Enhanced Sensor Response Research Articles

Synthesis, characterization and sensing applications of TiO2 doped MOF composites for selective detection of ammonia at room temperature

Herein, we have developed a highly sensitive chemiresistive TiO2 doped metal–organic framework(MOF) composite-based sensor for ammonia detection at room temperature. Two novel Ti-MOFs@TiO2 composites are developed employing terephthalic acid and 2-amino terephthalic acid as organic linkers with Titanium tetra isopropoxide (TTIP) as a metal source by solvothermal technique. The morphology and crystallinity of synthesized compounds were characterized by using Field-emission scanning electron microscopy (FE-SEM) with EDX analysis, X-ray diffraction (PXRD), XPS and Brunauer–Emmett–Teller (BET) analysis techniques. MIL-125@TiO2 sensors exhibited a more specific surface area (374.74 m2 g−1) than the other three compounds. For gas-sensing applications, all composite materials were exposed to different gas vapours like ammonia, formaldehyde, acetic acid, ethyl alcohol, acetone, xylene, toluene and benzene at room temperature. The sensing results indicate that the sensors exhibit excellent response at low concentrations of ammonia, formaldehyde and acetic acid gases (1 ppm level). The enhanced sensor response was attributed to MIL-125@TiO2 (85 response at 50 ppm) and NH2-MIL-125@TiO2 (71 response at 50 ppm) towards ammonia gas and shows a better selectivity, sensitivity and repeatability to ammonia gas. All the materials exhibited less response times (between 8 and 45 sec) and more recovery times (between 13 and 125 sec).

MOF-derived metal oxide (Cu, Ni, Zn) gas sensors with excellent selectivity towards H2S, CO and H2 gases

Metal-organic framework (MOF)-derived metal oxides blend the sensing properties of metal oxides with MOF porosity, enhancing gas sensing capabilities. In this study, M-MOFs (M = Cu, Ni and Zn) were synthesized and then calcined at different temperatures to obtain their corresponding metal oxides (CuO, NiO and ZnO). The synthesis method incorporated novel approaches to enhance sensor performance, such as optimizing calcination temperatures for improved selectivity. Structural and morphological analyses confirmed the high surface area and porosity of the metal oxide materials, facilitating efficient gas adsorption and promoting enhanced sensor response. Gas sensing studies revealed significantly enhanced performance of MOF-derived metal oxides over M-MOFs, strongly influenced by calcination temperature. Moreover, CuO, NiO and ZnO MOF-derived metal oxides showed improved selectivity towards H2S, CO and H2 gases, respectively. This study demonstrates that tuning MOF and calcination parameters can tailor sensor selectivity effectively.

Enhanced visible light-activated gas sensing properties of nanoporous copper oxide thin films

Metal oxide gas sensors are popular chemoresistive sensors. They are used for numerous tasks, including environmental and safety monitoring. Some gas-sensing materials exhibit photo-induced properties that can be utilized for enhanced gas detection by modifying the sensor selectivity and sensitivity when illuminated by light. Here, we present the gas sensing characteristics of highly nanoporous Cu2O thin films towards both electrophilic (NO2) and nucleophilic (C2H5OH, NH3) gas molecules under ambient temperature and modulated by visible light illumination of different colors (red: 632 nm, green: 530 nm, blue: 468 nm). Cu2O films were fabricated by reactive advanced gas deposition (AGD) technology. The surface and structural analysis of the samples confirm the deposition of nanoporous thin films of mixed copper oxide phases. The gas sensing property of Cu2O exhibited expected p-type semiconductor behavior upon electrophilic and nucleophilic gas exposures. Our results show that visible light illumination provides enhanced sensor response.

A comparative study on the gas sensing performance of SnO2 and GO-SnO2 sensor devices.

