Regner K T, Majumdar S, Malen J A
Department of Mechanical Engineering, Carnegie Mellon University, Pittsburgh, Pennsylvania 15213, USA.
Rev Sci Instrum. 2013 Jun;84(6):064901. doi: 10.1063/1.4808055.
This paper describes the instrumentation for broadband frequency domain thermoreflectance (BB-FDTR), a novel, continuous wave laser technique for measuring the thermal conductivity accumulation function. The thermal conductivity accumulation function describes cumulative contributions to the bulk thermal conductivity of a material from energy carriers with different mean free paths. It can be used to map reductions in thermal conductivity in nano-devices, which arise when the dimensions of the device are commensurate to the mean free path of energy carriers. BB-FDTR uses high frequency surface temperature modulation to generate non-diffusive phonon transport realized through a reduction in the perceived thermal conductivity. By controlling the modulation frequency it is possible to reconstruct the thermal conductivity accumulation function. A unique heterodyning technique is used to down-convert the signal, therein improving our signal to noise ratio and enabling results over a broader range of modulation frequencies (200 kHz-200 MHz) and hence mean free paths.
本文描述了用于宽带频域热反射（BB-FDTR）的仪器，这是一种用于测量热导率累积函数的新型连续波激光技术。热导率累积函数描述了具有不同平均自由程的能量载体对材料体热导率的累积贡献。它可用于绘制纳米器件中热导率的降低情况，当器件尺寸与能量载体的平均自由程相当时，就会出现这种情况。BB-FDTR利用高频表面温度调制来产生通过降低感知热导率实现的非扩散声子输运。通过控制调制频率，可以重建热导率累积函数。一种独特的外差技术用于对信号进行下变频，从而提高我们的信噪比，并能在更宽的调制频率范围（200 kHz - 200 MHz）以及因此更宽的平均自由程范围内获得结果。
