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Article

Highly Sensitive and Selective Defect WS2 Chemical Sensor for Detecting HCHO Toxic Gases

by
Zhen Cui
1,2,*,
Hanxiao Wang
1,
Kunqi Yang
1,
Yang Shen
1,
Ke Qin
1,
Pei Yuan
1 and
Enling Li
1,*
1
School of Science, Xi’an University of Technology, Xi’an 710054, China
2
School of Automation and Information Engineering, Xi’an University of Technology, Xi’an 710048, China
*
Authors to whom correspondence should be addressed.
Sensors 2024, 24(3), 762; https://doi.org/10.3390/s24030762
Submission received: 27 December 2023 / Revised: 14 January 2024 / Accepted: 17 January 2024 / Published: 24 January 2024
(This article belongs to the Special Issue Chemical Sensors for Toxic Chemical Detection)
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Abstract

:
The gas sensitivity of the W defect in WS2 (VW/WS2) to five toxic gases—HCHO, CH4, CH3HO, CH3OH, and CH3CH3—has been examined in this article. These five gases were adsorbed on the VW/WS2 surface, and the band, density of state (DOS), charge density difference (CDD), work function (W), current–voltage (I–V) characteristic, and sensitivity of adsorption systems were determined. Interestingly, for HCHO-VW/WS2, the energy level contribution of HCHO is closer to the Fermi level, the charge transfer (B) is the largest (0.104 e), the increase in W is more obvious than other adsorption systems, the slope of the I–V characteristic changes more obviously, and the calculated sensitivity is the highest. To sum up, VW/WS2 is more sensitive to HCHO. In conclusion, VW/WS2 has a great deal of promise for producing HCHO chemical sensors due to its high sensitivity and selectivity for HCHO, which can aid in the precise and efficient detection of toxic gases.

