•Pure and Pt-doped SnO2 hollow spheres were prepared by nanoscale Kirkendall diffusion.•Pure SnO2 hollow nanospheres showed high response to ppm-level ethanol.•Pt-doped SnO2 hollow spheres showed ...ultrahigh response and selectivity to ethanol.•Nanoscale Kirkendall diffusion can be used to prepare high performance gas sensors.
The pure and 0.3wt% Pt-doped SnO2 hollow nanospheres were prepared by the oxidation of pure and Pt-doped Sn nanoscrystals embedded in carbon matrix and their gas sensing characteristics were investigated. The formation of hollow morphology was attributed to the nanoscale Kirkendall effect due to rapid outward diffusion of Sn ions and relatively slow inward diffusion of oxygen. Pure SnO2 hollow nanospheres showed a high response (resistance ratio) of 93.3 when exposed to 5ppm ethanol. The response to 5ppm ethanol was significantly increased to 1399.9 with doping 0.3wt% Pt. In addition, selectivity to ethanol was also enhanced by Pt doping. Ultrasensitive and selective detection of ethanol in pure and Pt-doped SnO2 nanospheres is explained by the effective electron depletion in hollow structures and catalytic promotion of gas sensing reaction.
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•WO3 spheres doped with Nb were prepared by ultrasonic spray pyrolysis.•Doping of Nb into WO3 spheres leads to the formation of ferroelectric phase.•Nb-doped WO3 sensor showed ...ultrahigh response and selectivity to acetone.•Nb-doped WO3 sensor can be used for monitoring the efficiency of ketogenic diets.•Enhanced reaction between ferroelectric materials and polar acetone was verified.
A ketogenic diet (KD) can enable more effective weight loss when performed with a portable breath acetone sensor capable of monitoring KD efficiency. However, current portable sensors—such as oxide semiconductor gas sensors—cannot selectively detect low concentrations of acetone in human breath, hindering their practical applications. Herein, we report an ultraselective and highly sensitive breath acetone sensor, established using WO₃ doped with 5–20 atom% Nb. The pure WO₃ sensor showed low gas responses (S = resistance ratio – 1) to all analytic gases, including acetone, ethanol, carbon monoxide, ammonia, hydrogen, and toluene (S = 0.1–2.1). In contrast, the 10 atom% Nb-doped WO₃ sensor exhibited a high gas response (S = 15.0 at 1 ppm) and ultrahigh selectivity to acetone over ethanol interference (response ratio = 22.3), even in highly humid conditions (relative humidity: 80 %). Moreover, the response time was as short as 4 s, and the detection limit was as low as 8.9 ppb, enabling breath acetone to be monitored in a rapid and precise fashion. The excellent acetone sensing performance of Nb-doped WO₃ sensors was then examined from diverse perspectives, including changes in porosity, surface area, oxygen adsorption, and charge-carrier concentration, and with respect to the formation of ferroelectric ε-WO₃ domains caused by Nb doping. This work will trigger development of a new class of portable breath sensors that can be used to monitor KD efficiency.
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•WO3 yolk–shell spheres were prepared by one-pot spray pyrolysis reaction.•Triple-shelled WO3 spheres showed high response and selectivity to sub-ppm NO2.•High NO2 response was attributed to ...excellent gas accessibility of yolk–shell morphology.•Response and selectivity to NO2 were maintained in highly humid atmosphere.•The sensor can be used to monitor ground-level NO2 and diagnose asthma.
Triple-shelled, double-shelled, and dense WO3 spheres were prepared by ultrasonic spray pyrolysis and their NO2 gas sensing characteristics were investigated. Triple-shelled WO3 yolk–shell spheres showed an unprecedentedly high response (resistance ratio=100–49.0) to 50ppb NO2 at 100–200°C with negligible cross-responses to 5ppm acetone, CO, NH3, ethanol, and toluene, whereas dense WO3 spheres showed low NO2 response (8.9–3.1). The response and selectivity to NO2 were maintained in a highly humid (relative humidity 80%) atmosphere. The ultrahigh response and selectivity of triple-shelled WO3 spheres to several tens ppb levels NO2 was attributed to the enhanced gas accessibility of the yolk–shell morphology with thin and permeable multiple shells.
