Principle

XPS uses a soft X-ray source (Alkα and Mgkα) to ionise electrons from the surface of a solid sample. The binding energy of these electrons are measured and are characteristic of the elements and associated chemical bonds (chemical state) in the top few atomic layers of the material.

Samples can be tilted to affect the escape depth of the electrons and thus determine the depths of overlayers on the surface. For analysis beyond the top 1-5nm an inert gas ion gun (normally Argon) can be used to sputter off the surface layers before analysis. Alternating sputtering and XPS spectral acquisition permits chemical depth profiles to be obtained.

Information from XPS

Main Features of the Laboratory's XPS Capability:

• Quantitative analysis of elements and chemical states of all elements except hydrogen and helium.
• Typical element detection limits are 0.1 atomic% from the top few nm.
• Samples can be conductors, semiconductors or insulators.
• Area of analysis is typically 10mm² but small area to 150μm x 150μm is possible.

XPS Instrument - VG Scientific ESCALAB 200-D:

• Twin anode X-ray source (Alkα and Mgkα)
• 5 channeltron hemispherical sector analyser (HSA)
• Aperture system for small area XPS
• EX05 Inert gas ion source for sample cleaning and sputter depth profiling
• Optical camera alignment of samples
• Multiple sample loading on extended sample stubs
• Turbomolecular pumped fast entry air lock for rapid sample loading
• PC data acquisition and data processing system - www.casaxps.com
• 4 Axis stage with sample heating and cooling options

XPS Instrument - VG Scientific ESCA-III:

• Twin anode X-ray source (Alkα and Mgkα) with small area columnator
• Single channeltron Clam hemispherical sector analyser (HSA)
• Inert gas ion source for sample cleaning
• VG Smart IQ 300amu RGA (residual gas analyser)
• PC data acquisition and data processing system for XPS and RGA
• UHV Diffusion pumped fast entry air lock

XPS survey spectrum of stainless steel CRT gun compontent surface with an evaporated layer on top

Links to other sites

• Thermo VG Scientific http://www.vgscientific.com

Typical Applications:

• CRT (cathode ray tube) cathode heater coating improvement for improved heat transfer and cross-production tool process matching.
• Metal component thermal oxidation or reduction process effectiveness (growth or removal of oxide or surface segregating materials).
• Surface Ni/Cr ratio in a Nickel chromium alloy affecting catalytic gas cracking activity.
• Checking for weak boundary organic layers affecting paint or adhesive adhesion.
• Improvement of chemical cleaning or etching processes.
• Surface oxide thicknesses in semiconductor processes - depth profiling.
• Sputtered layer process chemical characterisation and depth profiling.

Our site expert on XPS is Steve Jenkins.