Electrically Controlled Heat Transport in Multilayer Graphene

Electrical control of the thermal conductivity of materials could lead to various innovative applications^1–3, enabling disruptive technology such as reconfigurable thermal management for space application⁴. These smart heat-dissipating materials would enable steering the heat flow in the desired directions^5,6 and electrically driven thermal circuits³. These applications, however, require an active device i.e. a thermal switch, that can be reversibly changed between an off-state (high thermal conduction) to an on-state (low thermal conduction) on-demand¹, mimicking the functionality of a transistor in electronics. This thermal action can be achieved by altering the lattice (k_p) or electronic (k_e) contribution to the overall thermal conduction (k_T)⁴.<br/>The ability to control heat transport with electrical signals has been an outstanding challenge due to the lack of efficient electrothermal materials. Previous attempts have mainly concentrated on phase-change and layered materials and encountered various problems such as low thermal conductivities and modest on/off ratios⁷<br/>We demonstrated a multi-layer graphene-based electrothermal switch enabling electrically tuneable heat flow. The device uses reversible electro-intercalations of ions to modulate the in-plane thermal conductivity of graphene film by ten-fold via electrically tuneable phonon scattering. The thermal conductivity measurements were independently performed using in situ time-domain thermoreflectance⁸ and implemented infrared thermography setups. An analytical thermal model was developed, which takes into account the different phonon scattering mechanisms and the different graphite intercalation stages. Finally, in situ electrical Hall measurements were performed to estimate the electronic contributions of the thermal conductivity at the different intercalated stages.<br/>Scanning thermal microscopy (SThM) was utilised to gain additional insight into the detailed features of these devices at the nanoscopic scale⁹<br/>Moreover, to showcase the promises of our approach, we demonstrated a device that enables the steering of heat waves with spatial control of in-plane thermal diffusivity via area selective intercalation of graphene film producing reconfigurable in-plane anisotropy.<br/>We anticipate that our results could provide practical adaptive thermal transport methods, enabling a new class of electrically driven thermal devices that would find a broad spectrum of applications in aerospace and microelectronics.<br/>References<br/>1. Wehmeyer, G., Yabuki, T., Monachon, C. Wu, J. & Dames, C. <i>Appl. Phys. Rev.</i> <b>4</b>, 041304 (2017).<br/>2. Cahill, D. G. <i>et al.</i> <i>J. Appl. Phys.</i> <b>93</b>, 793–818 (2003).<br/>3. Toberer, E. S., Baranowski, L. L. & Dames, C. <i>Annu. Rev. Mater. Res.</i> <b>42</b>, 179–209 (2012).<br/>4. Swanson, T. NASA’s new thermal management systems roadmap; what’s in it, what it means (Aerospace Thermal Control Workshop, EI Segundo, California, 2016).<br/>5. Cui, S., Jiang, F., Song, N., Shi, L. & Ding, P. <i>ACS Appl. Mater. Interfaces</i> <b>11</b>, 30352–30359 (2019).<br/>6. Hansson, J., Nilsson, T. M. J., Ye, L. & Liu, J. <i>Int. Mater. Rev.</i> <b>63</b>, 22–45 (2018).<br/>7. Swoboda, T., Klinar, K., Yalamarthy, A. S., Kitanovski, A. & Muñoz Rojo, M. <i>Adv. Electron. Mater.</i> <b>7</b>, 2000625 (2021).<br/>8. Chauhan, V. S. <i>et al</i>. <i>AIP Adv.</i> <b>10</b>, 015304 (2020).<br/>9. Chen, M. E. <i>et al.</i> <i>2D Mater.</i> <b>8</b>, 035055 (2021).<br/><b>Acknowledgements: </b>This research is supported by Airbus, EPSRC funding Centre for Doctoral Training (CDT) Graphene-NOWNANO and European Research Council through ERC-Consolidator Grant (grant no 682723, SmartGraphene). We also acknowledge Henry Royce Institute for Advanced Materials for the NanoIR characterisation facility.