Complexes [Mg2(thd)4] (1) and [Mg(thd)2(EtOH)2] (2) (Hthd = 2,2,6,6-tetramethyl-3,5-heptanedione) were prepared and characterized using various techniques, viz. X-ray diffraction, NMR and mass spectroscopy, and thermal analysis. Crystal structures of compounds 1 and 2 were determined. Complex 1 crystallizes as a dimer where three oxygen atoms from three different thd ligands join the Mg atoms together. Crystallization from ethanol results in a monomeric complex having solvent coordinated to Mg. Both complexes volatilize completely, but in 2, coordinated ethanol molecules do not stay intact in the gas phase. Complex 1 was used with H2O2 as precursors in the growth of MgO thin films by atomic layer deposition techniques. A rather constant growth rate of 0.10−0.14 A/cycle was observed at 325−425 °C.

Properties of [Mg2(thd)4] as a Precursor for Atomic Layer Deposition of MgO Thin Films and Crystal Structures of [Mg2(thd)4] and [Mg(thd)2(EtOH)2]

The synthesis, characterization, and incorporation in volatile metal−organic chemical vapor deposition (MOCVD) precursors of a new class of linked β-ketoiminate−polyether−β-ketoiminate ligands is presented. These ligands are designed to encapsulate alkaline-earth cations having low charges and large ionic radii. Barium complexes having the general formula Ba[(RCOCHC(R‘)N)2(R‘ ‘)] (R = tert-butyl or CF3; R‘ = tert-butyl, methyl, or CF3; R‘ ‘ = −(CH2CH2O)4CH2CH2− or −(CH2CH2O)5CH2CH2)−) were prepared and characterized by 1H and 13C NMR spectroscopy, elemental analysis, and mass spectrometry. Single-crystal X-ray diffraction analysis of 2,2,5,25,28,28-hexamethyl-9,12,15,18,21-pentaoxa-4,25-diene-6,24-diimino-3,27-pentacosadionatobarium(II) reveals a monomeric, nine-coordinate, tricapped trigonal prismatic coordination geometry. Single-crystal X-ray structural analysis of 1,1,1,24,24,24-hexafluoro-4,21-ditrifluoromethyl-8,11,14,17-tetraoxa-3,21-diene-5,20-diimino-2,23-tetracosadionatobarium(II)·2DMSO reveals ...

Encapsulating bis(β-ketoiminato) polyethers. Volatile, fluorine-free barium precursors for metal - Organic chemical vapor deposition

The grain boundary topography and grain boundary dislocation network structure of a 6° [001] bicrystal of YBa2Cu3O7−δ were studied using diffraction-contrast transmission electron microscopy (TEM). Saw-tooth-shaped arrays of facets composed of facets with lengths of a few tens of nanometers were observed in each of two widely separated sections of the boundary. The facet planes were {110}, {310}, and {221}. Further subfaceting of the (130) facets into a smaller-scale (a few nanometers) saw-tooth configuration of (010) and (110) facets produced a hierarchy of facets in at least one boundary section. The dislocation content observed in each type of facet agreed well with Frank's formula. However, the dislocations within individual facets frequently were inhomogeneously distributed, contrasting the picture of evenly spaced dislocations that is derived for boundaries of infinite extent. Certain types of dislocations repeatedly were grouped near the facet centers and ends. Well-separated partial dislocations frequently were observed near the facet midsections, but not near the facet junctions. Extended (∼30 nm) strain contrast was observed at all of the facet junctions formed by facets with dimensions on the order of tens of nanometers. This long-range strain may be due to the finite extent of the individual facets. These results all suggest that structural inhomogeneities occur on various length scales ranging from macroscopic to just a few nanometers. Such structural heterogeneity is consistent with the electrical heterogeneity that is indicated for many YBa2Cu3O7−δ grain boundaries.

https://www.cambridge.org/core/services/aop-cambridge-core/content/view/S0884291400023682

Faceting, dislocation network structure, and various scales of heterogeneity in a YBa2Cu3O7−δ low-angle [001] tilt boundary

