School of Civil and Environmental Engineering

Ph.D. Thesis Defense Announcement

Response of transition metal nanotubes and their Janus variants to mechanical deformations: an ab initio study

By Arpit Bhardwaj

Advisor: Dr. Phanish Suryanarayana (CEE)

Committee Members:  Dr. Arash Yavari (CEE), Dr. Rampi Ramprasad (MSE), Dr. Chaitanya S. Deo (ME), Dr. Seung Soon Jang (MSE)

Date and Time:  Tuesday April 11, 2023 1:00pm

Location:  O. Lamar Allen Sustainable Education Building; SEB 122

Complete announcement, with abstract, is attached.

Transition metal nanotubes, such as transition metal dichalcogenide (TMD) nanotubes, have gained attention due to their unique properties, including high tensile strength and mechanically tunable electronic properties, which make them ideal candidates for various applications such as reinforcement in nanocomposites, mechanical sensors and nanoelectromechanical (NEMS) devices.
 
In this thesis, we employ symmetry-adapted DFT (density functional theory) simulations to calculate the elastic properties of 45 select TMD and 27 select Janus TMD nanotubes, including Young's modulus, Poisson's ratio, and torsional modulus. Additionally, we investigate the electromechanical response of TMD nanotubes to torsional deformations and the behavior of Janus TMD and Janus TMH (transition metal dihalide) nanotubes under axial and torsional deformations. Furthermore, we investigate the effect of spin-orbit coupling on mechanically deformed TMD and Janus TMD nanotubes and observe Zeeman and Rashba spin-splitting. Our calculations reveal that the Young's and torsional moduli of TMD nanotubes follow the trend MS2 > MSe2 > MTe2, while for Janus TMD nanotubes, the trend is MSSe > MSTe > MSeTe. We also observe that strain engineering has no effect on metallic nanotubes, while it generally reduces the bandgap of semiconducting nanotubes, leading to semiconductor-to-metal transitions. Moreover, it results in a decrease in the effective mass of holes and an increase in the effective mass of electrons, leading to transitions from n-type to p-type semiconductors. The introduction of twist in these nanotubes breaks the inversion symmetry and induces Rashba spin-splitting, with relatively high values of the Rashba coefficient. Overall, we provide valuable insights into the mechanical, electronic and spintronic properties of these nanotubes, which could lead to their applications in a wide range of fields, such as sensors and electronics.