Mondal Mainak, Dash Ajit K, Singh Akshay
Department of Physics, Indian Institute of Science, Bengaluru 560012, India.
ACS Nano. 2022 Sep 27;16(9):14456-14462. doi: 10.1021/acsnano.2c04833. Epub 2022 Sep 8.
Optical contrast is the most common preliminary method to identify layer number of two-dimensional (2D) materials, but it is seldom used as a confirmatory technique. We explain the reason for variation of optical contrast between imaging systems, motivating system-independent measurement of optical contrast as a critical need. We describe a universal method to quantify the layer number using the RGB (red-green-blue) and RAW optical images. For RGB images, the slope of 2D flake (MoS, WSe, graphene) intensity vs substrate intensity is extracted from optical images with varying lamp power. The intensity slope identifies layer number and is system independent. For RAW images, intensity slopes and intensity ratios are completely system and intensity independent. Intensity slope (for RGB) and intensity ratio (for RAW) are thus universal parameters for identifying layer number. The RAW format is not present in all imaging systems, but it can confirm layer number using a single optical image, making it a rapid and system-independent universal method. A Fresnel-reflectance-based optical model provides an excellent match with experiments. Furthermore, we have created a MATLAB-based graphical user interface that can identify layer number rapidly. This technique is expected to accelerate the preparation of heterostructures and to fulfill a prolonged need for universal optical contrast method.
光学对比度是识别二维（2D）材料层数最常用的初步方法，但很少用作确证技术。我们解释了成像系统之间光学对比度变化的原因，强调了作为关键需求的与系统无关的光学对比度测量。我们描述了一种使用RGB（红绿蓝）和RAW光学图像量化层数的通用方法。对于RGB图像，二维薄片（MoS、WSe、石墨烯）强度与衬底强度的斜率是从具有不同灯功率的光学图像中提取的。强度斜率可识别层数且与系统无关。对于RAW图像，强度斜率和强度比完全与系统和强度无关。因此，强度斜率（用于RGB）和强度比（用于RAW）是识别层数的通用参数。RAW格式并非在所有成像系统中都存在，但它可以使用单个光学图像确证层数，使其成为一种快速且与系统无关的通用方法。基于菲涅尔反射的光学模型与实验结果非常吻合。此外，我们创建了一个基于MATLAB的图形用户界面，可以快速识别层数。预计该技术将加速异质结构的制备，并满足对通用光学对比度方法长期以来的需求。