Using Modified Hummer’s technique, eco-friendly carbon derivative (GO) nanoparticles were obtained from polyethylene terephthalate (PET) precursor. Nanocomposite of GO-SnO2 and undoped SnO2 were synthesized using the coprecipitation method. The as-prepared nanoparticles were subjected to diverse analytical processes employing Transmission electron microscopy (TEM) to study the internal morphological properties of the nanoparticles. Energy dispersive X-ray spectroscopy (EDX) was used to examine elemental quantifications of the nanopowders. Fourier-transform infrared (FTIR) spectroscopy was used to analyze bond structures and functional groups. Dynamic responses of various gas sensor devices to 20 ppm concentrations of methane (CH4) and hydrogen (H2) were investigated as a function of time at room temperature. The GO-SnO2 nanocomposite sensing device demonstrated an ideal detection response with values of 5.00 and 5.08, corresponding to methane and hydrogen analyte gases. The doped SnO2 sensor device outperformed the pure SnO2, accounting for the GO-SnO2 > SnO2 order. Regarding the target gases, the synthesized nanocomposite demonstrated stability and selectivity in the following order of magnitude: H2 > CH4. The GO doping effect was found to have introduced surface defects, increased pores, and enabled more oxygen-active sites to be formed on the sensor device’s surface for dynamic gas sensing response, providing a comparatively enhanced sensor response.

Enhanced Acetone Sensing Properties Based on Au-Pd Decorated ZnO Nanorod Gas Sensor.

The mature processes of metal oxide semiconductors (MOS) have attracted considerable interest. However, the low sensitivity of metal oxide semiconductor gas sensors is still challenging, and constrains its practical applications. Bimetallic nanoparticles are of interest owing to their excellent catalytic properties. This excellent feature of bimetallic nanoparticles can solve the problems existing in MOS gas sensors, such as the low response, high operating temperature and slow response time. To enhance acetone sensing performance, we successfully synthesized Au-Pd/ZnO nanorods. In this work, we discovered that Au-Pd nanoparticles modified on ZnO nanorods can remarkably enhance sensor response. The Au-Pd/ZnO gas sensor has long-term stability and an excellent response/recovery process. This excellent sensing performance is attributed to the synergistic catalytic effect of bimetallic AuPd nanoparticles. Moreover, the electronic and chemical sensitization of noble metals also makes a great contribution. This work presents a simple method for preparing Au-Pd/ZnO nanorods and provides a new solution for the detection of acetone based on metal oxide semiconductor.

Development of highly sensitive and solar blind surface acoustic wave UV-C photodetector based on the In2O3/Ta2O5 nano-heterojunction and its interface electronics

A highly sensitive surface acoustic wave (SAW) ultraviolet-C (UV-C) sensor based on In2O3/Ta2O5 nano-heterojunctions and its interface electronics was developed to detect solar blind corona discharge near high voltage power lines. The SAW sensor, based on pristine In2O3 nanoparticles, exhibits a weaker and slower response to UV-C light. To improve the response to deep UV light, In2O3 nanoparticles/Ta2O5 heterojunctions were formed by depositing Ta2O5 films of different thicknesses (2–10 nm) around the In2O3 nanoparticles via atomic layer deposition (ALD) on the cavity between two interdigital transducers (IDTs) in the SAW delay line. The experimental results show a significantly enhanced sensor response towards UV-C light, which is attributed to a high surface-to-volume ratio, an inhibited recombination rate of the photogenerated electron-hole pairs on the surface of the sensing material owing to Ta2O5 conformal coverage, and well-matched energy bandgap engineering. An empirical mechanism was proposed to elucidate the enhanced sensing behavior of the heterostructure. To observe the frequency shifts in real-time on a PC display, portable interface electronics were developed on a single printed circuit board (PCB) for the SAW UV-C sensor, eliminating the effect of frequency shifts caused by ambient temperature and humidity changes. The sensor characteristics were evaluated based on the size and annealing conditions of the In2O3 nanoparticles and the thickness of the decorated Ta2O5, and the scientific and technical causes and analysis of the results were thoroughly investigated. In the selectivity test, the fabricated sensor exhibited a strong response to a UV-C light beam with a sensitivity of 368.3 (ppm (μW/cm2)−1 at 254 nm, and its spectral response to UV-C light was 3.3 times higher than that under UV-A 365 nm light.

