Doped Monolayer Research Articles

Biodetector for chlordane using doped InP3 monolayers: a density functional theory study.

Chlordane is a serious pollutant in the environment, and it is necessary to monitor chlordane levels using biodetectors. We performed first-principles calculations to investigate the adsorption of chlordane on Ag, Pd, and Au doped InP3 semiconductor monolayers. The results indicated that the adsorption energies of chlordane adsorbed on Ag, Pd, and Au doped InP3 are -7.961 eV, -6.328 eV, and -7.889 eV respectively. The band gaps of the doped InP3 monolayers underwent drastic changes after coming in contact with chlordane, the largest change in band gap occurred for Pd-doped InP3, where the band gap changed from 0.024 eV to 0.335 eV. The large change in band gap shows that the monolayer is sensitive to the molecule, making it a good biodetector. Our results conclude that Pd-doped InP3 stands out as the most promising biodetector for chlordane. This result will benefit environmental experimentalists in their further research.

Non-metallic doped GeC monolayer: tuning electronic and photo-electrocatalysis for water splitting.

We conducted a first-principles study on the electronic, magnetic, and optical characteristics of non-metallic atoms (B, C, F, H, N, O, P, S, and Si) doped in single-layer carbon germanium (GeC). The findings indicate that the introduction of various non-metallic atoms into the monolayer GeC leads to modifications in its band structure properties. Different non-metallic atoms doped in single-layer GeC will produce both magnetic and non-magnetic properties. B-, H-, N-, and P-doped GeC systems exhibit magnetic properties, while C-, F-, O-, S-, and Si-doped single-layer GeC systems exhibit non-magnetic properties. Different non-metallic-doped single-layer GeC systems will produce semiconductor, semimetallic, and metallic properties. The C-, N-, O-, P-, S-, and Si-doped GeC systems still exhibit semiconductor properties. The H-doped GeC system exhibits semimetallic properties, while the B- and F-doped GeC systems exhibit metallic properties. Other than that, the doping of B, H, N, and P atoms can modulate the magnetism of single-layer GeC. Subsequently, we studied the influence of the doping behavior on the work function, where the work function of the single-layer GeC system doped with P atoms is very small, indicating that its corresponding doping system (P-doped GeC system) can produce a good field emission effect. In the optical spectrum, the doped systems have a certain influence in the far ultraviolet region. Furthermore, our results showed that S- and Si-doped single-layer GeC systems are conducive to photocatalysis compared to the single-layer GeC system.

First-principles study of Na adsorption and diffusion over substitutionally doped antimonene

The storage of the colossal amount of energy is the eminent research area for the era of eternal need of energy. Sodium-ion (Na-ion) battery emerged as an appropriate alternative to fulfil this. Here, we investigate the functionalities of doped antimonene monolayer (with Ge, Se, Sn and Te atom) as an anode material for Na-ion battery using First-principles Density Functional Theory (DFT) approach. The adsorption and diffusion of Na over the substitutionally doped antimonene is well supported thermodynamically with an adsorption energy of range −2.3 eV to −2.8 eV and minimum activation energy of range 0.1 eV to –0.8 eV. The conductivity of doped antimonene increases with the number of Na atoms adsorbed over it as seen by bandstructure, density of states (DOS) and electron difference density (EDD) plots. Inhomogeneities and structural disturbances were absent during adsorption and diffusion indicating a robust electrode material. The outcomes predict that the doped antimonene monolayer can be a potential candidate for Na-ion battery anode material application.

Symmetry and Value of the Order Parameter in 2d Nematic Superconductors

We derive equations for the superconducting nematic order parameter and chemical potential for the hexagonal lattice by accounting for nearest- and next-nearest-neighbor hoppings of electrons. By analyzing the energy of the superconducting ground state, we have found that the symmetry of the order parameter and some other superconducting properties of the system strongly depend on the sign and the magnitude of the next-nearest neighbor hopping. As we will demonstrate, both extended s- and d-pairings significantly contribute to the pairing in the system, that be tuned by changing the hopping parameters. We discuss a possible connection of the obtained results to the properties of several doped monolayer superconductors – graphene and transition metal dichalcogenides.

Photoluminescence of Chemically and Electrically Doped Two-Dimensional Monolayer Semiconductors.

