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. 2025 Oct 28;10(44):53549–53556. doi: 10.1021/acsomega.5c09352

Room-Temperature Methanol Gas Sensor Based on PEDOT:Tosylate Thin Films: Enhanced Sensitivity through Urea Surface Treatment

Mutee Ur Rehman 1,*, Md Ataur Rahman 1, Shanmuga Sundar Dhanabalan 1,2, Eliza Switalska 3, Robert Komljenovic 4, Sherif Abdulkader Tawfik 5, Sunil Gupta 5, Sharath Sriram 1, Drew Evans 3, Madhu Bhaskaran 1,*
PMCID: PMC12612939  PMID: 41244493

Abstract

PEDOT:Tosylate (PEDOT:Tos), a conducting polymer, has emerged as a versatile material, yet its potential for gas sensing remains unexplored. This study presents the first investigation of pristine PEDOT:Tos as a chemiresistive gas sensor for detecting methanol (MeOH), at room temperature. We demonstrate that pristine PEDOT:Tos can detect methanol down to 5 ppm. Furthermore, we examine the influence of a simple urea surface treatment, which significantly enhances the sensor’s performance. The urea-modified sensor exhibits an ∼3.7 times increase in response to 100 ppm MeOH (from ∼6 to ∼22% relative resistance change) and achieves a calculated limit of detection of 1.19 ppm. While the treatment improves response magnitude, it also increases the response and recovery times to 17 min and 8 h, respectively, suggesting strong analyte interaction suitable for cumulative sensing applications, such as long-term environmental or agricultural monitoring. Complementary density functional theory calculations confirm a charge transfer mechanism underpinning the sensing response. This work establishes PEDOT:Tos as a promising and easily modifiable material for room-temperature gas sensing, paving the way for new applications in industrial safety and environmental science. Furthermore, the demonstrated ease of surface modification offers a pathway for tuning electrical properties, enabling broader applicability.

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Introduction

Methanol (MeOH), with the chemical formula of CH3OH, is a colorless volatile organic compound (VOC) that has a myriad of applications ranging from biofuel, biomedical, and pharmaceutical to a solvent in laboratories. − MeOH, as a hydrocarbon in the atmosphere, has a concentration second to methane, and 60% of this total amount is produced by the territorial biospheres and plants. It is a major plant VOC as it is part of the plant’s cell wall pectins and is released as a result of the demethylation of DNA and proteins. Methanol also acts as a signaling molecule between plants as it is released when the plant is wounded or experiencing any stress, and the signaling induces the defense response in neighboring plants. , Though it plays a very important role in the growth and development of a plant, it is very toxic to humans and long-term exposure can result in blindness and other issues such as nerve deterioration and nasal mucosa. Therefore, due to its widespread industrial applications and its role as a plant health indicator coupled with its toxic nature to humans, it necessitates reliable, selective, and sensitive detection methods.

Several materials and their composites have been reported in their various forms under different sensing conditions for MeOH sensing. Metal oxide (MOx)-based gas sensors have garnered significant attention due to their potential for detecting a wide range of gases at low concentrations. − Although metal oxide semiconductors show excellent sensitivity toward MeOH with fast response and recovery time, their inability at room temperature operation limits their use for effective MeOH sensing for room-temperature applications.

