| 1. |
- Nguyen Van, Toan, et al.
(författare)
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Fabrication of highly sensitive and selective H2 gas sensor based on SnO2 thin film sensitized with microsized Pd islands
- 2016
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Ingår i: Journal of Hazardous Materials. - : Elsevier BV. - 0304-3894 .- 1873-3336. ; 301, s. 433-442
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Tidskriftsartikel (refereegranskat)abstract
- Ultrasensitive and selective hydrogen gas sensor is vital component in safe use of hydrogen that requires a detection and alarm of leakage. Herein, we fabricated a H2 sensing devices by adopting a simple design of planar–type structure sensor in which the heater, electrode, and sensing layer were patterned on the front side of a silicon wafer. The SnO2 thin film–based sensors that were sensitized with microsized Pd islands were fabricated at a wafer–scale by using a sputtering system combined with micro–electronic techniques. The thicknesses of SnO2 thin film and microsized Pd islands were optimized to maximize the sensing performance of the devices. The optimized sensor could be used for monitoring hydrogen gas at low concentrations of 25–250 ppm, with a linear dependence to H2 concentration and a fast response and recovery time. The sensor also showed excellent selectivity for monitoring H2 among other gases, such as CO, NH3, and LPG, and satisfactory characteristics for ensuring safety in handling hydrogen. The hydrogen sensing characteristics of the sensors sensitized with Pt and Au islands were also studied to clarify the sensing mechanisms.
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| 2. |
- Jiao, Mingzhi, et al.
(författare)
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Comparison of NO2 Gas-Sensing Properties of Three Different ZnO Nanostructures Synthesized by On-Chip Low-Temperature Hydrothermal Growth
- 2018
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Ingår i: Journal of Electronic Materials. - : Springer Science and Business Media LLC. - 0361-5235 .- 1543-186X. ; 47:1, s. 785-793
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Tidskriftsartikel (refereegranskat)abstract
- Three different ZnO nanostructures, dense nanorods, dense nanowires, and sparse nanowires, were synthesized between Pt electrodes by on-chip hydrothermal growth at 90°C and below. The three nanostructures were characterized by scanning electron microscopy and x-ray diffraction to identify their morphologies and crystal structures. The three ZnO nanostructures were confirmed to have the same crystal type, but their dimensions and densities differed. The NO2 gas-sensing performance of the three ZnO nanostructures was investigated at different operation temperatures. ZnO nanorods had the lowest response to NO2 along with the longest response/recovery time, whereas sparse ZnO nanowires had the highest response to NO2 and the shortest response/recovery time. Sparse ZnO nanowires also performed best at 300°C and still work well and fast at 200°C. The current–voltage curves of the three ZnO nanostructures were obtained at various temperatures, and the results clearly showed that sparse ZnO nanowires did not have the linear characteristics of the others. Analysis of this phenomenon in connection with the highly sensitive behavior of sparse ZnO nanowires is also presented.
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| 3. |
- Jiao, Mingzhi, et al.
(författare)
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Influence of annealing temperature on theperformance and stability of on-chip hydrothermally grown ZnO nanorod gassensor toward NO2
- 2018
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Ingår i: Academia Journal of Scientific Research. - 2315-7712. ; 6:5, s. 180-189
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Tidskriftsartikel (refereegranskat)abstract
- Nanorod-based gas sensors synthesized at low temperature should generally be stabilized by anneling before usage. However, the influence of annealing on the sensing performance and stability of these nanorods is rarely reported. In this study, we first fabricated gas sensors based on ZnO nanorods grown on-chip on glass substrate using hydrothermal method. Subsequently, these sensors were annealed at either 400 °C, 500 °C, or 600 °C in air for 4 h. The gas-sensing performance of the ZnO nanorods toward NO2 was tested before and after annealing. The sensitivity of the gas sensors to NO2 decreased, but the stability increased with the increase in annealing temperature. Photoluminescence spectroscopy and X-ray diffraction were used to investigate the material structure of ZnO nanorods. Results revealed that the oxygen-atom-related defects in the ZnO lattice in the region close to the surface influenced by annealing process were the most significant factors on the sensing properties and stability of ZnO nanorods.
