Description:A GAS SENSOR, WO3-SnO2 BASED GAS SENSING FILM AND A METHOD OF PREPARATION THEREOF
FIELD OF THE INVENTION
[001] The present invention relates to nanostructured thin films for gas sensing applications and, more specifically, to a method for enhancing the gas sensing performance of WO3-SnO2 nanocomposite thin films through low-energy ion beam irradiation.
BACKGROUND OF THE INVENTION
[002] Semiconducting metal oxides such as tungsten oxide (WO3) and tin oxide (SnO2) are widely used for gas sensing due to their high sensitivity, stability, and compatibility with microfabrication processes. However, there is a continuing need to enhance the selectivity, response time, and sensitivity of these sensors due to growing global demand for reliable, low-cost, and sensitive gas sensors for environmental monitoring, industrial safety, and automotive applications. Among various sensing technologies, semiconducting metal oxide-based gas sensors are widely used due to their simplicity, stability, and high sensitivity. These sensors operate based on changes in electrical conductivity caused by gas adsorption and desorption on the oxide surface, which is significantly influenced by surface area and material properties.
[003] Nitrogen dioxide (NO2), a hazardous pollutant, poses severe health and environmental risks. Therefore, detecting NO2 at low concentrations and temperatures has become increasingly critical. Among commonly used metal oxides, tungsten oxide (WO3) and tin oxide (SnO2) are promising materials due to their strong sensitivity, chemical stability, and compatibility with nanocomposite formation.
[004] US7911010B2, patent discloses a universal microelectromechanical MEMS nano-sensor platform having a substrate and conductive layer deposited in a pattern on the surface to make several devices at the same time, a patterned insulation layer, wherein the insulation layer is configured to expose one or more portions of the conductive layer, and one or more functionalization layers deposited on the exposed portions of the conductive layer. The functionalization layers are adapted to provide one or more transducer sensor classes selected from the group consisting of: radiant, electrochemical, electronic, mechanical, magnetic, and thermal sensors for chemical and physical variables.
[005] US11499933B2, patent discloses a method of manufacturing a graphene-tin oxide nanocomposite comprises dispersing graphene and tin oxide in an organic solvent to prepare a dispersion solution, drying the dispersion solution to obtain a powdery mixture, and irradiating the mixture with microwaves to obtain a graphene-tin oxide nanocomposite. Irradiation of graphene and tin oxide with microwaves results in the simplification of the manufacturing process of graphene-tin oxide nanocomposites and a decrease in manufacturing time and cost, and produce graphene-tin oxide nanocomposites at low temperatures. Further, the graphene-tin oxide nanocomposite with improved sensitivity to NO2 gas may be produced.
[006] Thus none of the above document or prior arts and existing technology discloses the WO3-SnO2 based gas sensor, gas sensing film and a method of preparation of thereof for the said gas sensor, and gas sensing film and the present disclosure also overcomes the drawbacks of the existing literature involve in this field of sensors to detect the NO2 or other gases.
[007] Thus the present invention is a need to improve the existing patented technology or literature proposed or written or published in this concerned field of science/technology as the Wo3-SnO2 nanocomposites have shown enhanced gas sensing performance compared to their individual components. However, further improvement in sensitivity, selectivity, and low-temperature operation remains a challenge. Recent studies suggest that introducing structural defects via ion beam irradiation can significantly improve the gas sensing behavior of metal oxide semiconductors by enhancing gas adsorption.
[008] Ion beam irradiation has emerged as a promising technique to modify the surface morphology, crystallinity, and electronic properties of thin films without changing their bulk composition. The present invention leverages helium ion beam irradiation to tailor the structural and surface characteristics of WO3-SnO2 nanocomposite thin films, resulting in superior NO2 sensing performance at low temperatures.
OBJECTS OF THE INVENTION
[009] A principal object of the present invention is to develop a gas sensor.
[010] Another object of the preset invention is to develop a WO3-SnO2 based gas sensor to detect the NO2 gas
[011] Another object of the preset invention is to develop a WO3-SnO2 based gas sensor to detect the NO2 gas at low temperatures ranging from 30°C to 90 °C.
[012] Yet another object of the present invention is to device a method of preparation of WO3 and SnO2 based gas sensing film.
[013] Still another object of the present invention is to device/unrap a method of fabrication a gas sensor based on WO3-¬SnO2.
SUMMARY OF THE INVENTION
[014] The present invention provides a method for enhancing the structural, optical, morphological, and gas-sensing characteristics of WO3-SnO2 nanocomposite thin films by subjecting them to low-energy He? ion beam irradiation.
[015] WO3-SnO2 thin films are deposited using radio-frequency (RF) sputtering and subsequently irradiated with 125 keV He ions at fluences of 1×10¹5, 5×10¹5, and 1×10¹6 ions/cm². The ion beam irradiation modifies key characteristics of the nanocomposite, leading to improved NO2 gas sensing response at low temperatures (30–90?°C).
[016] In an aspect, the present invention disclosure discloses a gas sensor device having a substrate selected from glass or silicon, a WO3-SnO2 nanocomposite thin film deposited on the substrate, a pair of interdigitated platinum electrodes disposed over the thin film, the electrodes being formed using RF magnetron sputtering with a titanium adhesion layer, wherein the WO3 -SnO2 thin film is subjected to low-energy helium ion (He?) beam irradiation at an energy of approximately 125 keV and a fluence in the range of 1×10¹5 to 1×106¹ ions/cm², wherein said irradiation induces structural and surface modifications in the nanocomposite, enhancing the gas sensing performance of the device by increasing defect density and charge carrier mobility.
[017] In an aspect, the WO3-SnO2 thin film is prepared by a process involving a number of steps starting with synthesizing WO3 -SnO2 nanocomposite powder by dissolving sodium tungstate dihydrate (Na2WO4•2H2O) in deionized water, adding glucose and sodium stannate monohydrate (Na2SnO3•H2O), and subjecting the mixture to hydrothermal treatment at 180 °C for 20 hours, recovering the precipitate by centrifugation, washing with ethanol and deionized water, and drying at 60 °C to obtain a nanocomposite powder, compressing the powder into a sputtering target using a hydraulic press, depositing the nanocomposite thin film on the substrate using RF magnetron sputtering under a base pressure of 1.64 × 10?5 mbar and argon flow rate of 15 sccm, with a substrate-to-target distance of 8 cm and substrate rotation rate of 10–12 rpm, and annealing the deposited film at 550°C in air to enhance crystallinity and surface morphology.
[018] In an aspect, the present invention futher discloses a method for detecting nitrogen dioxide (NO2) gas using the gas sensor WO3-SnO2 nano composite, wherein the WO3-SnO2 nanocomposite thin film is exposed to NO2 gas at a concentration of approximately 10 parts per million (ppm) within an operating temperature range of 30°C to 90 °C, wherein the sensor demonstrates an enhanced sensing response of at least 2.66 at 80°C when the film has been subjected to helium ion (He?) beam irradiation at an energy of 125 keV and a fluence of 1×10¹5 ions/cm², wherein the sensor exhibits a response time of approximately 1 second and a recovery time of approximately 30 seconds, and wherein the improved sensing performance is attributed to ion-beam-induced modifications in the nanocomposite film’s structural and electronic properties.
[019] In an aspect, said ion irradiation results in a reduction in the crystallite size of WO3 from approximately 17.74 nanometers to 9.43 nanometers and of Sn2O from approximately 5.56 nanometers to 2.71 nanometers, wherein the irradiation induces an increase in dislocation density and lattice strain, alongside a decrease in optical bandgap energy from 3.88 electron volts (eV) to 3.82 eV, as measured by UV-Visible spectroscopy, and wherein these microstructural and optical changes enhance the surface reactivity and carrier mobility of the nanocomposite, thereby improving sensitivity and selectivity toward NO2 gas.
[020] In an aspect, the present invention also discloses a method of preparation of WO3 and SnO2 based gas sensing film involving a number of steps with dissolving Na2WO4.2H2O in deionized water, Stirring continuously the solution prepared in step a to prepare a homogenous solution, Adding 5 grams of glucose and 0.5 m mol of Na2SnO3.H2O to the homogeneous solution as obtained in step b to make a resultant mixture and stirring the resultant mixture, Transferring the resultant mixture as obtained into an autoclave, Maintaining the resultant mixture in autoclave at a predetermined temperature T1 for a predetermined time period TP1, Cooling autoclaved mixture obtained at a temperature T2, Recovering solid precipitate of mixture obtained by centrifugation and washing with ethanol and deionized water to obtain a powder, Drying the powder at a predetermined temperature T3 to obtain WO3-SnO2 nanocomposite powder, Depositing WO3-SnO2 nanocomposite powder on a substrate using sputtering to obtain a substrate deposited with a thin film of WO3-SnO2, Annealing the substrate deposited with a thin film of WO3-SnO2 at a predetermined temperature T4, Irradiating annealed substrate deposited with a thin film of WO3-SnO2 as obtained with low energy He+ ions to obtain a WO3-SnO2 gas sensing film.
