Non-van der Waals superlattices of carbides and carbonitrides.

Abstract

Artificial superlattices, constructed from atomic layers such as graphene using layer-by-layer periodic stacking or sequential epitaxial growth, have emerged as a versatile platform for developing new materials with properties surpassing the existing materials^1-3. However, the explored superlattices are predominantly van der Waals (vdW) superlattices, constrained by weak interface coupling^4,5. Here we present an efficient synthetic protocol that achieves a family of non-vdW superlattices of carbides and carbonitrides, featuring hydrogen bonding between layers through a stiffness-mediated rolling-up strategy. The crucial step involves customizing the bending stiffness of the atomic layers derived from MAX phases by creating metal vacancies in MX slabs, triggering their ordered rolling-up under rapid flexural deformation. Unlike vdW superlattices, our non-vdW superlattices with hydrogen bonding afford robust interlayer electronic coupling with highly concentrated charge carriers (10²² cm^-3). Consequently, our superlattices exhibit a notable electrical conductivity of about 30,000 S cm^-1, which is around 22 times that of the counterparts. When used in electromagnetic interference shielding, the optimal non-vdW superlattice film demonstrates a remarkable shielding effectiveness of 124 dB, surpassing that of any known synthetic materials with comparable thickness. The non-vdW superlattices are anticipated to markedly broaden the material platform, offering variable compositions and crystal structures for new developments in artificially stacked systems.