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Thin film gas sensor based on tin oxide was fabricated and its characteristics were examined. Target gas is acetonitrile () that is simulant gas of blood agent gas. Sensing materials are , /Pt, and (Sn/Pt)oxidation with thickness from to . Sensor was consisted of sensing electrode with interdigit (IDT) type in front side and a heater in back side. Its dimension was . Fabricated sensor was measured as flow type and monitored real time using PC. The optimal sensing material for was {Sn()/Pt()}oxidation and its sensitivity and operating temperature were 30%, in 3 ppm.

Nitrogen oxides (NOx) and carbon monoxide (CO) are among the most dangerous chemical species to human health present in the atmosphere. Acute CO toxicity leading to unconsciousness, respiratory failure or death can occur after 1 hr of exposure when ambient CO levels reach 1000 ppm, whilst increase of NOx emissions can contribute to acid deposition, pollution of groundwater, eutrophication of surface waters, and tropospheric ozone and ecosystem damage. In this work, pure SnO2 sensors for CO and NOx were prepared by spin coating solutions derived from a washed Gel-precipitate followed by a calcining step. SnO2 sensors of nanometer grain size prepared by this process showed good sensitivity to CO and NOx gases. The increase of calcining temperature not only affected grain size and surface morphology, but also caused a decrease in sensitivity of the SnO2 sensors.

Optical fiber sensors have been used to detect small amounts of chemical species. In this work, a new thin polymer-clad fiber sensor is developed. Polyaniline is chemically synthesized and thin clad layers of the polymer are easily deposited on optical fiber by dip-coating technique. The optical property of polyaniline as a sensing material is analyzed by UV-Vis-NIR. The light source is stabilized He-Ne laser at 635 nm wavelength with 1 mW power. The light power transmitted through the optical fiber is measured with a spectrophotometer. By selecting a fixed incident angle, variation of transmitted light intensity through the optical fiber can be detected as gas molecules absorbed in the polyaniline clad layer. Among the various gases, the fabricated optical fiber sensor shows good sensitivity to gas. The optical fiber sensors was shown more improved properties than polymer based sensors which measure conductivity changes.

Indium tin oxide (ITO) films are widely used in optical devices for their high electrical conductivity and high transparency to visible light. Some relevant papers reported ITO thin films showed favorable sensitivity to NO2 and NO gases. However, researches on gas sensing with ITO films, especially thick films, had not been actively conducted until now. The crystal structure and particle size of ITO can be controlled in nanometer accuracy by coprecipitation method. To investigate the effects of crystal structure and particle size of nano-sized ITO powder on gas sensing properties, two kinds of ITO sensors, having cubic and rhombohedral crystal structures with 15 nm particle sizes, were investigated, and three kinds of ITO sensors having 15, 30, and 70 nm particle sizes, with the rhombohedral crystal structure, were investigated. Gas sensing properties were examined in a chamber with dry air (less than 1 ppm humidity concentration) or gaseous ethanol diluted in dry air. ITO gas sensors with the finer the particle sieze have better sensitivity than of large particle size. The sensitivity of ITO thick films were evaluated by sensing of gaseous ethanol.

The polypyrrole (Ppy) incorporated with DBSA and APS was synthesized by chemical polymerization at 0 °C under atmospheric conditions. Ppy films were prepared by the dip coating method on the alumina substrate with interdigitated electrodes in order to employ the gas sensor. The electrical properties of the sensors, such as sensitivity, response and recovery time, reproducibility and long-term stability were investigated in the flow systems after various pretreatments. The electrical properties of the sensors depended on the pretreatment conditions. Soaking pretreatment resulted in a quick response and recovery time of the sensor and maintained electrical properties of the sensor for 3 months. Initial resistance of the sensor decreased with thermal treatment and this improved the stability of the sensor.

Polypyrrole (PPy) and polypyrrole-poly (vinyl alcohol) (PVA) composite methanol sensors were prepared by chemical and in-situ vapor state polymerization method, respectively, and their chemical structures were identified by a FT-Raman spectroscopy. The sensing behaviors of two-type methanol gas sensors, such as sensitivity, response and recovery time, reproducibility and long-term stability were investigated by using a flow measuring system including mass flow controller (MFC), temperature controllers and bubbling bottle. The sensitivity of the sensors almost linearly increased with the increase of methanol concentration from 87ppm to 1059ppm. The sensitivity of vapor state polymerized PPy/PVA composite sensor was higher than that of chemically polymerized PPy sensor, while the response and recovery time and long-term stability were worse.

