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JPhys energy 5(2), 021501 (2023). doi:10.1088/2515-7655/acaa57, Published by IOP Publishing, Bristol

YBa2Cu3O7−δ thin films grown on a Nb-doped SrTiO3 substrate by a pulsed laser deposition method have been fully characterized by scanning transmission electron microscopy Z-contrast imaging and electron energy loss spectroscopy techniques. The Nb distribution was found to be uniform and unchanged across the interface, ensuring a high quality p–n junction heterointerface. We first observed the coexistence of 124 and 125 YBCO defect structure phases, appearing as planar defects in a YBCO thin film. Dispersive Y2O3 nanoparticles have also been observed in the thin film. The interaction of these defect structures and Y2O3 nanoparticles is thought to be beneficial for pinning flux through the entire film thickness.

The development of monochromators and aberration correctors for transmission electron microscopes (TEM) has paved the way for a level of imaging and analysis that is unmatched by other methods. While current instrumentation does not permit the optimum spatial resolution of the microscope to be coupled with this high energy resolution, detailed spectroscopic analyses can be performed with ~1nm spatial resolution. Combined with ~0.1 eV energy resolution this is particularly useful for the analysis of the low-loss region of the spectrum, permitting quantum confinement effects and optical responses of individual nanostructures to be measured. Higher spatial resolution can be obtained from aberration corrected STEM, where spectral resolution of ~0.4eV can be coupled with a spatial resolution of

We have studied the characteristics of intersubband absorption of polarized infrared (IR) radiation in as-grown and annealed self-organized InAs/GaAs quantum dots. It is observed that with the increase of annealing time and temperature, the dots tend to flatten and behave more like quantum wells. As a result, their sensitivity to TE (in-plane)-polarized light decreases and that to TM (out-of-plane)-polarized light increases. The effect could be utilized for the realization of polarization-sensitive IR detectors.

A crucial first step in understanding the effect that internal interfaces have on the properties of materials is the ability to determine the atomic structure at the interface. Because interfaces can contain atomic disorder, dislocations, segregated impurities and interphases, sensitivity to all of these features is essential for complete experimental characterization. By combining Z-contrast imaging and electron energy loss spectroscopy (EELS) in a dedicated scanning transmission electron microscope (STEM), the ability to probe the structure, bonding and composition at interfaces with the necessary atomic resolution has been obtained. Experimental conditions can be controlled to provide, simultaneously, both incoherent imaging and spectroscopy. This enables interface structures observed in the image to be interpreted intuitively and the bonding in a specified atomic column to be probed directly by EELS. The bonding and structure information can then be correlated using bond-valence sum analysis to produce structural models. This technique is demonstrated for , and symmetric and and asymmetric [001] tilt grain boundaries in . The structures of both types of boundary were found to contain partially occupied columns in the boundary plane. From these experimental results, a series of structural units were identified which could be combined, using continuity of grain boundary structure principles, to construct all [001] tilt boundaries in . Using these models, the ability of this technique to address the issues of vacancies and dopant segregation at grain boundaries in electroceramics is discussed.

High quality electron energy loss spectra (EELS) with high spatial resolution have been acquired using a parallel recording system attached to a scanning transmission electron microscope (STEM). The authors have found that the fine structure of the oxygen K-edge shows features which change as oxygen is removed. They have developed a simple method to quantify this change and applied it to estimate the oxygen stoichiometry in a series of spectra obtained from a bulk sintered sample of YBa2Cu3O7- delta .

We investigated the thickness effect on ferroelectric properties of vinylidene fluoride (VDF)/trifluoroethylene (TrFE) copolymer films in the region of 9.7–230 nm. Film thickness was estimated from cross-sectional transmission electron microscope (TEM) images. Relative permittivity calculated using precise thickness measurements decreased from 10 to 5.3 with decreasing thickness. Remnant polarization gradually decreased from 80 to 34 mC/m2 with decreasing thickness, whereas maximum polarization was almost constant. These results suggested the existence of a dead layer with a low permittivity at the interface between the VDF/TrFE copolymer films and electrodes. Finally, the thickness of the dead layer was estimated to be 4.1 nm by assuming the existence of two layers with different permittivities.

Energy loss spectra from a variety of cubic oxides are compared with ab-initio calculations based on the density functional plane wave method (CASTEP). In order to obtain agreement between experimental and theoretical spectra, unique material specific considerations were taken into account. The spectra were calculated using various approximations to describe core-hole effects and electron. The calculations are based on both the generalized gradient approach and the local spin density approximation when dealing with the correlation to show qualitative agreement with the sensitive oxygen K-edge spectra in ceria, zirconia, and urania. Comparison of experimental and theoretical results let us characterize the main electronic interactions responsible for both the electronic structure and the resulting EELS spectra of the compounds in question.