Au cluster adsorption on perfect and defective MoS2 monolayers: structural and electronic properties

First-principle study of shear deformation effect on Mg adsorption by monolayer SnS2

CONTEXT

In this study, the effects of different shear deformations on the structural stability, electronic structure, and optical properties of a Mg atom adsorption system of S vacancy defect SnS2 are systematically investigated based on density functional theory. It is shown that the presence of an S-vacancy defect makes the band gap of the SnS2 system significantly smaller than that of the perfect SnS2 system, and the SnS2 system is changed from a direct band gap semiconductor to an indirect band gap semiconductor. The optimal adsorption position of a Mg atom on the S-vacancy SnS2 system is above the S atom where the adsorption energy is the largest and the system is the most stable. The density of states of the adsorption system is predominantly contributed by the S-3p and Sn-5 s orbital electrons. The imposition of shear deformation leads to the introduction of certain impurity energy levels in the adsorption system, and the forbidden bandwidth near the Fermi energy level decreases. As compared to the intrinsic SnS2, the absorption and reflection peaks of adsorption systems under different shear deformation are red-shifted and appear in the ultraviolet region. This improves the utilization of the adsorption system for ultraviolet light to a great extent.

METHODS

The model calculations in this paper are performed using the CASTEP module of the Material Studio (MS) software based on the first principles of Density Functional Theory (DFT) (Wei et al. in Physica B 545:99-106, 2018) for plane wave artifacts. Geometrical optimization and computational procedures are used to calculate the exchange-correlation energy using the Perdew-Burke-Ernzerhof (PBE) generalized function (Perdew et al. in Phys Rev B Condens Matter 48:4978, 1993) of the generalized gradient approximation (GGA). The Monkhorst-Pack method (Monkhorst and Pack in Phys Rev B 13:5188-5192, 1976) was used to rationalize the sampling of the highly symmetric k-points in the Brillouin zone. The grid of k-points is set to be 6 × 6 × 1. The plane-wave truncation energy is set to be 400 eV. The energy convergence criterion is 1.0 × 10-5 eV. The residual stress of all atoms is 0.01 eV/Å. A vacuum layer with a thickness of 15 Å is set up in the z-direction, which ensures that the interactions of the system along the z-axis between the top and the bottom layers can be ignored during the whole simulation process. We construct a 3 × 3 × 1 SnS2 system containing 27 atoms as the computational model. The intrinsic SnS2 contains 9 Sn atoms and 18 S atoms.

Pt-Doped HfS2 Monolayer as a Novel Sensor and Scavenger for Dissolved Gases (H2, CO2, CH4, and C2H2) in Transformer Oil: A Density Functional Theory Study

Detecting the types and concentrations of dissolved gases in insulating oil by resistivity-type sensors is an extremely effective means for diagnosing faults in an oil-immersed transformer. However, further breakthroughs and innovations are needed in gas-sensitive materials for preparing high-performance resistivity-type sensors. In this investigation, the application possibility of using Pt-doped HfS2 (Pt-HfS2) as gas-sensitive materials for the detection of dissolved H2, CO2, CH4, and C2H2 in oil has been verified by analyzing the adsorption energy (Ead), differential charge density (DCD), density of states (DOS), frontier molecular orbital, and desorption time based on density functional theory (DFT). The outcomes suggest that the band gap of HfS2 is obviously narrowed after doping Pt at the position of the bridge between the S and Hf atoms, resulting in a significant increase in the conductivity of HfS2. The low adsorption energy implies that there is only weak physical adsorption between Pt-HfS2 and CO2 (-0.783 eV). In contrast, the highly hybridized atomic orbitals of Pt with H2, CH4, and C2H2 indicate that strong chemical adsorption reactions occur. Two-dimensional Pt-HfS2 as a gas sensor has a great monitoring performance for CH4 at 298 K (room temperature). This research serves as theoretical guidelines for probing the application potential of Pt-HfS2 in fault diagnosis and predictive maintenance of an oil-immersed transformer.

N-Nitrosamine sensing properties of novel penta-silicane nanosheets-a first-principles outlook

CONTEXT

N-Nitrosamine is one of the highly toxic carcinogenic compounds that are found almost in the entire environment. In the present work, novel penta-silicene (penta-Si) and penta-silicane (penta-HSi) are utilised to sense the N-nitrosamine in the air environment. Initially, structural firmness of penta-Si and penta-HSi is confirmed using cohesive energy. Subsequently, the electronic properties of penta-Si and penta-HSi are discussed with the aid of electronic band structure and projected density of states (PDOS) maps. The calculated band gap of penta-Si and penta-HSi is 0.251 eV and 3.117 eV, correspondingly. Mainly, the adsorption property of N-nitrosamine on the penta-Si and penta-HSi is studied based on adsorption energy, Mulliken population analysis along with relative energy gap changes. The computed adsorption energy range is in physisorption (- 0.101 to - 0.619 eV), which recommends that the proposed penta-Si and penta-HSi can be employed as a promising sensor to detect the N-nitrosamine in the air environment.

METHODS

The structural, electronic and adsorption behaviour of N-nitrosamine on penta-Si and penta-HSi are studied based on the density functional theory (DFT) approach. The hybrid generalized gradient approximation (GGA) with Becke's three-parameter (B3) + Lee-Yang-Parr (LYP) exchange correlation functional is used to optimise the base material. All calculations in the present work are carried out in Quantum-ATK-Atomistic Simulation Software.

