Universal thermodynamic framework for quasi-van der Waals epitaxy

TL;DR

This paper develops a comprehensive thermodynamic framework to explain and predict the orientation locking phenomena in van der Waals epitaxy, integrating electrostatic, chemical, and entropic interactions.

Contribution

It introduces a unified quantitative model with new descriptors to accurately predict epitaxial orientation locking in 2D-3D systems, resolving longstanding inconsistencies.

Findings

The framework accurately predicts interface interactions and growth modes.

It characterizes conditions for free versus locked epitaxy.

The model aligns well with diverse experimental data.

Abstract

van der Waals (vdW) epitaxy is conventionally regarded as a rotation-free and strain-free growth mode driven by weak, isotropic interactions, yet many interfaces paradoxically exhibit strictly locked orientations that defy standard surface-energy models. We resolve this inconsistency by establishing a unified quantitative framework for 2D-3D systems, in which strong electrostatic and chemical interactions compete with entropic forces. We introduce a two-tier descriptor set-the predictive index (I_pre) and the thermodynamic locking criterion (I_lock)-to quantify the energetic sufficiency for locked epitaxy. Our theory accurately predicted the competitive interactions at the interface within the 2D-3D system, precisely characterized whether the epitaxial layer underwent free growth or was constrained in a locked growth mode, demonstrating robust consistency with diverse experimental observations. This framework unifies orientation selection in 3D-on-2D films and rotational locking in 2D-on-3D layers within a single-phase diagram. Our work provides a generalizable, predictive route to controlling epitaxial orientation across a broad spectrum of layered heterostructure