1. Introduction

The majority of volatile organic compounds (VOCs) such as HCHO, CH4, CH3CHO, CH3OH, and CH3CH3 are hazardous to human health and safety, the environment, and cause cancer [1]. In order to identify harmful gases and lessen their damage, we need devices. Chemical sensors are commonly used to detect and analyze chemical substances and can measure the existence and specific concentration of experimental substances. Researchers have been continuously exploring and innovating chemical sensors to address the issue of harmful gas detection and monitoring in various domains.
In the current period of rapid scientific and technological advancement, chemical sensors are progressively becoming essential instruments across a wide range of fields. These sensors have the ability to detect sensitive signals and accurately identify chemicals, thus affecting our life, health, and environment. For instance, the use of chemical sensors is significant in the field of environmental protection. A number of toxic gases, including CO and SO2, are present in the atmosphere and are extremely dangerous to both human health and the environment. Scientists can track and identify the concentration of these dangerous gases in real time and take appropriate action to protect the environment by inventing high-performance chemical sensors. Furthermore, the use of chemical sensors in the industrial sector is very important. Consider a chemical plant as an example. During the production process, several hazardous gases are emitted, including H2S and NH3. High-performance chemical sensors allow workers to detect and identify the presence of dangerous gases in real time, allowing them to avoid potential hazards that could endanger their health. Furthermore, the medical industry is also involved in the application of chemical sensors. For instance, certain harmful gases, such as NO, will be created during respiratory therapy and will negatively affect the health of patients. Medical personnel can monitor the concentration of these dangerous gases in real time and take appropriate action to safeguard patients’ respiratory systems by employing chemical sensors with excellent sensitivity and selectivity.
To put it succinctly, chemical sensors are crucial for the identification and tracking of toxic gases. Continuous research and innovation can enhance the dependability, sensitivity, and accuracy of chemical sensors.
Chemical sensors have been designed using nanomaterials on a large scale in recent years due to the advancement of nanotechnology [2,3,4]. Chemical sensors’ performance has been greatly enhanced using nanomaterials, primarily in the following areas: Increasing specific surface area: in comparison to conventional materials, nanomaterials have a higher specific surface area per unit mass or volume. As a result, nanomaterials can offer more active sites and improve their interaction with target molecules, increasing the sensitivity of the sensor [5]. Enhance conductivity: nanomaterials often exhibit high levels of thermal and electrical conductivity, which helps to enhance sensors’ response times and signal conduction efficiency. This holds great significance for instantaneous monitoring and prompt reaction to specific compounds, particularly in the domains of environmental and medical monitoring. Introducing new features: nanomaterials exhibit physical and chemical properties distinct from large-scale materials due to the size effect and quantum effect. New properties, such as optics, electricity, and magnetism, can be added to nanomaterials with great care to improve the sensor’s selectivity and reactivity to target molecules. Boost stability and durability: the high surface area and unique structure of nanomaterials contribute to the sensors’ increased stability and durability. Realizing multifunctional design: By mixing several nanomaterial types, chemical sensors with multifunctional capabilities can be designed thanks to the multifunctional nature of nanomaterials. This multifunctional architecture enhances the sensor’s overall performance by simultaneously detecting numerous target molecules. As a result, the introduction of nanomaterials opens up new avenues for chemical sensor design.
Chemical sensors have advanced quickly in the last few years, but there are still a lot of restrictions. Certain chemical sensors can produce erroneous measurement findings due to cross-sensitivity to toxic gases, which occurs when other gases interfere with the sensor [6]. Different chemical sensors have varying degrees of stability and accuracy, and some are more sensitive to environmental factors like humidity, temperature, and pressure, which require calibration and adjustment [7,8,9]. High sensitivity and selectivity are necessary for the sensor to enable effective monitoring, and high performance is required for the detection of toxic gases. Thus, in order to address the needs of toxic gas detection and monitoring in many domains, we should keep researching and developing chemical sensors [10,11,12].
High-performance gas-sensitive materials must be developed in order to achieve the sensitive detection of toxic gases [13]. Transition metal dichalcogenides [14,15,16] have a number of superior properties in the realm of chemical sensors, which makes them perfect building blocks for the production of effective sensors. Through the deft application of these properties, we can achieve tremendous gains in sensor performance and design [17,18,19]. Cui researched how the photoelectric properties of WS2 and defect for the WS2 changed when it was adsorbed by CO, NH3, NO, and NO2 gas molecules in 2022 [11]. They came to the conclusion that WS2 is useful for toxic gas detection and gas sensing. WS2 has a large surface area, active sites, high sensitivity, and controllability, which are beneficial to molecular adsorption and interaction with target molecules, and can achieve highly selective recognition of specific molecules and improve the sensitivity and response speed of the sensor.
On the surface of WS2 and the W defect for WS2 VW/WS2, we adsorbed HCHO, CH4, CH3HO, CH3OH, and CH3CH3, and we computed their electronic properties and work function (W). We selected the VW/WS2 adsorption systems to further compute the I–V characteristic and sensitivity since the results were consistent that the electronic properties and W of HCHO-WS2 and HCHO-VW/WS2 changed most obviously in the WS2 adsorption systems and the VW/WS2 adsorption systems [20,21,22]. We discovered that VW/WS2 exhibited excellent sensitivity and selectivity for HCHO. Due to its high sensitivity, VW/WS2 is able to identify toxic gas with a very low concentration of HCHO [23]. Because HCHO is frequently damaging to human health at low concentrations, this is crucial for safeguarding both the environment and people. Second, selectivity refers to VW/WS2’s ability to recognize variations in various gases and solely react to the toxic gas (HCHO) [24]. Due to these benefits, VW/WS2 is a valuable tool for environmental monitoring, industrial safety, and personal safety. It also makes it easier to recognize and manage toxic gases, which is particularly useful for HCHO detection [25].

