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10 Oct 1988

Volume 53, Issue 15, pp. 1357-1451

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Nature of the pulsed laser process for the deposition of high Tc superconducting thin films

T. Venkatesan, X. D. Wu, A. Inam, Y. Jeon, M. Croft, E. W. Chase, C. C. Chang, J. B. Wachtman, R. W. Odom, F. Radicati di Brozolo, and C. A. Magee

Appl. Phys. Lett. 53, 1431 (1988); http://dx.doi.org/10.1063/1.100458 (3 pages) | Cited 75 times

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The pulsed laser thin‐film deposition process can enable preparation of thin films of complex composition with good control over the film stoichiometry. The film compositions are similar to that of the target pellet and as a consequence this technique appears to be an ideal method for preparing high Tc thin films on a variety of substrates.The factors which contribute to this beneficial phenomenon have been explored by a laser ionization mass spectrometry (LIMS) and a post ablation ionization (PAI) neutral velocity analysis technique in order to determine the mass and velocities of the laser ejected material. In addition, x‐ray absorption measurements on films deposited onto substrates at room temperature were performed in order to identify the presence of short‐range crystalline order in the films. Both of these studies rule out the ejection of stoichiometric clusters of material from the pellet during the laser ablation/deposition process. Instead, binary and ternary suboxides are emitted from the target pellet. These suboxides most likely have unit sticking coefficient to the substrate which could contribute to the preservation of the film stoichiometry. The velocity distribution of several neutral species (e.g., BaO) indicates that particles have energies of several eV. Thus the effective temperatures of the emitted species are ∼15×103 K, and these energetic particles may facilitate growth of the crystalline films at low substrate temperatures.
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81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces

Structural characterization of a TlCaBaCu oxide in Tc onset=155 K and Tc zero=123 K superconducting specimens

J. M. Liang, R. S. Liu, L. Chang, P. T. Wu, and L. J. Chen

Appl. Phys. Lett. 53, 1434 (1988); http://dx.doi.org/10.1063/1.100459 (3 pages) | Cited 6 times

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The crystal structure of a Tl‐Ca‐Ba‐Cu‐O compound in Tc onset=155 K and Tc zero=123 K superconducting specimens was characterized by transmission electron microscopy. Convergent beam electron diffraction analysis established that the phase is of P4/mcc space group. The lattice parameters of the phase were determined to be a=b=0.394 nm and c=3.95 nm. The phase was found to be primarily of a ten‐subcell structure by both high‐resolution lattice imaging and diffraction pattern analysis. The composition of the grains with the ten‐subcell structure being predominant was measured by energy dispersive spectrometry to be TlCa2Ba3Cu4Ox. Polytypes of the phase with four‐ and five‐subcell structures were also observed. The five‐subcell structure was identified to be of P4/mmm space group with a=b=0.394 nm and c=1.97 nm. The compositions of the specimens were measured to vary in composition ratios of Tl, Ca, Ba, and Cu from 1:2:2:3 to 1:2:3:4. The results strongly suggested that the TlCa2Ba3Cu4Ox phase is a high Tc superconducting phase with an exciting possibility that superconducting transition occurs at 155 K for this phase.
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74.70.-b Superconducting materials other than cuprates
07.79.Cz Scanning tunneling microscopes
61.05.-a Techniques for structure determination
74.25.Sv Critical currents
74.62.Bf Effects of material synthesis, crystal structure, and chemical composition

Interdiffusion and interfacial reaction between an YBa2Cu3Ox thin film and substrates

H. Nakajima, S. Yamaguchi, K. Iwasaki, H. Morita, H. Fujimori, and Y. Fujino

Appl. Phys. Lett. 53, 1437 (1988); http://dx.doi.org/10.1063/1.100460 (3 pages) | Cited 22 times

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Interdiffusion and interfacial reaction between a sputter‐deposited YBa2Cu3Ox thin film and substrates (MgO, sapphire, quartz, and Si) have been investigated by 2.7 MeV 4He+ Rutherford backscattering spectrometry. The diffusivities of Cu in the substrates and of the substrate elements (Mg, Al, and Si) in the Y‐Ba‐Cu‐O thin films have been determined over the annealing temperature range from 876 to 1226 K in an oxygen atmosphere. Among three metallic elements of Y, Ba, and Cu, Cu diffuses the fastest into the substrates. Copper silicide is observed in the interfacial region between the film and the Si substrate. Among these substrates, MgO is suggested to be the most stable on annealing.
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74.78.-w Superconducting films and low-dimensional structures
68.35.Fx Diffusion; interface formation
66.30.Ny Chemical interdiffusion; diffusion barriers

