射频反应磁控溅射掺杂MWCNTs的SnO2薄膜NO2气敏传感器的研究

采用射频反应磁控溅射方法制备了氧化锡/多壁碳纳米管（SnO2/MWCNTs）薄膜材料,并在此基础上研制NO2气敏传感器。采用X射线衍射仪（XRD）、X光电子能谱仪（XPS）、扫描电子显微镜（SEM）来研究WO3/MWCNTs材料的表面形貌、表面化学状态、表面化学元素等材料特性,研究结果表明MWCNTs已经掺杂进SnO2材料,合成的SnO2/MWCNTs气敏传感器表现出对低浓度（甚至低于10ppb）的NO2气体有较高的灵敏度和较好的反应-恢复特性,并解释了该传感器的工作机理是基于pn结（P型MWCNTs和N型SnO2)作用的结果。     

新型NO2薄膜气敏元件的研究

采用射频反应磁控溅射方法制备了氧化钨/多壁碳纳米管(WO3/MWCNTs)薄膜材料,并在此基础上研制NO2气敏元件.采用X射线衍射仪(XRD)、X光电子能谱仪(XPS)、扫描电子显微镜(SEM)来研究WO3/MWCNTs材料的表面形貌、表面化学状态、表面化学元素等材料特性.研究结果表明,MWCNTs已经掺杂进WO3材料,合成的WO3/MWCNTs气敏元件表现出对NO2气体有较高的灵敏度和较好的响应-恢复特性,并解释了该元件的工作机理.     

Sb掺杂SnO2/SiO2纳米光学气敏薄膜的制备及其性质

采用溶胶凝胶(sol-gel)工艺制备了Sb掺杂SnO2/SiO2复合膜。通过X射线衍射(XRD)、傅立叶变换红外谱(FT-IR)及原子力显微镜(AFM)表征了薄膜样品的物相结构与表面形貌,利用紫外-可见光谱研究了复合薄膜光学特性．利用p-偏振光双面反射法对薄膜的气敏特性进行了测试。实验结果表明,薄膜中的晶粒具有纳米尺寸(～35nm)的大小．比表面积大,孔隙率高;薄膜的透光率高,可见光波段近95％;纳米Sb：SnO2：SiO2复合膜的气敏灵敏度高于纯SnO2薄膜及Sb掺杂的SnO2薄膜。     

CTAB辅助合成氧化钨及其对乙二醇甲醚的气敏特性

以十六烷基三甲基溴化铵(CTAB)为表面活性剂,二水合钨酸钠(Na₂WO₄·2H₂O)为钨源,采用水热法合成纳米氧化钨(WO₃)。通过扫描电子显微镜(SEM)、X射线衍射仪(XRD)和X射线光电子能谱仪(XPS)对WO₃的表面形貌、晶体结构和化学成分进行表征,测试其对乙二醇甲醚的气敏特性,研究CTAB对WO₃的形貌、晶体结构和乙二醇甲醚气敏特性的影响。结果表明,CTAB可调控WO₃的形貌,添加质量分数5%的CTAB不仅将WO₃的形貌由不规则的纳米颗粒调控为疏松的纳米片状,而且提高了其对乙二醇甲醚的气敏特性,在最佳工作温度370℃下其对体积分数为1×10^-4的乙二醇甲醚的响应值达15.1,并且具有良好的重复性、长期稳定性与气体选择性。最后探讨了WO₃对乙二醇甲醚的气敏机理。     

薄膜厚度对钛酸钡类薄膜传感器敏感特性的影响

利用氩离子束溅射技术,分别在SiO2/Si衬底上淀积了0.5 mm、1 mm和2 mm的Ba1-xLaxNbyTi1–yO3薄膜,并探讨了薄膜厚度对MIS电容湿敏特性的影响以及薄膜厚度对薄膜电阻的光敏和热敏特性的影响。实验结果表明:0.5 mm膜厚的MIS电容传感器具有比2 mm膜厚的MIS电容传感器高9倍的湿敏灵敏度。用孔隙率和孔径分布物理模型分析得出,薄膜越薄,膜的孔隙率越高,器件的湿敏灵敏度越高。反之,薄膜越厚,光吸收越强,薄膜电阻的光敏灵敏度越高;但薄膜厚度对薄膜电阻热敏特性的影响甚微,敏感机理与薄膜的微观结构可解释这些现象。     

