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A first-principles study of propanol adsorption on Monolayer Molybdenum Diselenide (MoSe2) investigate the adsorption mechanism of propanol gas on the surface of monolayer MoSe2 by the quantum simulation method. The images of the potential energy surfaces for configuration of adsorbate on MoSe2 surface were investigated using the Computational DFT-based Nanoscope tool to explore the most stable configurations and diffusion possibilities.
A first-principles study of propanol adsorption on Monolayer Molybdenum Diselenide (MoSe2) Luong Thi Theu1, Tran Thi Nhan2, Tran Quang Huy3, Van An Dinh1,4 Institute of Applied Technology, Thu Dau Mot University, Binh Duong, Vietnam Faculty of Fundamental Sciences, Hnoi University of Industry, Hanoi, Vietnam Faculty of Physics, Hanoi Pedagogical University 2, Hanoi, Vietnam Department of Precision Engineering, Graduate School of Engineering, Osaka University, Osaka, Japan ABSTRACTS It is desirable to seek new sensors capable of detecting VOCs at low concentrations in the early stages of cancer Because of their high surface area to volume ratio, 2D TMDs are predicted to be appealing materials for gas sensitive sensors In this work, we investigate the adsorption mechanism of propanol gas on the surface of monolayer MoSe2 by the quantum simulation method The images of the potential energy surfaces for configuration of adsorbate on MoSe2 surface were investigated using the Computational DFT-based Nanoscope tool to explore the most stable configurations and diffusion possibilities The optPBE-wdW functional was used for discussing the adsorption mechanism, electronic structure, and charge transfer It is found that by using optPBE-vdW functional, the propanol-adsorbed MoSe2 is physisorbed with a pretty high energy of 436 meV, which indicates that MoSe2 is considerably sensitive with this gas The charge transfer between the substrate and VOCs was also addressed Keywords: Adsorption, VOCs, propanol, monolayer MoSe2, DFT Nghiên cứu nguyên lý ban đầu hấp phụ khí propanol lên đơn lớp Molybdenum Diselenide (MoSe2) Luong Thi Theu1, Tran Thi Nhan2, Tran Quang Huy3, Van An Dinh1,4 Institute of Applied Technology, Thu Dau Mot University, Binh Duong, Vietnam Faculty of Fundamental Sciences, Hnoi University of Industry, Hanoi, Vietnam Faculty of Physics, Hanoi Pedagogical University 2, Hanoi, Vietnam Department of Precision Engineering, Graduate School of Engineering, Osaka University, Osaka, Japan 56 TÓM TẮT Chúng ta mong muốn tìm cảm biến có khả phát hợp chất hữu dễ bay nồng độ thấp giai đoạn ung thư sớm Do tỷ lệ diện tích bề mặt thể tích cao, vật liệu kim loại chuyển tiếp dichalcogenides hai chiều dự đoán vật liệu hấp dẫn cho cảm biến nhạy khí Trong báo này, chúng tơi nghiên cứu chế hấp phụ khí propanol bề mặt MoSe2 đơn lớp phương pháp mô lượng tử Hình ảnh lượng bề mặt cho cấu hình chất hấp phụ bề mặt MoSe2 khảo sát cách sử dụng công cụ Nanoscope dựa tính tốn lý thuyết hàm mật độ để khám phá cấu hình ổn định khả khuếch tán Phiếm hàm optPBE-wdW sử dụng để thảo luận chế hấp phụ, cấu trúc điện tử truyền điện tích Bằng cách sử dụng phiếm hàm optPBE-vdW thấy rằng, hấp phụ propanol MoSe2 hấp phụ vật lý với lượng cao khoảng 436 meV, điều cho thấy MoSe2 nhạy với khí Sự dịch chuyển điện tích chất khí thảo luận Từ khóa: Hấp phụ, hợp chất hữu bay hơi, propanol, đơn lớp MoSe2, lý thuyết hàm mật độ Introduction Volatile organic compounds (VOCs), which are found in the breath of people with earlystage cancer, are considered as new cancer biomarkers for diagnostic purposes [1-4] It has been shown that early diagnosis increases the chances of survival in patients with various types of cancer [5,6] Breath analysis might provide the foundation of a non-invasive technique for early cancer detection by gas sensitive sensors Traditional semiconductor metal oxide based gas sensors have good selectivity and sensitivity [7], but they generally require high operating temperatures, which lead in high power consumption and inducing deviation in results 2D transition metal dichalcogenides (TMDs) have attracted a lot of interest as a chemical sensing device alternative to traditional metal oxides Because of its outstanding semiconductor characteristics, this material family has been found with applications in a variety of disciplines including photocatalysis, optoelectronics, electronics, spintronics, and gas sensors [8-12] Among the 2D TMD materials, monolayer (ML) MoSe2 displays appealing electronic properties including high surface-to-volume ratio, stability, high conductivity, and layered structure, and