Ni-Decorated PtS2 Monolayer as a Strain-Modulated and Outstanding Sensor upon Dissolved Gases in Transformer Oil: A First-Principles Study

The first-principles theory is conducted in this paper to investigate the adsorption and electronic properties of a Ni-decorated PtS₂ (Ni-PtS₂) monolayer upon two dissolved gas species (CO and C₂H₂) in the transformer oil, thus illustrating its sensing performance and related potential to evaluate the working condition of the oil-immersed transformers. We then highlight the effect of the biaxial strain on the configuration, charge transfer, and bandgap of the adsorbed systems to expound its potential as a strain-modulated gas sensor. Results indicate that the Ni-PtS₂ monolayer undergoes chemisorption upon two species, with an E _ad value of -1.78 eV for the CO system and -1.53 eV for the C₂H₂ system. The reduced bandgap by 0.164 eV (20.05%) in the CO system and 0.047 eV (5.74%) in the C₂H₂ system imply the large feasibility of the Ni-PtS₂ monolayer to be a resistance-type sensor for CO and C₂H₂ detection, which is also verified by the I-V analysis of these systems. Besides, the applied biaxial strain can exert geometric activations on the Ni-PtS₂ monolayer, and specifically, the compressive force can further reduce the bandgap in two systems, thus promoting its sensing response upon two gases. Our work is meaningful to broaden the exploration of noble transition metal dichalcogenides for gas sensing.

Structure, stability, and electronic and optical properties of TMDC-coinage metal composites: vertical atomically thin self-assembly of Au clusters

Composites of metal clusters supported on transition metal dichalcogenides (TMDCs) often provide promising opportunities for applications in nanoelectronics, catalysis, sensing, etc. In the present investigation, a systematic attempt has been made to unveil the structure and stability of coinage M₆ clusters supported on TMDC (MoS₂ and WS₂) monolayers. The more prominent objective is to explore potential candidates that stabilize the two-dimensional (2D) M₆ clusters on their surface. Periodic energy decomposition analysis (pEDA) was carried out to probe the various interaction energy (IE) components that govern the stability of the M₆ clusters in the composites. Attention has also been devoted to unravelling the electronic and optical properties of these TMDCs/M₆ composites. Moreover, ab initio molecular dynamics (AIMD) simulations were performed to scrutinize the dynamic behaviour of Au cluster on WS₂ monolayer. The results reveal that the coinage M₆ clusters form energetically more stable composites on MoS₂ than WS₂ monolayer. It is worth mentioning that WS₂ promotes the stability of 2D M₆ clusters. Inclusion of dispersion correction marginally altered the geometries of the TMDCs/M₆ composites but its impact on the IE values was significant. AIMD simulation explicitly emphasizes that the WS₂ surface preferentially facilitates the vertical 2D self-assembling of Au atoms and, interestingly, the planarity is mostly retained during the course of simulations. The adsorption of coinage M₆ clusters substantially influences the electronic and optical properties of the TMDCs. HSE06 calculation confirms that the decrease in energy gap is more pronounced in MoS₂/M₆ composites. The outcomes of this study render fundamental insights into the various TMDCs/M₆ composites that would certainly be worthwhile probing for diverse practical applications.

CuO-Modified PtSe2 Monolayer as a Promising Sensing Candidate toward C2H2 and C2H4 in Oil-Immersed Transformers: A Density Functional Theory Study

This work using the density functional theory simulates the strong potential of the CuO-decorated PtSe₂ (CuO-PtSe₂) monolayer as a recycle use C₂H₂ and C₂H₄ sensor in order to realize the arc discharge monitoring based on the nano-sensing method. Results indicate that CuO decoration causes strong n-type doping for the PtSe₂ monolayer with a binding force (E _b) of -2.49 eV, and the CuO-PtSe₂ monolayer exhibits strong chemisorption and electron-accepting properties in the two gas systems, with the adsorption energy (E _ad) and charge transfer (Q _T) obtained as -1.19 eV and 0.040 e for the C₂H₂ system and as -1.24 eV and 0.011 e for the C₂H₄ system, respectively. The density of states reveals the deformed electronic property of the CuO-PtSe₂ monolayer in gas adsorptions, and its sensing mechanism based on the change of electrical conductivity and the work function are uncovered. This work sheds light on the metal-oxide-decorated transition-metal dichalcogenides for gas sensor applications and would provide the guidance to explore novel sensing materials in many other fields as well.

First-Principles Study of Irn (n = 3-5) Clusters Adsorbed on Graphene and Hexagonal Boron Nitride: Structural and Magnetic Properties

Magnetic clusters have attracted great attention and interest due to their novel electronic properties, and they have potential applications in nanoscale information storage devices and spintronics. The interaction between magnetic clusters and substrates is still one of the challenging research focuses. Here, by using the density functional theory (DFT), we study the structural stability and magnetic properties of iridium clusters (Ir_n, n = 3–5) adsorbed on two-dimensional (2D) substrates, such as graphene and hexagonal boron nitride (hBN). We find that the most favorable configurations of free Ir_n clusters change when adsorbed on 2D substrates. In the meantime, the magnetic moments of the most stable Ir_n reduce to 53% (graphene) and 23.6% (hBN) compared with those of the free−standing ones. Interestingly, about 12-times enlargement on the magnetic anisotropy energy can be found on hBN substrates. These theoretical results indicate that the cluster–substrate interaction has vital effects on the properties of Ir_n clusters.

