Search Results (6)

In this paper, the adsorption effect of methane (CH₄) gas molecular on monolayer PbSe with and without vacancy defects is studied based on first-principles calculations. The effects of the adsorption of methane molecular on monolayer PbSe and on the Se vacancy (V_Se) and Pb vacancy (V_Pb) of monolayer PbSe are also explored. Our results show that methane molecules exhibit a good physical adsorption effect on monolayer PbSe with and without vacancy defects. Moreover, our simulations indicate that the adsorption capacity of CH₄ molecules on monolayer PbSe can be enhanced by applying strain. However, for the monolayer PbSe with Vse, the adsorption capacity of CH₄ molecules on the strained system decreases sharply. This indicates that applying strain can promote the dissociation of CH₄ from V_Se. Our results show that the strain can be used as an effective means to regulate the interaction between the substrate material and the methane gas molecules. Full article

Two-dimensional (2D) group IV metal chalcogenides are potential candidates for thermoelectric (TE) applications due to their unique structural properties. In this paper, we predicted a 2D monolayer group IV metal chalcogenide semiconductor $\gamma$-PbSn₂ (X = S, Se, Te), and first-principles calculations and Boltzmann transport theory were used to study the thermoelectric performance. We found that $\gamma$-PbSnX₂ had an ultra-high carrier mobility of up to 4.04 × 10³ cm² V⁻¹ s⁻¹, which produced metal-like electrical conductivity. Moreover, $\gamma$-PbSn₂ not only has a very high Seebeck coefficient, which leads to a high power factor, but also shows an intrinsically low lattice thermal conductivity of 6–8 W/mK at room temperature. The lower lattice thermal conductivity and high power factors resulted in excellent thermoelectric performance. The $ZT$ values of $\gamma$-PbSnS₂ and $\gamma$-PbSnSe₂ were as high as 2.65 and 2.96 at 900 K, respectively. The result suggests that the $\gamma$-PbSnX₂ monolayer is a better candidates for excellent thermoelectric performance. Full article

In the present work, the noncentrosymmetric 2D ternary Janus monolayers Al${}_2$XX’(X/X’ = S, Se, Te and O), Si${}_2$XX’(X/X’ = P, As, Sb and Bi), and A${}_2$PAs(A = Ge, Sn and Pb) have been studied based on first-principles calculations. We find that all the monolayers exhibit in-plane d${}_{12}$, and out-of-plane d${}_{13}$ piezoelectric coefficients due to the lack of reflection symmetry with respect to the central A atoms. Moreover, our calculations show that Al${}_2$OX(T = S, Se, Te) chalcogenide monolayers have higher absolute in-plane piezoelectric coefficients. However, the highest out-of-plane values are achieved in the Si${}_2$PBi monolayer, larger than those of some advanced piezoelectric materials, making them very promising transducer materials for lightweight and high-performance piezoelectric nanodevices. Full article

The exciton states and their influence on the optical absorption spectrum of CdSe and PbS nanoplatelets (NPLs) are considered theoretically in this paper. The problem is discussed in cases of strong, intermediate, and weak size quantization regimes of charge carrier motion in NPLs. For each size quantization regime, the corresponding potential that adequately describes the electron–hole interaction in this mode of space quantization of charge carriers is chosen. The single-particle energy spectra and corresponding wave functions for strong intermediate and weak size quantization regimes have been revealed. The dependence of material parameters on the number of monolayers in the sample has been considered. The related selection rules and the dependence of the absorption coefficient on the frequency and polarization direction of the incident light wave were obtained. The interband transition threshold energy dependencies were obtained for each size quantization regime. The effect of dielectric coefficient mismatch and different models of electron–hole interaction potentials have been studied in CdSe and PbS NPLs. It is also shown that with an increase in the linear dimensions of the structure, the threshold frequency of absorption decreases. The binding energies and absorption coefficient results for NPL with different thicknesses agree with the experimental data. The values of the absorption exciton peaks measured experimentally are close to our calculated values for CdSe and PbS samples. Full article

This paper reports first-principles calculations on PbBi${}_2$Te${}_2$S${}_2$, PbBi${}_2$Te${}_2$Se${}_2$ and PbBi${}_2$Te${}_4$ monolayers. The strain effects on their electronic and thermoelectric properties as well as on their stability have been investigated. Without strain, the PbBi${}_2$Te${}_4$ monolayer exhibits highest Seebeck coefficient with a maximum value of 671 $\mathsf{\mu }$V/K. Under tensile strain the highest power factor are $12.38\times {10}^{11}$ Wm${}^{-1}$K${}^{-2}$s${}^{-1}$, $10.74\times {10}^{11}$ Wm${}^{-1}$K${}^{-2}$s${}^{-1}$ and $6.51\times {10}^{11}$ Wm${}^{-1}$K${}^{-2}$s${}^{-1}$ for PbBi${}_2$Te${}_2$S${}_2$, PbBi${}_2$Te${}_2$Se${}_2$ and PbBi${}_2$Te${}_4$ at 3%, 2% and 1% tensile strains, respectively. These values are 85.9%, 55.0% and 3.3% larger than those of the unstrained structures. Full article

Semiconductor colloidal nanoplatelets (NPLs) are a promising new class of nanostructures that can bring much impact on lightning technologies, light-emitting diodes (LED), and laser fabrication. Indeed, great progress has been made in optimizing the optical properties of the NPLs for the visible spectral range, which has already made the implementation of a number of effective devices on their basis possible. To date, state-of-the-art near-infrared (NIR)-emitting NPLs are significantly inferior to their visible-range counterparts, although it would be fair to say that they received significantly less research attention so far. In this study, we report a comprehensive analysis of steady-state and time-dependent photoluminescence (PL) properties of four monolayered (ML) PbSe NPLs. The PL measurements are performed in a temperature range of 78–300 K, and their results are compared to those obtained for CdSe NPLs and PbSe quantum dots (QDs). We show that multiple emissive states, both band-edge and trap-related, are responsible for the formation of the NPLs’ PL band. We demonstrate that the widening of the PL band is caused by the inhomogeneous broadening rather than homogeneous one, and analyze the possible contributions to PL broadening. Full article