MoS2 has more to offer than its intrinsic band gap and 2D nature. It also provides a platform for manipulating spin and valley degrees of freedom. This is due to its large spin-orbit coupling and the two valleys having oppositely spin-split bands. However, most devices to date are fabricated on SiO2 substrates and suffer from low carrier mobility. Until this report from researchers at the University of California, Riverside (UCR), the intrinsic properties free from the influence of the substrate were yet to be explored.

Free-standing devices

Here, MoS2 devices become fully free-standing after release from the underlying SiO2 substrate by wet etching. A unique double-layer metal deposition method ensures good electrical contacts while protecting the device from the acidic solution during wet etching. The researchers treat the as-fabricated devices with flowing argon and hydrogen mixture gases at 200°C for 40 minutes. They then observe a dramatic improvement in the device conductance and mobility.

Identifying the bottleneck

By performing electronic transport on these suspended devices, the researchers conclude that the substrate is not the mobility bottleneck for MoS2 devices. Instead, the culprits are likely the defects and/or Schottky barriers at the metal-MoS2 interfaces. These suspended MoS2 devices with reasonably high mobility constitute a powerful platform for investigating properties and applications of MoS2 that are best performed in the absence of substrates. For example, thermal expansion, thermal conductivity, strain engineering, nanomechanical resonators and chemical and biological sensors.

More information about this research can be found in the journal Nanotechnology 26 105709.

Further reading

Multilayer molybdenum disulfide undergoes metallic transition under strain (Nov 2014)
Layered semiconductors: thickness changes conductivity (Sept 2014)
Putting a twist in molybdenum diselenide (Aug 2014)
Tweaking the magnetism of molybdenum sulphide nanoribbons (Mar 2014)