In this study, the chemically polymerized PPy and PANi films with different selectivity by controlling dedoping time were fabricated. Additionally, the sensing properties and mechanism of VOCs adsorption to conducting polymers were investigated with contact angles measurement, a scanning probe microscope (SPM) and a UV-Vis-NIR spectrophotometer. The thin sensor had higher sensitivity compared to the thick one, which the dedoped sensor at 1-minute had the highest ; sensitivity. Upon gas absorption, polypyrrole exhibited positive sensitivity while polyaniline had negative sensitivity. PPy film showed hydrophilic property and PANi film showed hydrophobic property. After gas absorption, the sensitivity increased as a function of the polarity of the absorbed molecules. These behaviors are due to the polar molecules absorbed with the movable polaron or free carrier, which then interrupts or generates the movement of polaron and carrier, and then changes the conductivity of the polymer. We found that conducting polymer sensors are very sensitive to the difference in polarity of gas molecules.

The thick type sensor having Pt/Na super ionic conductor(NASICON) Pt/Na 2 SO 4 /Pt catalyst system for SO 2 gas sensing was fabricated by screen printing method. The phases of NASICON with the variation of sintering temperature (1050°C, 1150°C, 1250 °C ) and sintering time (1.5hr, 2.5hr, 3.5hr) were investigated by XRD. The variation of electromotive force of the sensor with SO 2 concentration and operation temperature were also investigated. The major phase of NASICON film sintered at 1150°C for 3.5hr was sodium zirconium silicon phosphate (Na 3 Zr 2 Si 2 PO 12 ). The Nernest's slope of NASICON sensor for SO 2 gas with the variation of concentration from 10 to 100 ppm was 176.12 mV/decade at the operating temperature of 500°C. The increase of oxygen partial pressure was not affected to the variation of Nernst's slope.

A gas recognition system was fabricated using a conducting polymer (polypyrrole and polyaniline) sensor array that can recognize and analyze various kinds and quantities of volatile organic compounds (VOCs), such as ethanol, toluene, benzene, and chloroform. The sensors also exhibited different sensitivity curves to VOCs according to the different additive amounts and kinds of conducting polymer (polypyrrole or polyaniline) and electrode. Polypyrrole and polyaniline film sensors made by chemical polymerization were employed to detect the VOCs. The multi-dimensional sensor signals obtained from the sensor array were then analyzed using the principal component analysis (PCA) technique and a radial basis function network (RBFN). By implementing the sensing signals from the sensor array along with a multi-layer neural network using an Radial-Basis Function learning algorithm, the sensor array was successful in accurately classifying the gas species and also identifying the concentration of each VOC in a real-time process.

A three electrode type sensor was fabricated. This sensor consists of two parts. One is a tin doped indium oxide (or indium tin oxide: denoted ITO hereafter) film. It was fabricated by the metal thermal oxidation method. This produces a large surface area and low resistivity. So, this film has two functions, a gas sensitive film and an effective heater. The other part is a platinum resistor line covered with oxidized aluminum film. This part is located in the backside of the sensor. It plays three roles. The first is a load resistor for a measuring system. Secondly, it also acts as a heater. Most of the consumed power in the sensor is used as the thermal energy of gas sensing. The last role is catalytic combustible gas sensing in high gas concentrations. In this paper, the fabrication method of gas sensitive ITO film is researched. A complex sensor structure is fabricated. It acts as a hot wire semiconductor sensor at low gas concentration and a combustible catalytic sensor at high concentration.

A micro-gas sensor array with the four porous tin oxide thin films with noble metal catalysts on a micro-hotplate, dangling in air by Pt bonding wires and controlling the thickness by chemical mechanical process (CMP) has been fabricated. The sensing properties of sensors to some combustible gases, i.e. propane, butane, LPG, and carbon monoxide (CO), were evaluated. And we employed a principal component analysis (PCA) and a multi-layer neural network for classification of the gas species. The simulation and experimental results showed that the multi-layer neural network employing back-propagation learning algorithm with the micro-sensor array is very effective in identifying the kinds and some concentration levels of the combustible gases within the range of threshold limit values (TLVs).

In this work, a new optical gas sensor using thin polymer layers was developed. The polymer sensing layers were synthesized by chemical polymerization using the distilled aniline. The optical property of a polymer as a sensing material was analyzed using UV-Vis-NIR. These layers were prepared using centrifugal force. The polymer layer was uniformly deposited on inner glass pillar. The light source was red-light emitting diode (LED) with a 655 nm wavelength. The light power transmitted through the guide cell was measured with a photodiode. Variation of the light power transmitted was detected when the gas was absorbed into the polymer layer. The transmitted light intensity decreased because gas molecules were absorbed into the polymer layer. This optical sensor showed a good sensitivity to NH 3 gas.

