Electronic Sensitization Effect Research Articles

Switching and control mechanism between p-type and n-type in SnO2 nanorods using laser with added convex lens to control oxygen concentrations

In a significant advancement, a novel technology has been developed to precisely control the electronic sensitization of SnO2 nanorods. This control is accomplished in a matter of seconds through the external injection of energy via laser and convex lens pairs (LCP). Utilizing LCP, selective redox reactions can be induced on the surface of SnO2 nanorods. The study focused on the contrasting effects of NO2, an oxidizing gas, and H2, a reducing gas. In the presence of NO2, the electronic sensitization caused by LCP outweighs the chemical sensitization due to NO2, thereby resulting in both n-type and p-type behaviors. In contrast, when exposed to H2, the nanorods exhibit only n-type behavior, as the chemical sensitization effect of H2 is more significant than the electronic sensitization effect of LCP. The observed variations in electronic properties can be systematically accounted for by the differential bonding energies between oxidizing and reducing gases.

Formation of large-scale MoS2/Cu2O/ZnO heterostructure arrays by in situ photodeposition and application for ppb-level NO2 gas sensing

Photodeposition has been used extensively for nanomaterial growth on a substrate, but direct photodeposition of 2D transition metal dichalcogenides (TMDs) remains challenging. An alternative approach is to deposit 2D TMDs on a suitable nanomaterial template. In this work, large-scale MoS2/Cu2O/ZnO heterostructure arrays are formed by low-temperature in situ photodeposition and the nanocomposites are used for chemiresistive gas sensing at room temperature. Using 254 nm UV irradiation, Cu2O nanoclusters are photodeposited in solution on hydrothermally grown ZnO nanorod arrays and Cu2O/ZnO heterostructure arrays are first formed. MoS2 nanoparticles are subsequently photodeposited on Cu2O and MoS2/Cu2O/ZnO heterostructure arrays with good uniformity on a sub-millimeter scale are consequently produced. The ternary nanocomposite with a 45 min MoS2 photodeposition time shows the highest response of 890% toward 500 ppb NO2 under UV-activated sensing. An excellent linear sensitivity of 18.7 ppm–1 has been achieved and the estimated lowest detection limit is 1.3 ppb, exhibiting good potential for monitoring of environmental NO2 content. The outstanding performance is attributed to the combined chemical and electronic sensitization effects of the abundant heterojunctions in the nanocomposite. The present work reveals that facile in situ photodeposition is suitable for synthesis of large-scale MoS2/Cu2O/ZnO heterostructure arrays with remarkable gas sensing performance.

Au/CuO/Cu2O heterostructures for conductometric triethylamine gas sensing

Au decorated CuO/Cu2O composite was synthesized using a water bath method. Surface characterization results show that the materials are composed of needle-like nanoarchitectures. Cu and Au elements are uniformly distributed to form heterojunctions in the interfaces of CuO, Cu2O and Au. Gas sensing characterization results indicate that CuO/Cu2O composite exhibits enhanced response of 45.5–100 ppm triethylamine (TEA) gas at 160 ℃ and Au decoration dramatically improves its TEA gas sensing performance to 261.8 at 180 ℃. It also shows enhanced sensing selectivity as well as long-term stability. It is illustrated that the good gas sensing performance is attributed to the multi-heterojunctions in those materials. The heterojunction of CuO and Cu2O forms an accumulation layer of holes in copper oxide composite, which will be depleted by introduced reducing gas, further improving the response. Moreover, after decorating Au nanoparticles (NPs), the synergy effect between Au/CuO, Au/Cu2O, and CuO/Cu2O multi-heterojunctions induce an electronic sensitization effect, which facilitate the surface oxygen adsorptions and provide a larger content of adsorbed oxygen species, dramatically enhancing the response to analyte gas. The synthesis strategy presented in this work could benefit the development of highly sensitive gas sensors in the future.

