In thermionic energy converters, the absolute efficiency can be increased up to 40% if space-charge losses are eliminated by using a sub-10-µm gap between the electrodes. One practical way to achieve such small gaps over large device areas is to use a stiff and thermally insulating spacer between the two electrodes. We report on the design, fabrication and characterization of thin-film alumina-based spacers that provided robust 3–8 μm gaps between planar substrates and had effective thermal conductivities less than those of aerogels. The spacers were fabricated on silicon molds and, after release, could be manually transferred onto any substrate. In large-scale compression testing, they sustained compressive stresses of 0.4–4 MPa without fracture. Experimentally, the thermal conductance was 10–30 mWcm⁻²K⁻¹ and, surprisingly, independent of film thickness (100–800 nm) and spacer height. To explain this independence, we developed a model that includes the pressure-dependent conductance of locally distributed asperities and sparse contact points throughout the spacer structure, indicating that only 0.1–0.5% of the spacer-electrode interface was conducting heat. Our spacers show remarkable functionality over multiple length scales, providing insulating micrometer gaps over centimeter areas using nanoscale films. These innovations can be applied to other technologies requiring high thermal resistance in small spaces, such as thermophotovoltaic converters, insulation for spacecraft and cryogenic devices.

在热离子能量转换器中，如果通过使用电极之间的亚 10 µm 间隙来消除空间电荷损失，则绝对效率可提高至 40%。在大器件面积上实现如此小的间隙的一种实用方法是在两个电极之间使用坚硬且绝热的间隔物。我们报告了基于薄膜氧化铝的间隔物的设计、制造和表征，这些间隔物在平面基板之间提供了 3-8 μm 的稳健间隙，并且其有效热导率低于气凝胶。垫片是在硅模具上制造的，释放后，可以手动转移到任何基板上。在大规模压缩测试中，它们承受了 0.4-4 MPa 的压缩应力而没有断裂。实验上，热导率为 10–30 mWcm ^-2 K^-1并且令人惊讶的是，与薄膜厚度（100-800 nm）和间隔高度无关。为了解释这种独立性，我们开发了一个模型，该模型包括整个间隔结构中局部分布的凹凸不平和稀疏接触点的压力相关电导，表明只有 0.1-0.5% 的间隔-电极界面在传导热量。我们的垫片在多个长度尺度上显示出卓越的功能，使用纳米级薄膜在厘米区域内提供绝缘微米间隙。这些创新可以应用于在小空间中需要高热阻的其他技术，例如热光伏转换器、航天器绝缘和低温设备。