A DFT study on the possibility of embedding a single Ti atom into the perfect stanene monolayer as a highly efficient gas sensor

First-principles study of the effect of S-atom doping on the optoelectronic properties of stanene

CONTEXT

Based on the first principles, the influence of S-atom doping on the electronic and optical properties of stanene is comprehensively examined in this work. The results show that pure stanene is a quasi-metal with zero bandgap. After doping with an S atom, opening the bandgap of pure stanene becomes possible and the state of the stanene is converted from quasi-metal to semiconductor. Analysis of the density of states reveals that the density of states of all doped systems is primarily made of the p-orbital of the Sn. The overlap population analysis showed that charge transfer occurs between S and Sn atoms under different doping concentrations. The charge transfer increases with increasing doping concentration. The charge transfer reaches a maximum at a doping concentration of 9.38%. The increase in doping concentration causes blue-shifting of the absorption and reflection peaks of the doped system as compared to those of pure stanene. It is expected that these studies can provide theoretical guidance for the practical application of stanene in optoelectronic devices.

METHODS

All simulations are undertaken with the Cambridge Sequential Total Energy Package (CASTEP) (Wei et al. Physica B: Condensed Matter 545:99, 2018; Bafekry et al. Phys Chem Chem Phys, 2021; Zala et al. Appl Surf Sci, 2022; Bafekry et al. Nanotechnology, 2021; Bafekry et al. Phys Chem Chem Phys, 2021; Bafekry et al. J Phys: Condens Matter, 2021), which is based on density functional theory (DFT). For the exchange correlation, the generalized gradient approximation (GGA) is implemented with the Perdew-Burke-Ernzerhof (PBE) functional Perdew et al. Phys Rev B Condens Matter 48:4978, 1993. Using the Monkhorst-Pack technique, a specific K-point sample of the Brillouin zone was carried out Monkhorst and Pack Phys Rev B 13:5188, 1976. After the convergence tests, the K-point grid was set to 3 × 3 × 1. The plane-wave truncation energy was set to 400 eV. The residual stress for all atoms was 0.03 eV/Å. The energy convergence criterion was 1.0 × 10-5 eV. To prevent recurring interactions between the layers, a vacuum layer with a thickness of 20 Å was established in the Z-direction.

A first-principles study of electro-catalytic reduction of CO2 on transition metal-doped stanene

Employing first-principles calculations based on density functional theory, this work examines the activity of 3d transition metal-doped stanene for electro-catalytic CO2 reduction through the first two electron transfer steps to CO. Our results related to CO2 activation, the first and a crucial step of the reduction process revealed that, among the entire 3d transition metal row studied, only Ti- and Fe-doped stanene can bind and significantly activate the CO2 molecule, while the rest of the TM single atoms are inert in activating the molecule. The activation of the CO2 molecule on Ti- and Fe-doped stanene has been observed in the presence of water as well. In addition, the formation of OCHO has been observed to be energetically preferred over COOH formation as a reaction intermediate, indicating the preference for the formate path of the reduction reaction. Furthermore, despite the strong adsorption of H2O on the catalyst surface, the presence of water seems to enhance CO2 adsorption on the catalysts, contrary to what has been observed recently in graphene-based catalysts. Finally, our difference charge density and the Bader charge calculations reveal that the ability of Ti- and Fe-doped stanene in activating the CO2 molecule and their potential catalytic activity for CO2 reduction is to be attributed to the charge transfer between the catalyst and the molecule, providing new insights into the rational design of 2D catalysts beyond graphene.

Effect of shear strain on the electronic and optical properties of Al-doped stanane

CONTEXT

The quasi-metallic properties of stanene limit its prospects in optoelectronic devices. Based on first-principles calculations, a systematic study is conducted on the tuning effects of surface hydrogenation and Al atom doping on the electronic and optical properties of stanene. Surface hydrogenation serves as an ideal way to open the forbidden band of stanene, and Al atom doping further increases hydrogenated stanene (stanane) band gap to 0.460 eV. Deformation has a minor impact on the stability of the stanane-Al structure, while shear strain can effectively modulate the band gap engineering of the doped system, reducing the band gap value from 0.460 to 0.170 eV. Deformation induces a redshift in the absorption peak and reflectance, also slowing down the rate of decrease in the absorption coefficient, and enhancing the peak value of light reflectance, which is positively correlated with the degree of shear strain. These findings hold promise for expanding the potential application of monolayer stanane in semiconductor devices.

METHODS

All calculations are performed using CASTEP module in Materials Studio based on the density functional theory (DFT). The Perdew-Burke-Ernzerhof (PBE) generalized gradient approximation (GGA) is employed to describe the exchange-correlation energy (Perdew et al., Phys Rev Lett 77(18), 1996). We construct models for both stanene and stanane. The original unit cell of stanene has two Sn atoms, while stanane consists of two Sn atoms and two H atoms, and expand them to a 3 × 3 × 1 supercell with a vacuum layer of 20 Å in height to prevent interlayer coupling. After convergence testing, the plane-wave cutoff energy is set to 450 eV, and the energy convergence threshold is set to 1 × 10-5 eV. The maximum residual stress for each atom is set to 0.01 eV/Å. Brillouin zone sampling is performed using a 6 × 6 × 1 k-point mesh based on the Monkhorst-Pack method (Monkhorst and Pack, Phys Rev B 13(12), 1976). The k-point accuracy of the density of states and optical properties is 9 × 9 × 1. All calculations are performed using the more advanced OTFG ultrasoft pseudopotential, and structural relaxations are performed using supercells to ensure that the model is fully relaxed. We use the HSE06 functional to calculate the energy band structures of stanane-Al deformed to 0%, 4%, and 8%, resulting in band gap values of 1.465 eV, 1.368 eV, and 1.016 eV, respectively. These values are significantly higher than those obtained using the PBE functional (0.460 eV, 0.397 eV, and 0.170 eV). However, the shapes and trends of the band structures obtained from both PBE and HSE06 calculations are similar. Additionally, the calculation time needed by HSE06 is greatly longer than PBE, which exceeds the capabilities of our computer hardware, and cannot support all subsequent calculations. To investigate the influence of deformations on the variation of band gap values and to conserve computational resources, the subsequent calculations in this study use the PBE functional.

Emerging single atom catalysts in gas sensors

Single atom catalysts (SACs) offer unprecedented opportunities for high-efficiency reactions taking place in many important fields of catalytic processes, electrochemistry, and photoreactions. Due to their maximized atomic utilization and unique electronic and chemical properties, SACs can provide high activity and excellent selectivity for gas adsorption and electron transport, leveraging SACs that enhance the detection sensitivity and selectivity to target gases. In the past few years, SACs including both noble (Pt, Pd, Au, etc.) and non-noble (Mn, Ni, Zn etc.) metals have been demonstrated to be very useful in optimizing sensing performances. However, a comprehensive review on this topic is still missing. Herein, we summarize the synthesis technologies of SACs that are applicable to gas sensors. The electronic and chemical interactions between SACs and host sensing materials, which are crucial to sensor functions, are discussed. Then, we highlight the application progress of various SACs in gas sensors. Prospects in the creation of new sensing materials with emerging SACs and versatile supports are also present. Finally, the challenges and prospects of SACs in the future development of sensors are analyzed.