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| 4. |
- Jiao, Mingzhi, et al.
(författare)
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On-chip growth of patterned ZnO nanorod sensors with PdO decoration for enhancement of hydrogen-sensing performance
- 2017
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Ingår i: International journal of hydrogen energy. - : Elsevier BV. - 0360-3199 .- 1879-3487. ; 42:25, s. 16294-16304
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Tidskriftsartikel (refereegranskat)abstract
- In this study, we used a low-temperature hydrothermal technique to fabricate arrays of sensors with ZnO nanorods grown on-chip. The sensors on the glass substrate then were sputter decorated with Pd at thicknesses of 2, 4, and 8 nm and annealed at 650 °C in air for an hour. Scanning electron microscopy, high resolution transmission microscopy, X-ray diffraction, and surface analysis by X-ray photoelectron spectroscopy characterization demonstrated that decoration of homogenous PdO nanoparticles on the surface of ZnO nanorods had been achieved. The sensors were tested against three reducing gases, namely hydrogen, ethanol, and ammonia, at 350, 400, and 450 °C. The ZnO nanorods decorated with PdO particles from the 2 and 4 nm layers showed the highest responses to H2 at 450 and 350 °C, respectively. These samples also generally exhibited better selectivity for hydrogen than for ethanol and ammonia at the same concentrations and at all tested temperatures. However, the ZnO nanorods decorated with PdO particles from the 8 nm layer showed a reverse sensing behaviour compared with the first two. The sensing mechanism behind these phenomena is discussed in the light of the spillover effect of hydrogen in contact with the PdO particles as well as the negative competition of the PdO thin film formed between the sensor electrodes during sputter decoration, Pd-Zn heterojunction that forms at high temperature and thus influences the conductivity of the ZnO nanorods.
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| 5. |
- Jiao, Mingzhi, et al.
(författare)
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On-chip hydrothermal growth of ZnO nanorods at low temperature for highly selective NO2 gas sensor
- 2016
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Ingår i: Materials letters (General ed.). - : Elsevier BV. - 0167-577X .- 1873-4979. ; 169, s. 231-235
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Tidskriftsartikel (refereegranskat)abstract
- ZnO nanorods were selectively grown on-chip with a two-step low-temperature hydrothermal method and their gas sensing properties were investigated. Small zinc islands were deposited by sputtering on a glass substrate and used as nucleation sites for the ZnO nanorod growth. An equimolar aqueous solution of 0.005 M Zn(NO3)(2)center dot 6H(2)O and (CH2)(6)N-4 at 85 center dot C was used in two steps. The first step was used for nucleation and growth of short ZnO nanorods for 4 h, whereas the second step was used for elongation of the nanorods for 36 h. Long porous nanorods from neighboring islands connected to each other and formed nanorod junctions. A gas sensor with such nanorods was evaluated towards NO2, ethanol, hydrogen, and ammonia to characterize its sensing properties. It showed that the gas sensor has the highest sensitivity to NO2, and a very high selectivity to this gas when measured at 450 degrees C.
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| 6. |
- Ngoc, Trinh Minh, et al.
(författare)
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Ultralow power consumption gas sensor based on a self- heated nanojunction of SnO2 nanowires
- 2018
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Ingår i: RSC Advances. - : ROYAL SOC CHEMISTRY. - 2046-2069. ; 8:63, s. 36323-36330
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Tidskriftsartikel (refereegranskat)abstract
- The long duration of a working device with a limited battery capacity requires gas sensors with low power consumption. A self-heated gas sensor is a highly promising candidate to satisfy this requirement. In this study, two gas sensors with sparse and dense SnO2 nanowire (NW) networks were investigated under the Joule heating effect at the nanojunction. Results showed that the local heating nanojunction was effective for NO2 sensing but generally not for reduction gases. At 1 W, the sparse NW sensor showed a good sensing performance to the NO2 gas. The dense SnO2 NW network required a high-power supply for gas-sensitive activation, but was suitable for reduction gases. A power of approximately 500 W was also needed for a fast recovery time. Notably, the dense NW sensor can response to ethanol and H2S gases. Results also showed that the self-heated sensors were simple in design and reproducible in terms of the fabrication process.