The sensing characteristics of conducting polymers to several volatile organic compounds were investigated with a UV-Vis-NIR spectrophotometer, dynamic contact angles measurement and scanning probe microscopy (SPM). When gases were absorbed, the polypyrrole (PPy) and polyaniline (PANi) exhibited positive and negative sensitivity, respectively. The PPy-based sensor demonstrated decreasing conductivity while the PANi sensor exhibited increasing conductivity when the polarity of the molecules absorbed increased. PPy film has an hydrophilic property while the PANi film a hydrophobic one. These changes in polymer conductivity, it is speculated, are due to the interruption of free carrier movement or the generation of polarons by the absorbed molecules.

Two kinds of nanocrystalline indium tin oxide (ITO) powders with different crystal structures—rhombohedral and cubic—were prepared using a coprecipitation process through the control of pH of a mixing solution and aging time after coprecipitation. The two powders have the same particle size of 15 nm in diameter but different morphologies (spherical for rhombohedral and rectangular for cubic). The gaseous ethanol sensing characteristics of the sensors prepared by the two ITO powders were quite different. The sensitivity of rhombohedral ITO sensor was high compared to that of the cubic ITO sensor across all temperatures. The reason for this is explained through the viewpoint of the binding energy as shown in XPS measurement and the surface structure relating to the crystal structure.

Two different sensors were prepared with and without an oxidized tin black filter, and then the effect of the filter on detecting the properties of hydrocarbon gases was investigated. The oxidized tin black filter was prepared by Sn thermal evaporation in a low vacuum, Ar atmosphere of 0.6 Torr. Thereafter, the tin black film was oxidized at an operating temperature of 600 °C to maximize the chemical filtering effect. The SnO 2 sensing layer under the filter was prepared by the thermal oxidation of metallic tin film with a 2000 A thickness. Morphologically, the oxidized tin black filter exhibited a high porous and foam structure. The addition of a filter to the tin oxide sensing layer had a positive effect on the selectivity towards CH 4 in comparison with iso -C 4 H 10 and C 3 H 8 .

Micro gas sensor with single electrode was proposed for improving stability and sensitivity. Generally, metal oxide gas sensors have two electrodes for heating and sensing. This fabricated new type sensor have only a single electrode by forming a sensing material onto heating electrode. Pt as a heating and sensing electrode was sputtered on glass substrate and a sensing material was thermally evaporated on Pt electrode. was patterned by lift-off process and then thermally oxidized in condition for 1 hr., . The size of fabricated sensor was . As a result of CO gas sensing characteristics, this sensor showed 100 mV change for 1,000 ppm and linearity for wide range() of gas concentrations. And the sensor shows a good recovery characteristics of 1% deviation compared to initial resistance.

Two based sensing films(pure and /Pt) and a Pt thin film for temperature sensor on an alumina substrate were designed and fabricated for classifying the indoor environmental gases. By controlling the heating power in the shape of trapezoid, unique four sensing response curves created from both film and /Pt film. Then, various parameters were extracted from sensing response curves and carried out principal component analysis(PCA). The results confirm that a sensor array with the proposed operating mode was extremely effective in classifying indoor environmental gases such as , , .

Two SnO2-based sensing films (pure SnO2 and SnO2/Pt) and a Pt thin film as a temperature sensor were fabricated on an alumina substrate for classifying workplace environmental gases. By controlling the heating power in the shape of a trapezoid, a temperature profile of the SnO2 sensing films was created along with four unique sensing response curves to the tested gases. A principal component analysis (PCA) was performed using variables extracted from the sensing response curves. The results confirmed that the sensor array with the proposed operating mode was extremely effective in classifying workplace environmental gases, such as CO2, C3H8, and C4H10.

Ten different gas sensors were integrated as an array on a substrate to identify various kinds and quantities of volatile organic compounds (VOCs), such as benzene, toluene, ethyl alcohol, methyl alcohol, and acetone. The sensor array consists of gas-sensing materials with SnO2 as the base material and a platinum heater and is fabricated using silk printing methods on an alumina substrate. The sensors show a high and broad sensitivity and reproducibility to low concentrations based on the use of nano-sized sensing materials with different additives. Utilizing the sensing signals of the array, an artificial neural network with an error-back-propagation learning algorithm is then implemented as a recognition system for classifying and quantifying the VOCs. Simulation and experimental results demonstrated that the proposed gas sensor array with the neural network was effective in recognizing various kinds and quantities of VOCs.

