First transport measurements reveal intriguing properties of germanene

February 8, 2019, University of Groningen
Germanane is converted into germanene by thermal annealing, which removes the hydrogen (red). Credit: Ye Lab / University of Groningen

Germanene is a 2-D material derived from germanium and related to graphene. As it is not stable outside the vacuum chambers in which is it produced, no real measurements of its electronic properties have been made. Scientists led by Prof. Justin Ye of the University of Groningen have now produced devices with stable germanene. The material is an insulator, and it becomes a semiconductor after moderate heating and a very good metallic conductor after stronger heating. The results were published in the journal Nano Letters.

Materials of just one atomic layer are of interest in the construction of new types of microelectronics. The best known of these, graphene, is an excellent conductor. Materials like silicon and germanium could be interesting as well, as they are fully compatible with well-established protocols for , and could be seamlessly integrated into the present semiconductor technology.

"But the 2-D version of germanium, germanene, is very unstable," explains University of Groningen Associate Professor of Device Physics Justin Ye. Germanene is made from germanium by adding calcium. The create 2-D layers from a 3-D crystal and are then replaced by hydrogen. These 2-D layers of germanium and hydrogen are called germanane. But once the hydrogen is removed to form germanene, the material becomes unstable.

Ye and his colleagues solved this in a remarkably simple way. They made devices with the stable germanane, and then heated the material to remove the hydrogen. This resulted in stable devices with germanene, which allowed the scientists to study its .

Hydrogen

"The initial material was an insulator," says Ye. A Ph.D. student from his group heated these devices, which is a tried and tested method to increase conductivity. He noted that the material became very conductive, and its resistance was just one order of magnitude above that of graphene. "So it became an excellent metallic conductor." Further experiments showed that moderate heating (up to 200°C) produced semiconducting germanane.

Germanene can, therefore, be an insulator, a semiconductor or a metallic conductor, depending on the heat treatment with which it is processed. It remains stable after being cooled to room temperature. The heating causes multilayer flakes of germanene to become thinner—confirmation that the change in conductivity is most likely caused by the disappearance of hydrogen.

Germanene could be of interest in the construction of spintronic devices. These devices use a current of electron spins. This is a quantum mechanical property of electrons, which can best be imagined as electrons spinning around their own axis, causing them to behave like small compass needles. Graphene is an excellent conductor of electron spins, but it is hard to control spins in this material because of their with the ().

"The germanium atoms are heavier, which means there is a stronger spin-orbit coupling," says Ye. This would provide better control of spins. Being able to construct metallic germanene with both excellent conductivity and strong spin-orbit coupling should therefore pave the way to spintronic devices.

Explore further: Proper breeding ground for germanene

More information: Qihong Chen et al. Highly conductive metallic state and strong spin-orbit interaction in annealed germanane, Nano Letters (2019). DOI: 10.1021/acs.nanolett.8b04207

Related Stories

Proper breeding ground for germanene

June 22, 2016

Germanene is a one atom thick sheet of germanium, in a honeycomb structure. It has clear similarities with graphene, the material that induced massive research activity worldwide, especially after 2010's Nobel Prize.

Researchers developing 2-D materials similar to graphene

February 2, 2018

Chemists are working to synthesize the next generation of super materials for high-performance electronics, solar cells, photodetectors and quantum computers. While they have made progress with compound materials, they have ...

Magnetic graphene switches between insulator and conductor

February 1, 2019

Researchers have found that certain ultra-thin magnetic materials can switch from insulator to conductor under high pressure, a phenomenon that could be used in the development of next-generation electronics and memory storage ...

Recommended for you

Researchers make coldest quantum gas of molecules

February 21, 2019

JILA researchers have made a long-lived, record-cold gas of molecules that follow the wave patterns of quantum mechanics instead of the strictly particle nature of ordinary classical physics. The creation of this gas boosts ...

Sculpting stable structures in pure liquids

February 21, 2019

Oscillating flow and light pulses can be used to create reconfigurable architecture in liquid crystals. Materials scientists can carefully engineer concerted microfluidic flows and localized optothermal fields to achieve ...

0 comments

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.