Chang Yu-Chung, Wang Yu-Kai, Chen Yen-Ting, Lin Der-Yuh
Department of Electrical Engineering, National Changhua University of Education, Changhua 500, Taiwan.
Department of Electronic Engineering, National Changhua University of Education, Changhua 500, Taiwan.
Nanomaterials (Basel). 2020 Mar 14;10(3):526. doi: 10.3390/nano10030526.
Although large-scale synthesis of layered two-dimensional (2D) transition metal dichalcogenides (TMDCs) has been made possible, mechanical exfoliation of layered van der Waals crystal is still indispensable as every new material research starts with exfoliated flakes. However, it is often a tedious task to find the flakes with desired thickness and sizes. We propose a method to determine the thickness of few-layer flakes and facilitate the fast searching of flakes with a specific thickness. By using hyperspectral wild field microscopy to acquire differential reflectance and transmittance spectra, we demonstrate unambiguous recognition of typical TMDCs and their thicknesses based on their excitonic resonance features in a single step. Distinct from Raman spectroscopy or atomic force microscopy, our method is non-destructive to the sample. By knowing the contrast between different layers, we developed an algorithm to automatically search for flakes of desired thickness in situ. We extended this method to measure tin dichalcogenides, such as SnS and SnSe, which are indirect bandgap semiconductors regardless of the thickness. We observed distinct spectroscopic behaviors as compared with typical TMDCs. Layer-dependent excitonic features were manifested. Our method is ideal for automatic non-destructive optical inspection in mass production in the semiconductor industry.
尽管大规模合成层状二维（2D）过渡金属二硫属化物（TMDCs）已成为可能，但层状范德华晶体的机械剥离仍然不可或缺，因为每一项新材料研究都始于剥离的薄片。然而，找到具有所需厚度和尺寸的薄片往往是一项繁琐的任务。我们提出了一种确定少层薄片厚度的方法，并便于快速搜索具有特定厚度的薄片。通过使用高光谱宽场显微镜获取差分反射率和透射率光谱，我们展示了基于激子共振特征在一步中对典型TMDCs及其厚度的明确识别。与拉曼光谱或原子力显微镜不同，我们的方法对样品无损。通过了解不同层之间的对比度，我们开发了一种算法来原位自动搜索所需厚度的薄片。我们将此方法扩展到测量二硫属化锡，如SnS和SnSe，它们无论厚度如何都是间接带隙半导体。与典型的TMDCs相比，我们观察到了明显的光谱行为。展现出了与层数相关的激子特征。我们的方法非常适合半导体行业大规模生产中的自动无损光学检测。
