X-ray Photoelectron Spectroscopy
The study and analysis of surfaces can be used as a diagnostic tool to determine why a surface does or does not have desired optical, electrical, mechanical, or even decorative properties. When performing an XPS analysis, the sample is placed in a chamber under Ultra High Vacuum conditions. The sample is exposed to a low-energy monochromatic X-ray source, which results in the emission of photoelectrons from the atomic orbitals of the sample. The electrons knocked out of their orbits have an energy characteristic of each element and the molecular orbital from which they come.
By counting the number of electrons detected at each energy, a spectrum of peaks can be generated that correspond to the elements present in the sample. The area of each peak is a measure of the relative amount of each element present, while their shape and position indicate the chemical environment of each element.
Instrumental Facilities
NEXSA XPS SPECTROMETER, MANUFACTURER: THERMO-FISHER SCIENTIFIC.
Technical characteristics:
- Analyzer type: Hemispherical analyzer with 180° dual focus and 128-channel detector.
- Elemental range: All elements of the periodic table from Lithium (inclusive).
- Type of X-ray source: Monochromatic, microfocused, low-power K-alpha (Kα) aluminum X-ray source.
- Electrostatic charge compensation system: Double beam source of electrons and ions. Energy for charge compensation 0-5 eV.
- X-ray beam diameter: From 10 µm to 400 µm (adjustable in 5 µm steps).
- Three-camera display system.
- In-depth profiling: Dual mode ion source, monatomic ions, materials analysis, cleaning and MAGCIS Polyatomic special for profiling in polymers.
- Maximum display area: 60 X 60 mm (3600 mm2).
- Maximum sample thickness: 20 mm (2 cm).
- Salting system: Two turbomolecular pumps, with automated titanium sublimation pump and oil-free scroll pump. System base salting level 4×10-10 mbar.
- UPS (Ultraviolet Photoelectron Spectroscopy): Gas discharge font. Differential pumping, operation of the Helium font in He(I) or He(II) modes.
- Angle resolved XPS (ARXPS: Sample holder that allows the inclination of a sample in the range +/-90° with respect to the surface normal).
- Maximum sample dimensions 26 X 5 X 5 mm.
- Set of standard samples, apertures and knife edges integrated in the plate for calibration and alignment – Calibration samples: Cu foil, Ag foil, Au foil. Phosphorescent sample for X-ray spot alignment. Cu knife edge for X-ray spot size measurement: Apertures of 180 μm, 250 μm, 350 μm, 500 μm, 700 μm and 1000 μm for alignment and focusing and alignment of the ion beam.
Operating Modes
- Selectable area spectroscopy.
- In-depth profiling.
- Study of composition (elements and chemical species) and estimation of thicknesses in coatings, multilayer systems and oxide layers. Dual mode Source of monoatomic and polyatomic ions Gas Cluster.
- Microfocused monochromator from 10 to 400 µm adjustable in 5 µm steps.
- High-resolution chemical state spectroscopy.
- Analysis of any type of sample, except liquids.
- Acquisition of images with quantitative chemical characterization.
- Processing: quantification, peak adjustments, real-time profile visualization.
- Spectral sensitivity 0.1 AT%.
- UPS Spectroscopy: The UPS spectrum has a shape that corresponds or reflects the electronic structure of the energies of the molecular orbitals. It uses an Ultraviolet radiation source, exciting electrons from outermost levels. Greater surface sensitivity than XPS. Provides information on Valence Band, Fermi levels, Work function.
- Angle-resolved XPS spectroscopy (ARXPS) to characterize ultrathin films without sputtering, non-destructive analysis.
XPS K-ALPHA SPECTROMETER, MANUFACTURER: THERMO-FISHER SCIENTIFIC
Technical characteristics:
- Analyzer: hemispherical with dual 180° focus with 128-channel detector.
- X-ray source: microfocused Al Kα monochromator with variable spot size (from 30µm to 400µm in 5µm increments).
- Ion gun: energy range from 100 to 4000 eV.
- Load compensation: dual beam source.
- Sample handling: 4-axis sample plate, 60 x 60 mm sample surface, maximum sample thickness of 20 mm.
- Load system: 2 turbomolecular pumps of 220 l/s for the analysis chambers and feed.
- Angle resolved XPS (ARXPS): Special Sample holder that allows the sample tilt in the range +/-90° with respect to the surface normal).
Operating Modes
- Selectable area spectroscopy.
- Performing in-depth profiles. Study of composition (elements and chemical species) and estimation of thicknesses in coatings, multilayer systems and oxide layers.
- Microfocused monochromator.
- High-resolution chemical state spectroscopy.
- Analysis of any type of sample, except liquids.
- Acquisition of images with quantitative chemical characterization.
- Processing: quantification, peak adjustments, real-time profile visualization.
Applications
Materials and Metallurgy
- Identification of oxidation states in metals.
- Analysis of passivation and corrosion layers.
- Study of alloys and surface segregation.
- Evaluation of tribological and lubricant coatings.
Polymers and Organic Chemistry
- Identification of functional groups on surfaces.
- Control of plasma or corona treatments.
- Detection of contaminants (silicones, release agents).
- Study of adhesion and bonding of plastics.
Energy and Catalysis
- Characterisation of catalysts (active sites and poisoning).
- Analysis of electrodes in Li-ion batteries.
- Study of degradation in fuel cells.
- Development of materials for solar panels (perovskites).
Microelectronics and Nanotechnology
- Quality control in silicon wafers.
- Thin film thickness measurement (nanometres).
- Analysis of heterostructures and semiconductors.
- Characterisation of quantum dots and graphene.
Biomedicine
- Study of the biocompatibility of implants.
- Analysis of the functionalisation of nanoparticles for drugs.
- Detection of proteins adsorbed on biomaterials.
Environment
- Analysis of atmospheric particles (soot and aerosols).
- Study of pollutant absorption in soils and clays.
Sample requirements
- The samples must be in good condition and therefore must not contain traces of grease, oils, or any composition that endangers the integrity of the equipment and must be non-toxic or harmful.
- Do not handle the surface of the samples with bare hands. Always wear powder-free nitrile gloves. Our recommendation, in the case of a solid sample, is that before bagging the sample in the plastic bag, it should be protected with aluminium foil (commonly used).
- Samples should be of the appropriate size (dimension) for the technique…Samples exceeding the limits should be cut.It is recommended to contact the technical staff of the Service if there are doubts about the dimensions.
- When the samples are identical on both sides, the user must indicate with a mark the side of interest. If the samples are in powder form, they can be sent in a properly sealed and identified eppendorf vial.
- Samples can be powders, fragments, sheets, solutions, dispersions,
- Any type of sample (conductive, insulating, magnetic, organic, inorganic, powder, solid, viscous) as long as it is compatible with high vacuum, without the need for previous coatings or other specific preparations.
- Non-destructive analysis in spectroscopic and mapped modes
- Analyzed area: 20 μm – 400 μm
- Depth of analysis from 3- 12nm (expandable by thinning)
- Upon completion of the work, the samples will be returned to the user in the way is registered on the service form. Samples not delivered to users will be kept at the Service for a stablish period. After this time, the samples will be disposed of as laboratory waste.
More information
Carmen Serra Rodríguez – Tatiana Padín Gómez – Paula Barbazán Martín
+34 986 813 882 – Fax: 986 812 135
cserra@uvigo.es – tatiana.padin@uvigo.es – pbarbazan@uvigo.es