MWCNT-polymer composites as highly sensitive and selective room temperature gas sensors

Multi-walled carbon nanotubes (MWCNTs)-polymer composite-based hybrid sensors were fabricated and integrated into a resistive sensor design for gas sensing applications. Thin films of MWCNTs were grown onto Si/SiO(2) substrates via xylene pyrolysis using the chemical vapor deposition technique. Polymers like PEDOT:PSS and polyaniline (PANI) mixed with various solvents like DMSO, DMF, 2-propanol and ethylene glycol were used to synthesize the composite films. These sensors exhibited excellent response and selectivity at room temperature when exposed to low concentrations (100 ppm) of analyte gases like NH(3) and NO(2). The effect of various solvents on the sensor response imparting selectivity to CNT-polymer nanocomposites was investigated extensively. Sensitivities as high as 28% were observed for an MWCNT-PEDOT:PSS composite sensor when exposed to 100 ppm of NH(3) and - 29.8% sensitivity for an MWCNT-PANI composite sensor to 100 ppm of NO(2) when DMSO was used as a solvent. Additionally, the sensors exhibited good reversibility.     

Highly sensitive hydrogen sensor based on nickel incorporated TiO<Subscript>2</Subscript> nanostructures operating at room temperature

We demonstrate the effect of nickel doping on the sensing performance of TiO₂ nanospheres towards hydrogen at room temperature. A novel microwave assisted processing was adopted for the synthesis of Ni:TiO₂ nanospheres. The preferential (101) anatase phase of TiO₂ changed to anatase–rutile mixed phase after Ni doping. The vibrational spectra show significant shift in the peak with catalytic Ni addition. The energy gap of TiO₂ increased with Ni incorporation from 3.28 to 3.35 eV due to size confinement. Photoluminescence analysis confirmed the decreased intrinsic defect density in Ni doped TiO₂ nanostructures. The morphology of Ni:TiO₂ demonstrated nanospherical shaped grains with increased porosity favorable for sensing. The resistance of Ni:TiO₂ sensors fabricated with a multi-terminal network H₂ adsorption layer improved dramatically to 1100 MΩ, compared to 600 MΩ recorded for pristine TiO₂. The nanocomposite sensor showed fast recovery of 40 s, to even a low concentration of 100 ppm H₂ at room temperature.     

Synthesis of nanosized nickel hydroxide by solid-state reaction at room temperature

The nanosized cathode material Ni(OH)₂ powder for alkaline batteries was synthesized by solid-state reaction at room temperature through NiC₂O₄·2H₂O as precursor, which was also prepared with solid-state reaction from nickel acetate and oxalic acid at ambient temperature. The precursor and the Ni(OH)₂ samples were characterized by X-ray diffraction (XRD), infrared spectrometry (IR), transmission electron microscopy (TEM) and electrochemical testing. The results revealed that the as-synthesized Ni(OH)₂ sample by this method is β(II)-type phase, and its shape is fibroid with the average particle size of 6–9 nm. Compared with microsized spherical β-Ni(OH)₂, the nanosized β-Ni(OH)₂ exhibits excellent electrochemical performance, such as lower polarization and better charge–discharge properties.     

A highly sensitive thin-film capacitive pressure sensor

Translated from Izmeritel'naya Tekhnika, No. 12, pp. 47–48, December, 1991.     

Fabricating ZnO nanorods sensor for chemical gas detection at room temperature

We present a sensor fabricated by simply casting ZnO nanorods on a microelectrodes array for chemical gas detection at room temperature. The ammonia and ethanol gas sensing characteristics were carefully investigated. The sensor exhibited high sensitivity for both ammonia and ethanol gases. The response and recover time are less than 20 seconds, respectively. Present results demonstrate the potential application of ZnO nanorods for fabricating highly sensitive gas sensors.     

Transmission electron microscopy on nickel oxide single crystals deformed at room temperature

Transmission electron microscopy was performed on nickel oxide single crystals deformed under compression along the [0 0 1] direction, at room temperature. Foils for observation were obtained by mechanical thinning followed by ion beam thinning. The glide system and the Burgers vectors of dislocations were found to be the same as those of MgO and NaCl. For the origin of high rate work hardening, the intersection of glissile dislocations with other inactive dislocations followed by dipole formation, and edge dipole formation which serves as a strong barrier against active slip dislocations, were confirmed. The second stage of work hardening begins with the operation of an oblique second system.On leave of absence from the Department of Natural Science, Osaka Women's University, Daisen-cho, Sakai City, Osaka 590.     

Ar ion induced copper germanide phase formation at room temperature

The copper germanide phase Cu₃Ge which is emerging as an alternative material for making contacts and interconnects for semiconductor industry has been produced across the interface of Cu/Ge bilayers by ion beam mixing at room temperature using 1 MeV Ar ions. The dose dependence of the thickness of the mixed region shows a diffusion controlled mixing process. The experimental mixing rate and efficiency for this phase are 5·35 nm⁴ and 10·85 nm⁵/keV respectively. At doses above 8 × 10¹⁵ Ar/cm² the formation and growth of another copper rich phase Cu₅Ge has been observed. The present theoretical models are inadequate to explain the observed experimental mixing rate.     

Solid-state titania-based gas sensor for liquefied petroleum gas detection at room temperature

This paper reports the liquefied petroleum gas (LPG) sensing of titanium dioxide (Qualigens, India). Scanning electron micrographs and X-ray diffraction studies of samples were done. SEM shows that the material is porous and has grapes-like morphology before exposure to the LPG. XRD patterns reveal the crystalline nature of the material. The crystallites sizes of the TiO₂ were found in the range of 30–75 nm. Variations in resistance with exposure of LPG to the sensing element were observed. The average sensitivity for different volume percentages of gas was estimated. The maximum value of average sensitivity was 1·7 for higher vol.% of LPG. Percentage sensor response (%SR) as a function of time was calculated and its maximum value was 45%. Response time of the sensor was 70 s. The sensor was quite sensitive to LPG and results were found reproducible.     

