Quantum Interfaces of Dissimilar Materials

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Nontechnical description: This project is focused on investigating new quantum material properties that are provoked when two materials with dissimilar properties, such as, semiconductor and ferroelectric materials, are coupled together. One may expect to find the resulting material properties to be the sum of the properties of each material. However, this situation changes when the layers of each material are only a few atoms thick, creating a quantum interface material. For example, whereas short-range bonding between atoms dominates the material properties of semiconductors, in ferroelectrics the bonding between atoms is predominantly long-range. Combining the two materials at one interface creates a hybrid bonding that forms exciting new quantum material functionalities. The polarization in the ferroelectric oxide allows tuning and controlling the semiconductor electronic and optical properties for smaller and faster electronics. Likewise, mobile charges in the semiconductor is exploited to affect the polarization in the ferroelectric, creating the opportunity for smaller and faster memory storage devices. Basically, the interface is a "new quantum material" that creates new intriguing possibilities to investigate quantum effects, such as the fractional quantum Hall effect, as well as the manipulation of electrons, control of electrical current flow, electron spin, and the material interaction with light. These are the fundamental ingredients for novel scientific and technological opportunities for new discoveries and exciting new products in electronics and photonics. This research provides opportunities to graduate and undergraduate students who bring their excitement to regional middle school classrooms and public places, i.e. Arkansas Shopping Mall, to stimulate inquiry into science education. Recognizing the need for women and minorities in science, recruitment for students is at the annual National Black and Hispanic National meeting and Materials Research Society (MRS) meetings.Technical description: The project is investigating the properties of semiconductor-transition metal oxide quantum interfaces at the monolayer scale. The challenge arises mostly because of the difficulty of epitaxial growth with the disparity of structural properties and lattice parameters. This challenge, however, has proven to be very much ideal for the progress made in layer-by-layer growth by molecular beam epitaxy, with in-situ characterization capability for atomic-scale scanning tunneling microscopy and spectroscopy, and piezoelectric force microscopy, and is the approach taken in this proposal. For example, the research team is growing monolayers of: GaAs (001), InGaAs (001) and GaAsP (001) on BaTiO3 (110) and BiFeO3 (110) grown on SrTiO3 (110), to produce transition metal-semiconductor quantum interfaces. For analysis, the team is using scanning tunneling and piezoelectric force microscopy for morphology and spectroscopy to provide real-time data, by providing interactive feedback, needed to understand the interface from single monolayers to 10-20 nm thicknesses. For the interface between dissimilar materials, the team is evaluating the effects of the local density of states, polarization screening, surface reconstruction, electric and magnetic field coupling, bonding between sp-electrons and d-electrons, fractional quantum Hall effect, localization of charge, and lattice match, mismatch and strain on the interface electronic and photonic properties. As a more high-risk exciting opportunity the team is using high quality semiconductor/transition metal oxide and transition metal oxide/semiconductor interfaces, to stack interfaces, to form a superlattice of quantum interfaces with novel properties.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.