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To obtain integrated and miniaturized gas sensors with low cost and power consumption to meet the increasing request of the internet of things industry and other relative areas, this work presented an in-situ compatible manufacturing and high-throughout strategy to deposit gas sensing film on a 5-inch wafer integrated with more than 10,000 MEMS micro-hotplates (MHP). The-state-of-art atomic layer deposition (ALD) was employed to fabricate controllably the uniform ZnO thin film (20 nm) on Micro-Electro-Mechanical Systems (MEMS) chips for constructing gas sensors. The ALD ZnO based MEMS sensors display excellent sensing performance, including very high sensitivity and selectivity to H2S with a limit of detection (LOD) on ppb level, good stability and quick response and recover dynamics under 70 mW of power dissipation. The sensing film has higher to 1300 times in mechanical strength than the traditional film from drop-coating. Furthermore, The ALD technique offers a facile in-situ strategy and high-throughput fabrication of MEMS gas sensors.

A p-n heterostructure has been proved as a good strategy to enhance the gas sensing performance of metal oxide semiconductor (MOS). Here, we reported a xylene gas sensor based on CuO/WO3 p-n hierarchical structure. CuO/WO3 were prepared by a two-step route. First, WO3 was synthesized by a reaction between CaWO4 and HNO3 under reaction condition was at 25˚C for 18 h, and then CuO/WO3 were prepared by immersion pyrolysis method. The prepared hierarchical CuO/WO3 hollow microspheres features an ordered assembly of two dimensional (2D) nanosheets with the thickness about 20 nm. Gas sensing tests displayed CuO/WO3 sensor had a good linearity property between the sensing responses and xylene concentrations range from 0.3 ppm to 50 ppm, and CuO/WO3 -3 (the mass ratio of CuO to WO3 is 3) sensor exhibited the highest response of 304.8 toward 20 ppm xylene gas at the optimal working temperature of 260˚C. Furthermore, it is obvious that CuO/WO3 -3 not only possessed superior response and recovery properties of 3 s and 6 s under 20 ppm xylene gas, respectively, but also showed outstanding selectivity and stability. The advantages of high sensitivity, simple manufacturing and outstanding selectivity indicate the promising application of CuO/WO3 xylene sensors in the field of air-quality and environmental monitoring, and p-n heterostructure can significantly enhance the gas-sensing performance of metal oxide semiconductor. Figure 1

Multi-shelled hollow micro/nanostructures materials preferentially possessing high surface area demand attention due to their expectable sensing performances. However, controlled synthesis of multi-shelled hollow micro/nanostructures remains quite challenging. In this work, multi-shelled hollow SnO2 microspheres with tunable interior structure were successfully prepared by using alkali-treated carbonaceous microspheres as the templates following with a calcination process. The single-, double-, and multi-shelled SnO2 hollow nanospheres were selectively tailored by the simple regulation of Tin precursors concentration, and used as sensing material in high-performance MEMS sensors. The gas sensitivity test results indicated that the multi-shelled architecture displayed significantly enhancing formaldehyde detection properties due to large specific surface area, abundant interfaces, thin shells, and high proportion porous structure, which acts synergistically to the gas adsorption quantity and transport rate. Figure 1

Since the increasing concerns of the great harm to human and environment caused by H2S, to develop effective methods to detect this toxic and hazardous gas has become more and more important. The MEMS gas sensor is portable and gives a lower power waste than the general metal-oxide-semiconductor sensor. To fabricate this kind of instrument, the material with high gas sensitivity is needed. In this study, Ni doped CeO2 nanoparticles were prepared by using a simple hydrothermal reaction method andthe sensing mechanism of H2S on the surface of the material was studied by in situ IR. It proved that Ni doped CeO2 nanoparticles has a lower operating temperature than pure CeO2, and a certain amount of Ni doping in CeO2 has improved its gas sensitivity and selectivity a lot to H2S gas.The response of the MEMS gas sensor to 1 ppm H2S gas can reach to 1.47 at 200°C and it can even be used to detect 20 ppb H2S effectively. Figure 1