Sb∶SnO2/SiO2纳米复合薄膜的光学及气敏特性

采用溶胶 凝胶 (sol gel)工艺制备了Sb∶SnO2 /SiO2 复合膜。通过原子力显微镜 (AFM )观察了薄膜样品的表面形貌 ,利用紫外 可见光谱 ,p 偏振光反射比角谱研究了复合薄膜的光学特性。结果表明 ,薄膜中的晶粒具有纳米尺寸 (～ 35nm)的大小 ,比表面积大 ,孔隙率高 ;薄膜的透光率高 ,可见光波段近 95 % ;其光学禁带宽度约 3 6 7eV。因此Sb∶SnO2 /SiO2 纳米复合膜可作为气敏薄膜的理想选择。通过对三种不同的气体C3 H8,C2 H5OH及NH3气敏特性的测试表明 ,Sb掺杂大大提高了SnO2 薄膜对C2 H5OH的灵敏度 ,纳米Sb∶SnO2 /SiO2 复合膜的气敏灵敏度高于纯SnO2 薄膜及Sb掺杂的SnO2 薄膜     

溅射和激光淀积的ZnO多晶薄膜的结构和发光性质

我们分别通过直流反应溅射及脉冲激光淀积法制备了ZnO多晶薄膜。X射线衍射结果显示出薄膜的c轴取向。原子力显微镜证实薄膜的多晶结构。两种方法制备的ZnO在光子激发下都发射较强的带边荧光。绿色荧光未被观察到。激光淀积在(001)硅表面的ZnO的发光源自“自由激子”辐射。激光淀积在(0001)氧化铝晶体表面的ZnO的发光机制则在相当宽的激发强度范围内都呈现出电子．空穴等离子体(electron-hole plasma)的复合特性。     

在硅衬底上用HFCVD法生长的纳米SiC薄膜及其室温光致发光

用热丝化学汽相淀积(HFCVD)法在硅衬底上生长具有纳米晶粒结构的碳化硅薄膜.用X射线光电子谱仪(XPS)、X射线衍射(XRD)、傅里叶红外吸收光谱(FTIR)、紫外光Raman散射谱和高分辨透射电子显微镜(HRTEM)对薄膜样品进行了结构和组分分析,并在室温条件下观察到了薄膜的高强度可见光发射.     

在硅衬底上用HFCVD法生长的纳米SiC薄膜及其室温光致发光

用热丝化学汽相淀积(HFCVD)法在硅衬底上生长具有纳米晶粒结构的碳化硅薄膜.用X射线光电子谱仪(XPS)、X射线衍射(XRD)、傅里叶红外吸收光谱(FTIR)、紫外光Raman散射谱和高分辨透射电子显微镜(HRTEM)对薄膜样品进行了结构和组分分析,并在室温条件下观察到了薄膜的高强度可见光发射.     

掺杂纳米SnO2气敏传感器的研究进展

介绍了半导体气敏传感器的发展历史和掺杂纳米SnO2气敏传感器的特性与应用;详细分析了掺杂金属单质、金属氧化物和稀土元素对SnO2气敏性的影响,通过掺杂可以显著改善其对特定气体的灵敏度、稳定性和选择性等参数;利用元件表面的氧吸附理论分析掺杂纳米SnO2的气敏机理;展望了SnO2气敏传感器的发展前景.     

Nano-WO3 film modified macro-porous silicon（MPS） gas sensor

We prepared macro-porous silicon（MPS） by electrochemical corrosion in a double-tank cell on the surface of single-crystalline P-type silicon.Then,nano-WO₃ films were deposited on MPS layers by DC facing target reactive magnetron sputtering.The morphologies of the MPS and WO₃/MPS samples were investigated by using a field emission scanning electron microscope.The crystallization of WO₃ and the valence of the W in the WO₃/MPS sample were characterized by X-ray diffraction and X-ray photoelectron spectroscopy,respectively. The gas sensing properties of MPS and WO₃/MPS gas sensors were thoroughly measured at room temperature. It can be concluded that:the WO₃/MPS gas sensor shows the gas sensing properties of a P-type semiconductor gas sensor.The WO₃/MPS gas sensor exhibits good recovery characteristics and repeatability to 1 ppm NO₂.The addition of WO₃ can enhance the sensitivity of MPS to NO₂.The long-term stability of a WO₃/MPS gas sensor is better than that of an MPS gas sensor.The sensitivity of the WO₃/MPS gas sensor to NO₂ is higher than that to NH₃ and C₂H₅OH.The selectivity of the MPS to NO₂ is modified by deposited nano-WO₃ film.     