Recently, conducting polymers have attracted researchers’ attention for gas sensing applications owing to their unique properties like low-temperature operability, ease of fabrication, and comparable electrical and optical properties. Several conducting polymers have been used for gas sensing applications due to their low-temperature operation. For example, polypyrrole (PPy) has shown room-temperature NO2 sensing with high response. PPy has also shown MeOH sensing capability in 20% humidity conditions. Poly­(3,4-ethylenedioxythiphene) (PEDOT) is probably a conducting polymer that stands out because of its ease of synthesis, conductivity, and stability. PEDOT alone is insoluble, but in the presence of poly­(4-styrenesulfonate) (PSS) as a dopant, as PEDOT:PSS, it can be processed as a solution, which results in easy fabrication methods and a range of applications. PEDOT:PSS has also been studied for gas sensing applications. − For example, PEDOT:PSS with n-doped graphene quantum dots has been used for the sensing of MeOH vapor and NO2 gas at room temperature. However, due to the very high hydrophilicity of PSS, PEDOT:PSS shows very high sensitivity to humidity. , This makes it less desirable for certain applications, especially for gas sensing. Tosylate (Tos) on the other hand leads to a doped PEDOT film that is comparatively more hydrophobic due to the loss of excess sulfonic acid associated with the PSS. , PEDOT doped with Tos has attracted researchers' attention due to its solution processability, tunable conductivity, and tunable transparency by controlling the oxidation level. PEDOT:Tos has several applications ranging from thermoelectric, energy storage, and electrode applications. However, to the best of our knowledge, PEDOT:Tos has not been studied for its role as a gas sensor.

This study aims to investigate the capabilities of pristine PEDOT:Tos as a room-temperature-operated chemiresistive gas sensor for methanol detection. The research not only explores the intrinsic sensing properties of PEDOT:Tos but also examines the impact of surface modification through urea treatment on its gas sensing performance. By employing a combination of experimental characterization and theoretical modeling through density functional theory (DFT) calculations, this work seeks to provide a comprehensive understanding of the methanol sensing mechanism in PEDOT:Tos-based sensors.

As the demand for efficient, cost-effective, and reliable gas sensing technologies continues to grow, this study contributes to broader scientific efforts to develop advanced materials and devices for environmental and safety applications. Moreover, the insights gained from this research not only advance our understanding of conducting-polymer-based gas sensors but also pave the way for future innovations in the field of VOC detection and beyond.

Results and Discussion

Conducting polymers are well-known for their capability to operate effectively at room temperature, making them ideal for gas sensing applications, unlike the metal oxides that require elevated temperatures. ,− The chemiresistive sensing mechanism in conducting polymers is relatively straightforward. For p-type conducting polymers, oxygen (O2) molecules are chemisorbed onto the polymer’s surface, where they extract electrons from the polymer’s valence band, forming O2 – dopants. This process increases the hole density along the polymer’s conjugated backbone, thereby reducing its electrical resistance.

When exposed to a reducing gas, the O2 – dopants interact with the gas molecules, returning the extracted electrons to the polymer backbone. This interaction decreases the hole density, leading to an increase in the electrical resistance of the polymer material. This reversible modulation of resistance in response to gas exposure serves as the foundation for gas sensing in conducting polymers. In order to explain the detailed mechanism behind the change in resistance in the case of PEDOT:Tos, we performed density functional theory (DFT).

Sensing Mechanism of PEDOT:Tosylate

We examined the possible mechanism underpinning the shift in the resistivity during the gas sensing, in the case of PEDOT:Tos for MeOH, by applying DFT to perform quantum mechanical analysis of the charge transfer that occurs upon MeOH adsorption. We modeled the PEDOT:Tos surface structure by a thin periodic slab that is composed of 2 × 2 PEDOT monomers, on which a tosylate molecule is weakly bonded, as displayed in Figure a­(i,ii). We have constructed this slab structure based on the PEDOT:Tos bulk structure that was published by Kim and Brédas. Based on the insights by Singh et.al., we have adsorbed the MeOH molecule to the O2 –, which is bonded to a C atom in a PEDOT monomer. We examined two possible C atoms for O2 – bonding: the α–C and the β–C to which a OOH specie would be bonded. , When O2 – was positioned closer to the α–C, it was repelled away from the α–C site toward the tosylate molecule and ended up being bonded weakly to the surrounding H, C, and S atoms of the polymer. This is because the α–C is already negatively charged, and hence, it will repel negative species. However, when it was initially positioned closer to the β–C, it formed a covalent bond with the β–C atom. Importantly, this O2 – bonding configuration to β–C (Figure a) is more energetically stable than the bonding configuration where O2 – was initially at the α–C site.

