Excellence in Research: First Principles Defect Engineering of Plasmonic Diluted Magnetic Semiconducting Oxide Nanocrystals

Florida Agricultural And Mechanical University, Tallahassee FL

Investigators

Abstract

Non-technical Summary This HBCU-UP award supports theoretical and computational research to simulate and predict novel quantum dots on the one hand and to develop a multidisciplinary computational physics program within the Department of Physics on the other. Quantum dots have been termed artificial atoms or molecules depending on their size and composition. They range in size from 1 – 100 nm in diameter and in numbers of atoms from hundreds to tens of thousands. While the composition and properties of atoms are predetermined by nature, the properties of artificial atoms or molecules can be manipulated by varying their size and composition. Myriad opportunities exist to create novel nanostructures, and this makes quantum dots a rich system for investigating fundamental physics as well as for technological applications. The project seeks to merge two different kinds of quantum dots, namely plasmonic quantum dots and diluted magnetic quantum dots. Plasmonic materials are based on collective motions of electrons in solids known as plasmons. These materials had been studied mostly on the macroscopic scale with classical electromagnetism theory until recently. A new property of plasmons known as localized surface plasmons was discovered on the surface of quantum dots a decade ago. The existing approach of classical physics has to be replaced with quantum mechanics in order to understand the emergent phenomena. But developing a new theory for a finite system such as a quantum dot requires computational methodology, since the finiteness breaks the translational symmetry often invoked to solve problems for periodic systems. The PI will apply quantum-mechanical as well as semi-classical computational techniques to study a range of plasmonic quantum dots. These dots are expected to have application in photonics and optoelectronics. On a separate track, the project will investigate the plasmonic materials for the onset of ferromagnetism when doped with a dilute amount of magnetic ions. These materials are of interest in their own right for applications to prospective quantum computers and spintronics at large. Eventually, the two tracks will be combined to see the possibility of a multifunctional novel material. The award will support the establishment of a computational physics program. The PI will work with computational physicists and computer scientists to offer courses modelled after a similar program at the Texas Advanced Computing Center (TACC). TACC resources will be used to train the students on high-performance computing platforms. During their senior year, the students will work on research problems. The course offerings and training are expected to prepare the students for jobs in high tech industry or to continue their research and computational experience into graduate school. In addition, the award will support a graduate student. The PI will be involved in outreach programs to community colleges and high schools to increase the number of students in the computational physics program. Technical Summary This proposal aims to design multifunctional semiconducting oxide quantum dots by co-doping them with magnetic and non-magnetic dopants. The project will have three thrusts: 1) Semiconducting nanoplasmonic oxides: First-principles calculations with density functional theory and the kinetic Monte Carlo technique will be performed to develop new physical models that could address i) the effect of band-to-band transitions, ii) localization of carriers, iii) ligand and proximal effects, iv) quantum confinement effects for small-sized quantum dots, and v) fewer carriers than those of noble metal nanocrystals that are well described by the Drude-Lorentz model. 2) Semiconducting oxide quantum dots doped with TMs: The evolution of ferromagnetism in semiconducting oxides is controversial in general because of the large number of competing parameters involved in the synthesis. A detailed study of the electronic and magnetic structures of transition-metal-doped semiconducting oxide quantum dots throughout a wide parameter space which covers the incorporation of varying amounts of dopant impurities, vacancies, and crystalline defects such as interstitials will be conducted. 3) Plasmonic diluted magnetic semiconducting oxide quantum dots: After steps 1) and 2) have been undertaken, the combined system will be studied. The nanoplasmonic oxides will be doped with dilute amounts of transition metal atoms and the diluted magnetic oxide quantum dots with non-magnetic donors. Electronic and magnetic structures of the combined system will be compared to results from 1) and 2). The research will involve a graduate student and introduction of undergraduates to research protocols. In tandem with the research, a computational physics track will be launched that will train undergraduate students in scientific supercomputing. The computational physics program is expected to increase the number of physics majors. The PI will be also involved in outreach programs to community colleges and high schools. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.