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| 7. |
- Duoc, Vo Thanh, et al.
(författare)
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New Design of ZnO Nanorod- and Nanowire-Based NO2 Room-Temperature Sensors Prepared by Hydrothermal Method
- 2019
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Ingår i: Journal of Nanomaterials. - : HINDAWI LTD. - 1687-4110 .- 1687-4129.
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Tidskriftsartikel (refereegranskat)abstract
- Room-temperature gas sensors are attracting attention because of their low power consumption, safe operation, and long-term stability. Herein, ZnO nanorods (NRs) and nanowires (NWs) were on-chip grown via a facile hydrothermal method and used for room-temperature NO2 gas sensor applications. The ZnO NRs were obtained by a one-step hydrothermal process, whereas the NWs were obtained by a two-step hydrothermal process. To obtain ZnO NW sensor, the length of NRs was controlled short enough so that none of the nanorod-nanorod junction was made. Thereafter, the NWs were grown from the tips of no-contact NRs to form nanowire-nanowire junctions. The gas-sensing characteristics of ZnO NRs and NWs were tested against NO2 gas at room temperature for comparison. The gas-sensing characteristics of the sensors were also tested at different applied voltages to evaluate the effect of the self-activated gas-sensing performance. Results show that the diameter of ZnO NRs and NWs is the dominant parameter of their NO2 gas-sensing performance at room temperature. In addition, self-activation by local heating occurred for both sensors, but because the NWs were smaller and sparser than the NRs, local heating thus required a lower applied voltage with maximal response compared with the NRs.
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| 8. |
- Jiao, Mingzhi, et al.
(författare)
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Controlled Synthesis and Understanding of Growth Mechanism : Parameters for Atmospheric Pressure Hydrothermal Synthesis of Ultrathin Secondary ZnO Nanowires
- 2016
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Ingår i: Journal of Scientific Research and Reports. - 2320-0227. ; 9:5, s. 1-10
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Tidskriftsartikel (refereegranskat)abstract
- Synthesis of ultrathin ZnO nanowires gains great attention from research community because oftheir large potential in applications involving optoelectronics and sensors. In this study, a lowpressure and low-temperature hydrothermal synthesis of ultrathin ZnO nanowires is studied tounderstand the growth mechanisms better. To achieve this aim, an about 10 nm thin Zn seed layerwas sputter-deposited on a silicon (100) wafer for the hydrothermal growth of ZnO nanowires in anequimolar aqueous solution of Zn(NO3)2 and hexamethylenetetramine. X-ray diffraction analysis confirmed that the Zn layer was self-oxidized into ZnO in air soon after deposition and thenfunctioned as the seed for the preferred growth of c-oriented ZnO nanorods. Different growthconditions were investigated to identify how concentration, temperature, and time influence the finalmorphology of the synthesized ZnO nanostructures. It was found that under the atmosphericpressure, concentration and temperature have to be higher than 0.0025 M and 50°C, respectively,for the ZnO nanorods to nucleate and grow densely. Low concentration gives sparse and randomlyoriented nanorods, whereas high concentration gives dense and vertical nanorods. Ultrathin ZnOsecondary nanowires with an average diameter of less than 20 nm were successfully synthesizedin a solution with concentration of 0.005 M at 90°C for about 16 h. By analyzing the scanningelectron microscopy images of the ZnO nanostructures obtained at different growth conditions, amechanism is proposed for the growth of the ultrathin secondary ZnO nanowires. This findingprovides a cost-effective and straightforward pathway to prepare ultrathin ZnO nanowires.
