Strain Engineering of Metal Thio(Seleno)phosphates for Nonlinear Photonics and Photodetection

We present an experimental and computational study of engineering in-situ strain in two-dimensional metal thio(seleno)phosphate materials aiming to unlock and enhance their fundamental magnetic, electronic, ferroelectric, and flexoelectric properties. The material families under study include MPX3 (X = S, Se) materials and materials with P2X6 (X = S, Se) structural sublattice. The single-crystalline thio(seleno)phosphates exhibiting layered structure have been synthesized by vapor transport techniques reported in previous literature [1] and exhibit a wealth of promising nonlinear optoelectronic and magnetic properties, including bulk photovoltaic effect, second harmonic generation, and (anti)ferromagnetic response [1]. We will describe the process of fabricating optoelectronic cells from these materials via mechanical exfoliation as well as the process of engineering the in-situ strain fields with large, localized strain gradients in these cells by material bending, wrinkling, and nano-lithography [2]. Strain gradient mapping with Raman spectroscopy reveals the limits and advantages of different strain-engineering strategies, while the strain-induced linear and nonlinear optical responses and the surface polarization effects can be characterized by atomic force microscopy, second harmonic generation experiments, and spatially-resolved electrical current measurements.<br/><br/>This research has been supported by the Army Research Office (W911NF-13-D-0001, for the strain-engineering fundamentals development), Lincoln Laboratory, Massachusetts Institute of Technology Advanced Concepts Committee (ACC-777, for the cell design and fabrication process development), and the US Department of Energy (DE-FG02-02ER45977, for the development of a custom-designed optoelectronic microscopic measurement setup), and a Draper Fellowship to Morgan Blevins.<br/><br/>References:<br/><br/>[1] Susner, Michael A., et al. "Metal thio-and selenophosphates as multifunctional van der Waals layered materials." Advanced Materials 29.38 (2017): 1602852.<br/>[2] Lorenzi, Bruno, et al. "Self-powered broadband photo-detection and persistent energy generation with junction-free strained Bi 2 Te 3 thin films." Optics Express 28.19 (2020): 27644-27656.