2. Computational Methods

We calculated the density functional theory (DFT) by using the Vienna ab initio simulation software package 5.4.4 (VASP). The exchange–correlation interaction and the electron–ion interaction are described, respectively, by the extended gradient approximation of Perdew Burke Ernzerhof (PBE) and the projection-enhanced wave approach. In order to assure system stability, we built a 4 × 4 × 1 supercell model and a vacuum layer of 20 Å was added in the z direction for WS2, defect WS2, and the adsorption systems. For both structural and electronic structure optimization calculations, the sampling grid in the K space of the Brillouin zone is 9 × 9 × 1, the energy convergence criterion is 10−7 eV, the ideal convergence threshold is to guarantee that the force acting on atoms is less than 10−3 eV/Å, and the cutoff energy is set to 500 eV.
The adsorption energy (Eab) between molecules was further evaluated. The energy generated when free monolayers combine to form adsorption systems is known as the Eab, and it is expressed as [26,27,28,29]:
E abs = E adsorbedsystem − E monolayer + E targetmolecule
The energy released during the construction of the adsorption system is represented by the symbol Eabs in the above equation. The total energy of the adsorption systems is also indicated by the symbol Eadsorbedsystem. Additionally, the total energy of VW/WS2 and gas molecules is indicated by Emonolayer and Etargetmolecule. Lastly, the unit area under consideration is indicated by the sign S.
By utilizing computed differences in charge density difference (CDD) [30] and charge transfer (B) [31], we can analyze the transfer of charges between the adsorption systems. This formula can be expressed as follows:
Δ ρ = ρ h − ρ 1 − ρ 2
By employing computed variations in charge density (ρh, ρ1, and ρ2), we can examine the B mechanisms between the VW/WS2 and gas molecules. Here, ρh represents the charge density of the adsorption systems, while ρ1 and ρ2 correspond to the charge densities of the VW/WS2 and gas molecules.
We studied the I–V characteristic of the adsorption systems, which was obtained by calculating the current at different bias voltages. The current at a specific bias voltage can be obtained using the following equation [32]:
I = e h ∫ − ∞ + ∞ T ( E ; V b ) [ f L ( E ; E F L − V b / 2 ) − f R ( E ; E F R + V b / 2 ) ] d E
where f L ( E ; E F L − V b / 2 ) , E F L , f R ( E ; E F R − V b / 2 ) , and E F R are the Fermi energy level and Fermi distribution at the equilibrium state of the left and right electrodes, respectively. T ( E ; V b ) is the transmission probability function spectrum for electrons.
Lastly, we used the following formula to evaluate the adsorption systems’ sensitivity [33]:
S = ( G − G 0 ) / G 0 × 100 %
where G is the conductance of adsorption systems, and G0 is the conductance of VW/WS2.
We used Vienna ab initio simulation package (VASP) software to calculate the electronic properties of the systems, such as energy band, density of state (DOS), CDD, and B, and used Nanodcal 2023A software to calculate the electrical characteristics of I–V [34,35].

