Freestanding 2D Glasses by Atomic Layer Deposition

Atomic layer deposition (ALD) is notable for highly controlled syntheses of ultrathin materials through self-limiting reactions. However, ALD materials have strong bonding interactions with substrates, which have generally made substrate removal for the preparation of freestanding large-area 2D films challenging. Here, we report a strategy for the fabrication of freestanding, amorphous ultrathin films by growing on single-crystal NaCl. NaCl surfaces, typically poor substrates, are improved by inserting hydroxyl groups across the surface. This heterogeneous surface forms bonding and nonbonding interactions with ALD materials, allowing us to grow amorphous ultrathin alumina and titania on the surface and remove the films with minimal damage. We show that this tailored substrate can be removed under mild conditions and that the ultrathin material can be transferred to an arbitrary substrate with assistance from a poly(methyl methacrylate) scaffold. This simple process results in materials that span 1 cm² and have few cracks and pinholes. This strategy provides easy access to an expansive class of freestanding 2D glasses that have previously been challenging targets of fabrication at this scale.