On-Device Pressure-Tunable Moving Schottky Contacts.

Contact engineering enhances electronic device performance and functions but often involves costly, inconvenient fabrication and material replacement processes. We develop an in situ, reversible, full-device-scale approach to reconfigurable 2D van der Waals contacts. Ideal p-type Schottky contacts free from surface dangling bonds and Fermi-level pinning are constructed at structurally superlubric graphite-MoS2 interfaces. Pressure control is introduced, beyond a threshold of which tunneling across the contact can be activated and amplified at higher loads. Record-high figures of merits such an ideality factor nearing 1 and an off-state current of 10-11 A were reported. The concept of on-device moving contacts is demonstrated through a wearless Schottky generator, operating with an optimized overall efficiency of 50% in converting weak, random external stimuli into electricity. The device combines generator and pressure-sensor functions, achieving a high current density of 31 A/m2 and withstanding over 120,000 cycles, making it ideal for neuromorphic computing and mechanosensing applications.

Vertical strain engineering of Van der Waals heterostructures.

Van der Waals materials and their interfaces play critical roles in defining electrical contacts for nanoelectronics and developing vehicles for mechanoelectrical energy conversion. In this work, we propose a vertical strain engineering approach by enforcing pressure across the heterostructures. First-principles calculations show that the in-plane band structures of 2D materials such as graphene, h-BN, and MoS2as well as the electronic coupling at their contacts can be significantly modified. For the graphene/h-BN contact, a band gap in graphene is opened, while at the graphene/MoS2interface, the band gap of MoS2and the Schottky barrier height at contact diminish. Changes and transitions in the nature of contacts are attributed to localized orbital coupling and analyzed through the redistribution of charge densities, the crystal orbital Hamilton population, and electron localization, which yield consistent measures. These findings offer key insights into the understanding of interfacial interaction between 2D materials as well as the efficiency of electronic transport and energy conversion processes.

Robust structural superlubricity under gigapascal pressures.

Structural superlubricity (SSL) is a state of contact with no wear and ultralow friction. SSL has been characterized at contact with van der Waals (vdW) layered materials, while its stability under extreme loading conditions has not been assessed. By designing both self-mated and non-self-mated vdW contacts with materials chosen for their high strengths, we report outstanding robustness of SSL under very high pressures in experiments. The incommensurate self-mated vdW contact between graphite interfaces can maintain the state of SSL under a pressure no lower than 9.45 GPa, and the non-self-mated vdW contact between a tungsten tip and graphite substrate remains stable up to 3.74 GPa. Beyond this critical pressure, wear is activated, signaling the breakdown of vdW contacts and SSL. This unexpectedly strong pressure-resistance and wear-free feature of SSL breaks down the picture of progressive wear. Atomistic simulations show that lattice destruction at the vdW contact by pressure-assisted bonding triggers wear through shear-induced tearing of the single-atomic layers. The correlation between the breakdown pressure and material properties shows that the bulk modulus and the first ionization energy are the most relevant factors, indicating the combined structural and electronic effects. Impressively, the breakdown pressures defined by the SSL interface could even exceed the strength of materials in contact, demonstrating the robustness of SSL. These findings offer a fundamental understanding of wear at the vdW contacts and guide the design of SSL-enabled applications.