Julius Klerrer

Abstract: Carbon fibres have been prepared by pyrolysing a mixture of benzene and hydrogen at about 1100°C They have been studied by high resolution electron microscopy These fibres have various external shapes and contain a hollow tube with a diameter ranging from 20 to more than 500 A along the fibre axis They consist of turbostratic stacks of carbon layers, parallel to the fibre axis, and arranged in concentric sheets like the “annual ring structure of a tree” These fibres have two textures resulting from different growth processes; core regions, made of long, straight and parallel carbon layers, are primarily formed by catalytic effect; the external regions correspond to a pyrolytic deposit occuring during the secondary thickening growth process Very small cementite crystals, typically about 100 A in a diameter, have been identified by dark-field techniques at the tip of the central tube of each fibre A model of fibre growth related to a surface diffusion of carbon species on the catalyst particle has been established

Abstract: The anisotropic magnetoresistance effect in 3d transition metals and alloys is reviewed. This effect, found in ferromagnets, depends on the orientation of the magnetization with respect to the electric current direction in the material. At room temperature, the anisotropic resistance in alloys of Ni-Fe and Ni-Co can be greater than 5%. The theoretical basis takes into account spin orbit coupling and d band splitting. Other properties such as permeability, magnetostriction, and Hall voltage have no simple relationship to magnetoresistance. Anisotropic magnetoresistance has an important use as a magnetic field detector for digital recording and magnetic bubbles. Such detectors because of their small size are fabricated using thin film technology. Film studies show that thickness, grain size, and deposition parameters play a significant role in determining the percentage change in magnetoresistance. In general, the change is smaller in films than bulk materials. Several tables and graphs that list bulk and film data are presented.

Abstract: In a recent paper [6] a general theory of surface stress was presented. Here we discuss several simple solutions within this theory.

Abstract: In the presence of a nickel catalyst, acetylene decomposed to form carbonaceous solids with filamentary, amorphous, or laminar form. By observing the initiation processes continuously, parameters controlling the type of deposit have been established. Controlled atmosphere electron microscopy has shown the development of filaments behind particles of nickel (30–50 nm diameter) at relatively low temperatures (870 ± 20 K). At the same temperature, amorphous carbon nucleated around the nickel particles and spread until it covered the whole solid. In extended experiments, angular graphite laminae grew from large nickel particles (300 nm diameter) at 1300 K. The catalytic activity of the nickel particles for filament growth ceased after approximately 15 s at 870 K, but it could be regenerated by exposure to either hydrogen at 1100 K, or oxygen at 1000 K. A significant increase in catalyst efficiency for filamentous growth was noted when particles of nickel were formed in hydrogen at 875 K prior to the introduction of acetylene. An explanation of this phenomenon and the mechanisms of the catalytic, deactivation, and regeneration processes are proposed. Exposure of the carbonaceous deposits to oxygen demonstrated their different reactivities and suggested that filaments consisted of an easily oxidizable core with a relatively resistant skin.

Abstract: Note: This summary article first appeared in the Proceedings of the 22nd Annual Technical Conference of the Society of Vacuum Coaters in 1979 It is reproduced here, with permission, for both its technical and historical significance In it are found a number of the insights and instructive sketches characteristic of John Thornton, which in this case were known only to those few having access to the proceedings volume Virtually all vacuum-deposited coatings are in a state of stress The total stress is composed of a thermal stress and an intrinsic stress The thermal stress is due to the difference in the thermal expansion coefficients of the coating and the substrate materials The intrinsic stress is due to the accumulating effect of the crystallographic flaws that are built into the coating during deposition In soft, low melting point materials such as aluminum, bulk diffusion tends to relax the internal stresses and to prevent their accumulation However, these diffusion processes can cause flaws such as holes and hillocks to form In hard, higher melting point materials such as chromium deposited at low temperatures (eg the case of decorative coatings on plastic substrates), intrinsic stresses accumulate and tend to dominate over thermal stresses Stress cracking and buckling are commonly observed The fundamental nature of the internal stresses that are found in both evaporated and sputtered coatings is reviewed in this paper from the point of view of decorative coating applications Recent sputtering studies are described which indicate that apparatus geometry is particularly important in determining the state of stress that forms in deposits