层数对α-氧化铅振动、电子和光学性质的影响
Effects of the number of layers on the vibrational, electronic and optical properties of alpha lead oxide
摘要：
我们用第一性原理计算研究了层数对$α$ -PbO的结构、振动、电子和光学性质的影响。我们的理论计算表明，由于力常数的减小和键长的增加，$α$ -PbO的四个拉曼活性模有从体相到单分子层的红移趋势。它已被证明，而块体和多层$α$ -PbO具有间接带隙，单层形式具有2.59 eV的直接带隙值。虽然铅原子具有5d态，但自旋-轨道耦合并不显著影响$α$ -PbO的能带结构。计算的解理能值（0.67 J/m $^2$）证实，单层PbO可以很容易地从其本体对应物通过剥离方法获得。除了能带结构，我们还计算了$α$ -PbO结构的光学性质和吸收光子通量$J_{abs}$，以研究太阳吸收的可能性。我们的计算表明，虽然单层和双层PbO具有相对较大的带隙和较低的吸收系数，其$J_{abs}$值是不理想的太阳能吸收器件。相比之下，$α$ -PbO的多层相和体相显示出与太阳光谱的良好重叠，并产生高电流值。计算结果表明，$α$ -PbO复合薄膜（如厚度为3 nm）可以作为太阳能电池的理想材料。我们相信，我们的工作可以用来改善电子和光学器件的基础上的铅氧化物结构。
英文摘要：
We have investigated the effects of number of layers on the structural, vibrational, electronic and optical properties of $α$-PbO using first principles calculations. Our theoretical calculations have shown that four Raman active modes of $α$-PbO tend to red-shift from bulk to monolayer due to decreasing of force constants and increasing of bond lengths. It has been shown that while bulk and multilayer $α$-PbO have an indirect band gap, monolayer form has a direct band gap value of 2.59 eV. Although lead atoms have 5d states, spin-orbit coupling does not significantly affect the band structure of $α$-PbO. The computed cleavage energy value (0.67 J/m$^2$) confirms that monolayer PbO can be easily obtained from its bulk counterpart by exfoliation methods. In addition to the band structure, we also calculated the optical properties and absorbed photon flux $J_{abs}$ of $α$-PbO structures to investigate the possibility of solar absorption. Our calculations reveal that while monolayer and bilayer PbO have relatively larger band gaps and lower absorption coefficients, their $J_{abs}$ values are not ideal for solar absorption devices. In contrast, the multilayer and bulk phases of the $α$-PbOs show good overlap with the solar spectrum and yield high electrical current values. Our calculations have indicated that ultrathin films of $α$-PbO (such as 3nm thickness) could be excellent candidates for solar cells. We believe that our work can be utilized to improve electronic and optical devices based on lead oxide structures.
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