The investigation of ordering at solid-liquid interfaces is important both for fundamental science and for many technological processes. Theoretical and experimental approaches have been used to study ordering of a liquid adjacent to a crystalline solid for the last 40 years [1]. Transmission electron microscopy (TEM) provides a convenient tool for direct imaging of the solid-liquid interfaces, and high resolution TEM measurements correlated with theoretical approaches were recently used in order to unambiguously prove the existence of order in liquid Al adjacent to (0006) plane of crystalline sapphire, and to quantify the degree of order at the Al-Al2O3 interface [2,3].
While the geometrical structure of ordered liquid adjacent to sapphire surfaces can be resolved using advanced HRTEM methods, an additional technique should be used in order to probe the composition of the liquid. Electron energy loss spectroscopy (EELS) is known to be a very precise method for probing the energy of metal bulk plasmons. This energy can be directly correlated with the atomic nearest neighbors number (i.e. the local density). Consequently, EELS spectra of solid and liquid Al bulk plasmons have a distinctive temperature-dependent shift [4,5]. In the current study the energy of Al bulk plasmons was also found to be sensitive to local ordering of the liquid aluminum adjacent to sapphire surfaces. EELS spectra acquired from liquid aluminum at various sapphire surfaces showed an increase in density of the aluminum compared to the bulk liquid aluminum, confirming the ordering phenomenon shown by HRTEM. Moreover, comparison of the EELS data with that of HRTEM provides unique information regarding preferential oxygen segregation in liquid Al towards specific sapphire surfaces.
The in-situ heating experiments were conducted using a monochromated and Cs-corrected FEI Titan 80-300 S/TEM. The microscope is equipped with a Gatan double-tilt hot-stage and the Gatan Tridiem 866 high resolution energy filter for sub-eV EELS investigations.
References:
1. W. D. Kaplan and Y. Kauffmann, Annual Review of Materials Research 36 (1), 1 (2006).
2. S. H. Oh, Y. Kauffmann, C. Scheu, W. D. Kaplan, and M. Ruhle, Science 310 (5748), 661 (2005).
3. Y. Kauffmann, S. H. Oh, C. T. Koch, A. Hashibon, C. Scheu, M. Ruhle, and W. D. Kaplan, Acta Materialia 59 (11), 4378 (2011).
4. H. Abe, M. Terauchi, R. Kuzuo, and M. Tanaka, Journal of Electron Microscopy 41 (6), 465 (1992).
5. S. K. E. Moorthy and J. M. Howe, Journal of Applied Physics 110 (4) (2011).