原子层沉积封装石墨烯p-n结，用于柔性和透明的可穿戴温度传感器

摘要：随着可穿戴设备需求的增加，温度感应能力成为柔性透明应用的一项基本功能。尤其是在日常生活中使用时，设备的长期稳定性是非常重要的。本文，韩国成均馆大学Ji Won Suk等研究人员在《Journal of Materials Science & Technolog

1成果简介

随着可穿戴设备需求的增加，温度感应能力成为柔性透明应用的一项基本功能。尤其是在日常生活中使用时，设备的长期稳定性是非常重要的。本文，韩国成均馆大学Ji Won Suk等研究人员在《Journal of Materials Science & Technology》期刊发表名为“Highly air stable graphene p–n junctions encapsulated by atomic layer deposition for flexible and transparent wearable temperature sensors”的论文，研究通过使用封装了极薄金属氧化物层的一原子厚单层石墨烯，开发出了一种具有显著空气稳定性的柔性透明自供电温度传感器。

石墨烯热电偶是通过在置于透明聚合物薄膜上的高质量单层石墨烯上诱导p型和n型掺杂而制成的。整个石墨烯薄膜都经过调制氧等离子体处理，从而诱导了石墨烯上缺陷最小的p型掺杂。石墨烯的一半涂上聚乙烯亚胺，形成n型石墨烯。利用原子层沉积（ALD）技术，用14纳米厚的超薄 Al2O3封装了石墨烯p-n结。石墨烯热电偶的塞贝克系数高达81.6±2.4 μV/K，线性度高（确定系数为 0.999），响应速度快（时间常数为0.59秒），热滞后小，工作温度范围宽。由于采用了 ALD-Al2O3层，石墨烯热电偶具有优异的空气稳定性，其塞贝克系数可保持1028天。此外，石墨烯热电偶的极薄特性使其在 550 纳米波长下的光学透射率高达 94.8%，临界弯曲半径小至 5.71 毫米。

2图文导读

图1. (a) Schematic of a flexible and transparent thermocouple using a graphene p–n junction. (b) SEM image of monolayer graphene transferred onto SiO2. (c) Raman spectra of PG and NG films. (d) I2D/IG versus G peak position of graphene samples. (e) Schematic of a graphene-based back-gated FET. (f) Current–voltage transfer characteristics of graphene FETs. (g) Optical transmittance. (h-j) AFM topography images and line profiles of (h) NG-0.1, (i) NG-0.5, and (j) NG-2.5 films.

图2. (a) Schematic of EMF measurements of doped graphene films coupled with copper. (b) EMF changes of PG and NG films. (c-e) EMF changes and thermal hysteresis of graphene p–n junctions coated with various PEI concentrations: (c) NG-0.1, (d) NG-0.5, and (e) NG-2.5.

图3. Characteristics of Al2O3-encapsulated PG and NG-0.1 films. (a, b) Schematics of Al2O3 deposition on (a) PG and (b) NG films. (c, e) SEM images of (c) PG and (e) NG-0.1 films encapsulated with Al2O3. (d, f) AFM images of (d) PG and (f) NG-0.1 films encapsulated with Al2O3. (g, h) XPS Al 2p spectra of (g) PG and (h) NG-0.1 films encapsulated with Al2O3. (i, j) XPS O 1s spectra of (i) PG and (j) NG-0.1 films encapsulated with Al2O3. (k) Current–voltage transfer characteristics of FETs using Al2O3-encapsulated PG and NG-0.1. (l) Changes in the Dirac point voltage of FETs using NG-0.1 over time in air before and after Al2O3 encapsulation.

图4. Graphene thermocouple encapsulated with ultrathin Al2O3. (a) EMF changes of the graphene thermocouple consisting of PG and NG-0.1 with Al2O3 encapsulation. (b) Changes in the Seebeck coefficients of the graphene thermocouples with or without encapsulation over time in air. (c) Optical transmittances of the Al2O3-encapsulated PG and NG-0.1. The inset shows a digital photograph of the encapsulated graphene thermocouple attached to a smartwatch. (d) Comparison of the absolute Seebeck coefficients and optical transmittances of various thermoelectric materials. The numbers shown in brackets are reference numbers. (e) Estimation of the time constant from the EMF response of the graphene thermocouple under repeated contact with a heat source.

图5. Repeatability and flexibility of Al2O3-encapsulated graphene thermocouples. (a) EMF responses of the graphene thermocouple during cyclic heating and cooling. (b) Magnified EMF response of the graphene thermocouple shown in the purple box in (a). (c) Results of repeated EMF measurements after bending at a bending radius of 5.71 mm. (d) Comparison of the absolute Seebeck coefficients and critical bending radii of various thermoelectric devices. The numbers shown in brackets are reference numbers.

3小结

利用石墨烯 p-n 结和超薄Al2O3制成了高柔性和透明的热电偶。在 CVD 生长的单层石墨烯上进行调制氧等离子处理后，通过部分涂覆薄 PEI 来实现 p-n 结。表面化学掺杂层使用通过ALD工艺镀上的14纳米厚的 Al2O3 进行保护，这使得它与化学掺杂的石墨烯具有很高的兼容性，从而抑制了 p-n 结热电特性的退化。因此，单层石墨烯与 ALD-Al2O3 的结合不仅造就了一种具有高灵敏度、高线性度、快速响应、低热滞后和宽工作温度范围的高性能热电偶，还使其具有出色的空气稳定性，能在 1028 d 内保持其塞贝克系数。此外，考虑到石墨烯/Al2O3 复合材料的超薄结构，该热电偶具有 94.8% 的高光学透明度和高柔性。这项研究开创了一种制造具有长期稳定性的高性能温度传感器的方法，为开发可应用于可穿戴电子设备和显示器的柔性透明温度传感器提供了另一种策略。

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