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| 9. |
- Tan, Ha Minh, 1989-, et al.
(författare)
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Novel Self-Heated Gas Sensors Using on-Chip Networked Nanowires with Ultralow Power Consumption
- 2017
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Ingår i: ACS Applied Materials and Interfaces. - : American Chemical Society (ACS). - 1944-8244 .- 1944-8252. ; 9, s. 6153-6162
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Tidskriftsartikel (refereegranskat)abstract
- The length of single crystalline nanowires (NWs) offers aperfect pathway for electron transfer, while the small diameter of the NWshampers thermal losses to tje environment, substrate, and metal electrodes.Therefore, Joule self-heating effect is nearly ideal for operating NW gassensors at ultralow power consumption, without additional heaters. Therealization of the self-heated NW sensors using the “pick and place”approach is complex, hardly reproducible, low yield, and not applicable formass production. Here, we present the sensing capability of the self-heatednetworked SnO2 NWs effectively prepared by on-chip growth. Ourdeveloped self-heated sensors exhibit a good response of 25.6 to 2.5 ppmNO2 gas, while the response to 500 ppm H2, 100 ppm NH3, 100 ppm H2S,and 500 ppm C2H5OH is very low, indicating the good selectivity of thesensors to NO2 gas. Furthermore, the detection limit is very low, down to 82parts-per-trillion. As-obtained sensing performance under self-heating modeis nearly identical to that under external heating mode. While the power consumption under self-heating mode is extremely low,around hundreds of microwatts, as scaled-down the size of the electrode is below 10 μm. The selectivity of the sensors can becontrolled simply by tuning the loading power that enables simple detection of NO2 in mixed gases. Remarkable performancetogether with a significantly facile fabrication process of the present sensors enhances the potential application of NW sensors innext generation technologies such as electronic noses, the Internet of Things, and smartphone sensing.
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| 10. |
- Trinh, Minh Ngoc, 1978-, et al.
(författare)
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Effective design and fabrication of low-power-consumption self-heated SnO2 nanowire sensors for reducing gases
- 2019
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Ingår i: Sensors and actuators. B, Chemical. - : Elsevier BV. - 0925-4005 .- 1873-3077. ; 295, s. 144-152
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Tidskriftsartikel (refereegranskat)abstract
- Developing metal oxide gas sensors for internet-of-things (IoT) and portable applications require low-power consumption because of the limited battery in devices. This requirement is challenging because metal oxide sensors generally need high working temperatures, especially for reducing gases. Herein, we present an effective design and fabrication method of a SnO2 nanowire (NW) sensor for reducing gases by using the Joule heating effect at NW nanojunctions without needing an external or integrated heater. The sensor’s low-power consumption at around 4 mW was controlled by the size and nanojunction density of the device. The sensor has a simple design and is easy to fabricate. A proof-of-concept of a portable gas sensor module can be realised for monitoring highly toxic reducing gases, such as H 2S, NH3 and C2H5OH, by using the developed self-heated NWs.
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| 11. |
- Trinh, Minh Ngoc, 1978-, et al.
