2 research outputs found
Power Dissipation of WSe<sub>2</sub> Field-Effect Transistors Probed by Low-Frequency Raman Thermometry
The
ongoing shrinkage in the size of two-dimensional (2D) electronic circuitry
results in high power densities during device operation, which could
cause a significant temperature rise within 2D channels. One challenge
in Raman thermometry of 2D materials is that the commonly used high-frequency
modes do not precisely represent the temperature rise in some 2D materials
because of peak broadening and intensity weakening at elevated temperatures.
In this work, we show that a low-frequency E<sub>2g</sub><sup>2</sup> shear mode can be used to accurately
extract temperature and measure thermal boundary conductance (TBC)
in back-gated tungsten diselenide (WSe<sub>2</sub>) field-effect transistors,
whereas the high-frequency peaks (E<sub>2g</sub><sup>1</sup> and A<sub>1g</sub>) fail to provide reliable
thermal information. Our calculations indicate that the broadening
of high-frequency Raman-active modes is primarily driven by anharmonic
decay into pairs of longitudinal acoustic phonons, resulting in a
weak coupling with out-of-plane flexural acoustic phonons that are
responsible for the heat transfer to the substrate. We found that
the TBC at the interface of WSe<sub>2</sub> and Si/SiO<sub>2</sub> substrate is ∼16 MW/m<sup>2</sup> K, depends on the number
of WSe<sub>2</sub> layers, and peaks for 3–4 layer stacks.
Furthermore, the TBC to the substrate is the highest from the layers
closest to it, with each additional layer adding thermal resistance.
We conclude that the location where heat dissipated in a multilayer
stack is as important to device reliability as the total TBC
Bimodal Phonon Scattering in Graphene Grain Boundaries
Graphene has served as the model
2D system for over a decade, and the effects of grain boundaries (GBs)
on its electrical and mechanical properties are very well investigated.
However, no direct measurement of the correlation between thermal
transport and graphene GBs has been reported. Here, we report a simultaneous
comparison of thermal transport in supported single crystalline graphene
to thermal transport across an individual graphene GB. Our experiments
show that thermal conductance (per unit area) through an isolated
GB can be up to an order of magnitude lower than the theoretically
anticipated values. Our measurements are supported by Boltzmann transport
modeling which uncovers a new bimodal phonon scattering phenomenon
initiated by the GB structure. In this novel scattering mechanism,
boundary roughness scattering dominates the phonon transport in low-mismatch
GBs, while for higher mismatch angles there is an additional resistance
caused by the formation of a disordered region at the GB. Nonequilibrium
molecular dynamics simulations verify that the amount of disorder
in the GB region is the determining factor in impeding thermal transport
across GBs