New Databases for Surface Analysis by Auger-Electron Spectroscopy and X-Ray Photoelectron Spectroscopy

C. J. Powell (CSTL), A. Y. Lee, D. M. Blakeslee, J. R. Rumble, Jr. (SRDP), A. Naumkin, A. Kraut-Vass, A. Jablonski, and W. S. M. Werner (contractors)

Objective: To provide needed reference data for surface analyses by Auger-electron spectroscopy (AES) and X-Ray photoelectron spectroscopy (XPS).

Problem: Surface properties are crucial for the fabrication and performance of a wide range of materials, semiconductor devices, optoelectronic materials, high-density magnetic-storage media, sensors, catalysts, thin films, and coatings. Surface analysis is used not only to correlate the composition of an exposed surface with specific material properties but also for the investigation of interface properties. AES and XPS are the two most commonly used techniques for surface analysis, and reference data are needed to improve the reliability and efficiency of surface analyses made by these techniques.

Approach: NIST established a Surface Analysis Data Center in 1997 to give greater visibility to its existing and planned databases for applications in surface analysis. The development of databases is carried out with the NIST Standard Reference Data Program and with the assistance of contractors.

Results and Future Plans: Three databases are now available for AES and XPS applications, and the development of another has commenced. These databases will be described in turn.

Version 1.0 of the X-Ray Photoelectron Spectroscopy database (SRD 20) was released in 1989, and version 2.0 was released in 1997. These databases have been widely used to obtain binding-energy and related data for elemental and chemical-state analysis of a wide range of materials by XPS. Version 3.0, has been released, will be available for on-line access through the internet and will be free. It will contain a substantial amount of new data and additional information about the specimen material, the measurement conditions, and the data-analysis procedure for each reported measurement. The internet version has been redesigned to facilitate access, searches, and convenience. One feature will enable users to retrieve data by scientific citation. In this way, individual authors will be able to access their own (or others') data and will be able to check database entries. Work is ongoing to provide additional evaluated data for this database.

Version 1.0 of the Elastic-Electron-Scattering Cross-Section Database (SRD 64) was released in 1996. This database provides differential and total elastic-electron-scattering cross sections for elements with atomic numbers from 1 to 96 and for electron energies between 50 and 9,999 eV. It can be used for simulations of signal-electron transport in XPS and AES (and for other applications involving electron transport). Version 2.0, release in 2000, provides transport cross sections (needed for corrections of elastic-scattering effects in AES and XPS) and phase shifts (needed in some simulation codes); in addition, cross sections and phase shifts are available for electron energies up to 20,000 eV.

Version 1.0 of the Electron Inelastic-Mean-Free-Path Database (SRD 71) was released in September, 1999. This database provides calculated and measured electron inelastic mean free paths (IMFPs) for elements, inorganic compounds, and organic compounds. If no calculated or measured IMFPs are available for a material of interest, values can be estimated from two predictive formulae. IMFPs are needed for quantitative analyses by AES and XPS (corrections for matrix effects), determination of effective attenuation lengths (measurement of film thicknesses), determination of mean escape depths (average depths of analysis), and for simulations of the transport of signal electrons.

Work has commenced on a new database to be used for AES and XPS analyses of materials with complex morphologies. SRD 64 and SRD 71 will be combined with additional data to enable comparisons of measured and simulated spectra for particular specimen morphologies and specified analytical conditions.

Web Contact micro@nist.gov