Ultra-High Resolution Steady-State Micro-Thermometry Using a Bipolar Direct Current Reversal Technique

The suspended micro-thermometry technique is one of the most prominent methods for probing the in-plane thermal conductance of low dimensional materials (nanowires, nanotubes, and nanoplates), where a suspended mircrodevice containing two built-in platinum resistors that serve as both heater and thermometer is used to measure the temperature and heat flow across the sample. In previous lock-in-based measurement schemes, the thermal conductance resolution of this method is on the order of 1 nW/K. The presence temperature fluctuations in the sample chamber, background thermal conductance through the device, residual gases, and radiation are significant sources of error when the sample thermal conductance is comparable or smaller than the background thermal conductance, on the order of 300 pW/K at room temperature. In this thesis, a high resolution and high throughput thermal conductance measurement scheme is presented in which a bipolar direct current reversal technique is adopted to replace the lock-in technique. This scheme benefits from a bipolar direct current (DC) reversal measurement which is a well-established technique to remove offset and low frequency noises during measurement, and involves less instrumentation and simple data analysis. This modern DC reversal technique exhibits less than one half the amount of white noise and an order of magnitude lower 1/f noise than the most commonly used lock-in amplifiers. Over a temperature range of 30–375 K, we demonstrate a temperature resolution of 0.97–2.62 mK and a thermal conductance resolution of 2–26 pW/K. The background conductance of the suspended microdevice is determined accurately by this method and allows for straightforward isolation of this source of error. This simple and high-throughput measurement technique will allow for more accurate and effective investigation of fundamental phonon transport mechanisms in individual nanomaterials.