Glasses in the BaO–ZnO–B2O3 system were examined as potential replacement for PbO glass frits with low firing temperature (500–600 °C) for the dielectric layer of a plasma display panel (PDP). The glasses were evaluated for glass transition temperature (Tg), thermal expansion coefficient (α) and dielectric constant e. The electrical and the thermal properties were also compared with theoretical data calculated by a known empirical equation. Tg of the glasses varied between 480 and 560 °C, and α was in the range of 7–9×10−6 K−1. The dielectric constant ranges from 14 to 19 and the theoretical data showed lower α and e than the experimental data. The results suggest that BaO–ZnO–B2O3 glasses would be suitable as an alternative to Pb-based dielectric layer in PDPs.

In this paper, energy absorption capability of axial crush and bending collapse of aluminum/GFRP hybrid tubes were investigated. Glass fiber–epoxy composite prepregs were wrapped around an aluminum tube and then cured completely in the autoclave under the recommended cure cycle. Bonding process between composite and aluminum tubes was performed by excess resin extracted from the composite tube during curing process. For comparing energy absorption characteristics of the hybrid tube with those of pure aluminum and composite tubes, tests were performed using specimens made of an aluminum alloy and a composite material, respectively. Failure mechanisms of the hybrid tube under the axial compressive load and the bending load were experimentally investigated. For calculating energy absorption capability of axial crush and bending collapse behaviors of the hybrid tube, the modified plastic hinge collapse model and the modified Kecman's model for hybrid tube were suggested, respectively. Two suggested models for the hybrid tube showed a good agreement with the experimental results.

In order to get low cost and portability, semiconductor gas sensor need to have low operating temperature and high sensitivity. based sensors which were doped with metal oxide catalysts(, , , and CdO) were fabricated by screen printing method. To improve electrical stability of sensors, the sensors were annealed in at for 2 hours. The doped sensor showed about sensitivity at alcohol 1,000 ppm and have good selectivity to hydrocarbon gas and tobacco odors. The fabricated sensor and PIC-chip were employed for portable alarm system.

A micro sensor array with the highly sensitive porous tin oxide thin films employing the noble metal catalysts of Pt and Au on a new micro-hotplate, dangled in air by Pt bonding wires, has been designed and fabricated. The micro hot plate was made of N/O/N Si diaphragm with area of 1.9×2.1 mm2. The power consumption was reduced by decreasing the thickness of substrate. The sensor array was applied to recognizing the explosive gases within the range of threshold limit values (TLVs), employing principal component analysis. The result showed that the micro sensor array was qualified for classifying obviously the kinds and quantities of the explosive gases.

The properties of polypyrrole and polyaniline sensor made from chemical polymerization were investigated. It was found that the oxidant (ammonium persulfate) affected solubility, conductivity and the sensing characteristics of polypyrrole and polyaniline. Atomic force microscopy (AFM) was used to investigate the morphology of the sensing films. A sensor array with 6 sensors was developed to recognize various kinds and quantities of volatile organic compounds (VOCs), such as benzene, toluene and chloroform. Principal Components Analysis (PCA) was used to analyze the VOC sensing characteristics.

Epitaxial SnO 2 film was grown on a sapphire substrate using a reactive rf magnetron sputter. The microstructure of the thin film was investigated using the 3C 2 beam line from a Pohang Light Source (PLS) consisting of a 2 GeV electron accelerator, four circle X-ray diffractometer, atomic force microscopy (AFM), and transmission electron microscopy (TEM) comparing with the SnO 2 film on the polished alumina. It was confirmed that the thin film grew epitaxially on the sapphire substrate with a variant crystal structure [Development of microstructure controlled and ultrathin SnO 2 gas sensing film, in: Proceedings of the 5th International Meeting on Chemical Sensors, Rome, Italy, 1994]. No grain boundary was exhibited on the surface of the epitaxial thin film. A large portion of the sorption sites in SnO 2 films appears to react easily with the gas. An epitaxial SnO 2 gas sensor, with a Pt heater and electrodes, exhibited a high sensitivity to combustible gases and a particular sensitivity of 95% to alcohol at 2000 ppm and 350°C. The sensor also showed a good stability with small baseline drift and fast reaction and recovery times of about 5 and 30 s, respectively. This experiment confirms the good gas-sensing characteristics of an epitaxially-grown SnO 2 gas sensor.

