This article reports on the formation and electronic characteristics of conducting carbon nanowires produced by swift heavy ion irradiation of a fullerene thin film. This study shows that it is possible to create arrays of carbon nanowires, which are perfectly parallel to each other and perpendicular to the substrate. As-deposited fullerene films exhibit poor field emission characteristics with breakdown fields as high as 51 V/μm, whereas low dose ion irradiated fullerene film produces a threshold field as low as 9 V/μm. The present approach of making conducting carbon nanowires by ion irradiation for potential field emitters and large area applications is also discussed.

Here we report a ferroelectric capacitor structure obtained by alternating ferroelectric and insulator thin-film layers which allows an increase of up to 2ⁿ polarization states, with n the number of ferroelectric layers. Four and up to eight distinct, stable and independently addressed polarization states are experimentally demonstrated in this work. The experimental findings are supported by a theoretical model based on the Landau–Ginzburg–Devonshire theory. The key parameter is the change in the strain conditions of ferroelectric layers induced by the insulating separator. Notably, the 2ⁿ increase in the storage capacity can be achieved without major changes in the present technology used for FeRAM devices. The test structures demonstrate very good memory characteristics such as retention and fatigue, opening the way towards the design of high density ferroelectric memories.

Sequential two-step electron tunneling from nanoparticles has been studied from a transport point of view. A steady-state balance equation for the partial electron currents is derived and solved to obtain the stationary level occupancy, which leads to the overall tunneling current as a function of the applied field. Our model explains the steplike features observed in high field tunneling experiments involving composite cathodes that incorporate electronic quantum-confinement regions. In order to assess the validity of our model and to show the apparition of the steplike features in field-emission experiments, we have used the usual diode configuration to obtain current-voltage characteristics from a composite cathode. The theoretical model presented in this paper shows qualitative agreement with the experimental data.

The hysteretic behavior of the epitaxial Pb(Zr,Ti)O₃ thin films with different top metal electrodes is studied, with emphasis on the influence of the leakage current and trap generation current on the shape of the loop as well as on the magnitude of the measured polarization. Cu, Pt, and SrRuO₃ were used as top contacts and important differences were observed for measurements performed in both dynamic and static modes, although the contacts were deposited on the same epitaxial Pb(Zr,Ti)O₃ film grown on SrRuO₃/SrTiO₃ substrate. A peculiar behavior was observed especially for the static hysteresis loops where, depending of the top contact, the loop is influenced mainly by the leakage current (Pt) or by the trap generation current (Cu and SrRuO₃). The last one can contribute with an additive charge, having a linear dependence on the applied voltage, as suggested by the simple model developed to explain the abnormally high values of the dielectric constant extracted from the linear part of the static hysteresis loop. It is concluded that the properties of the top electrode interface can significantly impact the hysteretic behavior of the ferroelectric films.

The negative-capacitance effect in devices based on combined ferroelectric-dielectric gate oxides is thought to be a potential solution to break free from the so-called Boltzmann tyranny. To lower the power consumption in field-effect transistors, the subthreshold swing factor $S$ should be reduced below the thermodynamic limit of $60\mathrm{mV}$ per decade. Yet, despite numerous studies dedicated to this effect in the past decade, its origin in ferroelectric capacitors or ferroelectric-based superlattices remains unclear, being considered either a transitory product of polarization switching or an intrinsic phenomenon related to the presence of ferroelectric polarization. In this study it is shown, starting from simple electrostatic considerations, that negative capacitance is present during polarization switching and is accompanied by a significant increase of the current flowing through the ferroelectric capacitor. Coupled with piezo-force microscopy results, it is shown that the polarization orientation suddenly changes at the coercive voltage, accompanied by a complete reconfiguration of the potential barriers at the Schottky-like contacts present at the electrode-ferroelectric interfaces. A method to estimate the polarization-switching time, as the time associated with the presence of the negative-capacitance effect, is proposed. Values in the range from 100 to 1000 ns are obtained for epitaxial $\mathrm{Pb}{\mathrm{Zr}}_{0.2}{\mathrm{Ti}}_{0.8}{\mathrm{O}}_3$ films. These findings suggest that negative capacitance may be an intrinsic effect in ferroelectrics but that it is a transitory effect, present only when ferroelectric polarization passes through zero (switching).