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Quantum mechanical analysis using DFT. (a) Optimized structure of the MeOH molecule that is hydrogen-bonded to the O2 – species, which is covalently bonded to the β–C of the PEDOT monomer. (i) Structure in a 1 × 2 × 1 supercell of C and (ii) close-up view of the MeOH–O2 – hydrogen bond. We indicate the O–H bond distance between the MeOH and the O2 – species. (b) Electronic density difference that indicates the amount of charge that was transferred from the PEDOT:tosylate–O2 – system to the MeOH molecule. The isosurface is set at a fixed density value of 0.001 e/Å. Yellow: accumulation of charge; blue: depletion of charge.

For the optimized structure, we computed the atomic charges by using the Bader charge analysis code. We found that the PEDOT:Tos slab loses 1.035e, O2 gains 1e to become O2 –, and MeOH gains a small amount of charge, 0.039e. This means that MeOH attracts charge from the slab via the O2 – species, which becomes slightly polarized (the O atom H-bonded to the MeOH has 0.02e more charge). The charge transfer can be clearly seen in Figure b, which displays the charge density difference isosurface for the charge transfer process. This is a similar behavior to that predicted by Rabchinskii et al. where the MeOH molecule attracted 0.07e from the sensing surface, which was an O-terminated graphene sheet. Optimized configurations showed charge transfer from the polymer surface to methanol, reducing charge carriers and increasing the resistivity (Figure b). Moreover, the reversible weak bonding of methanol molecules suggests recyclability of the sensing surface. Computational details can be found in the Supporting Information.

PEDOT:Tosylate-Based Sensor Testing for MeOH

As explained above, PEDOT:Tos is capable of sensing the MeOH at room temperature. To practically test PEDOT:Tos’s sensing capability for MeOH, the sensor was fabricated using vapor phase deposition (VPP), as shown in Figure . The details of the fabrication method can be found in the Methods section.

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Fabrication and characterization of the PEDOT:Tos vapor phase polymerization (VPP) process for PEDOT:Tos on a glass substrate and transfer to a silicon substrate with gold electrodes that is fabricated using microfabrication.

To test the sensor’s response to MeOH, the chamber was supplied with the gas, and its response was recorded. As a reducing gas, MeOH reacted with the O2 – and resulted in higher resistance recorded as R gas. The mechanism behind this increase in resistance upon the exposure of methanol has been explained above by the DFT calculation. The generated response, as shown in Figure a, shows the ability of the polymeric film to sense the presence of the MeOH. To evaluate the sensor’s performance as a MeOH gas sensor, its response time is defined as the interval for the resistance to reach 90% of its maximum value upon gas exposure. Moreover, the recovery time refers to the time required for the resistance to return to within 10% above the baseline following gas removal and N2 purging. The response time of the sensor was recorded to be 8.4 min. In the case of recovery time once the resistance of the sensor stabilized, the supply was cut off, and it was left to recover. After the MeOH supply was cut off, the Linkam chamber was purged with N2 gas for 30 s to remove any residual gas. This purging created an inert environment in the chamber and removed moisture. The recovery time for the PEDOT:Tos-based sensor was found to be around 2.7 h, as shown in Figure a.

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Characterization of PEDOT:Tos as a MeOH gas sensor: (a) sensor’s response to MeOH at room temperature, (b) sensor’s response to MeOH at different temperatures, (c) limit of detection for MeOH, (d) sensitivity for lower concentrations, (e) repeatability testing for MeOH, and (f) selectivity testing.

To study the effect of temperature on the sensing capabilities of PEDOT:Tos, its performance was observed over a range of temperatures. It was observed that the sensitivity of the sensing layer to MeOH was highest at room temperature. It showed lower sensitivity at 50 °C, and the sensor seized to respond to MeOH at 75 °C, as shown in Figure b. The overall resistance of the sensing layer also decreased with an increase in temperature, thus increasing the conductivity of the material and signifying semiconducting behavior.

