hydrogen sulfide (H2S) which are biomarkers for the diagnosis of diabetes and halitosis, respectively. 0.1 wt % graphene oxide (GO)- and 0.1 wt % thin layered graphite (GR)- WO3hemitube composites showed response times of 11.5 ± 2.5 s and 13.5 ± 3.4 s to 1 ppm acetone as well as 12.5 ± 1.9 s and 10.0 ± 1.6 s to 1 ppm of H2S, respectively. In addition, low limits of detection (LOD) of 100 ppb (Rair/Rgas= 1.7 for acetone and Rair/Rgas= 3.3 for H2S at 300 °C) were achieved. The superior sensing properties were ascribed to the electronic sensitization of graphene based materials by modulating space charged layers at the interfaces between n-type WO3hemitubes and p-type graphene based materials, as identified by Kelvin Probe Force Microscopy (KPFM). Rapid response and superior sensitivity of the proposed sensing materials following cyclic thermal aging demonstrates good potential for real-time exhaled breath diagnosis of diseases.

Two different BaTiO3 (160nm) nanopowders coated with Y and with Dy were fabricated by an aqueous chemical coating method, and their dielectric properties and microstructures were investigated with X-ray diffraction, Impedance analyzer, SEM and TEM. Y and Dy were coated on the BaTiO3 powder using nitrates. Coated BaTiO3 powders were pressed in a disk shape and sintered at 1150~1200oC for 2 hours in reduced atmosphere of 10%H2 - 90%N2. Coating layer of the BaTiO3 particle was thin with a thickness of 3 ~ 5nm. Coated BaTiO3 sintered sample exhibited a larger lattice parameter (a, c) and smaller tetragonality (c/a) than pure BaTiO3 one. Y coated BaTiO3 sample sintered at 1200oC showed good dielectric properties with a high dielectric constant of around 2000 and a stable temperature coefficient of capacitance (TCC).

Self-assembled WO3thin film nanostructures with 1-dimensional villi-like nanofingers (VLNF) have been synthesized on the SiO2/Si substrate with Pt interdigitated electrodes using glancing angle deposition (GAD). Room-temperature deposition of WO3by GAD resulted in anisotropic nanostructures with large aspect ratio and porosity having a relative surface area, which is about 32 times larger than that of a plain WO3film. A WO3VLNF sensor shows extremely high response to nitric oxide (NO) at 200 °C in 80% of relative humidity atmosphere, while responses of the sensor to ethanol, acetone, ammonia, and carbon monoxide are negligible. Such high sensitivity and selectivity to NO are attributed to the highly efficient modualtion of potential barriers at narrow necks between individual WO3VLNF and the intrinsically high sensitivity of WO3to NO. The theoretical detection limit of the sensor for NO is expected to be as low as 88 parts per trillion (ppt). Since NO is an approved biomarker of chronic airway inflammation in asthma, unprecedentedly high response and selectivity, and ppt-level detection limit to NO under highly humid environment demonstrate the great potential of the WO3VLNF for use in high performance breath analyzers.

Single-crystalline Mn3O4nanowires were prepared using the vapor-phase transformation of ZnO nanobelts. Mn3O4-decorated ZnO nanobelts and ZnO–ZnMn2O4core–shell nanocables (NCs) were also obtained as reaction intermediates. Heteroepitaxial growth of tetragonal spinel Mn3O4(or ZnMn2O4) on wurtzite ZnO is a possible reason for the growth of single-crystalline Mn3O4nanowires. Growth interfaces are possibly formed between the wurtzite (101̅0)/(21̅1̅0) and spinel (1̅01)/(4̅11) planes. Various one-dimensional homonanostructures and heteronanostructures consisting of n-ZnO, p-Mn3O4, and p-ZnMn2O4can be used to design high-performance gas sensors.

We prepared fluorine-doped tin oxide (FTO) nanorod films and a conventional FTO thin film for the application of a semiconducting gas sensor by spray pyrolysis method. The lengths of FTO nanorods (FTON, 100 and 500 nm) were controlled by changing deposition times, and FTO thin film (FTOT) was also prepared as a reference. The gas sensitivity test shows FTON with long nanorods had higher sensitivity for both hydrogen and ethanol gases but slow response and recovery times, despite an advantage of the higher gas sensitivity. FTO nanorod film with short length about 100 nm showed relatively lower sensitivity, but fast gas response and recovery characteristics. The fast response and recovery for the analyte gases are attributed to the conductance of FTO nanorods, which is closely related to the diameter and length of nanorods.