Ag nanoparticles modified Fe3O4/reduced graphene oxide and their acetone sensing properties

Exhaled acetone in the non-invasive diagnosis of type Ⅰ diabetes is one of the representative biomarkers. In this work, the Ag nanoparticles (NPs) modified Fe3O4/rGO composites was synthesized through a simple hydrothermal reaction, which could be a potential acetone sensor for painless and rapid breathing analysis. Through SEM and TEM, it was found that Ag nanoparticles were uniformly distributed on the surface of rGO sheets embedded in rod-shaped Fe3O4. Compared with the matrix material, the Ag/Fe3O4/rGO sensor shows good selectivity to acetone, and the cross-response to interfering gases (methane, toluene, ammonia, ethanol) is negligible. Meanwhile, the Ag0.1/Fe3O4/rGO sensor shows an ultra-high response of 35.81–50 ppm acetone at 220 °C, which is 2.5 times higher than that of pure Fe3O4/rGO. The improvement of Ag/Fe3O4/rGO nanomaterial in acetone sensing properties comes from the chemical and electronic sensitization effects of Ag nanoparticles, and this nanostructure generates more oxygen species and active sites, and improves the gas response. As a result, Ag0.1/Fe3O4/rGO has a good response and selectivity to acetone vapor, indicating its potential application in breath acetone analysis.

An efficient hydrogen gas sensor based on hierarchical Ag/ZnO hollow microstructures

The design of hierarchical zinc oxide (ZnO) microstructures modified with silver (Ag) nanoparticles have emerged as an effective approach for improving the hydrogen gas sensing performance. Here, we report a simple, low-cost chemical co-precipitation method to obtain the Ag/ZnO hollow microstructures and morphologically characterized them by field emission scanning electron microscopy (FESEM). FESEM images revealed the clear hollow hexagonal tube-like morphology. The existence of Ag in ZnO was confirmed by X-ray diffraction (XRD) and energy-dispersive X-ray spectroscopy (EDS). UV visible absorption and photoluminescence (PL) spectra were also recorded to observe the effect of Ag nanofiller on the optical properties of ZnO. Furthermore, the gas sensing properties of the as-prepared bare ZnO and Ag/ZnO sensor were investigated. The thoroughly sensing experiments demonstrated that after modification with Ag nanoparticles the ZnO sensor shows superior sensitivity 479 % towards 300 ppm hydrogen gas concentration, whereas 101 % response was noted for the pure ZnO sensor at 250 °C working temperature. Meanwhile, Ag/ZnO hybrids exhibited excellent selectivity, fast response, and recovery time and also obtained a good and stable response signal at 5 ppm H2 exposure, which indicated that the lower concentration measurement is also attainable. This enhancement in the sensing performance of Ag/ZnO structures towards hydrogen is due to the chemical and electronic sensitization effect of Ag nanoparticles. As a result, such microstructure is attributed to more oxygen species and active sites, and it enhances the sensitivity of a sensor. Moreover, this type of hybrid opens a new path and supports the next generation of innovative materials to fabricate highly selective and sensitive H2 gas sensing devices.

Room temperature ammonia sensing performances of pure and Sn doped β-Ga2O3

Sn, being an excellent donor, has been doped into β-Ga2O3 lattice through hydrothermal method at 2 mol% and 4 mol% concentrations. Prior to this, Sn is primarily doped into Gallium.Oxy Hydrate (GaOOH) which is then thermally treated and transformed into β-Ga2O3. The obtained samples were characterized by TGA, XRD, SEM, EDAX, TEM, XPS, UV–Visible spectroscopy and BET surface analysis to assess their structural, morphological, optical and surface properties. Pure and Sn doped samples were used for room temperature NH3 vapour sensing. Among all samples, 2 mol% Sn doped sample showed enhanced sensing capability due to its prosperous materialistic properties attained through optimum doping into host material. Humidity dependent sensing studies have been done for 2 mol% Sn doped β-Ga2O3. Humidity mediated and oxygen mediated sensing mechanisms along with chemical & electronic sensitization effects of Sn in favor of enhanced room temperature NH3 sensing have been proposed. Short-term stability studies at room temperature have been performed on 2 mol% Sn doped β-Ga2O3 at 200 ppm of NH3 exposure for a period of 10 consecutive days and found with good stability.

Surface Activity-Tuned Metal Oxide Chemiresistor: Toward Direct and Quantitative Halitosis Diagnosis.