The sensor was found to be able to sense as low as 5 ppm MeOH at room temperature, a clear indication of the polymer’s sensing capabilities. This sensitivity toward lower concentrations of MeOH is shown in Figure c,d. Moreover, the PEDOT:Tos role as a MeOH sensor was further verified by the repeatability test, as shown in Figure e. PEDOT:Tos showed a selective response toward MeOH as compared to other gases like NO2, CO2, NH3, and H2S. All gases were tested under the same gas sensing conditions that were used for the MeOH sensing. The sensor was tested for the selectivity at the room temperature at the humidity level of ∼30% RH. All gases were supplied with the same flow rate of 500 sccm under the same applied voltage (1.5 V) to the sensor. The selectivity results, as shown in Figure f, show that sensors’ sensitivity toward other gases was lowest for NO2 and highest for MeOH. These gases were chosen for the methanol sensor’s selectivity testing because they represent a range of chemical properties such as reducing and oxidizing and are commonly found in environments where methanol detection is needed. Testing against these gases ensures that the sensor can distinguish methanol from potential interferents, making it reliable for real-world applications. It is important for the characterization of a material as a gas sensor to produce the same response when tested over a range of the devices. To test the ability of the PEDOT:Tos to reproduce the same response, we performed the sensor-to-sensor reproducibility test. We tested different sensors under the same testing conditions and recorded their sensitivity toward MeOH. We tested for the 100 ppm MeOH at room temperature. Testing results showed the ability of the material to produce the same response with minor difference in the sensitivity. Further testing results on sensor-to-sensor reproducibility can be found in the Supporting Information, Figure S3.

These tests showed the ability of PEDOT:Tos to sense at room temperature. Moreover, the selectivity results showed that the PEDOT:Tos was more selective toward MeOH. However, the percentage sensitivity (∼6%) of PEDOT:Tos toward MeOH is very low.

Urea-Treated PEDOT:Tosylate-Based Sensor Testing for MeOH

One of the many properties of PEDOT is its ability to modify its intrinsic properties by binding to different particles onto its surface. In the literature, it has been shown that amines (NH2) bond with the surface of the polymer. During this process, electrons are transferred from the amine to the PEDOT, resulting in higher resistance due to the reduction in hole density and insertion of defects in the π-conjugated structure. We employed the same concept here to improve the sensitivity of the material by binding the amine group to the sensor’s surface as the transfer of the electrons will allow more oxygen adsorbance to the surface of PEDOT:Tos. We used urea to bind the amine group to the sensor’s surface. To perform this experiment, samples were soaked in 1 M solution of urea for 2 h. The sensor was later washed with ethanol and water and dried with N2. The posturea treatment resistance of the sensor was measured to be higher than the preurea-treated samples. This increase in the resistance was due to the binding of the amines to the PEDOT and the transfer of the electrons to the material. Moreover, to characterize the surface of the sensing film after the urea treatment, SEM of the sensors before and after the urea treatment was performed and is shown in Figure . The surface of the PEDOT:Tos after the polymerization appeared smoother as shown in Figure a compared to the surface of the PEDOT:Tos after the urea treatment as shown in Figure b. An increase in the surface porosity is prominent for urea-treated samples. This surface roughness could be attributed to an increase in the sites for better gas sensitivity, as an increase in the surface porosity is also known to cause an improvement in the sensitivity. The images clearly show an increase in the surface improvement after the urea treatment, allowing more active sites for the MeOH to interact with the material’s surface. Moreover, the surface roughness increment is also confirmed by an atomic force microscopy (AFM) study. This detail can be found in the Supporting Information.

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Urea-treated PEDOT:Tos response to MeOH. (a) SEM image of the PEDOT:Tos. (b) SEM image of the PEDOT:Tos after the urea treatment. (c) Sensor’s response to MeOH, (d) repeatability of the sensor, (e) sensitivity to lower concentrations, and (f) selectivity of the sensor.

