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Ferroelectricity is a collective phenomenon, the characteristics of which depend on the combined effects of many factors, such as the ambient temperature, boundary conditions, sample dimensions, and misfit epitaxial stresses, etc. It is well known that ferroelectric thin films generally exhibit characteristics that are different from their bulk cou...
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... Ferroelectric materials lose their curious responses for temperatures above a critical temperature, T C , known as the Curie temperature [19,23,[277][278][279]. The Curie point, T C , of transition to the ferroelectric phase, can be tuned with the application of stress [280] or even material thickness [281], and can be very high, approaching the melting point for many ferroelectric materials [277]. The explosion and progress in the field of 2D and quasi-2D materials helped also bring ferroelectrics down to the scale of a few nanometers, despite that being initially thought of as impossible [282]. ...
Here, we review the progress and most recent advances in phonon-polaritonics, an emerging and growing field that has brought about a range of powerful possibilities for mid- to far-infrared (IR) light. These extraordinary capabilities are enabled by the resonant coupling between the impinging light and the vibrations of the material lattice, known as phonon-polaritons (PhPs). These PhPs yield a characteristic optical response in certain materials, occurring within an IR spectral window known as the reststrahlen band. In particular, these materials transition in the reststrahlen band from a high-refractive-index behavior, to a near-perfect metal behavior, to a plasmonic behavior – typical of metals at optical frequencies. When anisotropic they may also possess unconventional photonic constitutive properties thought of as possible only with metamaterials. The recent surge in two-dimensional (2D) material research has also enabled PhP responses with atomically-thin materials. Such vast and extraordinary photonic responses can be utilized for a plethora of unusual effects for IR light. Examples include sub-diffraction surface wave guiding, artificial magnetism, exotic photonic dispersions, thermal emission enhancement, perfect absorption and enhanced near-field heat transfer. Finally, we discuss the tremendous potential impact of these IR functionalities for the advancement of IR sources and sensors, as well as for thermal management and THz-diagnostic imaging.
In Chapter 5, we have discussed the unique physical properties of ferroelectric thin films, which generally exhibit characteristics that are different from their bulk counterparts. Due to the surface constraint on polarization, the para/ferroelectric transition temperatures of the film may be substantially lower than those of the bulk, so much so that the ferroelectric transformation may be totally suppressed in very thin films. The magnitude of this critical thickness can be calculated as shown in the last chapter. However, the theoretical calculations were performed for free standing or totally constrained films. As to the epitaxial films grown on compliant substrates, the influences of substrates over the critical thickness and Curie temperature of the film should be considered.
Software, MesoPoreImage, for transmission electron microscope (TEM) image simulation of mesoporous crystals was developed. MesoPoreImage provides two-dimensional (2D) projected potential distributions along any directions as well as corresponding 2D TEM images calculated from a three-dimensional (3D) density distribution of an ideal mesoporous structure. In order to adjust the contrast of simulated TEM images to that observed, a parameter representing surface roughness on the pore surface is introduced. Simulated TEM images of four typical silica mesoporous crystals, MCM-48, AMS-10, SBA-16 and SBA-6 are shown and compared with observed ones, which shows the usefulness of the software for identification of the mesoporous structure type. A procedure for the identification of structure types of mesoporous crystals by using TEM and the simulation software is fully described.
