Recent Publications

Scalable fabrication of high-performance NO2 gas sensors based on tungsten oxide nanowires by on-chip growth and RuO2-functionalization.

posted Sep 30, 2014, 3:22 AM by Sensors VN   [ updated Sep 30, 2014, 3:25 AM ]

By:  Phung Thi Hong Van, Nguyen Hoang Thanh, Vu Van Quang, Nguyen Van Duy, Nguyen Duc Hoa, Nguyen Van Hieu  (ACS Appl Mater Interfaces)
Abstract: The on-chip growth and surface-functionalization have been recently regarded as promising techniques for large-scale fabrication of high performance nanowires gas sensors. Here we demonstrate a good NO2 gas-sensing performance of the tungsten oxide nanowires (TONWs) sensors realized by scalable on-chip fabrication and RuO2-functionalization. The gas response (Rg/Ra) of the RuO2-functionalized TONWs to 5 ppm of NO2 was 186.1 at 250 °C, which increased up to ∼18.6-fold compared with that of the bare TONWs. On the contrary, the responses of the bare and functionalized sensors to 10 ppm of NH3, 10 ppm of H2S and 10 ppm of CO gases were very low of about 1.5, indicating the good selectivity. In addition, the TONW sensors fabricated by the on-chip growth technique exhibited a good reversibility up to 7 cycles switching from air-to-gas with a response of 19.8 ± 0.033 (to 1 ppm of NO2), and this value was almost the same (about 19.5 ± 0.027) for 11 cycles after three months storage in laboratory condition. The response and selectivity enhancement of RuO2-functionalzied TONWs sensors was attributed to the variation of electron depletion layer due to the formation of RuO2/TONWs Schottky junctions and/or the promotion of more adsorption sites for NO2 gas molecule on the surface of TONWs, whereas the good reversibility was attributed to the formation of the stable monoclinic WO3 from the single crystal of monoclinic W18O49 after annealing at 600 °C. Full paper

Outstanding gas-sensing performance of graphene/SnO2 nanowire

posted Jun 26, 2014, 9:18 PM by Sensors VN

By:  Vu Van Quang, Nguyen Van Dung, Ngo Sy Trong, Nguyen Duc Hoa, Nguyen Van Duy, Nguyen Van Hieu  (Applied Physics Letter)
Abstract: Schottky junctions (SJ) are considered devices for sensing applications due to their unique properties. Herein, we report on the design, facile fabrication and outstanding NO2 gas sensing properties of monolayer graphene (GP)/SnO2 nanowire (NW) SJ devices. The devices were prepared by directly growing single crystal SnO2 NWs on interdigitated Pt electrodes via thermal evaporation, followed by transferring a GP layer grown by chemical vapor deposition on top of the NW chip. The SJ-based sensor showed a reversible response to NO2 gas at concentrations of ppb levels with detection limits of about 0.024 ppb at a low operating temperature of 150oC and bias voltage (1 V) with a response/recovery time of less than 50 s. The outstanding gas-sensing characteristics of the device were attributed to tuning the Schottky barrier height and barrier width at the tiny area of contact between GP and SnO2 NW through the adsorption/desorption of gas molecules

Effective decoration of Pd nanoparticles on the surface of SnO2 nanowires for enhancement of CO gas-sensing performance

posted Dec 8, 2013, 10:20 PM by Sensors VN   [ updated Jan 28, 2014, 9:21 PM ]

By:  Do Dang Trung, Nguyen Duc Hoa, Pham Van Tong, Nguyen Van Duy, T.D. Dao, H. V. Chung, and T. Nagao, Nguyen Van Hieu  (J. Hazardous Materials)
Abstract: Decoration of noble metal nanoparticles (NPs) on the surface of semiconducting metal oxide nanowires (NWs) to enhance material characteristics, functionalization, and sensing abilities has attracted increasing interests from researchers worldwide. In this study, we introduce an effective method for the decoration of Pd NPs on the surface of SnO2 NWs to enhance CO gas-sensing performance. Single-crystal SnO2 NWs were fabricated by chemical vapor deposition, whereas Pd NPs were decorated on the surface of SnO2 NWs by in situ reduction of the Pd complex at room temperature without using any linker or reduction agent excepting the copolymer P123. The materials were characterized by advanced techniques, such as high-resolution transmission electron microscopy, scanning transmission electron microscopy, and energy-dispersive X-ray spectroscopy. The Pd NPs were effectively decorated on the surface of SnO2 NWs. As an example, the CO sensing characteristics of SnO2 NWs decorated with Pd NPs were investigated at different temperatures. Results revealed that the gas sensor exhibited excellent sensing performance to CO at low concentration (1 ppm to 25 ppm) with ultrafast response–recovery time (in seconds), high responsivity, good stability, and reproducibility. Full paper

