We experimentally demonstrate the operation of a radiative thermal transistor capable of switching, modulating, and amplifying far-field heat currents. This three-terminal device exploits the metal-insulator transition of ${\mathrm{VO}}_2$ thin films deposited on both surfaces of a substrate using pulsed laser deposition (PLD). This phase transition induces a sharp variation of the infrared emissivity of the ${\mathrm{VO}}_2/\mathrm{substrate}/{\mathrm{VO}}_2$ system, acting as the transistor base placed between two heat flux sensors playing the roles of the emitter and collector. Unlike previous studies, we consider substrates of r-cut and c-cut sapphire, and $\mathrm{Si}/{\mathrm{Si}\mathrm{O}}_2$ to correlate different microstructural properties of ${\mathrm{VO}}_2$ to its emissivity variations and optimize the thermal performance of the developed thermal transistor. By measuring the heat fluxes emitter-base and base-collector, we find that the thermal transistor implemented with a ${\mathrm{VO}}_2/{\mathrm{Si}\mathrm{O}}_2/\mathrm{Si}$ base exhibits the highest thermal switching efficiency (with a value of 3.6) and the largest modulation amplitude (60 W/${\mathrm{m}}^2$), while the ${\mathrm{VO}}_2$ on r-sapphire base yields the highest amplification factor of 126. These record figures of merit underscore the critical role of the ${\mathrm{VO}}_2$ substrate selection and demonstrate the potential of radiative thermal transistors for advanced thermal management applications.

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• Caloritronics
• Heat radiation
• Heat transfer
• Metal-insulator transition
• Phase-change materials
• Devices for digital logic, storage & processing
• Transistors
• Transition metal oxides