CAREER: Van der Waals-mediated epitaxy of Heusler compounds through properties-selective, atomically thin barriers

University Of Wisconsin-Madison, Madison WI

Investigators

Abstract

Non-technical summary Modern electronics rely on precisely controlled interfaces between crystalline semiconducting materials. Achieving this remains a challenge. This project, supported by the Solid State and Materials Chemistry Program in the Division of Materials Research, researches fundamentally new ways to fabricate such interfaces of magnetic materials and control them at the smallest length scale possible (atomic resolution). Focusing on a class of materials called Heusler compounds, the project explores the mechanisms for single-crystalline growth on atomically thin barrier materials. Application of these materials in energy-efficient magnetic and thermoelectric devices is also tested. The research efforts are integrated with an after-school workshop for middle-school students. "From atoms to iPhone: the science of materials and their applications in everyday life." is a workshop that engages young students in materials science and engineering topics through the lens of a common application, the smartphone. The principle investigator and his group carry out work with the SCIENCountErs program at the Boys and Girls Club of Dane County on this. Technical summary This project is supported by the Solid State and Materials Chemistry Program in the Division of Materials Research and aims to uncover and develop fundamentally new ways to control the transmission of ions, charge, and spins across Heusler interfaces. Heusler compounds have long been proposed as ideal materials for semiconductor spintronics and a platform for discovery and manipulation of topological quantum states of matter. However, interdiffusion across the Heusler/semiconductor interface has inhibited these realizations, since atomically sharp and stable epitaxial interfaces are required. This project addresses these challenges through the use atomically thin barrier materials such as graphene, where the barrier material serves as (1) a diffusion barrier, (2) a transparent decoupling layer for epitaxial alignment between film and substrate, and (3) a tunnel barrier for efficient charge and spin transport across the interface. By pairing highly controlled Heusler synthesis by molecular beam epitaxy (MBE) with in-situ spectroscopic tools, model experiments are being used to reveal the mechanisms for Van der Waals-mediated epitaxy and develop methods for the atomically controlled fabrication of Heusler interfaces. Fundamental insights from the research component are integrated into real life demonstrations for the "Atoms to iPhone" workshop and integrated into undergraduate and graduate courses taught by the principle investigator. First hand research experiences for undergraduate and graduate students provide a training ground for careers in STEM and related fields. 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.