We tested the urea-treated PEDOT:Tos for MeOH sensing to observe its effect on its role as a gas sensor. The sensor’s response to MeOH (100 ppm), as shown in Figure c, indicated the improvement in the sensing response. The sensitivity of the sensor was noted to be 22%, which is higher than the PEDOT:Tos, which was noted to be around 6%. This showed the surface modification impact on the gas sensing properties of the polymer. It was also observed that the response and the recovery times of the sensor also increased to ∼17 min and 8 h, respectively. This increase in turn could be attributed to the ability of MeOH gas to form hydrogen bonds with the amides. Moreover, the hydrogen bond is stronger than the weak physisorption forces. Thus, this results in a positive increase in the response but negatively impacts the recovery time. Meanwhile, the preurea-treated PEDOT:Tos samples showed lower response and recovery time due to simple interaction of the MeOH with the adsorbed O2 on the surface of the polymer, also confirmed by the DFT results. Repetitive sensing results, as shown in Figure d, indicated the ability of the sensor to generate the same response over a longer period. Similarly, the sensor’s response to the lower concentrations of the MeOH also showed higher response and indicated that the sensor was able to respond to as low as 5 ppm MeOH as shown in Figure e. While urea treatment enhances the overall response magnitude, the proportional sensitivity with concentration becomes slightly nonlinear due to the saturation of active amine sites and stronger MeOH adsorption. The selectivity of the urea-treated samples, as shown in Figure f, indicated that the sensor was most sensitive to MeOH compared to CO2, NO2, NH3, and H2S. This shows that the sensor is still capable of generating the highest response to MeOH compared to other gases. The increase in the response for the H2S in the case of urea treatment could be attributed to the ability of the H2S to bind with the amine functional group. However, the sensor still maintains the highest sensitivity to MeOH during the selectivity testing and can hence still act as the MeOH gas sensor. Similarly, based on the sensitivity results from Figures d and e, the LOD for the pristine PEDOT:Tos and urea-treated PEDOT:Tos were found to be 4.35 and 1.19 ppm, respectively. These values are consistent with the demonstrated detection down to 5 ppm in both cases.

To understand the effect of urea on the polymer’s surface, we carried out Fourier transform infrared spectroscopy (FTIR). FTIR results for PEDOT:Tos and urea-treated PEDOT:Tos in the wavenumber region of 800–4000 cm–1 are shown in Figure a and b, respectively. Both spectra show the characteristic peaks of the PEDOT:Tos material. The peak at 865 cm–1 corresponds to C–S–C deformation in the oxyethylene ring. The peak at 994 cm–1 corresponds to the C–O–C deformation. The peaks at 1124 and 1268 cm–1 represent the Cα–Cα and Cβ–Cβ stretching, respectively. Symmetric CαCβ stretching and asymmetric CαCβ stretching were observed at 1458 and 1558 cm–1, respectively. N–H stretching regions, in the case of urea-treated PEDOT:Tos, can be observed in the region above 3300 cm–1. The observed peaks are not sharp distinctive peaks, which reflects the weak bonding of the amine group with the PEDOT:Tos after the urea treatment.

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Characterization of the polymeric films. (a) FTIR results for PEDOT:Tos. (b) FTIR results for urea-treated PEDOT:Tos. (c) XPS survey scan of the PEDOT:Tos and urea-treated PEDOT:Tos. (d) N 1s spectra of the urea-treated PEDOT:Tos.