[021] In an aspect, the resultant mixture is stirred preferably for a time period of 10 minutes and the autoclave is preferably a Teflon-lined stainless steel autoclave.
[022] In an aspect, the predetermined temperature T1, T2, T3 and T4 are 180 °C, 27 °C (room temperature), 60 °C, 550 °C respectively.
[023] In an aspect, the substrate is a 2 inch diameter pellet and is blue star glass and silicon based substrate and wherein the sputtering is a Radio Frequency (RF) magnetron sputtering.
[024] In an aspect, the deposition of WO3-SnO2 nanocomposite powder on the substrate is controlled by a number of key deposition parameters including substrate to target distance, base pressure, working pressure, argon gas flow rate and substrate rotation rate and thickness of the thin film of WO3-SnO2 is approximately 100 nm, wherein irradiation of the WO3-SnO2 nanocomposite thin films are subjected to low-energy helium ion (He?) beam irradiation at an energy of 125 keV, using a beam current of 500 pA and the irradiation was performed at varying fluences of 1×10¹5, 5×10¹5, and 1×10¹6 ions/cm², wherein characterization of the WO3-SnO2 gas sensing film is done using techniques including X-ray diffraction (XRD), Atomic Force Microscopy (AFM), UV-visible spectroscopy, Raman spectroscopy and X-ray photoelectron spectroscopy.
[025] In an aspect, the present invention discloses a method of fabrication of a gas sensor to sense gas comprising the steps of starting with Sputtering a thin Titanium (Ti) adhesion layer on a glass substrate, depositing platinum (Pt) onto the glass substrate as obtained in step a by RF magnetron sputtering in a 100% Argon (Ar) atmosphere to fabricate interdigitated electrodes (IDEs), Pattering interdigitated electrodes (IDEs) as obtained in step b on to the surface of the WO3-SnO2 nanocomposite thin film to obtain the gas sensor, wherein the gas sensor senses preferably NO2 gas at low temperature ranging from 30°C-90°C, and wherein, the gas sensor's response towards NO2 gas is defined as the ratio of resistance fluctuation during NO2 gas interaction to resistance in the air atmosphere is expressed as where S is the sensor response of the material, Rg represents the sensors resistance when exposed to NO2 gas and Ra indicates the sensor resistance in the surrounding atmosphere.

BRIEF DESCRIPTON OF THE DRAWINGS
[026] Fig. 1 illustrates a Schematic of the Experimental Methodology
(a) WO3-SnO2 nanocomposite thin films created by the RF sputtering approach.
(b) Ion beam exposure by He ion with 125 keV at various fluences.
[027] Fig. 2 illustrates a Plot of Se and Sn for 125 keV Ion Beam-Implanted WO3-SnO2 Thin Film. The graph shows the variation of Se (electronic energy loss) and Sn (nuclear energy loss) for WO3-SnO2 thin films implanted with 125 keV He ions at different fluences.
[028] Fig. 3 illustrates WO3-SnO2 Thin Film Interaction with Ion Beam
A schematic showing the interaction of WO3-SnO2 thin film along the Y-axis.
(a) Target vacancies, (b) target ionization, (c) target phonons, and (d) ion implantation path.
[029] Fig. 4 illustrates a XRD Diffraction Pattern of Pristine and Ion-Implanted WO3-SnO2 Thin Films. X-ray diffraction patterns for pristine WO3-SnO2 thin films and He-implanted samples at fluences of 1E15, 5E15, and 1E16 ions/cm², showing changes in crystallinity.
[030] Fig. 5 illustrates a Raman Spectra of Pristine and Ion-Implanted WO3-SnO2 Thin Films.
Raman spectra of WO3-SnO2 thin films at various fluences:
(a) pristine, (b) 1E15 ions/cm², (c) 5E15 ions/cm², and (d) 1E16 ions/cm².
[031] Fig. 6 illustrates 2D and 3D Representation of Pristine and He Ion-Implanted WO3-SnO2 Thin Films. Two-dimensional and three-dimensional representations of WO3-SnO2 thin films before and after He ion implantation at varying fluences.
[032] Fig. 7 illustrates a Log Normal Fitting of Un-Implanted and Ion Beam Irradiated Thin Films. Log normal distribution fits for: (a) Virgin WO3-SnO2 thin film, (b) 1E15 ions/cm², (c) 5E15 ions/cm², and (d) 1E16 ions/cm².
[033] Fig. 8 illustrates a Plot of Absorbance vs. Wavelength for Pristine and Ion-Implanted WO3-SnO2 Thin Films. Absorbance spectra for WO3-SnO2 thin films at various fluences:
(a) pristine, (b) 1E15 ions/cm², (c) 5E15 ions/cm², and (d) 1E16 ions/cm².
[034] Fig. 9 illustrates a Variation in the Band Gap of Pristine and He Ion-Implanted WO3-SnO2 Thin Films. Plot of the optical band gap variation for WO3-SnO2 thin films at different fluences:
(a) pristine, (b) 1E15 ions/cm², (c) 5E15 ions/cm², and (d) 1E16 ions/cm².
[035] Fig. 10 illustrates a Urbach’s Energy and Skin Depth of WO3-SnO2 Thin Films
(a) Illustration of Urbach’s energy for pristine and ion-implanted WO3-SnO2 thin films at different fluences. (b) Variation of skin depth with photon energy for pristine and He ion-implanted WO3-SnO2 thin films.
[036] Fig. 11 illustrates an XPS Survey Spectra of Pristine and 125 keV Implanted WO3-SnO2 Thin Films. XPS survey spectra showing the surface composition of pristine and He-ion implanted WO3-SnO2 thin films at various fluences (1E15, 5E15, 1E16 ions/cm²).
[037] Fig. 12 illustrates a High-Resolution XPS Spectra of WO3-SnO2 Thin Films
High-resolution XPS spectra for pristine and ion-implanted WO3-SnO2 thin films:
(a) W4f, (b) Sn 3d, and (c) O1s.
[038] Fig. 13 illustrates Resistance Dependency of WO3-SnO2 Nanocomposite Sensor in Air
Graph depicting the resistance behavior of pristine and ion-implanted WO3-SnO2 nanocomposite sensors at various temperatures: (a) Pristine, (b) 1E15 ions/cm².
[039] Fig. 14 illustrates Resistance Behavior of WO3-SnO2 Nanocomposite Sensor Exposed to 10 ppm NO2 Gas. Graph showing the resistance behavior of pristine and ion-implanted WO3-SnO2 nanocomposite sensors at different temperatures in the presence of 10 ppm NO2 gas: (a) Pristine, (b) 1E15 ions/cm².
[040] Fig. 15 illustrates a Sensor Response with Varying Temperature
(a) Response of pristine WO3-SnO2 nanocomposite sensor, (b) Response of He ion-implanted WO3-SnO2 nanocomposite sensor with varying temperature.
[041] Fig. 16 illustrates a Response and Recovery Time of WO3-SnO2 Nanocomposite Sensor at 1E15 ions/cm² Fluence. Graph showing the response and recovery times of pristine and He ion-implanted WO3-SnO2 nanocomposite sensors at a fluence of 1E15 ions/cm².
[042] Fig. 17 illustrates a Response-Recovery Curve of WO3-SnO2 Nanocomposite Sensor at 1E15 ions/cm² Fluence. Plot of the response and recovery characteristics of pristine and He ion-implanted WO3-SnO2 nanocomposite sensors at a fluence of 1E15 ions/cm².
[043] Fig. 18 illustrates a Sensor Repeatability Curve for WO3-SnO2 Nanocomposite at 1E15 ions/cm² Fluence.Graph illustrating the repeatability of the sensing response of WO3-SnO2 nanocomposite sensors at a fluence of 1E15 ions/cm².
[044] Fig. 19 illustrates Selectivity of WO3-SnO2 Nanocomposite Sensor
Illustration of the selectivity of the WO3-SnO2 nanocomposite sensor towards different gases.
[045] Fig. 20 illustrates NO2 Gas Sensing by WO3-SnO2 Thin Films
Depiction of the NO2 gas sensing behavior of WO3-SnO2 thin films at varying fluences and temperatures.

DETAILED DESCRIPTION OF THE INVENTION
[046] An object of the present invention is to enhance the NO2 gas sensing properties of WO3-SnO2 nanocomposite thin films through low energy He+ ion beam implantation. The invention aims to improve the sensitivity and selectivity of nanocomposite-based gas sensors for NO2 detection at low temperatures by employing ion beam engineering methods for surface and structural modification of WO3-SnO2 thin films.
