Performance Of Metal Oxide Semiconductor Research Articles

Persistently boosted TEA sensing performance of In2O3 hollow spheres by sequentially modified with Bi2O3 and Pt nanoparticles

Exploring rational and feasible strategies to boost the gas sensing performance of metal oxide semiconductor (MOS) has attracted a growing concern because it is an inevitable path for advanced gas sensor. Herein, a Bi2O3 and Pt co-modification approach was proposed to upgrade the triethylamine (TEA) sensing performance of In2O3. To expound it, a series of hollow spheres (HSs) with different compositions including In2O3, Bi2O3-modified In2O3 (Bi2O3/In2O3), and Bi2O3 and Pt co-modified In2O3 (Pt/Bi2O3/In2O3) were prepared through a solvothermal-calcination route combined with subsequent chemical reduction. After the evolution from In2O3 to binary Bi2O3/In2O3 and ternary Pt/Bi2O3/In2O3 composites, the sensor exhibited a persistently boosted sensing performance to TEA, particularly of higher sensitivity (increased from 0.0219 to 0.0369 and 1.0319/ppm within 1–30 ppm), better selectivity (STEA/Methane increased from 17.6 to 23.7 and 257.2), and faster response speed (response time decreased from 7 to 3 and 1 s for 100 ppm TEA). Additionally, the best Pt/Bi2O3/In2O3 sensor also presented good repeatability and stability. The sensitization effects of Pt and Bi2O3-In2O3 p-n heterojunction were discussed in detail.

ZnO nanowires decorated with Pt nanoclusters for selective detection of ppb-level nitrogen dioxide

Noble metal loading is an efficient way to improve the sensing performance of metal oxide semiconductor (MOS) gas sensors. In this work, platinum (Pt) nanoclusters loaded ZnO nanowires (Ptc-ZnO) were used to fabricate a NO2 sensor. Pure ZnO nanowires were prepared by a solvothermal method and Pt nanoclusters were loaded via a sacrificial templating route. The Ptc-ZnO based sensor with a trace of Pt loading (0.17 wt%) shows a high response to ppb-level NO2 (26.1–100 ppb), 4.4 times higher than that of pure ZnO. Additionally, it also exhibits excellent selectivity, low theoretical limit of detection (1.19 ppb) and good stability to humidity. The enhancing mechanism on gas sensing performance by Pt loading was discussed and investigated via HAADF-STEM, XPS, NO2-TPD and other methods. This work provides a way to develop gas sensor for ultralow NO2 concentration real-time detection.

Improving the sensing performance of rambutan-like W18O49 based gas sensor for n-butanol by Ni doping

Element doping can improve the gas sensing performance of metal oxide semiconductor (MOSs). In this paper, the rambutan-like Ni-doped W18O49 are synthesized by one-step solvothermal route. The prepared Ni0.05W18O49 possesses larger specific surface area (130.5 m2g−1) and more plentiful oxygen vacancy than the pristine sample. Interestingly, compared with other sensors, the Ni0.05W18O49 sensor has the highest response (182.4) for 50 ppm n-butanol at 160℃ with short response-recovery time (14 s / 241 s). Moreover, the selectivity test shows that the Ni0.05W18O49 sensor has higher response for n-butanol than the other five volatile gases. The response value of the sensor to n-butanol is almost unchanged over five repeatability tests and the long-term stability tests.

Epitaxial growth of Co3O4/In2O3 p-n heterostructure with rich oxygen vacancies for ultrahigh triethylamine sensing

Although metal oxides based gas sensors have been researched extensively in previous works, there are enormous challenges on improving the deficiencies in poor selectivity, sensitivity, humidity resistance and so on. Hence, we developed an epitaxial growth method to prepare dendritic Co3O4/In2O3-(1−3) heterostructures of distinct Co/In mass ratios through perfect lattice matching between the two crystal domains at the interface, along with introducing large amounts of oxygen vacancies. As a result, the Co3O4/In2O3-2 heterostructure based gas sensor showed enhanced sensing properties towards triethylamine (TEA, 100 ppm) with a high response value of Ra/Rg = 576.1 at an optimal working temperature of 200 °C, which is 93 times higher than that of pristine In2O3. Moreover, the Co3O4/In2O3-2 sensor exhibited excellent gas selectivity, quick recovery time, repeatable cycling, long-term stability, as well as outstanding humidity resistance. The improved TEA gas sensing performance can be attributed to the integration of interfacial synergies in Co3O4/In2O3 p-n heterostructure and generation of rich oxygen vacancies, exposing more active sites to facilitate the adsorption/desorption of gas molecules. This work provides a feasible pathway to regulate TEA sensing performance of metal oxide semiconductor (MOS) gas sensors by capitalizing on self-sacrificial template strategy and reconstruction of novel metal oxide heterostructure.

