In 2010, Konstantin Novoselov and Andre Geim of The University of Manchester received the Nobel Prize in physics for pioneering experiments related to the two-dimensional (2D) material graphene.
Since then, there has been a significant interest in graphene and other 2D materials. Exfoliated flakes continue to remain the gold standard for low-defect graphene; however, this has only been used as a research tool. As a result, efforts have been made to find a feasible processing technique for graphene over a large area.
Chemical Vapour Deposition
Figure 1. Raman spectrum of graphene grown from nickel foil in OIPT Nanofab Agile tool
The most popular technique has been the growth of monolayer or multi-layer graphene from a metal foil using a Chemical Vapour Deposition (CVD) process.
In this process, a nickel or copper sheet is heated to up to 10000oC and exposed to a hydrocarbon gas. After the metal is cooled, carbon appears on the surface from the supersaturated solid solution. Significant efforts were made to manipulate the graphene’s grain size by controlling the grain size of the substrate metal. Graphene obtained through this process had to be transferred by dissolving the metal substrate and then transferring to the target substrate, which is a complicated process.
Nanofab Agile Tool
It has been shown that Oxford Instruments’ Nanofab Agile tool can be employed for the growth of graphene and other related materials. This tool can be used to perform CVD and PECVD processes. In the CVD process, a tool modified for higher temperature operation is used; copper or nickel foils were reduced in-situ with hydrogen plasma prior to exposing to hydrocarbon gas. The Raman spectrum (Figure 1) shows the presence of graphene via the sharp 'G' peak and '2D' peak.
Figure 2. Raman spectra of NCG on thermally grown SiOy sapphire and quartz glass
For plasma-based process, studies were performed in collaboration with Dr. Harold Chong at Southampton University to determine whether graphene and related materials can be developed at lower temperature directly on the substrate without a metal catalyst.
Study results were presented in Graphene 2012 and 2013 conferences. At temperatures less than 1000°C, layers were created with considerable amounts of graphene with an extremely small grain size. Such materials are called 'nanocrystalline graphene (NCG)'. Figure 2 shows the Raman spectra from 900°C material on different substrates.
Figure 3. Cross-sectional SEM image of vertical carbon nanosheets, scale bar is 200 nm5
Figure 3 shows another type of graphene-like material, a high density of vertical carbon plates, which has been dubbed 'carbon nanosheets'. This material is made in IMEC via a plasma-based process on a Nanofab tool from Oxford Instruments.
Oxford Instruments’ plasma technology offers a viable processing method for graphene and related materials. The Nanofab Agile tool, with the capability for both CVD and PECVD processes, proves suitable for growing these 2D materials.
This information has been sourced, reviewed and adapted from materials provided by Oxford Instruments Plasma Technology.
For more information on this source, please visit Oxford Instruments Plasma Technology.