[047] An object of the present invention is to enhance the NO2 gas sensing properties of WO3 -SnO2 nanocomposite thin films by utilizing low energy helium ion (He?) beam implantation.
[048] Another object of the present invention is to provide a novel method for the preparation of WO3-SnO2 nanocomposite thin films using a sol-gel or physical deposition technique, ensuring homogeneous composition and nanoscale mixing.
[049] Another object of the present invention is to modify the surface morphology and electronic structure of WO3 -SnO2 nanocomposite thin films via ion beam engineering, thereby increasing active sites for gas adsorption.
[050] Another object of the present invention is to develop a low-temperature NO2 gas sensor that can operate efficiently below 150 °C using ion beam-treated nanocomposite thin films.
[051] Another object of the present invention is to enhance the selectivity of WO3 -SnO2-based gas sensors toward NO2 over other interfering gases such as CO, NH3, and H2.
[052] Another object of the present invention is to increase the response and recovery speed of the gas sensor by optimizing ion beam parameters, such as ion energy, fluence, and exposure time.
[053] Another object of the present invention is to improve the stability and repeatability of N2 O sensing in WO3 -SnO2 nanocomposite films after ion beam treatment over prolonged operation.
[054] Another object of the present invention is to study the structural, morphological, and optical changes in the WO3 -SnO2 thin films induced by ion implantation using characterization techniques such as XRD, SEM, AFM, and UV-Vis spectroscopy.
[055] Another object of the present invention is to establish a reliable and scalable fabrication process for ion beam-treated WO3-SnO2 thin film gas sensors suitable for industrial or environmental monitoring applications.
[056] Another object of the present invention is to provide an environmentally friendly and energy- efficient method for the fabrication and operation of high-performance NO2 gas sensors based on metal oxide nanocomposites.
[057] Yet another object of the present invention is to synthesize a novel WO3-SnO2 nanocomposite material with tunable stoichiometry, represented as WxSnyOz, wherein x = 0.01 to 0.99, y = 0.01 to 0.99, and z = 0.01 to 0.99, to optimize gas sensing performance by tailoring the electronic and structural properties of the composite.
[058] Yet another object of the present invention is to investigate the effect of varying the molar ratios of tungsten to tin in the WO3 -SnO2 nanocomposite (WxSnyOz) on NO2 gas sensitivity, selectivity, and operating temperature, to identify the optimal composition for enhanced sensing.
[059] Yet another object of the present invention is to fabricate WO3 -SnO2 nanocomposite thin films on silicon and glass substrates using RF magnetron sputtering, enabling uniform deposition and strong adhesion for subsequent gas sensing applications.
[060] Yet another object of the present invention is to treat the synt3hesized WO3-SnO2 nanocomposite thin films with low-energy helium (He?) ion beams at controlled fluences of 1×10¹5, 5×10¹5, and 1×10¹6 ions/cm², in order to systematically alter their structural, optical, and surface properties.
[061] Yet another object of the present invention is to investigate the influence of He ion beam implantation on crystallite size, optical band gap, extinction coefficient, and Urbach energy of WO3 -SnO2 nanocomposite thin films through XRD, UV-Vis spectroscopy, Raman spectroscopy, and XPS analysis.
[062] Yet another object of the present invention is to evaluate the NO2 gas sensing characteristics of pristine and He? ion -irradiated WO3 -SnO2 thin films at various operating temperatures (30–90 °C), and determine the improvements in sensitivity, response time, and recovery time.
[063] Yet another object of the present invention is to demonstrate He implantation significantly enhances the NO2 gas sensing response of WO3 -SnO2 thin films—from 1.45 (pristine) to 2.66 (implanted at 1×10¹5 ions/cm²) —with faster response (1 s) and recovery (30 s) at low operating temperatures, making them suitable for real-time environmental monitoring.
[064] Yet another object of the present invention is to provide a series of WO3 -SnO2-based sensing materials with variable composition ratios (WxSnyOz; x = 0.01–0.99, y = 0.01–0.99, z = 0.01–0.99), enabling precise control over microstructure, crystallinity, and oxygen vacancies to achieve superior NO2 gas detection efficiency.
[065] Fabrication Method: WO3-SnO2 nanocomposite thin films are deposited on appropriate substrates using RF sputtering. Post-deposition, the films are irradiated with He? ions at an energy of 125 keV at varying fluences:
• 1×10¹5 ions/cm²
• 5×10¹5 ions/cm²
• 1×10¹6 ions/cm²
SRIM/TRIM simulations are used to evaluate the electronic and nuclear energy losses during irradiation.
[066] Characterization: Various analytical techniques are used to characterize the films before and after irradiation: X-ray Diffraction (XRD): Used to evaluate changes in crystallinity. The crystallite size increases with fluence, ranging from approximately 23.79 nm to 38.45 nm. Debye-Scherrer’s equation is used for analysis.
[067] Raman Spectroscopy: Confirms phase identification and structural modifications of the WO3 and SnO2 components pre- and post-irradiation. UV-Visible Spectroscopy: Determines the optical band gap, which is influenced by irradiation-induced defects and structural changes. Atomic Force Microscopy (AFM): Analyzes surface morphology and roughness variations. X-ray Photoelectron Spectroscopy (XPS): Confirms the presence and oxidation states of Sn, W, and O atoms, and provides insight into surface chemistry alterations due to ion irradiation.
[068] Gas Sensing Performance: Gas sensing measurements are conducted using NO2 (10 ppm) as the target gas. The sensing response is measured at temperatures ranging from 30 to 90?°C. The irradiated thin films demonstrate a significant enhancement in response compared to pristine films, attributable to changes in grain size, surface states, and electronic structure induced by He? ion exposure.
[069] Further, present invention may be described in more details as follows:
[070] Example: Synthesis and Deposition of WO3-SnO2 Nanocomposite Thin Films
[071] Synthesis of WO3-SnO2 Nanocomposite Powder:
[072] WO3-SnO2 nanocomposite powder was synthesized via a hydrothermal method. Initially, sodium tungstate dihydrate (Na2WO4•2H2O) was dissolved in deionized water under continuous stirring to form a homogeneous solution. Subsequently, 5 grams of glucose and 0.5 mmol of sodium stannate monohydrate (Na2SnO3•H2O) were added to the solution. The resultant mixture was vigorously stirred for 10 minutes and then transferred into a Teflon-lined stainless-steel autoclave.
[073] The autoclave was sealed and maintained at a temperature of 180?°C for 20 hours. Upon completion of the reaction, the autoclave was allowed to cool to room temperature naturally. The solid precipitate was recovered through centrifugation and repeatedly washed with ethanol and deionized water to remove impurities. The cleaned powder was then dried at 60?°C to obtain the final WO3-SnO2 nanocomposite powder.
[074] Target Fabrication: The dried WO3-SnO2 powder was used to fabricate a sputtering target. A 2-inch diameter pellet was prepared using a hydraulic press operated at a pressure of 6 tons. The target was fabricated at the Inter-University Accelerator Centre (IUAC), New Delhi.
[075] Thin Film Deposition via RF Sputtering: Radio Frequency (RF) magnetron sputtering was employed to deposit thin films of the WO3-SnO2 nanocomposite onto cleaned Blue Star glass and silicon substrates. The sputtering process was carried out at the Malaviya National Institute of Technology (MNIT), Jaipur, India.
[076] Key deposition parameters are Substrate-to-target distance: 8 cm, Base pressure: 1.64 × 10?5 mbar, Working pressure: 3 × 10?² mbar, Argon gas flow rate: 15 sccm, Substrate rotation rate: 10–12 rpm.
[077] The film thickness, measured using profilometry, was approximately 100 nm. Post-deposition, the thin films were annealed at 550?°C in air to enhance crystallinity and improve surface properties.
[078] Low-Energy Ion Beam Irradiation
[079] The WO3-SnO2 nanocomposite thin films were subjected to low-energy helium ion (He?) beam irradiation at an energy of 125 keV, using a beam current of 500 pA. The irradiation was performed at varying fluences of 1×10¹5, 5×10¹5, and 1×10¹6 ions/cm² to investigate the effect of ion dosage on the structural and functional properties of the nanocomposite films.
[080] The irradiation process was conducted at the Inter-University Accelerator Centre (IUAC), New Delhi, utilizing a Pelletron accelerator (15UD Tandem) capable of delivering high-precision ion beams.
