Han Wen-Peng, Shi Yan-Meng, Li Xiao-Li, Luo Shi-Qiang, Lu Yan, Tan Ping-Heng. The numerical-aperture-dependent optical contrast and thickness determination of ultrathin flakes of two-dimensional atomic crystals: A case of graphene multilayersJ. Acta Physica Sinica, 2013, 62(11): 110702. DOI: 10.7498/aps.62.110702