Stabilization of field electron emission from carbon nanofibers using ballast resistance

Abstract

Stabilization of field emission (FE) from carbon nanofibers grown on a metal tip has been extensively studied using ballast resistances of 1 ≤ R ≤ 1500 MΩ at electron currents of 1≲I≲100μA. The FE current stability ɛ(R) = ΔI(R)/Im strongly depends on the mean current Im, while the data points of the relative stability Γ(R) = ɛ(R)/ɛ(0) plotted as a function of R multiplied by Im could be crudely reduced into a curve. In the stabilization studied here, extracting voltage fluctuation ΔV(R) was weakly induced by the current fluctuation ΔI(R). The current stability ɛ(R) and the voltage fluctuation ΔV(R) could be interpreted by employing a dynamical impedance of z = (dI/dV)−1 evaluated from the experimental I–V curve. The optimum current stability of ɛ(R) ∼ 0.002 was achieved using the resistance of R ∼ 10 MΩ around the highest FE current of Im = 80 μA, while the extracting voltage stability was η(R) = ΔV(R)/V ∼ 0.001 [ΔV(R) ∼ 2 V] at R ∼ 10 MΩ and Im ∼ 80 μA.

Field Emission from Carbon Nanostructures

“…Further improvements can be achieved by introducing a ballast resistance in series with the extraction voltage [104]. Kita et al [105] have investigated the stabilization of the FE current by using a ballast resistance in the range from 1 to 1500 MΩ at an emission current of 1 to 100 µA. They demonstrated excellent stability where the ratio (∆I/I) of the current fluctuation with respect the absolute current was as small as 0.0018, using 10 MΩ ballast resistance on an average current of about 80 µA.…”

Highly reliable field electron emitters produced from reproducible damage-free carbon nanotube composite pastes with optimal inorganic fillers

“…Moreover, we have tried to estimate the reliability of HTE CNT field emitters in the triode configuration in the very harsh environment of a tiny vacuum-sealed vessel without any active vacuum pump. In most studies on field electron emitters the performance has been evaluated using the diode configuration in a chamber evacuated continuously by active vacuum pumps, such as turbo molecular pumps and ion pumps [37][38][39][40], which is an even friendlier environment than real field emission devices, including miniature x-ray tubes, encounter. Although field emitters in a diode structure can be easily implemented, the field emission current and the acceleration voltage are coupled to each other by the anode voltage, limiting their controllability and thus their applications.…”

Miniature x-ray tubes: current state and future prospects

“…This techique permits one to regulate the anode potential using the voltage drop at a resistance put in series in the electron-extacting circuit. Using ballast resistance, Kita et al [45] recently succeeded in stabilizing electron currents field-emitted from carbon nanofibers. Due to its simplicity, their method is far more practical than the current feedback.…”