Amount Of Charge Transfer Research Articles

First-Principles Investigation of the 1T-HfTe2 Nanosheet for Selective Gas Sensing

In this work, we have explored the sensing capabilities of a monolayer 1T-HfTe2 nanosheet for the environmental hazardous gases like CO, CO2, NO, NO2, NH3, and N2O, along with common environmental gases like O2, N2, H2, and H2O, using first-principles density functional theory and nonequilibrium Green’s function (NEGF) based methods. Through a detailed study of structural, electronic, vibrational, and device properties, we analyzed the strength of interactions and charge transfers between the adsorbent surface and the adsorbate molecules and revealed monolayer 1T-HfTe2 to be selective to effectively sense the NO gas at very low bias. In the case of NO (NO2 and O2) adsorption, we identified a significant (moderate) amount of charge transfer with the 1T-HfTe2 nanosheet surface which leads to a considerable (moderate) change in the electronic structure of that surface, that in turn affects the other properties of the surface also. In particular, a semimetal to metal transition in the case of adsorption of NO, NO2, and O2 is noticed, with more prominance in the case of NO, which we believe to be a major reason behind the higher interaction of these gases with the 1T-HfTe2 nanosheet and a selective sensing for NO. Our device simulations to attain the I–V characteristics for the pristine 1T-HfTe2 surface and all the adsorbed ones give a direct way to measure the resistance change due to adsorption of these gases, which is a basic tool to detect gas in a “resistance sensor”, and can also be measured experimentally. These calculations clearly indicate a significant (small) increase in the current when NO (NO2 and O2) was adsorbed on the nanosheet of 1T-HfTe2 and almost no increase for the rest of the examined gases. All together, by understanding the basic underlying principles, this work unlocks the potential selective NO gas sensing capability of the less explored transition metal dichalcogenide (TMD) 1T-HfTe2. Our work also reveals it to be an efficient NO sensor that works even at low voltage, leading to less power consumption, and can effectively find an application in environmental monitoring and various areas of the medical field.

Carbon nitride 2-D surface as a highly selective electrochemical sensor for V-series nerve agents

Herein, carbon nitride 2-D surface (C2N) was studied as an electrochemical sensor for chemical warfare agents (CWA; A-230, A-232, A-234, and VR). The deep insight of analytes@C2N complexation was obtained by interaction energy, SAPT0, NCI, QTAIM, EED, and FMO analyses. The interaction energies results indicate that these CWAs are physisorbed onto the surface where BSSE corrected interaction energies range from −14.42 kcal/mol to −15.99 kcal/mol. Moreover, SAPT0 analysis revealed that dispersion interactions are the dominant component which amount to nearly 61% of overall SAPT0 interaction energies. SAPT0 analysis results are consistent with interaction energies. The nature of interactions was also quantified by NCI and QTAIMs analysis. NBO analysis showed that the highest amount of charge transfer is observed in A232@C2N (−0.018 e−), while the least amount of charge transfer is seen in VR@C2N. The EDD analysis also verified the results of NCI, QTAIM and NBO analyses. A short recovery time of 0.027 s at 298 K for desorption of VR from C2N surfaces was calculated. VR adsorption onto C2N surface caused the highest change in the HOMO-LUMO energy gap (2.68 eV) compared to bare C2N (3.71 eV), which reveals the potential of C2N as an electrochemical sensor for VR. The complexation of A-230, A-232, and A-234 had a negligible effect on the HOMO-LUMO energy gap. Among all complexes, HOMO-LUMO excitation is associated with charge transfer from analytes to the C2N surface.

Palladium modified MoS2 monolayer for adsorption and scavenging of SF6 decomposition products: A DFT study

Based on the first principle calculation, Pd-doped MoS2 (Pd–MoS2) monolayer has been proposed to adsorb the main decomposition products of SF6: SOF2 and SO2F2. Pd–MoS2 monolayer, SF6 adsorbed Pd–MoS2 monolayer, SOF2 and SO2F2 adsorbed Pd–MoS2 monolayer are built and optimized to obtain the most stable structures. In order to meet to the actual situation, both of single and double gas molecules adsorption were considered in this study. The adsorption energy, charge transfer amount, total density of states (TDOS), projected density of states (PDOS), and the molecular orbits were calculated to analyze the adsorption mechanism of Pd–MoS2 monolayer to SOF2 and SO2F2. The results show that Pd–MoS2 monolayer can only adsorb a single molecule at one Pd doping site. Both of SOF2 and SOF2 adsorptions belong to chemisorption due to the strong chemical activity of the doped Pd atom. The simulation results show that Pd–MoS2 adsorbent could be a potential material for SOF2 and SO2F2 removing. This study lays a key foundation to design Pd–MoS2 monolayer adsorbent using in SF6-insulated equipment.

