2D materials, from novel electronics back to synthesis-kinetics and back to thermodynamic shape: how to define it when the edge-energy is undefinable?

Abstract: Theory and computational methods allow one to learn, explain, or predict about materials. An advent of two-dimensional (2D) crystals created a fertile ground, producing too much to be quickly reviewed even for just one class of TMD, transition metal dichalcogenides [1]. I briefly sample a few properties we have explored: light transmission-absorption-reflection, including the single photon emitting defects [2], Mott’s excitonic ground state in heterobilayers, electronic flat bands created by topography-undulation, spin split bands in Rashba effect in heterobilayers, and even robust spin-helix achieved by merely a wrinkle in 2D-sheet. We will then turn to the “road not (often) taken” by theory: how all those materials are synthesized, to a wafer-size and avoiding defects? In particular for TMD, what is the gas precursor, why adding simple salts enhance the 2D-layer growth, and how new understanding can guide synthesis improvements? Last topic goes even further back to Gibbs-time thermodynamics. How to predict the equilibrium shape of “difficult” low symmetry crystals, whose edge/surface energies are fundamentally undefinable (per John Cahn), obstructing the iconic Wulff construction utility. We will discuss how this conundrum can be resolved, by proceeding with auxiliary (arbitrary, even “fake”, so to speak) edge energies towards a constructive prediction, through well-planned computations, of a unique crystal shape. The method is illustrated by successful shape-prediction for challenging actual materials such as SnSe which is of C_2v symmetry, and even AgNO₂ of C₁, which has no symmetry at all.

[1] E.S. Penev, N. Marzari, B.I.Y., ACS Nano, 15, 5959-5976 (2021).

[2] S. Gupta, J.-J. Zhang, J. Lei, H. Yu, M. Liu, X. Zou & B.I.Y., Chemical Reviews, 125, 786-834, (2025).

[3] S. Gupta, W. Wu, S Huang, B.I.Y., J. Phys. Chem. Lett., 14, 3274-3284 (2023).

[4] L. Wang, S.N. Shirodkar, Zh. Zhang, B.I.Y., Nature Computational Science, 2, 729 (2022); “Predicting the shape of crystals with ‘unknowable’ surface energies”, B.I.Y., Nat. Comput. Sci. 2, 705 (2022).

Bio: Boris I. Yakobson is an expert in theory and computational modeling of materials and nanostructures, of synthesis, mechanics, defects, transport, electronics, optics. Presently, Karl F. Hasselmann Endowed Chair in Engineering, professor of Materials Science and Nano-Engineering, and professor of Chemistry, Rice University, Houston, Texas. Born in Moscow (USSR), raised in Odessa (Ukraine), obtained first BS/MS degrees in Novosibirsk (Russia), PhD 1982 in Physics and Applied Mathematics, from Russian Academy of Sciences. 1982-1989, Head of Theoretical Chemistry lab at the Institute of Solid Materials of the Russian Academy. 1990 in Columbia University, New York, Chemistry. 1990-1999, Research Professor, with tenure at the Department of Physics, North Carolina State University. Boris’ insights in nano-mechanics have set off a close collaboration with Richard Smalley (Nobel Laureate, 1996), and in 1999 Yakobson joined Rice’s School of Engineering. (One aspect of that early study is known in literature as “Yakobson Paradox”.) Over 500 papers, eight patents; mentor of many PhD students and postdoctoral associates.

All seminars are held on Wednesdays from 12:30 -1:30p.m. in the Bowen Hall Auditorium Room 222.   A light lunch is provided at 12:00p.m. in the Bowen Hall Atrium immediately prior to the seminar.