Continuous monitoring of hydrogen sulfide (H2S) in human breath for early stage diagnosis of halitosis is of great significance for prevention of dental diseases. However, fabrication of a highly selective and sensitive H2S gas sensor material still remains a challenge, and direct analysis of real breath samples has not been properly attempted, to the best of our knowledge. To address the issue, herein, we introduce facile cofunctionalization of WO3 nanofibers with alkaline metal (Na) and noble metal (Pt) catalysts via the simple addition of sodium chloride (NaCl) and Pt nanoparticles (NPs), followed by electrospinning process. The Na-doping and Pt NPs decoration in WO3 grains induces the partial evolution of the Na2W4O13 phase, causing the buildup of Pt/Na2W4O13/WO3 multi-interface heterojunctions that selectively interacts with sulfur-containing species. As a result, we achieved the highest-ranked sensing performances, that is, response (Rair/Rgas) = 780 @ 1 ppm and selectivity (RH2S/REtOH) = 277 against 1 ppm ethanol, among the chemiresistor-based H2S sensors, owing to the synergistic chemical and electronic sensitization effects of the Pt NP/Na compound cocatalysts. The as-prepared sensing layer was proven to be practically effective for direct, and quantitative halitosis analysis based on the correlation (accuracy = 86.3%) between the H2S concentration measured using the direct breath signals obtained by our test device (80 cases) and gas chromatography. This study offers possibilities for direct, highly reliable and rapid detection of H2S in real human breath without the need of any collection or filtering equipment.

Chemical and Electronic Sensitization Effects Promoted By Noble Metal Nanoparticles on Gas Sensors Based on SnO Nanobelts

IntroductionSemiconducting metal oxides (SMOx) are the most studied materials for gas sensing applications due to their outstanding capacity to detect flammable and toxic gases, and their low-cost processing and ease of handling. [1,2]Many strategies have been developed attempting to achieve materials with improved sensor performance, including surface functionalization. The most common SMOx surface functionalization species are noble metal nanoparticles (NPs) given the possibilities to present both chemical and electronic sensitization effects.[3]This work reports on the gas sensing response of pristine and Pt and Pd decorated stannous oxide nanobelts. The responses of devices to different analytes (H2, CO and NO2) were measured in dry air baseline atmosphere as function of the analyte concentration (1–1000 ppm) and temperature (150-350 °C). Method Stannous oxide nanobelts were synthesized by a carbothermal reduction method using a mixture of SnO2 powder (Sigma-Aldrich, 99.9% purity) and carbon black (Union Carbide, > 99% purity) in the molar ratio of 1.5:1 (SnO2:C) as starting material.[4] The nanoparticles (Pt and Pd) used to functionalize the surface of nanobelts were prepared by the polyol method.Samples were characterized by field-emission scanning electron microscopy (SEM) and transmission electron microscopy (TEM) to study their morphology and crystalline structure.Suspensions of pristine and functionalized materials were deposited onto interdigitated platinum electrode arrays to perform the gas sensor measurements. The devices were placed in a temperature-controlled tubular furnace chamber, where the electric current was monitored under a constant applied voltage. Synthetic dry air was used as baseline and the analytes (NO2, H2 and CO) were introduced into the chamber using mass flow controllers. Gas sensor measurements were performed ranging from 150 °C to 350 °C. Results and Conclusions SEM and TEM results showed that obtained materials were nanobelts in the SnO phase. Moreover, functionalization with noble metal nanoparticles was successful, presenting disperse nanoparticles (< 15 nm) over nanobelts surface.About the gas sensing measurements, pristine devices are both sensitive and selective for nitrogen dioxide (NO2) molecules between 100 and 250 °C. In addition, both Pd- and Pt- functionalized devices present excellent selectivity to H2 at 300 and 350 °C. Moreover, Pt- functionalized device presented good selectivity for high concentrations of CO (>200 ppm) at low temperatures (100 and 150 °C). Then, results showed that noble metal decorated devices exhibited enhanced chemical sensitization, resulting in increased sensitivity upon exposure to reducing gases at different working temperatures. Differences in enhancement levels are attributed to strong electronic sensitization effects that are dependent on the respective Pt and Pd work functions and the unique SnO band structure, characterized by a small band gap (0.6 eV). Values showed that while Pt0 and Pt2+ promotes a high potential barrier with SnO nanobelts, Pd0 does not have this effect. Based on these findings, we propose an array based on pristine and NPs-functionalized SnO structures capable of detecting and distinguishing reducing and oxidizing gases. Furthermore, electronic sensitization mechanism is elucidated based on the band diagram of materials.Results presented here are important to engineer high performance sensor devices by selecting the better work function of nanoparticles, depending on the Fermi level of semiconductor.

