Nguyen Duc Hoa | HCMC_International University Vietnam (original) (raw)
Papers by Nguyen Duc Hoa
Physica E-low-dimensional Systems & Nanostructures, 2009
Cupric oxide nanowires were successfully synthesized by thermal oxidation of copper wire in air a... more Cupric oxide nanowires were successfully synthesized by thermal oxidation of copper wire in air and their gas-sensing properties were investigated. High-resolution transmission electron microscopy (HRTEM) analysis indicated that single crystal CuO nanowires with an average diameter of about 60 nm and length up to several micrometers were grown. The sensor resistance increased upon exposure to reducing gases and decreased with oxidizing gas, indicating p-type semiconducting properties of CuO. The nanowires-based gas sensor could detect a wide range of gases including 1% H2, 60 ppm CO, 60 ppm NH3, and 60 ppm NOx and found a potential application in environmental monitoring.
Nanotechnology, 2006
A new triode-type field emitter structure using carbon nanotubes synthesized on an anodic alumini... more A new triode-type field emitter structure using carbon nanotubes synthesized on an anodic aluminium oxide template is demonstrated. The emitter structure is characterized by uniform diameters and heights, as well as by high mechanical stability. The structure is proven to be advantageous in mass production. In the structure, the leakage current to the gate can be reduced to near zero by coating the insulator on the gate. Through this, a very high current density of 5 mA cm-2 is achieved. The very high field enhancement factor of 1.5 × 106 cm-1 illustrates the high performance of the triode structure, which is realized by freely using well developed semiconductor processing technologies.
Journal of The Korean Physical Society, 2009
A fabrication process for a transparent eld-emission device based on a composite of spin-onglass ... more A fabrication process for a transparent eld-emission device based on a composite of spin-onglass (SOG) and single-walled carbon nanotubes (SWNTs) is developed. The highly crystalline single-walled carbon nanotubes were synthesized by using an arc discharge method. Amorphous carbon and metallic materials were removed by purication using thermal and chemical treatments to enhance the transparency of the emitter. A SOG-SWNT composite was then formed by spincoating the SOG on the puried SWNTs. The eld-emission device based on the SOG-SWNT composite exhibited a high current density of 4 mAcm 2 and a low turn-on eld emission of 1.6 Vm 1 . A very high eld enhancement factor of 2.5 ¢ 10 6 cm 2 demonstrated the high performance of the transparent eld-emission device. The emitter device was mechanically stable in its role as an adhesion medium, SOG.
Sensors and Actuators B-chemical, 2010
In this works, we report on the on-chip fabrication of SnO2-nanowire gas sensors by selective gro... more In this works, we report on the on-chip fabrication of SnO2-nanowire gas sensors by selective growth of the nanowires on Pt interdigitated at different grown time lengths. The gas-sensing properties of the on-chip fabricated sensors were characterized using liquefied petroleum gas (LPG) and NH3 gas at different operating temperatures. The effect of growth time on sensor performances was systematically investigated and reported. In addition, the influence of nanowire diameter and nanowire film thickness on gas sensor performance was also studied for thick film nanowire sensors fabricated by a screen-printing method to elucidate the sensing mechanisms of nanowire-based sensors. The results reveal that the diameter of SnO2 nanowires and their film thickness increased with increasing growth time. The response of the onchip fabricated SnO2-nanowire sensors varied from 1.4 to 21.8 with respect to the growth time, which was varied from 15 to 60 min. The increase of the sensor response with increasing growth time was attributed to the enhancement of wire-wire contact densities.
Sensors and Actuators B-chemical, 2009
A nanowire structured nanocomposite of tin oxide (SnO x ) and a single-walled carbon nanotube (SW... more A nanowire structured nanocomposite of tin oxide (SnO x ) and a single-walled carbon nanotube (SWNT) are fabricated using rheotaxial growth and thermal oxidation method for gas sensor application. The morphology, gas sensing properties, as well as the chemical and electrical properties are investigated. The oxidation temperature for Sn mainly determines the stoichiometry of the SnO x nano-beads, and consequently the electrical and gas sensing properties of the nanocomposite sensors. The gas sensing to nitrogen oxide, hydrogen, oxygen, xylene, acetone, carbon monoxide, and ammonia are also examined to determine the gas selectivity of the sensor. The high sensitivity and selectivity towards NO x of the nanocomposite sensor is realized via the porous structure of the SWNT template. The gas sensing mechanism of the nanocomposite structure is also discussed.