Hydrogen sulfide (H2S), as a typical colorless, flammable and poisonous gas having rotten eggs smell, can paralyze the nervous and respiratory system and even lead to death. Therefore, developing a fast and highly sensitive H2S gas sensor is urgently required. Metal clusters feature small size structures, large surface areas and polymetallic centers, demonstrating giant potential on catalysis applications. Moreover, the high-density absorption sites make it easier for clusters to interact with target molecules. Here, we reported a novel H2S gas sensor based on a polynuclear cobalt cluster compound {Co32}. At the optimal working temperature of 200 ℃, the sensor based on {Co32} exhibits an outstanding H2S selectivity against other interfering gases, such as carbon monoxide, methane, and ethanol. In addition, it is of great importance to design low detection limit H2S sensor with fast response and recovery time. Gas sensitivity test results show the presented {Co32} gas sensor exhibits fast response and recovery of 15 s and 34 s under 100 ppb H2S, respectively. Moreover, the sensor also has a good linearity property from 20 ppb to 1000 ppb, good reproducibility and stability with time and under different humidity conditions. Prominently, the distinctive sensing performance of cobalt cluster for H2S promotes the development of metal clusters in the field of gas sensing. Figure 1

In recent years, design and synthesis of heterostructured nanomaterials with high gas-sensing performance for detection of flammable and toxic gases has attracted much research interest. In this paper, pristine and tourmaline-modified BiFeO3(BFO) nanomaterials were successfully synthesized via a sol-gel method. The BiFeO3 modified with tourmaline could remarkably enhance the gas response and exhibit some novel properties. The tourmaline/BiFeO3 3wt% (tourmaline/BiFeO3 composite with the 3wt% tourmaline) MEMS sensor exhibited temperature-dependent dual selectivity to CO at 150 °C and H2S at 225 °C. The tourmaline/BiFeO3 3wt% based MEMS sensor response toward 0.77 ppm of acetone (C3H6O) is 4.3 at 150 °C and toward 0.75 ppm of hydrogen sulfide (H2S) reaches 11.6 at 225 °C. Furthermore, the sensor possessed good repeatability and antihumidity interference. The dramatically improved sensing performance could be ascribed to the spontaneous polarity of tourmaline, the electron transfer was modulated by the heterojunction in the interface between the BiFeO3 and tourmaline nanostructure. The easy fabrication and good gas sensing performances make our sensors highly attractive for ultrasensitive C3H6O and H2S gas detection with less power consumption. Figure 1

In this paper, SnO2 nanospheres with a lot of defects (SnO2-D) were synthesized simply by annealing SnO2 at the different temperature (300 °C, 400 °C and 500 °C) in the hydrogen (H2) atmosphere. There are many oxygen vacancies in SnO2 due to reaction between H2 and oxygen when the SnO2 was exposed in H2 atmosphere. The X-ray photoelectron spectroscopy (XPS) and Electron paramagnetic resonance (EPR) analysis showed that there are abundant oxygen vacancies on the surface of the SnO2-D4 (with the optimal annealing temperature of SnO2 is 400 °C). The gas sensitivity test results show that sensor based on SnO2-D4 showed an ultra-sensitive H2 detection ability down to 1 ppm. Moreover, the response of the sensor fabricated with SnO2-D4 to 10 ppm H2 at the optimal operating temperature of 250 °C is as high as 2.7, which is about 2 times higher than that of the SnO2 sensor. The improved gas sensing properties can be attributed to generation of oxygen vacancies in the SnO2-D4. Our present results demonstrate that SnO2 with abundant oxygen vacancies can significantly to detect the ultra-low concentration H2 and the method of manufacturing oxygen vacancies defects has great potential in improving the gas-sensing performance of metal oxide semiconductor. Figure 1

Hydrogen sulfide（H2S）is a colorless and odorous gas. Abnormal H2S concentration may be related to Alzheimer's disease, ischemia, Down syndrome, bad breath and other diseases. Therefore, rapid、sensitive and highly selective detection of H2S is essential for the early diagnosis of these diseases. In the research, a two-dimensional nanosheet self-assembly structure based on NiO-V2O3 was developed to construct a high-performance H2S gas sensor. Morphological and structural characterization proved that the NiO-V2O3 composite is a three-dimensional flower-like porous microspheres self-assembled from two-dimensional nanosheets with high surface area and rich active sites. The sensor can quantitatively detect H2S gas at ppb level. When exposed to 500 ppb H2S gas at the optimal working temperature of 200°C, the highest response of the sensor is 65, and the response time and recovery time are 8 s and 25 s, respectively. The sensor also has excellent stability, moisture resistance and selectivity, and has a low detection limit (20 ppb). Considering these advantages, the NiO-V2O3 sensor is expected to be used for the detection of H2S in the early diagnosis of certain diseases. Figure 1