the capacity to adjust the number of layers [13-15] 57 Therefore, MoSe2 is expected to be a promising semiconductor option for the design and manufacturing of high-performance gas sensing devices [16-20] In the present study, by first principle simulation method, we explore the mechanism, structural and electronic properties of MoSe2 monolayer adsorbed on the surface of propanol gas using the non-empirical van der Waals (vdW) density functional The most favored configuration of the gas-MoSe2 adsorption system was explored by optimizing the geometric structure and computing the interaction energy with the Computational DFT based Nanoscope tool [21-23] The adsorption energy profile was calculated in detail with the optPBE-vdW functional to evaluate the propanol sensitivity of MoSe2 In addition, the influence of gas adsorption on the electronic structure, as well as the charge transfer mechanism between the substrate and the gas molecule, are carefully considered with the appropriate optPBE-vdW functional Computational Method The adsorption mechanism of propanol toward the surface of a MoSe2 4x4 supercell was studied theoretically using Density Functional Theory (DFT) [24-26] Ab initio calculation simulation was done on High Performance Computers using the density functionals approach implemented in Vienna Ab initio Simulation Package (VASP) [27, 28] The van der Waals interaction is accounted for by using the optPBE-vdW functional [29, 30] Automatic scanning using a Computational DFT-based Nanoscope [21-23] was used to find the most optimal adsorption geometries of the adsorbate on the MoSe2 substrate, and the adsorption energy profile A cutoff energy of 500 eV for the plane-wave basis set and a 4x4x1 Gamma-centered kpoint mesh corresponding to the 4x4 super-cell were utilized A vacuum thickness of 20 Å was applied to eliminate the interaction between layers The structures were all thoroughly relaxed until the maximum residual Hellmann-Feynman force acting on each atom was less than 0.01 eV/Å The adsorption energy Ead is calculated by the following equation: Ead = Egas+sub − ( Egas + Esub ) , (1) where Egas+sub, Egas, and Esub are the total energies of the gas-MoSe2 system, isolated gas molecule, and isolated MoSe2, respectively Bader charge analysis was used to estimate the Charge Differential Density (CDD) of the most favorable adsorption configuration The charge 58 density difference is calculated using the equation = AB − A − B [31], in which ρAB is the total charge of the system, ρA and ρB are the charges are two separate systems The visualization using in this paper is VESTA, which was developed by K Momma and F Izumi [32] Results and Discussions 3.1 Geometrical structure of propanol and the stable position of adsorption system propanol-MoSe2 Propanol is an organic compound with the molecular formula CH3CH2CH2OH that belongs to the alcohol functional group Figure illustrates the molecular structure of propanol, with carbon, hydrogen, and oxygen atoms represented by the brown, light pink, and red spheres, respectively Propanol concentrations in the breath of patients with lung, liver, and stomach cancers have been reported [1, 2, 4], that play a critical role in early cancer detection Figure Molecular structure of propanol Figure Top (a) and side (b) views of propanol adsorption on MoSe2 The Se and Mo atoms are represented by the green and purple spheres, respectively 59 By carefully optimizing the geometry structures of the gas-MoSe2 adsorption systems using the Nanocope tool, the most stable configuration of the propanol-MoSe2 adsorption systems was explored, as shown in Figure This tool has been used to simulate the adsorption of organic gases on other 2D materials, such as brophene [22] and silicene [23] It is discovered that the most preferred adsorption site is the gas oriented parallel to the substrate, approximately 2.7 Å from the material's surface to the gas's lowest atomic position When the structures of gas and material were compared before and after adsorption, the bond angles and bond lengths showed very little variations in both This suggests that MoSe2 is a highly stable sensor material 3.2 Binding potential, adsorption energy profile of propanol onto MoSe2 The stable positions of adsorbent can be determined by the minima of the potential energy surface (PES) When PES equals zero, the adsorption system is in the most equilibrium state Because of the periodicity in the ML MoSe2 lattice structure, it is only necessary to compute PES of unitcell instead of supercell Figure shows the potential energy surface per unitcell of propanol