Nitrogen dioxide (NO2) sensing performance of p-polypyrrole/n-tungsten oxide hybrid nanocomposites at room temperature

Polypyrrole (PPy)–tungsten oxide (WO₃) hybrid nanocomposite have been successfully synthesized using different weight percentages of tungsten oxide (10–50%) dispersed in polypyrrole matrix by solid state synthesis method. The sensor based on PPy–WO₃ was fabricated on glass substrate using cost effective spin coating method for detection of NO₂ gas in the low concentration range of 5–100 ppm. The gas sensing performance of hybrid material was studied and compared with those of pure PPy and WO₃. It was found that PPy–WO₃ hybrid nanocomposite sensor can complement the drawbacks of pure PPy and WO₃. The structure, morphology and surface composition properties of PPy–WO₃ hybrid nanocomposites were employed by X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, field emission scanning electron microscopy (FESEM), Transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). The presence of WO₃ in PPy matrix and their interaction was confirmed using XRD, FTIR techniques. The porous surface morphology was observed with addition of WO₃ in PPy matrix which is useful morphology for gas sensing applications. TEM image of PPy–WO₃ hybrid nanocomposites shows the average diameter of 80–90 nm. X-ray photoelectron spectroscopy (XPS) was used to characterize the chemical composition of nanocomposites. It was observed that 50% WO₃ loaded PPy sensor operating at room temperature exhibit maximum response of 61% towards 100 ppm of NO₂ gas and able to detect low concentration of 5 ppm NO₂ gas with reasonable response of 8%. The hybrid sensor shows better sensitivity, selectivity, reproducibility and stability compared to pure PPy and WO₃. The proposed sensing mechanism of hybrid nanocomposite in presence of air and NO₂ atmosphere was discussed with the help of energy band diagram. Furthermore, the interaction of NO₂ gas with PPy–WO₃ hybrid nanocomposites sensor was studied by cole–cole plot using impedance spectroscopy.     

Room temperature NO2 gas sensing properties of DBSA doped PPy–WO3 hybrid nanocomposite sensor

We demonstrate the chemiresistive NO₂ gas sensor based on DBSA doped PPy–WO₃ hybrid nanocomposites operating at room temperature. The sensor was fabricated on glass substrate using simple and cost effective drop casting method. The gas sensing performance of sensor was studied for various toxic/flammable analytes like NO₂, C₂H₅OH, CH₃OH, H₂S and NH₃. The sensor shows higher selectivity towards NO₂ gas with 72% response at 100 ppm. Also the sensor can successfully detect low concentration of NO₂ gas upto 5 ppm with reasonable response of 12%. Structural, morphological and compositional analyses evidenced the successful formation of DBSA doped PPy–WO₃ hybrid nanocomposite with uniform dispersion of DBSA into PPy–WO₃ hybrid nanocomposite and enhance the gas sensing behavior. We demonstrated that DBSA doped PPy–WO₃ hybrid nanocomposite sensor films shows excellent reproducibility, high stability, moderate response and recovery time for NO₂ gas in the concentration range of 5–100 ppm. A gas sensing mechanism based on the formation of random nano p–n junctions distributed over the surface of the sensor film has been proposed. In addition modulation of depletion width takes place in sensor on interaction with the target NO₂ gas has been depicted on the basis of schematic energy band diagram. Impedance spectroscopy was employed to study bulk, grain boundary resistance and capacitance before and after exposure of NO₂ gas. The structural and intermolecular interaction within the hybrid nanocomposites were explored by Raman and X-ray photoelectron spectroscopy (XPS), while field emission scanning electron microscopy (FESEM) was used to characterize surface morphology. The present method can be extended to fabricate other organic dopent-conducting polymer–metal oxide hybrid nanocomposite materials and could find better application in the gas sensing.     

Enhanced ammonia sensing characteristics of tungsten oxide decorated polyaniline hybrid nanocomposites