Regulating the electronic status on open WO2.83 surfaces for ultrasensitive H2S sensors

Engineering open nanostructures with regulable surface electron status possess great potential to increase gas-sensing performance of metal oxide semiconductor. Here, we develop a mesoporous tungsten oxide with special non-stoichiometric nature and double-activated surface electron status to realize ultralow-concentration detection of hydrogen sulfide. We found that the ordered mesoporous framework plays a crucial role in inducing the kinetic evolution to selectively form fixed non-stoichiometric meso-WO2.83 crystal, while the bulk-WO3 trends to lead the formation of bulk-WO2.9 or bulk-WO2.72 crystal. Impressively, the meso-WO2.83 crystal and co-existing oxygen defects exhibit obviously enhanced surface electron resonance and delocalization, thus leading a marked localized surface plasmon resonance (LSPR) effect. Further theoretical and experimental results confirm that the LSPR effect and oxygen defects endow special surface electron status to markedly improve the adsorption and electron transfer process of H2S molecules. The as-obtained meso-WO2.83 based MEMS sensors exhibit superior sensitivity, rapid response (<7 s), and ultralow detection limit of 5 ppb H2S. Our proposed strategy of open nanostructures with regulable surface electron status may create a new path to design fast and highly-effective H2S detection.

Boosting TEA sensing performance of ZnO porous hollow spheres via in situ construction of ZnS-ZnO heterojunction

Upgrading the gas sensing performance of metal oxide semiconductor (MOS) to meet the practical demands of MOS sensor for detecting various harmful gases is a significant issue in the field of environmental protection. Herein, we propose a sensitization strategy to improve the gas sensing performance of ZnO by in-situ construction of ZnS-ZnO n-n heterojunction. To expound this strategy, nanoscale ZnS-ZnO heterojunctions were homogeneously modified on self-synthesized ZnO porous hollow spheres (PHSs) by sulfurating them under hydrothermal condition. The achieved hybrid ZnS/ZnO PHSs are about 1–1.5 µm in diameter, whose shell is assembled by secondary nanoparticles with the size of 40–70 nm. The results of gas sensing tests indicated that after modification with ZnS-ZnO heterojunctions, the gas sensing performances of the ZnO PHS sensor to triethylamine (TEA) were remarkably improved, especially in terms of faster response speed (4 s for 100 ppm TEA), higher sensitivity (0.520/ppm for 1–30 ppm TEA) and better selectivity (STEA/acetone = 8.8). The ZnS-ZnO heterojunction-related sensitization mechanism was discussed in detail.

Highly sensitive and selective xylene sensor based on p-p heterojunctions composites derived from off-stoichiometric cobalt tungstate

Although the construction of heterojunctions between two different oxides is an attractive strategy to improve the sensing performance of metal oxide semiconductor (MOS) based gas sensors, there are few research reports focus on constructing p-p heterojunctions. Here we presented the sensitive material of p-p heterojunctions CoWO4-Co3O4 nanocomposites derived from off-stoichiometric cobalt tungstate which are prepared through facile hydrothermal method. Owing to the presence of p-p heterojunctions can modulate the hole accumulation layer, the control of nanoarchitecture is beneficial for gas adsorption/diffusion and surface sensing reaction, and the catalytic activity is effectively tuned. The CoWO4-Co3O4 based gas sensor showed higher response to xylene in ppb-level (300 ppb) at 200 °C, and negligible cross-responses to interfering gases such as ethanol (Sxylene/Sethanol = 6.6), and has the capacity of long-term stability and strong anti-humidity. The gas sensing characteristics are greater than those of previously reported cobalt tungstate based gas sensor. Accordingly, this work provides a new perspective of preparing high-performance gas sensor based on p-p heterojunctions composites.