Journal of Crystal Growth, 2009
A transparent field emission device based on the composite of purified single-walled carbon nanot... more A transparent field emission device based on the composite of purified single-walled carbon nanotubes (SWNTs) and spin-on glass (SOG) was developed. Highly crystalline SWNTs were synthesized in situ on a tin-oxide-coated glass using the arc discharge method. A simple purification step by oxidation proved to be an effective process in enhancing the transparency and pureness of the SWNT film. The transparent SOG-SWNT composite was then formed by spin coating SOG on the SWNT film. The field emission device showed a maximum current density of 0.1 mA cm À2 and a low turn-on field emission of 1.6 V mm À1 with a high field enhancement factor of 1.5 Â 10 5 cm À1 .
Current Applied Physics, 2011
The large-scale nanowire-like (NW) structure of tungsten oxide is synthesized by deposition of tu... more The large-scale nanowire-like (NW) structure of tungsten oxide is synthesized by deposition of tungsten metal on the substrate of porous single-wall carbon nanotubes (SWCNTs) film, followed by thermal oxidation process. The morphology and crystallinity of the synthesized ...
Nanotechnology, 2006
A new triode-type field emitter structure using carbon nanotubes synthesized on an anodic alumini... more A new triode-type field emitter structure using carbon nanotubes synthesized on an anodic aluminium oxide template is demonstrated. The emitter structure is characterized by uniform diameters and heights, as well as by high mechanical stability. The structure is proven to be advantageous in mass production. In the structure, the leakage current to the gate can be reduced to near zero by coating the insulator on the gate. Through this, a very high current density of 5 mA cm −2 is achieved. The very high field enhancement factor of 1.5 × 10 6 cm −1 illustrates the high performance of the triode structure, which is realized by freely using well developed semiconductor processing technologies.
Sensors and Actuators B-chemical, 2009
Polyaniline nanofibers were prepared through the in situ oxidative polymerization method and were... more Polyaniline nanofibers were prepared through the in situ oxidative polymerization method and were used for the detection of aromatic organic compounds (AOCs). The nanofiber structures were characterized by scanning electron microscopy, infrared spectroscopy, UV-vis spectroscopy, and so on. The polyaniline nanofibers had diameters of 40-70 nm and a length of several hundred nanometers. Polyaniline was highly doped by HCl. The sensor response to AOC was investigated in several hundred ppm ranges. The sensor showed an increase in conductivity, and the maximum response measured at 1000 ppm was several tens of percent. The interaction mechanism was discussed through X-ray photoelectron spectroscopy study.
Journal of Crystal Growth, 2009
One-dimensional tin oxide nanotube structures are synthesized using single-walled carbon nanotube... more One-dimensional tin oxide nanotube structures are synthesized using single-walled carbon nanotubes (SWNTs) as templates. The thin films of porous SWNTs synthesized by arc-discharge method are first covered by a thin layer of metallic tin and then thermally oxidized in air to form tin oxide nanotubes. In this work, the details of the fabrication process and the effect of oxidation temperature on the microstructure and composition of materials are studied and discussed. The one-dimensional nano tin oxide-SWNTs nanocomposites are found to be a good candidate for gas sensor application.
