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arXiv · 2603.09225

Optically driven thermodynamic transition from free- to locked-epitaxy

Renhong Liang·Mao Ye·Yiran Ying·Longlong Shu·Renkui Zheng·Haitao Huang·Jianhua Hao·Shuk-Yin Tong·Shanming Ke
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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.

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Renhong Liang, Mao Ye, Yiran Ying, Longlong Shu, Renkui Zheng, Haitao Huang, Jianhua Hao, Shuk-Yin Tong, Shanming Ke. 2026-03-10. Optically driven thermodynamic transition from free- to locked-epitaxy. https://arxiv.org/abs/2603.09225

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