Gas Sensing Mechanism and Adsorption Properties of C2H4 and CO Molecules on the Ag3–HfSe2 Monolayer: A First-Principle Study

The detection of dissolved gases in oil is an important method for the analysis of transformer fault diagnosis. In this article, the potential-doped structure of the Ag₃ cluster on the HfSe₂ monolayer and adsorption behavior of CO and C₂H₄ upon Ag₃–HfSe₂ were studied theoretically. Herein, the binding energy, adsorption energy, band structure, density of state (DOS), partial density of state (PDOS), Mulliken charge analysis, and frontier molecular orbital were investigated. The results showed that the adsorption effect on C₂H₄ is stronger than that on CO. The electrical sensitivity and anti-interference were studied based on the bandgap and adsorption energy of gases. In particular, there is an increase of 55.49% in the electrical sensitivity of C₂H₄ after the adsorption. Compared to the adsorption energy of different gases, it was found that only the adsorption of the C₂H₄ system is chemisorption, while that of the others is physisorption. It illustrates the great anti-interference in the detection of C₂H₄. Therefore, the study explored the potential of HfSe₂-modified materials for sensing and detecting CO and C₂H₄ to estimate the working state of power transformers.

Adsorption and Sensing Performances of Pristine and Au-Decorated Gallium Nitride Monolayer to Noxious Gas Molecules: A DFT Investigation

In this study, the adsorption of noxious gas molecules (NO, Cl₂, and O₃) on GaN and Au-decorated GaN was systematically scrutinized, and the adsorption energy, bond length, charge, density of state (DOS), partial density of state (PDOS), electron deformation density (EDD), and orbitals were analyzed by the density functional theory (DFT) method. It is found that the interaction between NO and pristine GaN is physical adsorption, while GaN chemically reacts with Cl₂ and O₃. These observations suggest that pristine GaN may be a candidate for the detection of Cl₂ and O₃. The highly activated Au-decorated GaN can enhance the adsorption performance toward NO and convert the physical adsorption for NO into chemical adsorption, explaining the fact that precious metal doping is essential for regulating the electronic properties of the substrate material. This further confirms the well-established role of Au-decorated GaN in NO gas-sensing applications. In addition, the adsorption performance of Au-decorated GaN for Cl₂ and O₃ molecules is highly improved, which provides guidance to scavenge toxic gases such as Cl₂ and O₃ by the Au-decorated GaN material.

Mesoporous Ti0.5Cr0.5N for trace H2S detection with excellent long-term stability

Efficient, accurate and reliable detection and monitoring of H₂S is of significance in a wide range of areas: industrial production, medical diagnosis, environmental monitoring, and health screening. However the rapid corrosion of commercial platinum-on-carbon (Pt/C) sensing electrodes in the presence of H₂S presents a fundamental challenge for fuel cell gas sensors. Herein we report a solution to the issue through the design of a sensing electrode, which is based on Pt supported on mesoporous titanium chromium nitrides (Pt/Ti_0.5Cr_0.5N). Its desirable characteristics are due to its high electrochemical stability and strong metal-support interactions. The Pt/Ti_0.5Cr_0.5N-based sensors exhibit a much smaller attenuation (1.3%) in response to H₂S than Pt/C-sensor (40%), after 2 months sensing test. Furthermore, the Pt/Ti_0.5Cr_0.5N-based sensors exhibit negligible cross response to other interfering gases compared with hydrogen sulfide. Results of density functional theory calculation also verify the excellent long-term stability and selectivity of the gas sensor. Our work hence points to a new sensing electrode system that offers a combination of high performance and stability for fuel-cell gas sensors.

InP3 Monolayer as a Promising 2D Sensing Material in SF6 Insulation Devices

In this letter, we perform a first-principles study on the adsorption performance of the InP3 monolayer upon three SF6 decomposed species, including SO2, SOF2, and SO2F2, to investigate its potential as a resistance-type, optical or field-effect transistor gas sensor. Results indicate that the InP3 monolayer exhibits strong chemisorption upon SO2 but weak physisorption upon SO2F2. The most admirable adsorption behavior is upon SOF2, which provides a favorable sensing response (-19.4%) and recovery property (10.4 s) at room temperature as a resistance-type gas sensor. A high response of 180.7% upon SO2 and a poor one of -1.9% upon SO2F2 are also identified, which reveals the feasibility of the InP3 monolayer as a resistance-type sensor for SO2 detection with recycle use via a heating technique to clean the surface. Moreover, the InP3 monolayer is a promising optical sensor for SO2 detection due to the obvious changes in adsorption peaks within the range of ultraviolet and is a desirable field-effect transistor sensor for selective and sensitive detection of SO2 and SOF2 given the evident changes of Q T and E g under the applied electric field.

