BCC Ti/BCC Nb

HCP Ti/BCC Nb

Phase Stability in Thin Metallic MultilayersGregory B. Thompson, University of Alabama Tuscaloosa, DMR 1207220

Intellectual Merit

This research elucidates the phase stability of metals in small volumes. Using prototype multilayered thin films, where phase transformations can be predicted using a thermodynamic-based model, the influence of chemical intermixing and stresses are being investigated. Metallic films are paramount in various technologies, including being semiconductor contacts, optical coatings, and hard coatings.

APT: Atom probe tomography (APT) provides 3D reconstructions of individual atoms with near atomic spatial lattice registry. Using this technique, the amount of intermixing across the interfaces is being quantified to determine its influence on the thermodynamic stabilizing energies. A series of experiments were done to determine the fidelity and optimal operating conditions of the technique. A series of Cu films were grown with various Co underlayer thicknesses. The influence of thermal retention in the Co layer (which has ~4X lower thermal conductivity than Cu), was explored under thermal assisted field evaporation. The results showed significant loss of Cu mass resolution with increasing Co thickness, figure 1. This work was done by a REU student, Kristy Tippey, and presented at Microscopy & Microanalysis 2013. This work provides researchers insights into the operating boundaries of the technique.

Growth stresses: As a thin film grows, the adatoms undergo various intrinsic tensile or compressive stresses as they migrate over the surface. These stresses give insights into mobility. By comparing the phase state of the metal to the stress response, this research explores how stresses are changing under the phase transformation. These results are then coupled to the amount of intermixing determined from the APT studies. Figure 2 is plot of growth stresses in Ti/Nb, which shows that the amplitude of an oscillating stress decreases with a transition from HCP Ti/BCC Nb to BCC Ti/BCC Nb. Interestingly, BCC Ti and BCC Nb, which both have the same lattice parameter, still shows oscillatory stress behavior. It appears that chemical interactions and intermixing are influencing the adatom mobility even when each layer is crystallographically equivalent upon deposition. Work performed by graduate student, Li Wan.

Figure 1. Differences in the full width half maximum of the Cu 63+ peak for various specimen thicknesses and laser operation conditions.

Figure 2. Stress evolution during Ti/Nb growth

Engaging Teachers and Scientists through Materials Education Forums Gregory B. Thompson, University of Alabama Tuscaloosa, DMR 1207220

Broader Impact

Engaging students in materials science and engineering is a critical component in developing the rising generation work force for our national economy. As evident with several steel mills (Nucor, US Steel, TK) and casting companies in Alabama, materials manufacturing for the primary metals market is a key contributor to the state’s economy.

PI Thompson has teamed with Professor Martin Bakker (Chemistry) in hosting an ASM Materials Camp on the campus of the University of Alabama in June 2013. Approximately 30 secondary education teachers, figure 1, participated in a one-week workshop where they learned to incorporate materials education into physics, chemistry and mathematical curriculums. PI Thompson and Prof. Bakker personally recruited teachers from Tuscaloosa, Montgomery, and Huntsville areas.

As part of the camp, low cost materials-orientated demonstrations were shown that reinforce science-based concepts. By engaging the teachers, the impact of materials education can be realized for hundreds of Alabama middle/high school students.

The workshop included “Master Teachers” from ASM who provided instruction with PI Thompson and Prof. Bakker giving guest lectures and assistance in the demonstrations.

PI Thompson was the Chair for the 2012 International Field Emission Society meeting (www.ifes2012.ua.edu). This biennial meeting is the premiere gathering of high field nanoscience and atom probe researchers. The conference was held on the campus of UA and included over 170 participates, with 42 being students, from 15 countries. The symposium had 110 oral presentations and over 70 poster contributions.

Figure 2: IFES conference photo

Figure 1: (left) ASM Materials Camp participants; (right) Steel plant tour to Nucor as part of the ASM Camp