3. Results and Discussion

The focus of our research is toxic gases, and HCHO, CH4, CH3CHO, CH3OH, and CH3CH3 are the most common toxic gases. There is still a technical gap in the field of detection. So, we adsorbed five gas molecules, HCHO, CH4, CH3CHO, CH3OH, and CH3CH3, on WS2 and optimized their structures. The adsorption distance (H) of the adsorption systems before optimization is 3 Å, the optimized H values are 2.94 Å, 2.80 Å, 2.78 Å, 2.49 Å, and 2.52 Å in Table 1, respectively. We also calculated the Eab of the adsorption systems and determined the most stable model, as shown in Figure 1. Next, the energy bands of the adsorption systems were calculated, as shown in Figure 2. We can see that the energy bands have hardly changed, so the adsorption of gas molecules has little effect on the electronic properties of WS2. Gas molecules are physically adsorbed. In order to further investigate the physical adsorption of gas molecules, we calculated the DOS; the total DOS of the adsorption system is shown by the gray line in Figure 3, the DOS of WS2 is represented by the blue line. Compared with the DOS of WS2, the adsorption systems show a DOS contribution of gas molecules near the Fermi level and the DOS of gas molecules is represented by the red line. The DOS of CH4 and CH3CH3 disappeared near the Fermi level. The DOS of CH3OH and CH3CHO is further away from the Fermi level, while the DOS of HCHO is closest to the Fermi level. Therefore, HCHO adsorption has the greatest impact on the electronic properties near the Fermi level compared to other gas adsorption. Figure 4 is the CDD we calculated; the sky-blue area denotes the charge accumulation, and the purple area denotes the charge depletion. The electric field is usually formed by the charge accumulation, and the charge depletion leads to the flow and transport of charges, which in turn affects the electrical characteristics of materials. There is a difference between the energy level of the adsorbed substance and the energy level of the surface, and the movement of electrons leads to the resonance of electrons or the change in local electron density, thus causing B in the adsorption systems. We can see that there is B between the gas molecule and WS2. In Table 1, combined with the B of the adsorption systems (0.107 e, 0.092 e, 0.088 e, 0.091 e, and 0.089 e, respectively), the B of the HCHO-WS2 system is the largest, which is consistent with DOS. Next, we calculated the W of the WS2 adsorption systems, which are 5.72 eV, 5.53 eV, 5.01 eV, 5.15 eV, and 5.53 eV, respectively. Compared with the W of WS2 (5.39 eV), the W of HCHO-WS2 increased the most significantly, while the W of CH3CHO-WS2 and CH3OH-WS2 decreased. The W of CH4-WS2 and CH3CH3-WS2 show a slight increase. So, when detecting gas, WS2 is more likely to react with HCHO. In summary, WS2 has higher sensitivity and selectivity towards HCHO.
An important research object in the study of 2D materials is vacancy defects. By adding vacancy defects in certain ways, scientists can investigate how defects affect electrical conductivity, optical absorption, electronic structure, and other aspects. Researchers can gain a deeper understanding of the relationship between a material’s structure and properties, as well as expand the potential applications of 2D materials in areas like catalysis, sensing, and electrical devices through vacancy defects. Based on the WS2 model, we removed the W atom to construct VW/WS2, and similarly removed the S atom to construct S defect WS2 (VS/WS2), the model diagram of which is displayed in Figure 5a. Next, we computed the Ead of these two structures after fully relaxing them. The Ead of VW/WS2 is −17.33 eV, and that of VS/WS2 is −7.15 eV, as Figure 5b illustrates. We decided to focus our subsequent research on VW/WS2 since the more negative adsorption energy it has, the more stable it becomes [36]. To gain more insight into this structure’s thermal stability, we computed the ab initio molecular dynamics (AIMD) at 300 K [37,38,39]. VW/WS2 exhibits thermal stability, as evidenced by Figure 6b, where the total energy tends to stabilize across the simulation duration and the crystal structure is free of deformation and bond breaking. We computed the band structure [3] and DOS of VW/WS2 in order to comprehend its electronic properties. VW/WS2 is a direct band gap semiconductor with a band gap value of 0.379 eV, as can be seen in the band diagram in Figure 6c. The Fermi level is situated between the conduction band and the valence band, VW/WS2 is a semiconductor, and the 4f level of the W atom supplies the valence band maximum and conduction band minimum, which correlates to the energy band, as can be seen in the DOS diagram of Figure 6d.
