二维过渡金属硫化物–超薄金属膜异质结构中非局域的介质屏蔽效应及其光学性质

Heterojunctions consisting of two-dimensional transition metal dichalcogenides (TMDCs) and various metals have extensive applications in various fields such as photodetector, solar cells, and field effect transistors, etc. In particular, when the metal film thickness is smaller than the electron mean free path, the dielectric function of metal strongly depends on the film thickness, further affecting the nonlocal dielectric screening effect and the related optical properties of TMDCs. In this project, various heterostructures of TMDCs–ultrathin metal films will be fabricated by chemical vapor deposition and electron-beam evaporation. By combining with the transfer matrix method and the first principle theory, the evolutions of excitonic and trionic properties including electronic and optical bandgaps, energy levels and binding energies with the structural factors, e.g., the metal film thickness, the gap between two membrane materials in lateral “heterojunction”, will be explored. The model of one-dimensional photonic crystal consisting of TMDCs/ultrathin metal films will be designed. The photonic bandgap and localization will be modulated in a wide range by tuning the thickness ratio between TMDCs and metal films, permittivity ratio between different dielectric layers, periodic structure, and defect layer, etc. The effect of nonlocal dielectric screening induced by various ultrathin metal films on two-dimensional TMDCs and the related optical characteristics will be revealed from microcosmic aspect. This study can provide experimental and theoretical bases for the synthesis and applications of TMDCs–metal multi-films composite materials in optoelectronic devices.

二维过渡金属硫化物（TMDCs）与各种金属构成的异质结可以广泛应用于光电检测、太阳能电池、场效应晶体管等诸多领域。特别是当金属膜厚度小于电子平均自由程时，金属介电函数将显著依赖于膜厚变化，进而影响TMDCs受到的非局域介质屏蔽效应及其各种光学特性。本项目拟采用化学气相沉积与电子束蒸镀技术制备多种TMDCs–超薄金属膜异质结，结合传输矩阵法与第一性原理，探究二维TMDCs激子和trion的电子与光学带隙、能级分布、结合能等随金属膜厚度、横向“异质结”中两膜材料间隙等结构参数的演变规律，构建TMDCs/超薄金属多层膜一维光子晶体，通过改变介质层厚度比、折射率比、周期、缺陷层等结构参数实现光子带隙与光子局域的宽范围调制，从微观上揭示超薄金属膜对TMDCs非局域介质屏蔽效应及该效应对TMDCs光学特性的影响。该研究可为TMDCs–金属多层膜复合材料的制备及其在光电子器件中的应用提供实验和理论依据。

近年来，二维过渡金属硫化物（TMDCs）因其独特的光学性能而备受人们关注。当二维TMDCs从多层减薄至单层时，其能带结构也将发生变化，由间接带隙逐渐转变成直接带隙，并且引发谷间自旋耦合。此外，由于不受传统半导体外延生长晶格匹配的限制，二维TMDCs还可以与各种金属纳米膜自由结合，形成的异质结或复合材料在更广泛的光谱范围内表现出良好的器件性能。在该项目资助下，课题组主要开展了超薄金膜对单层WS2激子的非局域介质屏蔽效应、基于二维TMDCs与金属膜复合材料生物传感器与一维光子晶体的设计及光学性能调控、各向异性二维材料界面上的光子自旋霍尔效应等方面的研究。研究结果表明，随着超薄金膜厚度的增加，单层WS2受到的非局域介质屏蔽效应逐渐增强，激子基态的结合能逐渐减小，但由于金膜中自由电子的散射效应，WS2激子基态与第一激发态的共振吸收能逐渐增大；提出的基于埃洛石纳米管/二维TMDC/黑磷烯/金膜/三棱镜多层介质结构的表面等离子共振（SPR）生物传感器，相较于传统的裸金以及近年来提出的基于二维材料的SPR生物传感器，该生物传感器的相位探测灵敏度与角度探测灵敏度均有极大的提高，且当激发光束为p偏振时可以激发SPR，当激发光束为s偏振时可以激发泄漏模共振；由金属膜、PMMA间隔层、单层WS2和电介质布拉格反射镜（DBR，SiO2和TiO2介质层交替堆叠形成的一维光子晶体）构成的多层膜异质结构，在单层WS2与DBR之间的边界处不易激发Tamm等离激元，强耦合作用主要来自金属Tamm等离激元和单层WS2中激子的相互作用；在由金膜、单层TMDCs和缺陷层组成的一维光子晶体表面上发生的光子自旋霍尔效应，随着金膜厚度从2.4 nm逐渐增加到40.0 nm，光子自旋霍尔位移先增加后减小（当金膜的厚度为4.4 nm时达到最大）；在特定条件下，各向异性二维材料时间反演对称性的破缺能够显著增强光子自旋霍尔效应。这些研究结果有助于揭示光子与二维TMDCs的相互作用机制，可为新型二维量子材料光学性能的优化调控以及多功能光子器件的研发提供新的思路和重要理论基础。

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