Optically driven thermodynamic transition from free- to locked-epitaxy

TL;DR

This paper demonstrates that external light irradiation can dynamically induce a transition from free- to locked-epitaxy in quasi-vdW materials by enhancing interfacial chemical affinity, enabling programmable control over epitaxial states.

Contribution

It introduces a novel optical method to control epitaxial orientation transitions by modulating interfacial thermodynamics in quasi-vdW systems.

Findings

Light irradiation induces epitaxial transition in Fe4N/mica.

Photo-excited carriers enhance interfacial chemical affinity.

Transition from vdW-dominated to chemically locked epitaxy observed.

Abstract

Controlling crystallographic orientation in quasi-van der Waals (vdW) epitaxy remains a fundamental challenge, especially for material systems located near the boundary between weakly and strongly coupled growth regimes. In such marginal systems, epitaxial selection is governed by a delicate thermodynamic competition between surface-energy penalties and interfacial interaction gains, giving rise to two archetypal limits: vdW-dominated free-epitaxy and strong interfacial coupling dominated locked-epitaxy. However, dynamically driving transitions between these regimes has remained elusive. Here, we demonstrate that external light irradiation can deterministically induce such a transition. Using the thermodynamically frustrated Fe4N/mica interface as a model system, we show that photo-excited carriers act as a chemical potentiator, significantly enhancing the interfacial chemical affinity. Within a quantitative thermodynamic description, this optical modulation increases the locking criterion (I_lock)-defined as the ratio of interfacial energy gain to surface-energy cost-beyond its critical threshold. As a result, the system switches from vdW-dominated free-epitaxy with (001) orientation to chemically locked-epitaxy with (111) orientation. Our findings establish light as a non-invasive and switchable control knob to dynamically reconfigure the interfacial energy landscape in quasi-vdW epitaxy, enabling programmable access to distinct epitaxial states beyond intrinsic material limitations.