[081] To evaluate the interaction of the ion beam with the thin film material, simulations were performed using the SRIM (Stopping and Range of Ions in Matter) and TRIM (Transport of Ions in Matter) software. Developed by James F. Ziegler and collaborators, SRIM provides detailed analysis of ion energy losses—both electronic and nuclear—while TRIM uses Monte Carlo simulations to model ion penetration, defect generation, and atomic displacements in the target material.
[082] Simulation results revealed that, under low-energy ion beam conditions (125 keV), nuclear energy loss is predominant over electronic energy loss in the WO3-SnO2 nanocomposite system. This suggests that the primary mechanism responsible for structural and electronic property changes in the thin films is atomic displacement caused by nuclear collisions.
[083] Figure 2 illustrates the Comparison of electronic and nuclear energy losses for 125 keV He? ion irradiation.
[084] Figure 3 illustrates the Simulation output showing ion penetration depth, displacement of target atoms, phonon generation, and ionization effects.
[085] These structural disruptions and defect formations are critical in modifying the surface and electronic properties of the WO3-SnO2 nanocomposite thin films, contributing significantly to enhanced gas-sensing performance observed post-irradiation.
[086] Fabrication of Gas Sensor and Gas Sensing Measurements: To fabricate the gas sensor, interdigitated electrodes (IDEs) were patterned onto the surface of the previously prepared WO3-SnO2 nanocomposite thin film. The IDEs were fabricated by depositing platinum (Pt) onto a glass substrate using radio frequency (RF) sputtering in 100% argon (Ar) atmosphere. Prior to Pt deposition, a thin titanium (Ti) adhesion layer was sputtered for 2 minutes to enhance the adhesion of Pt to the glass substrate.
[087] After the successful deposition of IDEs, the platinum electrodes were carefully aligned and masked over the WO3-SnO2 thin film to ensure proper contact and conductivity. This assembly formed the basis of the gas sensor device, which was subsequently used to evaluate gas sensing characteristics under controlled experimental conditions.
[088] Gas Sensing Performance Evaluation: The gas sensing performance of the WO3-SnO2 nanocomposite thin film sensor was evaluated using a custom-built Gas Sensor Test Rig (GSTR). The setup comprised a sealed glass test chamber capable of introducing and removing gases with precision. A concentration of 10 ppm nitrogen dioxide (NO2) gas was injected into the chamber using a calibrated needle valve.
[089] Electrical resistance variations in response to gas exposure were measured using a Keithley 6514 electrometer (USA) connected to a computer system for real-time data acquisition. Resistance values were recorded at one-second intervals throughout the sensing cycle.
[090] After the resistance stabilized upon NO2 exposure, the test chamber was purged with ambient air to enable recovery of the sensor. This flushing process restored the chamber environment to its baseline condition for subsequent testing cycles. The sensor response (S) was calculated using the formula:
S=Rg-RaRaS = \frac{R_g - R_a}{R_a}S=RaRg-Ra
Where:
• S is the sensor response,
• R? is the resistance in air (baseline),
• R9 is the resistance in the presence of NO2 gas.
[091] The response time is defined as the time taken for the sensor resistance to reach 90% of its maximum change upon NO2 exposure. The recovery time is the duration required for the resistance to return to 90% of its original value after the removal of the gas.
[092] This setup and methodology enabled accurate evaluation of the sensor’s performance, including sensitivity, repeatability, response time, and recovery characteristics.
[093] Structural Analysis: XRD confirmed monoclinic WO3 (JCPDS 43–1035) and rutile SnO2 (JCPDS 41-1445). Ion implantation (125 keV He) reduced crystallite sizes from 17.74 nm to 9.43 nm (WO3) and 5.56 nm to 2.71 nm (SnO2) as fluence increased from pristine to 1×10¹6 ions/cm². Dislocation density and strain increased: WO3 (d: 0.31?1.12 ×10¹6 m?², strain: 0.39?0.74%), SnO2 (d: 3.23?10.61 ×10¹6 m?², strain: 1.39?2.51%).
[094] Raman Spectroscopy: WO3 peaks: 237, 305, 810 cm?¹; SnO2 peaks: Eg, A1g, B2g (A2g inactive, indicates oxygen vacancy). Raman confirms coexistence of WO3 and SnO2 phases post-implantation.
[095] Atomic Force Microscopy (AFM): Grain size increased from 23.79 nm (pristine) to 38.45 nm (1×10¹6 ions/cm²). Roughness (Rq) decreased initially, then increased: 35.8?22.8?27.5?29.8 nm. Skewness and kurtosis indicate increasing surface asymmetry and peak sharpness with fluence.
[096] UV-Visible Spectroscopy: Band gap decreased from 3.88 eV (pristine) to 3.82 eV (1×10¹6 ions/cm²), Urbach energy rose from 1.108 to 1.183 eV, indicating increased disorder. Skin depth dropped with photon energy rise, cutoff shifted from 3.95 eV to 3.97 eV.
[097] XPS Analysis: X-ray Photoelectron Spectroscopy (XPS) confirmed the presence of W, Sn, and O along with surface carbon impurities in both pristine and He ion-implanted WO3-SnO2 thin films at fluences of 1×10¹5, 5×10¹5, and 1×10¹6 ions/cm². No significant compositional changes were observed post-implantation. However, small shifts in binding energies (e.g., W4f7/2 from 35.6 to 34.5 eV, Sn3d5/2 from 486.8 to 486.4 eV) suggested minor changes in the electronic structure due to ion implantation.
[098] Gas Sensing Performance: The WO3-SnO2 nanocomposite thin film implanted at 1×10¹5 ions/cm² showed a significantly enhanced NO2 sensing response (2.66 at 80?°C) compared to the pristine film (1.45). The ion-implanted film also exhibited faster response (1?s) and recovery (30?s) times versus the pristine sample (7?s and 35?s, respectively). Improved sensing was attributed to defect-induced electronic modifications from ion implantation, leading to higher sensitivity and selectivity toward NO2.
[099] In this study, RF magnetron sputtering was used to fabricate WO3-SnO2 nanocomposite thin films on glass and silicon substrates, which were then exposed to a 125 keV He ion beam at different fluences. The effects of low-energy ion beam irradiation on the structural, optical, morphological, and gas sensing properties of the films were thoroughly analyzed.
[0100] The ion irradiation resulted in significant changes in the structural properties of the WO3 and SnO2 films. The X-ray diffraction (XRD) analysis showed that the crystallite size of the WO3 film decreased from 17.74 nm to 9.43 nm, while the SnO2 film size decreased from 5.56 nm to 2.71 nm as the fluence increased to 1E16 ions/cm². This reduction in crystallite size can be attributed to the implantation of ions at 125 keV.
[0101] Optically, the WO3-SnO2 nanocomposite films exhibited notable changes in their absorbance, optical band gap, extinction coefficient, skin depth, and Urbach energy. The optical band gap, determined via Tauc’s plot, decreased slightly from 3.88 eV to 3.82 eV as the ion fluence increased from pristine to 1E16 ions/cm². Raman spectroscopy confirmed the monoclinic phase of tungsten oxide and the rutile phase of tin oxide, while XPS analysis identified various surface components such as W4f, W4d, Sn3d, Sn3p, and O1s for both pristine and ion-implanted thin films.
[0102] In terms of gas sensing performance, both pristine and He ion-implanted WO3-SnO2 nanocomposite thin films were tested for NO2 sensing at 10 ppm in a temperature range of 30 to 90°C. The ion-implanted thin film exhibited an enhanced sensing response of 2.66, compared to the pristine film's response of 1.45 at 80°C. Furthermore, the ion-implanted films showed faster response and recovery times, with a response time of 1 second and recovery time of 30 seconds, compared to the pristine film's response time of 7 seconds and recovery time of 35 seconds.
[0103] Thus, the low-energy ion beam irradiation of WO3-SnO2 nanocomposite thin films improved their structural, optical, and gas-sensing properties, particularly enhancing their response times and sensitivity to NO2. This makes ion-implanted WO3-SnO2 nanocomposite films promising candidates for advanced gas sensing applications.
[0104] The present invention relates to the gas-sensing characteristics of RF Sputtered WO3-SnO2 nanocomposites thin films implanted by 125 keV energy at varying fluences 1×1015, 5×1015, and 1×1016ions/cm2 shown in schematic diagram 1. The sensing outcomes such as selectivity, sensing response, response time, selectivity, and measuring rage were calculated. The structural, morphological, and optical study of WO3-SnO2 thin films was done by various techniques including X-ray Diffraction (XRD), Atomic Force Microscopy (AFM), UV-visible spectroscopy, Raman Spectroscopy, X-ray Photoelectron Spectroscopy (XPS)and Photoluminescence Spectroscopy (PL).
[0105] Experimental: WO3-SnO2 powder was prepared by hydrothermal method by dissolving Na2WO4. 2H2O in deionized water and a homogeneous solution was formed by stirring the solution. After that, 5 g of glucose and 0.5 mmol Na2SnO3H2O were added to the mixture mentioned above. The mixture was put into a stainless autoclave lined with Teflon and heated to 180 °C for 20 hours after being vigorously stirred for 10 minutes. The resulting solid products have been extracted by centrifugation after being cooled to room temperature and repeatedly cleaned with ethanol and deionized water and the powder is dried at 60 °C.Then the target was made at IUAC, New Delhi by using 2-inch die at 6 tonn pressure. Radio Frequency (RF) Sputtering has been employed to create thin layers of tungsten oxide (WO3) and tin oxide (SnO2) on blue star glass and silicon substrates at MNIT in Jaipur, India. The substrate and target distance was fixed to 8 cm. The working and base pressures during deposition were 3×10-2 mbar and 1.64×10-5 mbar, respectively. The Ar gas was flowing with a rate of 15 sccm with a rotation rate of 10-12 rpm. The WO3-SnO2 nanocomposites thin films were observed to be ? 100 nm during sputtering by profilometry.After the deposition of nanocomposite thin films, they were annealed at 550 °C.
[0106] Low Ion Beam Irradiation: The nanocomposite thin films were targetedto low-energy ion beam irradiation at energy of 125 keV by He ion with current of 500 pnA with varying fluences from 1×1015, 5×1015, and 1×1016.WO3 thin films were subjected to ion beam radiation using a Pelletron accelerator tandem (15UD) at the Inter-University Accelerator Center in New Delhi. Numerous factors such as energy losses, generation of phonons, ionization and target range were calculated by the SRIM software which was developed by James F. Ziegler and Biersack and TRIM software gives the Monte Carlo Simulation. The SRIM/TRIM simulation program was utilized to study the damages caused by ion beam irradiation of the material.Fig. 2 shows the loss of nuclear and electronic energy using a 125 keV He ion beam.Nuclear energy is lost more than electronic energy in a low-energy ion beam irradiation of WO3-SnO2 nanocomposite thin films. Therefore, nuclear energy losses became the primary cause of fluctuations in thin film properties. Various parameters such as displacement of atoms, target ionization, depth and targeted phonons is shown in fig 3.
[0107] Characterization Techniques: Several techniquesincluding X-ray diffraction (XRD), Atomic Force Microscopy (AFM), UV-visible spectroscopy,Raman spectroscopy, and X-ray photoelectron spectroscopy were used to analyze the thin films bombarded with 125 keV He ions at fluence of 1×1015, 5×1015, and1×1016 ions/cm2. The structural investigation of pristine and ion beam implanted WO3-SnO2 thin film at a fluence of 1×1015, 5×1015, and 1×1016 was carried out by X-ray diffraction (XRD).Optical characterization was performed at the Inter-University Accelerator Centre (IUAC) in New Delhi, India, using a Hitachi U-3300 spectrophotometer in the 250-750 nm range. The modifications in morphological traits were analyzed by Atomic Force Microscopy using a Bruker multimode instrument in tapping mode at Malaviya National Institute of Technology, Jaipur. Raman spectroscopy was used to investigate the phase of WO3-SnO2 nanocomposite thin films and elemental analysis was done by XPS spectroscopy.
[0108] Fabrication of Gas Sensor and Gas Sensing Measurements: The gas sensor was fabricated by masking IDEs on prepared WO3-SnO2 nanocomposite thin film. Platinum target in a 100% argon atmosphere were used to grow Pt film on a glass substrate using RF sputtering. Sputtering of Ti metal for 2 minutes ensured Pt adhered well to the glass substrate. After the preparation of IDEs on WO3-SnO2 nanocomposite thins the gas sensing parameters were determined.
[0109] Gas Sensing: An indigenously created gas sensor test rig (GSTR) with a glass test chamber has been used to determine the gas sensing performance of the material. A 10 ppm of NO2 gas was injected into the GSTR with the needle valve. A data collecting system was used to record variations in resistance values of sensors in response to target gas interactions.The system employed is a Keithleyelectrometer (6514, USA) coupled with a computer for data gathering and processing. Resistance values were collected each second.After obtaining a steady resistance value, the gas in the GSTR was flushed out to return to the starting state.The sensor's response towards NO2 gas is defined as the ratio of resistance fluctuation during NO2 gas interaction to resistance in the air atmosphere is expressed as:
(1)
[0110] Where S is the sensor response of the material, Rg represents the sensors resistance when exposed to NO2 gas and Ra indicates the sensor resistance in the surrounding atmosphere. The gas sensors response time is identified as the time it takes to attain 0.9 times its highest resistance, while the recovery time is the time it requires to get back to 90% of the initial resistance after the evacuation of NO2gas.
[0111] Results: Structural Analysis: XRD pattern of pristine and 125 keV ion beam implanted WO3-SnO2 nanocomposite thin film at various fluence is shown in fig 4. We used X-ray diffraction to assess numerous aspects such as dislocation density, crystal structure, full-width half maxima, and strain of pristine and implanted WO3-SnO2 nanocomposite thin films. The XRD pattern was recorded in a range from 20° to 80°. The peak obtained at 2? = 25.32°, 29.7°, 42.8°, 58.7°, 63.07°, 71.8° and associated with the planes 200,112,222, 420, 143 and 440. These planes matched with the JCPDS No. 43–1035 and denoted the monoclinic nature of WO3 thin films. Similarly, the peaks were reflected at angles 26.5°, 34.1°, 37.8°, 52.9°, 55.8°, 65.9° with the planes 110,101,200,211,220 and 301 and these indicate the rutile phase of SnO2 with the JCPDS No. 41-1445.Small modifications in the peaks werenoticed after ion beam implantation of WO3-SnO2 thin films by 125 keV.The peak intensity of WO3-SnO2 thin films decreases as one raises ion fluence from pristine to 1×1016 ions/cm2due to defects, dislocations, and grain splitting. At higher fluence 1×1016 ions/cm2, some amorphization arises due to high localized temperature caused by the 125 keV He ion beam.
[0112] The Debye Scherrer formula was employed to determine the crystallite size of WO3-SnO2 thin films and ion-implanted samples for the plane (200) and (110) of WO3 and SnO2 thin films.
D = 0.94? \ß cos ? (2)
[0113] Where ? signifies the X-ray wavelength, ß defines full-width half maxima, and ? indicates the sample's diffraction angle.Table 1,2 illustrates the crystallite size of WO3-SnO2 thin films before and after ion implantation by He ion with an energy of 125 keV. The crystallite size of the virgin WO3 and SnO2 thin films for the crystallographic plane (200) and (110) has been estimated to be 17.74 nm and 5.56 nm. After ion beam implantation by He ion at different fluences varying from 1×1015, 5×1015, and 1×1016, ion/cm2the crystallite size of WO3 varies from 17.74 nm to 9.43 nm and the crystallite size of SnO2 varies from 5.56 nm to 2.71 nm as shown in table 1,2.The decrease in crystallite size of the WO3-SnO2 thin film as we go from virgin to He ion beam implanted with distinct fluences 1×1015, 5×1015, 1×1016 ion/cm2is a result of an increase in microstrain induced by implantation in the material, which causes defects in the thin film.Ion beam irradiation by He ion beam creates defects, predominantly oxygen vacancies in WO3-SnO2 thin films, which can be ascribed to the sputtering effect, thereby decreasing the sample's crystallinity.We explored that the oxygen vacancy created by ion beam may be exploited to enhance the electrical conductivity.
Equations 3 and 4 estimate the lattice strain and dislocation density of virgin and implanted WO3-SnO2 thin films at fluences 1×1015, 5×1015, 1×1016, ion/cm2 for the plane (200) and (110)
? = ?? /4 ???????? (3)
d = 1/ D2 (4)
[0114] where ? represents strain, ?? is the diffraction angle, d denotes the dislocation density, and D is the sample's crystallite size. The dislocation density and strain for virgin and implanted WO3 thin films are displayed in table 1 and SnO2 in table 2. The dislocation density and strain of WO3-SnO2 thin films increase as we go from pristine to a higher fluence of 1×1016 ions/cm2.When an ion is irradiated, two concurrent processes operate at the same time the generation and accumulation of vacancies, which collapse into disordering loops, the annihilation of possible sinks. Furthermore, the production and annihilation of vacancies are enhanced with sink density and ion fluences.As a result, dislocation density rises in proportion to ion fluence. When the ion fluence increases, energy transmission by He ions increases, leads to orientation of plane. This phenomenon leads to increased distortion and strain in the thin film.
[0115] Table 1.The calculated value of full-width half maxima, crystallite size, dislocation density, and strain (k) of WO3 for the plane (200) implanted with distinct ion fluences at 125 keV.

