M.R. Rosenberger, C.K. Dass, H.-J. Chuang, S.V. Sivaram, K.M. McCreary, J.R. Hendrickson, B.T. Jonker
U.S. Naval Research Laboratory,
Keywords: single photon emitter, WSe2, strain
Summary:We present a paradigm for encoding strain into two dimensional materials (2DM) to create and deterministically place single photon emitters (SPEs) in arbitrary locations with nanometer-scale precision. Our material platform consists of a 2DM placed on top of a deformable polymer film. Upon application of sufficient mechanical stress using an atomic force microscope (AFM) tip, the polymer layer plastically deforms. While the AFM tip is in contact with the sample, the AFM tip forces the 2DM to deform with the polymer layer, resulting in tensile strain buildup in the 2DM. When the AFM tip is removed, the adhesive interaction between the polymer and the 2DM prevents the 2DM from relaxing back to its original, strain-free geometry, resulting in a permanent and highly localized strain field in the 2DM. We demonstrate control of indent size by modifying the applied load. Also, we show excellent repeatability of both indent shape and size. We show that SPEs are created and localized at nanoindents in a WSe2/PMMA structure, as confirmed by antibunching measurements. The SPEs exhibit single photon emission up to 60 K. This quantum calligraphy allows deterministic placement and real time design of arbitrary patterns of SPEs for facile coupling with photonic waveguides, cavities, and plasmonic structures. We further use the AFM to create trenches in the WSe2/PMMA structure, leading to nominally one-dimensional strain profiles. We find that the linear polarization orientation of SPEs in the trenches correlates with the orientation of the one-dimensional strain profile. This result holds for trenches made at different orientations relative to the WSe2 crystal orientation, suggesting that the polarization orientation of SPEs in WSe2 is determined by the strain profile alone. In addition to enabling versatile placement of SPEs, these results present a general methodology for imparting strain into 2DM with nanometer-scale precision, providing an invaluable tool for further investigations and future applications of strain engineering of 2DM and 2DM devices. Reference: Rosenberger et al., “Quantum Calligraphy: Writing Single-Photon Emitters in a Two-Dimensional Materials Platform,” ACS Nano, 2019, https://pubs.acs.org/doi/10.1021/acsnano.8b08730.