Abstract
In this thesis work, the effects of environment on Coulomb blockade behavior in point-contact single junctions are studied experimentally. The devices consist of a lead top-electrode and a cobalt bottom-electrode which are separated by a thin Si3N4 membrane with a nanopore within which the two electrodes form a junction. The transport behaviors of the point-contacts with different contact areas were investigated for temperatures ranging between 2K and 300K. At room temperature, all devices exhibited linear current-voltage (IV) characteristics with a well defined asymptotic resistance Ra. The devices showing high resistance (Ra >RK≡h/e2) at room temperature exhibited insulating behavior with the zero-bias resistance Ro increases with decreasing temperature, and the IV curves showed a suppression in current at low-bias voltage region. On the contrary, the devices showing low resistance (Ra < RK) at room temperature exhibited metallic behavior with Ro decreases with decreasing temperature, and the IV curves were linear in the voltage region of interest. A model circuit was proposed to explain the observed behaviors. This model consists of a single tunnel junction (a capacitor shunted with a tunnel resistor) connecting in series with environment of variable impedance. The single junction represents the point contact, which sees an environment comprising randomly stacked metal grains.The IV and Ro(T) characteristics of this model circuit were calculated based on P(E) theory which describes the probability for energy exchange between tunneling electrons with energy E and the environment of various impedance, and a good agreement was obtained.During the course of device fabrication, we noticed the presence of chimney metal structures surrounding the nanopores. The chimneys are considered to be formed by nucleation process at the edge of the Si3N4 pores because this process can be observed by cooling the substrates with LN2. The nucleation process has been tested using different evaporation methods, evaporation rates with various metals and is found to be very robust.