[1] Univ Birmingham, Dept Mech Engn, Birmingham B15 2TT, W Midlands, England
[2] Rutherford Appleton Lab, Cent Microstruct Facil, Didcot OX11 0QX, Oxon, England
[3] Kings Coll London, Dept Phys, London WC2R 2LS, England
[4] Damascus Univ, Dept Design & Prod Engn, Damascus, Syria