Cedric Powell
I officially retired from NIST in 2006 but continued to work there as a Scientist Emeritus on a part-time basis. Much of my career has been summarized in the historical interview I had with Paul Holloway in 2007. I now provide some updates.
NIST databases for applications in AES and XPS continue to be popular. With the cooperation of Wolfgang Werner and other colleagues in Vienna, improved versions of the NIST Database for the Simulation of Electron Spectra for Surface Analysis (SESSA) have been developed. AES and XPS spectra can now be simulated for nanostructures such as islands, lines, spheres, and layered spheres on surfaces as well as for multilayer films. A new database was developed with Alex Jablonski in Warsaw to provide backscattering correction factors for AES, and another database was developed with Francesc Salvat in Barcelona and Alex Jablonski to give inner-shell ionization cross sections by electron impact. Finally, a new web-accessible version of the NIST Electron Elastic-Scattering Cross-Section Database has been developed with Alex Jablonski. While my main motivation for the development of NIST databases was to improve the availability of data needed for quantitative applications of AES and XPS, some are also of value for other applications.
I have continued my collaboration with Shigeo Tanuma in Tsukuba and David Penn (now also retired from NIST) on the calculation of electron inelastic mean free paths (IMFPs) in many materials. This work started when Shigeo came to NIST on a two-year assignment in 1986 during which we became aware of a powerful algorithm for IMFP calculations that had then just been developed by David. We were able to make these calculations for many elemental solids, inorganic compounds, and organic compounds and to develop a predictive IMFP formula for other materials. Our original focus was on “conventional” AES and XPS, with electron energies between 50 eV and 2 keV, but we expanded the energy range first to 30 keV (for applications in “hard” XPS or HAXPES) and then to 200 keV (for applications in transmission electron microscopy). I continue to have successful collaborations with Alex Jablonski on analyses of elastic-scattering effects in AES and XPS and with Wolfgang Werner on various applications of SESSA. I have also enjoyed collaborations with NIST scientists and with others.
I am very grateful for the opportunities I have had at NIST to develop my scientific career and to interact with many colleagues of different backgrounds. I have also been fortunate in being able to travel to national and international conferences and to serve many different types of professional organizations. I have been an AVS member for 45 years, and I particularly value my association with the Applied Surface Science Division which has been my professional “home” for 32 years. I have been pleased to see it grow and prosper, and particularly to see an influx of younger members.
During my retirement years, my wife and I have had the opportunity to travel to the Galapagos Islands, Costa Rica, China, Japan, Korea, Norway, Russia, France, Italy, Greece, Turkey, and Australia as well as to Alaska, Arizona, Oregon, Washington state, and Puerto Rico. We have enjoyed the scenic wonders of the US and many countries as well as seeing a wide variety of wildlife.
It would have been impossible to predict when I was a graduate student in Perth, Australia that I would have a 55-year career at NBS/NIST and that I would have such a rewarding life. I feel very fortunate. I would finally like to repeat the advice I received from the Principal of my elementary school: “Hitch your wagon to a star!”