S. R. Herd

Formation of an amorphous Rh‐Si alloy by interfacial reaction between amorphous Si and crystalline Rh thin films

Interfacial reaction in bilayers of amorphous Si and crystalline Rh thin films has been studied by transmission electron diffraction and microscopy. In a bilayer of ∼190‐A amorphous Si and ∼60‐A polycrystalline Rh films, we have observed the formation of an amorphous Rh‐Si alloy film upon thermal annealing at 300 °C. The amorphous alloy film crystallizes into the RhSi phase at 400 °C. On the other hand, no amorphous alloy formation was observed upon annealing a bilayer of ∼150‐A amorphous Si and ∼100‐A polycrystalline Rh films; instead, they react at 300 °C to form Rh2Si, followed by the formation of RhSi or a mixture of RhSi and Rh5Si3 around 400 °C.

Formation of second phase particles in aluminum-copper alloy films

The formation of second phase particles in Al+3% Cu alloy films was examined in order to find differences of the precipitation in thin films from that occurring in bulk alloys. Compared to bulk alloys in the thin film material the formation of Guinier-Preston zones is retarded. In well quenched thin films 60 h at 100°C or 6 h at 130°C are necessary to produce G.P. zones. θ′ particles are nucleated after approximately 100 h at 120°C without formation of θ″. The stable θ-Al2Cu precipitate was found at temperatures as low as 150°C on the film surface. The results show that excess vacancies cannot be retained in thin films and that the film surfaces provide preferential nucleation sites for the equilibrium precipitate θ-CuAl2.

Magnetic domain structures in multilayered NiFe films

The coercivity of NiFe (80/20) films can be lowered by laminating several layers with nonmagnetic spacers. A reduction by a factor of 10 can be achieved with a simple bi‐layer, regardless of spacer material, provided the spacer thickness is below a critical value. No further reduction is found for multilayers. Two peaks of Hc near thicknesses of 250A and 1000A for single layer films, associated with changes in domain structure, are suppressed by lamination. After a minimum spacer thickness (S) of 10–15A, the domain walls in the separate layers no longer coincide but track closely, their separation depending on S. With S?100A the layers switch independently, giving rise to multiple values of Hc.

Phase separation as source of perpendicular anisotropy in amorphous GdCo

The source of perpendicular anisotropy (PA) in 0.05 μ thick, evaporated amorphous GdCo films was investigated by correlating the magnetic domain structure, as observed in the Lorentz mode with film structure, as observed with high resolution electron microscopy and diffraction, as functions of post deposition in situ anneal and elevated substrate temperature. A strong void network was found to anneal out above 500 °K at an apparent glass transition. PA was developed either together with this or at slightly higher temperatures and could be correlated to the appearance of 60–100 A wide columnar arrays of two separate amorphous phases. The phase separation is evident also in a splitting of the single broad diffraction peak, normally observed in homogeneous amorphous deposits without PA, into two distinct components. Deposition at substrate temperatures above this glass transition results in amorphous films which crystallize on annealing without development of PA. From this, PA is thought to arise from anisotropically shaped Co‐rich regions in a transition stage between the homogeneous amorphous and crystalline states.The source of perpendicular anisotropy (PA) in 0.05 μ thick, evaporated amorphous GdCo films was investigated by correlating the magnetic domain structure, as observed in the Lorentz mode with film structure, as observed with high resolution electron microscopy and diffraction, as functions of post deposition in situ anneal and elevated substrate temperature. A strong void network was found to anneal out above 500 °K at an apparent glass transition. PA was developed either together with this or at slightly higher temperatures and could be correlated to the appearance of 60–100 A wide columnar arrays of two separate amorphous phases. The phase separation is evident also in a splitting of the single broad diffraction peak, normally observed in homogeneous amorphous deposits without PA, into two distinct components. Deposition at substrate temperatures above this glass transition results in amorphous films which crystallize on annealing without development of PA. From this, PA is thought to arise from anisot...

On the nature of perpendicular anisotropy in sputtered GdCo thin films

The development of perpendicular anisotropy in amorphous GdCo based alloys is still not clearly understood, since no single model has been able to explain all of the various experimental results. This paper presents evidence that links the perpendicular magnetic anisotropy (Ku) in sputtered films with phase separation on a 25A to 35A scale as a function of bias. High resolution electron microscopy, large and small angle scattering by electrons, and Lorentz microscopy were combined in this study. Analogous to annealing E‐beam evaporated pure GdCo in UHV [Herd, J. Appl. Phys. 49, (1978) 1744], the void network is seen to disappear at −50V bias. With a drop of the compensation point below room temperature, large perpendicular domains are observed at −100V bias, comparable to the development of Ku after the glass transition in evaporated and annealed films. Further increases of bias to −200V led to a decrease in strip width to 0.25μ. Application of bias in sputter deposition is seen to cause a continuous shif...