(författare)
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Self-heated Ag-decorated SnO2 nanowires with low power consumption used as a predictive virtual multisensor for H2S-selective sensing
- 2019
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Ingår i: Analytica Chimica Acta. - : Elsevier BV. - 0003-2670 .- 1873-4324. ; 1069, s. 108-116
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Tidskriftsartikel (refereegranskat)abstract
- Multisensor systems with low-power consumption are emerging for the Internet of Things. In this work, we demonstrate the use of self-heated networked Ag-decorated SnO2 NW sensors integrated into a portable module for selective detection of H2S gas at low power consumption, and the integrated system is simulated as a virtual multisensor under varying heating powers for identifying and quantifying different reducing gases. The H2S gas-sensing characterisations at the different self-heating powers of 2–10 mW showed that the gas response significantly increased with the increase in Ag density decoration and the heated power strongly affected the gas-sensing performance and sensor stability. Excellent response of 21.2 to 0.5 ppm H2S gas was obtained at a low heating power of 2 mW with an acceptable response/recovery time of 18/980 s. The increase of the heating power over 20 mW can destroy the devices. The integrated system could selectively detect H2S at the heating power below 4 mW and H2, C2H5OH and NH3gases at the heating power upon 4 mW. The virtual multisensor could discriminate qualitatively (with an accuracy of 100%) and quantitatively H2S, H2, NH3, C2H5OH (Ethanol) and CH3COCH3 (Aceton) gases with average errors of 13.5%, 14.7%, 16.8%, 16.9%, and 14.8%, respectively. The proposed sensing platform is a promising candidate for selective detection of H2S gas and virtual multisensor with low power consumption for mobile or wireless network devices.
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| 12. |
- Chu Thi, Quy, et al.
(författare)
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Ethanol-Sensing Characteristics of Nanostructured ZnO: Nanorods, Nanowires, and Porous Nanoparticles
- 2017
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Ingår i: Journal of Electronic Materials. - : Springer Science and Business Media LLC. - 0361-5235 .- 1543-186X. ; , s. 1-6
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Tidskriftsartikel (refereegranskat)abstract
- The morphology and crystalline size of metal oxide-sensing materials arebelieved to have a strong influence on the performance of gas sensors. In thispaper, we report a comparative study on the ethanol-sensing characteristics ofZnO nanorods, nanowires, and porous nanoparticles. The porous ZnOnanoparticles were prepared using a simple thermal decomposition of a sheetlikehydrozincite, whereas the nanorods and nanowires were grown byhydrothermal and chemical vapor deposition methods, respectively. Themorphology and crystal structure of the synthesized materials were characterizedby field-emission scanning electron microscopy and x-ray diffraction.Ethanol gas-sensing characteristics were systematically studied at differenttemperatures. Our findings show that for ethanol gas-sensing applications,ZnO porous nanoparticles exhibited the best sensitivity, followed by thenanowires and nanorods. Gas-sensing properties were also examined withrespect to the role of crystal growth orientation, crystal size, and porosity.
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| 13. |
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| 14. |
- Ngoc, Trinh Minh, 1978-, et al.
(författare)
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H2S Sensing Characteristics of Self-heated Ag-coated SnO2 nanowires
- 2017
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Ingår i: Proceeding of the 12th Asian Conference on Chemical Sensors (ACCS2017). - Hanoi. ; , s. 350-353
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- The H2S gas sensing characterization of gas sensors based on the SnO2 nanowires network has been reported by several research groups. However, the self-heated gas sensor using Ag-coated SnO2 nanowires network for sensing H2S was investigated the first times. In this study, we will report on the effected of density SnO2 nanowires network on H2S sensitivity. The SnO2 nanowires network density can be controlled bythe distance between sensor electrodes. After SnO2 nanowires decorated with Ag, the results showt hat the H2S gas sensing properties depend on the density of the SnO2 nanowires network. Asthe density of SnO2 nanowires network increases, the response of sensors decreases. Thesensor can operate at as low power as 2 mW to H2S gas concentration of 0.25 ppm. The responseand recovery times of sensor are about 200 s. Moreover, working at low operating power gives us the benefit of energy saving as well as the elongation of lifetime.
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| 15. |
- Nguyen, Thi Quynh Hoa, et al.