Physica E-low-dimensional Systems & Nanostructures, 2009
Cupric oxide nanowires were successfully synthesized by thermal oxidation of copper wire in air a... more Cupric oxide nanowires were successfully synthesized by thermal oxidation of copper wire in air and their gas-sensing properties were investigated. High-resolution transmission electron microscopy (HRTEM) analysis indicated that single crystal CuO nanowires with an average diameter of about 60 nm and length up to several micrometers were grown. The sensor resistance increased upon exposure to reducing gases and decreased with oxidizing gas, indicating p-type semiconducting properties of CuO. The nanowires-based gas sensor could detect a wide range of gases including 1% H 2, 60 ppm CO, 60 ppm NH 3, and 60 ppm NO x and found a potential application in environmental monitoring.
Journal of The Korean Physical Society, 2009
We introduce a simple method to synthesize one-dimensional tin-oxide-coated single-wall carbon na... more We introduce a simple method to synthesize one-dimensional tin-oxide-coated single-wall carbon nanotubes (SWNTs) for gas sensor applications The SWNTs are synthesized directly on a SiO2/Si substrate with comb-type electrodes via the arc-discharge method. Metallic Sn thin layers with various thicknesses are deposited over the grown SWNTs. After that, a rheotaxial and thermal oxidation is performed to spread and convert the tin metal on the surfaces of the SWNTs into tin oxide. The electrical and the NOx gas sensing properties of the sensor devices are then investigated. The as-grown SWNTs sensor exhibited a p-type semiconducting property whereas the tin-oxidecoated SWNTs exhibited an n-type semiconducting property. Moreover, the one-dimensional tinoxidecoated SWNTs sensor exhibited a higher sensitivity than the pure SWNTs sensor.
Sensors and Actuators B-chemical, 2010
A polymer-assisted deposition method was used to prepare nanocomposite structures of cobalt oxide... more A polymer-assisted deposition method was used to prepare nanocomposite structures of cobalt oxide and single-walled carbon nanotubes (SWCNTs) for a gas sensor application. Scanning electron microscopy images show that the deposition morphology of Co 3 O 4 is closely related to the viscosity and metal ion concentration in the precursor solution. X-ray diffraction data combined with Raman spectra show that the composite film has high crystalline quality. The basic sensing behavior was evaluated with NO x gas as an electron-accepting gas and H 2 as an electron-donating gas. The composite shows a response of ∼200% upon exposure to 4% H 2 at room temperature. This value is higher than that observed in SWCNT thin film and Co 3 O 4 film, as well as in other pure and functionalized CNTs. The enhancement may have originated from the combination of the nature of Co 3 O 4 particles that actively react with gases and the formation of an electrical continuum between Co 3 O 4 and SWCNTs. He is currently interested in synthesis and applications of ZnO-based oxide materials, including ZnO-based gas sensors and diluted magnetic semiconductors.
Sensors and Actuators B-chemical, 2010
A hydrogen sensor of high sensitivity and selectivity based on the composite of single-walled car... more A hydrogen sensor of high sensitivity and selectivity based on the composite of single-walled carbon nanotube (SWCNT) and chitosan was developed. The intrinsically limited response of SWCNT to hydrogen is greatly improved with the assistance of the conjugate material in the composite, or in the chitosan. Furthermore, the chitosan surrounding the SWCNTs selectively passes through the hydrogen molecules, filtering out other polar molecules, enhancing the selectivity of the SWCNT sensor towards hydrogen. The improvements are achieved with the amino and hydroxyl functional groups of chitosan in contact with the SWCNTs.
Nanotechnology, 2007
A triode-type field emission device based on carbon nanotubes (CNTs) synthesized on an anodic alu... more A triode-type field emission device based on carbon nanotubes (CNTs) synthesized on an anodic aluminum oxide (AAO) template was fabricated. For the improvement of device performance, in addition to the basic advantages of using AAO to obtain uniform CNTs with strong adhesion, several considerations were taken into account, including highly crystalline CNTs synthesized through thermal chemical vapor deposition (CVD) at 1200 • C, lowering the contact resistance with a Ti buffer layer and reducing the pixel size and gate-to-emitter distance. The triode-type field emitter showed a high current density of 20 mA cm −2 and a low turn-on voltage of 16 V. The very high field enhancement factor of 1.6 × 10 6 cm −1 confirmed the high efficiency of the triode structure in electron extraction.
