The Role of Interfacial Electronic Properties on Phonon Transport in Two-dimensional MoS2 on Metal Substrates
We investigate the role of interfacial electronic properties on the phonon transport in twodimensional MoS2 adsorbed on metal substrates (Au and Sc) using first principle density functional theory and the atomistic Greenâ?Ts function method. Our study reveals that the different degree of orbital hybridization and electronic charge distribution between MoS2 and metal substrates play a significant role in determining the overall phonon-phonon coupling and phonon transmission. The charge transfer caused by the adsorption of MoS2 on Sc substrate can significantly weaken the Mo-S bond strength and change the phonon properties of MoS2, which result in a significant change in TBC from one lattice-stacking configuration to another for same metallic substrate. In a lattice-stacking configuration of MoS2/Sc, weakening of the Mo-S bond strength due to charge redistribution results in decrease in the force constant between Mo and S atoms and substantial redistribution of phonon density! of states to low-frequency region which affects overall phonon transmission leading to 60 % decrease in TBC compared to another configuration of MoS2/Sc. Strong chemical coupling between MoS2 and the Sc substrate leads to a significantly (~19 times) higher thermal boundary conductance (TBC) than that of the weakly bound MoS2/Au system. Our findings demonstrate the inherent connection among the interfacial electronic structure, the phonon distribution, and TBC, which helps us understand the mechanism of phonon transport at the MoS2/metal interfaces. The results provide insights for the future design of MoS2-based electronics and a way of enhancing heat dissipation at the interfaces of MoS2-based nano-electronic devices.
Distillation based CO2 removal from natural gas
There are two technical challenges in the removal of CO2 from natural gas. The first significant problem is that the CO2 freezes out in the demethanizer distillation column. The other major problem associated with this process is that CO2 and ethane form a minimum boiling azeotrope in the heavier component or bottoms stream in the demethanizer thereby making their separation difficult. The objective of this investigation is to examine the feasibility of designing a distillation based CO2 removal system, where freezeout and azeotropes are avoided. A multi tower pseudo-closed loop distillation system with solvent recovery which can be recycled back to the system is developed and theoretically demonstrated.