Facile synthesis of Pd@ZnO core@shell nanoparticles for selective ethanol detection

In this work, we reported a high-performance ethanol gas sensor based on novel Pd@ZnO core@shell nanoparticles (CSNPs). The Pd@ZnO CSNPs were synthesized by chemical method and characterized by XRD, TEM and EDS techniques. Gas sensing results demonstrated that Pd@ZnO CSNPs show high sensitivity and remarkable selectivity towards ethanol at 250 °C. The response value of Pd@ZnO CSNPs is 152, which is almost six times higher than the response value (27) of ZnO NPs at 250 °C. The mechanism of enhancement in sensing properties can be ascribed to the chemical and electronic sensitization effect of Pd NPs and also due to the unique core@shell structure. These characteristics may shed light on the development of a selective ethanol sensor based on Pd@ZnO CSNPs.

Electrospun ZnO/Pd Nanofibers: CO Sensing and Humidity Effect.

Variable air humidity affects the characteristics of semiconductor metal oxides, which complicates the reliable and reproducible determination of CO content in ambient air by resistive gas sensors. In this work, we determined the sensor properties of electrospun ZnO and ZnO/Pd nanofibers in the detection of CO in dry and humid air, and investigated the sensing mechanism. The microstructure of the samples, palladium content, and oxidation state, type, and concentration of surface groups were characterized using complementary techniques: X-ray fluorescent spectroscopy, XRD, high-resolution transmission electron microscopy (HRTEM), high angle annular dark field scanning transmission electron microscopy (HAADF-STEM), energy-dispersive X-ray (EDX) mapping, XPS, and FTIR spectroscopy. The sensor properties of ZnO and ZnO/Pd nanofibers were studied at 100–450 °C in the concentration range of 5–15 ppm CO in dry (RH25 = 0%) and humid (RH25 = 60%) air. It was found that under humid conditions, ZnO completely loses its sensitivity to CO, while ZnO/Pd retains a high sensor response. On the basis of in situ diffuse reflectance IR Fourier transform spectroscopy (DRIFTS) results, it was concluded that high sensor response of ZnO/Pd nanofibers in dry and humid air was due to the electronic sensitization effect, which was not influenced by humidity change.

Chemical and Electronic Sensitization Effects Promoted By Noble Metal Nanoparticles on Gas Sensors Based on SnO Nanobelts

IntroductionSemiconducting metal oxides (SMOx) are the most studied materials for gas sensing applications due to their outstanding capacity to detect flammable and toxic gases, and their low-cost processing and ease of handling. [1,2]Many strategies have been developed attempting to achieve materials with improved sensor performance, including surface functionalization. The most common SMOx surface functionalization species are noble metal nanoparticles (NPs) given the possibilities to present both chemical and electronic sensitization effects.[3]This work reports on the gas sensing response of pristine and Pt and Pd decorated stannous oxide nanobelts. The responses of devices to different analytes (H2, CO and NO2) were measured in dry air baseline atmosphere as function of the analyte concentration (1–1000 ppm) and temperature (150-350 °C). Method Stannous oxide nanobelts were synthesized by a carbothermal reduction method using a mixture of SnO2 powder (Sigma-Aldrich, 99.9% purity) and carbon black (Union Carbide, > 99% purity) in the molar ratio of 1.5:1 (SnO2:C) as starting material.[4] The nanoparticles (Pt and Pd) used to functionalize the surface of nanobelts were prepared by the polyol method.Samples were characterized by field-emission scanning electron microscopy (SEM) and transmission electron microscopy (TEM) to study their morphology and crystalline structure.Suspensions of pristine and functionalized materials were deposited onto interdigitated platinum electrode arrays to perform the gas sensor measurements. The devices were placed in a temperature-controlled tubular furnace chamber, where the electric current was monitored under a constant applied voltage. Synthetic dry air was used as baseline and the analytes (NO2, H2 and CO) were introduced into the chamber using mass flow controllers. Gas sensor measurements were performed ranging from 150 °C to 350 °C. Results and Conclusions SEM and TEM results showed that obtained materials were nanobelts in the SnO phase. Moreover, functionalization with noble metal nanoparticles was successful, presenting disperse nanoparticles (< 15 nm) over nanobelts surface.About the gas sensing measurements, pristine devices are both sensitive and selective for nitrogen dioxide (NO2) molecules between 100 and 250 °C. In addition, both Pd- and Pt- functionalized devices present excellent selectivity to H2 at 300 and 350 °C. Moreover, Pt- functionalized device presented good selectivity for high concentrations of CO (>200 ppm) at low temperatures (100 and 150 °C). Then, results showed that noble metal decorated devices exhibited enhanced chemical sensitization, resulting in increased sensitivity upon exposure to reducing gases at different working temperatures. Differences in enhancement levels are attributed to strong electronic sensitization effects that are dependent on the respective Pt and Pd work functions and the unique SnO band structure, characterized by a small band gap (0.6 eV). Values showed that while Pt0 and Pt2+ promotes a high potential barrier with SnO nanobelts, Pd0 does not have this effect. Based on these findings, we propose an array based on pristine and NPs-functionalized SnO structures capable of detecting and distinguishing reducing and oxidizing gases. Furthermore, electronic sensitization mechanism is elucidated based on the band diagram of materials.Results presented here are important to engineer high performance sensor devices by selecting the better work function of nanoparticles, depending on the Fermi level of semiconductor.