Flexible and disposable electrodes based on SnO2 nanoparticle/Nb2CTx nanosheet composites for selective and ultrasensitive detection of propofol

A disposable electrochemical sensor for the detection of the propofol (PPF), an anesthetic drug, has been developed using a composite of SnO2 nanoparticle and Nb2CTx MXene (SnO2/Nb2CTx). The SnO2/Nb2CTx is modified on a flexible carbon cloth for highly sensitive and selective electrochemical detection of PPF. The ratio of SnO2 in the composite was optimized to get enhanced sensor response to cover the analyte range from 1 μM to 300 μM with a limit of detection of 0.24 µM. The developed sensor possesses the requisite sensor parameters viz. selectivity, sensitivity, reproducibility, and storage stability. Based on the flexibility analysis, it is confirmed that the developed sensor works for the detection of PPF on a flexible platform as well. The real sample analysis done by spiking PPF in human artificial serum further proves that the developed PPF sensor can effectively detect PPF in serum samples. Over all, the developed sensor improves patient safety by ensuring that they receive the appropriate amount of medication at the right time minimizing the risk of adverse effects associated with over-sedation or under-sedation.

Enhancing high sensitive hydrogen detection of Bi2O3 nanoparticle decorated TiO2 nanotubes

An electrochemical anodization technique was used to create a hydrogen gas sensor based on TiO2 nanotubes decorated with bismuth oxide (Bi2O3). Bismuth nitrate pentahydrate (Bi(NO3)3·5H2O) was employed as the source material for Bi2O3. The resulting nanotubes were annealed at 500 °C, revealing an amorphous structure with a mixed phase of rutile and anatase. Platinum (Pt) electrodes, with a thickness of 100 nm, were coated onto the Bi2O3@TiO2/Ti and TiO2/Ti structures for sensor testing. Energy dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and field emission scanning electron microscopy (FE-SEM) were used to examine the structural, morphological, and surface properties of the Bi2O3@TiO2 and TiO2 nanotubes. The hydrogen sensing properties of the Pt/Bi2O3@TiO2/Ti and Pt/TiO2/Ti devices were evaluated at room temperature, with hydrogen concentrations ranging from 1000 ppm to 10 %. The I–V characterization of the sensor devices under 1 % H2 exhibited typical Schottky-type behavior. Remarkably, the Pt/Bi2O3@TiO2/Ti structure demonstrated a sensor response 1 × 107 times higher than that of in a dry air environment when the same voltage was applied under up to 1 % H2 conditions. The uniform dispersion of Bi2O3 nanoparticles throughout the structure contributed to the enhanced sensor response in the presence of H2.

Optimization of Planar Interdigitated Microelectrode Array for Enhanced Sensor Responses

Immunoassays play a pivotal role in detecting and quantifying specific proteins within biological samples. However, its sensitivity and turnaround time are constrained by the passive diffusion of target molecules towards the sensors. ACET (Alternating Current Electrothermal) enhanced reaction emerges as a solution to overcome this limitation. The ACET-enhanced biosensor works by inducing vortices through electrothermal force, which stirs the analyte within the microchannel and promotes a reaction process. In this study, a comprehensive two-dimensional finite element study is conducted to optimize the binding efficiency and detection time of an ACET-enhanced biosensor without external pumping. Optimal geometries for interdigitated electrodes are estimated to achieve significant improvements in terms of probe utilization and enhancement factor. The study’s findings demonstrate enhancement factors of 3.21, 2.15, and 3.09 along with 71.22%, 75.80%, and 57.52% normalized binding for C-reactive protein (CRP), immunoglobulin (IgG), and SARS-CoV-2, respectively.