Performance of NiO intercalated rGO nanocomposites for NH3 sensing at room temperature

NiO intercalated reduced graphene oxide nanocomposites (rGO/NiO NC’s) with different amounts of NiO nanoparticles (NP’s) were fabricated via solvothermal technique. NH3 gas sensors was measured at room temperature. The rGO/NiO NC’s appeared uniformly distributed NiO NP’s anchored to both sides of the rGO sheets. The NH3 gas sensing performance based on these rGO/NiO NC’s exhibited excellent both fast response and recovery times when exposed to 20 – 100 ppm of NH3. In addition, increasing the amount of NiO NP’s has an effect to the gas response ability, the response time and recovery time due to the enhancement of the active adsorption sites. Moreover, the 20% rGO/NiO NC’s presented a significant gas response of 4.14% to 100 ppm of NH3, taking 290 and 166 s for response time and recovery time, respectively. Besides, the rGO/NiO NC’s have an excellent long-term stability. Therefore, the rGO/NiO NC’s in this study can be efficiently used for NH3 detection at room temperature. From these results, they showed that the combination of NiO NP’s with the rGO would be a promising strategy for enhancing the NH3 sensing performance of metal oxide semiconductor (MOS) based devices at room temperature.

Ultrasensitive and Selective MEMS Xylene Gas Sensor Based on CuO/WO3 Hierarchical Structure

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

Ultra-Low Detection Limit MEMS Hydrogen Sensor Based on SnO2 Nanospheres with Lots of Defects

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

Ultra-Low Detection Limit MEMS Hydrogen Sulfide Sensor Based on Tungsten Oxide Nanorods with Lots of Oxygen Vacancies

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

Enhanced CO Sensing Properties of Pd Modified ZnO Porous Nanosheets

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

Enhanced CO sensing properties of Pd modified ZnO porous nanosheets

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 nanocomposite 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 °C. Moreover, the pure ZnO sensor almost has no selectivity to CO, 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.

PdPt Bimetal-Functionalized SnO2 Nanosheets: Controllable Synthesis and its Dual Selectivity for Detection of Carbon Monoxide and Methane

Bimetallic nanoparticles (NPs) usually exhibit some novel properties due to the synergistic effects of the two distinct metals, which is expected to play an important role in the field of gas sensing. PdPt bimetal NPs with Pd-rich shell and Pt-rich core were successfully synthesized and used to modify SnO2 nanosheets. The 1P-PdPt/SnO2-A sensor obtained by self-assemblies of PdPt NPs exhibited temperature-dependent dual selectivity to CO at 100 °C and CH4 at 320 °C. Furthermore, the sensor possessed good long term stability and antihumidity interference. The activation energy of adsorption for CO and CH4 were estimated by the temperature-dependent response process modeled using Langmuir adsorption kinetics, which proved that the lower activation energy of adsorption corresponded to better sensing performance. The gas-sensing mechanism based on the diffusion depth of the tested gas in the sensing layer was discussed. The dramatically improved sensing performance could be ascribed to the high catalytic activity of PdPt bimetal, the electron sensitization of PdO, and Schottky barrier-type junctions at the interface between SnO2 and PdPt NPs. Our present results demonstrate that bimetal NPs with special structure and components can significantly improve the gas-sensing performance of metal oxide semiconductor and the obtained sensor has great potential in monitoring coal mine gas.

Single-crystalline porous nanoplates-assembled ZnO hierarchical microstructure with superior TEA sensing properties

Fabricating hierarchical structures has emerged as a powerful strategy to improve the gas-sensing performance of metal oxide semiconductor (MOS). In this work, we reported the synthesis of a hierarchical microstructure (HMS) of ZnO via a reliable sacrificial template method and its superior sensing performance to triethylamine (TEA). The synthesized ZnO HMS features an orderly assembly of single-crystalline porous nanoplates with the mean thickness about 27.7 nm, on which island-like nanopores are in situ created during the decomposition of Zn5(CO3)2(OH)6 sacrificial template. At the optimal working temperature (OWT) of 270 °C, the detection limit of the sensor based on ZnO HMS to TEA is as low as 50 ppb, and the sensitivity towards 50–2000 ppb TEA is as high as 20.69/ppm. Besides, the sensor also exhibits excellent selectivity, rapid response-recover rate, and good response linearity within a wide TEA concentration range from 50 ppb to 300 ppm. These characteristics make the present ZnO HMS a promising candidate for practical detection of TEA. The gas sensing mechanism was discussed in detail.