Polyaniline (PAni)-tungsten oxide (WO₃) hybrid nanocomposites sensor have been lucratively synthesized by in-situ chemical oxidative polymerization method by entrapping tungsten oxide nanoparticles (10–50%) in the polyaniline matrix on precleaned glass substrate. The structural, morphological and surface composition elucidation of PAni-WO₃ hybrid nanocomposites were explored by X-ray diffraction (XRD) technique, field emission scanning electron microscopy (FESEM) and X-ray photoelectron spectroscopy (XPS). The existence of WO₃ in PAni matrix and interaction between them was confirmed using XRD and Raman spectroscopy. The incorporation of WO₃ nanoparticles into the PAni matrix introduces porosity which enhanced gas sensing properties. The TEM image of PAni-WO₃ hybrid nanocomposite film exploded the average diameter of WO₃ nanoparticles ranging from 40 to 50 nm. Chemical composition of PAni-WO₃ hybrid nanocomposites was characterized by using X-ray photoelectron spectroscopy (XPS). In order to investigate the gas sensing parameter of PAni-WO₃ hybrid nanocomposite, hybrid nanocomposite film was exposed to different oxidizing gases (Cl₂, NO₂) and reducing gases (NH₃, H₂S, CH₃OH, C₂H₅OH) in range 5–100 ppm concentration of gas. It was observed that the sensors of PAni-WO₃ hybrid nanocomposites showed better sensitivity, selectivity, stability and reproducibility compared to pure PAni and pure WO₃. PAni-WO₃ (50%) hybrid nanocomposite sensor operating at room temperature reveals maximum response of 158% towards 100 ppm of NH₃ gas and also capable to respond very little concentration of 5 ppm NH₃ gas with reasonable response of 24%. The gas sensing mechanism of the nanocomposites in presence of air and with target NH₃ gas atmosphere was discussed in detail with the help of energy band diagram. The interaction of NH₃ and NO₂ gas with PAni-WO₃ hybrid nanocomposite sensor was investigated by employing an impedance spectroscopy also.     

Synthesis and Characterization of Chromium‐Doped Mesoporous Tungsten Oxide for Gas Sensing Applications

SBA‐15 (2D hexagonal structure) and KIT‐6 (3D cubic structure) silica materials are used as templates for the synthesis of two different crystalline mesoporous WO₃ replicas usable as NO₂ gas sensors. High‐resolution transmission electron microscopy (HRTEM) studies reveal that single‐crystal hexagonal rings set up the atomic morphology of the WO₃ KIT‐6 replica, whereas the SBA‐15 replica is composed of randomly oriented nanoparticles. A model capable of explaining the KIT‐6 replica mesostructure is described. A small amount of chromium is added to the WO₃ matrix in order to enhance sensor response. It is demonstrated that chromium does not form clusters, but well‐distributed centers. Pure WO₃ KIT‐6 replica displays a higher response rate as well as a lower response time to NO₂ gas than the SBA‐15 replica. This behavior is explained by taking into account that the KIT‐6 replica has a higher surface area as demonstrated by Brunauer–Emmett–Teller analyses and its mesostructure is fully maintained after the screen‐printing step involved in sensors preparation. The presence of chromium in the material results in a shorter response time and improved sensor response to the lowest NO₂ concentrations tested. Electrical differences related to mesostructure are reduced as a result of additive introduction.     

Polypyrrole, α-Fe2O3 and their hybrid nanocomposite sensor: An impedance spectroscopy study

Polypyrrole (PPy), α-Fe₂O₃ and their hybrid nanocomposites have been successfully prepared using chemical polymerization, sol–gel and solid state synthesis method respectively. Films of PPy, α-Fe₂O₃ and PPy/α-Fe₂O₃ nanocomposites were deposited on glass substrates using spin coating technique and characterized using FTIR, XPS, FESEM, TEM techniques as well as their gas sensing performance were studied towards NO₂ gas. FTIR and XPS study confirms the formation of PPy, α-Fe₂O₃ and PPy/α-Fe₂O₃ hybrid nanocomposites. FESEM studies revealed that, the films consists of porous granular type of morphology. TEM analysis revealed that the hybrid composite is in nano range. Impedance spectroscopy studies in presence of air and after exposure of NO₂ gas were carried out on PPy, α-Fe₂O₃ and PPy/α-Fe₂O₃ hybrid nanocomposite films in the frequency range of 20 Hz–10 MHz. Impedance spectroscopy results demonstrate that, the impedance is mainly contributed by the potential barrier at grain boundaries of the films. With the help of impedance spectroscopy results, sensing mechanism between PPy, α-Fe₂O₃ and PPy/α-Fe₂O₃ hybrid nanocomposite films and NO₂ gas molecules was studied and explored.     

