Dark-field second harmonic generation imaging of grain bound- aries in 2D semiconducting transition metal dichalcogenides Bruno R. Carvalho 1,∗ , Yuanxi Wang 2,3,4 , Kazunori Fujisawa 2,3 , Tianyi Zhang 3,5 , Ethan Kahn 3,5 , Ismail Bilgin 6 , Pulickel M. Ajayan 7 , Ana M. de Paula 8 , Marcos A. Pimenta 8 , Swastik Kar 6 , Vincent H. Crespi 2,3,4 , Mauricio Terrones 2,3,5 & Leandro M. Malard 8,∗ 1 Departamento de F´ ısica, Universidade Federal do Rio Grande do Norte, Natal, Rio Grande do Norte 59078-970, Brazil 2 Department of Physics, The Pennsylvania State University, University Park, PA 16802, USA 3 Center for 2-Dimensional and Layered Materials, The Pennsylvania State University, University Park, PA 16802, USA 4 2-Dimensional Crystal Consortium, The Pennsylvania State University, University Park, PA 16802, USA 5 Department of Materials Science and Engineering, The Pennsylvania State University, University Park, PA 16802, USA 6 Department of Physics, Northeastern University, Boston, Massachusetts 02115, USA 7 Department of Material Science and NanoEngineering, Rice University, Houston, TX, 77005, United States 8 Departamento de F´ ısica, Universidade Federal de Minas Gerais, Belo Horizonte, Minas Gerais 30123-970, Brazil ∗ E-mail: brunorc@fisica.ufrn.br (B.R.C.) and lmalard@fisica.ufmg.br (L.M.M.). 1 arXiv:1903.05139v1 [cond-mat.mes-hall] 12 Mar 2019