UC Berkeley

Mapping temperature with nanoscale spatial resolution is important for thermal transport studies and for device applications. Current state of the art techniques include scanning thermal microscopy, which requires physical contact, and optical thermoreflectance, which has diffraction limited spatial resolution. Scanning electron microscopy (SEM) is routinely used for topographic imaging due to the high spatial resolution and simple sample preparation, but the secondary electron signal has not been used as a temperature sensor.

In this work, the temperature dependence of SEM signals from a sample’s surface is investigated. The charge flowing through the SEM sample and the emitted secondary electron currents are measured at different temperatures to quantify the temperature dependence of secondary electron emission. I have measured several group III-V and IV semiconductors and have found 100s of ppm/K of thermal response coefficients. I have attempted to utilize the temperature coefficient to map temperature gradients in an SEM image by creating temperature profiles using a microfabricated structure and by implementing a double heater scheme. Technical challenges and practical limitations will require further future work on the effort of mapping temperature and demonstrating higher spatial resolution. This work generalizes the temperature response coefficient of secondary electron emission across various materials and investigates the challenges involved in mapping temperature. SEM thermometry is a novel means of measuring temperature and has the potential for high resolution temperature mapping which can open new research directions such as phonon mean free path spectroscopy.