Jul 13, 2011
Thin crystals suspended across specialized electrodes
A gentle, versatile method to produce freestanding thin crystals has been developed by researchers at the University of California Riverside, US. The technique can be applied to the vast majority of substrate, crystal and electrode materials, which should open the door to a better understanding of various phenomena such as electron-phonon coupling, transport of supercurrent or spin currents, and actuation of and dissipation in ultra-small electromechanical systems.
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.
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.
About the author
The study was a result of a collaboration between Prof. Jeanie Lau's and Prof. Jing Shi's groups, at the University of California Riverside. Jairo Velasco Jr is a PhD student in the Lau group and developed the multilevel lithography technique used to suspend the thin crystals. He has worked extensively on three-dimensional nanostructures of various materials throughout his studies. Zheng Zhao and Hang Zhang are PhD students in the Lau group and aided with sample fabrication and transport measurement. The BiSe samples were synthesized by Zhiyong Wang, a PhD student in Prof. Jing Shi's group.