Computational Appraisal of Silver Nanocluster Evolution on Epitaxial Graphene: Implications for CO Sensing

Early stages of silver nucleation on a two-dimensional (2D) substrate, here, monolayer epitaxial graphene (MEG) on SiC, play a critical role in the formation of application-specific Ag nanostructures. Therefore, it is of both fundamental and practical importance to investigate the growth steps when Ag adatoms start to form a new phase. In this work, we exploit density functional theory to study the kinetics of early-stage nuclei Ag n (n = 1-9) assembly of Ag nanoparticles on MEG. We find that the Ag1 monomer tends to occupy hollow site positions of MEG and interacts with the surface mainly through weak dispersion forces. The pseudoepitaxial growth regime is revealed to dominate the formation of the planar silver clusters. The adsorption and nucleation energies of Ag n clusters exhibit evident odd-even oscillations with cluster size, pointing out the preferable adsorption and nucleation of odd-numbered clusters on MEG. The character of the interaction between a chemisorbed Ag3 cluster and MEG makes it possible to consider this trimer as the most stable nucleus for the subsequent growth of Ag nanoparticles. We reveal the general correlation between Ag/MEG interaction and Ag-Ag interaction: with increasing cluster size, the interaction between Ag adatoms increases, while the Ag/MEG interaction decreases. The general trend is also supported by the results of charge population analysis, according to which the average charge per Ag adatom in a Ag n cluster demonstrates a drastic decrement with cluster size increase. 2D-3D structural transition in Ag n clusters was investigated. We anticipate that the present investigation is beneficial by providing a better understanding of the early-stage nucleation of Ag nanoparticles on MEG at the atomic scale. Specific interaction between odd-numbered Ag clusters preadsorbed onto the MEG surface and carbon monoxide (CO) as well as clusters' stability at 300 K is discussed in terms of sensing applications.

Adsorption of dissolved gas molecules in the transformer oil on silver-modified (002) planes of molybdenum diselenide monolayer: a DFT study

High-sensitivity gas sensor is a crucial online monitoring device to ensure the safe operation of the transformer. In this paper, based on density functional theory, an Ag-MoSe₂monolayer system was established by investigating four different positions of Ag doping to adsorb the dissolved gas (H₂, C₂H₂, CH₄, CO and CO₂) in transformer oil. The sensing properties of adsorption system for different dissolved gas were studied via the analysis of adsorption energy (E_ad), charge transfer, density of state, energy band, lowest unoccupied molecular orbit, highest occupied molecular orbit, and desorption time. Finally, Ag-MoSe₂had good adsorption and desorption properties for CO and CH₄at room temperature, and could be used as a sensor material for the two gases detection. It had strong adsorption and poor desorption performances for C₂H₂at room temperature, which could serve as C₂H₂scavenger, and simultaneously had good adsorption and desorption performance at a temperature of 358 K, therefore it could be used as a candidate material to detect C₂H₂at high temperatures. Ag-MoSe₂had a weak interaction with H₂and CO₂, thus was not suitable for detecting the two gases. The results indicated that Ag-MoSe₂had excellent potential in detecting dissolved gases in transformer oil.

First-principles Insights into Cu-Decorated GaN Monolayers for Sensing CO and HCHO in Dry-Type Transformers

This work using first-principles theory studies the sensing properties of Cu-decorated GaN (Cu-GaN) monolayers as a promising candidate for the detection of CO and HCHO in dry-type transformers. The Cu dopant prefers to be trapped on the TN site of the GaN surface with an E b of -1.13 eV. Chemisorption is identified for the two gas adsorption systems, given the large adsorption energy (E ad) of -1.35 and -1.09 eV. Caused by the chemisorption, the electronic property of the Cu-GaN monolayer is significantly deformed, narrowing its band gap of 0.548 eV to 0.00 eV, exhibiting metallic property, in two gas systems. Combined with the desirable recovery property for CO and HCHO desorption from the Cu-GaN surface, it could be proposed that the Cu-GaN monolayer is a promising gas sensor for toxic gas detection in dry-type transformers, so as to evaluate the operation status of the power system and guarantee safe working conditions for the maintenances.

First-Principles Study of Au-Doped InN Monolayer as Adsorbent and Gas Sensing Material for SF6 Decomposed Species

As an insulating medium, sulfur hexafluoride (SF₆) is extensively applied to electrical insulation equipment to ensure its normal operation. However, both partial discharge and overheating may cause SF₆ to decompose, and then the insulation strength of electrical equipment will be reduced. The adsorption properties and sensing mechanisms of four SF₆ decomposed components (HF, SO₂, SOF₂ and SO₂F₂) upon an Au-modified InN (Au-InN) monolayer were studied in this work based on first-principles theory. Meanwhile, the adsorption energy (E_ad), charge transfer (Q_T), deformation charge density (DCD), density of states (DOS), frontier molecular orbital and recovery property were calculated. It can be observed that the structures of the SO₂, SOF₂ and SO₂F₂ molecules changed significantly after being adsorbed. Meanwhile, the E_ad and Q_T of these three adsorption systems are relatively large, while that of the HF adsorption system is the opposite. These phenomena indicate that Au-InN monolayer has strong adsorption capacity for SO₂, SOF₂ and SO₂F₂, and the adsorption can be identified as chemisorption. In addition, through the analysis of frontier molecular orbital, it is found that the conductivity of Au-InN changed significantly after adsorbing SO₂, SOF₂ and SO₂F₂. Combined with the analysis of the recovery properties, since the recovery time of SO₂ and SO₂F₂ removal from Au-InN monolayer is still very long at 418 K, Au-InN is more suitable as a scavenger for these two gases rather than as a gas sensor. Since the recovery time of the SOF₂ adsorption system is short at 418 K, and the conductivity of the system before and after adsorption changes significantly, Au-InN is an ideal SOF₂ gas-sensing material. These results show that Au-InN has broad application prospects as an SO₂, SOF₂ and SO₂F₂ scavenger and as a resistive SOF₂ sensor, which is of extraordinary meaning to ensure the safe operation of power systems. Our calculations can offer a theoretical basis for further exploration of gas adsorbent and resistive sensors prepared by Au-InN.

