Terahertz spectroscopy of nanocrystal-carbon nanotube and -graphene oxide hybrid nanostructures

We employed terahertz (THz) spectroscopy to study the optical/electrical properties of various nanocrystal (NC)-carbon nanotube (i.e., single-, double-, and multiwalled) and -graphene oxide (GO) hybrid nanostructures. The power absorption and conductivity decrease following the order single-walled (SWNT) > double-walled (DWNT) > multiwalled carbon nanotubes (MWNT) ≈ GO showed a strong dependence on the crystallinity of the graphitic layers. The deposition of platinum (Pt), copper sulfide (Cu₂S), and tin oxide (SnO₂) NC reduced significantly the conductivity of the SWNT and DWNT, irrespective of the nature of the NC but negligibly that of the MWNT and GO. X-ray photoelectron and Raman spectroscopy analyses suggested that the conductivity of the NC hybrid nanostructures was mainly reduced by the electron trapping at the surface defects that formed during the in situ solvothermal growth of the NC. As the conductivity of the graphitic layers increases, such electron trapping effect becomes more significant.