Determination of oxygen content in high Tc superconductors by a charged particle activation method

Z. Tao, D. E. Alburger, K. W. Jones, Y. D. Yao, and Y. H. Kao

Appl. Phys. Lett. 53, 1440 (1988); http://dx.doi.org/10.1063/1.100461 (3 pages) | Cited 5 times

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A new method for determining the oxygen content in high Tc superconductors has been demonstrated using a charged particle activation technique. This method allows a measurement of the concentration of 16O atoms in the superconducting material by detection of the 17F produced with the 16O(d,n)17F nuclear reaction. By way of example, this technique is applied to the determination of oxygen content in a series of high Tc Y‐Ba‐Cu‐O samples in which the stoichiometry is varied by reducing the copper concentration. The stabilized oxygen content shows a nonlinear dependence on the copper deficiency in these specimens.
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74.70.-b Superconducting materials other than cuprates
74.25.Sv Critical currents
74.62.Bf Effects of material synthesis, crystal structure, and chemical composition
82.80.Jp Activation analysis and other radiochemical methods

Effect of the post‐deposition processing ambient on the preparation of superconducting YBa2Cu3O7−x coevaporated thin films using a BaF2 source

Siu‐Wai Chan, B. G. Bagley, L. H. Greene, M. Giroud, W. L. Feldmann, K. R. Jenkin, and B. J. Wilkins

Appl. Phys. Lett. 53, 1443 (1988); http://dx.doi.org/10.1063/1.100463 (3 pages) | Cited 42 times

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We have investigated the effect of the post‐deposition processing ambient on the preparation of YBa2Cu3O7−x thin films from a BaF2 source. The role of H2O vapor during the high‐temperature anneal is understood through a thermodynamic analysis of the fluorine removal reaction. The role of a HF getter (e.g., SiO2) is understood through the same type of analysis. We have demonstrated that a zero resistance transition temperature at 77 K can be obtained for an annealing temperature as low as 690 °C for films deposited on SrTiO3 substrates by increasing the PH2O and decreasing PHF during the high‐temperature soak cycle.
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74.78.-w Superconducting films and low-dimensional structures
74.25.Sv Critical currents
74.62.Bf Effects of material synthesis, crystal structure, and chemical composition
74.70.-b Superconducting materials other than cuprates
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy

Measurement of in‐plane magnetization by force microscopy

David W. Abraham, C. C. Williams, and H. K. Wickramasinghe

Appl. Phys. Lett. 53, 1446 (1988); http://dx.doi.org/10.1063/1.99964 (3 pages) | Cited 38 times

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We present data which show that the magnetic force microscope is capable of detecting the component of the magnetic field parallel to the surface of a sample under study. Images of bits in a Co‐alloy thin‐film disk and of laser‐written bits in a TbFe film were taken with a magnetized tip tilted at 45° with respect to the surface normal. In both cases the asymmetric part of the image of a domain is interpreted in terms of gradients in the in‐plane component of the magnetic field. The bits written in the Co‐alloy disk were decorated with small magnetized particles, allowing identification of the domain boundaries and the asymmetric component of the force microscope image due to in‐plane magnetization.
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07.55.-w Magnetic instruments and components
75.70.Ak Magnetic properties of monolayers and thin films
85.70.Kh Magnetic thin film devices: magnetic heads (magnetoresistive, inductive, etc.); domain-motion devices, etc.
75.30.Cr Saturation moments and magnetic susceptibilities

Theory of magnetic imaging by force microscopy

J. J. Sáenz, N. García, and J. C. Slonczewski

Appl. Phys. Lett. 53, 1449 (1988); http://dx.doi.org/10.1063/1.99965 (3 pages) | Cited 25 times

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A new method to obtain information about local surface magnetic properties has been proposed recently. This new technique is based on the idea of measuring magnetic forces with a scanning tunneling force microscope. In this work we present a theoretical analysis of the relevant forces involved in magnetic force microscopy. Recent experiments with high‐resolution images of laser‐written domains in a magnetic thin film are discussed.
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07.55.-w Magnetic instruments and components
07.79.Cz Scanning tunneling microscopes
61.05.-a Techniques for structure determination
75.70.Rf Surface magnetism
75.70.Kw Domain structure (including magnetic bubbles and vortices)
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