The seeding effects of (001) Nd123/MgO thin films and MgO single crystals were studied in isothermal solidification of YBa2Cu3Oy composite with the additions of 40 mol% Y2BaCuO5, 10 wt% Ag, and 0.5 wt% Pt. Seeding with the Nd123/MgO thin film resulted in single-domain growth of Y123 crystal with a stable growth along the “100”?direction, while seeding with MgO single crystal produced multidomain growth in which the dominant growth facet is rotated 45° about (100) plane of MgO. Multidomain growth in MgO seeded sample was suppressed by decreasing undercooling degree. The effects of undercooling degree and seed size on multidomain growth are discussed in view of classical nucleation and growth theory.

Effects of Nd123/MgO thin film and MgO single-crystal seeds in isothermal solidification of YBaCuO/Ag

On the basis of the study of the thermal behavior of [Mg(tmhd)2(TMEDA)] (1; tmhd =2,2,6,6-tetramethyl-3,5-heptanedionate; TMEDA = N,N,N′,N′-tetramethylethylenediamine), a novel procedure for magnesium oxide thin film growth has been developed for chemical vapor deposition (CVD) applications. Complementary studies (thermogravimetric measurements and IR and NMR spectroscopy) enabled revelation of the dissociation of TMEDA from 1, confirmed by the detection of both free TMEDA in the vapor phase and less volatile [Mg2(tmhd)4] (2) as a residue after sublimation. The effect of this dissociation is an unwanted changeable sublimation rate of the precursor 1 during the CVD process. The endeavor of a constant deposition rate by simultaneously exploiting the good volatility of 1 was achieved through its synthesis in situ by using 2 with a diamine enriched carrier. Laser reflectance interferometry (LRI) measurements testified that such a method ensured a good and constant deposition rate throughout the growth experim...

Stability Study of a Magnesium β-Diketonate As Precursor for Chemical Vapor Deposition of MgO

A low voltage argon ion sputter technique was used to form grain boundary junctions in YBa2Cu3O7−x thin films on MgO. The YBa2Cu3O7−x thin film grown on a pre‐sputtered region of MgO was rotated 45° about the [001] axis relative to the YBa2Cu3O7−x thin film grown on an adjacent unsputtered region of the substrate. YBa2Cu3O7−x thin films were grown using pulsed organometallic beam epitaxy (POMBE). The current‐voltage and resistance‐temperature characteristics of individual grain boundary junctions demonstrated weak‐link‐type behavior. Sputter‐induced 45° grain boundary junctions are advantageous in device applications because they are planar and simple to form in many configurations.

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Sputter‐induced grain boundary junctions in YBa2Cu3O7−x thin films on MgO

Tilt grain-boundary junctions with a 45° [001] misorientation were formed in YBa 2 Cu 3 O 7− x (YBCO) thin films grown by pulsed organometallic beam epitaxy on (100) MgO substrates. The junctions were introduced at predetermined locations due to a modification of the orientation relation between the thin film and substrate following a low-energy argon ion irradiation of specific areas of the substrate surface prior to film deposition. Rutherford backscatter spectrometry and certain surface features observed by atomic force microscopy indicate that implantation of ions is necessary to cause the modified epitaxy. The low-temperature transport characteristics of individual isolated grain boundaries were determined by electromagnetic characterizations of the junction behavior. The same grain boundaries were examined by transmission electron microscopy and high-resolution electron microscopy and it was found that the boundaries are for the most part free of precipitates and well structured at the atomic scale. Regardless of the average grain boundary inclination, asymmetric (110)(100) facets dominate the microstructure of the junctions. Possible mechanisms for epitaxy modification and the transport properties in relation to the observed microstructure are discussed.