Two-dimensional (2D) transition metal dichalcogenide (TMDC) monolayers exhibit unique physical properties, such as self-terminating surfaces, a direct bandgap, and near-unity photoluminescence (PL) quantum yield (QY), which make them attractive for electronic and optoelectronic applications. Surface charge transfer has been widely used as a technique to control the concentration of free charge in 2D semiconductors, but its estimation and the impact on the optoelectronic properties of the material remain a challenge. In this work, we investigate the optical properties of a WS2 monolayer under three different doping approaches: benzyl viologen (BV), potassium (K), and electrostatic doping. Owing to the excitonic nature of 2D TMDC monolayers, the PL of the doped WS2 monolayer exhibits redshift and a decrease in intensity, which is evidenced by the increase in trion population. The electron concentrations of 3.79×1013 cm-2, 6.21×1013 cm-2, and 3.12×1012 cm-2 were measured for WS2 monolayers doped with BV, K, and electrostatic doping, respectively. PL offers a direct and versatile approach to probe the doping effect, allowing for the measurement of carrier concentration in 2D monolayer semiconductors.

Theoretical insights into gas-sensitive properties of B, Ga and In doped WS2 monolayer towards oxygen-containing toxic gases

Oxygen-containing toxic gases such as CO and NOx (x = 1, 2) have presented significant challenges to both the atmospheric environment and human well-being, thus prompting the development of efficient gas sensors for their detection at room temperature. In this work, we investigated the feasibility of B, Ga, In-doped WS2 (B-WS2, Ga-WS2 and In-WS2) monolayers as potential gas-sensitive materials for monitoring CO and NOx based on first-principles calculations, with a specific focus on analyzing the adsorption energy, electronic properties and recovery time. The results show that the doping of B, Ga, In atoms enhances the conductivity of WS2 monolayer and significantly improves the adsorption properties of WS2 towards CO and NOx. With the exception of the CO@In-WS2 system, all the systems exhibit chemisorption with adsorption energies ranging from −0.56 eV to −3.18 eV. Interestingly, the presence of H2O, CO and N2 in the atmosphere does not affect the capturing ability of B-WS2, Ga-WS2 and In-WS2 towards the target gases. Moreover, with the exception of the CO@In-WS2 system, the critical desorption temperatures of CO and NOx all exceed 300 K, highlighting the potential of the B/Ga/In-WS2 as effective adsorbents for NO and NO2 at room temperature and standard atmospheric pressure. Finally, the sensitivity and recovery time of CO and NOx on doped WS2 are evaluated. The findings confirm that Ga-WS2 exhibits a well-balanced combination of sensitivity and response speed, making it suitable as a reusable gas sensor for the detection of CO and NO, while In-WS2 is suitable for detecting NO and NO2. This study offers valuable theoretical insights into the design of innovative gas nanosensors for the detection of oxygen-containing toxic gases.

Electron distribution regulating of nonmetal doped monolayer g-GaN for enhanced electrocatalytic CO2 reduction

Exploring inexpensive electrocatalysts that can efficiently and selectively convert CO2 into hydrocarbon fuels is important to promote carbon neutrality and solve the energy crisis. Current electrocatalysts, such as Cu-based alloys, single-atom catalysts, and dual-atom catalysts, use the d states of metal in the electrocatalytic CO2 reduction reaction. Inspired by this, this work studies CO2 reduction reaction from another approach. Herein, using first principles study, we systematically investigate the prospect of nonmetal (B, C, O and F) doped monolayers g-GaN as electrocatalysts for the CO2 reduction reaction. We found that nonmetal doping can effectively regulate the electron distribution and p-band center of the active center (N site), which can adjust the initial adsorption, activation degree, charge transfer amount of CO2, and promote the formation of intermediates. Interestingly, B and C doped systems have better catalytic activity for CH4, with limiting potentials of −0.61 and −0.53 V, respectively. More importantly, F doped system has higher activity and selectivity for CH3OH production and inhibit competitive HER, with lower limiting potentials of −0.60 V. This study provides a new theoretical basis for the design and screening of electrocatalysts with high activity and product selectivity using nonmetal as the active site.