Unraveling the effects of the coordination number of Mn over α-MnO2 catalysts for toluene oxidation

Herein, nanorod-like α-MnO2 catalysts with 5-, 4-, and 3-coordinated Mn exposed on the surface (α-MnO2-Mn5c, α-MnO2-Mn4c, and α-MnO2-Mn3c) were employed for toluene combustion. The toluene combustion performance followed an order of α-MnO2-Mn4c > α-MnO2-Mn3c > α-MnO2-Mn5c. The effects of the coordination number of Mn over α-MnO2 catalysts for toluene oxidation were unraveled. The excellent activity of α-MnO2-Mn4c was due to stronger interactions between Mn4c with reactants and a larger amount of charge transfer from the Mn4c to the adsorbed O2, as evidenced by computational results. The results of operando diffuse reflectance infrared Fourier transform spectroscopy and gas chromatography-mass spectrometry revealed that toluene oxidation over α-MnO2 catalysts proceeded by coordination number-dependent rate-determining step. For α-MnO2-Mn4c, the rate-determining step was the cleavage of benzene species, while decarboxylation of benzoic acid was more sluggish for α-MnO2-Mn5c. These findings strongly pave a way for understanding the coordination number-induced improvement of catalytic performance of nanorod-like α-MnO2 catalysts for toluene oxidation and a deeper understanding of the mechanism of toluene degradation.

Light-Driven Permanent Charge Separation across a Hybrid Zero-Dimensional/Two-Dimensional Interface

We report the first demonstration of light-driven permanent charge separation across an ultrathin solid-state zero-dimensional (0D)/2D hybrid interface by coupling photoactive Sn-doped In2O3 nanocrystals with monolayer MoS2, the latter serving as a hole collector. We demonstrate that the nanocrystals in this device-ready architecture act as local light-controlled charge sources by quasi-permanently donating ∼5 holes per nanocrystal to the monolayer MoS2. The amount of photoinduced contactless charge transfer to the monolayer MoS2 competes with what is reached in electrostatically gated devices. Thus, we have constructed a hybrid bilayer structure in which the electrons and holes are separated into two different solid-state materials. The temporal evolution of the local doping levels of the monolayer MoS2 follows a capacitive charging model with effective total capacitances in the femtofarad regime and areal capacitances in the μF cm–2 range. This analysis indicates that the 0D/2D hybrid system may be able to store light energy at densities of at least μJ cm–2, presenting new potential foundational building blocks for next-generation nanodevices that can remotely control local charge density, power miniaturized circuitry, and harvest and store optical energy.

Understanding the mechanism for the formation of initial deposition burning Zhundong coal: DFT calculation and experimental study

Zhundong coal as a high quality steam coal has not been widely utilized due to severe slagging and fouling problem during combustion. It is crucial to reveal the slagging and fouling mechanisms in a boiler burning Zhundong coal. In the article, the properties of Ca and Na particles adsorbed on iron oxide film were studied by quantum chemistry. Furthermore, two representative ash deposits at rear water wall and final superheater in a 330 MW utility boiler were also verified the calculation results. These results indicated that α-Fe2O3(1 1 0) is selected as the adsorption substrate. The binding energies of Na or Ca on α-Fe2O3(1 1 0) is −12.44 eV and −13.73 eV, respectively. The charge transfer of Ca on α-Fe2O3(1 1 0) is significantly higher than that of Na, and the orbital hybridization of Na on (1 1 0) surface can be weaker than that of Ca on (1 1 0) surface. Thus, Ca would combine with the oxide film more easily than Na. This indicates that compared with other coals with a high sodium, Ca burning Zhundong coal plays a critical role on severe ash deposition. In addition, the binding energy of Ca adsorbed on Fe or O defect surface for α-Fe2O3 (1 1 0) is −15.13 eV or −4.16 eV, respectively. The amount of charge transfer for Ca adsorption on Fe defect surface may be significantly higher than that on O defect surface, and the orbital hybridization of Ca adsorption on Fe defect surface can be stronger than that on O defect surface. Therefore, Fe defect surface have a higher propensity to Ca. Finally, the result of experiments is in accordance with calculation results.

