Layered van-der-Waals 2D materials, including transition metal dichalcogenides (TMD), enable a broad range of advanced electronic applications. Ability to manipulate electrical and optical properties by externally stimulated structural phase transitions in TMD materials opens a possibility for fabricating energy-efficient non-volatile memories and transport devices.
In this seminar, I will discuss controlled growth and reversible phase transitions in molybdenum ditelluride, MoTe2, single crystals targeting the above applications. MoTe2 crystallizes in 3 polytypes: 2H semiconducting phase, thermodynamically stable at room temperature; 1T’ metallic phase, stable above ~870 °C; and Td topological semimetal, stable below -25 °C. We have grown 2H and 1T’ bulk single crystals by chemical vapor transport and studied dynamics of temperature-induced 2H ↔ 1T’ phase transition using STEM, XRD, XPS and Raman. In addition, we manipulated the 2H-to-1T’ transition temperature by substituting Mo with W in Mo1-xWxTe2 alloys. Noteworthy, extending the alloys composition to pure WTe2 opens a possibility to elevate the 1T’ ↔ 1Td transition temperature from topologically trivial 1T’ to type-II Weyl Td phase to above room temperature.
The experimental knowledge about relationship between 2H, 1T’ and Td polytypes was mapped on the MoTe2 – WTe2 phase diagram and allowed our collaborators to fabricate RRAM , lateral homojunction FET  an orbital photogalvanic detector  devices.
Albert Davydov is a leader of Functional Nanostructured Materials Group at NIST, which focuses on materials and processes for advanced electronics, magnetics, energy, and catalysis. Albert received PhD in Chemistry from Moscow State University (Russia). He joined NIST almost 25 years ago and his research interests include fabrication, processing, and microstructural characterization of a wide range of electronic materials including semiconductor nanowires, 2D and quantum materials. His expertise also includes thermodynamic modeling and experimental study of phase diagrams for metal and semiconductor material systems.
He is a member of: Technical Committee 229 (Nanotechnology) at International Organization for Standardization (ISO); Science Advisory Board with the nanoelectronics COmputing REsearch (nCORE) program at Semiconductor Research Corporation (SRC); and at the Advisory Board of Applied Physics Review journal. He also serves as a Head of the Semiconductor Task Group for the International Centre for Diffraction Data (ICDD), co-Chair of the Reference Materials Task Group at ASTM Subcommittee on Compound Semiconductors, and co-Chair of SPIE Optics & Photonics Conference on Low-dimensional Materials and Devices.