A new type micro-gas sensor array and its operating mode were proposed in this paper. Sensor array has a heater, and three sensing electrode and temperature sensor pairs. Three different sensing materials, Fe 2 O 3 +V 2 O 5 , SnO 2 /Au+Pd and nanocrystalline SnO 2 , were synthesized by coprecipitation method and used for selective gas sensing. Even though fabricated sensor array has three sensing materials, 12 sensing responses in an array were implemented by using heating power-control method as a sensor operating mode. The gas-sensing characteristics were investigated as a function of the heating powers (35, 40, 45, and 50 mW). Principal component analysis (PCA) was employed to discriminate the various kinds of gases, which is known as one of the most effective sensing signal analysis methods. From the PCA result, we could confirm that the gas sensor array with excellent gas discriminating ability could be obtained by using a heating power-controlled method.

A sensor array with 10 sensors integrated on a substrate was developed to recognize various kinds and quantities of volatile organic compounds (VOCs), such as benzene, toluene, ethyl alcohol, methyl alcohol, and acetone. The sensor array consists of gas-sensing materials using SnO 2 as the base material, plus a heating element based on a meandered platinum layer, all deposited on the substrate. The sensors on the sensor array are designed to produce a uniform thermal distribution and show a high and broad sensitivity and reproductivity to low concentrations through the usage of nano-sized sensing materials with high surface areas and different additives. By utilizing the sensing signals of the array with an artificial neural network, a recognition system can then be implemented for the classification and quantification of VOCs. The characteristics of the multi-dimensional sensor signals obtained from 10 sensors are analyzed using the principal component analysis (PCA) technique, and a gas pattern recognizer is implemented using a multi-layer neural network with an error-back-propagation learning algorithm. Simulation and experimental results demonstrated that the proposed gas recognition system is effective in identifying VOCs. For real-time processing, a DSP board can be used to implement the proposed VOC recognition system in conjunction with a neural network.

Electrochromic devices are based on the reversible insertion of guest atoms into the structure of the host solid. However, after cyclic operation, the tungsten in a WO 3 film and the indium in an ITO (indium tin oxide) film were migrated with each other and the electrochromic property of the device was decreased. The trapped lithium is associated with the indium (diffuse out from ITO to WO 3 film). In order to block migration, a thin tungsten barrier film was deposited on the ITO film. With the tungsten barrier, the indium and tungsten migration was effectively blocked and the decrease of the maximum current of cyclic voltammogram was reduced to 1/10. We can now manufacture electrochromic devices that have long lifetimes and high transmittance variance.

The characteristics of electrochromic films (WO3, V2O5) prepared by sol-gel-spin coating and a vacuum evaporation process were compared to identify a new application of an electrochromic display. Polypyrrole films were prepared by electropolymerization in a pyrrole solution, acetonitrile, and TEPS (tetraethylammonium p-toluenesulfonate). The liquid electrolyte was prepared using LiClO4, propylene carbonate, polymethylmetacrylate, and ethyl acetate. The optical modulation of the electrochromic device was measured as the LiClO4: PMMA weight ratio changed from 10:3 to 10:5. The highest optical modulation value was when the LiClO4: PMMA weight ratio was 10:4. Each type of film was analyzed using a four-point probe, a differential scanning calorimeter (DSC), an X-ray diffractometer (XRD), and a UV-vis spectrophotometer (DR/4000H). The ESCA spectra of the WO3 films showed that the tungsten oxidation number decreased in a coloration state. © 2001 Kluwer Academic Publishers

A sensor array with nine discrete sensors integrated on a substrate was developed for recognizing the species and quantity of explosive gases such as methane, propane, and butane. The sensor array consisted of nine oxide semiconductor gas-sensing materials with SnO 2 as the base material plus a heating element based on a meandered platinum layer all deposited on the sensor. The sensors on the sensor array were designed to produce a uniform thermal distribution and show a high and broad sensitivity and reproductivity to low concentrations through the use of nano-sized sensing materials with high surface areas and different additives. Using the sensitivity signals of the array along with an artificial neural network, a gas recognition system was then implemented for the classification and identification of explosive gases. The characteristics of the multi-dimensional sensor signals obtained from the nine sensors were analyzed using the principal component analysis (PCA) technique, and a gas pattern recognizer was implemented using a multi-layer neural network with an error back propagation learning algorithm. The simulation and experimental results demonstrate that the proposed gas recognition system is effective in identifying explosive gases. For real time processing, a DSP board (TMS320C31) was then used to implement the proposed gas recognition system in conjunction with a neural network.

