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We demonstrated the sensing properties and adsorption mechanism of NO2 molecules of monolayer graphene and multilayer graphene encapsulated ZnO QDs for NO2 gas adsorption. The gas response value of ZnO-multilayer graphene (ZMLG) QDs was approximately 23 % and 7.2 and 25.5 times higher than that with ZnO-monolayer graphene (ZG) and ZnO QDs, respectively. The surface potential change of ZMLG QDs increased up to 14.25 times compared to ZnO QDs and 6.33 times increased compared to ZG QDs. We proposed an accurate adsorption mechanism for the improvement of the detection behavior that is occured by covering the graphene shells into ZnO QDs by the Brunauer–Emmett–Teller (BET), X-ray photoelectron spectroscopy (XPS), and SKPM measurement. These results are expected to increase the accuracy of gas sensor characteristic analysis.

Resistive RAM (ReRAM), which uses the anion-based resistive switching characteristic of transition metal oxide, is one of the strong candidates for next-generation non-volatile memory. The resistance switching characteristics depend on oxygen defects and their electrochemical migration. This study systematically investigated the Y3+ doping effect in CeO2 resistive switching behavior to control oxygen vacancy. The resistive switching devices of Ce1-xYxO2-y (CYO) (x = 0, 0.05, 0.1, 0.15, and 0.2) were fabricated by the photochemical metal-organic deposition method, which could successfully obtain directly patterned CYO films. The XRD pattern and Raman spectrum confirmed that the lattice shrink and structural distortion was induced and increased gradually by increasing the oxygen vacancy concentration with yttrium content. All the CYO devices showed bipolar filament-type resistive switching, and both resistance of the pristine state and forming voltage decreased with increasing Y content from an increase in oxygen vacancy concentration. And the on/off ratio decreased with increasing Y content because of reduced HRS resistance, even after the recovered insulation oxide region by HRS switching, due to fixed defect sites with trapped electrons formed by yttrium. And with a SPEM experiment, we found that ceria loses 24% oxygen for LRS resistive switching, which induced a resistance change of about five orders of magnitude.

The outstanding multifunctionality of ferroelectric oxides has opened up new fields in microelectronics. However, the high crystallization temperature of the ferroelectric oxides limits their integ...

Although knowledge of the physical state of aerosol particles is essential to understand atmospheric chemistry model and measurements, information on the viscosity and physical state of aerosol particles consisting of organic and inorganic salts is still rare. Herein, we quantified viscosities at 293 ± 1 K upon dehydration for the binary systems, sucrose–H2O and ammonium sulfate (AS)–H2O, and the ternary systems, sucrose–AS–H2O for organic-to-inorganic dry mass ratios (OIRs) = 4:1, 1:1, and 1:4 using bead-mobility and poke-and-flow techniques. Based on the viscosity value of the aerosol particles, we defined the physical states of the total aerosol particles studied in this work. For binary systems, the viscosity of sucrose–H2O particles gradually increased from ∼ 4 × 10−1 to > ∼ 1 × 108 Pa s when the relative humidity (RH) decreased from ∼ 81 % to ∼ 24 %, ranging from liquid to semisolid or solid state, which agrees with previous studies. The viscosity of AS–H2O particles remained in the liquid state (< 102 Pa s) for RH > ∼ 50 %, while for RH ≤∼ 50 %, the particles showed a viscosity of > ∼ 1 × 1012 Pa s, corresponding to a solid state. In case of the ternary systems, the viscosity of organic-rich particles (OIR = 4:1) gradually increased from ∼ 1 × 10−1 to ∼ 1 × 108 Pa s for a RH decrease from ∼ 81 % to ∼ 18 %, similar to the binary sucrose–H2O particles. This indicates that the sucrose–AS–H2O particles range from liquid to semisolid or solid across the RH. In the ternary particles for OIR = 1:1, the viscosities ranged from less than ∼ 1 × 102 for RH > 34 % to > ∼ 1 × 108 Pa s at ∼ 27 % RH. The viscosities correspond to liquid for RH > ∼ 34 %, semisolid for ∼ 34 % < RH < ∼ 27 %, and semisolid or solid for RH < ∼ 27 %. Compared to the organic-rich particles, in the inorganic-rich particles (OIR = 1:4), drastic enhancement in viscosity was observed as RH decreased; the viscosity increased by approximately 8 orders of magnitude during a decrease in RH from 43 % to 25 %, resulting in liquid to semisolid or solid in the RH range. Overall, all particles studied in this work were observed to exist as a liquid, semisolid, or solid depending on the RH. Furthermore, we compared the measured viscosities of ternary systems with OIRs of 4:1, 1:1, and 1:4 to the predicted viscosities using the Aerosol Inorganic–Organic Mixtures Functional groups Activity Coefficients Viscosity model (AIOMFAC-VISC) predictions with the Zdanovskii–Stokes–Robinson (ZSR) organic–inorganic mixing model, with excellent model–measurement agreement for all OIRs.

