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Definition: Colloidal metal nanoparticles in an electrolyte environment are not only electrically charged but also electrochemically active objects. They have the typical character of metal electrodes with ongoing charge transfer processes on the metal/liquid interface. This picture is valid for the equilibrium state and also during the formation, growth, aggregation or dissolution of nanoparticles. This behavior can be understood in analogy to macroscopic mixed-electrode systems with a free- floating potential, which is determined by the competition between anodic and cathodic partial processes. In contrast to macroscopic electrodes, the small size of nanoparticles is responsible for significant effects of low numbers of elementary charges and for self-polarization effects as they are known from molecular systems, for example. The electrical properties of nanoparticles can be estimated by basic electrochemical equations. Reconsidering these fundamentals, the assembly behavior, the formation of nonspherical assemblies of nanoparticles and the growth and the corrosion behavior of metal nanoparticles, as well as the formation of core/shell particles, branched structures and particle networks, can be understood. The consequences of electrochemical behavior, charging and self-polarization for particle growth, shape formation and particle/particle interaction are discussed. [ABSTRACT FROM AUTHOR]

Featured Application: Insight into the electrochemical nature of the growth of metal nanoparticles supports the development of new concepts and protocols for the production of non-spherical nanoparticles of high homogeneity, for control of particle geometry and for the development of new types of nanoparticles. The growth and aggregation behavior of metal nanoparticles can be modulated by surfactants and different other additives. Here the concept of how open-circuit mixed electrodes helps to understand the electrical aspects of nanoparticle growth and the consequences for the particle geometries is discussed. A key issue is the self-polarization effect of non-spherical metal nanoparticles, which causes a local decoupling of anodic and partial processes and asymmetry in the local rates of metal deposition. These asymmetries can contribute to deciding to the growth of particles with high aspect ratios. The interpretation of electrochemical reasons for particle growth and behavior is supported by experimental results of nanoparticle syntheses supported by microfluidics which can supply high yields of non-spherical nanoparticles and colloidal product solutions of high homogeneity. [ABSTRACT FROM AUTHOR]

[Display omitted] • Development of electrode-free piezoelectric nanogenerator. • Polyvinylidene fluoride–hexafluoropropylene as matrix and carbon black as filler. • Electrode-free signal transmission via interface polarization effect. • CB particles as both inner electrode and piezoelectric enhancer. • Facile repair via re-spraying due to self-polarization-based preparation. Flexible piezoelectric nanogenerators (PENGs) with high sensitivity, easy deformability, anti-corrosion features, and facile fabrication are highly advantageous for biological tissue sensing/monitoring applications in complex environments. The large-scale and low-cost preparation of flexible piezoelectric polymers requires additional electrode layers for charge collection, compromising the flexibility and corrosion resistance of the PENGs while increasing their fabrication difficulty and cost. In this study, we developed an electrode-free PENG based on a composite film composed of polyvinylidene fluoride–hexafluoropropylene (PVDF-HFP) as the matrix, and carbon black (CB) as the filler. With an appropriate content of approximately 5 wt%, and under the interface polarization effect, the CB particles in the composite film acted as both the inner electrode and the piezoelectric enhancer, thus realizing a sensing functionality without the use of an additional electrode. The effects of the positions of CB particles in the PVDF matrix on the potential distribution, and the functions of CB polarization in the inner electrode and piezoelectric enhancer were simulated using COMSOL Multiphysics software. An excellent piezoelectric performance was achieved, including a current of 0.66 μA, voltage of 17.6 V, and charge of 4.7 nC. Further, electrode-free PENGs, with the multi-self-polarization PVDF-HFP matrix exhibit a promising application as sensors for effectively monitoring human activities and complex environments and can be effectively repaired (up to 80 %) via a facile spray-coating process. [ABSTRACT FROM AUTHOR]

Highlights: [•] A phase-pure PMN-PT film can be formed on well-crystallized LaNiO3/Si at 500°C. [•] The Pr of PMN-PT film on well-crystallized LaNiO3/Si at 650°C is ∼23μC/cm2. [•] All the PMN-PT films are self-polarized. [ABSTRACT FROM AUTHOR]

In this work, the long-term stability of self-polarized ferroelectrics thin films consisting of a negative space charge region near the bottom electrode was investigated. This space charge acts against domain motion and polarizes the film when cooled down below the paraelectric-ferroelectric transition temperature. Self-polarized perovskite PZT layers were deposited by planar multi target sputtering on platinized silicon wafers. Ellipsometric measurements were performed for refractive index profiling in order to investigate the temperature stability of the space charge induced refractive index profile near the bottom Pt electrode. Self-polarized negative space charge compensated ferroelectric thin films were found to meet the life-time requirements for device application. [ABSTRACT FROM AUTHOR]

The CSD processed Strontium Bismuth Tantalate (SBT) ferroelectric films presents a certain degree of self-polarization when no further annealing after sputtered Pt top electrode deposition is performed. Using the measurement of the first pulsed hysteresis loop the percentage of switchable self-polarized polarization is quantitatively analyzed. Pyroelectric coefficient measurements assess the validity of the results obtained. The hysteresis loop measurements indicate that the polarization vector points to the bottom electrode. When the top electrode is a Hg drop instead of Pt, the degree of self-polarization obtained is different both in magnitude and sign. These results are explained as a competition between the self-polarization induced by the top and bottom platinum electrodes. [ABSTRACT FROM AUTHOR]