Seminarium Fizyki Ciała Stałego

Van der Waals materials, also called layered materials are anisotropic compounds where strong, covalent bonds appear only in two directions within the layer, and molecular or atomic thin sheets are linked via relatively weak van der Waals interactions. The seminar will cover few studies of a family of layered semiconductors – transition metal thiophosphates, with general formula MPSx, where M stands for a transition metal, P for phosphorus, S for sulfur, and x is equal to 3 or 4.Large crystals of chromium phosphorus tetrasulfide (CrPS4) [1] and iron phosphorus trisulfide (FePS3) [2] are prepared in a big amount by a vapor transport synthesis or chemical vapor transport. Received materials are structurally analyzed by X-ray diffraction and several electron microscopy techniques. Optical properties are determined using various spectroscopy methods (i.e. photoconduction, temperature-dependent absorption, photoreflectance, and photoacoustic spectroscopy) exposing the semiconducting properties of the materials: CrPS4 – direct bandgap 1.30 eV at room temperature and FePS3 indirect bandgap of 1.40 eV at room temperature. The results obtained for FePS¬3 are further corroborated with DFT calculations. A simple, one-step protocol for mechanical exfoliation directly onto transmission electron microscope grid is developed and multiple layers are characterized by advanced electron microscopy methods, including atomic resolution elemental mapping confirming the structure by directly showing the positions of the columns of different elements' atoms, presented for the first time for vdW compound. [1,2] Materials are also liquid exfoliated, and for CrPS4 in combination with colloidal few-layer graphite, an all-printed photodetector is presented. [1]Moreover, the large-scale project will be briefly described, where mechanically exfoliated crystals of CrPS4, MnPS3, FePS3, CoPS3, and NiPS3, are used for tunable X-ray emission, which is observed for the first time for van der Waals materials. [3]References:[1] A.K. Budniak, N.A. Killilea, S.J. Zelewski, M. Sytnyk, Y. Kauffmann, Y. Amouyal, R. Kudrawiec, W. Heiss, E. Lifshitz*, "Exfoliated CrPS4 with promising photoconductivity", Small, 2020, 16 (1), 1905924[2] A.K. Budniak †, S.J. Zelewski †, M. Birowska, T. Woźniak, T. Bendikov, Y. Kauffmann, Y. Amouyal, R. Kudrawiec, E. Lifshitz, "Spectroscopy and structural investigation of bulk and exfoliated iron phosphorus trisulfide – FePS3", manuscript in preparation[3] M. Shentcis*, A.K. Budniak, X. Shi, R. Dahan, Y. Kurman, M. Kalina, H. Herzig Sheinfux, M. Blei, M. Kamper Svendsen, Y. Amouyal, S. Tongay, K. Sommer Thygesen, F.H.L. Koppens, E. Lifshitz, F. J. García de Abajo, L.J. Wong, I. Kaminer*, "Tunable free-electron X-ray radiation from van der Waals materials", Nature Photonics, 2020, 14 (11), 686-692UwagaSeminarium w trybie zdalnympatrz instrukcja :instrukcja: (pdf file)AttentionThe seminar in the remote modesee instruction :instruction: (pdf file)