Mechanical tests followed by microstructural investigations provide engineers information to computationally predict the mechanical performance of components. Electron microscopy is one of the most well-known techniques for analyzing deformation features of materials allowing understanding their response to exterior solicitations [1]. Two kinds of electron microscopes are generally used and bring complementary information: at macro/meso-scopic scale, Scanning Electron Microscopy (SEM) and at micro/nano-scale, Transmission Electron Microscopy (TEM) [2,3]. Weak Beam Dark Field (WBDF) is a TEM techniques allowing fine characterization of dislocations [4]. Such comprehensive dislocation studies at microscopic scale bring valuable information for understanding macroscopic mechanical response of materials [5]. Full characterization of dislocations is not only synonym of TEM experiments. SEM can access diffraction contrast with Scanning Transmission Electron Microscopy in a SEM (STEM-in-SEM). Briefly, this technique is based on the classical STEM (in a TEM) [6]: the electron beam is scanned and diffraction contrast allows observing defects. Diffraction patterns are acquired from domains below 10 nm in diameter [7]. In this framework, we report here technological challenges of such groundbreaking development and the first comprehensive dislocation analyses by SEM on a thin foil. Technological challenges such as detector development and sample holder design will be presented. Moreover, first dislocation analyses, which clearly show the full potentialities of this new characterization technique will be discussed. References: [1] D. E. Newbury and D. B. Williams, Acta Mater. 48, (2000) [2] Roberts, W., Lehtinen, B. and Easterling, K. E., Acta Metall. 24, (1976). [3] L. Liu, J. Wang, S. K. Gong and S. X. Mao, Phys. Rev. Lett. 106, (2011). [4] D. J. H. Cockayne, I. L. F. Ray and M. J. Whelan, Philos. Mag. 20, (1969). [5] P. Beran, M. Heczko, T. Kruml, T. Panzner, S. van Petegem, J. Mech. Phys. Solid. 95, (2016). [6] D. M. Maher and D. C. Joy, Ultramicroscopy 1, (1976) [7] P.G. Callahan, J.-C. Stinville, E.R. Yao, M.P. Echlin, M.S. Titus, M. De Graef, D.S. Gianola, and T.M. Pollock, Ultramicroscopy 186, (2018).