Colloquium: Physics & Astronomy – Dr. Rui He

About the event

The Department of Physics and Astronomy invites you to a colloquium featuring Dr. Rui He, Electrical & Computer Engineering, Texas Tech University. Dr. He will present their talk, “Raman Spectroscopy of Interlayer Phonons and Charge Density Waves in Transition Metal Dichalcogenide Atomic layers”

Meet for refreshments before the lecture at 3:45 – 4:10 p.m. in the foyer on floor G above the lecture hall.

Abstract:

Transition metal dichalcogenides (TMDs), e.g. MoS2, MoSe2, WS2, and WSe2, have risen as a new generation of materials with remarkable properties. While much research has been directed to explore the novel electronic properties of TMD atomic layers, it is also important to study their vibrational properties that may affect device performance through electron-phonon interactions. In this first part of my talk, I will present our research on the interlayer phonon modes in van der Waals heterostructures formed from MoS2, MoSe2, and WSe2 monolayers, and interlayer phonon modes from atomically thin ReS2 and NbSe2 crystals. In the second part of my talk, I will present our recent studies of nearly commensurate to commensurate charge density wave (CDW) transitions in ultrathin 1T-TaS2. We identified additional CDW modes from surface layers of 1T-TaS2. I will also present our variable-temperature Raman spectroscopy studies of thin flakes of MoTe2. We find that in moderately thin MoTe2 samples below ~12 nm, a single orthorhombic phase exists up to and beyond room temperature by monitoring characteristic Raman lines from the orthorhombic phase. Our results reveal that Raman spectroscopy is an effective tool in probing interlayer interactions and fundamental properties of 2D materials.