(författare)
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Numerical study of a wide incident angle- and polarisation-insensitive microwave metamaterial absorber based on a symmetric flower structure
- 2019
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Ingår i: AIP Advances. - : AIP Publishing. - 2158-3226. ; 9:6
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Tidskriftsartikel (refereegranskat)abstract
- In this study, we propose a wide incident angle- and polarisation-insensitive metamaterial absorber covered with structures comprising a metallic flower shape layer, a dielectric layer and a metallic ground plane. The influences of the structural parameters on the absorptivity are investigated numerically. The proposed absorber exhibits polarisation insensitivity as the number of symmetric petals of a flower shape reaches as high as 4, 6 and 8. Particularly, the absorber based on 8 petals shows an absorptivity of above 90% for wide incident angles up to 70° under transverse electric and transverse magnetic polarisations. The physical mechanism of these observations is clarified by investigating the electric, power loss density and induced current distributions, which is also supported by the retrieved constitutive electromagnetic parameters. That is, the absorption phenomenon is considerably affected by magnetic resonance. By modifying the petals into hollow shapes, the absorber becomes effective in confining the magnetic resonance and can thus minimise the resonant frequency variation to 0.22% without affecting the absorption performance. In comparison with other reported metamaterial absorbers, our design shows considerable practical feasibility in terms of resonant frequency stability, wide incident angle and polarisation insensitivity, thereby making it suitable for various applications in microwave frequency region.
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| 16. |
- Hoa, Nguyen Thi Quynh, et al.
(författare)
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Numerical Study of a Wide-Angle and Polarization-Insensitive Ultrabroadband Metamaterial Absorber in Visible and Near-Infrared Region
- 2019
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Ingår i: IEEE Photonics Journal. - : IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC. - 1943-0655. ; 11:1
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Tidskriftsartikel (refereegranskat)abstract
- An ultrabroadband metamaterial absorber structure based on a periodic array of metallic-dielectric multilayered conical frustums is numerically investigated and proposed. The metamaterial absorber indicated an absorptivity of higher than 90%, which covered the visible and near-infrared region at 480-1480 nm, and a relative absorption bandwidth of 102%. The high absorptivity can be maintained with large incident angles up to 60 degrees under both transverse electric and transverse magnetic polarizations. Furthermore, the proposed absorber exhibits polarization insensitivity owing to its rotational symmetry structure. Compared with the previously reported ultrabroadband metamaterial absorbers, the design in this work indicates high practical feasibility in terms of a compact structure for a large bandwidth, a wide incident angle, and polarization insensitivity, thereby suggesting its promising application, for example, in solar cells and thermal emitters.
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| 17. |
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| 18. |
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| 19. |
- Carter, Sarah-Sophia, 1994-, et al.
(författare)
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Medical grade titanium on-chip : assessing the biological properties of biomaterials for bone regeneration
- 2019
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Medical grade titanium on-chip: assessing the biological properties of biomaterials for bone regeneration Sarah-Sophia D. Carter1, Hugo Nguyen2, Milena Moreira1, Maria Tenje1, and Gemma Mestres11Department of Engineering Sciences, Science for Life Laboratory, Uppsala University, Sweden2Department of Engineering Sciences, Uppsala University, Sweden IntroductionBefore entering the clinic, biomaterials need to be thoroughly evaluated, which requires accurate in vitro models. In this work, we have developed a microfluidic device that could be used to assess the biological properties of biomaterials, in a more in vivo-like environment than what is currently possible. MethodsOur device consists of a polydimethylsiloxane (PDMS, Sylgard 184) microfluidic channel (l= 6 mm, w= 2 mm, h= 200 µm) and a titanium disc (Ti6Al4V, at bottom), held together by an additively manufactured fixture (Fig. 1A). PDMS was cured overnight at 65°C on a silicon wafer master. Once the microchannel and titanium disc were positioned, MC3T3-E1 pre-osteoblast-like cells were seeded (50,000 cells/cm2). After 5 hours incubation under standard culture conditions, flow was started (2 μl/min). As a control, MC3T3-E1 cells were seeded onto plain titanium discs off-chip. Cell viability and morphology were assessed after 20 hours by calcein-AM/propidium iodide (PI), staining live and dead cells respectively. Results and discussionFigure 1B and 1C show calcein-AM/PI stained MC3T3-E1 cells cultured on-chip and figure 1D shows the control, MC3T3-E1 cells cultured off-chip. The potential to culture cells in our chip was confirmed by the presence of a majority of viable cells (green) with a similar morphology as the control sample. The reason for the increased amount of dead cells (red) on-chip compared to the control needs to be further examined, which requires longer-term experiments.ConclusionWe have set the first steps towards a microfluidic tool for the assessment of biological properties of biomaterials.