The H of the adsorption systems before optimization is 3 Å. In Table 2, the most stable model (the H values are 2.92 Å, 2.79 Å, 2.65 Å, 2.67 Å, and 2.51 Å, respectively) for VW/WS2 to adsorb the five toxic gases—HCHO, CH4, CH3CHO, CH3OH, and CH3CH3—is depicted in Figure 7 [11,40]. The band gap values of VW/WS2 and the five adsorption systems are displayed in Figure 8 [41]. We can see that compared with VW/WS2 the band gap undergoes certain changes after adsorbing gas molecules. The DOSs of adsorption systems are displayed in Figure 9. Compared with other gas molecules, due to the structure and electronic configuration of HCHO, its oxygen atom may introduce more electrons, and some special electronic states may be introduced near the Fermi level, resulting in the formation of a local electronic state near the Fermi level. The DOS of HCHO is closer to the Fermi level and its contribution is greater near the Fermi level. The DOSs of CH4 and CH3CH3 disappear near Fermi level, while the DOSs of CH3CHO and CH3OH are far away from Fermi level and their contribution is smaller. Therefore, VW/WS2 has high sensitivity and selectivity for HCHO. The CDD of the adsorption systems is shown in Figure 10. We can see the accumulation and dissipation of charge in the adsorption systems, which shows that the conductivity of VW/WS2 has changed to some extent after adsorbing gas molecules. In order to describe which gas molecules VW/WS2 is most sensitive to, we calculated B. As shown in Table 2, HCHO-VW/WS2 has the highest B, which shows that the conductivity of HCHO-VW/WS2 has the most obvious change, and VW/WS2 has high sensitivity and selectivity to HCHO [12,41,42,43].
The relationship between W and the sensitivity of chemical sensors is mainly reflected in the change in electronic structure caused by the interaction between materials and target molecules. This relationship is very important for understanding the working mechanism of the sensor, optimizing the sensor’s performance, and designing a more selective and sensitive sensor. Additionally, we computed the W of five adsorption systems and the VW/WS2 [44]. ΔW represents the change in the W after adsorption, as seen in Table 2. The ΔW of the CH4-VW/WS2 (0.005 eV) and CH3CH3-VW/WS2 (0.008 eV) systems show a minor increase, and the CH3HO-VW/WS2 and CH3OH-VW systems show a decrease [45,46]. The W clearly increases for the HCHO-VW/WS2 system, and the change value is 0.205 eV, which is noticeably larger than for other adsorption systems. This indicates that VW/WS2 has high sensitivity and selectivity for HCHO and that HCHO will interact with VW/WS2 more readily when it is in contact with experimental gas. Device models can be used to predict the performance of electronic devices, including I–V characteristic, power consumption, and speed [47]. We constructed device models, as Figure 11a illustrates. The gadget is separated into a center scattering zone and left and right electrodes. The buffer layer can adjust the charge distribution in the device and prevent excessive charge from accumulating in a certain area, thus maintaining the stability and reliability of the device. The buffer layer can also block the diffusion of external impurities, protect the internal purity of the device, and reduce the negative impact on the performance of the device, so, at the intersection of the electrodes and the central scattering region, we inserted three buffer layers to prevent any interference of the device center [48]. We utilized Materials studio software to compute the I–V characteristic of five adsorption systems and VW/WS2, which were represented by the I–V curve, so that we could clearly see the change in conductivity. The I–V curve is displayed in Figure 11b–f, where the gray lines in each figure correspond to the VW/WS2 I–V curve. We can observe that the current starts to increase when a bias voltage of 1.8 V is applied [49]. Compared with the I–V curve of BC6N adsorption systems [33], the slope change of the I–V curve after VW/WS2 adsorbed gas molecules is more obvious, and the conductivity change is more sensitive when detecting gas molecules. Figure 11b shows us that hardly any current passes through HCHO-VW/WS2 when the bias voltage is less than 1.8 V. The current increases dramatically when the applied bias voltage rises above the threshold value (1.8 V). The current of 1.14 × 10−7 A is reached at 2.4 V, which is much greater than that of VW/WS2 (7.99 × 10−8 A). Following adsorption, VW/WS2 is clearly sensitive to HCHO, as seen by the sharply altered I–V curve, higher slope (under the bias voltage of 1.8 V~2.4 V), and clearly increased conductivity. The I–V curves of the four types of adsorption systems in Figure 11c–f have altered somewhat when compared to the I–V curve of the VW/WS2. By examining the slope, we can also observe that VW/WS2 has the maximum sensitivity to HCHO, as seen by the I–V curves of the five adsorption systems (which is compatible with the W calculation results). It can also demonstrate the selectivity of the sensor, allowing us to differentiate HCHO from other gases through the observation of the conductivity shift. To validate the work function and I–V curve results, we computed VW/WS2 sensitivity at 1.8 V, 2.0 V, 2.2 V, and 2.4 V bias voltages [50,51]. Table 3 displays the results of the calculation [52]. The sensitivity of VW/WS2 to HCHO, CH4, CH3HO, CH3OH, and CH3CH3 is 98.1%, 96.7%, 88.9%, 94.9%, and 96.0%, respectively, when a bias voltage of 1.8 V is applied to the adsorption systems. This indicates that VW/WS2 has high sensitivity to these five gases at a voltage of 1.8 V. The sensitivity of Pt-NiS2 to HCHO is −99.2% [53], and the sensitivity of VW/WS2 to HCHO is −98.1% under 1.8 V, so it is necessary to study further. Significantly higher than that of other adsorbed gas molecules, the sensor’s sensitivity to HCHO is 108.0% and 42.9% at 2.2 V and 2.4 V, respectively [54,55,56]. This suggests that VW/WS2 can selectively detect HCHO, and the calculated results are in agreement with those of W and the I–V characteristic.