Liquid phase exfoliated WS2 nanosheet-based gas sensor for room temperature NO2 detection

Journal of Materials Science: Materials in Electronics - Layered transition metal dichalcogenide (TMD) materials possess novel and unique semiconducting properties when exfoliated into thin sheets...     

Defect controlled room temperature ferromagnetism in Co-doped barium titanate nanocrystals

Defect mediated high temperature ferromagnetism in oxide nanocrystallites is the central feature of this work. Here, we report the development of room temperature ferromagnetism in nanosized Co-doped barium titanate particles with a size of around 14 nm, synthesized by a solvothermal drying method. A combination of x-ray diffraction with state-of-the-art electron microscopy techniques confirms the intrinsic doping of Co into BaTiO3. The development of the room temperature ferromagnetism was tracked down to the different donor defects, namely hydroxyl groups at the oxygen site (OH·(O) and oxygen vacancies (V··(O), and their relative concentrations at the surface and the core of the nanocrystal, which could be controlled by post-synthesis drying and thermal treatments.     

Interdiffusion and phase formation at room temperature in evaporated gold-tin films

Interdiffusion at room temperature in evaporated Au-Sn films was studied by the in situ backscattering of 2.0 MeV ⁴He ions. The interdiffusion resulted in the formation and growth of an AuSn phase region. The growth of the phase followed a parabolic growth rate law, and the growth rate constant was found to be about 9 × 10^?15 cm²s^?1 at room temperature.     

Electrical control of the ferromagnetic phase transition in cobalt at room temperature

Electrical control of magnetic properties is crucial for device applications in the field of spintronics. Although the magnetic coercivity or anisotropy has been successfully controlled electrically in metals as well as in semiconductors, the electrical control of Curie temperature has been realized only in semiconductors at low temperature. Here, we demonstrate the room-temperature electrical control of the ferromagnetic phase transition in cobalt, one of the most representative transition-metal ferromagnets. Solid-state field effect devices consisting of a ultrathin cobalt film covered by a dielectric layer and a gate electrode were fabricated. We prove that the Curie temperature of cobalt can be changed by up to 12 K by applying a gate electric field of about ±2 MV cm(-1). The two-dimensionality of the cobalt film may be relevant to our observations. The demonstrated electric field effect in the ferromagnetic metal at room temperature is a significant step towards realizing future low-power magnetic applications.     

Spray synthesis of rapid recovery ZnO/polyaniline film ammonia sensor at room temperature

As an excellent room temperature sensing material, polyaniline (PANI) needs to be further investigated in the field of high sensitivity and sustainable gas sensors due to its long recovery time and difficulty to complete recovery. The ZnO/PANI film with p‒n heterogeneous energy levels have successfully prepared by spraying ZnO nanorod synthesized by hydrothermal method on the PANI film rapidly synthesized at the gas‒liquid interface. The presence of p‒n heterogeneous energy levels enables the ZnO/PANI film to detect 0.1‒100 ppm (1 ppm = 10⁻⁶) NH₃ at room temperature with the response value to 100 ppm NH₃ doubled (12.96) and the recovery time shortened to 1/5 (31.2 s). The ability of high response and fast recovery makes the ZnO/PANI film to be able to detect NH₃ at room temperature continuously. It provides a new idea for PANI to prepare sustainable room temperature sensor and promotes the development of room temperature sensor in public safety.     

Nanostructured ZnFe2O4 thick film as room temperature liquefied petroleum gas sensor

In the present work, thick film of nanostructured zinc ferrite was prepared by screen printing method and its liquefied petroleum gas (LPG) sensing properties were investigated. The structural and surface morphological characterisations of the sample were analysed by means of X-ray diffraction (XRD) and scanning electron microscopy (SEM). The minimum crystallite size of ZnFe₂O₄ calculated from Scherrer's formula is found to be 4 nm. SEM images exhibit the porous nature of the sensing material with a number of active sites. Optical characterisation of the film was carried out by ultraviolet–visible spectrophotometer. The estimated value of band gap of the film was found 1.91 eV. The LPG sensing properties of the zinc ferrite film were investigated at room temperature for different vol.% of LPG. The variations in electrical resistance of the film were measured with the exposure of LPG as a function of time. The maximum values of sensitivity and percentage sensor response were found 16 and 1785, respectively, for 5 vol.% of LPG. These experimental results show that nanostructured zinc ferrite is a promising material for LPG sensor.     

四方相纳米氧化锆低温稳定机制的研究现状

介绍了近几十年t-ZrO2纳米晶在室温下稳定机制的研究现状,并且重点分析表面能理论和氧空位理论等主要机制,在此基础上对镀膜、水蒸气、杂质离子、形核位置以及结构相似对其稳定性的影响进行进一步的讨论.     

A highly linear single p-n junction temperature sensor

A temperature sensor based on the use of two forward-biased p-n junctions is known to exhibit good linearity. An alternative sensor configuration, based on the same principle, but employing only one p-n junction is presented in this paper. The forward current through the p-n junction is switched alternately between two fixed values, and the difference between the corresponding voltages is shown to vary linearly with temperature. This scheme eliminates the problems associated with close matching required for the two p-n junction sensors. Experimental results obtained with the proposed scheme are presented. A configuration to exploit the temperature dependence of the p-n junction incremental resistance is also presented