An overview of the state of art in ferroelectric thin films is presented. First, we review applications: microsystems’ applications, applications in high frequency electronics, and memories based on ferroelectric materials. The second section deals with materials, structure (domains, in particular), and size effects. Properties of thin films that are important for applications are then addressed: polarization reversal and properties related to the reliability of ferroelectric memories, piezoelectric nonlinearity of ferroelectric films which is relevant to microsystems’ applications, and permittivity and loss in ferroelectric films—important in all applications and essential in high frequency devices. In the context of properties we also discuss nanoscale probing of ferroelectrics. Finally, we comment on two important emerging topics: multiferroic materials and ferroelectric one-dimensional nanostructures.

The contrast mechanisms of domain imaging experiments assisted by atomic force microscope (AFM) have been investigated by model experiments on nonpiezoelectric (silicon oxide) and piezoelectric $[{\mathrm{Pb(Zr,Ti)O}}_3]$ thin films. The first step was to identify the electrostatic charge effects between the tip, the cantilever, and the sample surface. The second step was to explore the tip–sample piezoelectric force interaction. The static deflection of the cantilever was measured as a function of dc bias voltage ${\mathrm{(V}}_{\mathrm{dc}})$ applied to the bottom electrode $\mathrm{(n}\mathrm{-type}$ Si wafers) for noncontact and contact modes. In addition, a small ac voltage ${\mathrm{(V}}_{\mathrm{ac}} \sin \mathrm{ \omega t)}$ was applied to the tip to measure the amplitude ${\mathrm{(A}}_{\omega })$ and phase ${\mathrm{(\Phi }}_{\omega })$ of the first harmonic (ω) signal as a function of $V_{\mathrm{dc}}.$ By changing from the noncontact to the contact mode, a repulsive contribution to the static deflection was found in addition to the attractive one and a 180° phase shift in ${\Phi }_{\omega }$ was observed. These results imply that in the contact mode the cantilever buckling is induced by the capacitive force between the cantilever and the sample surface. This interaction adds to the tip–sample piezoelectric interaction thereby overlapping the obtained tip vibration signal. Therefore, the antiparallel ferroelectric domain images obtained at zero dc bias voltage will show a variation in $A_{\omega }$ but a negligible one in ${\Phi }_{\omega }.$ The capacitive force contribution to the tip vibration signal was further verified in piezoelectric hysteresis loop measurement assisted by the AFM. The observed vertical offset of the loops was explained by the contact potential difference between the cantilever and the bottom electrode. The shape of the curve could be explained by the capacitive force interaction combined with the tip–sample piezoelectric interaction. The experimental results obtained in this study support the interpretation of the cantilever–sample capacitive force contribution to the tip vibration signal in ferroelectric domain imaging experiments using AFM as a probing tool. The use of a large area top electrode between the tip and the sample resulted in the elimination of the electrostatic cantilever–sample interaction with negligible degradation of the domain contrast. This method proved to be successful because the cantilever–sample interaction was hardly detected and only the tip–sample interaction was observed.

Flexible organic materials possessing useful electrical properties, such as ferroelectricity, are of crucial importance in the engineering of electronic devices. Up until now, however, only ferroelectric polymers have intrinsically met this flexibility requirement, leaving small-molecule organic ferroelectrics with room for improvement. Since both flexibility and ferroelectricity are rare properties on their own, combining them in one crystalline organic material is challenging. Herein, we report that trisubstituted haloimidazoles not only display ferroelectricity and piezoelectricity—the properties that originate from their non-centrosymmetric crystal lattice—but also lend their crystalline mechanical properties to fine-tuning in a controllable manner by disrupting the weak halogen bonds between the molecules. This element of control makes it possible to deliver another unique and highly desirable property, namely crystal flexibility. Moreover, the electrical properties are maintained in the flexible crystals.

The size, shape, and polarization orientation of fatigued areas formed during the suppression of the switchable polarization ${\mathrm{(P}}_r^s)$ (fatigue) in Pt–PZT–Pt ferroelectric capacitors (FECAPs), were observed by means of atomic force microscopy and by imaging the phase of the piezoelectric vibration induced by a low ac field applied between the top and bottom electrodes. In the virgin state (FECAP as prepared), the pattern of the polarization domains with opposite orientation was randomly distributed with typical sizes of 1–3 μm. The application of a dc field larger than the coercive field ${\mathrm{(E}}_c)$ enabled to fully orient the polarization of the regions in either directions. During the initial fatigue (<35% of suppressed $P_r^s$ ), polarized regions with frozen orientation and size ranging between 100 nm and 1 μm became visible. In the fatigued state (>65% of suppressed $P_r^s$ ), two main configurations of the frozen polarization domains were distinguished. One was characterized by a strong preferential direction (top to bottom electrode) and the other by randomly distributed regions of opposite oriented frozen polarization. The degrees of fatigue obtained by analyzing the vibration phase images are in good agreement with those obtained by standard polarization measurements. It is concluded that the $P_r^s$ suppression (fatigue) is due to “region by region” or “grain by grain” freezing of $P_r^s$ and that the frozen $P_r^s$ can have a preferential orientation.

Copper (Cu) nanoparticles (NPs) have received extensive interest owing to their advantageous properties compared with their bulk counterparts. Although the natural oxidation of Cu NPs can be alleviated by passivating the surfaces with additional moieties, obtaining non-oxidized bare Cu NPs in air remains challenging. Here we report that bare Cu NPs with surface excess electrons retain their non-oxidized state over several months in ambient air. Cu NPs grown on an electride support with excellent electron transfer ability are encapsulated by the surface-accumulated excess electrons, exhibiting an ultralow work function of ~3.2 eV. Atomic-scale structural and chemical analyses confirm the absence of Cu oxide moiety at the outermost surface of air-exposed bare Cu NPs. Theoretical energetics clarify that the surface-accumulated excess electrons suppress the oxygen adsorption and consequently prohibit the infiltration of oxygen into the Cu lattice, provoking the endothermic reaction for oxidation process. Our results will further stimulate the practical use of metal NPs in versatile applications.