Silicene synthesis beyond graphene: a critical review of methods, stability challenges, and scalable pathways

Silicene, a buckled honeycomb-lattice allotrope of two-dimensional (2D) silicon, has attracted strong interest as a candidate for post-silicon electronics, owing largely to its compatibility with existing silicon-based fabrication methods and its theoretically predicted massless Dirac fermions. However, the material suffers from three persistent obstacles that prevent its device-level deployment. First, a naturally layered silicon parent crystal does not exist, which makes top-down exfoliation fundamentally difficult. Second, silicene is rapidly oxidised in air and moisture, which limits its ambient handling. Third, no current synthesis route has been able to deliver scalable production, defect-controlled layers, and preservation of the intrinsic electronic structure simultaneously. The main objective of this review is to compare, within a unified framework, the four widely investigated silicene synthesis routes: electrochemical exfoliation, epitaxial growth on metallic substrates, plasma-enhanced chemical vapour deposition (PECVD), and Zintl phase topotactic deintercalation, against three application-driven criteria, namely scalability, ambient stability, and electronic fidelity. The lithiation delithiation electrochemical route is found to produce few-layer nanosheets of approximately 2.4 nm thickness under ambient conditions, yet the dimensional control is poor, and the product degrades almost instantly in air. The epitaxial growth on Ag(111) is found to provide the highest crystallographic precision; however, the Dirac cone is suppressed by the strong silicene Ag hybridisation, whereas the Au(111) substrate is shown by simulation to preserve the cone with reduced buckling. The PECVD route is found to yield hydrogenated silicene with measurable oxidation resistance, as confirmed by X-ray photoelectron spectroscopy (XPS), but the method demands tight control over multiple deposition parameters and requires a mandatory Al₂O₃ capping layer. The Zintl phase route is found to produce multilayer silicene flakes up to 100 µm in lateral extent, and the recent vacuum-nitrogen-assisted synthesis (VANS) variant dramatically reduces the reaction time from five days to the order of minutes, while operating at room temperature and preserving the structural properties of the conventional product. From the above comparison, it is concluded that no single method satisfies all three criteria concurrently. A hybrid pathway, in which VANS grown silicene is encapsulated by PECVD-derived Al₂O₃ capping, is therefore proposed as a promising near-term route toward scalable and air-stable silicene.