Date of Award
Doctor of Philosophy
Materials Science and Engineering
David Mandrus Dr.
David G. Mandrus Dr., Veerle M. Keppens Dr., Philip D. Rack Dr., Thomas Z. Ward Dr.
Moore’s Law, stating that the number of transistors that can fit on an integrated circuit should double every two years, stood strong for more than 50 years, but is now rapidly reaching its limits. In order to keep up with the need for ever-increasing computer power, focus is shifting towards new materials and technologies. Following the discovery of stable, atomically-thin graphene sheets in 2004, many materials composed of layered sheets have been (re)discovered with great potential to become the “new silicon”, including hexagonal boron nitride (h-BN), metal halides such as RuCl3, or metal chalcogenides MoS2 and CrGeTe3. With the variety of compositions also comes a multitude of different material properties: from materials exhibiting a metal-insulator transition, to thermoelectrics, and even magnetic semiconductors.
The layers in these materials are considered quasi two-dimensional (2D), as they are just atoms thick and weakly bonded together. Although graphene does not have the required bandgap for transistor applications, with the discovery of a suitable material, devices could be made from an atomically thin layer. However, because the field of single layer materials is so new, there are many materials that have not been completely characterized, leaving their full potential for new applications still unknown.
One particular category of 2D materials that is promising but has much left to be explored is the family of MXY3 magnetic semiconductors, with M = Cr, Mn, Fe, Co, Ni; X = P, Si, Ge; and Y = S, Se, Te, along with CrPS4. While much is known about the materials’ magnetic and electronic behavior, thermal conductivity has only been partially characterized for CrGeTe3 and CrSiTe3. To better understand the behavior of this class of materials, single crystals of each material have been synthesized, characterized, and their in-plane thermal conductivity temperature dependence measured. By measuring one property across an entire class of vi materials, behavioral trends can be more easily analyzed and understood and perhaps applied to future layered materials. At the same time, important intrinsic material properties are being provided, which will be useful for future applications of these materials.
Haglund, Amanda, "Thermal Conductivity of MXY3 Magnetic Layered Trichalcogenides. " PhD diss., University of Tennessee, 2019.