In situ deposited hierarchical CuO/NiO nanowall arrays film sensor with enhanced gas sensing performance to H2S

Hierarchical and heterogeneous CuO/NiO nanowall arrays were in situ grown on ceramic tubes via a facile template-free hydrothermal route, and then were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and nitrogen adsorption–desorption techniques. The resultant composites exhibit network-like CuO/NiO array structures constructed by interconnected porous nanosheets, in which the decoration of CuO nanoparticles in NiO nanowall arrays was confirmed by XRD, XPS and TEM analyses. The 2.84 at % CuO decorated NiO sensor exhibits excellent sensing properties at 133 °C. The response to 5 ppm H2S attains 36.9, which increases as high as 5.6 times compared to the NiO one. The detection limit to H2S is further decreased from 1 ppb for the pure NiO sensor to 0.5 ppb. The CuO/NiO sensor shows a wide linear range from 50 to 1000 ppb, good repeatability, selectivity and long-term stability, which is expected to be a candidate for ppb-level H2S detection in real and complex environment of industrial production. Furthermore, the dominant H2S sensing mechanism is discussed from the view of the homo- and hierarchical architecture of the CuO/NiO arrays as well as the chemical and electronic sensitization effects of CuO decoration.

Investigation of electronic and chemical sensitization effects promoted by Pt and Pd nanoparticles on single-crystalline SnO nanobelt-based gas sensors

This work reports on the gas sensor response of undecorated 1D stannous oxide nanobelts and those decorated with Pt and Pd nanoparticles. The sensor device responses to H2, CO and NO2 were measured in dry air baseline atmosphere as functions of the analyte concentration (1–1000 ppm) and temperature (100-350 °C). Noble metal decorated SnO devices exhibited enhanced chemical sensitization, resulting in increased sensitivity upon exposure to reducing gases at different working temperatures. Differences in enhancement levels are attributed to strong electronic sensitization effects that are dependent on the respective Pt and Pd work functions and the unique SnO band structure, characterized by a small band gap. Gas sensing results also showed superior selectivity to H2 for metal-decorated nanobelts. Based on the findings in this work, we propose an array based on SnO structures capable of detecting and distinguishing reducing and oxidizing gases.