As a robust radioanalytical method for tracking carbonaceous particulates in vivo, polycyclic aromatic hydrocarbons from diesel exhaust were labeled with a radioactive-iodine-tagged pyrene analogue. Single-photon emission computed tomography and biodistribution studies showed high uptake and slow clearance of this matter in the respiratory system, which may underlie its severe toxicity.

The demand for high-performance two-dimensional gas barrier materials is increasing owing to their potential for application in optoelectronic devices. These materials can help the devices maintain their properties over a long period. Therefore, in this study, we investigated the gas barrier performance of hexagonal boron nitride (h-BN) monolayers grown on copper foils via electrochemical polishing (ECP). The ECP treatment helped reduce the surface roughness of the copper foils. As a result, the nucleation density was reduced and highly crystalline h-BN monolayers were produced. The gas barrier performance of h-BN monolayers on copper foils with ECP was comparable to that of graphene. Our finding demonstrates the potential of monolayer h-BN as a high-performance and economical gas barrier material for organic-based optoelectronic devices.

The lacking of laboratory black carbon (BC) samples have long challenged the corresponding toxicological research, furthermore, the toxicity tests of engineered carbon nanoparticles were unable to reflect atmospheric BC. As a simplified approach, we have synthesized artificial BC (aBC) for the purpose of representing atmospheric BC. Surface chemical properties of aBC were controlled by thermal treatment, without transforming its physical characteristics, thus, we were able to examine the toxicological effects on A549 human lung cells arising from aBC with varying oxidation surface properties. X-ray photoelectron spectroscopy, as well as Raman and Fourier transform infrared spectroscopy, verified the presence of increased amounts of oxygenated functional groups on the surface of thermally-treated aBC, indicating aBC oxidization at elevated temperatures, aBC with increased oxygen functional group content displayed increased toxicity to A549 cells, specifically by decreasing cell viability to 45% and elevating reactive oxygen species levels up to 294% for samples treated at 800 °C.

Exposure to particulate matter (PM) is related to various respiratory diseases, and this affects the respiratory immune system. Alveolar macrophages (AMs), which are defenders against pathogens, play a key role in respiratory inflammation through cytokine production and cellular interactions. Coconut oil demonstrates antioxidant and anti-inflammatory properties, and it is consumed worldwide for improved health. However, reports on the protective effects of coconut oil on the PM-induced respiratory immune system, especially in AMs, are limited. In this study, we generated artificial PM (APM) with a diameter approximately of 30 nm by controlling the temperature, and compared its cytotoxicity with diesel exhaust particles (DEP). We also investigated the antioxidant and anti-inflammatory effects of coconut oil in APM– and DEP–stimulated AMs, and the underlying molecular mechanisms. Our results showed that APM and DEP had high cytotoxicity in a dose-dependent manner in AMs. In particular, APM or DEP at 100 μg/mL significantly decreased cell viability (p < 0.05) and significantly increased oxidative stress markers such as reactive oxygen species (p < 0.01); the GSSH/GSH ratio (p < 0.01); and cytokine production, such as tumor necrosis factor-α (p < 0.001), interleukin (IL)-1β (p < 0.001), and IL-6 (p < 0.001). The expression of the genes for chemokine (C-X-C motif) ligand-1 (p < 0.05) and monocyte chemoattractant protein-1 (p < 0.001); and the proteins toll-like receptor (TLR) 4 (p < 0.01), mitogen-activated protein kinase (MAPK), and c-Jun N-terminal kinase (p < 0.001), p38 (p < 0.001); and extracellular receptor-activated kinase (p < 0.001), were also upregulated by PM. These parameters were reversed upon treatment with coconut oil in APM– or DEP–stimulated AMs. In conclusion, coconut oil can reduce APM– or DEP–induced inflammation by regulating the TLR4/MAPK pathway in AMs, and it may protect against adverse respiratory effects caused by PM exposure.