Brush-shaped ZnO heteronanostructures were synthesized using a newly designed thermal-assisted pulsed laser deposition (T-PLD) system that combines the advantages of pulsed laser deposition (PLD) and a hot furnace system. Branched ZnO nanostructures were successfully grown onto CVD-grown backbone nanowires by T-PLD. Although ZnO growth at 300 °C resulted in core–shell structures, brush-shaped hierarchical nanostructures were formed at 500–600 °C. Materials properties were studied via photoluminescence (PL), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) characterizations. The enhanced photocurrent of a SnO2–ZnO heterostructures device by irradiation with 365 nm wavelength ultraviolet (UV) light was also investigated by the current–voltage characteristics.

The humidity dependence of the gas‐sensing characteristics in SnO2‐based sensors, one of the greatest obstacles in gas‐sensor applications, is reduced to a negligible level by NiO doping. In a dry atmosphere, undoped hierarchical SnO2nanostructures prepared by the self‐assembly of crystalline nanosheets show a high CO response and a rapid response speed. However, the gas response, response/recovery speeds, and resistance in air are deteriorated or changed significantly in a humid atmosphere. When hierarchical SnO2nanostructures are doped with 0.64–1.27 wt% NiO, all of the gas‐sensing characteristics remain similar, even after changing the atmosphere from a dry to wet one. According to diffuse‐reflectance Fourier transform IR measurements, it is found that the most of the water‐driven species are predominantly absorbed not by the SnO2but by the NiO, and thus the electrochemical interaction between the humidity and the SnO2sensor surface is totally blocked. NiO‐doped hierarchical SnO2sensors exhibit an exceptionally fast response speed (1.6 s), a fast recovery speed (2.8 s) and a superior gas response (Ra/Rg= 2.8 at 50 ppm CO (Ra: resistance in air, Rg: resistance in gas)) even in a 25% r.h. atmosphere. The doping of hierarchical SnO2nanostructures with NiO is a very‐promising approach to reduce the dependence of the gas‐sensing characteristics on humidity without sacrificing the high gas response, the ultrafast response and the ultrafast recovery.

The effect of Ag decoration on the gas sensing characteristics of SnO2nanowire (NW) networks was investigated. The Ag layers with thicknesses of 5–50 nm were uniformly coated on the surface of SnO2NWs via e-beam evaporation, which were converted into isolated or continuous configurations of Ag islands by heat treatment at 450 °C for 2 h. The SnO2NWs decorated by isolated Ag nano-islands displayed a 3.7-fold enhancement in gas response to 100 ppm C2H5OH at 450 °C compared to pristine SnO2NWs. In contrast, as the Ag decoration layers became continuous, the response to C2H5OH decreased significantly. The enhancement and deterioration of the C2H5OH sensing characteristics by the introduction of the Ag decoration layer were strongly governed by the morphological configurations of the Ag catalysts on SnO2NWs and their sensitization mechanism.

The CdS-sensitized solar cells (CdS-SSC) were fabricated by spray pyrolysis deposition (SPD) method. The performance of the cells was greatly improved through post-treatments that included thermal oxidation at 500 °C for 30 min in an air atmosphere and subsequent chemical etching by 40 mM aqueous HCl solution at room temperature for 30 min, as compared to as-deposited CdS-SSC. The CdS-SSC in a I−/I3−electrolyte system was resulted in the improvement of Jsc(3.3 → 5.2 mA/cm2), Voc(697 → 758 mV), FF (41.4% → 46.9%), and (0.95% → 1.84%). Similarly, the efficiency of CdS-SSC in a noncorrosive polysulfide electrolyte system was also enhanced by the proposed thermal oxidation and etching process. The increase in the cell efficiency is attributed to the reduced charge recombination among sensitizer themselves through the mitigation of overaggregated CdS sensitizers deposited by SPD.

Low temperature co-fired ceramic (LTCC) process combined with thick film photolithography was employed to fabricate ceramic-based microfluidic devices. To check the applicability of novel process, three types of passive mixers, diffusion-driven T-type mixers with different channel width and convection-driven chaotic mixer, were fabricated and their microfluidic performance was evaluated. It was confirmed that the degree of mixing in ceramic-based microfluidic passive mixers was well matched with the numerical simulation data.

Abstract: A new method for preparing SnO2 whiskers by the decomposition of SnC2O4 is suggested. A Whisker-like morphology of a SnC2O4 precipitate was attained via the gradual addition of an oxalic acid solution to a hot SnCl2 aqueous solution (T > 50∘C). In comparison, when the solution temperature was either lower than 50∘C or when ethanol was used as the solvent, the SnC2O4 precipitate showed an angular and relatively isotropic morphology. The morphology of the SnC2O4 precipitate remained even after its thermal decomposition into SnO2 at 400∘C indicating that SnC2O4 precipitation is a key step in preparing the whiskers. The formation mechanism of SnO2 whiskers was explained by the supersaturation during the precipitation of SnC2O4.

Abstract: ZnO nanorods were prepared via a hydrothermal reaction in a solution containing Zn(NO3)2⋅6H2O, NaOH, cyclohexylamine, ethanol and water, and their NO2 and CO sensing behaviors were investigated. The morphology and agglomeration of ZnO nanorods could be manipulated by controlling the amount of water in the solution, which was explained by the variation in the [OH−] due to an interaction between the water and cyclohexylamine. Sea-urchin-like and well-dispersed ZnO nanorods were prepared at low and high water content, respectively. Well-dispersed ZnO nanorods showed 1.8 fold change in resistance at 1 ppm NO2 while there was no significant change in resistance at 50 ppm CO. The present ZnO nanorods can be used in automated car ventilation systems to detect NO2 in the presence of CO.

Abstract: Mono-disperse and spherical Ni powders were prepared using a N2H4-based solution reduction route. The main focus was on manipulating the particle size by varying the source materials (Ni-chloride, Ni-sulfate and Ni-acetate) and impurity concentrations. The morphology and size of the Ni particle closely depended on the source materials. In addition, the particle size became significantly smaller with increasing Co concentration ranging from 0 to 350 ppm. The decrease in the Ni particle size was attributed to the promotion of nucleation by the rapid decomposition of the CoCl2–N2H4 complex when adding a NaOH solution and the more active reduction of Co than that of Ni in the initial stages of the reaction.

Magnetite (Fe3O4) particles were prepared for biomedical application through three different routes. Each route had the difference in the selection of pH controlling agents. Ammonia, Urea and combined use of ammonia and urea were tested in the synthesis through co-precipitation. With the combined use of urea and ammonia, the size of particles could be reduced as small as 10 nm while effectively suppressing the agglomeration among particles. The surface charge measured at physiological condition explained the good dispersion behavior of nano-magnetite particles. The superparamagnetism observed in nano magnetite particles was expected to be useful for biomedical application in the respect of magnetic localization and dispersion.

Abstract: Cancer metastasis is a significant contributor to breast cancer patient morbidity and mortality. In order to develop new anti-metastatic therapies, we need to understand the biological and biochemical mechanisms of metastasis. Toward these efforts, we and others have studied metastasis suppressor genes, which halt metastasis in vivo without affecting primary tumor growth. The first metastasis suppressor gene identified was nm23, also known as NDP kinase. Nm23 represents the most widely validated metastasis suppressor gene, based on transfection and knock-out mouse strategies. The biochemical mechanism of metastasis suppression via Nm23 is unknown and likely complex. Two potential mechanisms include binding proteins and a histidine kinase activity. Elevation of Nm23 expression in micrometastatic tumor cells may constitute a translational strategy for the limitation of metastatic colonization in high risk cancer patients. To date, medroxyprogesterone acetate (MPA) has been identified as a candidate compound for clinical testing.

The effects of B addition up to 0.4 wt% (i.e., 1.61 at%) to Fe-40Al alloy on microstructures and tensile properties were investigated. The vacancy-annealed specimens following casting and extrusion were examined by optical and scanning electron microscopy and thermal neutron-induced microradiography. The addition of a large amount of B resulted in grain refinement and changed the fracture mode from intergranular to transgranular to increase the tensile elongation. Especially, the alloy containing 0.3wt% B exhibited the elongation of 16.4% under the strain rate of 1x100s-1 at room temperature. The increase in elongation with increasing strain rate was discussed in terms of suppression of hydrogen embrittlement.