We prepared by vapor deposition at room temperature thin (500 A) Co/Pt multilayers or layered structures directly onto glass or Si substrates. They show a preferential magnetization perpendicular to the film plane for Co thicknesses below 12 A and a 100% perpendicular remanence for Co thicknesses below 4.5 A. The magnetic anisotropy can be explained by an interface contribution to the anisotropy. We also investigated the magneto‐optical (MO) polar Kerr effect of these multilayers. Because of their excellent magnetic properties and their potentially high oxidation and corrosion resistance, these Co/Pt‐layered structures are very promising candidates for MO recording. The Kerr rotation θk at λ=820 nm for a 35×(4.0 A Co+12.7 A Pt)‐layered structure, which has 100% magnetic remanence, is modest (−0.12°), but the reflectivity R is high (70%), which results in a respectable figure of merit Rθ2k. Furthermore, the Kerr effect increases towards shorter wavelengths and thus favors future higher‐density recording.

Perpendicular magnetic anisotropy and magneto-optical Kerr effect of vapor-deposited Co/Pt-layered structures

Formation of metastable cellular microstructures in selective laser melted alloys

Growth of thin, crystalline oxide, nitride and oxynitride films on metal and metal alloy surfaces

Single‐crystal niobium nitride (NbN) thin films were fabricated at ambient substrate temperature so that photoresist lift‐off techniques could be used in fabricating Josephson tunnel junctions In this article, we describe the superconducting properties and crystal structure of the NbN films Even though the substrates were not heated, the NbN films had excellent superconducting properties: a high Tc of 16 K, low normal‐state resistivity (ρ20=62 μΩ cm), and residual resistivity ratios RRR=ρ300/ρ20 above one The film structures, which were investigated by x‐ray diffraction, electron diffraction patterns and transmission electron micrographs, show a single‐phase orientation without columnar and granular structures We have found that the superconducting properties depend on the lattice parameter, and the best films had a lattice parameter of 0446 nm NbN/AlN/Nb tunnel junctions were fabricated to measure the superconducting energy gap of the NbN films We estimated the energy gap ΔNbN to be 26 meV and th

Superconducting properties and crystal structures of single‐crystal niobium nitride thin films deposited at ambient substrate temperature

NbN, NbC and Nb are known to be chemically inert with passivating oxides only solvable in HF acid. Despite Nb2O5 as outermost oxide layer, the oxides of Nb compounds show large differences in thickness and in electronic properties. To quantify the differences, angle-resolved XPS (ARXPS) measurements have been performed. The simultaneous fitting for different angles and preparations of the Nb, C, N and O XPS lines of the oxides yielded the following stoichiometries and distributions:

(a)Nb2O5 is the outermost oxide layer on NbN, NbC and Nb, followed by:
(b)Nb2N2−xO3+x(x<1) on NbN. Dielectric Nb oxicarbides were not identified for NbC.
(c)Underneath the dielectric metallic oxides NbN1−xOx for NbN, NbC1−xOx for NbC and NbO and NbOx for Nb (x<0.5) occur.


The oxide growth (a)–(c) is not planar; instead, the oxides serrate the metal surface on an nm scale. The serration is strongest for the soft Nb and smallest for the harder compounds NbN and NbC in parallel to the oxidation rate which is slowest for NbC.

The improved oxide quality and better quality of tunnel junctions in comparison with Nb is explained by this first identification of oxinitrides and of reduced serration of NbN (NbC). The first identification of Nb(N, C)1−xOx compounds extending into the metals explains, e.g., regions of depressed superconductivity, leakage current and pinning. The fluxoid pinning is enhanced by dielectric oxides existing for sputtered NbN between the grains and thus explaining the superior superconducting properties of granular NbN.