To further confirm the bonding of the amine group to PEDOT:Tos after the urea treatment, X-ray photoelectron spectroscopy (XPS) for both PEDOT:Tos and urea-treated PEDOT:Tos samples was performed. It was observed that the urea-treated samples showed the nitrogen peak, which was absent in the case of the original PEDOT:Tos samples. The presence of a strong N 1s peak in the urea-treated samples indicated the bonding of the amine group to the PEDOT:Tos. The results are shown in the Figure c, where the N 1s peak in the case of urea-treated PEDOT:Tos is indicated. Similarly, further analysis of the N 1s peak showed a spectrum with three component peaks as shown in Figure d where the peak of the unreacted amine is represented by R–NH2, 46%, and the low-concentration peak (RR′NH2+:tosylate (6.2%)) at high binding energy can be assigned to the positively charged nitrogen (N) atom bonded with the carbon (C). Similarly, the high-concentration peak bonded at the low binding energy (RR′NH, 46.9%) can be assigned to the thiophene ring C covalently bonded with the N atoms. These results clearly showed the presence of the NH2 group in the PEDOT:Tos film after the urea treatment, which in turn resulted in the sensitivity improvement of the polymer toward MeOH.

Conclusions

This study demonstrates the potential of PEDOT:Tosylate (PEDOT:Tos) as a novel room-temperature chemiresistive gas sensor for methanol detection. Pristine PEDOT:Tos exhibits a detection limit of 5 ppm for methanol with good selectivity and repeatability. Urea treatment significantly enhances the sensor’s performance, increasing sensitivity from 6 to 22% for 100 ppm methanol. Although the response and recovery time for the sensor increased to 17 min and 8 h, respectively, the material is tested in its pristine form without any doping or addition of other stimuli such as heat or light. Urea treatment enhances the properties of the material, paving the way for further modifications such as doping with other materials to further improve response and recovery time. While this work confirms the efficacy of the 1 M urea treatment in enhancing sensor performance, a detailed study to optimize the functional group density and establish a precise quantitative relationship between urea concentration and sensor sensitivity is a subject for future investigation. Density functional theory calculations provide insights into the methanol sensing mechanism, confirming the increase in resistance upon methanol exposure. These findings establish PEDOT:Tos as an innovative and promising candidate for volatile organic compound sensing, particularly for applications requiring room-temperature operation. Additionally, the ease of surface modification and tunable electrical properties of PEDOT:Tos further demonstrate its potential as a versatile sensing material. This work establishes PEDOT:Tos as an innovative room-temperature chemiresistive gas sensor; as such, future work should focus on exploring additional surface modifications and investigating the incorporation of metal oxides or noble metal dopants to further enhance sensing performance. This research contributes significantly to the development of efficient, low-power gas sensing technologies for industrial safety and environmental monitoring applications.

Materials and Methods

PEDOT:Tosylate-Based Sensor Fabrication

PEDOT:Tosylate was fabricated using vacuum phase polymerization (VPP). The Si-based substrate with a 300 nm-thick SiO2 layer was prepared using the standard photolithographic steps involving the subsequent electronic beam deposition of 100 nm Au on 10 nm Cr grown on a Si wafer. To prepare the oxidation solution, 15 g of Clevios CB-54 (54 wt % iron tosylate in n-butanol, Heraeus), 10 g of a triblock copolymer (5800 Mw PEG–PPG–PEG, Pluronic P123, Sigma-Aldrich), and solvents (butanol and ethanol at 5 and 30 g, respectively) were mixed and heated at 60 °C for 1 h in an orbital shaker at 200 rpm and just prior to deposition were further shaken by hand for uniform mixing. The oxidant solution was pipetted onto a glass substrate surface and spin-coated at 1500 rpm for 25 s. The substrates were then placed into a vacuum chamber oven, which was held at a constant 36 °C. Three drops of the EDOT monomer were then deposited onto a flat glass dish, which was placed on top of a Peltier device set to 45 °C. The vacuum oven was pumped down to 45 mbar, and the chamber/monomer temperature was maintained at 36/45 °C during the 60 min polymerization time. After polymerization, samples were removed from the oven and gently spray-rinsed with a methanol spray to remove the unreacted and/or residual oxidant from the polymer sample. The glass slides with the PEDOT film were then placed into a Petri dish filled with methanol. The film was then gently floated off the glass slide and placed onto the substrate with electrodes, which were then removed from the methanol bath and dried with low-pressure compressed air to remove excess solvent. The fabrication flow of the conducting polymer is shown in Figure .

