[1] Univ Exeter, Coll Engn Math & Phys Sci, Stocker Rd, Exeter EX4 4QL, Devon, England
[2] Univ Durham, Dept Engn, South Rd, Durham DH1 3LE, England
[3] Natl Phys Lab, Teddington TW11 0LW, Middx, England
[4] Bruker Nano Surfaces UK, Coventry CV4 9GH, W Midlands, England