Fluence (ions/cm2) FWHM (radians) Crystallite Size (nm) Dislocation Density(d) (×1016 m-2) Strain (×10-2)
Pristine 0.009 17.74 0.31 0.39
1×1015 0.012 13.30 0.56 0.52
5×1015 0.015 10.64 0.88 0.66
1×1016 0.017 09.43 1.12 0.74

[0116] Table 2. The estimated value of crystallite size, full-width half maxima,dislocation density, and strain (k) of SnO2 for the plane (110) implanted with distinct ion fluences at 125 keV.
Fluence (ions/cm2) FWHM (radians) Crystallite Size (nm) Dislocation Density(d) (×1016 m-2) Strain (×10-2)
Pristine 0.0279
5.56 3.23 1.39
1×1015 0.0296 5.25 3.62 1.46
5×1015 0.0404 3.85 6.74 2.00
1×1016 0.0503 2.71 10.61 2.51

[0117] 3.2 Raman Spectroscopy:
At room temperature with an excitation wavelength of 532 nm, Raman spectra were captured in the 200–1200 cm-1 wavelength rangeand used to demonstrate phase of virgin and implanted WO3-SnO2 thin films at different fluences 1×1015, 5×1015, and 1×1016, ion/cm2, as shown in Fig. 5.This methodology accurately describes the expected vibration modes of a material based on its purity and phase. The Raman peak observed at wavelengths 237 cm-1 and 305 cm-1 relates to the O-W-O bending mode of WO3. The peak obtained at 810 cm-1 is due to stretching modes such as O deformation modes, W-O stretching and W-O bending modes and shows the monoclinic phase. Four peaks of SnO2 thin film were observed which is attributed to lattice vibrational mode: Eg, A2g, A1g and B2g. In the observed spectrum, visible lattice vibrational modes Eg, A1g, and B2g are Raman active, whereas A2g is inactive modeand shows rutile structure.The presence of oxygen vacancies in SnO2 causes its Raman inactive mode. The Raman analysis of virgin and implanted WO3-SnO2 nanocomposite thin films shows typical peaks related to the vibrational modes of WO3 and SnO2, which were explained above.This validates the existence of both WO3 and SnO2 in the virgin and implanted WO3/ SnO2 thin films.
[0118] Atomic Force Microscopy: The surface characteristics of pristine and He ion beam implanted WO3-SnO2 nanocomposite thin film were studied using atomic force microscopy in tapping mode. The 2D and 3D images of pristine and implanted nanocomposite thin films at varied fluences 1×1015, 5×1015, and 1×1016, ion/cm2 are displayed in Fig 6.
[0119] The grain size of pristine and ion implanted WO3-SnO2 nanocomposite thin films at various fluences was measured by Gwyddion software. AFM scans were used to calculate the grain size of WO3-SnO2 thin films, as can be seen in the bar graph in Figure 7. The pristine WO3-SnO2 thin film shows a grain size of 23.79 nm and after implantation with 125 keV He ion at higher fluence, it becomes 38.45 nm. The alteration in grain size may be due to cluster breakage caused by energy transfer from incident ions. During the ion beam irradiation, the kinetic energy of released secondary electrons is transferred from the target atom to the lattice through electron-phonon interaction, leading to a rise in grain size. This mechanism causes morphological changes by raising the temperature of the material lattice.
[0120] The optical surface of the sample's thin films is determined by the root mean square roughness (rms). The standard deviation of thin film surface height is known as root mean square roughness. The deviation of thin-film surface irregularities from the mean line on the specimen length is identified as the average surface roughness (Ra).The vertical distance across a thin film's surface between its highest peak and the smallest valley is termed as the Rmax value. Theskewness, average roughness, root mean square, and kurtosis is shown in table 3. The alteration in root mean square value and average surface roughness is found for pristine and WO3-SnO2 implanted thin film. Material transportation-induced surface diffusion cause a reduction in surface roughness.
[0121] Table 3. The measured value of grain size, Root mean square roughness (Rq), Roughness average (Ra), Skewness, andKurtosis for pristine and implanted WO3-SnO2 thin films at distinct fluences.

Sample Grain Size Root mean square roughness (Rq) Roughness average (Ra) Maximum peak to valley roughness (Rmax) Skewness Kurtosis
Pristine 23.79 35.8059 26.1198 512.710 0.255621 9.62527
1E15 ions/cm2 34.27 22.8370 15.8455 376.768 0.675773 20.0727
5E15 ions/cm2 35.47 27.4686 17.8722 458.630 1.51712 26.0178
1E16 ions/cm2 38.45 29.7820 19.0687 549.282 0.494418 23.2218

[0122] 3.4 UV-Visible Spectroscopy:
[0123] UV-Visible spectroscopy is a significant tool for the characterization of different materials; it identifies various properties such as band gap, urbach energy, skin depth, extinction coefficient, and functional groups. The optical band gap is a vital characteristic for identifying the unique area of application of semiconducting material. Hence band gap value is required to be calculated properly to establish optimum device application and their performance.The UV-vis spectra of virgin and ion irradiated WO3-SnO2 nanocomposite thin film at different fluence measured between 200nm and 800nm. An absorption peak for pristine and ion beam irradiated WO3-SnO2 nanocomposite thin films is detected in the region of the wavelength range of 300-400 nmas displayed in fig 8. The thin film absorption spectrum of radiation on glass and silicon substrate is mainly influenced by oxygen deprivation, impurity centers, RMS, and average surface roughness.
[0124] The band gap energy (Eg) for pristine and ion-irradiated samples is derived using Tauc's relation shown in eq.5
(5)
[0125] The eq. displays a is the optical absorption coefficient, hv is the photon energy, Amis the sample constant, and Eg is the optical energy bandgap.The optical bandgap energy will be interpreted as the direct bandgap of the material if factor n has a value of ½ and the indirect band gap has a value of 2. The direct band gap value for pristine and ion beam implanted WO3-SnO2 nanocomposite thin film is shown in fig 9. Pristine WO3-SnO2 nanocomposite thin film shows a band gap of 3.88 eV and ion beam implantation at higher fluence 1×1016, ion/cm2 it becomes 3.82 eV as shown in table 4.The decrease in the band gap after ion beam implantation is due to growth in the grain size, defect level development, quantum confinement effect, generation of ions and free radicals in the valance band. As the bandgap reduces, the valance band energy increases, increasing the conductance.
[0126] Table 4. The direct band gap and Urbach energy for pristine and He ion implanted samples at various fluences.
Fluence Direct Band Gap(eV) Urbach Energy(eV)
Pristine 3.88 1.108
1E15 3.86 1.111
5E15 3.83 1.171
1E16 3.82 1.183

[0127] The trajectory of the absorption coefficient curve's straight line vs incident photon energy was employed to calculate the Urbach energy. The exponential portion of the coefficient of the absorption curve can be used to identify the Urbach tail. In view of this disorder that developed in the material, the band gap is affected by the prolonged portion of the localized state in the absorption coefficient curve. Equations 6 and 7 were employed to determine the Urbach energy of both implanted and pristine materials.
(6)
ln + ln ( (7)
where a0 is the steady, a is the absorption coefficient, and Eu is the thin-film band tail width energy. The fluctuation of ln(a) versus hv(eV) is shown in fig 10 a. The Urbach energy for pristine WO3-SnO2 nanocomposite thin film is observed to be 1.108 eV and after ion beam implantation at fluence it becomes1.183 eV.
[0128] Fig. 10(b) illustrates the extinction coefficient (k) WO3-SnO2 nanocomposite thin film for various ion fluence varies with the incoming light wavelength. The small enhancement in the extinction coefficient was observed with an increase in the thickness of the sample as well as incorporating surface roughness. The extinction coefficient can be obtained through the relation where denotes the coefficient of absorption and is the incident light wavelength. The extinction coefficient significantly influences the material's optical characteristics. It determines the amount of scattering and absorption loss per unit distance in the thin film.
[0129] Skin depth (d) is the thickness of a thin film where the optical photon density equals 1/a at the lateral surface. It depends on the conductivity of thin films and intensity of incoming photon in UV-Visible range. The optical band gap significantly affects conductivity in semiconductor materials. Skin depth and optical properties are clearly connected and can also be seen from the relation.
(8)
[0130] The plot between the skin depth and photon energy is illustrated in fig 10 (c). As increases in photon energy of WO3-SnO2 nanocomposite thin film the skin depth decreases with the fluences. The cut-off energy refers to the incoming photon energy at which the skin depth becomes zero. The cut-off energy for pristine WO3-SnO2 nanocomposite thin film is 3.95 eV and for higher fluence 3.97eV.
