Carrier mobility of polycrystalline-amorphous carbon nanocoils and its distribution in length direction

Polycrystalline-amorphous carbon nancoils (CNCs) have been discovered and studied for years. Herein, carrier mobility ( μ ) and concentration ( n ) of CNCs are probed for the first time, using electric field regulation and finite element analysis, which are calculated to be 21 cm 2 /Vs and 1.6×10 19 cm -3 at room temperature. Temperature dependence characterization from 290 to 350 K reveals 0.8 to 1.6 folds increase of μ , but only 5%∼14% increase of electrical conductivity. This determines a significant decrease of n with temperature increasing. Variable X-ray diffraction characterization attributes this illogical decrease of n to the thermal expansion in c-axis direction of sp 2 grains, when there are abundant vacancies in CNCs providing spaces for the expansion. Upon expansion, the compression of the space between sp 2 grains results in reduced carrier scattering and increased μ . The weakened atomic interaction in a sp 2 grain increases band gap and decreases density of state, determining the decrease of n . Four-electrode characterization along the length direction of single CNCs uncovers a decrease (increase) tendency of μ ( n ) along with the growth process, which clarifies a negative (positive) relation between defect level and μ ( n ), and predicts the potential optoelectronic applications of CNCs.