4. Conclusions

This research uses a series of simulations to study the gas sensitivity of VW/WS2 to HCHO, CH4, CH3HO, CH3OH, and CH3CH3. Initially, we used first-principles calculations to determine the system’s electronic properties. According to the DOS, HCHO contributes more than other gas molecules to an energy level close to the Fermi level. The HCHO-VW/WS2 B is the biggest (0.104 e). The system’s W was then computed, and the HCHO system’s W clearly rose. We also calculated the I–V characteristic. It was observed that in the case of adsorbed HCHO, the corresponding conductivity increased most dramatically and the slope increased most noticeably once the bias voltage rose beyond the threshold voltage. Therefore, VW/WS2 can solve the cross-sensitivity and other defects of general chemical sensors, and then develop into HCHO chemical sensors with high sensitivity and selectivity, which can be further integrated into flexible wearable devices to realize real-time monitoring of individual health and environmental factors.

Author Contributions

Z.C.: Supervision, Writing—review & editing. H.W.: Conceptualization, Writing—original draft, Methodology. K.Y.: Data curation Y.S.: Software, Validation. K.Q.: Data curation. P.Y.: Data curation. E.L.: Supervision, Writing-review & editing. All authors have read and agreed to the published version of the manuscript.

Funding

This work was funded by the National Natural Science Foundation of China (No. 12104362), the Natural Science Basic Research Plan in Shaanxi Province of China (Program No. 2021JM-345), the China Postdoctoral Science Foundation (Program No. 2020M683684XB), and the Shaanxi Province Innovative Talents Promotion Plan-Young Science and Technology Star Project (No. 2022KJXX-61).

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

Data are contained within the article.

Acknowledgments

We gratefully acknowledge HZWTECH for providing the computation facilities and thank Xiaowen Shi (from HZWTECH) for the help and discussions regarding this study.