Microbial nanowires with genetically modified peptide ligands to sustainably fabricate electronic sensing devices

Nanowires have substantial potential as the sensor component in electronic sensing devices. However, surface functionalization of traditional nanowire and nanotube materials with short peptides that increase sensor selectivity and sensitivity requires complex chemistries with toxic reagents. In contrast, microorganisms can assemble pilin monomers into protein nanowires with intrinsic conductivity from renewable feedstocks, yielding an electronic material that is robust and stable in applications, but also biodegradable. Here we report that the sensitivity and selectivity of protein nanowire-based sensors can be modified with a simple plug and play genetic approach in which a short peptide sequence, designed to bind the analyte of interest, is incorporated into the pilin protein that is microbially assembled into nanowires. We employed a scalable Escherichia coli chassis to fabricate protein nanowires that displayed either a peptide previously demonstrated to effectively bind ammonia, or a peptide known to bind acetic acid. Sensors comprised of thin films of the nanowires amended with the ammonia-specific peptide had a ca. 100-fold greater response to ammonia than sensors made with unmodified protein nanowires. Protein nanowires with the peptide that binds acetic acid yielded a 4-fold higher response than nanowires without the peptide. The protein nanowire-based sensors had greater responses than previously reported sensors fabricated with other nanomaterials. The results demonstrate that protein nanowires with enhanced sensor response for analytes of interest can be fabricated with a flexible genetic strategy that sustainably eliminates the energy, environmental, and health concerns associated with other common nanomaterials.

On-chip CuFe2O4 nanofiber for conductometric NO2 and H2S gas-sensors

xCuO-(1-x)Fe2O3 composite nanofibers (NFs) for gas-sensing applications were thoroughly investigated in this work employing on-chip electrospinning. The fabricated NFs had a characteristic spider-net-like morphology and had diameters of 50–100 nm. The NFs composed of nanograins with diameters ranging from 16 to 35 nm have multi-porous structures. The composite NFs enhanced sensor response compared to that of single metal oxides. At the optimal composition of 0.5CuO-0.5Fe2O3 NFs, which formed a complex oxide of copper ferrite (CuFe2O4), the sensor showed the highest response (15.3 and 10) to 1 ppm H2S gas at 350 °C and 10 ppm NO2 gas at 300 °C, respectively. Additionally, the detection of on-chip NF sensors to target gases was considerably impacted by the electrospinning time. The maximum response to H2S gas was achieved after 30 min of the electrospinning process, while that to NO2 gas is 10 min. The enhanced gas-sensing performance was attributed to nanograin-based NF structure, the formation of binary complex CuFe2O4 oxide, and the heterojunctions between CuFe2O4 and single oxide (CuO or α-Fe2O3) in composite NFs. Furthermore, the high sensitivity and selectivity of the CuFe2O4 NF sensor toward target gases are also discussed by using density functional theory (DFT) calculation.

TiO2-modified MoS2 monolayer films enable sensitive NH3 sensing at room temperature.

The research and development of high-performance NH3 sensors are of great significance for environment monitoring and disease diagnosis applications. Two-dimensional (2D) MoS2 nanomaterials have exhibited great potential for building room-temperature (RT) NH3 sensors but still suffer from relatively low sensitivity. Herein, the TiO2-modified monolayer MoS2 films with controllable TiO2 loading contents are fabricated by a facile approach. A remarkable enhancement in the RT NH3 sensing performance is achieved after the n-n hetero-compositing of the TiO2/MoS2 system. The device with 95% surface coverage of TiO2 shows enhanced sensor response, low detection limit (0.5 ppm), wide detection range (0.5-1000 ppm), good repeatability, and superior selectivity against other gases. In situ Kelvin potential force microscopy results revealed that the TiO2 modification not only improved the surface reactivity of the sensing layers but also contributed to the NH3 sensing performance by serving as the "gas-gating" layers that modulated the electron depletion layer and the conductivity of the MoS2 films. Such an n-n hetero-compositing strategy can provide a simple and cost-effective approach for developing high-performance NH3 sensors based on 2D semiconductors.

