1/fPermittivity Fluctuation in Fullerene C60

Abstract

Listen

Translate article

The existence of 1=f fluctuation in an electrical device is a serious problem from the viewpoint of accuracy. Carbon nanotubes (CNTs) are very useful for field-effect transistors, sensors, and microscopes, but their 1=f resistance fluctuation intensity is particularly large. 1–4) Graphene attracts attention as a new material for an electric device, but it also generates a large 1=f fluctuation. 5) Many hypotheses have been proposed about the origin of 1=f fluctuation. 6,7) Regarding the carbon material, some investigations reported that the origin of 1=f fluctuation is the mobility fluctuation in the sample, 1) but some reports insisted that the origin is the trap potential fluctuation at the sample/electrode or sample/ surrounding dielectric interface. 2–4) The potential height fluctuation by the trap and de-trap of electrons modulates the mobility or tunneling probability of the barrier between the sample and the electrode. The studies of the 1=f fluctuation in electrical devices are performed mainly by focusing on the electrical resistance. We have investigated the permittivity fluctuation of a dielectric substance, but it was about the critical fluctuation near Curie temperature. 8) In the present study, fullerene C60 is used as a sample material and the permittivity fluctuations of the real and imaginary parts are measured. Fullerene has the same hexagonal structure of carbon atoms as CNTs and graphene, but it is a dielectric substance. The fluctuation of complex permittivity provides new information. In the present study, the cross-correlation coefficient of the permittivity fluctuations of the real and imaginary parts is calculated. Furthermore, the effect of air adsorption on the surface of fullerene is investigated. A flat board capacitor, whose inside is filled with fullerene, is used to measure the permittivity fluctuation. Fullerene powder of 40 mg is packed between the metal plates with a size of 100 � 100 mm 2 and the distance between the plates is 30m. The real part of the relative permittivity of fullerene C60 is 4–4.5 and it is considered that the imaginary part of it at a low frequency is very small owing to the result of optical measurement. 9) The fluctuation of permittivity is measured by using the bridge circuit and two-phase lock-in amplifier shown in Fig. 1. Part of the bridge circuit is constructed by the fullerene capacitor and the other parts are constructed by low-noise polystyrene capacitors and series resistors. The amplitude and frequency of the applied voltage V0 are 2 V and 5 kHz, respectively. The mean value of V1 is adjusted to V0=2 by the capacitor C and the series resistor R. The value of the capacitance C is 1.7 nF and the value of the equivalent series resistance R is 93 � . The complex capacitance of the fullerene capacitor can be described as