A highly sensitive chemical gas detecting transistor based on highly crystalline CVD-grown MoSe<Subscript>2</Subscript> films

Layered semiconductors with atomic thicknesses are becoming increasingly important as active elements in high-performance electronic devices owing to their high carrier mobilities,large surface-to-volume ratios,and rapid electrical responses to their surrounding environments.Here,we report the first implementation of a highly sensitive chemical-vapor-deposition-grown multilayer MoSe2 field-effect transistor (FET) in a NO2 gas sensor.This sensor exhibited ultra-high sensitivity (S =ca.1,907 for NO2 at 300 ppm),real-time response,and rapid on-off switching.The high sensitivity of our MoSe2 gas sensor is attributed to changes in the gap states near the valence band induced by the NO2 gas absorbed in the MoSe2,which leads to a significant increase in hole current in the off-state regime.Device modeling and quantum transport simulations revealed that the variation of gap states with NO2 concentration is the key mechanism in a MoSe2 FET-based NO2 gas sensor.This comprehensive study,which addresses material growth,device fabrication,characterization,and device simulations,not only indicates the utility of MoSe2 FETs for high-performance chemical sensors,but also establishes a fundamental understanding of how surface chemistry influences carrier transport in layered semiconductor devices.     

Effect of thickness on nanostructured SnO2 thin films by spray pyrolysis as highly sensitive H2S gas sensor

Nanostructured SnO2 thin films were prepared by spray pyrolysis technique onto glass substrates with different thickness by varying quantity of precursor solution. The structural, optical and electrical properties of these films have been studied. The crystallographic structure of the films was studied by X-ray diffraction (XRD). It is found that the films are tetragonal with (110) orientation. The grain size increases with thickness. Atomic Force Microscopy (AFM) showed that the nanocrystalline nature of the films with porous nature. The grain size increased 14 to 29 nm with increase in film thickness. The studies on the optical properties show that the direct band gap value decreases from 3.75 to 3.50 eV. The temperature dependence of the electrical conductivity was studied. The activation energies of the films are calculated from the conductance temperature characteristics. The nanostructured SnO2 thin films were used as sensing layers for resistive gas sensors. The dependence of gas sensing properties on the thickness of SnO2 thin films was investigated. The gas response of the SnO2 thin films towards the H2S gas was determined at an operating temperature of 150 degrees C. The sensitivity towards H2S gas is strongly depending on surface morphology of the SnO2 thin films.     

Template-free to fabricate highly sensitive and selective acetone gas sensor based on WO3 microspheres

In this paper, we described how WO₃ microspheres have been synthesized by a simple hydrothermal treatment from the precursor of Na₂WO₄ and CO (NH₂)₂ at 160 °C for 3 h. The sample was characterized by X-ray diffraction (XRD), energy dispersive spectrum (EDS), scanning electronic microscopy (SEM), transmission electronic microscopy (TEM), high resolution transmission electronic microscopy (HRTEM), selected area electron diffraction (SAED), and X-ray photoelectron spectroscopy (XPS). Obtained results indicated that the average diameter of the as-prepared WO₃ microspheres is ∼1 μm with orthorhombic phase. The WO₃ microspheres are constructed of polycrystalline WO₃ nanoparticles. The thickness of the WO₃ coating of the gas sensor is ∼2 μm. The WO₃-based gas sensor exhibited a good sensitivity and high selectivity to acetone vapor at 200 °C. A possible mechanism for the acetone vapor gas sensing was proposed.     

Influence of additives on the morphological,phase and chemical characteristics of gas sensitive SnO2 sprayed films

The morphology, and also the chemical and phase composition of sprayed SnO₂ films doped with Cu, Zr, Fe and P have been investigated. It was found that in general, the film morphology was characterized by a fine grained basic layer with a few large crystallites located on the surface. All the doping elements decreased the grain size in the basic layer. For Fe, Zr and P the grain size depended on the doping level in the spray solution. It was established that the dopant: Sn ratio in the films was much lower than that in the spray solution. The doping element was preferentially accomodated in the large crystallites with only a small quantity of the dopant being introduced into the basic layer. The gas sensing properties of the films have are discussed on the basis of these results.     