Adsorption of gas molecules on group III atoms adsorbed g-C3N4: A first-principles study

The first-principles based on density functional theory are used to calculate the adsorption of gas (CO, NO) molecules on group III (B, Al, Ga, In) atoms adsorbed g-C3N4. It is revealed that the B, Al, Ga, and In-g-C3N4 adsorption systems exhibit magnetic semiconducting behavior, while pristine g-C3N4 is a non-magnetic semiconductor. Next, adsorption of the gas molecules on g-C3N4 was investigated. The results show that the charge transfer amount of NO/g-C3N4 is larger than that of CO/g-C3N4. The CO/g-C3N4 system exhibits non-magnetic semiconductor. However, the NO/g-C3N4 system exhibits magnetic semiconductor behavior. Lastly, adsorption of the gas molecules on III-g-C3N4 was also investigated. It is revealed that all gas molecule adsorbed III-g-C3N4 exhibit a magnetic semiconductor. Interestingly, all the gas/III-g-C3N4, except NO/Al-g-C3N4, NO/Ga-g-C3N4, and NO/In-g-C3N4 systems, can promote the charge (electron) transfer from gas molecule to the III-g-C3N4 system, which is conducive to gas sensing. The absorption spectrums of gas molecules adsorbed III-g-C3N4 systems have many strong visible light absorption peaks. Especially, the absorption peak intensity of NO adsorbed In-g-C3N4 system at 436 nm reached 1.19 × 105 cm−1. Thus, above results indicate that the gas molecules adsorption systems will facilitate design of spintronics, gas sensing and high efficiency photocatalytic device.

Charge transfer as a ubiquitous mechanism in determining the negative charge at hydrophobic interfaces

The origin of the apparent negative charge at hydrophobic–water interfaces has fueled debates in the physical chemistry community for decades. The most common interpretation given to explain this observation is that negatively charged hydroxide ions (OH–) bind strongly to the interfaces. Using first principles calculations of extended air–water and oil–water interfaces, we unravel a mechanism that does not require the presence of OH–. Small amounts of charge transfer along hydrogen bonds and asymmetries in the hydrogen bond network due to topological defects can lead to the accumulation of negative surface charge at both interfaces. For water near oil, some spillage of electron density into the oil phase is also observed. The computed surface charge densities at both interfaces is approximately -0.015 {rm{e}}/{{rm{nm}}}^{2} in agreement with electrophoretic experiments. We also show, using an energy decomposition analysis, that the electronic origin of this phenomena is rooted in a collective polarization/charge transfer effect.

Density functional calculations of organic pollutants adsorbed on Hittorf's violet phosphorene

Abstract Hittorf's violet phosphorene with large specific surface area and high hole mobility is a potential candidate for gas sensing. Here, a case about adsorption behavior of organic chemicals on violet phosphorene has been systematically studied based on density functional theory. From our results, all seven considered organic chemicals (benzoapyrene, benzene, methylbenzene, formaldehyde, m-xylene, o-xylene and p-xylene) on violet phosphorene show molecular adsorption with exothermic process. Among them, the adsorption of benzopyrene with −0.881 eV adsorption energy is most conducive for complete adsorption-desorption cycles, which is an essential feature of reversible gas sensors. Small amounts of charge transfer indicate that the adsorption mechanism is mainly van der Waals type interaction. In particular, further work function and electronic structure analysis indicates that the electrical conductivity changes significantly after benzoapyrene exposure. That makes it possible to transmit gas sensing signals using electrical strategy. We also found that violet phosphorene multilayer maintains consistent benzoapyrene adsorption performance with its monolayer, which is conducive to practical application. Our simulations could provide theoretical basis for the exploration of two-dimensional organics sensing materials.