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| 20. |
- Jeong, Seung Hee, 1978-, et al.
(författare)
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High Resolution Patterning of Liquid Alloy by Shrinking the Substrate
- 2016
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Konferensbidrag (refereegranskat)abstract
- In order to overcome the current limitation in the resolution of the previous developed, liquid alloy patterning method, a shrinking substrate is, for the first time, employed. The current printing technique combining spraying a liquid alloy and transferring a tape mask can be processed with a 100 μm level resolution. This is limited by the resolution of a mask fabricated by using a cutting plotter. By shrinking a substrate, a smaller scale of the liquid alloy pattern can be created without changing the current printing process with a tape mask, which has the advantage of quick and easy processing. We have found that the shrinking process by relaxing a radially 200% pre-strained substrate makes to increases twofold in the resolution of the liquid alloy line pattern.
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| 21. |
- Jeong, Seung Hee, 1978-, et al.
(författare)
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High Resolution Patterning of Liquid Alloy with Stretch Shrink Printing for a High Density Array of Small, Stretchable Strain Sensors
- 2016
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Konferensbidrag (refereegranskat)abstract
- A liquid alloy allows large strain due to its liquid state in a stretchable and deformable system and thus,a resistive strain sensor made of liquid alloy can measure large strain of human motion. Liquid alloy-based strainsensors have been demonstrated with various designs for a better understanding of human motion dynamics and toimprove the design of wearable robotics. So far, the sensors have a large size of several centimeters.To expand the applicability of liquid alloy-based strain sensors, a high resolution patterning technique would enable asmall size and high density of the strain sensor. This allows strain measurements in area-limited situations ordirectional strain measurement with high density arrays. A small-size, high-density stretchable strain sensor array canbenefit many DOF (degree of freedom) dynamics measurements on, e.g., a shoulder, hand, foot, or neck.For realizing a highly stretchable strain sensor, a novel soft, highly stretchable and sticky elastomer was used toencapsulate the liquid alloy. A quick and simple patterning technique for high density design has been developed. Thiscombined our previously developed spray printing technique of the liquid alloy with a stretched elastomer substrateand encapsulation of it. The substrate could be stretched either one dimensionally or radially, depending on thedesign.High resolution patterns that were radially stretched and uniformly shrunken on an elastomer substrate weresuccessfully achieved with the stretch-shrink-printing technique. This technique enables large area fabrication withone step processing. High density patterns that have a low resistance and large stretchability were realized with theliquid alloy for a small and highly stretchable strain sensor. A high density array of small strain sensors wasdemonstrated in measuring strains in different directions of neck movements of the human body.
