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褶皱结构引起的周期性连续变化应变为调控二维材料电子和光电性质提供了重要手段. 然而, 目前关于褶皱状二维材料的形成机理及其对相关物性的调控研究仍缺乏理解. 本文基于原子键弛豫理论和连续介质力学方法, 系统研究了褶皱状单层GeSe能带结构随波长和位置的变化规律. 结果表明, 由于各向异性的力学性质和褶皱引起的周期性连续变化应变, 褶皱状单层GeSe表现出各向异性的能带漏斗效应, 激子会定向聚集在褶皱的谷区域, 且聚集能力随着波长的减小而增强. 此外, 当波长减小至106 nm, 锯齿型褶皱状单层GeSe的能带漏斗消失, 而扶手椅型褶皱状单层GeSe的能带漏斗依然得以保持. 这些结果为褶皱状单层GeSe在激子输运中的应用提供了理论基础, 并为设计高性能基于二维材料的光电器件提供了新策略.Two-dimensional materials with tunable wrinkled structures open up a new way to modulate their electronic and optoelectronic properties. However, the mechanisms of forming wrinkles and their influences on the band structures and associated properties are still unclear. Here, we investigate the strain distribution, bandgap, and anisotropic energy funneling effect of wrinkled monolayer GeSe and their evolution with the wrinkle wavelength based on the atomic-bond-relaxation approach and continuum medium mechanics. We find that the top region and valley region of wrinkled monolayer GeSe exhibit tensile and compressive strains, respectively, and the strain increases with wrinkle wavelength decreasing. Moreover, the periodic undulation strain in the wrinkles can lead to continuously adjustable bandgaps and band edges in wrinkled monolayer GeSe. For zigzag wrinkled monolayer GeSe, when the wrinkle wavelength is long, the conduction band minimum value (valence band maximum value) continuously decreases (increases) from the top to the valley, forming an energy funnel. As a result, the excitons accumulate in the valleys of wrinkles, and their accumulation capability increases with wrinkle wavelength decreasing. However, as the wavelength further decreases, the energy funnel will disappear, causing some excitons to t accumulate at the top of wrinkles, while the remaining excitons will accumulate in the valleys of wrinkles. The critical wavelength for the energy funnel of zigzag wrinkled GeSe to disappear is 106nm. The physical origin is that when the top strain exceeds 4%, the bandgap will decrease. Owing to the monotonic variation of bandgap with strain, the energy funneling effect of armchair wrinkled monolayer GeSe is still retained when the wavelength decreases to 80 nm, and the accumulation of excitons is further enhanced. Our results demonstrate that the energy funneling effect induced by nonuniform can realize excitons’ accumulation in one material without the need of p-n junctions, which is of great benefit to the collection of photogenerated excitons. Therefore, the proposed theory not only clarifies the physical mechanism regarding the anisotropic energy funneling effect of wrinkled monolayer GeSe, but also provides a new avenue for designing the next-generation optoelectronic devices.
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Keywords:
- GeSe /
- wrinkle /
- energy funneling effect /
- atomic-bond-relaxation approach
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图 1 褶皱状单层GeSe/衬底结构示意图以及单层GeSe的俯视图和侧视图
Fig. 1. Schematic illustration of wrinkled monolayer GeSe/substrate as well as the top and side views of monolayer GeSe.
图 2 (a) 褶皱状单层GeSe振幅与波长之间的关系; (b) 不同波长下褶皱状单层GeSe应变的分布情况; (c) 单层GeSe带隙随应变的变化规律; (d) 不同波长下褶皱状单层GeSe带隙的分布情况
Fig. 2. (a) The relationship between the amplitude and wavelength of wrinkled monolayer GeSe; (b) distribution of strain of wrinkled monolayer GeSe with different wavelengths; (c) strain dependent bandgap of monolayer GeSe; (d) distribution of bandgaps of wrinkled monolayer GeSe with different wavelengths.
图 3 (a) 锯齿型褶皱状单层GeSe和 (b) 扶手椅型褶皱状单层GeSe在不同波长下单个周期内带边的分布情况
Fig. 3. Energy profiles of (a) zigzag wrinkled monolayer GeSe and (b) armchair wrinkled monolayer GeSe with different wavelengths.
图 4 褶皱状单层GeSe峰导带底和价带顶的一阶导数随波长的变化规律
Fig. 4. The first derivatives of CBM and VBM of top as a function of wavelength in zigzag wrinkled GeSe and armchair wrinkled GeSe.
图 5 褶皱状单层GeSe驱动力和激子转移速率随波长的变换规律
Fig. 5. The driving force and exciton transfer rate of wrinkled GeSe as a function of wavelength.
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