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Structure and Mechanical Properties of Copper/Niobium Multilayers
Author(s) -
Mitchell Terence E.,
Lu Yong Cheng,
Jr. Alfred J. Griffin,
Nastasi Michael,
Kung Harriet
Publication year - 1997
Publication title -
journal of the american ceramic society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.9
H-Index - 196
eISSN - 1551-2916
pISSN - 0002-7820
DOI - 10.1111/j.1151-2916.1997.tb03037.x
Subject(s) - materials science , niobium , nanoindentation , copper , dislocation , transmission electron microscopy , crystallography , sputtering , composite material , hardening (computing) , condensed matter physics , layer (electronics) , metallurgy , thin film , nanotechnology , chemistry , physics
Copper/niobium multilayers prepared by sputtering onto Si substrates with layer thicknesses ranging from 11 to 5000 Å have been characterized by transmission electron microscopy and nanoindentation. The films are strongly textured with {110} close‐packed planes of the bcc Nb parallel to the {111} close‐packed planes of the fcc Cu and close‐packed directions tending to be parallel as well. For the 11 Å layers, the Cu is found to grow pseudomorphically on Nb in the bcc structure. It is thought that, for thicker layers, the bcc Cu loses coherency and transforms martensitically to the fcc phase, thus resulting in the observed Kurdjumov—Sachs orientation relationship. As the layer thickness, d , decreases from 5000 to 500 Å, the hardness increases as d ‐1/2 ; i.e., it follows a Hall—Petch relationship so that hardening is due to grain boundaries and interfaces. The slope is the same as in pure Cu, but there is a large intercept which is ascribed to internal stresses and a large dislocation density. As the layer thickness decreases from 100 to 11 Å, the hardness increases as (1/ d ) l n (0.69 d ), which is a line tension formulation such as would be expected for Orowan dislocation bowing between the layers. Again there is a large intercept which is ascribed to cutting through the Cu/Nb interfaces. The interfacial energy is calculated to be 0.46 J/m 2 .