WO 3 -based thin film micro-gas sensor was fabricated and the NO x gas sensing as well as electrical properties have been investigated. To obtain the optimal heat distribution, the structure of micro-hot plate was designed from the result of finite element simulation and was prepared by backside etching with KOH solution. The micro-hot plate was made out of N/O/N diaphragm with the thickness of 0.6 μm and area of 1.5×1.5 mm 2 . The power consumption to maintain the device temperature of 300°C was about 60 mW. WO 3 thin film was thermally evaporated on micro-diaphragm. The film exhibited a fast response to NO 2 gas and the relationship between sensitivity and NO 2 concentration showed good linearity in the gas concentration range of 0–30 ppm NO 2 . The sensitivity of micro-gas sensor to NO x was correlated with the microstructure of the thin film.

Two different sensing materials of TiO2–WO3 system with the grain size of nanometer are synthesized; one is a complete 2-nm-sized coprecipitate ((Ti,W)O2) made by sol-coprecipitation of TiCl4 and WCl6, and the other is a complex 8-nm-sized material (TiO2+WO3) by mixing the sol-precipitation of TiCl4 and WCl6. The TiO2–WO3 system showed different characteristics between the coprecipitate and the complex material of TiO2 and WO3. The sensitivity and sorption properties were improved in the coprecipitate. In the coprecipitate, the sensitivity defined as RG/RA, where RG and RA are resistance in gas ambient and in air, respectively, was about 100 for 30 ppm NO2 at 340°C, which is suited for facility combustion furnace. The coprecipitated sensing materials had different resistance and grain size of 6 nm after calcination in air at 600°C for 2 h. The properties of precursor have been investigated by SEM, X-ray diffraction (XRD) and BET analyses.

To investigate the effect of including carbon beads on the mechanical properties of epoxy resin, the fracture toughness of carbon bead-filled epoxy was earlier evaluated using a CT (compact tension) specimens and Mode I fracture toughness was observed. Based on those results, in this study, the Mode II interlaminar fracture toughness of carbon bead filled epoxy/glass fiber hybrid composites was evaluated using end notch flexure (ENF) specimens. The hybrid composites showed increased Mode II interlaminar fracture toughness. The optimal bead volume fraction was around 15%.

In this paper, numerical simulation analyses of the thermal buckling behavior of laminated composite shells with embedded shape memory alloy (SMA) wires were performed to investigate the effect of embedded SMA wires on the characteristics of thermal buckling. In order to simulate the thermomechanical behavior of SMA wires, the constitutive equation of the SMA wires was formulated in the form of an ABAQUS user subroutine. The computational program was verified by showing the response of the pseudoelasticity and shape memory effect (SME) at various temperatures and stress levels. Modeling of the laminated composite shells with embedded SMA wires and thermal buckling analyses were performed with the use of the ABAQUS code linked with the subroutine of the formulated SMA constitutive equations. The thermal buckling analyses of the composite shells with embedded SMA wires show that the critical buckling temperature can be increased and the thermal buckling deformation can be decreased by using the activation force of embedded SMA wire actuators.

Mechanical behavior, such as tensile and fatigue strength, of the optical fiber sensor embedded within the composite laminate was investigated. Tensile and fatigue tests were performed to evaluate the static and fatigue characteristics of optical fibers embedded within three types of laminated composite specimens, [06/OF/06]T, [02/904/OF/904/02]T and [03/903/OF/903/03]T. The initiation of damage and fracture of the optical fiber were detected by observation of the intensity drop-off of laser signal transmitted through the optical fiber during test. Experimental results showed that the fatigue strength of optical fiber embedded within the cross-ply laminate is much lower than the fatigue strength of optical fiber within the unidirectional ply laminate. It was also found that the optical fiber embedded within unidirectional ply laminate fractured due to the fatigue damage accumulation of internal defects of optical fiber itself. However the optical fiber embedded within the cross-ply laminate fractured due to the growth of transverse matrix crack of host composite laminate.

A drop-weight impact test and delamination buckling test were performed to investigate the development of impact damage and post-impact compression behavior of cross-ply composite laminates with optical fibers embedded in the interface of two different angle plies. It was found that the presence of optical fibers had little or marginal effect on the shape and size of damage area of the laminate when the optical fibers were embedded parallel to the host reinforcing fibers. Non-parallel optical fibers promoted unstable crack growth through the formation of resin rich regions, which in turn increased slightly the impact damage area. It was also shown that a large number of parallel optical fibers may have an ameliorating effect on delamination buckling strength as they promote the waviness of the delamination fracture surface.