Biosensors that can analyze a single drop of biological fluid can overcome limitations such as extraction volume from humans or animals, ethical problems, time, and cost. In this work, we have developed a highly sensitive electrochemical (EC) biosensor based on a nanowell array (NWA) for the detection of alkaline phosphatase (ALP), a serum indicator of bone formation. The size of the electrode is 2 × 1 mm

Chemiresistive electronic nose (CEN) composed of villi-like nanostructures (VLNs) of SnO2 and WO3, and Au-functionalized VLNs was fabricated by applying electron-beam evaporation in a glancing angle deposition mode. The VLNs-based CEN with a back-heater (212 °C) shows high responses with low detection limits of parts per billion (ppb)-levels for NO and NH3 vapors at 80% relative humidity atmosphere. The enhanced sensitivities in a high humidity condition turn out to be attributed to the spillover effect by the Au nanoparticles and a large surface-to-volume ratio in porous VLNs. Employing Au NPs on VLNs leads to the increase of O− ions via the spillover effect which impedes the adsorption of water molecules, maintaining the enhanced responses against environmental humidity. Consequently, high responses for NO and NH3 vapors maintain even in the high humidity condition. Herein, with the principal component analysis (PCA), we demonstrate highly selective detection of NO and NH3 vapors against C2H5OH, CO, C7H8, C6H6, and CH3COCH3 vapors. These results open up wide applications of the VLNs-based CEN as an inexpensive and non-invasive diagnostic tool for asthma and kidney disorder.

Hollow-structured nanomaterials are presented as an outstanding sensing platform because of their unique combination of high porosity in both the micro- and nanoscale, their biocompatibility, and flexible template applicability. Herein, we introduce a bacterial skeleton method allowing for cost-effective fabrication with nanoscale precision. As a proof-of-concept, we fabricated a hollow SnO2 hemipill network (HSHN) and a hollow Pt-functionalized SnO2 hemipill network (HPN). A superior detecting capability of HPN toward acetone, a diabetes biomarker, was demonstrated at low concentration (200 ppb) under high humidity (RH 80%). The detection limit reaches 3.6 ppb, a level satisfying the minimum requirement for diabetes breath diagnosis. High selectivity of the HPN sensor against C6H6, C7H8, CO, and NO vapors is demonstrated using principal component analysis (PCA), suggesting new applications of HPN for human-activity monitoring and a personal healthcare tool for diagnosing diabetes. The skeleton method can...

We report on InGaZnO (IGZO) thin film transistors (TFTs)-based bio-chemical sensors which can detect the chemical/biological species. As novel sensing platform, the IGZO TFT with Ag nanowire (NW) mesh showed pronounced output voltage changes responding to all analytes of H 2 O 2 , b- d -glucose, d -glucono-1,5-Lactione, and lactic acid, which are reproducible and reversible. Herein, porous Ag NW-functionalized top gate electrode plays a major role in sensing platform for enhanced sensing capability in aqueous medium. Moreover, these top gate geometry serve as a stable backplane for electrical modulation. As a result, analytes solutions become acidic or basic and such pH alterations induce significant turn-on voltage shifts on our devices. For implementation of a resistive load inverter, the output sensing voltage signals can be directly extracted, and such signals are reproducible and reversible. The proposed IGZO TFTs with Ag NW mesh top gate electrode based sensing platform pave the way for development of portable and reusable real-time non-destructive label-free chemical/biological sensors.