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| 22. |
- Jiao, Mingzhi
(författare)
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Microfabricated Gas Sensors Based on Hydrothermally Grown 1-D ZnO Nanostructures
- 2017
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In this thesis, gas sensors based on on-chip hydrothermally grown 1-D zinc oxide (ZnO) nanostructures are presented, to improve the sensitivity, selectivity, and stability of the gas sensors.Metal-oxide-semiconductor (MOS) gas sensors are well-established tools for the monitoring of air quality indoors and outdoors. In recent years, the use of 1-D metal oxide nanostructures for sensing toxic gases, such as nitrogen dioxide, ammonia, and hydrogen, has gained significant attention. However, low-dimensional nanorod (NR) gas sensors can be enhanced further. Most works synthesize the NRs first and then transfer them onto electrodes to produce gas sensors, thereby resulting in large batch-to-batch difference.Therefore, in this thesis six studies on 1-D ZnO NR gas sensors were carried out. First, ultrathin secondary ZnO nanowires (NWs) were successfully grown on a silicon substrate. Second, an on-chip hydrothermally grown ZnO NR gas sensor was developed on a glass substrate. Its performance with regard to sensing nitrogen dioxide and three reductive gases, namely, ethanol, hydrogen, and ammonia, was tested. Third, three 1-D ZnO nanostructures, namely, ZnO NRs, dense ZnO NWs, and sparse ZnO NWs, were synthesized and tested toward nitrogen dioxide. Fourth, hydrothermally grown ZnO NRs, chemical vapor deposited ZnO NWs, and thermal deposited ZnO nanoparticles (NPs) were tested toward ethanol. Fifth, the effect of annealing on the sensitivity and stability of ZnO NR gas sensors was examined. Sixth, ZnO NRs were decorated with palladium oxide NPs and tested toward hydrogen at high temperature.The following conclusions can be drawn from the work in this thesis: 1) ZnO NWs can be obtained by using a precursor at low concentration, temperature of 90 °C, and long reaction time. 2) ZnO NR gas sensors have better selectivity to nitrogen dioxide compared with ethanol, ammonia, and hydrogen. 3) Sparse ZnO NWs are highly sensitive to nitrogen dioxide compared with dense ZnO NWs and ZnO NRs. 4) ZnO NPs have the highest sensitivity to ethanol compared with dense ZnO NWs and ZnO NRs. The sensitivity of the NPs is due to their small grain sizes and large surface areas. 5) ZnO NRs annealed at 600 °C have lower sensitivity toward nitrogen dioxide but higher long-term stability compared with those annealed at 400 °C. 6) When decorated with palladium oxide, both materials form alloy at a temperature higher than 350 °C and decrease the amount of ZnO, which is the sensing material toward hydrogen. Thus, controlling the amount of palladium oxide on ZnO NRs is necessary.
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| 23. |
- Jiao, Mingzhi, et al.
(författare)
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Pd decoration of on-chip grown ZnO nanorods for ethanol detection
- 2016
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- We have decorated on - chip grown ZnO nanorods (NRs) with Pd particles by sputtering for better ethanol detection . Size of the sputtered Pd particles determines response of the ZnO NRs to ethanol . ZnO - Pd 2 nm sample is about twice to three times more sensitive to ethanol compared with ZnO - Pd 4 nm and ZnO - Pd 8 nm samples depending on temperature and concentration of ethanol . ZnO - Pd 2 nm response s and recover s also very fast , e specially at 450 °C . Bigger Pd particles will worsen and even terminate sensing performance of the sensor to ethanol , as seen with 4 nm and 8 nm Pd.
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| 24. |
- Sahlberg, Arne, et al.
(författare)
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High-Resolution Liquid Alloy Patterning for Small Stretchable Strain Sensor Arrays
- 2018
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Ingår i: Advanced Materials Technologies. - : Wiley. - 2365-709X. ; 3:4
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Tidskriftsartikel (refereegranskat)abstract
- Soft material applied technology has in recent years become more advanced, enabling for, e.g., soft robotics, skin electronics, and wearable systems. Yet, the processing technology of soft materials has not been sufficiently developed to create high performance in soft and stretchable systems, as compared to the processing technology of conventional electronics or electromechanical systems. Liquid alloys have shown excellent properties for soft and stretchable electrical interconnectors and conductors, which is a basic building block to produce electric or electromechanical systems. In order to overcome the limited resolution of previously developed liquid alloy patterning methods for large-area printed circuits, this work explores the possibility of employing shrinking substrates. By utilizing the characteristics of liquid alloys and elastomers the pattern resolution is improved through a stretch-shrink patterning (SSP) process. The process provides highly conductive liquid conductors of high resolution and can be combined with existing printing techniques for liquid alloys. The SSP process increases design flexibility of soft and stretchable systems that use liquid alloys and enables designs with finer and denser patterns, and cost-effective production for small scale systems.
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