Rh-Doped ZnO Monolayer as a Potential Gas Sensor for Air Decomposed Species in a Ring Main Unit: A First-Principles Study

Using the first-principles theory, this paper studies the Rh-doping behavior on the ZnO monolayer and investigates the adsorption and sensing behaviors of a Rh-doped ZnO (Rh-ZnO) monolayer to NO2 and O3 to explore its potential as a gas sensor to evaluate the operation status of the ring main unit in the power system. The results indicate that the Rh dopant can be stably anchored on the TO site of the ZnO monolayer with an E b of -2.11 eV. The Rh-ZnO monolayer shows chemisorption of NO2 and O3, with E ad values of -2.11 and -1.35 eV, respectively. Then, the electronic behavior of the Rh-ZnO monolayer before and after gas adsorption is analyzed in detail to uncover the sensing mechanism for gas detection. Our findings indicate that the Rh-ZnO monolayer is a promising resistance-type gas sensor with a higher response to O3 and can be explored as a field-effect gas sensor with a higher response to NO2. Our theoretical calculations provide the basic sensing mechanism of the Rh-ZnO monolayer for gas detection and would be meaningful to explore novel sensing materials for gas detection in the field of electrical engineering.

Platinum-Doped Anatase (101) Surface as Promising Gas-Sensor Materials for HF, CS2, and COF2: A Density Functional Theory Study

In order to find promising sensor materials for HF, CS₂, and COF₂ detection to realize the online internal insulation defect diagnosis of a SF₆ gas electrical device, the gas sensing property, binding energy, adsorption distance, charge transfer, and density of states distribution, of Pt-doped anatase TiO₂ (101) surfaces on HF, CS₂, and COF₂ gas molecules was calculated and analyzed in this paper based on the density functional theory. The work suggested that the Pt-TiO₂ surface has a nice gas sensing upon CS₂ and COF₂ because of the increase of the conductivity of the Pt-TiO₂ surface and the suitable adsorption parameter after CS₂ and COF₂ adsorbing on it. However, this material is not suitable as a gas sensor for HF gas. All of the works provide theoretical adsorption information of Pt-TiO₂ as a gas sensor material for HF, CS₂, and COF₂ detection.

Al-Doped MoSe2 Monolayer as a Promising Biosensor for Exhaled Breath Analysis: A DFT Study

Exhaled breath analysis by nanosensors is a workable and rapid manner to diagnose lung cancer in the early stage. In this paper, we proposed Al-doped MoSe2 (Al-MoSe2) as a promising biosensor for sensing three typically exhaled volatile organic compounds (VOCs) of lung cancer, namely, C3H4O, C3H6O, and C5H8, using the density functional theory (DFT) method. Single Al atom is doped on the Se-vacancy site of the MoSe2 surface, which behaves as an electron-donor and enhances the electrical conductivity of the nanosystem. The adsorption and desorption performances, electronic behavior, and the thermostability of the Al-MoSe2 monolayer are conducted to fully understand its physicochemical properties as a sensing material. The results indicate that the Al-MoSe2 monolayer shows admirable sensing performances with C3H4O, C3H6O, and C5H8 with responses of -85.7, -95.6, and -96.3%, respectively. Also, the desirable adsorption performance and the thermostability endow with the Al-MoSe2 monolayer with good sensing and desorbing behaviors for the recycle detection of three VOCs. We are hopeful that the results in this paper could provide some guidance to the experimentalists fulfilling their exploration in the practical application, which can also broaden the exploration of transition-metal dichalcogenides (TMDs) in more fields as well.

First-Principle Insight into the Ru-Doped PtSe2 Monolayer for Detection of H2 and C2H2 in Transformer Oil

Using first-principles theory, this paper investigates the sensing behavior of the Ru-doped PtSe₂ (Ru-PtSe₂) monolayer for two dominant gases, namely, H₂ and C₂H₂, in the transformer oil to explore its potential as a gas sensor to evaluate the operation status of the electrical transformers. Ru-doping prefers to go through the S₁ site with the largest E _b of -3.71 eV. Chemisorption is identified in the H₂ and C₂H₂ systems with E _ad obtained as -0.83 and - 2.09 eV, respectively, indicating the stronger performance of the Ru-PtSe₂ monolayer upon C₂H₂ adsorption. Meanwhile, the obvious improvement of bandgap in the C₂H₂ system suggests the potential of Ru-PtSe₂ monolayer as a resistance-type gas sensor for C₂H₂ detection. Moreover, the applied biaxial strains ranging at 1-5% give rise to various Q _T and E _g in two systems, indicating the tunable sensing response of the Ru-PtSe₂ monolayer for gas detection with modulated strains. Our calculation proposes a novel 2D sensing material for H₂ and C₂H₂ detection, which would be beneficial to stimulate more edge-cutting research in the gas sensing field as well.