We report the highly sensitive and selective downsized gas sensors for the IoT application. Sensing areas of Pt-interdigitated electrodes (IDEs) were varied to investigate the relation between sensing materials and electrodes. In2O3 nanocolumns were deposited on the pre-patterned Pt IDEs using glancing angle deposition (GLAD). The effect of the interface resistance between electrodes and sensing materials, and the intergrain resistance between nanocolumns is analyzed by linear regression at different sensing area and incident angle of GLAD. In2O3 (angle: 85°, sensing area: 0.3 mm × 0.3 mm) nanocolumns with double Schottky barriers show the highest response and selectivity with fast response time of 10 s to VOCs among the samples fabricated in this study. The analysis reveals that the intrinsic response of In2O3 (angle: 85°, sensing area: 0.3 mm × 0.3 mm) nanocolumns are dominantly affected by intergrain resistance, resulting in a high response. Our demonstration for the fundamental aspect of downsizing gas sensor makes an important contribution to the chemical sensor field with broad interest.

Vanadium dioxide (VO 2 ) as strong correlated oxide has been intensively studied due to the unique properties accompanied by metal-insulator transition (MIT) near room temperature. Their extrinsic electrical and optical transformations on MIT have been greatly attracted in many potential applications. In this study, we propose to apply an intrinsic electrical property of VO 2 in metallic phase as doping agent of chemiresistive sensor. Self-doped nanocoulmnar vanadium oxides (SNVO) thin films are simply fabricated by glancing angle deposition without any template and chemical additives. The nanocolumnar VO 2 thin films were deposited by e-beam evaporator, and then the SNVO with residual VO 2 in V 2 O 5 nanocolums were synthesized by an air atmosphere annealing, which are composed of dominant oxidized V 2 O 5 which plays a sensing role on the surface and the residual VO 2 with self-doping effect inside nanocolumns. Especially at low temperature (150 °C), SNVO sensor shows an ultra-high performance (R gas /R air > 100) to NO 2 (5 ppm) gas. It is supposed that the residual VO 2 which shows metallic properties above Mott transition temperature (∼67 °C) acts as an intrinsic electron donor by pseudo-free electron, which helps adsorption of oxygen ions on the surface and extends the depletion region of few nanometers of narrow necks between nanocolumns.

Detection of gas-phase chemicals finds a wide variety of applications, including food and beverages, fragrances, environmental monitoring, chemical and biochemical processing, medical diagnostics, and transportation. One approach for these tasks is to use arrays of highly sensitive and selective sensors as an electronic nose. Here, we present a high performance chemiresistive electronic nose (CEN) based on an array of metal oxide thin films, metal-catalyzed thin films, and nanostructured thin films. The gas sensing properties of the CEN show enhanced sensitive detection of H2S, NH3, and NO in an 80% relative humidity (RH) atmosphere similar to the composition of exhaled breath. The detection limits of the sensor elements we fabricated are in the following ranges: 534 ppt to 2.87 ppb for H2S, 4.45 to 42.29 ppb for NH3, and 206 ppt to 2.06 ppb for NO. The enhanced sensitivity is attributed to the spillover effect by Au nanoparticles and the high porosity of villi-like nanostructures, providing a large surface-to-volume ratio. The remarkable selectivity based on the collection of sensor responses manifests itself in the principal component analysis (PCA). The excellent sensing performance indicates that the CEN can detect the biomarkers of H2S, NH3, and NO in exhaled breath and even distinguish them clearly in the PCA. Our results show high potential of the CEN as an inexpensive and noninvasive diagnostic tool for halitosis, kidney disorder, and asthma.

We report the facile synthesis and the chemoresistive performances of villi-like WO 3 nanostructures (VLWNs) which were fabricated by RF sputter with glancing angle deposition (GAD) mode. A fast deposition of GAD effectively forms self-assembled anisotropic nanostructures with high porosity and surface-to-volume ratio. The sensing tests were examined for NO 2 detection in dry air and a mixture of reducing gases. As a result, these sensors at 200 °C exhibit an highly selective and sensitive NO 2 detection down to 800 parts per trillion (ppt) level, and could also respond well to NO 2 in the concentration range of 0.2–1 parts per million (ppm) without the interference of gas mixture. These results show that the enhanced sensing properties to NO 2 are attributed to the highly efficient surface modulation by double potential barriers at nano-necks of WO 3 nanostructures.

