Electron hopping conduction in highly disordered carbon coils

Carbon coils of micrometer to nanometer wire diameter were grown bi-directionally by catalyst-assisted chemical vapor deposition. Electron microscope images showed the highly disordered structure of the carbon coils. Chemical compositions of the coils were identified with elemental analysis, atmospheric pressure-laser desorption ionization-Fourier-transform ion cyclotron resonance-mass spectroscopy and secondary ion mass spectrometric characterizations, and attenuated total reflection-infrared spectroscopic examination. Micro-Raman scattering spectroscopy and electron energy loss spectroscopy were also used to study the vibrational and electronic properties of the helical structure. The electric transport in a single carbon coil was measured from ambient temperature to 64 mK. The temperature-dependent resistance was analyzed with the Efros-Shklovskii variable range hopping model, indicating three-dimensional electron hopping conduction in the disordered helical wires. The analysis also provides a basic understanding of the electron transport with an electron hopping length of ∼5 nm inside the disordered carbon coils.