Adsorption and dissociation of hydrogen molecules over S-vacancies in a Nb-doped MoS2 monolayer

Motivated by the recent interest in the hydrogen energy, we have carried out a complete study of the catalytic activity of a defective molybdenum disulfide monolayer (MoS2) by means of density functional theory (DFT) calculations. The MoS2 monolayer is characterized by a nonreactive basal plane. In principle, its catalytic activity is concentrated at the edges, but an alternative way to increase such activity is obtained by creating active sites where the molecules can dissociate. These defects can be easily produced experimentally by different techniques. In our study, we have performed an atomic, energetic and electronic analysis of a hydrogen molecule adsorbed on a MoS2 monolayer. In a first step, we have found that the H2 molecule remains physisorbed over both doped-free and Nb-doped MoS2 monolayers, showing that the Nb atom does not increase the poor reactivity of the clean MoS2 layer. Interestingly, our energetic results suggest that the vacancies will prefer to be formed close to the Nb atoms in the doped monolayer, but the small energy difference would allow the formation in non-doped like sites. Theoretically, we found out the conditions for the molecular dissociation on a S vacancy. In both cases, with and without Nb, the molecule should rotate from the original perpendicular position to an almost parallel orientation jumping an energetic barrier. After that, the atoms are separated binding to the Mo atoms around the missing S atom. Our ab initio molecular dynamics simulations show that for low pressure conditions (using one single molecule in the system) the H2 prefers to desorb from the vacancy, while for larger pressures (when additional H2 molecules are added to the system) the molecule is finally dissociated on the vacancy. Our long simulations confirm the great stability of the structure with the two H atoms binding to the Mo atoms close to the vacancy. Finally, the inclusion of a third (or a fourth) H atom in the vacancy leads to the formation and desorption of a H2 molecule, leaving one (or two) atoms in the vacancy.

Exploring optoelectronic properties of non-metal doped Be3N2 monolayer under mechanical strain

This paper investigates the effects of nonmetal doping, different mechanical strains, and the coexisting effects of doping and strain on the optoelectronic properties of Be3N2 monolayers based on first principles. The biaxial strain has the most significant influence on the properties of Be3N2, such as chemical bonding, bandgap size, charge transfer, and light absorption, which can effectively regulate its optoelectronic properties. The coexistence of doping and strain can further radicalize the interatomic orbital hybridization effect to increase the activity and conductivity of the system, even leading to a metallic state. These insights are crucial for Be3N2 applications in optoelectronics.

The Negative Differential Resistance Effect of Substitutional Doped Monolayer GeS and Its Application in Gas Sensor

The Negative Differential Resistance Effect of Substitutional Doped Monolayer GeS and Its Application in Gas Sensor

Electrode wettability and capacitance of electrical double layer capacitor: a classical density functional theory study

We suggest a coarse-grained water model for use in classical density functional theory (cDFT) to describe aqueous inorganic salt solutions that act as working electrolytes in electrical double-layer capacitors (EDLCs) with electrodes comprising two face-to-face doped carbon monolayers. Focus of the cDFT calculations lies on the influence of solvent electrode wettability (SEW) on capacitance and energy storage behaviors, while also considering its interaction with factors like electrolyte bulk concentration, pore size, electrode voltage, and temperature. New phenomena are disclosed theoretically. Remarkably, this study challenges the traditional notion that energy storage is consistently boosted by enhancing the electrode’s ionophobicity. Contrarily, the SEW effect reduces energy storage below the standard aqueous electrochemical window voltage (around 1.2 V) and only enhances the energy storage as the voltage surpasses a certain threshold up to the optimal window voltage (2 V–2.5 V). Furthermore, a non-monotonic SEW effect on energy storage is demonstrated under appropriate conditions, shedding new light on the complex relationship between ionophobicity and energy storage. Moreover, the present coarse-grained water model enables the prediction of the experimentally observed inverse relationship between temperature and capacitance. In contrast, the widely used electrolyte primitive model predicts the existence of a maximum value. The decisive factor for the impact of SEW on capacitance and energy storage is identified as congestion within the electrode pore, while other factors contribute by affecting this congestion. The present research offers valuable insights, highlighting the significance of SEW in the innovative and strategic design of aqueous inorganic EDLC devices.

Anisotropic RKKY interaction in doped monolayer germanene: spin–orbit coupling effects

Anisotropic RKKY interaction in doped monolayer germanene: spin–orbit coupling effects

Four-Phonon Enhanced the Thermoelectric Properties of ScSX (X = Cl, Br, and I) Monolayers.