[0131] X-ray Photoelectron Spectroscopy: X-ray photoelectron spectroscopy (XPS) was applied to elucidate the chemical composition of pristine and He ion beam implanted WO3-SnO2 thin film at various fluences 1×1015, 5×1015, and 1×1016, ion/cm2 is displayed in fig. The XPS analysis was performed using the Omicron ESCAþ system, Oxford Instruments, Germany. Throughout the procedure, the chamber temperature was regulated at 24°C, while the operating current and voltage were maintained at 20 mA and 15 kV, respectively. The samples were extensively degassed overnight within the XPS FEL chamber, achieving a vacuum level of 5.2 × 10?¹° mbar. The angle of view between the analyzer and the source was 90°. The XPS spectra were recorded employing a monochromatic excitation source with energy of 1486.7 eV. The survey spectra in fig 11. illustratean appearance of W, Sn, and O together with surface impurity carbon in pristine and He ion implanted WO3-SnO2 thin films. The photoelectron peaks were obtained W4f, W4d,C1s, W4p, Sn3d, O1s, Sn3p, OKLL and Sn MNN with the binding energy of 25.6 eV, 245.8 eV, 283 eV, 425.7 eV, 487.21 eV, 529.6 eV, 720.2 eV, 975.4 eV, and 1062.3 eV. The data collected agree with earlier reported data[79]. XPS survey spectra revealno difference between before and after implantation of WO3-SnO2 thin film at different fluences 1×1015, 5×1015, 1×1016 ion/cm2.
[0132] Table 5: The survey spectra and observed core level with the binding energy of pristine and He ion implanted WO3-SnO2 thin films.
Sample Binding Energy (W4f7/2) Binding Energy (W4f5/2) Spin-orbit splitting (d4f) Binding Energy
Sn3d5/2 Binding Energy
Sn3d3/2 Spin-orbit splitting(d3d)
Pristine 35.6 eV 37.7 eV 2.0 486.8 eV 495.3 eV 8.5
5E14 ions/cm2 34.5 eV 36.4 eV 1.9 486.4 eV 494.9 eV 8.6
1E15 ions/cm2 35.4 eV 37.5 eV 2.1 486.6 eV 495.0 eV 8.4
5E15 ions/cm2 35.3 eV 37.4 eV 2.9 486.4 eV 494.2 eV 7.8

[0133] Figure 12 shows the high-resolution spectra of tungsten, tin and oxygen.The XPS spectra exhibit two peaks, W4f7/2 and W4f5/2, for tungsten atom from pristine to fluences of 1×1016 ion/cm2. The binding energy and spin-orbit splitting of pristine to higher fluence 1×1016ion/cm2is shown in table 5. Similarly, tin shows two states Sn3d5/2and Sn3d3/2corresponding to photoelectron peaks at 486.8 eV and 495.3 eV respectively with the spin-orbit splitting of 8.5. The XPS peak of tin indicates the +4 state of oxidation of SnO2. The oxygen peak (O1s) was identified at 530.7 eV for pure WO3-SnO2 thin film, while for higher fluence 1×1016, ion/cm2, becomes 530.5 eV. After implantation with 125 keV at different fluences, a small shifting of peaks was seen; this might be because the electronic structure of the nanocrystals fluctuates, affecting the binding energy as well.
[0134] Sensing attributes:
The sensing properties of pristine and He ion beam-treated WO3-SnO2 nanocomposite thin film at fluence of 1E15 ions/cm2 are investigated by measuring the fluctuations in the resistance of the oxide thin film when interacting with the oxidizing gas NO2 and in the ambient air. The resistance profile of pristine and 1E15 ions/cm2 WO3-SnO2 nanocomposite thin film in the atmosphere is displayed in fig 13.and towards 10 ppm NO2 gas with the temperature range 30 °C–90 °C is shown in fig14.The value of resistance in the environment decreases with the rise in temperature revealing its semiconducting nature. The sensing response for pristine and ion-implanted thin film towards the 10 ppm of NO2 gas with the temperature range from 30°C to 90°C is shown in fig15. It can be observed that the pristine and 1E15 ions/cm2 implanted WO3-SnO2 nanocomposite thin film sensor response initially enhances up to an operating temperature and then seems to decrease. The optimal operating temperature depends on several factors including rapid recovery time, fast response time and quick sensor response. Pristine WO3-SnO2 nanocomposite thin film shows a maximum sensing response of 1.45 and at a fluence 1E15 ions/cm2 it is observed to be 2.66 with an operating temperature of 80°C towards the 10 ppm NO2 gas.
[0135] The variation in response time and recovery time of pristine and ion-implanted WO3-SnO2 nanocomposite thin film with the temperature is depicted in fig. 16. The response time and recovery time decrease with the escalation in temperature because of the faster adsorption and desorption process of NO2 molecules occurring on the surface of sensors. Pristine WO3-SnO2 nanocomposite thin film shows a response time of 7 seconds and recovery at 35 seconds and ion implanted thin film at fluence 1E15 ions/cm2 responds at 1 second and recovery at 30 seconds. The ion beam treated WO3-SnO2 nanocomposite thin film at a fluence of 1E15 ions/cm2 shows a good response with fast response and recovery as compared to pristine sample and is considered for gas sensing studies.The pristine and ion implanted WO3-SnO2 nanocomposite thin film response-recovery curve is illustrated in fig. 17. The creation of defects in the material is the reason of the improvement in the sensor response following ion beam implantation. The response-recovery curves have been recorded at 80 °C as shown in fig. 18. to further verify the sensor's repeatability.In contrast to NO2 gas, the gases H2S, CO, NH3, and CO2 had a significantly lower response, indicating that the WO3-SnO2 sensor is extremely selective for NO2 gas detection. Figure 19 displays the reactions to several gases.
[0136] Sensing Mechanism: WO3 and SnO2 have been recognized as an n-type semiconductor, with their electrical conductivity primarily attributed to the free electrons generated by surface oxygen vacancies and can also be seen from fig. 20. These vacancies act as electron donors, significantly contributing to the material's conductive properties. On the WO3 surface, the oxygen molecules are adsorbed and acquire free electrons, changing into different oxygen species including 2O-, O2-, or O- depending on the operating temperature. The depletion layer is developed at tungsten oxide surface because of the high resistance of WO3 sensors. The free electrons in the donor stage cause this depletion area to vary when the temperature rises, which affects the sensor's resistance.
(9)
(10)
(11)
[0137] When NO2 interacts with the WO3 sensor, it tends to capture free electrons from its surface since it is an oxidizing gas. When the gas is exposed in the chamber, a redox reaction occurs with the ionic species absorbed at the surface and capturing electron from conduction band as followed by the reaction
(12)
(13)
[0138] These two equations represent the potential reactions occurring at the sensor surface and in contrast to eq. 12, eq. 13 appears to be prevailing.Because the NO2 molecules are probably going to interact directly with the W sites at lower temperatures up to 200°C, eq. 12 is the primary reaction that occurs at the sensor's surface.
[0139] When WO3 and SnO2 both are integrated they form n–n type heterojunction. The work function of tin oxide is lower than that of tungsten oxide, so integration of SnO2 and WO3 created a depletion area near the SnO2 junction and an accumulation region arises in WO3 because of the transfer of electrons from SnO2 to WO3.In WO3-SnO2 composite sensor both the WO3 and SnO2 sensing sites are impacted by NO2 gas. The NO2 molecules interact by absorption and desorption place as explained in the equation. In the desorption process NO2–species transformed into NO molecules keeping behind the O- species which release electrons to restore the sensor's resistance to its initial level.
[0140] NO2 gas interacts with both the WO3 and SnO2 detecting sites in the WO3-SnO2 composite sensor device.As previously mentioned, the WO3 site interaction causes the NO2 gas molecules to be adsorbed into unstable nitrosyl species (NO2-), which are capable of losing electrons.Therefore, these NO2- species react with free Sn (from SnO2) sites in addition to NO2 gas molecules, leading to a larger Rgvalue and, consequently, an improved sensing response at a lower temperature than that achieved for both the pristine WO3 and pristine SnO2 sensors.