In this paper, tungsten oxide nanorods were successfully synthesized by using ordered mesoporous silica of SBA-15 as a template and 12-phosphotungstic acid as a precursor of tungsten oxide under a hydrogen (H2) atmosphere. XRD and HRTEM characterization show that the composition of tungsten oxide synthesized is WO2.83. The gas sensing test results show that WO2.83 can detect 5 ppb H2S. Moreover, the response of the sensor fabricated with WO2.83 to 200 ppb H2S at the optimal operating temperature of 280 °C is as high as 1.8, which is increased by nearly 50% than that of the common WO3 without redundant oxygen vacancies. The improved gas sensing properties can be attributed to rich oxygen vacancies in the WO2.83. Our present results also demonstrate that WO2.83 with a lot of oxygen vacancies can significantly enhance the gas response to ultra-low concentration H2S, and this method of manufacturing defects has great potential in improving the gas-sensing performance of metal oxide semiconductor. Figure 1

In this work, 1,3,6,8-tetrakis(4-formylphenyl)pyrene (TFPPy) was synthesized and used as polymer precursor, and then two kinds of fluorescent conjugated polymers (CPs) are synthesized through Schiff base reactions with two kinds of tri-amine as the other part of precursor, namely CPshu-1 and CPshu-2, respectively. By using D2h symmetry tetra-aldehyde and C3 symmetry tri-amine as precursors, aggregation-caused quenching (ACQ) of fluorophore can be reduced to minimum, to make the greatest fluorescent sensing performance. The resulting CPs were firstly characterized by Fourier transform infrared spectroscopy (FT-IR), solid-state 13C nuclear magnetic resonance (13C NMR). The morphology of resulting CPs were characterized by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Fluorescent spectra indicated that the sample showed orange luminescene at around 610nm. Before detecting the sensing performance, the CPs were firstly dispersed into acetonitrile to make a 1 mg/mL suspension, and the suspension showed a high sensitive to picric acid (PA). The suspension of CPshu-1 was totally quenched at a PA concentration of 5.2×10-4 M, and the limit of detection was calculated to be 3.18 ppm. For CPshu-2, the suspension was totally quenched at a PA concentration of 3.5×10-4 M, and the limit of detection was calculated to be 2.11 ppm. This work demonstrated that we can design 3D polymer structure to avoid ACQ negative effects, and build high performance fluorescent chemosensing materials. Introduction Fluorescent chemosensors is a kind of sensors which is attracting increasing attention from scientists. Aromatic π-electron conjugated polymers(CPs) is a very important kind of organic polymers used as fluorescent chemosensors due to the advantages of signal amplification, ease of device fabrication and the ability to combine different outputs. Although there has been a fast progress in the development of fluorescent CPs, there are still great requirements on materials with high efficiency, low cost, and eco-friendly, and also the design strategy of building CPs should also be developed. Making use of AIE and ACQ phenomena can rationally and tactfully enhance the fluorescene performance and avoid unexpected quenching, resulting in increasing importance for design strategy of fluorescent CPs. In this study 1,3,6,8-tetrakis(4-formylphenyl)pyrene (TFPPy) was used as fluorophore to build CPs through Schiff base reaction. The monomer of TFPPy was synthesized through a Suzuki coupling according to literature with a modified solvent condition. Two kinds of CPs named as CPshu-1 and CPshu-2, respectively, have been grown by solvothermal method using TFPPy as aldehyde monomer. The structures of both CPs were designed as 3D structure in which π-π stacking of fluorophores were avoided, decreasing the ACQ phenomenon to the minimum. The formation of CPs from the condensation reactions of the monomers was supported by FT-IR and 13C NMR spectra. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) indicated the rod-like morphology of resulting CPs, which could also prove the non-stacking structure of aromatic fluorophores. Furthermore the CPs were dispersed into acetonitrile and the suspension was used to detect picric acid. Both suspensions of CPshu-1 and CPshu-2 showed great chemical sensitive to picric acid, and the limit of detection (LOD) was 3.18ppm for CPshu-1, and 2.11ppm for CPshu-2, respectively. Figure 1

Noble metal is usually used to improve the gas sensing performance of metal oxide semiconductor (MOS) due to its better catalytic properties. In this work, we reported a synthesis of Pd/ZnO composite by an in situ reduction with ascorbic acid (AA). It was found that Pd/ZnO sensor has excellent selectivity to CO and the response of the Pd/ZnO sensor towards 100 ppm CO was as high as 15 (Ra/Rg), obviously higher than that of the pristine ZnO sensor (1.4) when the working temperature is 220 oC. Moreover, the pure ZnO sensor almost has no selectivity to Coal mine gas (CH4, CO and H2S), but the Pd/ZnO sensor has excellent selectivity to CO, which may be ascribed to the electronic sensitization of Pd. Our present results demonstrate that the Pd can significantly improve the gas-sensing performance of metal oxide semiconductor and the obtained sensor has great potential in monitoring coal mine gas. Figure 1