In-stitute decoration of Pd nanocrystal on crystalline mesoporous NiO nanosheets for effective hydrogen gas sensors

posted Aug 1, 2013, 12:48 AM by Sensors VN   [ updated Aug 1, 2013, 1:08 AM ]

By:  Phan Van Tong, Nguyen Duc Hoa, Vu Van Quang, Nguyen Van Duy, Nguyen The Lam Nguyen Van Hieu (International Journal of Hydrogen Energy)
Abstract: The synthesis of cost-effective, high-performance hydrogen gas sensors is eliciting increasing interest because of their advantages in early detection of hydrogen leakages. Herein, we report the in- situ synthesis and decoration of Pd nanocrystals (NCs) on the surface of mesoporous NiO nanosheets for effective hydrogen gas sensor application. The use of large specific surface area of the mesoporous NiO nanosheets and the catalytic activity of the Pd NCs are the key points to improve the hydrogen gas sensing performances through the enhancement of the interaction between the hydrogen molecule and the sensing surface. The mesoporous NiO nanosheets were fabricated by a surfactant-less hydrothermal method in sequence to thermal oxidation, whereas the Pd NCs were decorated by in-situ reduction of palladium complex. The crystal structure and growth mechanism of the materials were investigated by several advanced techniques. The gas-sensing measurements revealed that the Pd-NiO nanosheets based sensor exhibited effectively detection of hydrogen at low concentration with fast response, high sensitivity and stability.

Polyaniline Nanowires-Based Electrochemical Immunosensor for Label Free Detection of Japanese Encephalitis Virus

posted Apr 21, 2013, 7:19 PM by Sensors VN   [ updated Jul 11, 2013, 3:04 AM ]

By: Chu Van Tuan, Tran Quang Huy, Nguyen Van Hieu, Mai Anh Tuan & Tran Trung (Analytical Letters)
Abstract: Polyaniline (PANI) conducting polymers have attracted increasing interest as a transducer material for biosensors applications. In this study, we demonstrate the use of PANI nanowires (NWs) as immobilization platforms in the configuration of an electrochemical immunosensor for label free detection of Japanese encephalitis virus. The PANI NWs were synthesized on the surface of an interdigitated platinum (Pt) microelectrode via electrochemical growth. The morphology and characteristics of the PANI NWs on the Pt microelectrode were verified by scanning electron microscopy and Fourier transform infrared spectroscopy. The anti- Japanese encephalitis virus polyclonal IgG antibody was then covalently immobilized on the PANI NWs-coated Pt microelectrode by using 1-ethyl-3-(3-dimethyaminopropyl) carbodiimide (EDC) and N-hydroxysuccinimde (NHS). The detection of Japanese encephalitis virus antigens was analyzed by electrochemical impedance spectroscopy (EIS). The developed PANI NWs-based electrochemical immunosensor could detect the Japanese encephalitis virus with a detection limit below 10 ng/ml. The results from EIS analysis also indicate that when the PANI NWs were exposed to nonspecific molecules, a negligible response was found, and it did not impact to the specificity of the sensor in the virus detection. This work shows the potential use of PANI NWs in electrochemical immunosensors for label free detection of other pathogens and small biomolecules.Full paper

On-chip growth of wafer-scale planar-type ZnO nanorod sensors for effective detection of CO gas

posted Apr 21, 2013, 7:11 PM by Sensors VN   [ updated Apr 21, 2013, 7:26 PM ]

By: Nguyen Duc Khoang, Hoang Si Hong, Do Dang Trung, Nguyen Van Duy, Nguyen Duc Hoa, Dao Duc Thinh, Nguyen Van Hieu (Sensors and Actuators B: Chemical)
Abstract: The facile engineering of sensing devices is an important technological achievement that will lead to large-scale and cost-effective fabrication of gas nanosensors. This study demonstrates the on-chip and selective growth process of zinc oxide (ZnO) nanorods (NRs) for wafer-scale fabrication of planar-type gas sensors using combined lithography and chemical hydrothermal techniques. This facile route can effectively fabricate ZnO NR gas sensors at low temperatures without the requirement of novel metal catalyst. The gas-sensing characteristics of the ZnO NR sensors to carbon monoxide (CO) and ammonia (NH3) were evaluated as a function of growth time in correlation with operating temperature and target gas concentration. The ZnO NR sensors showed good response and recovery characteristics with a maximum response to CO and NH3gas at 400 °C. The ZnO NR sensors grown at 6 h exhibited the highest response to CO and NH3 gases with sensitivities of 0.37 and 0.05 %/ppm, respectively. Furthermore, the gas-sensing mechanism of the ZnO NR sensors was also discussed in terms of three types NR/NR junctions, namely, point-junctions, across-junctions, and block-junctions. reduction...Full paper

Single-crystal zinc oxide nanorods with nanovoids as highly sensitive NO2 nanosensors

posted Jan 1, 2013, 7:30 PM by Sensors VN   [ updated Jul 11, 2013, 3:09 AM ]