Sensors and Actuators B-chemical, 2010
Porous nanowire-structured cupric oxide (CuO) film is synthesized by deposition of Cu on porous s... more Porous nanowire-structured cupric oxide (CuO) film is synthesized by deposition of Cu on porous singlewalled carbon nanotube (SWNT) substrate followed by a thermal oxidation process. Oxidation is done in air at a temperature range of 300-800 • C to oxidize the Cu while removing the SWNT template. The oxidation temperature determines the stoichiometry of the CuO formed, and thus the electrical property. The structures and electrical properties of the synthesized materials are investigated by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), Raman, X-ray photoelectron spectroscopy (XPS), and current-voltage measurements. Sensing property is examined using hydrogen gas. Gas sensing mechanism and the advantages of nanowire structure as a sensor are also discussed. The best response and recovery results are observed with the CuO nanowires oxidized at 400 • C at a working temperature of 250 • C.
Physica Status Solidi (a), 2007
We introduce a simple method to fabricate an ammonia gas sensor with a nanocomposite of single-wa... more We introduce a simple method to fabricate an ammonia gas sensor with a nanocomposite of single-walled carbon nanotubes (SWNTs) and SnO 2 . The nanocomposite showed a semiconducting property. With exposure to ammonia gas, the electrical resistance of the nanocomposite sensor increases rapidly. It was found that the sensor can detect the concentration of NH 3 down to the 10 ppm level at room temperature. The sensor exhibited a fast response time of less than 100 s and good sensing response and recovery.
Physica Status Solidi (a), 2007
We introduce a simple method to fabricate an ammonia gas sensor with a nanocomposite of single-wa... more We introduce a simple method to fabricate an ammonia gas sensor with a nanocomposite of single-walled carbon nanotubes (SWNTs) and SnO2. The nanocomposite showed a semiconducting property. With exposure to ammonia gas, the electrical resistance of the nanocomposite sensor increases rapidly. It was found that the sensor can detect the concentration of NH3 down to the 10 ppm level at room temperature. The sensor exhibited a fast response time of less than 100 s and good sensing response and recovery. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
Current Applied Physics, 2011
The large-scale nanowire-like (NW) structure of tungsten oxide is synthesized by the deposition o... more The large-scale nanowire-like (NW) structure of tungsten oxide is synthesized by the deposition of tungsten metal on the substrate of porous single-wall carbon nanotubes (SWCNTs) film, followed by thermal oxidation process. The morphology and crystallinity of the synthesized materials are analyzed by SEM, TEM, XRD, and Raman spectroscopy. Results showed that tungsten oxide NWs deposited on SWCNTs have a porous structure with an average diameter of about 70 nm and a length of up to micrometers. The NH 3 gas-sensing properties of tungsten NWs were measured at different temperatures. A maximum response of 9.7e1500 ppm at 250 C with rapid response and recovery times of 7 and 8 s are found, respectively. In addition, the gas sensing mechanism of fabricated NWs is also discussed in term of surface resistivity and barrier height model.
Sensors and Actuators B-chemical, 2010
Nanostructured CuO thin films are synthesized by deposition and thermal oxidation of Cu on SiO 2 ... more Nanostructured CuO thin films are synthesized by deposition and thermal oxidation of Cu on SiO 2 substrates. The effects of oxidation temperatures on the morphologies and crystallinity of the CuO thin films are investigated by SEM, XRD and XPS. The electrical and hydrogen sensing properties of CuO are studied by electrical resistance measurements. In addition, the effects of carrier gases on the gas response of CuO are investigated. The results showed that Cu was oxidized into monoclinic cupric oxide in the investigated temperature range from 300 to 800 o C. The p-type semiconducting CuO thin film showed increases in electrical resistance upon exposure to hydrogen. The CuO thin film oxidized at 400 o C showed the highest response as compared to others, and it was 3.72 for 6% H 2 at an operating temperature of 250 o C. The carrier gases played very importance roles in the hydrogen sensing by CuO. That is, the sensor showed good response and recovery with a carrier gas of air but not with nitrogen.