Ab initio insights into the stabilization and binding mechanisms of MoS2 nanoflakes supported on graphene

An atomistic understanding of transition-metal dichalcogenide (TMD) nanoflakes supported on graphene (Gr) plays an important role in the tuning of the physicochemical properties of two-dimensional (2D) materials; however, our current atom-level understanding of 2D-TMD nanoflakes on Gr is far from satisfactory. Thus, we report a density functional theory investigation into the stabilization and binding mechanisms of (MoS2)n/Gr, where n = 1, 4, 6, 9, 12 and 16. We found an evolution of the (MoS2)n…Gr interactions from covalent and hybridization contributions for smaller nanoflakes (n = 1, 4) to vdW interactions for larger (MoS2)n nanoflakes (n ≥ 6); however, the coupling of the (MoS2)n and Gr electronic states for n = 1 and 4 is not intense enough to change the Dirac cones at the Gr monolayer. On average, the 1T'- and 2H-(MoS2)n nanoflakes bind with similar adsorption/interaction energies with Gr, and hence the (MoS2)n…Gr interactions do not change the high energetic preference of the 1T'- structures, which can be explained by the stabilizing role of the S-terminated edges in the 1T'-(MoS2)n in contrast with the destabilizing role of the edges in the 2H-(MoS2)n nanoflakes.

Cu-Doped MoSe2 Monolayer: A Novel Candidate for Dissolved Gas Analysis in Transformer Oil

Dissolved gas analysis (DGA) in transformer oil is a workable approach to evaluate the operation status of transformers. In this paper, we proposed a Cu-doped Se-vacancy MoSe2 (Cu-MoSe2) monolayer as a promising sensing material for DGA based on first-principles theory. Three typical dissolved gases, namely, CO, C2H2, and C2H4, are the representatives to investigate the potential of the Cu-MoSe2 monolayer upon their adsorption and sensing. Our results indicate that Cu-doping causes strong n-doping for the Se-vacancy MoSe2 monolayer, and the Cu-MoSe2 monolayer exhibits strong chemisorption the three gas molecules, with a calculated adsorption energy (E ad) of -1.25, -1.06, and -1.16 eV, respectively. Such strong interactions lead to remarkable changes in the electrical conductivity of the Cu-MoSe2 monolayer, allowing its application as a resistance-type sensor. Besides, work function (WF) analysis shows the potential of the Cu-MoSe2 monolayer as a promising field-effect transistor sensor as well. It is our hope that our work can stimulate more leading-edge studies of the TM-doped MoSe2 monolayer for sensing applications in many fields.

Adsorption Behavior of Ni-Doped ZnO Monolayer upon SF6 Decomposed Components and Effect of the Applied Electric Field

In this article, Ni-doped ZnO (Ni-ZnO) monolayer is proposed as a potential sensing material for detection of two SF6 decomposed components (namely, SO2 and SOF2), based on the density functional theory (DFT) method, to monitor the operation status of SF6 insulation devices in the power system. The Ni-doping effect on the physicochemical properties of the pure ZnO monolayer is first studied, with the binding energy (E b) calculated as -1.49 eV. Then, the adsorption of a Ni-ZnO monolayer upon SO2 and SOF2 molecules shows that the Ni-ZnO monolayer exhibits strong chemisorption upon the two gas species, with the adsorption energy (E ad) obtained as -2.38 and -2.19 eV, respectively. The electronic properties of the Ni-ZnO monolayer upon gas adsorption are studied through the density-of-state (DOS) analysis, whereas the band structure (BS) and work function (WF) analysis provide the sensing mechanism of the Ni-ZnO monolayer upon two gases. In addition, the charge-transfer behavior during adsorption in the applied electric fields is analyzed to expound the possibility of Ni-ZnO monolayer as a field-effect-transistor gas sensor. Our calculations can stimulate the study on adsorption and sensing behaviors of TM-ZnO monolayers for their applications in many fields.

First-Principles Insight into Pd-Doped ZnO Monolayers as a Promising Scavenger for Dissolved Gas Analysis in Transformer Oil

ZnO monolayers with desirable n-type semiconducting properties are full of potential for sensing applications. In this work, we investigate using first-principles theory the adsorption and sensing behaviors of Pd-doped ZnO (Pd-ZnO) monolayers with two typical dissolved gases, namely, H2 and C2H2, to explore their sensing use for dissolved gas analysis in transformer oil. For Pd doping on the pristine ZnO monolayer, the TO site is identified as the most stable configuration with an E b of -1.44 eV. For the adsorption of H2 and C2H2, chemisorption is determined given the large adsorption energy (E ad) and formation of new bonds. Analyses of the charge density difference and density of state provide evidence of the strong binding force of Pd-H and Pd-C bonds, while band structure analysis provides the sensing mechanism of the Pd-ZnO monolayer as a resistance-type sensor for H2 and C2H2 detection with high electrical responses. Also, analysis of the work function (WF) provides the possibility of selective detection of H2 and C2H2 using a Pd-ZnO monolayer-based field-effect transistor sensor given the opposite changing trend of the WF after their adsorption. Our work may broaden the application of ZnO-based gas sensors for application in the field of electrical engineering.

