b'Accelerating pathwaysThe synthesis and computation of complex heterostructures provides to actinide materialsa new route for understanding actinide material systems.discovery throughT he lack of capabilities to rapidly fabricate, test, and screen actinides has stifled design and innovation in this critical family of nuclear materials. combinatorial deposition Developing pathways that enable key transport propertiesmass and energyin this family to be pre-selected prior to fabrication would constitute a major innovation in nuclear material science. This research focused on the generation of a complete science basissynthesis, characterization, and computationfor the study of lanthanide thin film surrogates and superlattice heterostructures that function as a platform for the investigation of actinides. PROJECT NUMBER:High-mobility transistor two-dimensional electron gas structures consisting of an 21A1050-052FP indium arsenide (InAs) quantum well surrounded by gallium antimonide (GaSb) TOTAL APPROVED AMOUNT:barriers were synthesized. An interfacial misfit technique was employed whereby $1,078,606 over 3 years an array of in-plane 90 misfit dislocations relieves the large compressive strain at the GaSb/gallium arsenide (GaAs)(001) interface. X-ray diffraction measurements PRINCIPAL INVESTIGATOR:showed that the GaSb films had excellent crystalline quality with almost complete Brelon May strain relaxation and rocking curve peak full width half maxima of less than 300 arc CO-INVESTIGATORS:sec. Next, an adapted interfacial misfit technique developed for the (001) surface Cody Dennett, INL was used on GaAs(111)A substrates. In general, growth on (111) is more challenging David Hurley, INL than (001) surfaces due to a reduction in the group V sticking coefficient and the Jackson Harter, INL propensity for pyramidal defect formation. Surprisingly, an even better rocking curve Krzysztof Gofryk, INL full width half maximum of 125 arc sec was observed, but the surface roughness Narayan Poudel, INL was significantly worse. To the best of our knowledge, this was the first time that Shuxiang Zhou, INL interfacial misfit arrays were successfully demonstrated for (111) interfaces. Alex Greaney, University of California, Riverside Transport properties and phonon and electron scattering properties for cerium Ashutosh Tiwari, University of Utah dioxide, aluminum gallium arsenide, GaSb, and uranium diboride were computed. Paul Simmonds, Boise State University andThe electron and phonon dispersion over the full band structure were calculated Tufts University along with corresponding intrinsic scattering rates. These were then collapsed into a COLLABORATORS: reduced set of transport groups that included the whole phonon spectrafrequency, Columbia University density of states, group velocity, relaxation timefor use in the Boltzmann National Institute of Standardstransport equation simulations. A theoretical framework was developed for doing and Technologies the group reduction of the per q-point phonon properties by using appropriate weighted averages of properties over the Brillouin zone and partitioning the transport distribution into groups with different mean free paths. The partitioning between group boundaries was selected such that each group provides a similar contribution to the total thermal conductivity. A reduced order model for representing the thermal conductivity suppression function across the full phonon spectrum in nanostructured materials was also developed. This provides new understanding for how the thermal conductivity in these semiconductor alloys varies with composition, particularly the rapid and nonlinear conductivity changes at dilute concentration. 30'