Improved TEA sensing performance of ZnCo2O4 by structure evolution from porous nanorod to single-layer nanochain

Improving the gas sensing performance of metal oxide semiconductor (MOS) by structural modification has attracted intensive interest in the field of gas sensor. In this work, two kinds of ZnCo2O4 nanostructures, including porous nanorod (PNR) and single-layer nanochain (SLNC), were prepared by annealing pre-synthesized ZnC2O4/CoC2O4 hybrid nanorods at different temperatures. The ZnCo2O4 PNRs obtained at 350 °C were constructed by numerous densely stacked nanoparticles with the size about 7 nm. While, the ZnCo2O4 SLNCs obtained at 500 °C featured an assembly of nanoparticles with the size about 20 nm, and along the diameter direction there is only one layer of nanoparticles. It was found that through the structure evolution from PNR to SLNC, the specific surface area of the synthesized ZnCo2O4 was decreased from 91.6 m2/g (ZCO-350) to 24.7 m2/g (ZCO-500). However, the results of gas sensing tests indicated that the sensor fabricated with ZnCo2O4 SLNC showed an remarkable improvement of TEA sensing performance as compared with that fabricated with ZnCo2O4 PNR, especially in terms of response value and response/recover speed. Such abnormal relationship between specific surface area and gas sensing performance was attributed to the higher available surface area of ZnCo2O4 SLNC.

Synthesis of Co3O4/Ta2O5 heterostructure hollow nanospheres for enhanced room temperature ethanol gas sensor

Designing and constructing heterostrucutres is the trend of enhancing sensing performance of metal oxide semiconductor based gas sensors. A new kind of porous Co3O4/Ta2O5 heterostructure hollow nanospheres was successfully synthesized by the assistance of carbon colloidal nanospheres and following annealing. The Ta2O5 nanostructures with ultrathin hollow spherical shell (∼5 nm) were attached with numerous Co3O4 nanoparticles, forming heterojunction in the contact surface. The Ta2O5 hollow spheres act as the supporting model, hindering the aggregation of Co3O4 nanoparticles and possessing more specific surface area. For room temperature (25 °C) gas sensing application, the Co3O4/Ta2O5 hollow nanospheres exhibited outstanding ethanol detecting properties. The gas response toward 10, 20, 50, and 100 ppm of ethanol achieved 20%, 50%, 90% and 180%, respectively. The Co3O4/Ta2O5 hollow nanospheres also exhibited outstanding selectively and reliable stability, which can be attributed to the formation of the heterojunction in the contact surface of Co3O4 and Ta2O5, leading to the extension of electron depletion layer.

Understanding the Role of TiN Barrier Layer on Electrical Performance of MOS Device with ALD-TiN/ALD-TiAlC Metal Gate Stacks

The role of TiN barrier layer on electrical performance of metal oxide semiconductor (MOS) with Si/SiO2/HfO2/ALD-TiN/ALD-TiAlC structure is investigated. It is found that the effective workfunction of TiN/TiAlC decreases with thinner TiN (in the range of 0∼3 nm). This is attributed to the lower workfunction of thinner TiN. The gate leakage Jg of the MOS capacitor with TiN barrier is slightly higher than that without TiN, while the equivalent oxide thickness is smaller. The reason is that the insertion of TiN between TiAlC and HfO2 can suppress Al diffusion and boost Ti diffusion into HfO2, leading to smaller EOT and larger leakage current. Moreover, the Jg with and without TiN are both 6 orders of magnitude lower than the traditional poly-Si/SiO2 stacks, which are lower enough for their application in device. These results are helpful to engineering the gate stacks of MOSFET.

Wearout, Quasi Breakdown, and Annealing of Ultrathin Dielectrics Impact on Complementary Metal Oxide Semiconductor Performance and Reliability

Wearout, Quasi Breakdown, and Annealing of Ultrathin Dielectrics Impact on Complementary Metal Oxide Semiconductor Performance and Reliability