Fabrication and highly sensitive gas sensors based on h-MoO3/SnO2 hollow nanostructures operated at low temperatures

Simulated by the synthesis of one dimensional hollow nanostructures with significant sensing, electrical, and optical properties, we have successfully synthesized 1D hollow nanostructures of h-MoO3/SnO2 with well-defined multi-side walls. These hollow nanostructured materials synthesized via a hydrothermal method with SnCl2.2H2O as the precursor and h-MoO3 as the template. SnO2 nanoparticles grew on the surface of h-MoO3 with preferential direction [001]. The morphological change was observed with variation of the growth conditions, such as HNO3, and h-MoO3 concentration. 1D hollow nanostructures of h-MoO3/SnO2 were studied and their growth mechanism was discussed. The result revealed that the existence of h-MoO3 caused to increase the sensor response to ethanol gas and downshift the sensor operating temperature at low temperatures.     

A highly sensitive nuclear recoil detector based on superfluid3He-B

The excitations in superfluid³He have a dispersion curve in which the energy minimum does not coincide with the momentum minimum. As a result, when a mechanical resonator moves through a gas of such excitations, normal and Andreev scattering processes introduce a large asymmetry into the momentum exchange and the mechanical resonator experiences a very large drag force. A gas of such excitations is thus very easy to detect even at very low densities. We have exploited this effect to monitor the increase in excitation density in a small volume caused by a particle interaction. The working volume is filled with superfluid³He-B at around 100 K. A particle undergoing an interaction in the volume releases a shower of quasiparticle excitations which can be detected by the increase in damping on a vibrating wire resonator. A small hole in the container allows the excitations to leak out into the outside colder liquid to reset the working liquid to the resting state. Using an existing experiment we can detect nuclear recoil interactions depositing energies as low as 500 eV. Two simple modifications should allow us to detect interactions in the 10 eV range.     

A theoretical study of gas adsorption on tin arsenic and its application as a highly sensitive NO2 sensor

Journal of Materials Science - The sensing performance of tin arsenic (SnAs) monolayer with adsorption of different gas molecules at room temperature was systematically investigated by the...     

A nitrite sensor based on a highly sensitive nitrite reductase mediator-coupled amperometric detection

Highly sensitive nitrite sensors have been developed for the first time based on mediator-modified electrodes. Tetraheme cytochrome c nitrite reductase from Sulfurospirillum deleyianum and cytochrome cd(1) nitrite reductase from Paracoccus denitrificans are able to accept electrons from artificial electron donors, which simultaneously act as electron mediators between the enzyme and an amperometric electrode. In addition to methyl viologen, redox-active compounds such as phenazines (phenosafranin, safranin T, N-methylphenazinium, 1-methoxy-N-methylphenazinium) and triarylmethane redox dyes (bromphenol blue and red) were selected from a range of redox compounds exhibiting the most efficient performance for nitrite detection. After precipitation, the electron mediators were incorporated in a graphite electrode material. Enzyme immobilization is performed by entrapment in a poly(carbamoyl sulfonate) (PCS) hydrogel. Diffusion coefficients and apparent heterogeneous rate constants of the mediators as well as homogeneous rate constants of nitrite sensors were determined by chronoamperometry and cyclic voltammetry. The phenosafranin-modified electrode layered with the PCS hydrogel immobilization of tetraheme cytochrome c nitrite reductase yielded linear current responses up to 250 μM nitrite with a sensitivity of 446.5 mA M(-)(1) cm(-)(2). The detection limit of the enzymatic nitrite sensor was found to be 1 μM nitrite.     

A highly sensitive, dual-readout assay based on gold nanoparticles for organophosphorus and carbamate pesticides

This report presents a highly sensitive, rhodamine B-covered gold nanoparticle (RB-AuNP) -based assay with dual readouts (colorimetric and fluorometric) for detecting organophosphorus and carbamate pesticides in complex solutions. The detection mechanism is based on the fact that these pesticides can inhibit the activity of acetylcholinesterase (AChE), thus preventing the generation of thiocholine (which turns the RB-AuNP solutions blue and unquenches the fluorescence of RB simultaneously). The color of the RB-AuNP solution remains red and the fluorescence of RB remains quenched. By use of this dual-readout assay, the lowest detectable concentrations for several kinds of pesticides including carbaryl, diazinon, malathion, and phorate were measured to be 0.1, 0.1, 0.3, and 1 μg/L, respectively, all of which are much lower than the maximum residue limits (MRL) as reported in the European Union pesticides database as well as those from the U.S. Department Agriculture (USDA). This assay allows detection of pesticides in real samples such as agricultural products and river water. The results in detecting pesticide residues collected from food samples via this method agree well with those from high-performance liquid chromatography (HPLC). This simple assay is therefore suitable for sensing pesticides in complex samples, especially in combination with other portable platforms.     

