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Nanometer-Scale Thermal, Optical, and Mechanical Properties Using Atomic Force Microscopy: Transistors, Carbon Nanotubes, and Polymers

This work presents atomic force microscope (AFM)-based measurements of nanometer-scale thermal, optical, and mechanical behavior. The first part of this work describes the use of AFM to measure transient thermomechanical deformation in operating AlGaN/GaN high electron mobility transistors. We found that drain-source voltage has a strong effect on thermomechanical expansion, with higher drain-source voltage leading to lower thermomechanical deformation, especially above the gate. An electro-thermo-mechanical finite element model closely matches with and helps to explain the measurements. As drain-source voltage increases, the device hotspot moves away from the gate, leading to lower gate temperature rise and lower tensile thermal stress, which has important consequences for device degradation. The second part of this work presents photothermal induced resonance (PTIR) measurements of single walled carbon nanotubes with diameters < 3 nm. In PTIR, an AFM tip measures nanometer-scale thermomechanical expansion induced by an infrared laser, which is proportional to local infrared absorption. This technique has typically been limited to samples which have large thermomechanical expansion, such as polymer layers or relatively thick (100's of nm) metal and semiconducting structures. In this work, we achieved up to two orders of magnitude improvement in PTIR sensitivity by placing a thin layer of polymer beneath the sample which serves as a thermomechanical amplifier. This advancement enables measurement of new types of materials with PTIR. The final part of this work presents measurements of nanometer-scale mechanical properties using contact resonance AFM (CR-AFM). In CR-AFM, the resonance frequency of an AFM cantilever in contact with a sample depends on the mechanical properties of the sample. This work describes a novel approach to CR-AFM, which uses a calibration sample with a large range of known contact stiffness over which the cantilever can be calibrated. A combination of experiments and finite element modeling validates the calibration sample. We present mechanical property measurements of several polymers using this calibration approach.

For further information please contact andrea.centrone [at] (Andrea Centrone), 301-975-8225

Matt Rosenberger

University of Illinois, Urbana Champaign

Created May 12, 2016, Updated September 12, 2016