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Title: Effect of native oxide layers on copper thin-film tensile properties: A reactive molecular dynamics study

Metal-oxide layers are likely to be present on metallic nano-structures due to either environmental exposure during use, or high temperature processing techniques such as annealing. It is well known that nano-structured metals have vastly different mechanical properties from bulk metals; however, difficulties in modeling the transition between metallic and ionic bonding have prevented the computational investigation of the effects of oxide surface layers. Newly developed charge-optimized many body [Liang et al., Mater. Sci. Eng., R 74, 255 (2013)] potentials are used to perform fully reactive molecular dynamics simulations which elucidate the effects that metal-oxide layers have on the mechanical properties of a copper thin-film. Simulated tensile tests are performed on thin-films while using different strain-rates, temperatures, and oxide thicknesses to evaluate changes in yield stress, modulus, and failure mechanisms. Findings indicate that copper-thin film mechanical properties are strongly affected by native oxide layers. The formed oxide layers have an amorphous structure with lower Cu-O bond-densities than bulk CuO, and a mixture of Cu{sub 2}O and CuO charge character. It is found that oxidation will cause modifications to the strain response of the elastic modulii, producing a stiffened modulii at low temperatures (<75‚ÄČK) and low strain values (<5%), and a softenedmore » modulii at higher temperatures. While under strain, structural reorganization within the oxide layers facilitates brittle yielding through nucleation of defects across the oxide/metal interface. The oxide-free copper thin-film yielding mechanism is found to be a tensile-axis reorientation and grain creation. The oxide layers change the observed yielding mechanism, allowing for the inner copper thin-film to sustain an FCC-to-BCC transition during yielding. The mechanical properties are fit to a thermodynamic model based on classical nucleation theory. The fit implies that the oxidation of the films reduces the activation volume for yielding.« less
Authors:
 [1] ;  [1] ;  [2]
  1. Materials Science Program, University of Rochester, Rochester, New York 14627 (United States)
  2. (United States)
Publication Date:
OSTI Identifier:
22493074
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Applied Physics; Journal Volume: 118; Journal Issue: 23; Other Information: (c) 2015 AIP Publishing LLC; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; ANNEALING; BCC LATTICES; BONDING; COMPUTERIZED SIMULATION; COPPER; COPPER OXIDES; FCC LATTICES; MANY-BODY PROBLEM; MOLECULAR DYNAMICS METHOD; NANOSTRUCTURES; NUCLEATION; STRAIN RATE; STRAINS; STRESSES; SURFACES; TEMPERATURE RANGE 0065-0273 K; TENSILE PROPERTIES; THERMODYNAMIC MODEL; THIN FILMS; YIELDS