Ru-implanted WS2 nanosheet gas sensors to enhance sensing performance towards CO gas in self-heating mode

Ru-implanted (low-dose: 2 ×10 13 ions/cm 2 and high-dose: 2 ×10 14 ions/cm 2 ) p -type WS 2 nanosheet (NS) gas sensors were investigated for CO gas sensing in self-heating mode. X-ray photoelectron spectroscopic analysis showed that the implanted Ru existed as Ru 3+ (~38 at%) and Ru 4+ (~62 at%). A decrease of the resistivity after Ru implantation was attributed to the substitution of W 4+ with Ru 3+ . The enhanced sensor response of the Ru-implanted (2 ×10 14 ions/cm 2 ) WS 2 was attributed to the enhanced adsorption of oxygen onto the sulfur vacancies after Ru ion implantation. Decoration of Au nanoparticles (NPs) onto this gas sensor not only led to an enhancement of the response to CO gas but also improved the selectivity and dynamics of the gas sensor. The related sensing mechanism was explained in terms of the catalytic effect of Au and the spillover effect. The optimized gas sensor showed good response to CO in the presence of humidity ( R g / R a = 3 to 50 ppm CO at 60% relative humidity, where R a is the resistance of the sensor in air and R g is its resistance in the presence of the target gas). • Ru ions were implanted into WS 2 to improve its gas-sensing properties. • Improved oxygen adsorption due to sulfur vacancies enhanced sensor response. • Ru implantation lowered the resistivity by substituting Ru 3+ for W 4+ . • CO gas sensing in self-heating mode was studied under applied voltages up to 5 V. • Au decoration enhanced CO selectivity and the response even when humidity is present.

Facile strategy for advanced selectivity and sensitivity of SnO2 nanowire-based gas sensor using chemical affinity and femtosecond laser irradiation

This study proposes an effective strategy to improve the selectivity and response of SnO2 nanowire (NW)-based gas sensors. Self-assembled monolayer (SAM) functionalization of SnO2 NWs enhances the gas selectivity by tuning the surface chemical states. Different chemical moieties with alkyl and fluoroalkyl of the SAM molecules are adopted for the chemical affinities toward the corresponding target gas molecules. The alkyl and fluoroalkyl moieties show excellent selectivity toward CH4 and C3F8, respectively, owing to the strong chemical affinity between the moieties and gases. Post-treatment femtosecond (FS) laser irradiation with different laser fluences is applied to the SAM-functionalized SnO2 NW-based gas sensor. The FS laser-irradiated SnO2 NWs show an enhanced sensor response with higher resistance values and shorter response and recovery times compared to those of the pristine SnO2 NWs. Transmission electron microscopy analysis reveals that the FS laser irradiation induces the formation of embossing surface on the SnO2 NW, creating additional gas adsorption sites. Moreover, twin structures develop on the SnO2 NWs with increasing laser fluences. Electron energy loss spectroscopy analysis supports that the FS laser irradiation creates non-stoichiometric SnO and SnOx phases, providing O vacancies and improved response.

A Bilayer SnO2/MoS2-Coated Evanescent Wave Fiber Optic Sensor for Acetone Detection-An Experimental Study.

