Exploring surface properties and premelting in crystals

Author(s)

Tipeev, Azat O. ; Gurashkin, Alexander L. ; Zanotto, Edgar D.

• Document type: Journal article
• Source: Journal of Chemical Physics; v. 160, n. 22, p. 12-pg., 2024-06-14.

Abstract

Crystal surfaces play a pivotal role in governing various significant processes, such as adsorption, nucleation, wetting, friction, and wear. A fundamental property that influences these processes is the surface free energy, gamma. We have directly calculated gamma(T) for low-index faces of Lennard-Jones (LJ), germanium, and silicon crystals along their sublimation lines using the computational cleavage technique. Our calculations agree well with experimental values for Si(111) and Ge(111), highlighting the accuracy of the method and models used. For LJ crystals, we identified a premelting onset at T-pm = 0.75T(m), marked by a sharp increase in atom mobility within the second outermost surface layer. Notably, T-pm closely aligned with the endpoint of the LJ melting line at negative pressures, T-end = 0.76T(m). We hypothesize that the emergence and coexistence of a liquid film atop the LJ crystal at T-pm < T < T-m correspond to the metastable melting line under negative pressures experienced by stretched crystal surfaces. Furthermore, our study of thin LJ crystal slabs reveals that premelting-induced failure leads to recrystallization below the homogeneous freezing limit, offering a promising avenue to explore crystal nucleation and growth at extremely deep supercoolings. Finally, no evidence of premelting was detected in the model crystals of Ge and Si, which is consistent with the experimental observations. Overall, our findings offer valuable insights into crystal surface phenomena at the atomic scale. (AU)

• FAPESP's process: 22/05837-5 - Crystal growth dynamics in supercooled liquids probed by molecular dynamics
• Grantee: Azat Tipeev
• Support Opportunities: Scholarships in Brazil - Post-Doctoral
• FAPESP's process: 13/07793-6 - CEPIV - Center for Teaching, Research and Innovation in Glass
• Grantee: Edgar Dutra Zanotto
• Support Opportunities: Research Grants - Research, Innovation and Dissemination Centers - RIDC