Super-Planckian Radiative Heat Transfer between Macroscale Surfaces with Vacuum Gaps Down to 190 nm Directly Created by SU-8 Posts and Characterized by Capacitance Method

Abstract

In this work we experimentally demonstrated the near-field thermal radiation enhancement over the blackbody limit by 11 times between highly doped silicon chips with 1×1 cm 2 size at a vacuum gap distance of 190±20 nm under a temperature difference of 74.7 K above room temperature. SU-8 polymer posts, which significantly reduced the conduction less than 6% of the total heat transfer due to its low thermal conductivity, were carefully fabricated with different heights to directly create vacuum gaps from 507±47 nm down to 190±20 nm precisely determined in-situ by capacitance measurement. Experimental results were validated by theoretical calculations based on fluctuational electrodynamics, which revealed the enhancement mechanism mainly as coupled surface plasmon polariton. The experimental method developed here will facilitate the potential applications of near-field radiative devices made of electrically conductive materials like metals, graphene, and transparent conductive oxide besides heavily doped semiconductors for thermal energy conversion, radiative thermal rectification, and radiative heat modulation.

Radiative heat transfer at the nanoscale: experimental trends and challenges

“…2 can be associated with various applications. Large-area experiments [46][47][48][49][50][51][52][53][54][55][56][57][58] address in particular the requirements for near-field thermophotovoltaic (TPV) conversion 44,[59][60][61][62] , where infrared (IR) energy emitted by a hot body is converted into electrical energy by a dedicated IR photovoltaic cell 63 . High-temperature thermal sources are expected to be used for energy harvesting.…”

“…However, scaling up laboratory proofs of concept system sizes 71 must chiefly address the challenge of building nanoscale gaps between macroscale planes with sufficiently large temperature differences, for example by using thermally low-conducting but mechanically stable spacers up to high temperature. Spacers made of polystyrene beads 48,51 , pillars in SU-8 photoresist 56 or silica 49 , or suspended devices 72,73 were used, leading to fixed distances for many current large-area experiments. Currently best gaps are of the order of few tens of nanometers for these experiments, with a recent claim of having reached the sub-10 nm region 74 with piezoelectric alignment.…”

Thermophotovoltaic energy conversion in far-to-near-field transition regime

“…Because the doped-Si emitter and the thin Au layer of the PV cell are designed to serve as capacitive electrodes in parallel, we can estimate the main vacuum gap distance (i.e., described as d in Fig. 1b) between the emitter and the PV cell by measuring the capacitance [17,[19][20][21]. In addition, three doped-Si sub-capacitive electrodes (sub1, sub2, and sub3) are symmetrically fabricated around the emitter to obtain three additional vacuum gap distances between each sub-capacitive electrode and the Ag/Cr electrode of the PV cell.…”

Design of a calorimeter for near-field heat transfer measurements and thermal scanning probe microscopy

“…4 This effect, in which the heat flux increases rapidly with diminishing separations and exceeds the black-body limit due to near-field effects, has since then been observed and quantified by several research groups. The measurement systems employed for this measurement can be roughly classified into three archetypes: (1) two closely spaced parallel plates in which one plate is kept at a constant temperature, while the temperature of the other is measured as a function of their separation; [5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24] (2) a miniature thermocouple scanning over a surface in which the temperature of the tip is measured as a function of separation; 25-31 and (3) a thermo-mechanical probe scanning over a surface in which the deformation of the probe is used to determine the probe temperature or the heat flux. [32][33][34][35][36][37] Closely spaced parallel plates are ideal to mimic the conditions described in theoretical work and can be used to study applications such as thermophotovoltaics and photonic cooling.…”