We demonstrate workings of a near-field thermal rectification device that uses phase change material to achieve asymmetry in heat transfer. We exploit the temperature dependent dielectric properties of VO2 due metal-insulator transition near 341 K. The device operates near the critical temperature of the phase change material. Analogous to an electrical diode, heat transfer coefficient is very high in one direction (forward bias) while it is very small when the polarity of temperature gradient is reversed (reverse bias). Rectification as high as 15 can be obtained for minimal temperature difference of 5 K. We show that high rectification is achieved by using 1-D triangular and rectangular surface gratings. The rectification factor is dramatically enhanced in the near-field due to the spectral mismatch between dissimilar materials for the negative polarity.

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