Optical contrast determination of the thickness of SiO₂ film on Si substrate partially covered by two-dimensional crystal flakes

Abstract

SiO₂/Si substrate has been widely used to support two-dimensional (2-D) crystal flakes grown by chemical vapor deposition or prepared by micromechanical cleavage. The visibility of 2-D flakes is very sensitive to the thickness of the SiO₂ layer $(h_{{\mathrm{SiO}}_2})$, which can not be determined precisely after the deposit of 2-D flakes. Here, we demonstrated a simple, fast and nondestructive technique to precisely determine $h_{{\mathrm{SiO}}_2}$ of SiO₂ films on Si substrate only by optical contrast measurement with a typical micro-Raman confocal system. Because of its small lateral resolution down to the micrometer scale, this technique can be used to access $h_{{\mathrm{SiO}}_2}$ on SiO₂/Si substrate that has been partially covered by 2-D crystal flakes, and then further determine the layer number of the 2-D crystal flakes. This technique can be extended to other dielectric multilayer substrates and the layer-number determination of 2-D crystal flakes on those substrates.

导读

二维晶体材料的可见度显著地依赖于SiO₂/Si衬底的SiO₂层厚度, 因此SiO₂层厚度的测定对研究二维晶体材料至关重要. 本文提出一种基于光学衬度的显微测量技术. 由于该技术具有微米级别的空间分辨率, 因此, 即使衬底已经被二维晶体材料部分覆盖, 该技术仍然可以用来测定衬底SiO₂层的厚度. 作为应用实例, 本文成功地鉴别了SiO₂层厚未知的SiO₂/Si 衬底上少层石墨烯的层数. 这项技术可以推广到测定其他多层介质结构衬底的厚度和在这些衬底上的二维晶体材料的层数.