02-03-2021 | | By Sam Brown
Recently, a team of international researchers demonstrated how liquid gallium can protect delicate single-layer graphene sheets. What disadvantages do atom-thick layers provide, what did the researchers demonstrate, and how can it help future technologies?
Graphene is a single layer of carbon atoms arranged in a honeycomb structure that forms a sheet. The material has been touted as the wonder material that will transform the electronics industry due to its many superior properties when compared to traditional materials used to produce electronics.
As a material, graphene is the thinnest currently known to researchers and is also the strongest. The single atomic height of graphene also poses unusual quantum properties including a fixed resistance no matter its length. The playable material is ideal for separating gasses as a membrane, can be used to produce high-frequency transistors, and is a superior conductor of both electricity and heat.
Graphene was theorised, discovered, and is now used in some products. However, graphene used in products is disordered (i.e. used as a mix of sheets), and its true potential is barely touched. If electronics, for example, are to utilise the benefits of graphene the material needs to be producible as a singular large sheet that can be carefully manipulated and controlled.
Furthermore, even though graphene is the strongest known material, a single graphene layer is extremely fragile. Current manufacturing processes used to construct layered materials (such as those found in the semiconductor industry), can be too rough with graphene layers resulting in breakage.
Graphene layers are also vulnerable to high-energy particles (such as cosmic rays). If graphene layers are to be utilised in an electronic circuit then the graphene structure must handle such radiation as cosmic rays are commonplace in everyday life. Since graphene's quantum properties are dependent on the structure, designing a quantum system using graphene can be challenging due to its fragility.
Recently, a team of international researchers discovered a method for protecting graphene from damage while retaining its electrical and quantum properties. According to the researchers, graphene sheets can be protected with a layer of gallium oxide (Ga2O3), which increases the graphene sheet's robustness and therefore allows for operation in everyday environments.
The researchers first obtained a small drop of gallium to create the gallium armour and exposed the drop to the air. The oxidisation of gallium in air creates a 3nm thick gallium oxide glass layer, and the drop of liquid gallium was then placed onto of the graphene samples.
From there, a glass slide was used to compress and spread the liquid gallium with the result being the gallium oxide layer sticking to the graphene perfectly. The transfer of the gallium oxide layer to the graphene sheets can be done on centimetre scales making it an economical solution for the protection of graphene.
The gallium oxide layer is glass-like in nature, and has excellent optical transparency. As a result of this, the underlying graphene sheet is not optically impeded. The gallium oxide layer's use also improves the performance of graphene at cryogenic temperatures, and the gallium oxide layer also allows for the deposition of other layers without harming the graphene layer.
Graphene really is a superior material for creating electronic circuits. Still, the complex nature of producing graphene reliably and connecting materials to it is one of the many reasons why graphene electronics currently do not exist. Creating a single layer of graphene across a semiconductor is possible, but if layers cannot be added to the graphene then creating more than one switching device simultaneously is unlikely to happen.
The use of the gallium oxide armour will not only enable layering of other materials, but could potentially kickstart a whole semiconductor industry based on graphene. Transistors that can operate at significantly higher frequencies could see faster processors while the low resistance of graphene could help to create power-efficient devices.
Of course, this is still early days, and graphene is a material that is still being heavily researched. The next steps for researchers in graphene would be to determine how to create a wafer-scale graphene sheet, how to etch the material to create regions and patterns, and then how to create both P and N varieties of graphene (remember, graphene does not have a bandgap and thus does not have semiconductor properties).