Unconventional Heteroanion Ceramics: 2D Layered Seleno- and Thio-Phosphates

Northwestern University, Evanston IL

Investigators

Abstract

NON-TECHNICAL DESCRIPTION: The performance of silicon-based architecture is now approaching fundamental limits governed by physics. Thus, there is a critical need for new materials and novel structures that may follow the meteoritic growth of conventional silicon microelectronic technology of the past few decades. In this context, new scientific opportunities are presented by emerging two-dimensional (2D) materials, especially those whose composition can be tailored and optimized. Ever since the discovery of graphene, a single 2D layer of carbon atoms, which was the subject of Physics Nobel prize a decade ago, other 2D layered structures are being pursued worldwide. This research focuses on a new class of 2D layered materials, called chalcophosphates where phosphorous, sulphur and analogous elements are arranged in an intricate planar mosaic pattern. This research develops and explores metal chalcophosphates as a new class of ceramic materials for their magnetic, ferroelectric, and coupled properties, with unusual quantum behavior. This unique combination of non-linear phenomena provide rich opportunities to advance science of ceramics, and creates a potential platform for new generation of magneto-electronic devices. This emerging research field is likely to generate new technology industries and require workforce with extensive hands-on expertise in novel multicomponent ceramic materials and their characterization. As a result, research activities are integrated with educational and societal outreach initiatives, anchored by the unique platform for 2D layered ceramic materials. The other broader impact goals include training of undergraduate and graduate students in advanced materials research and incorporation of research results into course and curricula. Through an innovative "Materials-Journalism" program, Medill school journalism students immerse to witness the scientific process and report their findings in their journalism blogs and reports. Conversely, the research team members learn journalism practices of story-telling and how to synthesize complex scientific undertaking into meaningful discourse with the public. Collectively, the research advances scientific insights with prospects for technology breakthroughs in the new class of 2D ceramics, with educational opportunities for graduate and undergraduate students, and societal outreach through the journalism initiative. TECHNICAL DETAILS: This research revolves around synthesis and advanced characterization of 2D layered metal chalcophosphates (MCP), i.e. thiophosphates and selenophosphates, as a new and novel class of 2D layered ceramic systems. Anchored on a variety of possible chemical combinations, especially with heteroanions, the synthesized structures are readily amenable to extensive multimodal characterization methods to map their complex structural characteristics in conjunction with their linear and non-linear properties. Of specific interest are single- and few layered 2D structures to explore the role of spatial and dimensional constraints. This goal is accomplished by classical mechanical exfoliation as well as vapor-based deposition methods developed in the laboratory. Also, this project investigates the nature and extent of coupling between ferroelectric and ferromagnetic properties, especially in the few- and single layers. The primarily focus is on magnetic M2P2Q6 (M= Cr, Mn, Fe, Co, Ni, Q=S, Se) and ferroelectric/ferromagnetic AMP2Q6 (A=Ag,Cu, M=In,Ga,Cr,Mn,Fe,Gd). A diverse yet integrated multimodal techniques and characterization methods are employed to unravel the complex labyrinth of microstructure across multiple length-scales. Advanced scanning and transmission electron microscopy techniques probe the local structure, phases, chemical partitioning, and related phenomena. Theoretical work conducted in close connection with the experimental efforts examines the bulk properties of materials and analyzes the meso and nano-scale phenomena in heterostrucure architectures of thio- and selenophosphates and its interaction with substrates. The scientific insights governed by unusual combination of heteroanion systems with spatial and dimensional constraints are expected to display unusual linear and non-linear ferroelectric and ferromagnetic as well as coupled properties and phenomena. 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.