In an attempt to promote the sensitivity of tin oxide-based sensors to methane gas, the parent tin oxide powder, pure or loaded with Ca and/or Pt (0.1 wt.%), was mixed with a fixed amount (5 wt.%) of alumina-supported Pd catalyst (net Pd loading 0.25 wt.%). The resulting sensor was found to exhibit excellent sensing properties to methane in the concentration range of 500–10 000 ppm at 658 K regardless of the difference in starting tin oxide powder. It gave higher sensitivity to methane than any other sensors for which the tin oxide powder was either mixed similarly with supported Pt, Rh or Ni catalyst or loaded with the same amount of Pd by conventional methods. The high dispersion of Pd (or PdO) particles appears to be responsible for the excellent promoting action of the supported Pd catalyst. At lower temperature of 573 K, however, the use of the Ca and/or Pt loaded powder of tin oxide gave higher sensitivity to methane than that of the unloaded powder. It is suggested that the mechanism of methane sensing consists of two steps, i.e. activation of methane molecules on the supported Pd catalyst and surface reaction of the activated species on the tin oxide particles. The first step is rate determining at 658 K, while the second step becomes also important kinetically at 573 K, allowing the promoting action of Pt to take place.

Lateral field emission diodes were fabricated by using separation by implantation of oxygen (SIMOX) wafer and their current-voltage characteristics (I-V) were analyzed. Applying conventional photolithography and local oxidation of silicon (LOGOS) process, we fabricated single-crystalline lateral silicon field emitters with very sharp cathode and anode tips and very short cathode to anode spacing ranging from 0.3 to 0.8 /spl mu/m as well. Two different types of tips, tapered and wedge-shaped emitters, were typically formed according to oxidation time. The turn-on voltages for both types of diodes were as low as 22/spl sim/25 V and the emission currents were as high as 6 /spl mu/A/tip at voltages of 35/spl sim/38 V. From the Fowler-Nordheim (FN) equation, field emitting area (A) and field enhancement factor (/spl beta/) for both types of diodes were estimated to explain the low turn-on voltages and the high emission currents.

Transient two-dimensional model of bismuth germanium oxide (BGO) crystal growth by the heat exchanger method has been developed. The moving boundary problems for the melt/solid interface location, the temperature field in the whole calculation domain and the flow field in the melt were solved by the two mapping rule method, which enabled the simulation of the melt/solid interface, changing from hemispherical to planar shape. The maximum deflection of the interface was observed when the melt/solid interface is at the corner of crucible. The effects of the various growth parameters were studied on the interface shape, the temperature profile and the stream function using this model. As the excess heating temperature was increased, the maximum deflection of the interface decreased. The heat exchanger temperature hardly affects the maximum deflection of the melt/solid interface. The maximum deflection of the melt/solid interface is not very sensitive to the value of the thermal conductivity of the melt of BGO.

The growth of high quality ZnSe by organometallic vapor phase epitaxy (OMVPE) has been investigated fortertiary-butyl allyl selenide (tBASe), combined with dimethylzinc-triethylamine (DMZn : NEt3). Single crystalline ZnSe films were grown on GaAs at temperature as low as 350°C with a reasonable growth rate (~1 µm/h). Secondary ion mass spectrometry (SIMS) spectra show a negligible carbon incorporation in ZnSe films from tBASe even at high VI/II ratio, in contrast the carbon concentration of 1021 cm-3 in ZnSe films grown from diallyl selenide (DASe)and methylallylselenide (MASe). Good surface morphology, crystalline and interface quality of ZnSe on (001) GaAs are confirmed by scanning electron microscopy, double crystal diffractometry (DCD) and Rutherford backscattering spectrometry (RBS). Photoluminescence at 10K shows sharp near-band-edge excitonic spectra.

The growth of ZnSe by organometallic vapor phase epitaxy (OMVPE) was investigated for diallyl selenide (DASe) and methylallyl selenide (MASe), combined with dimethylzinc: triethylamine (DMZn: NEt3). The allyl selenide compounds are shown to reduce the growth temperature relative to that needed with diethyl selenide (DESe). The surface morphology of the grown ZnSe films varies on growth temperature and VI/II ratios. Secondary ion mass spectrometry (SIMS) measurements show increasing carbon incorporation with the VI/II ratio, and for a value of VI/II =~4 in MASe and VI/II=~1 in DASe. The amount of incorporated carbon abruptly jumps to concentrations of 1021 cm3, whereupon the films become polycrystalline. The results are interpreted in terms of dominant intramolecular decomposition pathways compared to homolysis pathway.

