Improved Graphene Blisters by Ultrahigh Pressure Sealing

Thermal dynamics of few-layer-graphene seals

Being of atomic thickness, graphene is the thinnest imaginable membrane. While graphene's basal plane is highly impermeable at the molecular level, the impermeability is, in practice, compromised by leakage pathways located at the graphene-substrate interface. Here, we provide a kinetic analysis of such interface-mediated leakage by probing gas trapped in graphene-sealed SiO2 cavities versus time and temperature using electron energy loss spectroscopy. The results show that gas leakage exhibits an Arrhenius-type temperature dependency with apparent activation energies between 0.2 and 0.7 eV. Surprisingly, the interface leak rate can be improved by several orders of magnitude by thermal processing, which alters the kinetic parameters of the temperature dependency. The present study thus provides fundamental insight into the leakage mechanism while simultaneously demonstrating thermal processing as a generic approach for tightening graphene-based-seals with applications within chemistry and biology.

Determining the interlayer shearing in twisted bilayer MoS2 by nanoindentation

The rise of twistronics has increased the attention of the community to the twist-angle-dependent properties of two-dimensional van der Waals integrated architectures. Clarification of the relationship between twist angles and interlayer mechanical interactions is important in benefiting the design of two-dimensional twisted structures. However, current mechanical methods have critical limitations in quantitatively probing the twist-angle dependence of two-dimensional interlayer interactions in monolayer limits. Here we report a nanoindentation-based technique and a shearing-boundary model to determine the interlayer mechanical interactions of twisted bilayer MoS₂. Both in-plane elastic moduli and interlayer shear stress are found to be independent of the twist angle, which is attributed to the long-range interaction of intermolecular van der Waals forces that homogenously spread over the interfaces of MoS₂. Our work provides a universal approach to determining the interlayer shear stress and deepens the understanding of twist-angle-dependent behaviours of two-dimensional layered materials.

The study of the mechanical properties of twisted van der Waals structures can provide important information about their interlayer coupling and electronic behaviour. Here, the authors report a nanoindentation-based technique to determine the interlayer shear stress in bilayer MoS2, showing its independence as a function of the twist angle.

Self-Sealing Complex Oxide Resonators

Although 2D materials hold great potential for next-generation pressure sensors, recent studies revealed that gases permeate along the membrane-surface interface, necessitating additional sealing procedures. In this work, we demonstrate the use of free-standing complex oxides as self-sealing membranes that allow the reference cavity beneath to be sealed by a simple anneal. To test the hermeticity, we study the gas permeation time constants in nanomechanical resonators made from SrRuO₃ and SrTiO₃ membranes suspended over SiO₂/Si cavities which show an improvement up to 4 orders of magnitude in the permeation time constant after annealing the devices. Similar devices fabricated on Si₃N₄/Si do not show such improvements, suggesting that the adhesion increase over SiO₂ is mediated by oxygen bonds that are formed at the SiO₂/complex oxide interface during the self-sealing anneal. Picosecond ultrasonics measurements confirm the improvement in the adhesion by 70% after annealing.