Conflicts of Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

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Sensors 24 00762 g001
Figure 1. The most stable adsorption configurations of (a) HCHO, (b) CH4, (c) CH3CHO, (d) CH3OH, and (e) CH3CH3 adsorbed on WS2. The white, blue, brown, pink, and red spheres represent S, W, C, H, and O atoms, respectively.
Figure 1. The most stable adsorption configurations of (a) HCHO, (b) CH4, (c) CH3CHO, (d) CH3OH, and (e) CH3CH3 adsorbed on WS2. The white, blue, brown, pink, and red spheres represent S, W, C, H, and O atoms, respectively.
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Figure 2. The band of (a) WS2, (b) HCHO-WS2, (c) CH4-WS2, (d) CH3CHO-WS2, (e) CH3OH-WS2, and (f) CH3CH3-WS2.
Figure 2. The band of (a) WS2, (b) HCHO-WS2, (c) CH4-WS2, (d) CH3CHO-WS2, (e) CH3OH-WS2, and (f) CH3CH3-WS2.
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Figure 3. The DOS of (a) HCHO, (b) CH4, (c) CH3CHO, (d) CH3OH, and (e) CH3CH3 adsorbed on WS2.
Figure 3. The DOS of (a) HCHO, (b) CH4, (c) CH3CHO, (d) CH3OH, and (e) CH3CH3 adsorbed on WS2.
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Figure 4. The CDD of (a) HCHO, (b) CH4, (c) CH3CHO, (d) CH3OH, and (e) CH3CH3 adsorbed on WS2 with the isosurface value of 3 × 10−4 e Å−1. The W and S atoms are colored in blue and grey, the sky-blue area denotes the accumulation of electrons, and the purple area denotes the depletion of electrons.
Figure 4. The CDD of (a) HCHO, (b) CH4, (c) CH3CHO, (d) CH3OH, and (e) CH3CH3 adsorbed on WS2 with the isosurface value of 3 × 10−4 e Å−1. The W and S atoms are colored in blue and grey, the sky-blue area denotes the accumulation of electrons, and the purple area denotes the depletion of electrons.
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Figure 5. The (a) configuration and (b) adsorption energy of VW/WS2 and VS/WS2, the W and S atoms are colored in blue and grey.
Figure 5. The (a) configuration and (b) adsorption energy of VW/WS2 and VS/WS2, the W and S atoms are colored in blue and grey.
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Figure 6. The (a) configuration, (b) graph of total energy and simulation time, (c) band structure, and (d) DOS of VW/WS2, the W and S atoms are colored in blue and grey.
Figure 6. The (a) configuration, (b) graph of total energy and simulation time, (c) band structure, and (d) DOS of VW/WS2, the W and S atoms are colored in blue and grey.
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Figure 7. The most stable adsorption configurations of (a) HCHO, (b) CH4, (c) CH3CHO, (d) CH3OH, and (e) CH3CH3 adsorbed on VW/WS2, the W and S atoms are colored in blue and grey.
Figure 7. The most stable adsorption configurations of (a) HCHO, (b) CH4, (c) CH3CHO, (d) CH3OH, and (e) CH3CH3 adsorbed on VW/WS2, the W and S atoms are colored in blue and grey.
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Figure 8. The band gap of HCHO, CH4, CH3CHO, CH3OH, and CH3CH3 adsorbed on VW/WS2.
Figure 8. The band gap of HCHO, CH4, CH3CHO, CH3OH, and CH3CH3 adsorbed on VW/WS2.
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Figure 9. The DOS of (a) HCHO, (b) CH4, (c) CH3CHO, (d) CH3OH, and (e) CH3CH3 adsorbed on VW/WS2.
Figure 9. The DOS of (a) HCHO, (b) CH4, (c) CH3CHO, (d) CH3OH, and (e) CH3CH3 adsorbed on VW/WS2.
