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The structure and electronic and spintronic properties of two-dimensional (2D) ternary compounds ABC (A = Sb, Bi; B = Se, Te; C = Br; I) monolayers are investigated using the first-principles method. The ABC monolayers possess typical Janus structures with a considerable potential gradient normal to the surface, inducing intrinsic Rashba spin splitting (RSS) at the conduction band minimum near the Γ point. Among them, the splitting strength of the BiSeI monolayer is the largest and its Rashba coefficient can reach 1.84 eV Å. The projected energy band of the BiSeI monolayer suggests that the RSS state is mainly rooted in the Bi-pz orbital. The RSS strength can be modulated by applying the in-plane strain. The tensile strain can improve the RSS strength, which is ascribed to the increase of the potential gradient normal to the surface. These results indicate that these 2D ternary compounds have great potential for application in tunable spintronic devices.
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The electrical contact and graphene (Gr) doping for Gr/XPtY (X, Y = S, Se, and Te) van der Waals (vdW) heterostructures are studied by using first-principles methods. The intrinsic electronic properties of Gr and PtXY are preserved due to the weak vdW interactions. We find that the types of interfacial electrical contact and Gr doping are closely related to the interface chalcogen atoms. The n-type Ohmic contact is formed in the Gr/SPtY (Y = S, Se, and Te) systems. The n-type and p-type Schottky contacts are realized in the Gr/SePtY and Gr/TePtY systems, respectively. The physical mechanism of different contact types can be analyzed based on the charge transfer between the Gr and XPtY layers. For all the heterostructures, the contact type and Schottky barrier height can be effectively modulated by the external electric field and interlayer coupling. The Gr doping type and charge-carrier concentration are also investigated. The p-doping, p-doping, and n-doping are obtained in Gr for the Gr/SPtY, Gr/SePtY, and Gr/TePtY systems, respectively. The highest carrier concentration of the Gr layer can reach 1.69 × 1013 cm-2 for the Gr/TePtTe system. The results indicate that Gr/XPtY heterostructures are potential candidates for improving the performance of high-efficiency nano electronic devices.
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Using density functional theory calculations, the adsorption of gaseous molecules (NO, NO2, NH3, SO2, CO, HCN, O2, H2, N2, CO2, and H2O) on the graphitic SiC monolayer and bilayer has been investigated to explore the possibilities in gas sensors for NO, NO2, and NH3 detection. The strong adsorption of NO2 and SO2 on the SiC monolayer precludes its applications in nitride gas sensors. The nitride gases (NO, NO2, and NH3) are chemisorbed on the SiC bilayer with moderate adsorption energies and apparent charge transfer, while the other molecules are all physisorbed. Further, the bilayer can effectively weaken the adsorption strength of NO2 and SO2 molecules, that is, NO2 molecules are only weakly chemisorbed on the SiC bilayer with an E ads of -0.62 eV, while SO2 are physisorbed on the bilayer. These results indicate that the SiC bilayer can serve as a gas sensor to detect NO, NO2, and NH3 gases with excellent performance (high sensitivity, high selectivity, and rapid recovery time). Moreover, compared with other molecular adsorptions, the adsorption of NH3 molecules significantly changes the work function of the SiC monolayer and bilayer, indicating that they can be used as optical gas sensors for NH3 detection.
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We systemically investigate the effect of dopants on the geometrics, electronic and magnetic properties of asymmetric washboard structure of antimonene (aW-Sb) by using density functional theory (DFT) calculations. The large binding energies and short bond lengths indicate the doped systems still maintain high stability. Pristine aW-Sb is a nonmagnetic semiconductor with a narrow band gap, while the doped aW-Sb exhibit metallic by doping. Furthermore, the Ti, V, Cr, Mn and Fe doping induced magnetic states, and the result of spin density indicates that the magnetic moments are mainly localized at dopant and the adjacent Sb atoms.
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Spin splitting of the nonmagnetic two dimensional (2D) layered NIIIXVI (N = Ga, In; X = S, Se, Te) monolayer is investigated based on the density functional theory. Due to the mirror symmetry, there is no Rashba spin splitting (RSS) in the freestanding NX plane. It is found that applying the external electric field perpendicular to the NX plane can result in sizable RSS around the Γ point due to the mirror symmetry breaking. The induced RSS is mainly influenced by the anions X and gradually strengthens with the increase of external electric field. The considerable RSS is observed in NTe systems. Moreover, the influence of in-plane biaxial strain on RSS is explored, and the tensile strain can enhance the RSS, especially for those bands around the Fermi level. Our theoretical investigation provides a deep insight in spin splitting behaviors in NX monolayers and agrees well with the experimental report.
