Silicon-based thermoelectric nanosystems

直接安装在废气回流(EGR)冷却器中的热电(TE)发电机可以帮助收集大量日常废热的一部分。它们必须承受高达500°C左右的恒定和循环温度负载，这是Bi2Te3基TE材料无法满足的，只有硅才能实现。然而，由于体硅具有较高的热导率，因此具有较低的优值系数(ZT~0.01)。在第一个资助期，我们发现通过将硅图案化成直径约200 nm的纳米线，再加上粗糙的纳米棒表面，在保守的塞贝克系数和电阻率假设下，热导率显著降低，对应于ZT~0.14。计划在第二个资助期进一步降低热导率，从而提高实际采集设备所需的效率(10%至20%)，这将通过以下方式实现：1)通过进一步将纳米线直径减小到100 nm或通过增加内表面(硅纳米管)来提高表面体积比从而提高声子表面散射，2)设计纳米线表面以实现更有效的声子粗糙度散射，3)将多层结构集成到硅纳米线(Si/SiGe，Si/SiOx，28Si/29Si)中，以利用异质界面、边界和同位素对声子散射的影响。

Thermoelectric (TE) generators directly mounted into the exhaust gas return (EGR) cooler can help to harvest a portion of the huge amount of day-to-day wasted heat. They have to endure constant and cycling temperature loading up to around 500°C, which cannot be fulfilled by Bi2Te3 -based TE material but by silicon. Bulk silicon, however, has a low figure of merit (ZT ~ 0.01) owing to high thermal conductivity. In the first funding period we found that by patterning silicon into nanowires of ~ 200 nm in diameter in combination with a rough nanorod surface thermal conductivity was strongly reduced corresponding to ZT ~ 0.14 at conservative assumptions for the Seebeck coefficient and the resistivity. Further reduction of thermal conductivity and thus improvement towards ZT > 1 resulting in efficiencies necessary for a practical harvesting device (10 to 20 %) is planned for the second funding period which shall be achieved by 1) enhancing the surface-to-volume ratio and thus phonon surface scattering via further reducing the nanowire diameter to < 100 nm or by adding an inner surface (Si nanotube), 2) engineering the nanowire surface for more efficient phonon roughness scattering, 3) integration of multilayer structures into silicon nanowires (Si/SiGe, Si/SiOx, 28Si/29Si) to exploit the effect of heterointerfaces, boundaries, alloys and isotopes on phonon scattering.