The need for sensors that measure the acetone content of exhaled breath for diabetes severity has recently increased. Clinical researchers have reported less than 0.8 ppm acetone concentration in the exhaled breath of an average individual, while that for a diabetic patient is higher than 1.8 ppm. This work reports the development of two sets of evanescent wave-based fiber optic sensor coated with SnO2 thin film and bilayer of SnO2/MoS2 to detect different acetone concentrations (0–250 ppm). In each set, we have studied the effect of clad thickness (chemical etch time 5min, 10 min, 15 min, 25 min, 40 min, and complete clad removal) to optimize the clad thickness for a better response. In Set 1, SnO2 thin film was used as the sensing layer, while in Set 2 a bilayer of SnO2 thin film/ MoS2 was used. Enhanced sensor response of ~23.5% is observed in the Set 2 probe with a response and recovery time of ~14 s/~17 s. A SnO2/MoS2-coated sensor prototype is developed using LEDs of different wavelength and intensity detector; its potential to detect different concentrations of acetone is tested. X-ray Diffraction (XRD), Scanning Electron Microscope (SEM), Ultraviolet (UV) Spectroscopy, and Ellipsometry were used to study the structural, morphological and optical properties of the sensing layers. The present study indicates that the SnO2/MoS2-coated sensor has the potential to create a handheld sensor system for monitoring diabetes.

An investigation on GaN/ porous-Si NO2 gas sensor fabricated by pulsed laser ablation in liquid

Pulsed-laser ablation in liquid was used to prepare GaN nanostructure. The P-type GaN nanostructure was deposited onto the porous-silicon substrate through the drop-casting method for NO2 gas-sensor fabrication. Ablation was performed in ethanol using two laser wavelengths, namely, 532 and 1064 nm. The XRD pattern showed a high and sharp peak at 2θ= 29.49°, indicating enhanced GaN formation using a 532 nm laser wavelength. AFM and FESEM analyses confirmed increased GaN grain growth at the same wavelength. The optical reflectance of the GaN sample showed higher reflectance at 532 nm than at 1064 nm. The optical-energy bandgap was more elevated at 532 nm than at 1064 nm. Photoluminescence analysis revealed that the 532 nm sample had a higher-intensity peak than the 1064 nm one. Device-performance studies showed the most enhanced sensor response (158.49%), highest sensitivity (2.109 ppm), and best response time (13.5 s) at 250 °C for the sample prepared using 532 nm laser wavelength.

Transforming 3D-printed mesostructures into multimodal sensors with nanoscale conductive metal oxides

Additively manufactured (AM) three-dimensional (3D) mesostructures exhibit geometrically optimal mechanical, thermal, and optical properties that could drive future microrobotics, energy harvesting, and biosensing technologies at the micrometer to millimeter scale. We present a strategy for transforming AM mesostructures into 3D electronics by growing nanoscale conducting films on 3D-printed polymers. This highly generalizable method utilizes precision atomic layer deposition (ALD) of conducting metal oxides on ultrasmooth photopolymer lattices printed by high-resolution microstereolithography. We demonstrate control of 3D electronic transport by tuning conformal growth of ultrathin amorphous and crystalline conducting metal oxides. To understand the scaling of 3D electrical properties, we apply graph theory to compute network resistance and precisely design the 3D mesostructures' conductivity. Finally, we demonstrate 3D-enhanced multimodal sensing of chemical, thermal, and mechanical stimuli, geometrically boosting sensitivity by 100× over 2D films and enabling a new class of low-power, 3D-printable sensors. • Microstereolithography is integrated with low-temperature atomic layer deposition • Conducting oxides (ZnO, AZO, SnO 2 ) functionalize 3D mesostructured lattices • Nanometer thickness control determines oxide coating electrostatics • The 3D geometries enhance sensor response to chemical, thermal, and mechanical stimuli Huddy et al. present a strategy for transforming additively manufactured mesostructures into 3D electronics by growing nanoscale conducting oxides on 3D-printed polymers. The authors apply graph theory to design mesostructures for sensing chemical and thermophysical stimuli, geometrically boosting sensitivity 100× over conventional films to enable a new class of 3D-printable sensors.

