Date: Thursday, Nov 5th
Presenter: John Donovan, Director, Microanalysis Facility, Center for Advanced Materials Characterization for Oregon
The homogeneous bulk assumption used in traditional electron probe microanalysis (EPMA) can be applied for thin-layered systems with individual layers as thick as 50 nm provided the penetration depth of the lowest accelerating voltage exceeds the total film thickness. Analysis of an NIST Ni-Cr thin film standard on Si using the homogeneous model yielded certified compositions and application of the same model to ultra-thin Ni-Si layers on GaAs yielded their expected compositions. In cases where the same element is present in multiple layers or in the substrate as well as the film, the homogeneous assumption in EPMA alone is not sufficient to determine composition. By combining x-ray reflectivity (XRR) thickness and critical angle data and using an iterative approach, quantitative compositional data in EPMA can be achieved. This technique was utilized to determine the composition of Ni-Si ultra-thin films grown on silicon. The Ni-Si composition determined using this multi-instrumental technique matched that of Ni-Si films simultaneously deposited on GaAs.
Currently Director of the Microanalysis Facility in the Center for Advanced Materials Characterization for Oregon (CAMCOR) Facility at the University of Oregon where he is a recognized expert in electron beam instruments including the electron microprobe and scanning electron microscope.
John specializes in the development of new quantitative techniques and algorithms to improve accuracy quantitatively at the micro and nano scales of both chemical information and spatial dimensions. Recently his work has focussed on improving methods for accurately quantifying thin film chemistry using the electron microprobe. He is the author of several papers on various techniques for quantifying spectral interferences, modeling of background corrections and the atomic number effect in electron solid interactions. He has developed the popular software package (Probe for EPMA) available for acquisition, automation and analysis on electron microprobes, which is used by over 60 leading research institutions and many commercial companies including Berkeley, Stanford, Yale, Washington University, Exxon, Lockheed-Martin, Dow Corning, Westinghouse, General Electric, Babcock and Wilcox, Battelle, Cal Tech, NASA and NIST.