Gas Sensing Setup

The sensor was tested using a Linkam (LTS420E-P) chamber with a gas inlet/outlet and a connection for the temperature controller for precise chamber temperature. The gas supply to the chamber was controlled using a mass flow controller (MFC), which was connected to a gas cylinder for the MeOH (100 ppm) and nitrogen (N2). The MFC was controlled by a multichannel flow controller (MKS 47B). For the power supply to the sensor and to record its response, a Keysight source/measurement unit (B2912A) was used. Moreover, a water bubbler connected to the Linkam gas outlet was used to visually observe the gas flow through the chamber. Figure S1 shows the gas sensor measurement setup. The sensitivity of the sensor to the supplied gas was calculated as

|sensitivity|=(Rgas−Rair/Rair)×100

where R air is the resistance in the air at a particular temperature whereas R gas is the resistance when the gas is supplied. We used the absolute value of the sensitivity to reflect the change in the value of the sensitivity.

Electrical Data Collection

For electrical data acquisition from the sensor, we used a Keysight source/measurement unit (B2912A) for biasing and recording the response to the sensor to MeOH along with Quick IV measurement software for real-time data acquisition and visualization. A Linkam LTS420E-P was used as a gas sensing chamber that was equipped with the probes for electrical connections. These probes were connected to B2912A for the biasing. The supplied voltage of 1.5 V for PEDOT:Tos and urea-treated PEDOT:Tos was used. The sampling time was set at 1 sample/s.

Material Characterization

Fourier Transform Infrared (FTIR) Spectroscopy

To characterize the PEDOT:Tos and urea-treated PEDOT:Tos surface, Fourier transform infrared (FTIR) spectroscopy was employed. It was performed using a PerkinElmer Spotlight 400 FTIR imaging system with a microscope and equipped with Spectrum Image viewing software for spectrum acquisition. The scan was obtained in the reflectance mode and in the wavenumber region of 800–4000 cm–1. The spectrum was acquired for a scanned area of 100 μm × 100 μm. The same process was repeated for the urea-treated PEDOT:Tos sensors.

Scanning Electron Microscopy (SEM)

Similarly, to find the thickness of the material, we performed scanning electron microscopy (SEM). We used an FEI Verios 460L XHR-SEM, operating at 10.0 kV and 25 pA for PEDOT:Tos samples. Similarly, to obtain the thickness of the coated polymer on SiO2, we used 3.00 kV and 25 pA after scratching the samples to remove the PEDOT:Tos from the edge for a cross-sectional image.

X-ray Photoelectron Spectroscopy (XPS)

X-ray photoelectron spectroscopy (XPS) of the PEDOT:Tos and urea-treated PEDOT:Tos-based samples was conducted using a spectrometer (Kratos AXIS Supra; Kratos Analytical Ltd., Manchester, UK) equipped with monochromated Al Kα (1486.7 eV). The binding energy (BE) scale of all spectra was referenced relatively to the aliphatic carbon peak at 285 eV using the software CasaXPS (version 2.3.24 PR 1.0; Casa Software Ltd., Teignmouth, UK).

Supplementary Material

ao5c09352_si_001.pdf (535.5KB, pdf)

Acknowledgments

This work was performed in part at the Micro Nano Research Facility (MNRF) at RMIT University in the Victorian Node of the Australian National Fabrication Facility (ANFF). Facilities and technical support from the RMIT Microscopy and Microanalysis Facility (RMMF) are acknowledged. Scholarship support from the Research Training Program (RTP) scheme of the Australian government is acknowledged. Figure was created using BioRender.com.

The Supporting Information is available free of charge at https://pubs.acs.org/doi/10.1021/acsomega.5c09352.

  • Exploring the potential of PEDOT:Tosylate thin films for gas sensing applications; gas sensing setup, sensor-to-sensor repeatability testing results, MeOH response in humid conditions, and computational details of the DFT (PDF)

The authors declare no competing financial interest.

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