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XPS techniques for surface analysis
Understanding the chemistry of surfaces and sub-surface interfaces relies on the use of several different XPS experiment modes, and even the use of complementary analysis techniques such as UPS, REELS, or Raman spectroscopy. From single point-and-shoot analysis to complex multi-modal methods, Thermo Scientific surface analysis instruments can offer the methodology you need to maximize the information from your samples.
What is X-ray photoelectron spectroscopy?
XPS can measure the elemental composition, empirical formula, chemical state, and electronic state of the elements within a material. XPS spectra are obtained by irradiating a solid surface with a beam of X-rays while simultaneously measuring the kinetic energy of electrons that are emitted from the top 1 to 10 nm of the material being analyzed.
X-ray photoelectron spectroscopy of small areas
Small-area or selected-area X-ray photoelectron spectroscopy (SAXPS) is used to analyze small features on a solid surface, such as surface blemishes or particles. This technique maximizes the detected signal from a specific area while minimizing the signal contribution from the surrounding area.
Spectra acquired from specific regions of interest of a fluoropolymer deposited on an acrylic acid polymer substrate.
Mitigating XPS charging effect
In cases where the surface is electrically insulating, the accumulation of positive charge on the surface significantly impacts the XPS spectrum. Charge compensation counteracts this effect by supplying electrons from an external source, neutralizing the surface charge. This process stabilizes and regulates the charging to maintain the surface in a nearly neutral state, within a few electron volts.
C1s spectrum of an insulating fluoropolymer coating
XPS depth profiling
Basics of depth profiling
Depth profiling involves the controlled removal of material using an ion beam, followed by data collection at each etching step. This technique provides a high-resolution composition profile, making it possible to examine composition changes from the surface to the bulk. Depth profiles are useful for studying phenomena like corrosion, surface oxidation, and the chemistry of material interfaces.
Depth profiling allows you to move the analysis position into the sample, making it possible to measure the chemistry of interfaces and other layers.
Monatomic and gas cluster ion-depth profiling
The Thermo Scientific MAGCIS Dual-mode Ion Source enables depth profiling analysis and surface cleaning of soft and hard materials on a single XPS instrument. New gas cluster ion sources enable analysis of several classes of materials previously inaccessible to XPS depth profiling.
XPS imaging
In addition to identifying points or small features on a surface, XPS is also used to image the surface of a sample. This is useful for understanding the distribution of chemistries across a surface, finding the limits of contamination, or examining the variation in thickness of an ultra-thin coating. Two approaches — mapping (serial acquisition) and parallel imaging (parallel acquisition) — are used to obtain XPS images.
N1s At% XPS image of BN (red) and residual organic N precursor (green) on a Cu substrate
Angle-resolved XPS
Angle-resolved X-ray photoelectron spectroscopy (ARXPS) collects electrons at varying emission angles, enabling electron detection from different depths. This technique provides valuable insights into the thickness and composition of ultra-thin films.
The variation in the signal intensity seen by changing the detected emission angle for a simple oxide on metal sample.
Hard X-ray photoelectron spectroscopy
Employing X-ray sources with higher energy levels than the standard Al K-alpha source can enhance XPS analysis. This is commonly referred to as HAXPES. The higher photon energy enables deeper analysis and allows access to core levels that are otherwise inaccessible. It can also be combined with X-ray-induced Auger features to generate Wagner plots, aiding interpretation of surface chemical states.
Fe2p data from a NiFeCo surface showing the difference in the depth of analysis using an Al K-alpha and an Ag L-alpha X-ray source.
Correlative imaging and surface analysis workflow
Harness the combined powers of SEM and XPS with the Thermo Scientific Correlative Imaging and Surface Analysis Workflow. By integrating datasets from our XPS and SEM instruments, you can gain deeper insights into your samples.
To gain a comprehensive understanding of a sample, it’s often necessary to analyze it with different instruments. While imaging a sample in an SEM with EDX provides composition information, it may not reveal crucial surface chemistry. On the other hand, XPS offers surface chemistry details but may lack high-resolution imagery to explain the interplay between chemistry and structure. The CISA Workflow bridges this gap, enabling comprehensive sample understanding.
The CISA Workflow combines XPS with SEM analysis to accurately integrate quantitative chemical composition information of the surface with structural information from microscope imagery.
For Research Use Only. Not for use in diagnostic procedures.