本期学术论坛由Universityof Colorado Boulder 的Ronggui Yang 教授主讲
题目：Thermal Conductivity of Two-DimensionalMaterials
报告人： Ronggui Yang 教授
Two-dimensional(2-D) materials, such as graphene, black phosphorus and transition metaldichalcogenides, have attracted increased interest due to their potentialapplications in electronic, optoelectronic, and energy systems. Understandingthe phononic thermal properties in 2-D materials could be very important forthe design of novel devices using 2-D materials.
Inthe first part of this talk, the first-principles based Boltzmann transportequation approach is developed to predict a series of novel 2-D materials,including silicene and single-layer transition metal dichalcogenides (TMDs).Their thermal conductivities are found to be highly correlated to their crystalstructure and atomic masses. Using the same approach, we also study the layerthickness-dependence of thermal conductivity of MoS2. Unlike conventionalthin film materials, whose thermal conductivity is usually suppressed when thethickness decreases due to phonon-boundary scattering, the thermal conductivityof MoS2 decreases when increasing its thickness. It appears thatboth the phonon dispersion and the anharmonicity changes with the thickness ofMoS2.
Inthe second part of this talk, a variable spot size time-domainthermoreflectance (TDTR) approach is developed to systematically measure boththe basal plane and cross plane thermal conductivity, Kr and Kz,of four TMD crystals, MoS2, MoSe2, WS2 and WSe2,over a wide range of temperature at 80 – 300 K. We consistently observedfrequency dependence in both the through-plane thermal conductivity Kzand the Al/TMD interface thermal conductance G for all these TMDcompounds, which we attributed to the non-equilibrium thermal resistancebetween different groups of phonons in the substrate during the TDTRexperiments.
Dr. Ronggui Yang is a Professor of MechanicalEngineering directing the Nano-enabledEnergy Conversion, Storage,and Thermal ManagementSystems group (NEXT) at the (CU-Boulder). Dr. Yang receivedhis Ph.D degree focusing on Nanoscale Heat Transfer with ProfessorGanUniversity of Colorado Boulder g Chen in Mechanical Engineering fromMIT in February 2006. His innovative research has won him numerous awardsincluding the 2014 ITS Young Investigatorin Thermoelectrics from International Thermoelectric Society (ITS),the 2010 ASME Bergles-Rohsenow Young Investigator Award in HeatTransfer, an NSF CAREER Award in 2009, the MIT Technology Review’s TR35Award and the DARPA Young Faculty Award in 2008. Dr. Yang is also wellrecognized for his professional services. Dr. Yang is currently the Chair(2015-2017) of the K-9 Technical Committee on Nanoscale Thermal Transport ofASME Heat Transfer Division. He is also an Associate Editor for ASME Journal ofHeat Transfer and and Associate Editor for Heat Transfer Research. He waselected ASME Fellow in 2015