Physica E-low-dimensional Systems & Nanostructures, 2009
Cupric oxide nanowires were successfully synthesized by thermal oxidation of copper wire in air a... more Cupric oxide nanowires were successfully synthesized by thermal oxidation of copper wire in air and their gas-sensing properties were investigated. High-resolution transmission electron microscopy (HRTEM) analysis indicated that single crystal CuO nanowires with an average diameter of about 60 nm and length up to several micrometers were grown. The sensor resistance increased upon exposure to reducing gases and decreased with oxidizing gas, indicating p-type semiconducting properties of CuO. The nanowires-based gas sensor could detect a wide range of gases including 1% H2, 60 ppm CO, 60 ppm NH3, and 60 ppm NOx and found a potential application in environmental monitoring.
Nanotechnology, 2006
A new triode-type field emitter structure using carbon nanotubes synthesized on an anodic alumini... more A new triode-type field emitter structure using carbon nanotubes synthesized on an anodic aluminium oxide template is demonstrated. The emitter structure is characterized by uniform diameters and heights, as well as by high mechanical stability. The structure is proven to be advantageous in mass production. In the structure, the leakage current to the gate can be reduced to near zero by coating the insulator on the gate. Through this, a very high current density of 5 mA cm-2 is achieved. The very high field enhancement factor of 1.5 × 106 cm-1 illustrates the high performance of the triode structure, which is realized by freely using well developed semiconductor processing technologies.
Journal of The Korean Physical Society, 2009
A fabrication process for a transparent eld-emission device based on a composite of spin-onglass ... more A fabrication process for a transparent eld-emission device based on a composite of spin-onglass (SOG) and single-walled carbon nanotubes (SWNTs) is developed. The highly crystalline single-walled carbon nanotubes were synthesized by using an arc discharge method. Amorphous carbon and metallic materials were removed by purication using thermal and chemical treatments to enhance the transparency of the emitter. A SOG-SWNT composite was then formed by spincoating the SOG on the puried SWNTs. The eld-emission device based on the SOG-SWNT composite exhibited a high current density of 4 mAcm 2 and a low turn-on eld emission of 1.6 Vm 1 . A very high eld enhancement factor of 2.5 ¢ 10 6 cm 2 demonstrated the high performance of the transparent eld-emission device. The emitter device was mechanically stable in its role as an adhesion medium, SOG.
Sensors and Actuators B-chemical, 2010
In this works, we report on the on-chip fabrication of SnO2-nanowire gas sensors by selective gro... more In this works, we report on the on-chip fabrication of SnO2-nanowire gas sensors by selective growth of the nanowires on Pt interdigitated at different grown time lengths. The gas-sensing properties of the on-chip fabricated sensors were characterized using liquefied petroleum gas (LPG) and NH3 gas at different operating temperatures. The effect of growth time on sensor performances was systematically investigated and reported. In addition, the influence of nanowire diameter and nanowire film thickness on gas sensor performance was also studied for thick film nanowire sensors fabricated by a screen-printing method to elucidate the sensing mechanisms of nanowire-based sensors. The results reveal that the diameter of SnO2 nanowires and their film thickness increased with increasing growth time. The response of the onchip fabricated SnO2-nanowire sensors varied from 1.4 to 21.8 with respect to the growth time, which was varied from 15 to 60 min. The increase of the sensor response with increasing growth time was attributed to the enhancement of wire-wire contact densities.
Sensors and Actuators B-chemical, 2009
A nanowire structured nanocomposite of tin oxide (SnO x ) and a single-walled carbon nanotube (SW... more A nanowire structured nanocomposite of tin oxide (SnO x ) and a single-walled carbon nanotube (SWNT) are fabricated using rheotaxial growth and thermal oxidation method for gas sensor application. The morphology, gas sensing properties, as well as the chemical and electrical properties are investigated. The oxidation temperature for Sn mainly determines the stoichiometry of the SnO x nano-beads, and consequently the electrical and gas sensing properties of the nanocomposite sensors. The gas sensing to nitrogen oxide, hydrogen, oxygen, xylene, acetone, carbon monoxide, and ammonia are also examined to determine the gas selectivity of the sensor. The high sensitivity and selectivity towards NO x of the nanocomposite sensor is realized via the porous structure of the SWNT template. The gas sensing mechanism of the nanocomposite structure is also discussed.