By: Hoang Van Han, Nguyen Duc Hoa, Pham Van Tong, Hugo Nguyen, Nguyen Van Hieu (Materials Letters)
Abstract: Design and synthesis of nanostructured materials with a highly porous crystal structure and high specific surface area are the key issues to an enhanced gas sensing performance. This letter introduces a simple and scalable hydrothermal method to fabricate single-crystal ZnO nanorods (NRs) with nanovoids (NVs) for highly sensitive NO2 nanosensors. The fabricated ZnO NRs have a single-crystal structure with an average length and diameter of about 900 nm and 23 nm, respectively. NVs of less than 5 nm size are found frequently along the NRs. Gas-sensing characterizations revealed that the ZnO NR sensors exhibited a relatively high response to sub-ppm NO2 with excellent stability after 8 cycles of switching from NO2 to dry air without significant response reduction...Full paper

Crystalline mesoporous tungsten oxide nanoplate monoliths synthesized by directed soft template method for highly sensitive NO2 gas sensor applications

posted Dec 26, 2012, 11:58 PM by Sensors VN   [ updated Jul 11, 2013, 3:10 AM ]

By: Nguyen Duc Hoa, Nguyen Van Duy, Nguyen Van Hieu (Materials Research Bulletin)
Abstract: Controllable synthesis of nanostructured metal oxide semiconductors with nanocrystalline size, porous structure, and large specific surface area is one of the key issues for effective gas sensor applications. In this study, crystalline mesoporous tungsten oxide nanoplate-like monoliths with high specific surface areas were obtained through instant direct-templating synthesis for highly sensitive nitrogen dioxide (NO2) sensor applications. The copolymer soft template was converted into a solid carbon framework by heat treatment in an inert gas prior to calcinations in air to sustain the mesoporous structure of tungsten oxide. The multidirectional mesoporous structures of tungsten oxide with small crystalline size, large specific surface area, and superior physical characteristics enabled the rapid and effective accession of analytic gas molecules. As a result, the sensor response was enhanced and the response and recovery times were reduced, in which the mesoporous tungsten oxide based gas sensor exhibited a superior response of 21,155% to 5 ppm NO2. In addition, the developed sensor exhibited selective detection of low NO2concentration in ammonia and ethanol at a low temperature of approximately 150 °C. Full paper

Comparative study on CO2 and CO sensing performance of LaOCl-coated ZnO nanowires

posted Dec 26, 2012, 11:47 PM by Sensors VN   [ updated Jul 11, 2013, 3:11 AM ]

By: Nguyen Van Hieu, Nguyen Duc Khoang, Do Dang Trung, Le Duc Toan, Nguyen Van Duy, Nguyen Duc Hoa (Journal of Hazardous Materials)
Abstract: Carbon dioxide (CO2) and carbon monoxide (CO) emissions from industries and combustion fuels such as coal, oil, hydrocarbon, and natural gases are increasing, thus causing environmental pollution and climate change. The selective detection of CO2 and CO gases is important for environmental monitoring and industrial safety applications. In this work, LaOCl-coated ZnO nanowires (NWs) sensors are fabricated and characterized for the detection of CO2 (250–4000 ppm) and CO (10–200 ppm) gases at different operating temperatures. The effects of the LaCl3 coating concentration and calcination temperature of the sensors are studied. They are found to have a strong influence on the sensing performance to CO2 gas, but a relatively slight influence on that to CO. The LaOCl coating enhances the response and shortens the response and recovery times to CO2 compared with those to CO. The enhanced response of the LaOCl-coated ZnO NW sensors is attributed to the extension of the electron depletion layer due to the formation of p-LaOCl/n-ZnO junctions on the surfaces of the ZnO NWs Full paper

Giant enhancement of H2S gas response by decorating n-type SnO2 nanowires with p-type NiO nanoparticles

posted Dec 18, 2012, 7:12 PM by Sensors VN   [ updated Dec 26, 2012, 11:48 PM ]

By: Nguyen Van Hieu, Phung Thi Hong Van, Le Tien Nhan, Nguyen Van Duy, and Nguyen Duc Hoa (Applied Physics Letter).
Abstract: Metal oxide nanowires (NWs) are widely considered as promising materials for gas sensor applications. Here, we demonstrate that by decorating NiO nanoparticles on SnO2NWs, the gas response to 10 ppm H2S increased up to ∼351-fold. The response of the NiO-decorated SnO2 NWs sensor to 10 ppm H2S at 300 °C reached ∼1372, whereas the cross-gas responses to 5 ppm NH3, 200 ppm C2H5OH, and 1 ppm NO2 were negligible (1.8 to 2.9). The enhanced H2S sensing performance was attributed by the catalytic effect of NiO and the formation of a continuous chain of n-p-n-p junctions.. Full paper

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