Sensing behaviors of tin oxide (SnO2)-based gas sensors prepared with various nanomaterials such as nanoparticles, nanochains, flower-like nanoparticles and nanowires were investigated for the detection of a very low concentration of NO2(ppb level). Various SnO2nanomaterials were prepared by the precipitation and thermal evaporation methods. A SnO2 thick film gas sensor fabricated by screen printing method showed a sensor response of about 20%. On the other hands, tin oxide nanowires (TNW) gas sensor synthesized by the thermal evaporation method showed a very high sensor response in the detection of a low concentration of NO2 at 0.1 ppm.

New allyl selenide and trialkylphosphine selenide reagents; specifically, t-butylallyl selenide (tBASe) and tripropylphosphine selenide, are described for the metalorganic vapor phase epitaxy (MOVPE) of ZnSe. The gas-phase chemistry of allyl selenide precursors is discussed, with emphasis on reactions leading to carbon incorporation. Secondary ion mass spectrometry shows a negligible carbon incorporation in ZnSe films grown from tBASe even at high [VI]/[II] ratios, in contrast to a carbon concentration of 10 21 cm −3 in ZnSe films grown from diallyl selenide and methyl allyl selenide. The low carbon concentration is attributed to the t-butyl group precluding internal rearrangement reactions responsible for carbon incorporation. Low temperature growth and short residence times are critical to minimizing alkyl group redistribution reactions that lead to formation of potential carbon precursors; specifically, diallyl selenide. Good surface morphology on (001) GaAs and photoluminescence spectra with sharp near-band-edge excitonic emission is reported. The need to reduce hydrogen incorporation to improve nitrogen doping characteristics motivates the development of alternative Se precursors circumventing formation of Se-H moieties. Phosphine selenides are proposed as a promising family of reagents and results are presented for growth of ZnSe with tripropylphosphine selenide and dimethylzinc.

Breath tests are attractive since they are noninvasive and can be repeated frequently changing state of critically ill patients. Analysis of exhaled breath for recognition of human diseases using endogenous volatile organic compounds offers the possibility of noninvasive diagnosis. We investigated screening method of lung cancer. The system for screening of lung cancer was made by using metal oxide gas sensor array with solid phase microextraction(SPME) fiber. The system tested breath gas of lung cancer patient and health person and the breath gas was analyzed and compared with the components by GC-MS.

In the present study, we deal with the controlled synthesis of ZnO nanoparticles (ZNPs), nanorods (ZNRDs), nanotubes (ZNTs), and nanorings (ZNRs) by combining sonochemical process and etching treatment. Gas sensors based on these fancy nanostructures are fabricated and the gas sensing properties towards VOC gases are investigated. The investigation demonstrates that the ZnO nanostructures based sensors have great potential for ppb‐level VOC detection.

The growth and nitrogen doping of ZnSe by low pressure organometallic vapor phase epitaxy (OMVPE) have been investigated in a vertical downflow reactor equipped with a laser interferometer for in-situ growth rate measurements, and a microwave plasma cavity for precracking of ammonia for nitrogen doping. Particular emphasis is placed on understanding growth characteristics obtained with H2Se and the new adduct source dimethylzincrtriethylamine (DMZn:NEt3), as compared to those obtained with H2Se and DMZn. At higher temperatures and pressures, growth results obtained with DMZn:NEt3 are similar to those obtained using DMZn with the morphology exhibiting familiar hillock-shaped features. At lower temperatures (

Microencapsulation of drugs into solid biodegradable polymeric microspheres via solvent evaporation technique remains challenging especially with those having low molecular weight and high hydrophilicity nature. This paper presents an efficient encapsulation protocol for this group of drugs, demonstrated using hydrogen peroxide as a model compound that is encapsulated into poly(lactic-co-glycolic acid) microspheres. Hydrogen peroxide can be employed as antiseptic agent or its decomposed form into oxygen can be useful in various pharmaceutical applications. The new encapsulation technique was developed based on the modification of conventional double emulsion and solvent evaporation protocol with a backward concentration gradient of hydrogen peroxide. This was achieved by adding and controlling the concentration of hydrogen peroxide at the continuous phase during the solidification stage of the microspheres. Parameters involved in the production and the formulation aspect were optimized to achieve the best protocol having controlled efficiency of encapsulation that is simple, safe, practical, and economical. Evaluation on the encapsulation efficiency and the release profile has been made indirectly by monitoring the dissolved oxygen level of the solution where the microspheres were incubated. Morphology of the microspheres was investigated using scanning electron microscopy. This proposed method has successfully used to prepare batches of microspheres having different encapsulation efficiencies and its potential applications have been demonstrated accordingly.