Journal of Crystal Growth, 2009
A transparent field emission device based on the composite of purified single-walled carbon nanot... more A transparent field emission device based on the composite of purified single-walled carbon nanotubes (SWNTs) and spin-on glass (SOG) was developed. Highly crystalline SWNTs were synthesized in situ on a tin-oxide-coated glass using the arc discharge method. A simple purification step by oxidation proved to be an effective process in enhancing the transparency and pureness of the SWNT film. The transparent SOG-SWNT composite was then formed by spin coating SOG on the SWNT film. The field emission device showed a maximum current density of 0.1 mA cm À2 and a low turn-on field emission of 1.6 V mm À1 with a high field enhancement factor of 1.5 Â 10 5 cm À1 .
Current Applied Physics, 2011
The large-scale nanowire-like (NW) structure of tungsten oxide is synthesized by deposition of tu... more The large-scale nanowire-like (NW) structure of tungsten oxide is synthesized by deposition of tungsten metal on the substrate of porous single-wall carbon nanotubes (SWCNTs) film, followed by thermal oxidation process. The morphology and crystallinity of the synthesized ...
Nanotechnology, 2006
A new triode-type field emitter structure using carbon nanotubes synthesized on an anodic alumini... more A new triode-type field emitter structure using carbon nanotubes synthesized on an anodic aluminium oxide template is demonstrated. The emitter structure is characterized by uniform diameters and heights, as well as by high mechanical stability. The structure is proven to be advantageous in mass production. In the structure, the leakage current to the gate can be reduced to near zero by coating the insulator on the gate. Through this, a very high current density of 5 mA cm −2 is achieved. The very high field enhancement factor of 1.5 × 10 6 cm −1 illustrates the high performance of the triode structure, which is realized by freely using well developed semiconductor processing technologies.
Sensors and Actuators B-chemical, 2009
Polyaniline nanofibers were prepared through the in situ oxidative polymerization method and were... more Polyaniline nanofibers were prepared through the in situ oxidative polymerization method and were used for the detection of aromatic organic compounds (AOCs). The nanofiber structures were characterized by scanning electron microscopy, infrared spectroscopy, UV-vis spectroscopy, and so on. The polyaniline nanofibers had diameters of 40-70 nm and a length of several hundred nanometers. Polyaniline was highly doped by HCl. The sensor response to AOC was investigated in several hundred ppm ranges. The sensor showed an increase in conductivity, and the maximum response measured at 1000 ppm was several tens of percent. The interaction mechanism was discussed through X-ray photoelectron spectroscopy study.
Journal of Crystal Growth, 2009
One-dimensional tin oxide nanotube structures are synthesized using single-walled carbon nanotube... more One-dimensional tin oxide nanotube structures are synthesized using single-walled carbon nanotubes (SWNTs) as templates. The thin films of porous SWNTs synthesized by arc-discharge method are first covered by a thin layer of metallic tin and then thermally oxidized in air to form tin oxide nanotubes. In this work, the details of the fabrication process and the effect of oxidation temperature on the microstructure and composition of materials are studied and discussed. The one-dimensional nano tin oxide-SWNTs nanocomposites are found to be a good candidate for gas sensor application.
Physica E-low-dimensional Systems & Nanostructures, 2009
Cupric oxide nanowires were successfully synthesized by thermal oxidation of copper wire in air a... more Cupric oxide nanowires were successfully synthesized by thermal oxidation of copper wire in air and their gas-sensing properties were investigated. High-resolution transmission electron microscopy (HRTEM) analysis indicated that single crystal CuO nanowires with an average diameter of about 60 nm and length up to several micrometers were grown. The sensor resistance increased upon exposure to reducing gases and decreased with oxidizing gas, indicating p-type semiconducting properties of CuO. The nanowires-based gas sensor could detect a wide range of gases including 1% H 2, 60 ppm CO, 60 ppm NH 3, and 60 ppm NO x and found a potential application in environmental monitoring.