Effect of Direct Current on Precipitation in Quenched Al + 4% Cu Thin Films

Resistance changes associated with precipitation in Al–Cu thin films were monitored during power annealing at current densities up to 4×106 A/cm2 and temperatures of ∼178 and 200 °C. The rate of change of resistance decreased as the current increased. It is argued that this decrease is due to the current inhibiting the precipitation of θ Al2Cu.

Formation and crystallization of amorphous silicides at the interface between thin metal and amorphous silicon films

We investigated the interaction of extremely thin (less than 10 nm) crystalline gold and rhodium films with amorphous silicon by transmission electron microscope in situ annealing. In thin Au/Si bilayers an amorphous phase with a diffraction peak at d ≈ 0.226 nm is formed by thermal annealing between 150 and 200 °C. Depending on the thickness and composition, silicon sputtered onto thin gold films leads to the formation of a layer of amorphous silicon and a partially amorphous AuSi layer during deposition. The silicon layer crystallizes by itself at temperatures as low as 150 °C, and at 300 °C the amorphous AuSi layer crystallizes into a metastable gold silicide (for silicon-rich compositions). In Rh/Si bilayers an amorphous RhSi phase is formed by annealing to 300 °C and can be detected by electron diffraction for a rhodium thickness of less than 5 nm and compositions with more than 50% Si if completely reacted. Above 300 °C the amorphous RhSi crystallizes preferentially in the cubic form of RhSi for intermediate silicon compositions and in the orthorhombic form of RhSi for high silicon compositions. Excess amorphous silicon is not found to have a lowered crystallization temperature when in contact with the amorphous RhSi alloy, and crystalline silicon is only observed above 730 °C together with the cubic and/or orthorhombic RhSi. In Rh/Si bilayers with a thicker rhodium layer, no formation of an amorphous phase was observed on annealing; instead crystalline Rh2Si forms during annealing above 300 °C.

SiO2 film decomposition reaction initiated by carbon impurities located at a Si‐SiO2 interface

We have annealed Si‐SiO2 structures at an elevated temperature in He(g) with SiO(g) added to the ambient. A SiO2 decomposition reaction that normally forms large voids in a thin SiO2 film during annealing in He(g) is not detected with the added SiO(g). Instead, chemically reactive SiC impurity sites which initiate the SiO2 decomposition reaction are found segregated along crystallographic planes in the substrate at the Si‐SiO2 interface. The mechanism and technological importance of this interfacial reaction are discussed.

Structure and growth kinetics of RhSi on single crystal, polycrystalline, and amorphous silicon substrates

Growth kinetics of rhodium silicide in the temperature range of 375–450 °C have been studied on three different silicon substrates: single crystal, polycrystalline, and amorphous. The methods of analysis and specimen characterization utilized in this study are Rutherford backscattering spectroscopy (RBS), Seemann–Bohlin x‐ray diffraction, cross‐sectional transmission electron microscopy (TEM), sheet resistivity via four‐point probe, and Schottky barrier height measurements obtained from the current‐voltage relationship. Our results conclude that all three silicon substrates form an identical rhodium silicide compound, RhSi, indicating that the crystallinity of the substrate has no effect on the resulting rhodium silicide. The growth of RhSi was determined to be diffusion‐limited and the activation energy of growth was similar for single crystal (1.88±0.04 eV) and amorphous silicon (1.86±0.07 eV), yet it was slightly lower (1.71±0.08 eV) for polycrystalline silicon. The difference can be attributed to the ...

Laser writing on metal‐silicon bilayers for optical storage. I. Optical properties

Various bilayer structures consisting of metal and silicon were investigated as possible candidates for the optical recording medium. The silicon‐on‐metal bilayers offer tunability with a reasonable thickness of Si in the visible spectrum with a typical reflectivity less than 5%. Of the two possible writing processes, the low‐power process of silicide formation has a threshold power of 30 mW for a Rh‐Si bilayer which provides a reflectivity change in excess of 40%. The absence of raised rims around the written spots offers a smooth morphology that is compatible with encapsulation.