Hollow-structured nanomaterials are presented as an outstanding sensing platform because of their unique combination of high porosity in both the micro- and nanoscale, their biocompatibility, and flexible template applicability. Herein, we introduce a bacterial skeleton method allowing for cost-effective fabrication with nanoscale precision. As a proof-of-concept, we fabricated a hollow SnO

We present a heterosensor array that exploits the collective recognition ability of a set of different gas sensors to identify individual chemical vapors. In contrast to the conventional sensing approach based on the "lock-and-key" design, the heterosensor array rely on the response patterns produced over the collection of different sensors. Diverse sensors with different operating principles are employed to provide as much chemical diversity as possible. We demonstrate that this platform provides a highly discriminative tool with single element precision.

As highly sensitive H2S gas sensors, Au- and Ag-catalyzed SnO2 thin films with morphology-controlled nanostructures were fabricated by using e-beam evaporation in combination with the glancing angle deposition (GAD) technique. After annealing at 500 °C for 40 h, the sensors showed a polycrystalline phase with a porous, tilted columnar nanostructure. The gas sensitivities (S = Rgas/Rair) of Au and Ag-catalyzed SnO2 sensors fabricated by the GAD process were 0.009 and 0.015, respectively, under 5 ppm H2S at 300 °C, and the 90% response time was approximately 5 s. These sensors showed excellent sensitivities compared with the SnO2 thin film sensors that were deposited normally (glancing angle = 0°, S = 0.48).

With the widespread use of wearable electronics, the flexible piezoelectric energy harvesting devices have been extensively studied to efficiently convert the physical motion of the human body into electrical energy. The major obstacles for realizing a flexible piezoelectric generator include the insufficient output power generation and the poor efficiency at the low-frequency regime. Here, we demonstrate a curved piezoelectric generator favorable for wearable applications, generating a high output power. The curved structure plays a key role to improve the power generation, by effectively distributing the applied force across the piezoelectric layer, as well as to allow operation at the low frequency vibration range. Accordingly, this generator produces � 120 V of peak output voltage and � 700 mA of peak output current during a cycle. Furthermore, our generator can operate at low frequencies below 50 Hz, generating � 55 V of output voltage and 250 mA of output current at 35 Hz, and it even works at frequencies as low as 1 Hz. With this generator, we successfully lit up 476 commercial LED bulbs. In addition, we experimentally demonstrate the possibility that the generator can be used in shoes, watches, and clothes as a power source. Our results will provide a framework to enhance the output power of conventional piezoelectric generators, and open a new avenue for realization of self-powered systems, such as wearable electronic devices.

In this study, a chemiresistive sensor based on one-dimensional WO 3 nanostructures is presented for application in non-invasive med-ical diagnostics. WO 3 nanostructures were used as an active gas sensing layer and were deposited onto a SiO 2 /Si substrate using Pt inter-digitated electrodes (IDEs). The IDE spacing was 5µm and deposition was performed using RF sputter with glancing angle depositionmode. Pt IDEs fabricated by photolithography and dry etching. In comparison with thin film sensor, sensing performance of nano-structure sensor showed an enhanced response of more than 20 times when exposed to 50 ppm acetone at 400°C. Such a remarkablefaster response can pave the way for a new generation of exhaled breath analyzers based on chemiresistive sensors which are les s expen-sive, more reliable, and less complicated to be manufactured. Moreover, presented sensor technology has the potential of being usedas a personalized medical diagnostics tool in the near future. Keywords: Metal oxide gas sensors, Chemiresistive sensor, Exhaled breath analyzer, One-dimensional WO

The electrocaloric effect of 9/65/35 PLZT thin film fabricated by the sol-gel method, which has not been studied yet, was investigatedfor its structural, electrical properties as well as temperature change property. The relaxor ferroelectric property of 9/65/35 PLZT thinfilm was confirmed by examining its dielectric and electrical properties. The relaxor property can cause a more pronounced elec-trocaloric effect (ECE) in a wider temperature range than normal ferroelectric film. To avoid errors caused by using an indirect mea-surement method, the leakage current generated by increasing temperatures was minimized by using the optimal maximum electric field(350 kVcm -1 ) in the thin film. The largest temperature change ΔT (0.23 K) and the electrocaloric strength ξ (0.68 mkcm/kV), calculatedby equations were obtained. The maximum field change ΔE (191 kVcm -1 ) was in the vicinity of the curie temperature (200 o C).Keywords: Electrocaloric effect, Cooling device, PLZT, Ferroelectric material

