| AVS 62nd International Symposium & Exhibition | |
| Advanced Surface Engineering | Monday Sessions |
| Session SE+AS+NS+TR-MoM |
| Session: | Nanostructured Thin Films and Coatings |
| Presenter: | Qianying Guo, University of Alabama |
| Authors: | Q.Y. Guo, University of Alabama L. Wan, University of Alabama R.L. Martens, University of Alabama G.B. Thompson, University of Alabama |
| Correspondent: | Click to Email |
As the length scale of individual layers are reduced in a Cu/Nb multilayer, fcc to bcc and bcc to fcc transformations were noted for Cu and Nb respectively. These transitions have been modeled using a thermodynamic phase diagram where interfacial and volumetric energy considerations determine stability and the bilayer thickness of the multilayer is a state variable for predicting those transformations. Using HRTEM, the evolution of the interface from incoherent-to-semicoherent-to-coherent is determined and related to the structural component of the interfacial energy reduction that drives the crystalline transformations. When equal thicknesses of each layer were < 1 nm, the layers underwent an additional transformation from a crystalline to amorphous structure. This has been rationalized by the positive enthalpy of mixing between these two species as they intermixed during the sputter deposition process. The chemical intermixing and local clustering at and near the interface has been quantified by atom probe tomography. These phase transformations have been related to real-time, intrinsic growth stress measurements. All of the multilayers were in a compressive stress state, but a notable reduction in the compressive stress value occurred with each transformation. The collective characterization of the film, via TEM, atom probe, and stress evolution, have provided insights into the structural stability of crystalline phases at the nanoscale.