A novel NO/sub 2/ gas sensor based on Bis[phthalocyaninato] samarium complex/silicon hybrid charge-flow transistor

A new kind of sandwich-like bis[2,3,9,10,16,17,23,24-octakis(octyloxy)phthalocyaninato] samarium complex Sm[Pc/sup */]/sub 2/(Pc/sup */=Pc(OC/sub 8/H/sub 17/)/sub 8/) is used as film-forming material. Pure Sm[Pc/sup */]/sub 2/ and mixture of Sm[Pc/sup */]/sub 2/ and octadecanol(OA) deposited from both pure water and 10/sup -4/M Cd/sup 2+/ subphases are investigated. It is found that a mixture of 1:3 Sm[Pc/sup */]/sub 2/:OA forms an excellent material for the fabrication of the gas-sensing Langmuir-Blodgett (LB) film by studying the film-forming characteristics. A new gas sensor has been fabricated by incorporating the multilayer LB film into the gate electrode of a metal-oxide-semiconductor field effect transistor, forming an array of charge-flow transistor. On the application of a gate voltage (V/sub GS/), greater than the threshold voltage (V/sub TH/), a delay was observed in the response of the drain current. This is due to the time taken for the resistive gas-sensing film to charge up to V/sub GS/. This delay characteristic was found to depend on the concentration of NO/sub 2/. Results are presented showing that the device can detect reversibly the concentration of NO/sub 2/ gas down to 5 ppm at room temperature.     

基于WO3薄膜的双声路声表面波型SO2气体传感器

以金属钨粉,H2O2,CH3OH和PVP(聚乙烯吡咯烷酮)为原料,利用热喷射方法在双声路声表面波器件的测量声路上制作了细微多网孔状WO3薄膜,提出并实现了一种在常温下可以实现对二氧化硫(SO2)气体进行物理吸附和解吸附的基于WO3薄膜的双声路声表面波型SO2气体传感器.声表面波器件的双声路结构消除了由于外界测量条件改变引起的测量误差,也进一步提高了传感器的可靠性和准确性.实验结果表明,该传感器具有好的重复性,在测量范围内对各种浓度的SO2气体具有好的响应特性;传感器在0.5ppm到20ppm浓度范围内的线性灵敏度大约为6.8KHz/ppm.     

基于半透膜的钻井液油气分离检测技术

在钻井过程中,录井对钻井液油气的检测是发现和评价油气层重要手段之一,定量获取油气组分信息是有效评价油气层和油气性质的基础.目前录井气测技术所检测的烃组分通常由电动脱气器获得,受钻井液温度、液面高度和黏度的影响较大,所获得的油气定量信息较少,影响了油气解释与评价的准确性.半透膜对油气具有选择性分离的特性,能直接从钻井液中获取烃类组分,能够为油气解释与评价提供定量的基础信息.通过对半透膜和气体分离技术的研究,制备适合现场油气分离要求的半透膜,并在此基础上研制了半透膜油气分离装置,通过稳定性和灵敏度、耐温和抗冲击性能试验,以及钻井现场的应用,其结果证明了该半透膜钻井液油气分离装置适用于钻井现场的油气检测,扩展了油气检测内容,丰富了油气评价信息.     

Phase transitions in adsorbed films V: Perturbational approach to adsorption on crystalline solids

Monolayer adsorption of simple gases on crystalline solids is discussed using a perturbational approach. The effects of the periodicity of the gas-solid potential on various phase transitions occurring in adsorbed films are considered. In particular, we discuss monolayer films of hard disk (HD) and Lennard-Jones (LJ) fluids formed on a triangular (graphite-like) lattice. It is found that non-uniformity of the gas-solid potential does not influence the gas-liquid transition but leads to a considerable lowering of the freezing point in both HD and LJ films. Moreover, we discuss the effects of an increase in density on the localized-to-mobile transition.     

Development of a specific and highly sensitive optical chemical sensor for determination of Hg(II) based on a new synthesized ionophore

A novel optode for determination of Hg(II) ions is developed based on immobilization of a recently synthesized ionophore, 7-(1H-imidazol-1-ylmethyl)-5,6,7,8,9,10-hexahydro-2H-1,13,4,7,10 benzodioxatriaza cyclopentadecine-3,11(4H,12H)-dione, in a PVC membrane. Dioctyl sebacate was used as a plasticizer, sodium tetraphenylborate as an anionic additive and ETH5294 as a chromoionophore. The response of the optode was based on the complexation of Hg(II) with the ionophore in the membrane phase, resulting an ion exchange process between Hg(II) in the sample solution and H⁺ in the membrane. The effects of pH and amounts of the ionophore, chromoionophore, ionic additive and type of plasticizer on the optode response were investigated. The selectivity of the optode was studied in the present of several cations. The optode has a linear response to Hg(II) in the range of 7.2 × 10^? 13–4.7 × 10^? 4 mol L^? 1 with detection limit of 0.18 pmol L^? 1. The optode was successfully applied to the determination of Hg(II) in real samples.     

