In the previous post, I made a prediction that a Space Elevator tether created from multi-layered single crystal graphene would look metallic and probably mirror-like.
A graphene manufacturer has been in touch. They are one of the few companies in the world that can make polycrystalline sheet graphene and layer it up. They told me that as they increase the number of layers of their graphene it looks to them progressively black, not mirror like.
So, we have a tale of two tethers, will a graphene tether look metallic and mirror-like or will it look black?
I will admit to disappointment contemplating this empirical observation from industry experts. But then I dived back into the literature to find out more…
A colleague at the International Space Elevator Consortium (ISEC) pointed me in the direction of a paper from 2010 that I had not seen . This observed the optical reflection and transmission properties of graphite from a graphene monolayer to several hundred graphene layers. They focussed their attention on a 35-layer sample.
This work is one of very few that is based on experimental data. The team from McGill University in Montreal, Canada, isolated 35 layers of graphene from graphite. This is a very small-scale representation of what multilayer single crystal graphene will look like in reflected visible light.
The team found that the multilayer graphene reflected light across the visible part of the spectrum with a tendency towards the blue end of the spectrum. This means that the bulk material such as the tether will have a silvery metallic appearance with a slight bluish hue.
Then another colleague made me aware of a discovery by the Manitoba Mineral Society in Canada. The society has identified an unlabelled exhibit in a Canadian museum as an exceptional example of graphite crystals ten to fifteen centimetres in scale.
If this discovery is confirmed by Raman spectroscopy, you are looking at a material that contains the largest crystals of graphite ever found. This will be a very good guide to the appearance of a tether made from multilayer single crystal graphene.
So, we have a tale of two tethers. On the one hand we have information telling us that multilayer graphene will be black. On the other, we have alternative evidence showing it will be metallic silvery, possibly with a blue tint.
Neither pieces of evidence are definitive at present. However, I’ll stay with my original prediction that the space elevator tether will be silvery, metallic and mirror-like.
Time will tell which is correct.
 Skulason, H., Gaskell, P. and Szkopek, T., 2010. Optical reflection and transmission properties of exfoliated graphite from a graphene monolayer to several hundred graphene layers. Nanotechnology, 21(29), p.295709.
 File:Kimmirut Graphite.jpg – Wikimedia Commons
https://commons.wikimedia.org/wiki/File:Kimmirut_Graphite.jpg [accessed 20th January 2021]
This post originally appeared as a newsletter entry for the International Space Elevator Consortium (ISEC) and can be accessed at the following link: