Thin crystals (for example, graphene, Bi2Se3 and Bi2Te3) extracted from bulk layered materials have recently become researchers' favorite toys in the lab. These thin crystals, when freestanding, offer fascinating platforms to achieve ultrahigh mobility, study the transport of Cooper pairs or spins, or to make tiny, atomically thin electromechanical resonators.

Traditionally, these freestanding structures are prepared by acid etching the supporting oxide substrate beneath the thin crystal, but this limits the choice of membrane and electrode materials.

Multilevel lithography

Now, scientists at the University of California Riverside, US, have overcome this challenge with a new multilevel lithography technique. By exploiting the different exposure and developing parameters of several types of electron beam resists, the team was able to fabricate electrodes that "hold up" thin crystals like a suspension bridge.

Using this procedure, the group has suspended Bi2Se3 – a topological insulator – across metal electrodes. Topological insulators, which are insulating in the bulk, but allow the movement of charges on the surface, are of great interest because they are predicted to host dazzling physical phenomena such as spintronics (spin related electronics) and majorana fermions (a particle that is its own antiparticle) that could lead to robust quantum computing.

A freestanding topological insulator device paves the way for high-quality samples that might one day realize these predictions.

The researchers presented their work in the journal Nanotechnology.