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Figure 10. The CDD of (a) HCHO, (b) CH4, (c) CH3CHO, (d) CH3OH, and (e) CH3CH3 adsorbed on VW/WS2. The W and S atoms are colored in blue and grey, the sky-blue area denotes the accumulation of electrons, and the purple area denotes the depletion of electrons. The value of the isosurface is set to 3 × 10−4 e Å−1.
Figure 10. The CDD of (a) HCHO, (b) CH4, (c) CH3CHO, (d) CH3OH, and (e) CH3CH3 adsorbed on VW/WS2. The W and S atoms are colored in blue and grey, the sky-blue area denotes the accumulation of electrons, and the purple area denotes the depletion of electrons. The value of the isosurface is set to 3 × 10−4 e Å−1.
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Figure 11. Device model for VW/WS2 adsorption systems of (a) and the I–V curve of (b) HCHO, (c) CH4, (d) CH3CHO, (e) CH3OH, and (f) CH3CH3 adsorbed on VW/WS2.
Figure 11. Device model for VW/WS2 adsorption systems of (a) and the I–V curve of (b) HCHO, (c) CH4, (d) CH3CHO, (e) CH3OH, and (f) CH3CH3 adsorbed on VW/WS2.
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Table 1. The Ead, the H, band gap (Eg), B, and W for WS2, and HCHO, CH4, CH3CHO, CH3OH, and CH3CH3 adsorbed on WS2.
Table 1. The Ead, the H, band gap (Eg), B, and W for WS2, and HCHO, CH4, CH3CHO, CH3OH, and CH3CH3 adsorbed on WS2.
ConfigurationEad (meV)H (Å)Eg (eV)B (e)W (eV)ΔW (eV)
WS2--1.775-5.39
HCHO-WS2196.722.941.7720.1075.720.337
CH4-WS2149.552.801.7720.0925.530.140
CH3CHO-WS2233.052.781.7730.0885.01−0.374
CH3OH-WS2206.272.491.7730.0915.15−0.232
CH3CH3-WS2246.022.521.7730.0895.530.146
Table 2. The Ead, H, Eg, and B for HCHO, CH4, CH3CHO, CH3OH, and CH3CH3 adsorbed on VW/WS2.
Table 2. The Ead, H, Eg, and B for HCHO, CH4, CH3CHO, CH3OH, and CH3CH3 adsorbed on VW/WS2.
ConfigurationEad (meV)H (Å)Eg (eV)B (e)W (eV)ΔW (eV)
VW/WS2--0.379-5.432-
HCHO-VW/WS2−207.82.920.3400.1045.6370.205
CH4-VW/WS2−144.52.790.341−0.0115.4370.005
CH3CHO-VW/WS2−188.22.650.3730.0904.993−0.439
CH3OH-VW/WS2−207.92.670.3720.0875.069−0.363
CH3CH3-VW/WS2−236.92.510.367−0.0165.4400.008
Table 3. The sensitivity (%) of the sensor based on VW/WS2 with left and right electrodes toward HCHO, CH4, CH3CHO, CH3OH, and CH3CH3 at bias voltage of 1.8 V, 2.0 V, 2.2 V, and 2.4 V. Negative (positive) sensitivity means that the current of the sensor dropped (enhanced) after interaction with the adsorption.
Table 3. The sensitivity (%) of the sensor based on VW/WS2 with left and right electrodes toward HCHO, CH4, CH3CHO, CH3OH, and CH3CH3 at bias voltage of 1.8 V, 2.0 V, 2.2 V, and 2.4 V. Negative (positive) sensitivity means that the current of the sensor dropped (enhanced) after interaction with the adsorption.
Bias Voltage (V)HCHOCH4CH3CHOCH3OHCH3CH3
1.8−98.1−96.7−88.9−94.9−96.0
2.0−67.7−67.9−60.0−64.1−65.8
2.2+108.0+18.9+15.3+13.2+16.2
2.4+42.9+14.6+9.75+8.46+11.7
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Cui, Z.; Wang, H.; Yang, K.; Shen, Y.; Qin, K.; Yuan, P.; Li, E. Highly Sensitive and Selective Defect WS2 Chemical Sensor for Detecting HCHO Toxic Gases. Sensors 2024, 24, 762. https://doi.org/10.3390/s24030762

AMA Style

Cui Z, Wang H, Yang K, Shen Y, Qin K, Yuan P, Li E. Highly Sensitive and Selective Defect WS2 Chemical Sensor for Detecting HCHO Toxic Gases. Sensors. 2024; 24(3):762. https://doi.org/10.3390/s24030762

Chicago/Turabian Style

Cui, Zhen, Hanxiao Wang, Kunqi Yang, Yang Shen, Ke Qin, Pei Yuan, and Enling Li. 2024. "Highly Sensitive and Selective Defect WS2 Chemical Sensor for Detecting HCHO Toxic Gases" Sensors 24, no. 3: 762. https://doi.org/10.3390/s24030762

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