High Surface Area MoS2/Graphene Hybrid Aerogel for Ultrasensitive NO2 Detection

A MoS₂/graphene hybrid aerogel synthesized with two‐dimensional MoS₂ sheets coating a high surface area graphene aerogel scaffold is characterized and used for ultrasensitive NO₂ detection. The combination of graphene and MoS₂ leads to improved sensing properties with the graphene scaffold providing high specific surface area and high electrical and thermal conductivity and the single to few‐layer MoS₂ sheets providing high sensitivity and selectivity to NO₂. The hybrid aerogel is integrated onto a low‐power microheater platform to probe the gas sensing performance. At room temperature, the sensor exhibits an ultralow detection limit of 50 ppb NO₂. By heating the material to 200 °C, the response and recovery times to reach 90% of the final signal decrease to <1 min, while retaining the low detection limit. The MoS₂/graphene hybrid also shows good selectivity for NO₂ against H₂ and CO, especially when compared to bare graphene aerogel. The unique structure of the hybrid aerogel is responsible for the ultrasensitive, selective, and fast NO₂ sensing. The improved sensing performance of this hybrid aerogel also suggests the possibility of other 2D material combinations for further sensing applications.     

Microstructure and Characteristics of Thin-Film La<Subscript>0.8</Subscript>Sr<Subscript>0.2</Subscript>Co<Subscript>0.5</Subscript>Ni<Subscript>0.5</Subscript>O<Subscript>3</Subscript>/ZnO:Al Heterocontact CO Sensors Prepared by RF Magnetron Sputtering

Highly sensitive CO gas sensors based on heterocontacts of ZnO:Al on La_0.8Sr_0.2Co_0.5Ni_0.5O₃ (LSCNO) were fabricated successfully. La_0.8Sr_0.2Co_0.5Ni_0.5O₃ thin films were coated on (100) silicon wafers by a sol-gel method including the Pechini process followed by a spin-coating procedure. Then, ZnO:Al films prepared by radiofrequency (RF) magnetron sputtering at various oxygen partial pressures and deposited on as-deposited La_0.8Sr_0.2Co_0.5Ni_0.5O₃ films were investigated. The results revealed that the CO sensing ability of the film prepared with the ratio of O₂/Ar = 5/5 (ratio of volume flow rate) was the worst, owing to the highest (002) plane orientation in the ZnO:Al film. In contrast, the ZnO:Al film prepared with O₂/Ar = 3/7 exhibited better CO sensitivity. Furthermore, all two-layer samples showed higher CO sensitivities than single-layer samples. The CO sensitivity of ZnO:Al/La_0.8Sr_0.2Co_0.5Ni_0.5O₃ thin film was 45% for 500 ppm CO at a sensing temperature of 200°C.     

Surface morphology dependent tungsten oxide thin films as toxic gas sensor

Tungsten oxide (WO₃) films are of great importance in gas sensing technology due to its selectivity towards toxic gases. In this paper, structural, morphological and compositional properties of spray deposited and chemical vapor deposited WO₃ thin films were investigated using XRD, TEM, SEM, EDAX and Raman spectroscopy. These films have monoclinic crystal structure; and a filamentous network surface for spray deposited films whereas small flake-shaped microstructure was observed on the surface of chemical vapor deposited films. These films were studied for their gas sensing ability towards toxic gases like ammonia (NH₃) and sulphur dioxide (SO₂) as a function of temperature and concentration. Response-recovery characteristics were studied by varying gas concentration. The spray deposited films displayed higher gas response than the chemical vapor deposited films whereas the later exhibited lower optimum operating temperature as well as faster response and recovery. A correlation between the morphological, compositional, electrical and gas sensing properties of these films is also established.     

In Situ Formation of Multiple Schottky Barriers in a Ti3C2 MXene Film and its Application in Highly Sensitive Gas Sensors

The main gas‐sensing mechanisms of 2D materials are surface charge transfer by analytes and Schottky barrier (SB) modulation at the interface between the metallic and semiconducting surfaces. In particular, dramatic differences in the gas‐sensing performances of 2D materials originate from SB modulation. However, SB sites typically exist only at the interface between the semiconducting channel material and the metal electrode. Herein, in situ formed multiple SBs in a single gas‐sensing channel are demonstrated, which are derived from the heterojunction of metallic Ti₃C₂ and semiconducting TiO₂. In stark contrast with previous techniques, edge‐oxidized Ti₃C₂ flakes are synthesized by solution oxidation, allowing the uniform formation of TiO₂ crystals on all flakes that comprise the gas sensing channel. Oxidized colloidal solutions are subjected to vacuum filtration to automatically form SB sites at the multiple inter‐flake junctions in both the outer surface and inner bulk regions of the film. The TiO₂/Ti₃C₂ composite sensor shows 13.7 times higher NO₂ sensitivity as compared with pristine Ti₃C₂ MXene, while the responses of the reducing gases are almost unchanged. The results suggest a new strategy for improving gas‐sensing performance by maximizing the density of SB sites through a simple method.