Modified impregnation synthesis of Ru-loaded WO3 nanoparticles for acetone sensing

In this paper, WO3 nanoparticles in a lamellar-structured were fabricated via an acidification method and the surface of nanoparticles were catalytically modified by Ru through a modified impregnation method based on an electronic adsorption mechanism. Gas sensors based on neat and Ru-loaded WO3 nanoparticles were fabricated based on screen printing and sensor responses of acetone were evaluated under a dry and humid ambient, respectively. Experimental results clearly indicated that most of Ru was removed from the WO3 during the washing process, however, a strong sensitization effect of Ru was achieved with a very few loading amount. Accordingly, the basic sensitization mechanism of Ru was investigated based on TPR results and oxygen adsorption behaviors. It is revealed that Ru is loaded on the surface with an oxidized state contributing to an electronic sensitization effect. In addition, Ru on the surface of WO3 as a catalyst significantly enhanced the activity of surface lattice oxygens. As a consequence, surface lattice oxygens could also react with acetone and reduce sensor resistance leading to a sensitization effect. However, we do not expect that reactions of lattice oxygens dominate the sensing process.

Sensors: Pt Nanoparticles Sensitized Ordered Mesoporous WO3 Semiconductor: Gas Sensing Performance and Mechanism Study (Adv. Funct. Mater. 6/2018)

In article number 1705268, Yonghui Deng and co-workers report the rational design and synthesis of Pt nanoparticles sensitized ordered mesoporous WO3. A facile co-assembly strategy results in superior performance in carbon monoxide sensing owing to the rationally combined merits of the high porosity of mesoporous WO3 and the chemical and electronic sensitization effects of Pt.

Highly sensitive and selective NO2 sensor based on Au-impregnated WO3 nanorods

In this work, Au-impregnated WO3 nanorods with high-aspect-ratio were synthesized by a modified precipitation/impregnation method and systematically investigated for NO2 detection. Characterizations by electron microscopy, X-ray diffraction and X-ray photoelectron spectroscopy revealed the formation of 5–20nm spherical and oval Au nanoparticles loaded on the surface of polycrystalline WO3 nanorods. WO3 sensing films with varying Au loading levels from 0 to 2wt% fabricated by powder pasting and spin coating were tested towards NO2 over operating temperatures ranging from 25 to 350°C. It was found that an optimal Au loading of 0.5wt% led to significant enhancement of NO2-sensing performances. In particular, the optimal Au-loaded WO3 sensing film exhibited the highest response of 836.6 with response time of 64.2s to 5ppm NO2 at the optimal operating temperature of 250°C. Moreover, the sensor displayed high NO2 selectivity against NO, N2O, C2H5OH, CO, NH3, SO2 and H2. The observed enhancement could be attributed to the formation of metal-semiconductor ohmic junctions and electronic sensitization effects of Au nanoparticles on the porous network of WO3 nanorods. Therefore, the Au-impregnated WO3 nanorods are highly potential for sensitive and selective NO2 detection.

Synthesis, Characterization and Gas Sensing Properties of Ag@α-Fe₂O₃ Core-Shell Nanocomposites.

Ag@α-Fe2O3 nanocomposite having a core–shell structure was synthesized by a two-step reduction-sol gel approach, including Ag nanoparticles synthesis by sodium borohydride as the reducing agent in a first step and the subsequent mixing with a Fe+3 sol for α-Fe2O3 coating. The synthesized Ag@α-Fe2O3 nanocomposite has been characterized by various techniques, such as SEM, TEM and UV-Vis spectroscopy. The electrical and gas sensing properties of the synthesized composite towards low concentrations of ethanol have been evaluated. The Ag@α-Fe2O3 nanocomposite showed better sensing characteristics than the pure α-Fe2O3. The peculiar hierarchical nano-architecture and the chemical and electronic sensitization effect of Ag nanoparticles in Ag@α-Fe2O3 sensors were postulated to play a key role in modulating gas-sensing properties in comparison to pristine α-Fe2O3 sensors.

Sea urchin-like Ag–α-Fe2O3 nanocomposite microspheres: synthesis and gas sensing applications

Sea urchin-like Ag–α-Fe2O3 nanocomposite microspheres are developed for gas sensing applications. Such hierarchical nanostructures were synthesized by a two step approach including a hydrothermal reaction and a subsequent incipient wetness impregnation process. The large Brunauer–Emmett–Teller (BET) area and highly porous structure of the hierarchical architecture and the chemical and electronic sensitization effect of Ag nanoparticles endow the Ag–α-Fe2O3 nanocomposite microspheres with enhanced gas-sensing properties in comparison to pristine α-Fe2O3 sensors. The possible formation mechanism of the sea urchin-like nanostructures, and their sensing mechanism are discussed.