Phthalocyanines and Porphyrins/Polyaniline Composites (PANI/CuPctBu and PANI/TPPH2) as Sensing Materials for Ammonia Detection.

We combined a conducting polymer, polyaniline (PANI), with an organic semiconducting macrocyclic (MCs) material. The macrocycles are the phthalocyanines and porphyrins used to tune the electrical properties of the PANI, which benefits from their ability to enhance sensor response. For this, we proceeded by a simple ultrasonically assisted reaction involving the two components, i.e., the PANI matrix and the MCs, to achieve the synthesis of the composite nanostructure PANI/MCs. The composite nanostructure has been characterized and deposited on interdigitated electrodes (IDEs) to construct resistive sensor devices. The isolated nanostructured composites present good electrical properties dominated by PANI electronic conductivity, and the characterization reveals that both components are present in the nanostructure. The experimental results obtained under gas exposures show that the composite nanostructures can be used as a sensing material with enhanced sensing properties. The sensing performance under different conditions, such as ambient humidity, and the sensor’s operating temperature are also investigated. Sensing behavior in deficient humidity levels and their response at different temperatures revealed unusual behaviors that help to understand the sensing mechanism. Gas sensors based on PANI/MCs demonstrate significant stability over time, but this stability is highly reduced after experiments in lower humidity conditions and at high temperatures.

Macrocycle-Functionalized RGO for Gas Sensors for BTX Detection Using a Double Transduction Mode

To fabricate mass and resistive sensors based on reduced graphene oxide (RGO), we investigated the functionalization of RGO by tetra tert-butyl phthalocyanine (PcH2tBu), which possesses a macroring and tert-butyl peripheral groups. Herein, we present the gas sensor responses of the functionalized RGO toward benzene, toluene, and xylene (BTX) vapors. The RGO was obtained by the reduction of graphene oxide (GO) using citrate as a reducing agent, while the functionalization was achieved non-covalently by simply using ultrasonic and heating treatment. The sensor devices based on both QCM (quartz crystal microbalance) and resistive transducers were used simultaneously to understand the reactivity. Both the GO and the RGO showed less sensitivity to BTX vapors, while the RGO/PcH2tBu presented enhanced sensor responses. These results show that the p-network plays a very important role in targeting BTX vapors. The resistive response analysis allowed us to state that the RGO is a p-type semiconductor and that the interaction is governed by charge transfer, while the QCM response profiles allowed use to determine the differences between the BTX vapors. Among BTX, benzene shows the weakest sensitivity and a reactivity in the higher concentration range (>600 ppm). The toluene and xylene showed linear responses in the range of 100–600 ppm.

An 8 MeV Electron Beam Modified In:ZnO Thin Films for CO Gas Sensing towards Low Concentration.

In the present investigation, electron beam-influenced modifications on the CO gas sensing properties of indium doped ZnO (IZO) thin films were reported. Dose rates of 5, 10, and 15 kGy were irradiated to the IZO nano films while maintaining the In doping concentration to be 15 wt%. The wurtzite structure of IZO films is observed from XRD studies post electron beam irradiation, confirming structural stability, even in the intense radiation environment. The surface morphological studies by SEM confirms the granular structure with distinct and sharp grain boundaries for 5 kGy and 10 kGy irradiated films whereas the IZO film irradiated at 15 kGy shows the deterioration of defined grains. The presence of defects viz oxygen vacancies, interstitials are recorded from room temperature photoluminescence (RTPL) studies. The CO gas sensing estimations were executed at an optimized operating temperature of 300 °C for 1 ppm, 2 ppm, 3 ppm, 4 ppm, and 5 ppm. The 10 kGy treated IZO film displayed an enhanced sensor response of 2.61 towards low concentrations of 1 ppm and 4.35 towards 5 ppm. The enhancement in sensor response after irradiation is assigned to the growth in oxygen vacancies and well-defined grain boundaries since the former and latter act as vital adsorption locations for the CO gas.