Billie Wang

Application of Atom Probe Tomography in Understanding Thin Film Chemical Ordering and Stress Behavior

Thin films exhibit large surface-to-volume ratios, allowing interfacial thermodynamics to play a significant role in the microstrutural evolution. Atom probe tomography’s (APT) ability to detect atoms of equal sensitivity with near atomic spatial reconstruction resolution makes it an ideal technique to quantify the interfacial chemistry in these films. For example, in multi-element thin films, preferential partitioning or intermixing of species can regulate stresses or phases by changing the relative thermodynamic energies at the interfaces. In this study, three particular cases have been characterized using APT in order to evaluate the role of atomic-level chemical structure on either the stress or phase stability in thin films.

Ta clustering and microstructural evolution in the A1 to L10Fe52PtX(Ta1−X) phase transformation

A series of Fe52Pt48,Fe52.3Pt46.3Ta1.4 and Fe52Pt40.7Ta7.3 thin films were sputter deposited and subsequently annealed at 550 and 750 °C for 30 min. The as-deposited films, which adopted the A1 phase, had a change from a predominate (111) fiber texture to (200) with the Ta additions. This has been explained in terms of the competition between the surface energy and strain energy. Annealing at 550 °C facilitated the L10 order in Fe52Pt48 and Fe52.3Pt46.3Ta1.4. Upon annealing at 750 °C, all three composition films phase transformed into L10. Atom probe tomography revealed nanoscale clustering in the annealed Ta containing films. The formation of these clusters appeared to be a necessary initial step to allow the L10 ordering reaction to occur but clustering in of itself is not sufficient for order. For the Fe52Pt40.7Ta7.3 film, the Ta must be depleted within the matrix to a sufficient level to allow the binary Fe–Pt to order. For the Fe52.3Pt46.3Ta1.4 film, these clusters were qualitatively observed within ...