**7. Overview of carbon nanotubes (CNTS)**

With its discovery in 1991, CNTS are carbon tubes (nanometer diameters range) also termed as "bucky-tubes", are significant contribution in technological nanosciences. CNTS are distinguished in "multi-walled CNTs (MW-CNT)" and "single-walled CNTS (SW-CNT), respectively. CNTS are synthesized using thermal decomposition, catalytic growth, and arc-ablation, respectively. Structure of graphite (crystalline) need to be well understood to visualize single walled carbon nanotubes. As graphite contains stacked-layers of hexagonally-arranged C-atoms with sp2 -configuration. Owing to inter-molecular forces, stcking layer give us single layer which is graphene. Single nanotube consist of C-atoms (millions) but thickness of tube is ~1 atom which may prove benefucial from technological perspective. The structures of SW-CNTS and MW-CNTS are shown in the **Figure 3**.