Two-dimensional graphitic carbon nitride (g-C4N3) for superior selectivity of multiple toxic gases (CO, NO2, and NH3)

Using first principles calculations, we investigated the possibility of selecting multiple toxic gases using one substrate material. Here, we explored the transport property of H2, N2, O2, CO, CO2, NO2, and NH3 gas molecules on two-dimensional graphitic carbon nitride (2D g-C4N3). The homonuclear molecule such as H2, N2, and O2 has very weak adsorption energy (equal to or less than 0.1 eV) and also CO2 has an adsorption energy of 0.23 eV. In the typical toxic gas molecule adsorption systems, we found an appreciable charge transfer. In CO and NH3 adsorption systems, the charge transfer of 0.397 and 0.418 electrons from the molecule to the substrate was found, while the NO2 molecule gained 0.124 electrons from the substrate. Due to this large amount of charge transfer, we obtained large adsorption energies of 4.57, 1.29, and 1.93 eV in CO, NO2, and NH3 systems. Moreover, through the I–V curve calculations, we found large difference in the current. The calculated current was 21, 13.11, and 16.16 μA for CO, NO2, and NH3 systems at the bias voltage of 0.5 V. Our results imply that the 2D g-C4N3 can be a superior substrate material for sensing of multiple toxic gases.

The electron transfer mechanism between metal and amorphous polymers in humidity environment for triboelectric nanogenerator

Humidity tends to deteriorate the output performance and the stability of triboelectric nanogenerator (TENG). However, the microscopic mechanism of how water molecules adsorbed on the surface affect electron transfer in the metal-amorphous polymer contact electrification of TENG remains elusive. Here in order to investigate the effect of humidity on the electron transfer process between metal-amorphous polymer in TENG, we employ first-principles calculations to study the typical material pair Al- polyethylene (PE). We find that water molecules adsorbed between the interfaces replace the original electron donor Al in the electron transfer between Al/PE pair, providing the electron to the LUMO (lowest unoccupied molecular orbital) of PE and the surface atoms of Al and reducing the amount of charge transfer for Al/PE pair. Most importantly, we demonstrate that the existence of hydrogen bonds makes water molecules the electron donor (positively charged) in metal/polymer interface, in which only the non-hydrogen bond H atom is the main electron donor. In addition, it is also found that the number of transferred charge is closely related to the number of electron donors, which can explain the declining trend of the amount of charge transfer. The gained insights provide a theoretical basis for the regulation of the contact electrification process and the design of TENG in humidity environment.

Tuning Schottky barrier in graphene/InSe van der Waals heterostructures by electric field

The contacts between semiconductor and metal are vital in the fabrication of nano electronic and optoelectronic devices. The contact type has a great influence on the function realization and performance of the device. In order to prepare multifunctional devices with high performance, it is necessary to modulate the barrier height and contact type at the interface. First-principles calculations based on the density functional theory (DFT) are implemented in the VASP package. The generalized gradient approximation of Perdew, Burke, and Ernzerhof (GGA-PBE) with van der Waals (vdW) correction proposed by Grimme (DFT-D3) is chosen due to its good description of long-range vdW interactions. It is demonstrated that weak vdW interactions dominate between graphene and InSe with their intrinsic electronic properties preserved. We find that the n-type ohmic contact is formed at the graphene/InSe interface with the Fermi level through the conduction band of InSe (<i>Φ</i><sub>Bn</sub> < 0). The Fermi level of graphene/InSe heterostructure moves down to below the Dirac point of graphene layer, which results in p-type (hole) doping in graphene. Moreover, the external electric field is effective to tune the Schottky barrier, which can control not only the Schottky barrier height but also the type of contact. With the negative external electric field varying from 0 to –1 V/nm, the conduction band minimum of InSe below the Fermi level declines gradually but the n-type ohmic contact is still preserved. Nevertheless, with the positive external electric field varying from 0 to 0.8 V/nm, the conduction band minimum of InSe shifts upward and across the Fermi level, the conduction band minimum of InSe is closer to the Fermi level than the valence band maximum, which indicates that the n-type Schottky contact is formed. The Fermi level moves from the the conduction band minimum to the valence band maximum of InSe when the positive external electric field increases from 0.8 V/nm to 2 V/nm. The n-type Schottky barrier height exceeds the p-type Schottky barrier height gradually, which demonstrates that the positive external electric field transforms the n-type Schottky contact into the p-type Schottky contact at the graphene/InSe interface. When the positive external electric field exceeds 2 V/nm, the valence band of InSe moves upward and cross the Fermi level (<i>Φ</i><sub>Bp</sub> < 0), the ohmic contact is obtained again. Meanwhile, p-type (hole) doping in graphene is enhanced under negative external electric field and a large positive external electric field is required to achieve n-type (electron) doping in graphene. The external electric field can control not only the amount of charge transfer but also the direction of charge transfer at the graphene/InSe interface.

Effect of biaxial strain on the gas-sensing of monolayer GeSe

The adsorptions of various gas molecules (H<sub>2</sub>, H<sub>2</sub>O, CO, NH<sub>3</sub>, NO, and NO<sub>2</sub>) on monolayer GeSe versus the external biaxial strain in a range of –8% to 8% are investigated by first-principles calculations. The band structures, the equilibrium heights, the adsorption energy, and the amount of charge transfer are determined. The calculated results show that monolayer GeSe changes from indirect-to-direct and semiconducting-to-metallic under a certain biaxial strain. The adsorbed gas molecules hardly change the band gap of monolayer GeSe even under a biaxial strain in the whole range from –8% to 8%. The calculated adsorption energies under different strains reveal that the external biaxial strain has no significant effect on the adsorption stability of the gas molecules on monolayer GeSe, so it seems impossible to promote the desorption of the gas molecules by applying strain. It is found that NO<sub>2</sub> under the biaxial tensile strain of 8% tends to be bound with the monolayer GeSe by chemical bond which leads to being-difficult-to-desorb. Besides that case, the investigated gas molecules are physisorbed on the GeSe surface and have a certain probability of adsorption and desorption. The charge transfers of CO, NH<sub>3</sub>, NO and NO<sub>2</sub> adsorbed systems under the biaxial strain from –8% to 8% change somehow but are still non-negligible, while for H<sub>2</sub> and H<sub>2</sub>O, their charge transfers are too small to be detected by the monolayer-GeSe-based gas-sensor. Thus, due to the moderate adsorption energy and charge transfer, monolayer GeSe can be a promising candidate as a sensor for CO, NH<sub>3</sub> and NO under the biaxial strain from –8% to 8%, and for NO<sub>2</sub> in the range from –8% to 6%. It is worth noting that because of the appropriately lower adsorption energy and bigger charge transfer, a bigger biaxial compressive strain, ranging from –6% to –8%, can improve the response speed and sensibility to CO and NO of monolayer GeSe. Furthermore, the effect of the external biaxial strain on the adsorption stability and the charge transfer are discussed based on the two mechanisms of charge transfers, i.e. the traditional and the orbital mixing charge transfer theory. The charge transfer of NH<sub>3</sub> is governed by mixing the molecular HOMO with the orbital of GeSe, while for CO, NO and NO<sub>2</sub>, their charge transfers are most likely determined by different mechanisms under different external strains, which results in different influences on the charge transfer. The present study would be valuable for fully excavating the gas-sensing potential of the two-dimensional GeSe, and then providing sufficient theoretical basis for designing high performance gas sensors based on two-dimensional materials.

Spin-orbit coupling is the key to unraveling intriguing features of the halogen bond involving astatine.

The effect of spin-orbit coupling (SOC) on the halogen bond involving astatine has been investigated using state-of-the-art two- and four-component relativistic calculations. Adducts between Cl-X (X = Cl, Br, I and At) and ammonia have been selected to establish a trend on going down the periodic table. The SOC influence has been explored not only on the geometric and energetic features that can be used to characterize the halogen bond strength but also on the three main contributions to it that are the charge transfer, the "σ-hole" (i.e. the localized region with a net positive electrostatic potential at the halogen site) and the "polar flattening" (which is related to the effective shape of the halogen site). A surprisingly large increase of the Cl-At dipole moment, due to the inclusion of SOC, has been worked out using four-component CCSD(T) reference calculations, indicating that this bond is significantly more ionic than one may predict. Due to the SOC effect, which induces a peculiar charge accumulation on the At side in the Cl-At dimer, a weakening of the astatine-mediated halogen bond occurs arising from the (i) reduced amount of charge transfer, (ii) decrease of the polar flattening and (iii) lowering of the short-range Coulomb potential. The analysis of the electronic structure of the Cl-At moiety allows for a rationalization of the SOC effects on all the considered features of the halogen bond, including an unprecedented unsymmetrical charge back-donation from Cl-At to ammonia.