Journal of The Korean Physical Society, 2009
We introduce a simple method to synthesize one-dimensional tin-oxide-coated single-wall carbon na... more We introduce a simple method to synthesize one-dimensional tin-oxide-coated single-wall carbon nanotubes (SWNTs) for gas sensor applications The SWNTs are synthesized directly on a SiO2/Si substrate with comb-type electrodes via the arc-discharge method. Metallic Sn thin layers with various thicknesses are deposited over the grown SWNTs. After that, a rheotaxial and thermal oxidation is performed to spread and convert the tin metal on the surfaces of the SWNTs into tin oxide. The electrical and the NOx gas sensing properties of the sensor devices are then investigated. The as-grown SWNTs sensor exhibited a p-type semiconducting property whereas the tin-oxidecoated SWNTs exhibited an n-type semiconducting property. Moreover, the one-dimensional tinoxidecoated SWNTs sensor exhibited a higher sensitivity than the pure SWNTs sensor.
Sensors and Actuators B-chemical, 2010
A polymer-assisted deposition method was used to prepare nanocomposite structures of cobalt oxide... more A polymer-assisted deposition method was used to prepare nanocomposite structures of cobalt oxide and single-walled carbon nanotubes (SWCNTs) for a gas sensor application. Scanning electron microscopy images show that the deposition morphology of Co 3 O 4 is closely related to the viscosity and metal ion concentration in the precursor solution. X-ray diffraction data combined with Raman spectra show that the composite film has high crystalline quality. The basic sensing behavior was evaluated with NO x gas as an electron-accepting gas and H 2 as an electron-donating gas. The composite shows a response of ∼200% upon exposure to 4% H 2 at room temperature. This value is higher than that observed in SWCNT thin film and Co 3 O 4 film, as well as in other pure and functionalized CNTs. The enhancement may have originated from the combination of the nature of Co 3 O 4 particles that actively react with gases and the formation of an electrical continuum between Co 3 O 4 and SWCNTs. He is currently interested in synthesis and applications of ZnO-based oxide materials, including ZnO-based gas sensors and diluted magnetic semiconductors.
Sensors and Actuators B-chemical, 2010
A hydrogen sensor of high sensitivity and selectivity based on the composite of single-walled car... more A hydrogen sensor of high sensitivity and selectivity based on the composite of single-walled carbon nanotube (SWCNT) and chitosan was developed. The intrinsically limited response of SWCNT to hydrogen is greatly improved with the assistance of the conjugate material in the composite, or in the chitosan. Furthermore, the chitosan surrounding the SWCNTs selectively passes through the hydrogen molecules, filtering out other polar molecules, enhancing the selectivity of the SWCNT sensor towards hydrogen. The improvements are achieved with the amino and hydroxyl functional groups of chitosan in contact with the SWCNTs.
Nanotechnology, 2007
A triode-type field emission device based on carbon nanotubes (CNTs) synthesized on an anodic alu... more A triode-type field emission device based on carbon nanotubes (CNTs) synthesized on an anodic aluminum oxide (AAO) template was fabricated. For the improvement of device performance, in addition to the basic advantages of using AAO to obtain uniform CNTs with strong adhesion, several considerations were taken into account, including highly crystalline CNTs synthesized through thermal chemical vapor deposition (CVD) at 1200 • C, lowering the contact resistance with a Ti buffer layer and reducing the pixel size and gate-to-emitter distance. The triode-type field emitter showed a high current density of 20 mA cm −2 and a low turn-on voltage of 16 V. The very high field enhancement factor of 1.6 × 10 6 cm −1 confirmed the high efficiency of the triode structure in electron extraction.