Angle-resolved XPS studies of oxides at NbN, NbC, and Nb surfaces

The preparation of cubic NbN films by reactive dc magnetron sputtering is described. These superconductive films are deposited at a sufficiently low temperature (<90 °C) that photoresist liftoff techniques and can be used in fabricating Josephson junctions. The superconducting transition temperature has been measured as a function of gas composition and pressure. It reaches a maximum of 14.2 K at 15% N2–85% Ar and 1.06 Pa total pressure. The resistivity ratio of these films is close to unity. Structural studies by transmission electron microscopy and electron diffraction show that films 100‐nm thick or less are randomly oriented, and noncolumnar with a crystallite diameter of 5 nm and a lattice parameter of 4.46 A, which is significantly higher than the bulk value for cubic NbN. The films are dense with void diameters no larger than 0.7 nm. Films 300‐400 nm thick show a small degree of texturing in x‐ray studies with a Read camera. Auger analysis shows a monotonic increase in the N/Nb ratio with increase in the N2/Ar ratio in the sputtering ambient up to 30% N2. From 30% to 50% N2 in the sputtering mixture the N/Nb ratio is constant. Small amounts of carbon impurity are found in all films.

Properties of NbN thin films deposited on ambient temperature substrates

We have developed the ability to deposit niobium nitride thin films routinely having a superconducting transition temperature of 14 K by dc reactive magnetron sputtering onto substrates held near room temperature (Ts <90 °C). This allows the use of conventional photoresist liftoff techniques for patterning. Pb‐counterelectrode tunnel junctions formed on these films show excellent V‐I characteristics, suitable for device applications and offering potential advantages over conventional Pb‐alloy/Pb‐alloy and Nb/Pb‐alloy junctions. These high quality junctions are also suitable for tunneling investigations of superconductivity in the Nb‐N system.

Superconductive tunneling into NbN deposited near room temperature

We have prepared polycrystalline Fe and amorphous Tb(FeCo) films using both dc diode‐ and magnetron‐sputtering techniques. Magnetic properties and aging characteristics of these films were measured by a vibrating sample magnetometer and an automatic torque magnetometer. Film morphologies were studied by transmission electron microscopy. The magnetic and aging characteristics are closely correlated to the film morphology. It was also found that different sputtering methods can be tailored to produce a similar film morphology. Among the sputtering parameters, the Ar pressure during deposition at room or lower temperature strongly influences the film morphology.

dc magnetron‐ and diode‐sputtered polycrystalline Fe and amorphous Tb(FeCo) films: Morphology and magnetic properties

We have studied and compared the aging characteristics of the amorphous Tb(FeCo) films from both dc getter diode and magnetron sputtering. No protecting layer such as SiO2 or Al2O3 was put on the films. Fresh films of 1.0‐μm thickness from diode sputtering showed a perpendicular anisotropy and well‐behaved magnetic properties using a vibrating sample magnetometer and an automatic torque magnetometer. We noticed a decrease in perpendicular anisotropy when the films were exposed to the air. However, this aging phenomenon was not observed in films of the same thickness prepared by magnetron sputtering even after seven months’ exposure to the air. The reasons for the difference are due to two distinct reaction mechanisms: bulk reaction in diode‐sputtered films and surface reaction in magnetron‐sputtered films. A variation of the microstructure is believed to attribute to this. The surface reaction was studied in thinner magnetron‐sputtered films of 10 and 25 nm, where the surface‐to‐bulk ratio is larger. A decrease in perpendicular anisotropy with aging was observed in these thinner films.

Aging effects on amorphous Tb–transition‐metal films prepared by diode and magnetron sputtering

A transmission electron microscope was used to characterize the microstructure of Te0.26Fe0.74 and Fe films obtained by magnetron and dc diode sputtering techniques. The films obtained by magnetron sputtering were very smooth, whereas those by diode sputtering were not smooth but islandlike, similar to the columnar structure. The microstructures were further examined by varying the pressure of argon gas. In both sputtering systems, an increase in the pressure promotes a tendency of the columnar structure to form.

D. D. Bacon

Papers

Properties of NbN thin films deposited on ambient temperature substrates

Superconductive tunneling into NbN deposited near room temperature

dc magnetron‐ and diode‐sputtered polycrystalline Fe and amorphous Tb(FeCo) films: Morphology and magnetic properties

Aging effects on amorphous Tb–transition‐metal films prepared by diode and magnetron sputtering

Microstructures of thin sputtered amorphous Tb0.26Fe0.74 and polycrystalline Fe films