Recently, the FeOCl-type two-dimensional materials have attracted significant attention owing to their versatile applications in fields such as thermoelectricity and photocatalysis. This study aims to systematically investigate the thermoelectric properties of ScSX (X = Cl, Br, and I) monolayers by a combination of the first-principles calculations and the machine-learning interatomic potential approach. These monolayers are indirect semiconductors with band gaps of 3.22 (ScSCl), 3.27 (ScSBr), and 2.87 eV (ScSI), respectively. The lattice thermal conductivity is decreased by 25.72% (20.90%), 44.05% (40.00%), and 30.96% (34.76%) for ScSCl, ScSBr, and ScSI along the x-axis (y-axis) when the four-phonon scattering is introduced, indicating its important role in phonon transport. Anharmonic phonon scattering yields high Grüneisen parameter and scattering rate values, hence causing these low lattice thermal conductivities. Additionally, the large Seebeck coefficients and electrical conductivities of n-type doped ScSX monolayers contribute to their excellent power factors (24.69, 25.66, and 24.99 mW/K2·m for ScSCl, ScSBr and ScSI at 300 K, respectively). Based on the excellent power factor and low thermal conductivity, the maximum values of the figure of merit are calculated to be 2.68, 3.39, and 3.21 for ScSCl, ScSBr, and ScSI monolayers at 700 K, respectively. Our research provides valuable insights into the phonon thermal transport of ScSX monolayers and suggests a promising approach to address high-order anharmonicity.

Dissolved gases analysis in transformer oil using TM (Pd, Ir, Au) modified MoSSe monolayer: A DFT study

This study applied density functional theory to investigate gas-sensitive devices based on transition metal-doped MoSSe (Pd-MoSSe, Ir-MoSSe, Au-MoSSe), exploring their adsorption and sensing performance towards three characteristic gases (CO, C2H2, C2H4) generated during the use or faults of transformer oil. The results indicate that Pd, Ir, and Au transition metal atoms preferentially anchor to the S surface of the pristine MoSSe monolayer. The doped monolayers exhibit significantly improved sensing characteristics in all aspects, suggesting chemical adsorption of the three characteristic gases. Through the analysis of band structures (BS), adsorption configurations, deformation charge densities (DCD), density of states (DOS), recovery time, and various adsorption parameters, the conclusion is drawn that while TM-MoSSe outperforms the pristine MoSSe monolayer in terms of adsorption and sensing performance, Pd-MoSSe and Au-MoSSe exhibit relatively good recovery times across a broader temperature range, whereas Ir-MoSSe is limited in this aspect. This study provides theoretical guidance for the potential application of transition metal-doped MoSSe monolayers as sensors for gases generated during the thermal runaway of transformer oil.

Effects of Vanadium Doping on the Optical Response and Electronic Structure of WS2 Monolayers

Abstract2D dilute magnetic semiconductors have been recently reported in transition metal dichalcogenides doped with spin‐polarized transition metal atoms, for example vanadium‐doped WS2 monolayers, which exhibit room‐temperature ferromagnetic ordering. However, a broadband characterization of the electronic band structure of these doped WS2 monolayers and its dependence on vanadium concentration is still lacking. Therefore, power‐dependent photoluminescence, resonant four‐wave mixing, and differential reflectance spectroscopies are performed here to study optical transitions close to the A exciton energy of vanadium‐doped WS2 monolayers at three different doping levels. Instead of a single A exciton peak, vanadium‐doped samples exhibit two photoluminescence peaks associated with transitions from a donor‐like level and the conduction band minima. Moreover, resonant Raman and second‐harmonic generation experiments reveal a blueshift in the B exciton energy but no energy change in the C exciton after vanadium doping. Density functional theory calculations show that the band structure is sensitive to the Hubbard U correction for vanadium, and several scenarios are proposed to explain the two photoluminescence peaks around the A exciton energy region. This work provides the first broadband optical characterization of these 2D dilute magnetic semiconductors, shedding light on the novel and tunable electronic features of V‐doped WS2 monolayers.

Electronic and optical properties of doped monolayer MoS2 under shear deformation

The effect of O-atom doping on the electronic and optical properties of monolayer MoS2 under shear deformation has been systematically investigated using first principles. The results show that shear deformation reduces the structural stability of the doped system. The forbidden band width of the doped system decreases sequentially with increasing shear deformation, while conductivity increases. The density of states of both intrinsic and doped systems is primarily contributed by the 4d and 3p orbitals of the Mo and S atoms, respectively. Analysis of the optical properties reveals that shear deformation enhances the static permittivity of the doped systems, leading to an increased ability to bind charges. Additionally, absorption and reflection peaks of all doped systems occur in the ultraviolet region. Compared to the doped system without shear deformation, absorption peaks of the remaining doped systems shift towards the high energy region, resulting in enhanced utilization of ultraviolet light. In the energy range of 16.7–17.3 eV, peak energy loss of all doped systems decreases sequentially, suggesting that shear deformation can reduce energy loss. These results demonstrate that shear deformation can modulate the optoelectronic properties of O-doped monolayer MoS2 and provide a theoretical foundation for practical applications in semiconductor devices.