The formation, transport properties and microstructure of 45° [001] grain boundaries induced by epitaxy modification in YBa2Cu3O7-x thin films

MgO films and YBa{sub 2}Cu{sub 3}O{sub 7{minus}{delta}}/MgO multilayer films were developed with the pulsed organometallic beam epitaxy (POMBE) growth technique, and grain boundary junctions were fabricated from the films to demonstrate the utility of the multilayers. High-quality MgO films were grown on LaAlO{sub 3} substrates by POMBE using a Mg(dpm){sub 2} precursor. MgO crystallinity, as assessed by x-ray diffraction rocking curves, improved with the use of CuO{sub {ital x}} or YBa{sub 2}Cu{sub 3}O{sub 7{minus}{delta}} buffer layers. YBa{sub 2}Cu{sub 3}O{sub 7{minus}{delta}} films grown on the MgO layer by POMBE exhibited a {ital T}{sub {ital c}0} of 83 K and a {ital J}{sub {ital c}}(12 K) exceeding 10{sup 6} A/cm{sup 2} for applied magnetic fields up to 3{times}10{sup 4} Gauss. Grain boundary junctions were formed by growing YBa{sub 2}Cu{sub 3}O{sub 7{minus}{delta}} on MgO films that had been pretreated with a simple sputtering technique. This sputtering induces a controlled, 45{degree} grain boundary in subsequently deposited YBa{sub 2}Cu{sub 3}O{sub 7{minus}{delta}} films. The resulting boundary showed weak-link current-voltage behavior and an {ital I}{sub {ital c}R}{sub {ital n}} product of 52 {mu}V at 10 K, demonstrating that sputter-induced grain boundary junctions are compatible with multilayer technology. copyright {ital 1995} {ital Materials} {ital Research} {ital Society}.

YBa2Cu3O7-δ on MgO films grown by pulsed organometallic beam epitaxy and a grain boundary junction application

Grain boundaries can act as weak links in the high T/sub c/ materials. If properly controlled, these grain boundaries can be used in various device applications. We have been able to reproducibly form 45/spl deg/ [001] tilt grain boundary junctions in YBa/sub 2/Cu/sub 3/O/sub 7-x/ thin films. The films were grown-on MgO substrates using a pre-growth substrate treatment. A low energy broad beam argon ion source was used to irradiate a select region of (100) MgO substrates. The film on the milled portion of the substrate grows predominantly with a grain orientation rotated 45 degrees about the c-axis with respect to the grain on the unmilled portion. Backscattered electron Kikuchi patterns have been used to confirm that the rotation occurs across the entire milled portion of the substrate. Transport properties of these films are discussed and related to high resolution electron microstructural and microchemical analyses of the grain boundaries. This technique has potential use in device applications as a method for controlled grain boundary engineering. >

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YBa/sub 2/Cu/sub 3/O/sub 7-x/ 45/spl deg/ [001] tilt grain boundaries induced by controlled low-energy sputtering of MgO substrates: transport properties and atomic-scale structure

A versatile multilayer technique has been developed to form 45° YBa2Cu3O7−x [001] tilt grain boundary junctions on LaAlO3 substrates. An epitaxial MgO layer is initially deposited on a (100) LaAlO3substrate using pulsed organometallic beam epitaxy (POMBE). After a pregrowth sputter treatment, an YBa2Cu3O7−x thin film is then grown using POMBE. The resultant film is c‐axis oriented with a cube‐on‐cube orientation over the unsputtered portion of the MgO, and rotated by 45° about the [001] axis on the sputtered region of the substrate. The resulting grain boundary junction shows weak‐link behavior. The advantage of this technique is the ability to place the grain boundary anywhere on the substrate in any configuration, and the potential to use any substrate upon which MgO can be epitaxially grown.

B. V. Vuchic

Papers

Sputter‐induced grain boundary junctions in YBa2Cu3O7−x thin films on MgO

The formation, transport properties and microstructure of 45° [001] grain boundaries induced by epitaxy modification in YBa2Cu3O7-x thin films

YBa2Cu3O7-δ on MgO films grown by pulsed organometallic beam epitaxy and a grain boundary junction application

YBa/sub 2/Cu/sub 3/O/sub 7-x/ 45/spl deg/ [001] tilt grain boundaries induced by controlled low-energy sputtering of MgO substrates: transport properties and atomic-scale structure

Integrated multilayer sputter‐induced 45° YBa2Cu3O7−x grain boundary junctions