Monodispersed ZnSnO3 microspheres are successfully prepared via a facile microwave-assisted method combing with subsequently calcination treatment process. Powder X-ray diffraction (PXRD) results indicate that the structure of the products evolved from crystalline to amorphous with high-temperature treatments. Field emission scanning electron microscope (FESEM) and the transmission electron microscope (TEM) observations demonstrate that the as-obtained products are composed of uniform microspheres with rough surfaces and the mean diameter is measured as ~700 nm. Moreover, the morphology of ZnSnO3 microspheres can be well controlled by adjusting the ratio of Zn2+ and Sn4+. The gas sensing properties of ZnSnO3 microspheres with different ratios of Zn2+/Sn4+ are investigated. Our results indicate that the ZnSnO3 microspheres exhibit good selectivity and high sensitivity towards ethanol at the optimum working temperature of 230oC. When the sensor is exposed 50 ppm ethanol, the value of response reaches 47 and the response/recovery times are 11 s and 12 s, respectively. Figure 1

Introduction Single atom catalysts have draw increasing attention of enormous researchers due to its atomically disperation on supports, high efficiency and high catalytic performance. Despite those obvious advantages, there is still rare study about the single atom catalyst’s application in sensors. It was firstly reported the palladium single atoms on TiO2 used as a photocatalytic sensing platform to analyzed organophosphorus pesticide chlorpyrifos[1]. Catalyst-based sensing platform opens up a new pathway for exploring novel strategy of design sensors. Micro-electro-mechanical system (MEMS) process have advantages such as, miniaturization, small size, mechanical parts high resonance frequency, and low power consumption. However, the MEMS prepared by traditional method possess poor stability. Here, we employed the atomic layer deposition to prepare ZnO layer on MEMS. Atomic layer deposition (ALD) is a powerful technique for depositing nanoparticles or thin films and has outstanding advantages, including precise control of size and thickness and excellent uniformity[2], except that the substrate is exposed separately to each gaseous precursor and that the deposition is broken into cycles[3]. ALD functionalized method could gain high performance in thermal stability, mechanical and catalytic performance[4]. It was interesting to obtain single atom MEMS sensors via ALD. Method Prior to ALD, MEMS (Shanghai lingpan Electronic Technology Co., Ltd) were put into ethanol and cleaned by ultrasonic agitation for ten minutes. MEMS were put on quartz wafers and dried in air. ZnO films were deposited onto the MEMS by a hot-wall, closed-chamber ALD reactor. N2 (99.999%) was used as carrier gas. The precursors of ZnO were diethyl zinc and water (H2O). Water acts as an oxidant and enables growth over a wide temperature range. The deposition temperature was 150 °C, and the diethyl zinc was kept at room temperature. After the deposition of ZnO layers, Pt single atoms ALD was subsequently deposited with (methylcyclopentadienyl)trimethylplatinum (MeCpPtMe3) and O3 as precursors at the same temperature as our precious work[2]. Ultimately, the MEMS sensors were tested. Results and Conclusions Fig.1 Response performance for ALD SnO2 layer on MEMS It can be seen from the Fig.1 that sensor response increased with the concentration increase gradually. With the concentration increase for about 1 PPM, response value of sensors gradually reduced. It could also be seen that ALD ZnO sensor have a response time of 90 s and recovery time of 120 s. Baseline with drift less than 4 also demonstrated its good stability. It has little increase in response performance as the concentration increased to 80 PPM, it could be caused by the surface electron transfer arrived balance within high concentrations References [1] X. Ge, P. Zhou, Q. Zhang, Z. Xia, S. Chen, P. Gao, Z. Zhang, L. Gu, S. Guo, Palladium single atoms on TiO2 as a photocatalytic sensing platform for analyzing organophosphorus pesticide chlorpyrifos, Angew Chem Int Ed Engl, (2019). [2] Q. Hu, S. Wang, Z. Gao, Y. Li, Q. Zhang, Q. Xiang, Y. Qin, The precise decoration of Pt nanoparticles with Fe oxide by atomic layer deposition for the selective hydrogenation of cinnamaldehyde, Applied Catalysis B: Environmental, 218 (2017) 591-599. [3] Z. Gao, Y. Qin, Design and Properties of Confined Nanocatalysts by Atomic Layer Deposition, Acc Chem Res, 50 (2017) 2309-2316. [4] M.M. Biener, J. Biener, A. Wichmann, A. Wittstock, T.F. Baumann, M. Baumer, A.V. Hamza, ALD functionalized nanoporous gold: thermal stability, mechanical properties, and catalytic activity, Nano Lett, 11 (2011) 3085-3090. Figure 1