Piezoelectric characteristics of doped β-Ga2O3 monolayer: a first-principles study

Two-dimensional (2D) piezoelectric materials have been widely concerned because of their important applications in nano-piezoelectric generators. Finding two-dimensional materials with large piezoelectric effects is still a great challenge. In this work, the inversion center of the β-Ga2O3 monolayer was broken by substitutional doping. Not only the in-plane piezoelectric effect but also the uncommon out-of-plane piezoelectric effect is induced in the doped β-Ga2O3 monolayer. In addition, we analyzed the cause of the piezoelectric effects from their electronic properties. The values of out-of-plane (in-plane) piezoelectric coefficient for Cu-doped and Al-doped β-Ga2O3 reach −4.04 (3.95) pm/V and −2.91 (0.37) pm/V, respectively. The results are comparable with those of the commonly used bulk piezoelectric materials such as α-quartz (d11 = 2.3 pm V−1), AlN (d33 = 5.1 pm V−1), and GaN (d33 = 3.1 pm V−1), even though they are both two-dimensional structures. Our study shows a great potential application of doped β-Ga2O3 monolayer in micro and nano-electromechanical devices such as smart wearables, sensors, energy converters, and micro energy collectors.

Computational insights into the electronic structure of functionalized monolayer hBN supercapacitor electrodes

In this study, we examined a collection of functionalized hBN monolayers’ electronic structure and quantum capacitance. Different ad-atom adsorption techniques have been used to functionalize the hBN monolayer. Density functional theory calculations are performed to precisely determine the electrical structure of an ad-atom doped hBN monolayer with a range of doping concentrations. The quantum capacitance of every functionalized system was then calculated. Above 500 μF/cm2, a noticeable quantum capacitance has been seen. Our calculations demonstrate that ad-atom doping at hollow position of hBN honeycomb lattice greatly increases the quantum capacitance of hBN monolayer. The microscopic cause of this system’s increased quantum capacitance has been investigated. Our DFT-based calculation shows that the system has a very large quantum capacitance due to the creation of new electronic states in the vicinity of the band edge and the Fermi level shift caused by the ad-atom adsorption.

Sensing behavior of modified two-dimensional GeTe monolayer to detect air discharge components: A first-principles study

It is crucial to determine the operating condition of air-insulated equipment by monitoring air discharge components (O3, NO2, CO) to detect any occurrence of partial discharges (PD). Although GeTe is widely applied in gas sensing technology, its performance in selective detection is relatively subpar. This study investigatesthe modification of structures of GeTe monolayers by doping single transition-metal (TM) atom (Fe, Co, Ir, Pt, Pd, and Rh) to enhance its gas adsorption capability and selectivity of different doped GeTe monolayers to gases according to competitive adsorption. Multiple properties such as adsorption energy, charge transfer, charge difference density (CDD), density of states (DOS), occupation function, desorption time, and work function were discussed, indicating that doped GeTe exhibits greater adsorption capabilities. Specifically, Ir-GeTe demonstrates the highest absolute value of adsorption energy for O3 at 2.75 eV, while Co-GeTe exhibits the highest absolute value of adsorption energy for NO2 at 2.13 eV. Furthermore, the analysis of atomic orbital overlap reveals stronger chemical interactions between Ir-GeTe and O3, as well as Co-GeTe and NO2. Considering selectivity and working function, Fe-GeTe emerges as a potential sensing material for detecting NO2. This research offers promising and practical applications for single TM atom-doped GeTe as gas-sensitive materials.

Enhancement of thermoelectric performance in monolayer AlP3 via Ga and In doping: A first-principles study

Recently, two-dimensional (2D) triphosphides have attracted much attention in the thermoelectric field due to their semiconductor properties and excellent electronic transport properties. In our study, the performances of AlP3, Al0.5Ga0.5P3, and Al0.5In0.5P3 doped monolayers in the thermoelectric transport are studied. First, the dynamic structural stabilities of the three monolayers are verified through phonon dispersion curves. Moreover, all monolayers are indirect band-gap semiconductors, which can be used as thermoelectric materials. The results show that larger electronic relaxation time and carrier mobilities of doped monolayers lead to larger electronic transport parameters and higher dimensionless thermoelectric figure-of-merit (ZT). It is found that after doping via Ga and In, the thermoelectric performances of AlP3 are increased by 1.31–1.79 times. Our findings show that AlP3 and its doped monolayers hold significant promise as thermoelectric materials within the temperature span of 300–700 K and the doping mechanism could significantly improve the thermoelectric properties of 2D structures.