Robert M. Fisher

Decohesion of thin films from ceramic substrates

Decohesion of thin films from ceramic or semiconductor substrates is strongly influenced by internal stresses in films and stress concentrations from edges or flaws as well as by interfacial fracture energy. Residual stresses can cause spontaneous delamination, splitting and curling of films under tension or delamination, buckling and spal ling of films under residual compression, even with good interfacial bonding. Delamination behavior is considered using simple fracture mechanics models, supplemented with preliminary measurements of interfacial fracture energies. Formation conditions largely control internal stresses in films; whereas fracture energies are dictated by interfacial chemistry and mechanical factors such as plasticity.

Low-angle atomic scattering factors and charge density of aluminum

Abstract All the published experimental and theoretical atomic scattering (form) factors for aluminum have been carefully reviewed and only the low angle 111, 200 and 220 crystal form factors appear to be significantly different from the best free atom values. The best powder X-ray diffraction and high accuracy 111 and 200 electron diffraction form factors for Al are in good agreement with each other and with the best theoretical calculations. The equivalent scattering factors measured by X-ray Pendellosung methods seem somewhat high and are not a good representation of the charge density of aluminum. A (110) deformation charge density map based on the best experimental form factors indicates that bonding in aluminum is achieved by the spherical depletion of electrons from atomic sites and redistribution so that there is a build-up between nearest-neighbor (n.n.), second n.n. atoms, etc; this, of course, is the traditional plcture of a metallic bond. A comparison of the aluminum (110) deformation density map with the equivalent map for copper shows that the bonding schemes for the two elements follow an almost identical pattern. This indicates that even though copper and aluminum have large differences in atomic number and valency, their bonding schemes are primarily determined by the face-centered-cubic crystal structure.

Accurate structure factor determination and electron charge distributions of binary cubic solid solutions

Abstract By combining the accurate low-angle X-ray structure factors of binary cubic solid solutions determined by high-energy electron diffraction (HEED) with higher-angle values obtained by interpolation between best pure-element form factors, a complete set of accurate X-ray structure factors for these alloys can be produced. This approach is an improvement over previous analyses of this sort, where the pure-element form factors were considered unchanged by alloying (except for lattice parameter changes). This new method has been applied to the alloy systems CuAu, CuAl and FeCr, where sufficient electron diffraction information is available for a full analysis. The results show that the average low-angle form factors are significantly modified by alloying. These electron charge distribution changes can be explained in terms of the known Fermi surface behaviour of these alloys. In addition to these electron charge distribution studies, the effects of short-range order (s.r.o.) were also investigated. Ch...

Microstructural and Chemical Components of Ceramic-Metal Interfacial Fracture Energies

Failure of ceramic-metal interfaces induced by residual or applied stress is often brittle in nature although plastic strain in one or more bonding layers may add to the fracture energy for decohesion. Thus, the fracture toughness depends on chemical bonding across the interface, the plasticity and flow stress of the metal as well as other factors, arising from local internal stresses and the microstructure of the ceramic-metal couple, that cause crack tip branching, deflection, bridging, blunting or shielding. Electron microscopy and DCB testing of metal-glass systems provide insights into the relative importance of factors that determine the decohesion resistance.

Influence of Substrate on Cracking of Vapour-Deposited Thin Films Due to Residual Stresses

The influence of the substrate material on the column and grain microstructure, the residual stresses, crack patterns and delamination of Cr films has been investigated using TEM, SEM, and X-ray diffraction. The inter-influence of these factors which determine the long term reliability of microelectronics is discussed. When interfacial adhesion is very low, as may be the case with some polymer substrates, cracking occurs discontinuously during film formation each time the stress exceeds the critical value for fracture.

Book Reviews : Studies of Troublesome Children, D. H. Stott. Pp. 208. New York, Humanities Press, 1966.

must gain identity, he says-but white leadership in the Negro revolt must be retained. According to Bernstein, private industry can train the poor and provide jobs; even the military can furnish solutions for the problems of slum youth. In general, Bernstein favors change through existing institutions, and at a pace that does not offend. It would be fair to say that his position reflects a cautious humanistic orientation, yet contains a sense of urgency. The perspective, unfortunately, is dated. In a previous book (1964), Bernstein surveyed several major ghetto areas and wrote that he viewed the situation as

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