We have investigated the conductance of gold point contacts using a scanning tunneling microscope ͑STM͒ inside a transmission electron microscope ͑TEM͒. Measuring the conductance of these point contacts as a function of radius, we could directly compare it with theories both in the ballistic regime ͑Sharvin͒ as well as in the diffusive regime ͑Maxwell͒. The width of the contacts were between a single atom and 20 nm. Using an interpolation formula ͑Wexler͒ between the two limits, we obtain a mean free path of 4 nm, which is about ten times shorter than the room-temperature bulk value. The low value indicates an enhanced scattering, which is not due to high temperature in the point contact, instead a large number of scattering centers is created during the point contact formation process.
Sr-deficient and stoichiometric epitaxial (001) SrTiO3 films, deposited on (110)rhombohedral LaAlO3 substrates by rf magnetron sputtering, have been characterized using high-resolution transmission electron microscopy. A subsequent heat treatment in oxygen had a positive influence on the dielectric properties. Sr-deficiency had a large negative impact on the microwave dielectric constant of the films. These changes were correlated to changes in lattice parameters. In all samples, at the film/substrate interface, were misfit dislocations present. The residual elastic strain compressed the SrTiO3 unit cell in the substrate surface plane and expanded it an equal amount in the [001] direction. X-ray diffraction revealed that the tetragonal distortion, due to the mismatch strain, was concentrated to a narrow region closest to the film/substrate interface.
We have demonstrated that electron energy-loss spectroscopy in transmission electron microscopy is a useful technique for analysis of the high-frequency dielectric properties on a microstructural level. Compositional variations and interfacial elastic strain of epitaxial (001) SrTiO3 thin films had a small effect on the imaginary part, ε2, of the complex dielectric function, εr(E). Changes in the low-frequency dielectric function, between Sr deficient and stoichiometric films, were much larger compared to the changes in the high-frequency function. Improved film stoichiometry and absence of strain caused the absolute value of ε2 to approach that of a stoichiometric single crystal bulk sample. Simultaneously, the low-frequency dielectric function of the films improved. The electronic polarizability, αe, was also extracted from the dielectric function. Indications were found that strain and compositional deviations from the bulk value, resulted in decreased ability to withstand dielectric breakdown.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.