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A free-standing, flexible, and semi-transparent MoO 3 nanopaper was fabricated using ultralong MoO 3 nanobelts (length ∼ 200 μm; width 200–400 nm), and its gas-sensing characteristics were ...investigated. The sensor exhibited high responses (resistance ratio) of 49 to 5 parts per million (ppm) hydrogen sulfide (H 2 S) at 250 °C and 121 to 5 ppm trimethylamine (TMA) at 325 °C with excellent gas selectivity, demonstrating its dual function for gas detection. Moreover, the sensor showed promising potential for the all-in-one detection of three representative offensive odors (TMA, H 2 S, and NH 3 ) simply by tuning of the sensing temperature. This particular performance is attributed to the high chemical affinity of MoO 3 to H 2 S and the acid–base interaction between basic TMA/NH 3 and acidic MoO 3 . The mechanism underlying the control of gas selectivity by modulating the sensor temperature was investigated by Diffuse Reflectance Infrared Fourier Transform (DRIFT) measurements.
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The purpose of this study was to characterize the putative anxiolytic-like effects of the aqueous extract of the rhizome of Gastrodia elata along with its phenolic constituents, 4-hydroxybenzyl ...alcohol (HA) and 4-hyroxybenzaldehyde (HD), using an elevated plus maze (EPM) in mice. The mice were administered either the aqueous G. elata extract orally or received an intraperitoneal injection of the phenolic constituents, 1 h before the behavioral evaluation in the EPM. A single treatment of the aqueous G. elata extract significantly increased the percentage of time spent and arm entries into the open arms of the EPM versus the saline controls. Among the phenolic constituents of G. elata, HA and HD significantly increased the percentage of time spent and arm entries into the open arms of the EPM versus saline controls (p<0.05). Moreover, there were no changes in the locomotor activity and myorelaxant effects in any group compared with the saline controls. In addition, the anxiolytic-like effects of G. elata extract were blocked by both WAY 100635 (0.3 mg/kg, i.p.), a 5-HT1A receptor antagonist, and flumazenil (10 mg/kg, i.p.), a GABAA receptor antagonist. The anxiolytic-like effects of HA were inhibited by WAY 100635 and the effects of HD were antagonized by flumazenil. These results indicate that G. elata is an effective anxiolytic agent, and suggests that the anxiolytic-like effects of G. elata via the serotonergic nervous system depends on HA and those effects of G. elata via the GABAergic nervous system depends on HD.
The electrical resistance switching (RS) properties of amorphous HfO
2
(a-HfO
2
) and crystalline HfO
2
(c-HfO
2
) thin films grown on a TiN substrate
via
atomic layer deposition were examined using ...DC current-voltage (
I
-
V
) sweep and AC impedance spectroscopic (IS) analyses. The rapid thermal annealing of the a-HfO
2
film at 500 °C under a N
2
atmosphere for 5 min crystallized the HfO
2
film and induced an interfacial TiON barrier layer. The a-HfO
2
sample showed fluent bipolar RS performance with a high on/off ratio (∼500), whereas the c-HfO
2
sample showed a much lower on/off ratio (<∼10), but its switching uniformity was better than that of a-HfO
2
. Such critical differences can be mainly attributed to the absence and presence of the TiON barrier layer in the a-HfO
2
and c-HfO
2
samples, respectively. The AC IS especially enabled the resistance states of the HfO
2
/Pt interface and the HfO
2
/TiN interface to be separately examined during one complete switching cycle of each sample. Although the Pt/c-HfO
2
interface has a Schottky barrier in the pristine state, it disappeared once the c-HfO
2
was electroformed and was not recovered even after the reset step. In contrast, the Pt/a-HfO
2
interface partly recovered the Schottky barrier after the reset.
Microscopic-level changes such as the dynamic evolutions in conducting filament, interfacial TiON region, and matrix phase during various steps of resistance switching were studied using AC impedance spectroscopy.