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InSe monolayer, belonging to group III-VI chalcogenide family, has shown promising performance in the realm of spintronic. Nevertheless, the out-of-plane mirror symmetry in InSe monolayer constrains the electrons' degrees of freedom, and this will confine its spin-related applications. Herein, we construct Sb/InSe van der Waals heterostructure to extend the electronic and spintronic properties of InSe. The density functional theory is utilized to verify the tunable electronic properties and Rashba spin splitting (RSS) of Sb/InSe heterostructure. According to the obtained results, the Sb/InSe heterostructure can be considered as a direct band gap semiconductor with typical type-II band alignment, where the electrons and holes are localized in the InSe and Sb layers, respectively. The RSS is recognized at conduction band minimum around Γ point in Sb/InSe, which is induced by the spontaneous internal electric field with electric dipole moment of 0.016 e Å from Sb to InSe. The vertical strain, in-plane strain, and external electric field are employed to modulate the strength of RSS. The Rashba coefficient and dipole moment exhibit the similar variation tendency, suggesting the strength of RSS depends on the magnitude of dipole moment. The controllable RSS makes Sb/InSe heterostructure become an appropriate candidate material for spintronic devices.
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The structural, electronic, and magnetic properties of 3d transition metal (TM) atom (Sc, V, Cr, Mn, Co, and Cu) doped Stone-Wales (SW) defect arsenene were systematically investigated by density functional theory (DFT). The results indicated that the properties of arsenene were effectively changed by the SW-defect and TM-doping. Furthermore, chemical bonds formed between the TM-dopants and the adjacent As atoms of the SW-defect. The dopants Sc, Mn, and Cu induced an indirect-to-direct bandgap transition, and the doping of V, Cr, and Mn in SW-defect arsenene exhibited magnetic states. The magnetic moments of the systems depended on the number of spin-localized valence electrons. The functionalized electronic and magnetic properties of arsenene highlight the applications for electronics, optoelectronics, and spintronics.
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Properties of gas molecules (NO, NH3, and NO2) adsorbed on two-dimensional GaN with a tetragonal structure (T-GaN) are studied using first-principles methods. Adsorption energy, adsorption distance, Hirshfeld charge, electronic properties, electric conductivity, and recovery time are calculated. It is found that these three molecules are all chemisorbed on the T-GaN with reasonable adsorption energies and apparent charge transfer. The electronic properties of the T-GaN present dramatic changes after the adsorption of NO2 and NO molecules, especially its electric conductivity, but NH3 molecule hardly changes the electronic properties of the T-GaN. Furthermore, the recovery time of the T-GaN sensor at T = 300 K is estimated to be quite short for NO2 and NO but very long for NH3. Moreover, the magnetic properties of the T-GaN are changed obviously due to the adsorption of NO (or NO2) molecule. Therefore, we suggest that the T-GaN can be a prominent candidate for application as NO2 and NO molecule sensors.
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Motivated by the recent realization of cluster-assembled nanomaterials as gas sensors, first-principles calculations are carried out to explore the stability and electronic properties of Zn12O12 cluster-assembled nanowires and the adsorption behaviors of environmental gases on the Zn12O12-based nanowires, including CO, NO, NO2, SO2, NH3, CH4, CO2, O2 and H2. Our results indicate that the ultrathin Zn12O12 cluster-assembled nanowires are particularly thermodynamic stable at room temperature. The CO, NO, NO2, SO2, and NH3 molecules are all chemisorbed on the Zn12O12-based nanowires with reasonable adsorption energies, but CH4, CO2, O2 and H2 molecules are only physically adsorbed on the nanowire. The electronic properties of the Zn12O12-based nanowire present dramatic changes after the adsorption of the NO and NO2 molecules, especially their electric conductivity and magnetic properties, however, the other molecules adsorption hardly change the electric conductivity of the nanowire. Meanwhile, the recovery time of the nanowire sensor at T = 300 K is estimated at 1.5 µs and 16.7 µs for NO and NO2 molecules, respectively. Furthermore, the sensitivities of NO and NO2 are much larger than that of the other molecules. Our results thus conclude that the Zn12O12-based nanowire is a potential candidate for gas sensors with highly sensitivity for NO and NO2.