New approaches for achieving more perfect transition metal oxide thin films

This perspective considers the enormous promise of epitaxial functional transition metal oxide thin films for future applications in low power electronic and energy applications since they offer wide-ranging and highly tunable functionalities and multifunctionalities, unrivaled among other classes of materials. It also considers the great challenges that must be overcome for transition metal oxide thin films to meet what is needed in the application domain. These challenges arise from the presence of intrinsic defects and strain effects, which lead to extrinsic defects. Current conventional thin film deposition routes often cannot deliver the required perfection and performance. Since there is a strong link between the physical properties, defects and strain, routes to achieving more perfect materials need to be studied. Several emerging methods and modifications of current methods are presented and discussed. The reasons these methods better address the perfection challenge are considered and evaluated

Direct Observation of Electrostatically Driven Band Gap Renormalization in a Degenerate Perovskite Transparent Conducting Oxide

We have directly measured the band gap renormalization associated with the Moss-Burstein shift in the perovskite transparent conducting oxide (TCO), La-doped BaSnO_{3}, using hard x-ray photoelectron spectroscopy. We determine that the band gap renormalization is almost entirely associated with the evolution of the conduction band. Our experimental results are supported by hybrid density functional theory supercell calculations. We determine that unlike conventional TCOs where interactions with the dopant orbitals are important, the band gap renormalization in La-BaSnO_{3} is driven purely by electrostatic interactions

Near-field examination of perovskite-based superlenses and superlens-enhanced probe-object coupling

A planar slab of negative index material works as a superlens with sub-diffraction-limited imaging resolution, since propagating waves are focused and, moreover, evanescent waves are reconstructed in the image plane. Here, we demonstrate a superlens for electric evanescent fields with low losses using perovskites in the mid-infrared regime. The combination of near-field microscopy with a tunable free-electron laser allows us to address precisely the polariton modes, which are critical for super-resolution imaging. We spectrally study the lateral and vertical distributions of evanescent waves around the image plane of such a lens, and achieve imaging resolution of wavelength/14 at the superlensing wavelength. Interestingly, at certain distances between the probe and sample surface, we observe a maximum of these evanescent fields. Comparisons with numerical simulations indicate that this maximum originates from an enhanced coupling between probe and object, which might be applicable for multifunctional circuits, infrared spectroscopy, and thermal sensors.Comment: 20 pages, 6 figures, published as open access article in Nature Communications (see http://www.nature.com/ncomms/

EPITAXIAL-GROWTH OF CUPRATE SUPERCONDUCTORS FROM THE GAS-PHASE

SCHLOM DG, Anselmetti D, BEDNORZ JG, GERBER C, MANNHART J. EPITAXIAL-GROWTH OF CUPRATE SUPERCONDUCTORS FROM THE GAS-PHASE. Journal of Crystal Growth. 1994;137(1-2):259-267.The growth mechanism of c-axis oriented thin epitaxial films of the most widely studied cuprate superconductor, YBa2Cu3O7-delta, formed by a variety of gas phase codeposition methods on common substrate materials is described. The evolution of the surface microstructure, as revealed by scanning tunneling microscopy (STM), indicates that growth is dominated by the accommodation of depositing species at ledges. These ledges, which provide energetically favorable positions for this process, lie either along growth spirals emanating from screw dislocations, or, when a vicinal substrate is used, separate the low energy (001) planes at the film surface. If the substrate is misoriented sufficiently, growth occurs by step propagation. Otherwise, a high density of screw dislocations (approximately 10(9) cm-2) is nucleated during the initial stages of growth, providing a continual supply of ledge incorporation sites for the depositing species. Two likely mechanisms for the generation of these screw dislocations are described. The surface evolution reported appears to be an intrinsic feature of c-axis oriented YBa2Cu3O7-delta, films for a wide range of growth conditions, irrespective of the substrate material or vapor phase deposition method

PINNING CENTERS IN YBA2CU3O7-DELTA FILMS

MANNHART J, Anselmetti D, BEDNORZ JG, GERBER C, MULLER KA, SCHLOM DG. PINNING CENTERS IN YBA2CU3O7-DELTA FILMS. Superconductor Science and Technology. 1992;5(1S):S125-S128.Pinning centers in epitaxial YBa2Cu3O7-delta films have been investigated by scanning tunneling microscopy and transport studies. An astonishing surface morphology has been found which includes a high density congruent-to 10(9) cm-2 of screw dislocations and nanometer-sized holes. The density of screw dislocations can be controlled by varying the growth conditions of the YBa2Cu3O7-delta films, allowing correlations between critical currents and screw dislocation density to be investigated. Films with higher screw dislocation densities are observed to have higher critical current densities and a slower drop of J(c)(H)

CORRELATION BETWEEN JC AND SCREW DISLOCATION DENSITY IN SPUTTERED YBA2CU3O7-DELTA FILMS

MANNHART J, Anselmetti D, BEDNORZ JG, et al. CORRELATION BETWEEN JC AND SCREW DISLOCATION DENSITY IN SPUTTERED YBA2CU3O7-DELTA FILMS. Zeitschrift für Physik B Condensed Matter. 1992;86(2):177-181.Electric transport properties of sputtered YBa2Cu3O7-delta films were studied as a function of screw dislocation density, ranging from 5.10(7) cm-2 to 1.3.10(9) cm-2 as determined at the film surface. A correlation was found between the number of screw dislocations and the critical current density (J(c)). Films with higher screw dislocation densities have higher critical current densities and a slower drop of J(c) as a function of applied magnetic field H