Graft copolymer-templated mesoporous TiO(2) films micropatterned with poly(ethylene glycol) hydrogel: novel platform for highly sensitive protein microarrays

In this study, we describe the use of organized mesoporous titanium oxide (TiO(2)) films as three-dimensional templates for protein microarrays with enhanced protein loading capacity and detection sensitivity. Multilayered mesoporous TiO(2) films with high porosity and good connectivity were synthesized using a graft copolymer consisting of a poly(vinyl chloride) (PVC) backbone and poly(oxyethylene methacrylate) (POEM) side chains as a structure-directing template. The average pore size and thickness of the TiO(2) films were 50-70 nm and 1.5 μm, respectively. Proteins were covalently immobilized onto mesoporous TiO(2) film via 3-aminopropyltriethoxysilane (APTES), and protein loading onto TiO(2) films was about four times greater than on planar glass substrates, which consequently improved the protein activity. Micropatterned mesoporous TiO(2) substrates were prepared by fabricating poly(ethylene glycol) (PEG) hydrogel microstructures on TiO(2) films using photolithography. Because of non-adhesiveness of PEG hydrogel towards proteins, proteins were selectively immobilized onto surface-modified mesoporous TiO(2) region, creating protein microarray. Specific binding assay between streptavidin/biotin and between PSA/anti-PSA demonstrated that the mesoporous TiO(2)-based protein microarrays yielded higher fluorescence signals and were more sensitive with lower detection limits than microarrays based on planar glass slides.     

Hall effect measurements in gas sensors based on nanosized Os-doped sol-gel derived SnO/sub 2/ thin films

The influence of dopants on the electrical properties of gas sensitive layers used in semiconductor gas sensors has to be carefully understood for getting a deeper insight in the relationship between the sensor performance and its chemical composition. In this work, undoped and Os-doped SnO/sub 2/ thin films have been prepared by the sol-gel process with an Os-Sn atomic ratio of 5%. The films have been characterized by resistivity and Hall effect measurements in a temperature range from 100 K to 500 K, both in air and in vacuum. The results have been investigated according to grain boundary scattering mechanism. We found that in air, the ambient oxygen species adsorbed on the film increase the height of the grain boundary barriers and the activation energy for the electrical conductivity increases in the doped film. In vacuum, the results showed that the height of the intergranular barrier is lower than the corresponding value in air. Both in air and in vacuum, the conductivity of the Os-doped sample is higher than the value in the undoped SnO/sub 2/ sample. The same occurs for the Hall mobility and the carrier concentration. The experimental results have been used to explain the better methane sensitivity, at low temperature, of the Os-doped films as compared with the undoped ones.     

Perhydropolysilazane-derived silica-polymethylmethacrylate hybrid thin films highly doped with spiropyran: Effects of polymethylmethacrylate on the hardness, chemical durability and photochromic properties

Polymethylmethacrylate (PMMA)-perhydropolysilazane (PHPS) hybrid thin films doped with spiropyran were prepared by spin-coating, which were then converted into 0.26-1.7 μm thick, spiropyran-doped PMMA-silica hybrid films by exposure treatment over aqueous ammonia. The spiropyran/(spiropyran + PHPS + PMMA) mass ratio was fixed at a high value of 0.2 so that the films exhibit visual photochromic changes in color, while the PMMA/(PMMA + PHPS) mass ratio, r, was varied. The spiropyran molecules in the as-prepared films were in merocyanine (MC) and spiro (SP) forms, with and without an optical absorption at 500 nm, at low (r ≤ 0.2) and high (r ≥ 0.4) PMMA contents, respectively. When PMMA content r was increased from 0 to 0.2, the degree of the MC-to-SP conversion on vis light illumination was enhanced, while at higher r's the spiropyran molecules underwent photodegradation. When the silica film (r = 0) was soaked in xylene under vis light, the spiropyran molecules were almost totally leached out, while not on soaking in the dark. On the other hand, no leaching occurred for the film of r = 0.2 either in the presence or absence of vis light. These suggest that the introduction of PMMA is effective in improving the chemical durability of the films, while the silica film (r = 0) is an interesting material with a photoresponsive controlled-release ability. The pencil hardness of the films decreased with increasing PMMA content, but remained over 9H at r ≤ 0.4.