Sensors and Actuators B-chemical, 2010
Porous nanowire-structured cupric oxide (CuO) film is synthesized by deposition of Cu on porous s... more Porous nanowire-structured cupric oxide (CuO) film is synthesized by deposition of Cu on porous singlewalled carbon nanotube (SWNT) substrate followed by a thermal oxidation process. Oxidation is done in air at a temperature range of 300-800 • C to oxidize the Cu while removing the SWNT template. The oxidation temperature determines the stoichiometry of the CuO formed, and thus the electrical property. The structures and electrical properties of the synthesized materials are investigated by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), Raman, X-ray photoelectron spectroscopy (XPS), and current-voltage measurements. Sensing property is examined using hydrogen gas. Gas sensing mechanism and the advantages of nanowire structure as a sensor are also discussed. The best response and recovery results are observed with the CuO nanowires oxidized at 400 • C at a working temperature of 250 • C.
Physica Status Solidi (a), 2007
We introduce a simple method to fabricate an ammonia gas sensor with a nanocomposite of single-wa... more We introduce a simple method to fabricate an ammonia gas sensor with a nanocomposite of single-walled carbon nanotubes (SWNTs) and SnO 2 . The nanocomposite showed a semiconducting property. With exposure to ammonia gas, the electrical resistance of the nanocomposite sensor increases rapidly. It was found that the sensor can detect the concentration of NH 3 down to the 10 ppm level at room temperature. The sensor exhibited a fast response time of less than 100 s and good sensing response and recovery.
Physica Status Solidi (a), 2007
We introduce a simple method to fabricate an ammonia gas sensor with a nanocomposite of single-wa... more We introduce a simple method to fabricate an ammonia gas sensor with a nanocomposite of single-walled carbon nanotubes (SWNTs) and SnO2. The nanocomposite showed a semiconducting property. With exposure to ammonia gas, the electrical resistance of the nanocomposite sensor increases rapidly. It was found that the sensor can detect the concentration of NH3 down to the 10 ppm level at room temperature. The sensor exhibited a fast response time of less than 100 s and good sensing response and recovery. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
Current Applied Physics, 2011
The large-scale nanowire-like (NW) structure of tungsten oxide is synthesized by the deposition o... more The large-scale nanowire-like (NW) structure of tungsten oxide is synthesized by the deposition of tungsten metal on the substrate of porous single-wall carbon nanotubes (SWCNTs) film, followed by thermal oxidation process. The morphology and crystallinity of the synthesized materials are analyzed by SEM, TEM, XRD, and Raman spectroscopy. Results showed that tungsten oxide NWs deposited on SWCNTs have a porous structure with an average diameter of about 70 nm and a length of up to micrometers. The NH 3 gas-sensing properties of tungsten NWs were measured at different temperatures. A maximum response of 9.7e1500 ppm at 250 C with rapid response and recovery times of 7 and 8 s are found, respectively. In addition, the gas sensing mechanism of fabricated NWs is also discussed in term of surface resistivity and barrier height model.
Sensors and Actuators B-chemical, 2010
Nanostructured CuO thin films are synthesized by deposition and thermal oxidation of Cu on SiO 2 ... more Nanostructured CuO thin films are synthesized by deposition and thermal oxidation of Cu on SiO 2 substrates. The effects of oxidation temperatures on the morphologies and crystallinity of the CuO thin films are investigated by SEM, XRD and XPS. The electrical and hydrogen sensing properties of CuO are studied by electrical resistance measurements. In addition, the effects of carrier gases on the gas response of CuO are investigated. The results showed that Cu was oxidized into monoclinic cupric oxide in the investigated temperature range from 300 to 800 o C. The p-type semiconducting CuO thin film showed increases in electrical resistance upon exposure to hydrogen. The CuO thin film oxidized at 400 o C showed the highest response as compared to others, and it was 3.72 for 6% H 2 at an operating temperature of 250 o C. The carrier gases played very importance roles in the hydrogen sensing by CuO. That is, the sensor showed good response and recovery with a carrier gas of air but not with nitrogen.