product review
XPS Up Close XPS instruments have followed chemistry to smaller and smaller scales. Elizabeth Zubritsky
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nalytical techniques focus more and more on smaller samples and faster analyses, and X-ray photoelectron spectroscopy (XPS)—the surface chemical analysis technique that is also known as electron spectroscopy for chemical analysis, or simply ESCA—is no exception. Although the applications for XPS remain largely the same—qualitative and quantitative inspections of surfaces and studies of growing and modified surfaces— researchers want to perform ever more detailed analyses. As samples become smaller, thinner, and more heterogeneous, “We’re doing a lot more analyses where people want to know, ‘What’s within this 10-micron feature? What’s this particle?’” says Julia Fulghum, a professor at Kent State University whose laboratory is a test site for XPS instruments from Kratos Analytical. In addition, the analysis of organic samples such as polymers and biomaterials has become increasingly important, she adds. In keeping with this trend, experts point to three areas in which most of the progress in XPS has occurred over the past five or six years: small-area spectroscopy, depth profiling, and imaging. The selected instruments listed in Table 1, which is not meant to be a comprehensive list, reflect this change. In particular, current instruments tend to have better spatial and energy resolution and faster data acquisition than their predecessors (Anal. Chem. 1995, 67, 675 A–678 A).
Small-area analysis In basic XPS spectroscopy, an X-ray beam hits the sample and ejects photoelectrons
M A Y 1 , 2 0 0 1 / A N A LY T I C A L C H E M I S T R Y
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product review
Table 1. Summary of selected commercial X-ray photoelectron spectroscopy instruments. Product
Axis Ultra
Quantum 2000
UNISPECS 3
Company
Kratos Analytical 100 Red Schoolhouse Rd. Bldg. A Chestnut Ridge, NY 10977 845-426-6700 www.kratos.com
Physical Electronics 6509 Flying Cloud Dr. Eden Prarie, MN 55344 952-828-6100 www.phi.com
SPECS GmbH Voltastrasse 5 13355 Berlin, Germany +49 30 467 8240 www.specs.de
Other techniques AES
SEM
AES, scanning AES, ISS, LEED, SIMS, and UPS
Source
Dual-anode Mg/Mg or Mg/Al and/or 500-mm Rowland circle monochromator
Scanned, focused monochromatic X-ray source
Dual-anode achromatic source; Rowland circle monochromator optional
Charge neutralization
Integral with base of analyzer input lens; uniform flood of low-energy electrons
Dual-beam flood of low-energy electrons and Nonfocused electron flood gun low-energy ions
Energy analyzer
165-mm hemispherical analyzer and concentric spherical mirror analyzer with electrostatic and magnetic lenses
Hemispherical analyzer with electrostatic input lens
Electrostatic hemispherical analyzer with multielement, multimode electrostatic lensing
Real-time parallel imaging
Focused, scanned X-ray beam
No imaging
Resolution