Reaction of HSSS. radical with guanine and formation of 8-thioguanine: a computational study

Density functional calculations have been applied to study reactions of the HSSS. radical with guanine at the C2, C4, C5, and C8 sites of guanine that yields [GCn-SSSH].n = 2, 4, 5, and 8 adducts. Also, formation of 8-thioguanine from [GC8-SSSH]. adduct has been studied. In all the adducts [GCn-SSSH]., HSSS. radical is placed on the top of the plane of the guanine ring. The results show that there is a possibility of intraresidue S-H…N hydrogen bonding in each [GCn-SSSH]. adduct. Besides, the C8 site of guanine is the most reactive site to add to HSSS. radical with appreciably high rate constant, and the adduct formed at this site would be significantly stable. According to NBO analysis, delocalization energies for all the hydrogen bondings, i.e., E(2) for nN⟶σ*SH interactions, are obtained to be in the range of 1.31–3.46 kcalmo1−1. The biggest E(2) and the largest amount of charge transfer is found for [GC8-SSSH]. adduct, i.e., for the S-H…N7 (Gua) interaction, in which RN…H = 2.588 A, to be 1.78 kcalmo1−1 and 0.0024e, respectively, well correlated with the prediction of most of its stability among the [GCn-SSSH]. adducts. The ZPE-corrected enthalpy changes for the reactions are obtained to be 0.2–1.4 kcalmo1−1. The reaction enthalpy changes and the barrier energies related to the different sites of guanine are found to be in the order of C8 < C2 < C5 < C4. Starting with the adduct [GC8-SSSH]., 8-thioguanine could be achieved in two steps with two transition states (TS1 and TS2) and an intermediate complex (IM); the overall reaction is exothermic. The first reaction step, the rate-determining step, involves going from the adduct [GC8-SSSH]. to IM via TS1, in which HSS moiety gets dissociated from the HSSS moiety attached to the C8 site of guanine.

A comparative study on the high and low symmetric structures of (LaMnO3)n/(LaNiO3)n superlattices by first-principles calculations

We have employed the + U extension of Generalized Gradient Approximation (GGA) of the Density Functional Theory (DFT) to study the (LaMnO3)n/(LaNiO3)n oriented (0 0 1) superlattices. We built superlattices for both high (cubic) and low (rhombohedral) symmetry structures. Structural, electronic, and interfacial energy calculations reveal charge transfer from Mn to Ni interfacial atoms in both structures inducing magnetic moment at the Ni atom. Magnetic calculations show that the Mn and Ni atoms are ferromagnetically coupled. Our results indicate that the amount of charge transfer and magnetic moment are largest in the (LaMnO3)1/(LaNiO3)1 than (LaMnO3)2/(LaNiO3)2, and in the low symmetry (rhombohedral) than the high symmetry (cubic) superlattices, because of the Transition Metal-Oxygen (TMO) bonds created, and suggest the low symmetric structure for more efficient magnetic moment in the (LaMnO3)/(LaNiO3) superlattices.

Understanding the Role of Solvents and Spin-Orbit Coupling in an Oxygen-Assisted SN 2-Type Oxidative Transmetalation Reaction.