We present gas sensing performance based on 22 sensor array with four different elements (TiO2, SnO2, WO3 and In2O3 thin films) fabricated by rf sputter. Each thin film was deposited onto the selected SiO2/Si substrate with Pt interdigitated electrodes (IDEs) of 5 m spacing which were fabricated on a SiO2/Si substrate using photolithography and dry etching. For 5 ppm NO2 and 50 ppm CO, each thin film sensor has a different response to offers the distinguishable response pattern for different gas molecules. Compared with the conventional micro-fabrication technology, 22 sensor array with such remarkable response pattern will be open a new foundation for monolithic integration of high-performance chemoresistive sensors with simplicity in fabrication, low cost, high reliablity, and multi- functional smart sensors for environmental monitoring.

Integrating a highly ordered TiO2 nanotube array with patterned substrates is an effective design strategy for taking advantage of one-dimensional nanotube structures such as high surface-to-volume ratio and novel functionalities of TiO2, but many challenges remain in synthesis. Here we report a novel synthesis-in-place method for highly ordered vertical TiO2 nanotube films on various patterned substrates and the application of the films to chemiresistive sensors. A unique synthetic strategy, in which the Pt bottom electrodes were clamped during anodization, leads to the complete anodization of the Ti layer to TiO2 nanotubes not only on SiO2/Si substrates but also on glass and sapphire substrates, which can be used as chemiresistors without additional processes. TiO2 nanotube sensors on SiO2/Si substrates show unprecedentedly ultrahigh responses to ethanol and acetone with detection limits down to parts per billion levels. Beyond the high sensitivity, selective responses to ethanol and acetone create oppo...

0.5 wt.% Pd-catalyzed SnO2 thin-film gas sensors with microstructures controlled on a nanometer scale were fabricated by an e-beam evaporator using the glancing angle deposition (GAD) method. After annealing at 500 degrees C for 1 h, the sensors produced were polycrystalline with a nanoporous, tilted columnar microstructure. The gas-sensing properties of these SnO2 sensors were measured in the concentration range of 1 to 5 ppm NO2 at 250 degrees C and of 10 to 50 ppm C2H5OH at 400 degrees C, respectively. The sensors fabricated by e-beam evaporation in combination with the GAD method showed much higher sensitivities than normally prepared sensors and exhibited rapid response times. The gas sensitivity (S = R(gas)/R(air)) of the SnO2 sensor using the GAD method was 43.4 for 5 ppm NO2 and 0.08 for 10 ppm C2H5OH, respectively. These sensors showed excellent sensitivities compared to the normal thin film sensors (S = 2 for 5 ppm NO2 and 0.92 for 10 ppm C2H5OH). We consider that the nanostructured sensors produced using the GAD process could be used to detect various gases emitted by automobiles and industrial installations.

Multifunctional structures with two kinds of materials have been intensively investigated in order to improve their electrical characteristic with two functions simultaneously. However, the research regarding of multifunctional ceramic sensor is still in a preliminary stage and how to integrate them with low-cost and high-yield mass production process remains a challenge issue. In this study, we fabricated the multifunctional ceramic sensor composed of temperature and gas sensors. Moreover, we investigated the CO sensing properties of three dimensional nanostuctured thin film gas sensors fabricated with silica ( nanosphere (

Embossed thin films with high surface areas are achieved using soft-templates composed of monolayer polystyrene beads. The form of links between the beads in the templates is controlled by varying the plasma etching time on the templates, resulting in various templates with close-linked, nano-linked, and isolated beads. Room-temperature deposition of on the plasma-treated templates and calcination at result in embossed films with tailored links between anatase hollow hemispheres. Although all the embossed films have similar surface areas, the sensitivity of films with nano-linked hollow hemispheres to 500 ppm CO and ethanol gases are much higher than that of films with close-linked and isolated hollow hemispheres, and the detection limits of them are as low as 0.6 ppm for CO and 0.1 ppm for ethanol. The strong correlation of sensitivity with the form of links between hollow hemispheres reveals the critical role of potential barriers formed at the links. The facile, large-scale, and on-chip fabrication of embossed films with nano-linked hollow hemispheres on Si substrate and the high sensitivity without the aid of additives give us a sustainable competitive advantage over various methods for the fabrication of highly sensitive -based sensors.

