Significant thermal conductivity reduction of CVD graphene with relatively low hole densities fabricated by focused ion beam processing

Abstract

The detrimental effect of nanoscale hole defects on the in-plane thermal conductivity (k) was first examined for supported CVD graphene. A focused ion beam punctured equally spaced 50-nm diameter holes with different hole spacings (200, 400, and 800 nm) in supported graphene on an 8-nm thin SiO2 substrate. For the relatively low 4.91% porosity, the thermal conductivity showed a significant reduction to 212.6 W/mK from 1045 W/mK in supported graphene with no holes and even more dramatically so from 3500 W/mK in suspended pristine graphene. The thermal conductivity showed an order-of-magnitude faster reduction with increasing porosity compared to the Eucken model, which is based on the diffusive thermal transport reduction due to the void holes on the macroscale. This is believed to be attributed to the enhanced phonon scattering by the nanoscale hole edges and also by the reduced phonon passage length-scale that became comparable to the phonon mean-free-paths. Furthermore, a phenomenological fitting model is presented to comprehensively describe the k dependence on porosity, hole spacing, and the spectral dependence of the phonon mean-free-path in nanoscale holey graphene.

Dimension Effects of Graphene Sheets as Building Blocks: Implications for Thermal Conductivity Improvement of Graphene Films

“…The results reveal that the κ eff decreases dramatically with the increasing porosity, which is consistent with experimental results. 16,55 Normally, the GFs have a density in the 1.9−2.15 g/cm 3 range, corresponding to porosity in the 5.12−16.15% range. To control the effect of irrelevant variables, the porosity of the modeling was set to 10% in this section.…”

Work Function Tunability of Graphene with Thermally Evaporated Rhenium Heptoxide for Transparent Electrode Applications

“…Nevertheless, the desired functionality of graphene in a wide range of fields is gained when graphene is combined with another class of materials, resulting in the formation of composite materials with improved properties . The recent investigations of hole transport layers suggest a new class of materials for modification of graphene properties with aim of application in optoelectronics . Particularly, heterostructures made of graphene and thin transition metal oxide (TMO) films seem to be very attractive in optoelectronics and may play the role of hole or electron injection layers (HIL/EIL) .…”

A Review on Investigation of Graphene Thermal Property: Recent Development in Measurement Techniques

“…It is experimentally demonstrated that the grain boundaries effects from grain sizes [25,26] and grain misorientation [27,70] significantly influence on the thermal conductivity of graphene using the opto-thermal Raman method. Recently, various types of graphene such as doped graphene [11,28], hole defected graphene [30,31] and graphene with vacancies [32,33] have been produced and the opto-thermal Raman technique has revealed the modified graphene exhibits the reduced thermal conductivity compared to pristine graphene. Likewise, graphene will be further structurally modified to alter its unique properties and the opto-thermal Raman thermometry will act as a useful tool for estimating the altered thermal properties of graphene.…”

“…With those techniques, volumetric papers regarding thermal properties of graphene were reported. However, the characterization of thermal properties of graphene is still important since many researches nowadays focus on controlling the thermal conductivity of graphene [24] by inducing defects such as grain boundaries [25][26][27], dopants [11,28,29], holes [30,31] and vacancies [32,33]. Thus, a thorough examination on the altered thermal properties of graphene is necessary to elaborate the effect of induced defects.…”