[0141] RF magnetron sputtering was used to fabricate WO3-SnO2 nanocomposite thin films on glass and silicon substrate and exposed to a He ion beam with 125 keV at different fluences.The findings demonstrate the effect of low energy ion beam irradiation of WO3-SnO2 nanocomposite thin films on structural, optical, morphological, and gas sensing characteristics. When nanocomposite thin films were exposed to low-energy ion beams, it possessed a larger nuclear loss than electronic energy losses. The X-ray diffraction study reveals that the crystallite size of WO3 thin film decreased from pristine to fluence of 1E16 ions/cm2 from 17.74 nm to 9.43 nm and SnO2 thin film from 5.56 nm to 2.71 nm due to implantation at 125 keV.The optical analysis revealed numerous characteristics of WO3-SnO2 nanocomposite thin films including absorbance, optical band gap, extinction coefficient, skin depth, and urbach energy. WO3-SnO2 nanocomposite thin films optical band gap was calculated by Tauc’s plot and it varies from 3.88 eV to 3.82 eV from pristine to a higher fluence of 1E16 ions/cm2.The Raman spectroscopy illustrates the monoclinic phase of tungsten oxide and the rutile phase of tin oxide. XPS spectra illustrate the existence of W4f, W4d, C1s, W4p, Sn3d, O1s, Sn3p, OKLL and Sn MNN for pristine and ion-implanted thin films. Pristine and He ion implanted WO3-SnO2 nanocomposite thin film at a fluence of 1E15 ions/cm2 have been investigated for their NO2 (10 ppm) sensing response characteristics in a temperature range of 30 to 90°C. The pristine thin film displaysa sensing response of 1.45 and after ion implantation, it exhibits a sensing response of 2.66 at an operating temperature of 80°C. The ion-implanted thin film illustrates a response of 1 second and recovery at 30 seconds, whereas the pristine WO3-SnO2 nanocomposite thin film indicates a response of 7 seconds and recovery at 35 seconds.
[0142] Advantages of the Invention:
• Enhanced gas sensing response at low operating temperatures.
• Controlled tuning of film properties through ion beam fluence adjustment.
• Improved understanding of ion irradiation effects on nanocomposite thin films.
, Claims:We claim:
1. A gas sensor device comprising:
a substrate selected from glass or silicon;
a WO3-SnO2 nanocomposite thin film deposited on the substrate;
a pair of interdigitated platinum electrodes disposed over the thin film, the electrodes being formed using RF magnetron sputtering with a titanium adhesion layer; wherein the WO3 -SnO2 thin film is subjected to low-energy helium ion (He?) beam irradiation at an energy of approximately 125 keV and a fluence in the range of 1×10¹5 to 1×106¹ ions/cm²; wherein said irradiation induces structural and surface modifications in the nanocomposite, enhancing the gas sensing performance of the device by increasing defect density and charge carrier mobility.
2. The gas sensor device as claimed in Claim 1, wherein the WO3-SnO2 thin film is prepared by a process comprising the steps of:
a) synthesizing WO3 -SnO2 nanocomposite powder by dissolving sodium tungstate dihydrate (Na2WO4•2H2O) in deionized water, adding glucose and sodium stannate monohydrate (Na2SnO3•H2O), and subjecting the mixture to hydrothermal treatment at 180 °C for 20 hours;
b) recovering the precipitate by centrifugation, washing with ethanol and deionized
water, and drying at 60 °C to obtain a nanocomposite powder;
c) compressing the powder into a sputtering target using a hydraulic press;
d) depositing the nanocomposite thin film on the substrate using RF magnetron sputtering under a base pressure of 1.64 × 10?5 mbar and argon flow rate of 15 sccm, with a substrate-to-target distance of 8 cm and substrate rotation rate of 10–12 rpm; and
e) annealing the deposited film at 550°C in air to enhance crystallinity and surface
morphology.
3. A method for detecting nitrogen dioxide (NO2) gas using the gas sensor WO3-SnO2 nano composite as claimed in Claim 1, wherein the WO3-SnO2 nanocomposite thin film is exposed to NO2 gas at a concentration of approximately 10 parts per million (ppm) within an operating temperature range of 30°C to 90 °C;
wherein the sensor demonstrates an enhanced sensing response of at least 2.66 at 80°C when the film has been subjected to helium ion (He?) beam irradiation at an energy of 125 keV and a fluence of 1×10¹5 ions/cm²;
wherein the sensor exhibits a response time of approximately 1 second and a recovery time of approximately 30 seconds; and
wherein the improved sensing performance is attributed to ion-beam-induced modifications in the nanocomposite film’s structural and electronic properties.
4. The method as claimed in Claim 3, wherein said ion irradiation results in a reduction in the crystallite size of WO 3from approximately 17.74 nanometers to 9.43 nanometers and of Sn2Ofrom approximately 5.56 nanometers to 2.71 nanometers;
wherein the irradiation induces an increase in dislocation density and lattice strain, alongside a decrease in optical bandgap energy from 3.88 electron volts (eV) to 3.82 eV, as measured by UV-Visible spectroscopy; and
wherein these microstructural and optical changes enhance the surface reactivity and carrier mobility of the nanocomposite, thereby improving sensitivity and selectivity toward NO2 gas.
5. A method of preparation of WO3 and SnO2 based gas sensing film comprising steps of:
a) Dissolving Na2WO4.2H2O in deionized water;
b) Stirring continuously the solution prepared in step a to prepare a homogenous solution;
c) Adding 5 grams of glucose and 0.5 m mol of Na2SnO3.H2O to the homogeneous solution as obtained in step b to make a resultant mixture and stirring the resultant mixture;
d) Transferring the resultant mixture as obtained in step c into an autoclave;
e) Maintaining the resultant mixture in autoclave at a predetermined temperature T1 for a predetermined time period TP1;
f) Cooling autoclaved mixture obtained in step e at a temperature T2;
g) Recovering solid precipitate of mixture obtained in step f by centrifugation and washing with ethanol and deionized water to obtain a powder;
h) Drying the powder at a predetermined temperature T3 to obtain WO3-SnO2 nanocomposite powder;
i) Depositing WO3-SnO2 nanocomposite powder on a substrate using sputtering to obtain a substrate deposited with a thin film of WO3-SnO2;
j) Annealing the substrate deposited with a thin film of WO3-SnO2 at a predetermined temperature T4;
k) Irradiating annealed substrate deposited with a thin film of WO3-SnO2 as obtained in step j with low energy He+ ions to obtain a WO3-SnO2 gas sensing film.
6. The method of preparation of WO3 and SnO2 based gas sensing film as claimed in claim 5, wherein the resultant mixture is stirred preferably for a time period of 10 minutes and the autoclave is preferably a Teflon-lined stainless steel autoclave.
7. The method of preparation of WO3 and SnO2 based gas sensing film as claimed in claim 5, wherein the predetermined temperature T1, T2, T3 and T4 are 180 °C, 27 °C (room temperature), 60 °C, 550 °C respectively.
8. The method of preparation of WO3 and SnO2 based gas sensing film as claimed in claim 5, wherein the substrate as claimed in step i of claim 5 is a 2 inch diameter pellet and is blue star glass and silicon based substrate and wherein the sputtering is a Radio Frequency (RF) magnetron sputtering.
9. The method of preparation of WO3 and SnO2 based gas sensing film as claimed in claim 5, wherein the deposition of WO3-SnO2 nanocomposite powder on the substrate is controlled by a number of key deposition parameters including substrate to target distance, base pressure, working pressure, argon gas flow rate and substrate rotation rate and thickness of the thin film of WO3-SnO2 is approximately 100 nm; wherein irradiation of the WO3-SnO2 nanocomposite thin films are subjected to low-energy helium ion (He?) beam irradiation at an energy of 125 keV, using a beam current of 500 pA and the irradiation was performed at varying fluences of 1×10¹5, 5×10¹5, and 1×10¹6 ions/cm²; wherein characterization of the WO3-SnO2 gas sensing film is done using techniques including X-ray diffraction (XRD), Atomic Force Microscopy (AFM), UV-visible spectroscopy, Raman spectroscopy and X-ray photoelectron spectroscopy.
10. A method of fabrication of a gas sensor to sense gas comprising:
Sputtering a thin Titanium (Ti) adhesion layer on a glass substrate;
depositing platinum (Pt) onto the glass substrate as obtained in step a by RF magnetron sputtering in a 100% Argon (Ar) atmosphere to fabricate interdigitated electrodes (IDEs);
Pattering interdigitated electrodes (IDEs) as obtained in step b on to the surface of the WO3-SnO2 nanocomposite thin film as claimed in claim 1 to obtain the gas sensor;
wherein the gas sensor senses preferably NO2 gas at low temperature ranging from 30°C-90°C; and Wherein, the gas sensor's response towards NO2 gas is defined as the ratio of resistance fluctuation during NO2 gas interaction to resistance in the air atmosphere is expressed as:

Where S is the sensor response of the material, Rg represents the sensors resistance when exposed to NO2 gas and Ra indicates the sensor resistance in the surrounding atmosphere.
Dated this 16th day of May, 2025


MADHU SMITA (IN/PA-3454) DURRO IP,
Agent for the Applicant(s)
To
THE CONTROLLER OF PATENTS,
THE PATENT OFFICE,
DELHI