XPS is widely used for Quality Control and Quality Assurance that can be either Qualitative or Quantitative Analysis of a product with a surface that has specific chemistry features. Those features can be determined by measuring a single XPS signal from a single element which allows the QC or QA meaurement to be very fast for high throughput checks. The C (1s) signal, the Si (2p) signal, the Al (2p) signal are a few signals that display 2 well separated peaks that appear within a 20-30 eV spectral window.
For example, the amount of Fluorine that bonded to an activated surface of Polyethylene can be estimated by looking the Carbon-Fluorine peak at 290 eV and comparing its’ intensity to the Carbon-Carbon peak at 285 eV.
In a similar fashion, Aluminum bond pads are analyzed by recording only the Al (2p) signal and comparing the Aluminum-Oxide peak at 75 eV to the pure Aluminum-Aluminum peak at 73 eV. When the Aluminum-Oxide peak intensity is too large, bonding often fails.
Gold is often coated onto electrical leads. The gold should not have any Nickel or Copper on the surface when the Gold coating is designed to be part of a Military level specification. A survey spectrum of the gold lead can easily reveal the presence of trace level Copper or Nickel peaks at 932 eV and 855 eV, respectively because Gold does not have any peaks that overlap the main Copper and main Nickel peaks.
There is however a common problem with Gold leads. Gold easily collects Adventitious Carbon compounds from the air, handling and packaging. When this Adventitious Carbon layer becomes too thick (>8 nm) a very low current of electricity can not properly pass through the thick Carbon layer. As a result, low current or low capacitance circuitry fails. A fast survey scan will easily reveal a large carbon signal at 285 eV.
Other examples of how XPS is used for Qualitative Analysis include: Carbon coating thickness for HDD, Silicone oil contamination on paper labels that will cause adhesion failure when the label is removed.
Qualitative analyses using XPS are often simple “Sample A” vs “Sample B” or Good versus Bad comparisons. The resulting survey spectra can be similar or radically different as revealed by overlaying the two spectra.