Thermal, Magnetic, and Electrical Properties of Thin Films and Nanostructures: From Magnetic Insulators to Organic Thermoelectrics

<p>Modern fabrication and growth techniques allow for the development of increasingly smaller and more complex solid state structures, the characterization of which require highly specialized measurement platforms. In this dissertation I present the development of techniques and instrumentation used in magnetic, thermal, and electrical property measurements of thin films and nanostructures. The understanding of trapped-flux induced artifacts in SQUID magnetometry of large paramagnetic substrates allows for the resolution of increasingly small moments. Using these methods, the antiferromagnetic coupling of the interface between a Y₃Fe₅O₁₂ film and Gd₃Ga₅O₁₂substrate is quantitatively characterized, along with a number of other thin films. The use of custom fabricated silicon-nitride membrane thermal isolation platforms for temperature-dependent measurements is then presented for in-plane thermal conductivity, electrical conductivity, and thermopower of thin films. The size- and temperature-dependent properties of two types of semiconducting single-walled carbon nanotube thin films deposited and measured on these platforms reveal differing phonon contributions to thermal conductivity, and the interaction of dopant molecules and phonon transport in the disordered nanotube networks is explored. Experimental techniques for studying freestanding nanotube films is then presented, revealing a largely phonon-driven thermal conductivity that is greatly decreased by the introduction of phonon scattering sites. Next, time-dependent measurements on the suspended micromachined platforms was developed to allow for thermal detection of tiny depositions of energy from chemical reactions or physical processes in nanoscale systems. These experiments show our platforms have promise for open-chamber calorimetry of viral detection, and were expanded to include heat capacity into our suite of precision in-situ thermal measurements. Finally, copper thin films fabricated for heat capacity calibration are characterized and show a sharp reduction in thermal conductivity that ’violates’ the Wiedemann-Franz law.</p>

Name thesis:degree_name

Ph.D.

Level thesis:degree_level

Dissertation

Year

2023

Author dc:creator

• Roos, Michael J. M.

Contributors dc:contributor

• Barry L. Zink
• Brian W. Michel
• Mark E. Siemens
• Davor Balzar

• Carbon nanotube
• Characterization
• Magnetic materials
• Magnetism
• Microcalorimetry
• Wiedemann-Franz violation
• Condensed Matter Physics
• Materials Science and Engineering
• Physical Sciences and Mathematics
• Physics
• Semiconductor and Optical Materials

Statement dc:rights

• <p>Copyright is held by the author. User is responsible for all copyright compliance.</p>

Language dc:language

English (eng)

Repository record dc:identifier

https://digitalcommons.du.edu/etd/2322

OAI identifier oai:identifier

oai:digitalcommons.du.edu:etd-3307