Abstract. Raman scattering is used to study the temperature-driven structural transformations of bundled single-walled carbon nanotubes (SWCNTs) observed in HiPCO and ARC synthesis by electron microscopy, i.e., tube–tube coalescence 1300–1400 oC, coalesced tubes to multi-walled tubes (MWCNT) at 1600–1800 oC and finally (only ARC tubes) MWCNT to graphitic nanoribbons (GNRs) at 18…