Rh-doped MoTe2 Monolayer as a Promising Candidate for Sensing and Scavenging SF6 Decomposed Species: a DFT Study

In this work, the adsorption and sensing behaviors of Rh-doped MoTe2 (Rh-MoTe2) monolayer upon SO2, SOF2, and SO2F2 are investigated using first-principles theory, wherein the Rh doping behavior on the pure MoTe2 surface is included as well. Results indicate that TMo is the preferred Rh doping site with Eb of - 2.69 eV, and on the Rh-MoTe2 surface, SO2 and SO2F2 are identified as chemisorption with Ead of - 2.12 and - 1.65 eV, respectively, while SOF2 is physically adsorbed with Ead of - 0.46 eV. The DOS analysis verifies the adsorption performance and illustrates the electronic behavior of Rh doping on gas adsorption. Band structure and frontier molecular orbital analysis provide the basic sensing mechanism of Rh-MoTe2 monolayer as a resistance-type sensor. The recovery behavior supports the potential of Rh-doped surface as a reusable SO2 sensor and suggests its exploration as a gas scavenger for removal of SO2F2 in SF6 insulation devices. The dielectric function manifests that Rh-MoTe2 monolayer is a promising optical sensor for selective detection of three gases. This work is beneficial to explore Rh-MoTe2 monolayer as a sensing material or a gas adsorbent to guarantee the safe operation of SF6 insulation devices in an easy and high-efficiency manner.

First-Principles Insight into a Ru-Doped SnS2 Monolayer as a Promising Biosensor for Exhale Gas Analysis

Realizing the diagnosis of lung cancer at an inchoate stage is significant to get valuable time to conduct curative surgery. In this work, we relied on a density functional theory (DFT)-proposed Ru-SnS2 monolayer as a novel, promising biosensor for lung cancer diagnosis through exhaled gas analysis. The results indicated that the Ru-SnS2 monolayer has admirable adsorption performance for three typical volatile organic compounds (VOCs) of lung cancer patients, which therefore results in a remarkable change in the electronic behavior of the Ru-doped surface. As a consequence, the conductivity of the Ru-SnS2 monolayer increases after gas adsorption based on frontier molecular orbital theory. This provides the possibility to explore the Ru-SnS2 monolayer as a biosensor for lung cancer diagnosis at an early stage. In addition, the desorption behavior of three VOCs from the Ru-SnS2 surface is studied as well. Our calculations aim at proposing novel sensing nanomaterials for experimentalists to facilitate the progress in lung cancer prognosis.

Size-dependent electrocatalytic activity of ORR/OER on palladium nanoclusters anchored on defective MoS2monolayers

The catalytic performance of MoS₂monolayer for oxygen reduction/evolution can be effectively tuned by carefully controlling the sizes of the deposited Pd clusters.

Phase transition and electronic structure investigation of MoS2-reduced graphene oxide nanocomposite decorated with Au nanoparticles

In this work a simple approach to transform MoS₂ from its metallic (1T' to semiconductor 2H) character via gold nanoparticle surface decoration of a MoS₂ reduced graphene oxide (rGO) nanocomposite is proposed. The possible mechanism to this phase transformation was investigated using different spectroscopy techniques, and supported by density functional theory theoretical calculations. A mixture of the 1T'- and 2H-MoS₂ phases was observed from the Raman and Mo 3d high resolution x-ray photoelectron spectra analysis in the MoS₂-rGO nanocomposite. After surface decoration with gold nanoparticles the concentration of the 1T' phase decreases making evident a phase transformation. According to Raman and valence band spectra analyzes, the Au nanoparticles (NPs) induce a p-type doping in MoS₂-rGO nanocomposite. We proposed as a main mechanism to the MoS₂ phase transformation the electron transfer from Mo 4d _xy,xz,yz in 1T' phase to AuNPs conduction band. At the same time, the unoccupied electronic structure was investigated from S K-edge near edge x-ray absorption fine structure spectroscopy. Finally, the electronic coupling between unoccupied electronic states was investigated by the core hole clock approach using resonant Auger spectroscopy, showing that AuNPs affect mainly the MoS₂ electronic states close to Fermi level.

Adsorption and Sensing Behaviors of Pd-Doped InN Monolayer upon CO and NO Molecules: A First-Principles Study

A transition metal (TM) doped InN monolayer has demonstrated with superior behavior for gas adsorption and sensing. For this paper, we studied the adsorption behavior of a Pd-doped InN (Pd-InN) monolayer upon CO and NO using the first-principles theory. Our results show that the Pd-InN monolayer has a stronger interaction with the CO molecule, compared with the NO molecule, with larger adsorption energy of 2.12 eV, compared to −1.65 eV. On the other hand, the Pd-InN monolayer undergoes more obvious deformation of the electronic behavior in the NO system, making the surface become semimetallic with a 0 eV band gap. Thus, the Pd-InN monolayer could be a promising candidate as a resistance-type sensor for NO detection and as a gas adsorbent for CO removal. We are hopeful that this work can offer the basic physicochemical properties and potential applications of the Pd-InN monolayer, which is beneficial for its further exploration in many fields.

Au Catalyst-Modified MoS2 Monolayer as a Highly Effective Adsorbent for SO2F2 Gas: A DFT Study

To ensure the stable operation of gas-insulated equipment, removal of SF₆ decomposition products of sulfur hexafluoride (SF₆) is one of the best methods. SO₂F₂ is one of the typical decomposition products of SF₆, while the Au-modified MoS₂ (Au-MoS₂) monolayer is a novel gas adsorbent. Therefore, based on the first-principles calculation, the adsorption properties of the SO₂F₂ molecule on the Au-MoS₂ monolayer are calculated. Furthermore, the adsorption energy, charge transfer, and structure parameters were analyzed to obtain the most stable adsorption structure. These results indicate that all of the adsorption processes are exothermic. To better study the adsorption mechanism between the SO₂F₂ molecule and the Au-MoS₂ monolayer, the density of states, the highest occupied molecular orbital, the lowest unoccupied molecular orbital, and electron density difference were obtained. At last, we conclude that the interaction between the SO₂F₂ molecule and the Au-MoS₂ monolayer was chemisorption. This study provides a theoretical basis to prepare the Au-MoS₂ monolayer for the removal of SF₆ decomposition products.

Structural defects in 2D MoS2 nanosheets and their roles in the adsorption of airborne elemental mercury

In this research, ab initio calculations and experimental approach were adopted to reveal the mechanism of Hg⁰ adsorption on MoS₂ nanosheets that contain various types of defects. The ab initio calculation showed that, among different structural defects, S vacancies (Vs) in the MoS₂ nanosheets exhibited outstanding potential to strongly adsorb Hg⁰. The MoS₂ material was then prepared in a controlled manner under conditions, such as temperature, concentration of precursors, etc., that were determined by adopting the new method developed in this study. Characterisation confirmed that the MoS₂ material is of graphene-like layered structure with abundant structural defects. The integrated dynamic and steady state (IDSS) testing demonstrated that the Vs-rich nanosheets showed excellent Hg⁰ adsorption capability. In addition, ab initial calculation on charge density difference, PDOS, and adsorption pathways revealed that the adsorption of Hg⁰ on the Vs-rich MoS₂ surface is non-activated chemisorption.

Rh-doped MoSe2 as a toxic gas scavenger: a first-principles study

Using first-principles theory, we investigated the most stable configuration for the Rh dopant on a MoSe₂ monolayer, and the interaction of the Rh-doped MoSe₂ (Rh-MoSe₂) monolayer with four toxic gases (CO, NO, NO₂ and SO₂) to exploit the potential application of the Rh-MoS₂ monolayer as a gas sensor or adsorbent. Based on adsorption behavior comparison with other 2D adsorbents and desorption behavior analysis, we assume that the Rh-MoSe₂ monolayer is a desirable adsorbent for CO, NO and NO₂ storage or removal given the larger adsorption energy (E _ad) of -2.00, -2.56 and -1.88 eV, respectively, compared with other materials. In the meanwhile, the Rh-MoSe₂ monolayer is a good sensing material for SO₂ detection according to its desirable adsorption and desorption behaviors towards the target molecule. Our theoretical calculation would provide a first insight into the TM-doping effect on the structural and electronic properties of the MoSe₂ monolayer, and shed light on the application of Rh-MoSe₂ for the sensing or disposal of common toxic gases.

Inorganic molecule (O2, NO) adsorption on nitrogen- and phosphorus-doped MoS2 monolayer using first principle calculations

We performed a systematic study of the adsorption behaviors of O2 and NO gas molecules on pristine MoS2, N-doped, and P-doped MoS2 monolayers via first principle calculations. Our adsorption energy calculations and charge analysis showed that the interactions between the NO and O2 molecules and P-MoS2 system are stronger than that of pristine and N-MoS2. The spin of the absorbed molecule couples differently depending on the type of gas molecule adsorbed on the P- and N-substituted MoS2 monolayer. Meanwhile, the adsorption of O2 molecules leaves N- and P-MoS2 a magnetic semiconductor, whereas the adsorption of an NO molecule turns this system into a nonmagnetic semiconductor, which may provide some helpful information for designing new N- and P-substituted MoS2-based nanoelectronic devices. Therefore, P- and N-MoS2 can be used to distinguish O2 and NO gases using magnetic properties, and P-MoS2-based gas sensors are predicted to be more sensitive to detect NO molecules rather than pristine and N-MoS2 systems.

Electronic and magnetic properties of 3D transition-metal atom adsorbed arsenene

To utilize arsenene as the electronic and spintronic material, it is important to enrich its electronic properties and induce useful magnetic properties in it. In this paper, we theoretically studied the electronic and magnetic properties of arsenene functionalized by 3D transition-metal (TM) atoms (TM@As). Although pristine arsenene is a nonmagnetic material, the dilute magnetism can be produced upon TM atoms chemisorption, where the magnetism mainly originates from TM adatoms. We find that the magnetic properties can be tuned by a moderate external strain. The chemisorption of 3D TM atoms also enriches the electronic properties of arsenene, such as metallic, half-metallic, and semiconducting features. Interestingly, we can classify the semiconducting feature into three types according to the band-gap contribution of spin channels. On the other hand, the chemisorption properties can be modified by introducing monovacancy defect in arsenene. Present results suggest that TM-adsorbed arsenene may be a promising candidate for electronic and spintronic applications.

Insights into the electronic properties and reactivity of graphene-like BC3 supported metal catalysts

Graphene-like BC₃ monolayer is a new two-dimensional nanomaterial with many unique properties, but is still largely unknown.

Theoretical study on geometric, electronic and catalytic performances of Fe dopant pairs in graphene

The formation geometries, electronic structures and catalytic properties of monovacancy and divacancy graphene sheets with two embedded Fe dopants (2Fe-MG and 2Fe-DG) have been systematically investigated using the first-principles calculations.