In this paper, a nitrogen dioxide (NO 2 ) gas sensor using nitrogen-doped double-walled carbon nanotubes (N-DWCNTs) with different types of nitrogen is demonstrated, and the sensor performance to the pyridinic nitrogen is related. The ratio of nitrogen is controlled by the temperature applied for the synthesis. It is found that the fabricated sensor from N-DWCNTs enable an approximately threefold improvement in NO 2 detection compared to the sensor from DWCNTs. Also, the improvement of sensor response of N-DWCNTs more depends on the pyridinic site than the other types of nitrogen, because it can strongly interact with the NO 2 molecule. The sensing mechanism is attributed to the charge transfer between the NO 2 molecule and the sensing materials (especially with pyridinic site), which shifts the Fermi level, resulting in a decrease of the electrical resistance. Furthermore, the relation between the sensor response and the concentration of NO 2 is derived based on Langmuir adsorption isotherm, and the calculated detection limit can be down to 0.14 ppm, which suggests that the N-DWCNTs-based sensor is a promising approach for low concentration NO 2 detection at room temperature.
Intermetallic compounds due to their promising corrosion resistance and high-temperature mechanical strength give hope for their application as high-temperature structural materials. Intermetallics of L1 0 type structure in recent years in addition have attracted great interest as potential recording media. These alloys are ferromagnetic and display marked mechanical and magnetic anisotropy with the tetragonal c-axis of the ordered domains as the ''easy axis'' of magnetization. High-density magnetic recording may be achieved by a preferential domain orientation with the c-axis perpendicular to the surface, if these materials can be stabilized as low-dimensional magnetic structures. Knowledge of kinetic parameters that determine alloy stability is essential for alloy design, technical application, and performance of materials. We used FePd as a model system for this class of L1 0 -ordered intermetallics and have studied the changes of long-range order during heat treatments in the bulk and in thin films produced by different techniques. Results of X-ray diffraction (XRD), resistivity measurement, Mößbauer spectroscopy, and measurement of magnetization in both geometries are compared.
A room-temperature hydrogen gas (H2) sensor was successfully fabricated by dispersion of palladium nanoparticles (Pd NPs) on graphene sheets (GRs) (hereafter referred to as “Pd NPs/GRs”). GRs and Pd NPs were synthesized by chemical vapor deposition technique and by polyol process, respectively. A colloidal solution of Pd NPs with an average diameter of 11 nm was then dispersed onto the GRs by spin coating technique. The density of dispersed Pd NPs on GRs was controlled by varying the volume of the dispersed solution within the range of 50 – 150 μL. The fabricated Pd NPs/GRs sensors exhibited a high sensitivity for H2 gas with a concentration of 1500 – 6000 ppm at room temperature. Upon H2 exposure, the Pd NPs/GRs sensors showed an increase in electrical resistance, which could easily be measured. The relationship between sensor response and H2 concentration is in correspondence with the Langmuir adsorption model. The H2 detection limit is estimated to be 1 ppm. The results demonstrate that the Pd NPs/GRs sensor is an easily fabricated, but very effective means for room-temperature detection of H2at ppm level.
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