gas on ML MoSe2 The color gradient represents the PES value, with brighter colors exhibiting a higher PES values and vice versa According to this convention, the blue and black regions correspond to favorable adsorption areas Unfavorable adsorption areas are represented by the yellow and orange colors Diffusion allows gas molecules to move between adsorption regions Because the minimum energy difference between the propanol adsorption regions is 15 meV, the adsorption regions will be linked, indicating that MoSe2 is quite sensitive to this gas Figure The 3D projected Potential Energy Surface for the adsorption of propanol on the surface of MoSe2 60 Table shows the adsorption characteristics of propanol on MoSe2 with the optPBE-vdW functional The optimal adsorption distance dz (dc) is the distance from the lowest atom (center of mass –COM) of the gas molecule to the surface of MoSe2 It was discovered that the propanol-adsorbed MoSe2 is physisorbed with a pretty high energy of 436 meV The adsorption distance between the lowest atom and the substrate is 2.631 Å, the response length l is 9.867 Å, and the recovery time τ is quite small, 20 microseconds According to the findings, MoSe2 is extremely sensitive to propanol vapor Table Adsorption energy (Ead), equilibrium height of the lowest atom (dc), equilibrium height of the massed center (dz), response length (l), and recovery time (τ) for the adsorption of propanol on MoSe2 using optPBE-vdW functional Molecule Propanol Adsorption properties optPBEvdW Ead (meV) -436 dz(Å) 2.631 dc(Å) 3.513 l(Å) 9.867 τ (µs) 20.34 3.3 Electronic band structure and charge transfer of propanol gas on MoSe2 monolayer 3.3.1 Electronic band structure To investigate the nature of propanol adsorption on MoSe2, we computed the band dispersion and density of states along high symmetry k-points We observed that ML MoSe2 exhibits a direct band gap involved to the Brillouin zones' K-K shift with the band gap value of approximately 1.418 eV, in good agreement with previous calculations [33, 34] Based on the calculation results shown in Figure 4, the electronic band structure of MoSe2 shows a decrease in the band gap by about 7.8 meV Decreasing a band gap might lead to the increasing of electrical conductivity, which implies the possibility of detecting VOCs by monitoring the conductance of MoSe2 upon exposure to a breath containing VOCs 61 Figure Band structures and density of states (DOS) of propanol on MoSe2 (optPBE-vdW functional) The dashed lines represent Fermi level DOS is in units of state/eV 3.3.2 Charge transfer mechanism Bader charge analysis was used to determine charge transfer The amount and direction of charge transfer may be determined by comparing the charge before and after adsorption of a VOC molecule After adsorption, the positive sign indicates electron accumulation, which is represented by the yellow color, whereas the negative sign shows electron depletion, which is represented by the blue hue Figure Top (a) and side (b) views of charge density difference (CDD) by the adsorption of propanol on monolayer MoSe2 We discovered that, propanol acts as an electron acceptor from substrate The amount of charge transferred about 0.4e are higher by far than its chemical-adsorption on single-layer 62 stanane in previous work[35] The donated charge is believed to change the resistivity of the adsorbent, MoSe2, making it a selective and sensitive material to propanol gas Conclusion We have investigated the interaction between freestanding ML MoSe2 and propanol gas by the quantum simulation based on the Density functional theory with the use of the optPBE-vdW functional The picture of PES, favorable adsorption configuration, electronic structure, and charge transfer were computed Upon propanol gas adsorption, a decrease in the band gap by about 7.8 meV appears in the electronic structure of MoSe2, resulting in changeable conductivity It is also found the charge transfer of 0.4 electrons between VOC and material, suggesting a possibility of the use of MoSe2 material in the sensing devices, especially in VOC sensors References [1] Z Jia, A Patra, V.K Kutty, T Venkatesan, (2019), Critical review of 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Electronic band structure and charge transfer of propanol gas on MoSe2 monolayer 3.3.1 Electronic band structure To investigate the nature of propanol adsorption on MoSe2, we computed the band... (a) and side (b) views of charge density difference (CDD) by the adsorption of propanol on monolayer MoSe2 We discovered that, propanol acts as an electron acceptor from substrate The amount of