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4 Dec 1989

Volume 55, Issue 23, pp. 2377-2461

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Laser wavelength dependent properties of YBa2Cu3O7−δ thin films deposited by laser ablation

G. Koren, A. Gupta, R. J. Baseman, M. I. Lutwyche, and R. B. Laibowitz

Appl. Phys. Lett. 55, 2450 (1989); http://dx.doi.org/10.1063/1.101999 (3 pages) | Cited 113 times

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YBa2Cu3O7−δ thin films were deposited onto (100) SrTiO3 substrates using 1064, 532, 355, 248, and 193 nm laser ablation. Transport measurements show lower normal‐state resistivities and higher critical currents in films deposited by the shorter wavelength lasers. The surface morphology of the films was rough with large particulates when the 1064 nm laser was used whereas much smoother surfaces with fewer and smaller particulates were obtained with the UV lasers. It is suggested that the better film quality obtained when the UV lasers are used is due to a small absorption depth of the UV photons in the ceramic target and to higher absorption by the ablated fragments. This leads to smaller ablated species and further fragmentation in the hotter plume and, therefore, to smoother and denser films.
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74.78.-w Superconducting films and low-dimensional structures
68.55.-a Thin film structure and morphology
74.70.-b Superconducting materials other than cuprates
74.25.Sv Critical currents

Breit–Wigner description of resonant tunneling

D. D. Coon, K. M. S. V. Bandara, and H. Zhao

Appl. Phys. Lett. 55, 2453 (1989); http://dx.doi.org/10.1063/1.102000 (3 pages) | Cited 2 times

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Analytic properties of scattering amplitudes are used to develop Breit–Wigner parametrizations of resonant tunneling currents in heterostructures. The analysis reveals a problem in using conventional Breit–Wigner resonance expressions to describe the important regions of peak current and negative differential resistance which occur when resonances are near the emitter threshold. Commonly used Breit–Wigner expressions (a) do not incorporate the correct threshold branch points, (b) do not possess the correct limit at threshold, and (c) do not satisfy unitarity both above and below threshold. Expressions which avoid such difficulties are deduced and used to parametrize tunneling current formulas.
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73.40.Gk Tunneling
79.60.Dp Adsorbed layers and thin films
79.70.+q Field emission, ionization, evaporation, and desorption
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
85.30.Mn Junction breakdown and tunneling devices (including resonance tunneling devices)

Annular dark field electron microscope images with better than 2 Å resolution at 100 kV

D. H. Shin, E. J. Kirkland, and J. Silcox

Appl. Phys. Lett. 55, 2456 (1989); http://dx.doi.org/10.1063/1.102297 (3 pages) | Cited 26 times

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High‐resolution scanning transmission electron microscope (STEM) images in the annular dark field (ADF) imaging mode approaching the theoretical point‐to‐point resolution limit are presented. The ADF images were obtained from a high Tc superconducting YBa2Cu3O7−x thin‐film specimen at 100 kV. The 1.9 Å resolution lattice image, which is the smallest lattice spacing in the specimen, corresponds to the minimum resolvable spatial frequency with 5% contrast in the contrast transfer function for annular dark field, and is smaller than the resolution limit given by the Rayleigh criterion. This demonstrates that STEM ADF imaging can have a resolution approximately 40% better than that of the bright field conventional transmission electron microscope (CTEM) imaging at Scherzer condition.
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07.78.+s Electron, positron, and ion microscopes; electron diffractometers
07.79.Cz Scanning tunneling microscopes
61.05.-a Techniques for structure determination
74.70.-b Superconducting materials other than cuprates
74.78.-w Superconducting films and low-dimensional structures

Fabrication of thin‐film metal nanobridges

K. S. Ralls, R. A. Buhrman, and R. C. Tiberio

Appl. Phys. Lett. 55, 2459 (1989); http://dx.doi.org/10.1063/1.102001 (3 pages) | Cited 54 times

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Thin‐film fabrication techniques for forming three‐dimensional ‘‘point contacts’’ are presented. As‐fabricated nanobridges can be modified using electromigration to make the constriction region smaller or dirtier. Scientific applications to quantum transport studies, 1/f noise, and electromigration are discussed.
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73.40.Jn Metal-to-metal contacts
74.50.+r Tunneling phenomena; Josephson effects
73.50.Td Noise processes and phenomena
73.61.At Metal and metallic alloys
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