Thermal hysteresis measurement of the VO2 emissivity and its application in thermal rectification
Thermal hysteresis measurement of the VO2 emissivity and its application in thermal rectification
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DOI：
10.1038/s41598-018-26687-9
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发表时间：
2018-05-31
影响因子：
4.6
通讯作者：
Joulain, K.
中科院分区：
文献类型：
--
作者：
Gomez-Heredia, C. L.;Ramirez-Rincon, J. A.;Joulain, K.
用热波谐振腔技术测量了脉冲激光沉积在蓝宝石和硅衬底上生长的VO2薄膜发射率的磁滞回线。在绝缘体到金属和金属到绝缘体的转变过程中，观察到两种VO2薄膜的发射率都有大约43%的显著变化。结果表明：1)VO2+硅样品的VO2发射率的主滞回宽度(最大斜率)比相应的VO2+蓝宝石样品高(低)约3倍。因此，由于硅衬底和蓝宝石衬底对VO2薄膜微结构的显著不同，在硅衬底上合成的VO2表现出比在蓝宝石上合成的VO2更宽的主磁滞回线，MIT慢于蓝宝石衬底上的VO2。Ii)VO2+衬底样品中的磁滞宽度以及VO2发射率的变化率可以通过其二次磁滞回线进行调节。Iii)VO2样品可以用来制作辐射热二极管，当其两端的温差在17摄氏度左右时，其整流系数可高达87%。这种破纪录的整流是文献中报道的最高整流，因为二极管端子的温度变化相对较小。
Hysteresis loops in the emissivity of VO2 thin films grown on sapphire and silicon substrates by a pulsed laser deposition process are experimentally measured through the thermal-wave resonant cavity technique. Remarkable variations of about 43% are observed in the emissivity of both VO2 films, within their insulator-to-metal and metal-to-insulator transitions. It is shown that: i) The principal hysteresis width (maximum slope) in the VO2 emissivity of the VO2 + silicon sample is around 3 times higher (lower) than the corresponding one of the VO2 + sapphire sample. VO2 synthesized on silicon thus exhibits a wider principal hysteresis loop with slower MIT than VO2 on sapphire, as a result of the significant differences on the VO2 film microstructures induced by the silicon or sapphire substrates. ii) The hysteresis width along with the rate of change of the VO2 emissivity in a VO2 + substrate sample can be tuned with its secondary hysteresis loop. iii) VO2 samples can be used to build a radiative thermal diode able to operate with a rectification factor as high as 87%, when the temperature difference of its two terminals is around 17 degrees C. This record-breaking rectification constitutes the highest one reported in literature, for a relatively small temperature change of diode terminals.