Van der Waals devices for surface-sensitive experiments

TL;DR

This paper introduces a resist-free, stencil lithography method for fabricating van der Waals devices that preserves pristine surfaces, enabling advanced surface-sensitive experiments like photoemission spectroscopy.

Contribution

The authors develop a novel resist-free fabrication technique using stencil lithography and exfoliation in ultra-high vacuum for vdW devices, maintaining surface integrity for sensitive measurements.

Findings

Successful fabrication of vdW devices with clean surfaces

Reliable electrical contacts for transport measurements

Compatibility with surface-sensitive spectroscopic techniques

Abstract

In-operando characterization of van der Waals (vdW) devices using surface-sensitive methods provides critical insights into phase transitions and correlated electronic states. Yet, integrating vdW materials in functional devices while maintaining pristine surfaces is a key challenge for combined transport and surface-sensitive experiments. Conventional lithographic techniques introduce surface contamination, limiting the applicability of state-of-the-art spectroscopic probes. We present a stencil lithography-based approach for fabricating vdW devices, producing micron-scale electrical contacts, and exfoliation in ultra-high vacuum. The resist-free patterning method utilizes a shadow mask to define electrical contacts and yields thin flakes down to the single-layer regime via gold-assisted exfoliation. As a demonstration, we fabricate devices from 1$T-$TaS$_2$ flakes, achieving reliable contacts for application of electrical pulses and resistance measurements, as well as clean surfaces allowing for angle-resolved photoemission spectroscopy. The approach provides a platform for studying the electronic properties of vdW systems with surface-sensitive probes in well-defined device geometries.