Fast, sensitive and stable detection of humidity is essential. In this paper, a 2D ultra-thin nanosheet Mxene was used as the material to form a sensitive film to construct the quartz crystal microbalance (QCM) humidity sensor by drop coating method. The element A in the MAX phase was dislodged by a simple liquid phase etching method. The morphology and composition of Mxene were studied by means of a series characterization methods, it was found the sample take on a ultrathin grapheme-like nanosheet. The test results show that the humidity sensor has 12.8Hz/% RH sensitivity, 6s and 2s (@ 90%)response/recovery time, maximum humidity hysteresis of 1.16%RH, good stability and selectivity. Finally, the adsorption enthalpy of water molecules on the surface of Mxene was explored by DFT calculation. It was found that residual F- played an important role in humitity sensing Introduction: The new two-dimensional (2D) material Mxene has been widely used in energy storage , battery , catalysis , electromagnetic shielding and other directions since it was discovered by the research team of Professor Yury Gogotsi of Drexel University in 2011.Ti3C2Tx has good electronic conductivity and hydrophilicity, it is the most widely studied and mature of all Mxenes. This work combines Mxene-Ti3C2Tx with the QCM test platform to further enhance the application of Mxene materials on humidity sensors. By optimizing the method in the previous literature, the Ti3AlC2 powder was etched in LiF / HCl solution to remove the Al element, some post-treatment such us ultrasonic was carry out to obtain a single-layer Ti3C2Tx solution that can be used to directly prepare the device. The obtained samples were characterized by XRD, SEM, TEM, EDS, XPS and BET, etc, it was found that Mxene with a large specific surface area has a good single-layer sheet structure, and the surface contains a large number of -OH, -O, -F functional groups. This single-layer sheet structure with large specific surface area and abundant active sites is more conducive to the adsorption of water molecules. By detecting the relative humidity of 11.3% - 97.3% shows that the sensor with the best performance has excellent sensitivity of 12.8Hz/% RH, 6s and 2s (@ 90%) rapid response/recovery time, maximum humidity hysteresis of 1.16%RH, good short-term repeatability, long-term stability, and excellent cross-sensitivity. Through characterization and simulation, it is found that -F functional group plays a certain role in the excellent humidity sensitivity. This not only provides a new possibility for the application of 2D materials in humidity sensor, but also widens the application of Mxene materials in sensor field. Figure 1

Volatile gas of triethylamine (TEA) may cause serious pollution to the environment and have a great impact on the respiratory system. Once inhaled into the lungs, it can cause pulmonary edema and even death. According to Occupational Safety and Health Administration (OSHA) regulation, the concentration of TEA allowed in air is limited to 10 ppm. Herein, we reported a TEA gas sensor, it can quantitatively detect on ppb level based on metal-organic frameworks-derived In2O3 hollow porous structure, which was successfully synthesized by calcinating the precursor In-MIL-68 at a suitable temperature 500˚C, and exhibited the highest response of 226 when exposed to 5 ppm TEA gas at the optimal working temperature 120˚C. Furthermore, In2O3-500 sensor not only possessed superior response and recovery properties of 9 s and 36 s under 5 ppm TEA gas, respectively, but also demonstrated outstanding selectivity, stability and moisture resistance. In addition, the In2O3-500 sensor exhibited the good response linearity within a wide TEA concentration range from 100 ppb to 5 ppm, and lower detection limit. Considering the superiority including facile fabrication, low cost and simple structure, In2O3-500 hollow porous structure is a promising candidate for high-performance TEA sensing applications. key words: Gas sensor, Triethylamine , In2O3, Metal-organic frameworks Figure 1

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In this paper, we report a novel porous silicon (PSi) process to realize controllable micro-to-nano scale features after FIB treatment. It is interested to notice that a “shielding area”, where the etching is enhancedly suppressed, exists around the patterns treated by FIB. This shielding area is ascribed to the secondary knocked-on effect during the FIB process. The diameter of shielding area has positive correlation to the voltage used in the FIB step. Also, the diameter of shielding area decreases when the resistivity of the silicon substrate declines. We achieved a shielding area with width of approximately 4μm on PSi. Typically, a circular feature of PSi with a diameter as large as 10μm is demonstrated for the first time, inside of which dramatically no pore appears at all while outside shielding area remains.