We report the kilogram-scale, simple, and cost-effective synthesis of Pd-loaded quintuple-shelled Co3O4 microreactors by spray drying of aqueous droplets containing cobalt nitrate, palladium nitrate, ...citric acid, and ethylene glycol and subsequent heat treatment. Highly viscous gel spheres containing Co and Pd salts were successfully converted into multi thin-shelled Co3O4 reactors uniformly loaded with Pd catalysts by the sequential combustion of carbon and decomposition of the metal salts from the outer to the inner regions during one-step heat treatment. The responses (resistance ratio) of the Pd-loaded quintuple-shelled Co3O4 microreactors to 5 ppm toluene and p-xylene were 30.8 and 64.2, respectively, and the selectivity values to toluene and p-xylene against ethanol interference (response ratio) were 14.5 and 30.1, respectively. The unprecedented high response and selectivity were attributed to the effective dissociation of less reactive methylbenzenes into more active smaller species assisted both by catalytic Co3O4 and Pd during the prolonged retention within the microreactors. Kilogram-scale preparation of noble metal-loaded multishelled microreactors and their unique gas-sensing characteristics based on a novel microreactor concept can pave a new way to design of high-performance gas sensors for practical applications.
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A hybrid material composed of silver nanowires (AgNWs) and carbon nanotubes (CNTs) is investigated by a laser direct patterning method. A femtosecond laser system with a wavelength of 1027nm and a ...pulse width of 380fs is applied for the patterning of AgNW/CNT hybrid film. The Gaussian and square quasi-flat-top beam profiles are used for the patterning lines. The laser fluence and overlapping rate were optimized for patterning at 67.9mJ/cm2 and 70%, respectively. The patterned AgNW/CNT film is evaluated using an optical microscope and scanning electron microscope. The partially ablated area of AgNW/CNT films around the patterned line is observed and discussed. The measurement results explain that the uniformity of the laser beam profile and the beam shape are key factors for development of AgNW/CNT films with fine edges.
•The AgNW/CNT hybrid film was patterned using a femtosecond laser direct patterning technique.•The Gaussian and square quasi-flat-top beam profile was applied for patterning line.•The AgNW/CNT film patterning using the square quasi-flat-top beam profile had finer edge shape and less partially ablated area near the patterned.•The uniformity of the beam energy distribution and the shape of the focused beam were key factors for patterning of the AgNW/CNT with fine edge qualities.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
This paper presents a reference-free readout method for the phase-change memory (PCM) that compensates for the temperature drift of the cell resistance. The proposed method reconfigures the sense ...amplifier (SA) array into flash analog-to-digital converters (ADCs) in order to extract the optimum decision threshold for the given temperature from the distribution of the data output therefrom. The resolution of the reconfigured flash ADC, the number of flash ADCs for data averaging, and the required number of samples are determined for a target bit error rate of 1 ppm. The proposed SA drives a bit line (BL) rapidly with switchable current sources. A proof-of-concept prototype chip is fabricated via the 180-nm CMOS process. A single-channel readout path occupies <inline-formula> <tex-math notation="LaTeX">137 \times 27\,\,\mu \text{m}^{\mathbf {2}} </tex-math></inline-formula> and consumes <inline-formula> <tex-math notation="LaTeX">305~\mu \text{W} </tex-math></inline-formula> under a 3.3-V supply, with readout latency less than 100 ns.
The highly selective detection of trace gases using transparent sensors at room temperature remains challenging. Herein, transparent nanopatterned chemiresistors composed of aligned 1D Au-SnO
...nanofibers, which can detect toxic NO
gas at room temperature under visible light illumination is reported. Ten straight Au-SnO
nanofibers are patterned on a glass substrate with transparent electrodes assisted by direct-write, near-field electrospinning, whose extremely low coverage of sensing materials (≈0.3%) lead to the high transparency (≈93%) of the sensor. The sensor exhibits a highly selective, sensitive, and reproducible response to sub-ppm levels of NO
, and its detection limit is as low as 6 ppb. The unique room-temperature NO
sensing under visible light emanates from the localized surface plasmonic resonance effect of Au nanoparticles, thereby enabling the design of new transparent oxide-based gas sensors without external heaters or light sources. The patterning of nanofibers with extremely low coverage provides a general strategy to design diverse compositions of gas sensors, which can facilitate the development of a wide range of new applications in transparent electronics and smart windows wirelessly connected to the Internet of Things.
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