The aerial oxidation of PdII to PdIV has emerged as an integral component of sustainable catalytic C-H functionalization processes. However, a proper understanding of the factors that control the viability of this oxidative process remains elusive. An investigation of the intricate mechanism of the transmetalation reaction of the aerial oxidative transformation of [(Me3 tacn)PdII Me2 ] (Me3 tacn=N,N',N''-trimethyl-1,4,7-triazacyclononane) to [(Me3 tacn)PdIV Me3 ]+ has been conducted by using DFT, along with multireference methods, such as second-order n-electron valence-state perturbation theory (NEVPT2) with complete active space self-consistent field theory (CASSCF). The present endeavor predicts that the thermodynamics and kinetics of the oxygen activation step are primarily dictated by the polarity of the solvents, which determine the amount of charge transfer to the oxygen molecule from the PdII center. Additionally, it is observed that the presence of a protic solvent has a significant effect on the spin-orbit coupling term at the minimum energy crossing point of the triplet and singlet surfaces. Moreover, it is shown that the intermetal ligand-transfer phenomenon is an important instance of an oxygen-assisted SN 2 reaction.

Electric field-modulated high sensitivity and selectivity for NH3 on α-C2N2 nanosheet: Insights from DFT calculations

An electric field-modulated α-C2N2 of high sensitivity and selectivity toward NH3 has been studied by using the first-principle calculations. Firstly, the structural stability of α-C2N2 nanosheet is proved by phonon dispersion and molecular dynamics calculations. Then, the adsorption energies and electronic properties of CO, CO2, H2, NO2, NH3, O2, N2, SO2 or CH4 on α-C2N2 are calculated, with the discussion about the possibility of α-C2N2 used as NH3 sensors. The results show that the amount of charge transfer for NH3 on α-C2N2 is the most in these nine adsorption systems. Therefore, NH3 could be easier detected in experiments. Next, we find that the adsorption energies of NH3 on α-C2N2 varied from −0.83 eV to −0.24 eV under the external electric field (VE) from VE = −0.6 V/Å to VE = +0.3 V/Å. Therefore, the adsorption and desorption of NH3 on α-C2N2 can be well realized under the control of VE. α-C2N2 nanosheet has the potential to be used as highly sensitive and selective NH3 sensor by controlling VE. More importantly, the current-voltage curves of NH3 before and after adsorption on α-C2N2 has changed significantly, which means that NH3 can be measured directly in practical application.

Electronic properties of graphene-ZnO interface: a density functional theory investigation

Electronic properties of graphene/ZnO interface have been theoretically investigated by applying first principles density functional theory calculations. This interface is demonstrated to have interesting electrical, optical and chemical properties and therefore, is employed in different applications. In our investigation the interface between graphene and different ZnO surfaces such as polar Zn-terminated and O-terminated surfaces as well as nonpolar surface are considered. Different interface properties such as equilibrium atomic structure, binding energy, charge transfer and band alignment are calculated for these interfaces. The calculated binding energies between graphene and different ZnO surfaces are within the range of van der Waals or physical adsorption. The results clearly reveal the essential role of oxygen density at the interface. The O- and Zn-terminated ZnO surfaces show the lowest and highest binding energies, respectively. The amount of charge transfer and the direction of interfacial dipole are also dominated by the number of oxygen atoms at the graphene/ZnO interface. Calculations for the interfacial band alignment reveal that a high/low density of oxygen atoms at the interface results in a Schottky/Ohmic contact. It is also shown that inducing oxygen vacancies at an oxygen rich interface leads to the lowering of the Schottky barrier.

Van der Waals heterostructures of blue phosphorene and scandium-based MXenes monolayers

Stacked layers in the form of van der Waals (vdW) heterostructures can significantly extend the applications of its building materials. In this study, based on hybrid functional (HSE06) with vdW corrections, we systematically investigated the electronic structure and optical properties of BlueP/Sc2CX2 (X=O,F,OH) vdW heterostructures and their corresponding monolayers. All three heterostructures are indirect bandgap semiconductors with type-II band alignment. The calculated bandgap of BlueP/Sc2CF2 is found to be 1.528 eV. A small amount of charge transfers from BlueP to Sc2CF2 and from Sc2CO2 [Sc2C(OH)2] to BlueP, rendering it p- and n-doped, respectively. The formation of heterostructures enhanced the optical absorption in the visible light region as compared to their parent monolayer, particularly in BlueP/Sc2CF2 and BlueP/Sc2C(OH)2. Heterostructures show excellent device absorption efficiencies (70%–80%) from infrared to ultraviolet spectrum of light. These results suggest that BlueP/Sc2CX2 heterostructures are potential for nanoelectronics, optoelectronics, and photovoltaic device applications.