Layer-Dependent Band Gaps of Platinum Dichalcogenides
Layer-Dependent Band Gaps of Platinum Dichalcogenides
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DOI：
10.1021/acsnano.1c02971
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发表时间：
2021-08-16
期刊：
影响因子：
17.1
通讯作者：
Batzill, Matthias
中科院分区：
文献类型：
--
作者：
Li, Jingfeng;Kolekar, Sadhu;Batzill, Matthias
由于相对较强的层间相互作用，二硫属铂化合物通过控制层的数目而表现出其电子性质的可调谐性。PtSe2和PtTe2都显示半金属到半导体的转变，因为它们被还原为双层或单层。然而，基本带隙的值仅从密度泛函理论（DFT）计算中推断出来，这是众所周知的挑战，因为不同的方法给出不同的结果，并且目前没有实验数据。在这里，我们确定的带隙作为一个功能的层数通过局部扫描隧道光谱的分子束外延（MBE）生长的PtSe2和PtTe2岛。我们发现带隙为1.8和0.6 eV的单层和双层PtSe2，分别为0.5 eV的单层PtTe2。三层PtSe 2和双层PtTe 2是半金属的。实验数据进行了比较DFT计算在不同的理论水平。计算的带隙可能与实验值有很大的不同，强调了实验工作的重要性。我们进一步表明，在双层PtSe 2的计算的基本带隙的变化有关的计算分离的层，这取决于选择的货车德瓦尔斯功能。带隙对层间分离的这种敏感性还表明，差距可以通过单轴应力来调节，并且我们的模拟表明，对于差距的显著减小，仅需要适度的压力，使得Pt二硫属化物适合于压力传感的材料。
Owing to the relatively strong interlayer interaction, the platinum dichalcogenides exhibit tunability of their electronic properties by controlling the number of layers. Both PtSe2 and PtTe2 display a semimetal to semiconductor transition as they are reduced to bi- or single layers. The value of the fundamental band gap, however, has been inferred only from density functional theory (DFT) calculations, which are notoriously challenging, as different methods give different results, and currently, there is no experimental data. Here, we determine the band gap as a function of the number of layers by local scanning tunneling spectroscopy on molecular beam epitaxy (MBE)- grown PtSe2 and PtTe2 islands. We find band gaps of 1.8 and 0.6 eV for mono- and bilayer PtSe2, respectively, and 0.5 eV for monolayer PtTe2. Trilayer PtSe2 and bilayer PtTe2 are semimetallic. The experimental data are compared to DFT calculations carried out at different levels of theory. The calculated band gaps may differ significantly from the experimental values, emphasizing the importance of the experimental work. We further show that the variations in the calculated fundamental band gap in bilayer PtSe2 are related to the computed separation of the layers, which depends on the choice of the van der Waals functional. This sensitivity of the band gap to interlayer separation also suggests that the gap can be tuned by uniaxial stress, and our simulations indicate that only modest pressures are required for a significant reduction of the gap, making Pt dichalcogenides suitable materials for pressure sensing.