We report a novel process that uses highly ordered colloidal templating to fabricate nanostructured TiO2 thin film gas sensors. An O2 plasma treatment is used to decrease the contact angle of a water droplet on a SiO2/Si substrate from 46 degrees to 3 degrees. The formation of this hydrophilic surface enhances the adhesion of polystyrene microspheres to the substrate during the spin coating of the colloidal solution, leading to a large-area colloid template of closely packed monolayer microspheres on the substrates. Embossed TiO2 thin film gas sensors fabricated through highly ordered colloidal templating using O2 plasma exhibit substantially enhanced gas sensing performance as compared to those without surface treatments prior to colloidal templating.

We report fabrication and gas sensing properties of semiconducting metal oxide gas sensors using conducting oxide electrodes. Indium–tin oxide (ITO) and aluminum-doped zinc oxide (AZO) films are used to replace Pt electrodes in WO 3 or SnO 2 thin-film gas sensors. Before and after thermal annealing at 300 °C for 3200 min, the resistivity of the ITO film increases from 1.3 × 10 −4 to 7.0 × 10 −4 Ω cm, whereas the AZO film shows a significant increase in resistivity from 2.0 × 10 −3 to 5.1 × 10 1 Ω cm due to the annihilation of oxygen vacancies in the film. Upon exposure to 50 ppm CO at 300 °C, WO 3 or SnO 2 thin-film sensors with ITO interdigitated electrodes (IDEs) on glass substrates display higher responses than sensors with Pt IDEs, attributed to the low-resistance ohmic contacts between the electrode (ITO) and the sensing material (WO 3 or SnO 2 ). The reproducible response, the concentration-dependent modulation in sensitivity, and a sub-ppm detection limit indicates the reliable operation of sensors made with ITO IDEs. The high transmittance, exceeding 75%, of the sensors at visible wavelengths holds promise for future applications to transparent gas sensors.

Embossed TiO2 thin films with high surface areas were achieved using soft templates composed of monolayer polystyrene beads. The structure of links between beads in the templates could be controlled by varying O2 plasma etching time, resulting in a variety of templates with close-linked, nanolinked, or isolated beads. Room-temperature deposition of TiO2 on the plasma-treated templates and calcination at 550 °C resulted in embossed films with tailored links between anatase TiO2 hollow hemispheres. Although all embossed TiO2 films displayed a similar increase in the surface-to-volume ratio compared with a plain TiO2 thin film, the response of embossed TiO2 films with nanolinked hollow hemispheres to CO or ethanol gases was much higher than the response of films with close-linked or isolated hollow hemispheres. The strong correlation between gas sensitivity and the structure of links between the TiO2 hollow hemispheres revealed the critical importance of tailoring links between individual oxide nanostructure...

We report a novel route for the fabrication of highly sensitive and rapidly responding Nb2O5-based thin film gas sensors. TiO2 doping of Nb2O5 films is carried out by co-sputtering without the formation of secondary phases and the surface area of TiO2-doped Nb2O5 films is increased via the use of colloidal templates composed of sacrificial polystyrene beads. The gas sensitivity of Nb2O5 films is enhanced through both the TiO2 doping and the surface embossing. An additional enhancement on the gas sensitivity is obtained by the optimization of the bias voltage applied between interdigitated electrodes beneath Nb2O5-based film. More excitingly, such a voltage optimization leads to a substantial decrease in response time. Upon exposure to 50 ppm CO at 350 °C, a gas sensor based on TiO2-doped Nb2O5 film with embossed surface morphology exhibits a very high sensitivity of 475% change in resistance and a rapid response time of 8 s under 3 V, whereas a sensor based on plain Nb2O5 film shows a 70% resistance change and a response time of 65 s under 1 V. Thermal stability tests of our Nb2O5-based sensor reveal excellent reliability which is of particular importance for application as resistive sensors for a variety gases.

