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Single-crystal ZrN films, 830 nm thick, are grown on MgO(001) at 450 °C by magnetically unbalanced reactive magnetron sputtering. The combination of high-resolution x-ray diffraction reciprocal lattice maps, high-resolution cross-sectional transmission electron microscopy, and selected-area electron diffraction shows that ZrN grows epitaxially on MgO(001) with a cube-on-cube orientational relationship, (001)ZrN|(001)MgO and [100]ZrN|[100]MgO. The layers are essentially fully relaxed with a lattice parameter of 0.4575 nm, in good agreement with reported results for bulk ZrN crystals. X-ray reflectivity results reveal that the films are completely dense with smooth surfaces (roughness = 1.3 nm, consistent with atomic-force microscopy analyses). Based on temperature-dependent electronic transport measurements, epitaxial ZrN/MgO(001) layers have a room-temperature resistivity ρ300K of 12.0 μΩ-cm, a temperature coefficient of resistivity between 100 and 300 K of 5.6 × 10-8 Ω-cm K-1, a residual resistivity ρo below 30 K of 0.78 μΩ-cm (corresponding to a residual resistivity ratio ρ300Κ/ρ15K = 15), and the layers exhibit a superconducting transition temperature of 10.4 K. The relatively high residual resistivity ratio, combined with long in-plane and out-of-plane x-ray coherence lengths, ξ| = 18 nm and ξ⊥ = 161 nm, indicates high crystalline quality with low mosaicity. The reflectance of ZrN(001), as determined by variable-angle spectroscopic ellipsometry, decreases slowly from 95% at 1 eV to 90% at 2 eV with a reflectance edge at 3.04 eV. Interband transitions dominate the dielectric response above 2 eV. The ZrN(001) nanoindentation hardness and modulus are 22.7 ± 1.7 and 450 ± 25 GPa. [ABSTRACT FROM AUTHOR]

We demonstrate a spurious contribution to low-frequency critical current noise in Josephson junctions-normally attributed to charge trapping in the barrier-arising from temperature instabilities inherent in cryogenic systems. These temperature fluctuations modify the critical current via its temperature dependence. Cross-correlations between measured temperature and critical current noise in Al-AlOx-Al junctions show that, despite excellent temperature stability, temperature fluctuations induce observable critical current fluctuations. Particularly, because 1/f critical current noise has decreased with improved fabrication techniques in recent years, it is important to understand and eliminate this additional noise source. [ABSTRACT FROM AUTHOR]

Digital superlattices of (LaMnO3)m/SrMnO3)2m (m≤3) having the same nominal composition as La1/3Sr2/3MnO3, an antiferromagnetic insulator, have been synthesized by means of molecular beam epitaxy. All superlattices show a sharp resistive maximum at temperatures near to or higher than the Néel temperature of bulk La1/3Sr2/3MnO3. No discernible signatures of magnetic ordering are observed near the resistivity peak for m≤2, but m=3 has a susceptibility peak consistent with antiferromagnet ordering, which is canted when cooled in a small magnetic field. Analogies are drawn to dx2-y2 orbitally ordered, layered antiferromagnetic manganites to explain the observations [ABSTRACT FROM AUTHOR]

We describe a reversible, spatially controlled doping method for cuprate films. The technique has been used to create superconductor-antiferromagnetic insulator-superconductor (S-AFI-S) junctions and optimally doped superconductor-underdoped superconductor-optimally doped superconductor cuprate structures. We demonstrate how the S-AFI-S structure can be employed to reliably measure the transport properties of the antiferromagnetic insulator region at cryogenic temperatures using the superconductors as seamless electrical leads. We also discuss applied and fundamental issues which may be addressed with the structures created with this doping method. Although it is implemented on a cuprate film (YBa2Cu3O7-δ) in this work, the method can also be applied to any mixed-valence transition metal oxide whose physical properties are determined by oxygen content. [ABSTRACT FROM AUTHOR]

We report the temperature and field dependence of anisotropic magnetoresistance (AMR) in fully strained tetragonal thin films of the colossal magnetoresistance manganite La[sub 0.7]Ca[sub 0.3]MnO[sub 3]. The behavior of the AMR is very different from that found in conventional metallic alloys. Its magnitude is peaked near the Curie temperature T[sub C] and becomes small at low temperature. It has two distinct symmetry components: one twofold symmetric about the transport current direction dominant near T[sub C], the other fourfold symmetric with symmetry axes of the crystal, appearing at low temperature. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

We report the growth of untwinned epitaxial thin films of Bi-Sr-Ca-Cu-O by atomically layered heteroepitaxy on SrTiO3 substrates. These films are c-axis oriented as-layered and do not exhibit 90° in-plane defects, i.e., a-b ‘‘twinning.’’ By misorienting the surface normal from {100} by approximately 4° towards <111>, the cubic symmetry of the {100} surface is adequately broken to completely align the b axis of the superconducting film with respect to the substrate. Reflection high-energy electron diffraction patterns observed during growth and post-growth x-ray diffraction analysis indicate that the incommensurate structural modulation occurs along the same direction as the step edges. [ABSTRACT FROM AUTHOR]

Atomic layering of high-temperature superconducting compounds has been employed to grow films of Bi2Sr2Ca2Cu3Ox, in situ, on SrTiO3 substrates. Atomic monolayers of the constituent atoms were sequentially deposited by shuttering the fluxes from thermal effusion cells, and oxidation of the film was accomplished using a beam of ozone. The films were superconducting as-grown, with complete resistive transitions as high as 86 K. Moreover, reflection high-energy electron diffraction patterns observed during growth, as well as post-growth analysis by x-ray diffraction and high-resolution scanning electron micrography, indicate the films to be single crystal and heteroepitaxial, with in-plane a-b twinning. [ABSTRACT FROM AUTHOR]

