Stabilizing van der Waals NbOI2 by SiO2 encapsulation for Photonic Applications

TL;DR

This paper demonstrates that SiO2 encapsulation effectively stabilizes NbOI2, a promising nonlinear photonic material, preserving its structure and optical properties under ambient conditions for practical applications.

Contribution

It introduces a SiO2 encapsulation method to prevent environmental degradation of NbOI2, enabling its stable use in photonic and quantum technologies.

Findings

Encapsulation preserves NbOI2's structural integrity.

Nonlinear optical performance remains stable after encapsulation.

NbOI2 becomes viable for integrated photonic applications.

Abstract

Niobium oxide diiodide (NbOI2) is an emerging material for photonics and electronics, distinguished by its exceptional second-order nonlinearity and pronounced in-plane ferroelectricity, both originating from its highly anisotropic ABC-stacked crystal structure. Its broken inversion symmetry enables its optical nonlinear efficiency to scale with thickness, making multilayer NbOI2 highly promising for nonlinear frequency conversion like second harmonic generation or and spontaneous parametric down-conversion in bulk or waveguides. However, under ambient conditions NbOI2 degrades into an amorphous oxide within weeks, severely diminishing its nonlinear response. To overcome this, we investigate SiO2 encapsulation via physical vapor deposition to protect NbOI2 multilayers from environmental degradation. Our systematic study reveals that encapsulation preserves structural integrity and nonlinear optical performance, establishing NbOI2 as a stable candidate for heterogeneous integration in foundry-compatible photonic platforms and quantum technologies.