We investigate the mechanism of the sensitivity enhancement in TiO2 hollow-hemisphere gas sensors. Using monolayer close-packed polystyrene microspheres as a sacrificial template, a TiO2 thin film based on a network of ordered hollow hemispheres is formed by room-temperature sputtering deposition and subsequent calcination at 550°C. A thin film gas sensor based on the TiO2 hollow hemispheres exhibits a 225% change in its resistance when exposed to 50 ppm CO at 250°C, whereas a gas sensor based on a flat TiO2 film shows an 85% change. Numerical analysis reveals that the enhancement of the gas sensitivity in the hollow-hemisphere gas sensor is simply the result of an increase in the effective surface area for the adsorption of gas molecules.

We report the fabrication of a highly sensitive gas sensor based on a network of nanostructured TiO 2 hollow hemispheres (NTHH). O 2 plasma etching induces cross-linking of hexagonal-close-packed polystyrene array, which is adopted as a template substrate for room-temperature deposition of TiO 2 thin film. High-temperature calcination effectively removes polystyrene template beads and promotes crystallization of TiO 2 , finally producing cross-linked NTHH via nanobridges. The gas-sensing capability of a NTHH-based sensor is demonstrated using 1–500 ppm CO. Our sensor exhibits a very high response of 4220% change in resistance when exposed to 500 ppm CO at 250 °C, whereas a gas sensor based on a plain TiO 2 film shows a 195% change. The high sensitivity of the NTHH-based sensor is attributed to the enhanced gas sensing performance of the narrow nanobridges between hollow hemispheres.

This study investigates the CO sensing properties of nanostructured TiO2 thin film gas sensors fabricated with colloidal templates using different sizes of polymer spheres. Compared to plain films, the nanostructured films show enhanced gas sensing in the form of greater sensitivity and a faster response. More interestingly, the use of colloidal templates with smaller spheres (300 nm in diameter) leads to close-packed nanostructured TiO2 thin films with very large-scale uniformity and a more pronounced improvement in CO sensing compared to the use of larger spheres (1 μm in diameter). This result suggests that an understanding of the sphere size effects on the gas sensing properties of nanostructured TiO2 thin films created by colloidal templating is important in the development of these films for actual applications.

The PZT based piezoelectric thick films prepared by screen printing method have been mainly used as a functional material for MEMS applications due to their compatibility of MEMS process. However the screen printed thick films generally reveal poor electrical and mechanical properties because of their porous microstructure. To improve microstructure we mixed attrition milled powder with ball milled powder of 0.01Pb-0.41Pb--+0.1 wt% +1.5 wt% ZnO composition. By mixing 25 % of attrition milled powder and 75 % of ball milled powder, the broadest particle size distribution was obtained, leading to a dense thick film with crack-free microstructure and improved dielectric properties. The X-ray diffraction analysis revealed that the film was in wellcrystallized perovskite phase. The remanent polarization was increased from to at the addition of 25 % attrition milled powder.

Graphene is a promising material for vapor sensor applications because of its potential to be functionalized for specific chemical gases. In this work, we present a graphene gas sensor that uses single-stranded DNA (ssDNA) molecules as its sensing agent. We investigate the characteristics of graphene field effect transistors (FETs) coated with different ssDNAs. The sensitivity and recovery rate for a specific gas are modified according to the differences in the DNA molecules’ Guanine (G) and Cytosine (C) content. ssDNA-functionalized devices show a higher recovery rate compared to bare graphene devices. Pattern analysis of a 2-by-2 sensor array composed of graphene devices functionalized with different-sequence ssDNA enables identification of NH3, NO2, CO, SO2 using Principle Component Analysis (PCA).

Arrays of partially selective chemical sensors have been the focus of extensive research over the past decades because of their potential for widespread application in ambient air monitoring, health and safety, and biomedical diagnostics. Especially, vapor sensor arrays based on functionalized nanomaterials have shown great promise with their high sensitivity by dimensionality and outstanding electronic properties. Here, we introduce experiments where individual vapors and mixtures of them are examined by different chemical sensor arrays. The collected data from those sensor arrays are further analyzed by a principal component analysis (PCA) and targeted vapors are recognized based on prepared database.