SUBJECT: Ph.D. Dissertation Defense
   
BY: Sampath Kommandur
   
TIME: Monday, March 4, 2019, 3:00 p.m.
   
PLACE: MRDC Building, 4211
   
TITLE: Applications of Thermophysical Characterization Using the 3-Omega Technique
   
COMMITTEE: Dr. Shannon Yee, Chair (ME)
Dr. Andrei Fedorov (ME)
Dr. Michael Filler (CHBE)
Dr. Peter Hesketh (ME)
Dr. Zhuomin Zhang (ME)
 

SUMMARY

The 3-omega technique is an electrothermal technique to characterize thermal conductivity. While frequently used to characterize isotropic thin films on substrates, the high accuracy and versatility of the technique can be extended to a broader application space. This dissertation will focus on exploring a few selected applications of thermophysical characterization. 3-omega excels in measuring low thermal conductivities (<1 W/m-K) with high accuracy, making it a prime choice for characterizing gases and amorphous polymers. Using experiments on gas mixtures, a gas sensing technique has been developed that can determine binary mixture concentrations based on their thermophysical properties. This has been demonstrated using two sensor geometries with sensitivities comparable to other electrothermal techniques, but with a lower power consumption. Using experimental data, an empirical model is proposed to aid in predicting temperature-dependent thermal conductivity of amorphous polymers. The model is based on kinetic theory and accounts for the different vibrational modes in polymers, and depends on only the density, monomer molecular weight, and speed of sound. The model’s predictions were then validated using the 3-omega measurements across a range of temperatures. Two variants of the 3-omega technique to characterize anisotropic thermal conductivity in polymer films and nanowires are explored. A suspended film configuration to measure anisotropic thermal conductivity of polymers is presented along with the experimental guidelines for the validity of a simplified heat transfer model for data analysis. This method is then used to determine the anisotropic thermal conductivity of common semiconducting polymers and recently developed n-type organic thermoelectric materials. Finally, a suspended microbridge configuration to measure temperature-dependent thermal conductivity in axially modulated nanowires with repeated doped and undoped segments with the doped segments etched to varying degrees. Measurements are performed using a modified 3-omega method with data analysis performed using an effective thermal circuit. The effect of diameter modulation on thermal conductivity is experimentally determined.