Abstract:
In the present manuscript, we have investigated the fluctuations in the tunneling current (noise) from vertically aligned Carbon nanotube (CNT) emitters using home-built tuning-fork based Scanning Tunneling Microscopy/Spectroscopy (tf-STM/S). The fluctuations in the tunneling current are recorded in near field geometry (i. e. tunneling geometry, the distance between tip and CNT emitters is ∼1 nm) and in far field geometry (i.e. Fowler-Northeim tunneling (F-N), the distance between tip and CNT emitters is ≥100 nm). The recorded fluctuations in the tunneling current for near field are showing a Random Telegraphic Noise (RTN) and extrinsic 1/f type noise for various time domains. An observed fluctuation is explained with plausible mechanism of a two-level on-off trap state model. The average lifetime for the on state is τ1 = 3.36 sec, and for the off state τ2 = 0.89 sec. The calculated trap energy level is ΔE = 0.034 eV. The calculated slope from the power spectral density plot ∼1.9 for RTN, and ∼1.1 for extrinsic 1/f type noise. Furthermore, the extrinsic 1/f type noise is observed in the tunneling current recorded in far field geometry, where the tunneling current is generated by tunneling of electrons through a triangular barrier. The calculated slope from power spectral density plot is ≈1.0. The understanding of noise from surface interface of CNTs is important in different tunneling geometries for device applications.