Heteroepitaxial Dy-Ba-Cu-O films have been grown in situ on SrTiO3 substrates using an oxygen plasma beam and elemental source beams in a modified molecular beam epitaxy machine. By periodically shuttering the Dy and Ba beams during growth, flat surfaces of layered Dy-Ba-Cu-O compounds have been obtained. Periodic oscillations in the intensity of the in situ reflection high-energy electron diffraction pattern were observed during shuttered growths. Depending on growth conditions, the as-grown layers have ranged from insulating to superconducting with onset temperatures above 60 K. [ABSTRACT FROM AUTHOR]

We report the use of in situ, near-threshold photoemission to study the dynamics of GaAs surfaces during epitaxial crystal growth and, in particular, the observation of oscillations in the photoemitted current. These oscillations are found to depend upon the growth rate in the same manner as do reflecting high-energy electron diffraction intensity oscillations, occurring at the monolayer accumulation rate. We believe that they depend upon a cyclical variation in the step edge density on the growing surface and discuss the mechanism through which the oscillatory current may result from surface states or surface dipoles. [ABSTRACT FROM AUTHOR]

We have fabricated thin films of La1-xCaxMnOδ with tetragonal symmetry. For low temperatures and magnetic fields the measured magnetoresistance is anisotropic: initially positive for applied magnetic field perpendicular to the film plane and negative for field applied parallel to the film plane. At high temperatures the magnetoresistance is negative for all fields and field orientations. We also observe an in-plane magnetoresistance anisotropy with an angular dependence corresponding to that observed in transition metal ferromagnets. We suggest an interpretation requiring a substantial spin-orbit interaction in the material. © 1996 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Thin films of the high-temperature superconductor DyBa2Cu3O7-x have been grown on SrTiO3 substrates using molecular beam epitaxy techniques. Reflection high-energy electron diffraction patterns observed during deposition indicate incomplete oxidation of copper and growth of oriented metallic copper microcrystals in a matrix of amorphous barium and dysprosium oxides. After post-growth anneal the films exhibited sharp superconducting transitions with zero resistance observed as high as 89 K and critical current densities of 4.8×105 A/cm2 at 4.2 K and 3.9×104 A/cm2 at 77 K. [ABSTRACT FROM AUTHOR]

The transformation from quasi-two-dimensional to three-dimensional behavior of the free-electron gas in GaAs-Ga1-xAlxAs multiple quantum well structures was observed. This transformation corresponds to the establishment of well defined three-dimensional plasmon modes measured by Raman scattering, which propagate across layers of an n-type doped superlattice when the layer thicknesses are reduced to 20 Å or less. This type of behavior is consistent with the Kronig–Penney type model describing coupling between the wells and formation of energy minibands in a superlattice. [ABSTRACT FROM AUTHOR]

Heterostructure p-n junction tunnel diodes with high peak to valley ratios (12: 1) at room temperature are demonstrated. The variation of peak and valley currents in diodes with different tunnel barriers is described, and the mechanisms responsible for the valley current and its temperature dependence are proposed. Ways to improve the peak to valley ratio and reduce junction capacitance are discussed. [ABSTRACT FROM AUTHOR]

Double quantum well resonant tunnel diodes are demonstrated in InAlAs/InGaAs for the first time. Peak-to-valley ratios of greater than 70:1 at room temperature and 125:1 below 200 K are observed. [ABSTRACT FROM AUTHOR]

Using molecular-beam-epitaxy growth techniques, we have synthesized ferromagnet/insulator/ferromagnet trilayer heterostructures with the "colossal" magnetoresistance material La[sub 1-x]Sr[sub x]MnO[sub 3] as the ferromagnet. These trilayer films were fabricated into magnetic tunnel junctions which exhibit magnetoresistance ΔR/R(H) of as much as 450% in 200 Oe applied field at 14 K, and which persists up to ∼250 K. In situ reflection high-energy electron diffraction (RHEED) allows us to correlate the quality of the epitaxial growth with the magnetoresistive properties. Samples which showed signs of disorder in RHEED also exhibit disorder effects in low-temperature transport and have smaller magnetoresistance which vanishes at lower temperatures. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

We report the results of magnetization measurements on pseudomorphic (fully strained) c-axis oriented colossal magnetoresistance manganite thin films grown by molecular beam epitaxy. We observe uniaxial magnetic anisotropy (hard axis/easy plane) with the easy plane being the film plane. Within the plane a weaker biaxial anisotropy is observed with [100] (Mn–O bond direction) easy axes. The magnetization dependence of the uniaxial anisotropy constant follows the predicted magnetization dependence of the magnetostriction constants within single-ion models indicating that the anisotropy energy is dominated by strain-induced anisotropy from the lattice constant mismatch with the SrTiO[sub 3] substrate. These results indicate a magnetostriction constant λ[sub 100]approx. +7×10[sup -5], and an induced orbital moment of at least 0.02μ[sub b]/Mn ion. We predict that by appropriate substrate selection an equilibrium out-of-plane magnetization can be produced. © 1998 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Digital superlattices of (LaMnO3)m/SrMnO3)2m (m≤3) having the same nominal composition as La1/3Sr2/3MnO3, an antiferromagnetic insulator, have been synthesized by means of molecular beam epitaxy. All superlattices show a sharp resistive maximum at temperatures near to or higher than the Néel temperature of bulk La1/3Sr2/3MnO3. No discernible signatures of magnetic ordering are observed near the resistivity peak for m≤2, but m=3 has a susceptibility peak consistent with antiferromagnet ordering, which is canted when cooled in a small magnetic field. Analogies are drawn to dx2-y2 orbitally ordered, layered antiferromagnetic manganites to explain the observations [ABSTRACT FROM AUTHOR]