X-Ray Photoelectron Spectroscopy

Thermo ScientificTM ESCALAB Xi+ 

The Thermo ScientificTM ESCALAB Xi+ X-ray Photoelectron Spectrometer (XPS) is the latest development in the ESCALAB product series. The ESCALAB Xi+ is an expandable, optimized, multi-technique platform with unparalleled flexibility and configurability. Cutting edge technology, driven by intuitive software and hardware, leads to world class results and productivity. System control, data acquisition, processing and AvantageTM reporting are seamlessly integrated by the powerful Thermo ScientificTM data system.

Principle

XPS uses a soft X-ray source of Al Kα (1486.6 eV) or Mg Kα (1253.6 eV) to ionise electrons from the surface of a solid sample. The emitted electrons have measured kinetic energies given by;
                


Where, hν is the energy of the photon, BE is the binding energy of the atomic orbital from which the electron originates, and ϕ is the spectrometer work function. XPS is a quantitative spectroscopic technique which analyses the average surface chemistry of a sample up to a depth of approximately 5nm. This technique quantitatively measures the elemental composition, atomic concentrations and chemical states of elements present at a samples surface. XPS can detect all elements with an atomic number greater than 3, therefore Hydrogen and Helium are not possible to detect. 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.

Strengths

Large Area Spectroscopy (LAXPS) 
The combination of high efficiency lenses and detectors ensures the highest sensitivity for large area spectroscopy applications; high resolution spectra acquired in seconds
• Maximum chemical detectability
• Six channel electron multipliers for maximum dynamic range
• Twin crystal monochromator for maximum X-ray flux

Small Area Spectroscopy (SAXPS)
ESCALAB Xi provides fast and precise small area analysis.
• Small feature analysis from greater than 900 µm to 20 µm
• Source-defined analysis from greater than 900 µm to less than 200 µm
• Lens-defined small area down to less than 20 µm
• Software enabled feature selection via real time iris and image control

Fast Parallel Imaging (XPI) 
Parallel imaging produces rapid, high-resolution XPS chemical images.
• Less than 3 µm chemical imaging resolution
• Small area retrospective spectroscopy less than 6 µm
• Signature free detection system
• Imaging of both large and small features
• Single input lens and analyser for imaging and spectroscopy
• Collection of image stacks for quantitative chemical state imaging

Depth Profiling
The advanced new ion gun provides high current density even at low beam energy. Auto-tuning of the ion gun ensures optimum crater quality and profiling speed.
• Azimuthal and off-axis sample rotation during profiling
• Full computer control of the ion gun operation modes
• Automated gas handling for etch rate repeatability

Angle Resolved XPS 
• Software controlled angular resolution ensures optimum repeatability
• Eucentric tilt for constant analysis position regardless of sample thickness
• Direct mechanical drive ensures accuracy and precision of tilt position
• Integrated suite of ARXPS processing tools, including Max-Ent (profile reconstruction) and multilayer thickness calculator

Reflection Electron Energy Loss Spectroscopy (REELS) 
Complementary electronic, structural and phase information can be provided using the ESCALAB Xi in-lens electron source.
• Hydrogen identification and quantification for polymers and other materials
• Narrow energy spread and an energy range of 0 to 1000 eV

Ion Scattering Spectroscopy (ISS)
Reversible polarity lens and analyzer power supplies make ISS a standard feature.
• Channel electron multipliers provide maximum dynamic range while avoiding image detector damage

SEM, SAM  
The ESCALAB Xi can be configured with a Schottky field emission source.
• Multiple channel electron multiplier detector essential for high count rates

Ultra-violet Photoelectron Spectroscopy (UPS)
Rapid, high-resolution UPS measurements are possible with the high-flux UV lamp option.
• Excellent electronics stability and low-energy performance required for work-function measurements
• Mu-metal analysis chamber provides optimum magnetic shielding

Limitations

XPS
· The smallest analytical area XPS can measure is ~10 um
· Samples for XPS must be compatible with the ultra high vacuum environment
· As XPS is a surface technique, there is a limited amount of organic information XPS can provide
· XPS is limited to measurements of elements having atomic numbers of 3 or greater, making it unable to detect hydrogen or helium
· XPS spectra also take a long time to obtain. The use of a monochromator can also reduce the time per experiment.

UPS
· UPS is capable only of ionizing valence electrons, which limits the range and depth of UPS surface experiments
· Conventional UPS has relatively poor resolution.

Applications

• Surface contamination/abnormality analysis
XPS is a surface analytical technique to measure the material composition of elements and chemical states in the surface range between 1 and 10nm. Thus it is used to explore surface abnormality, such as contamination, discoloration, defection, and metal corrosion.

• Thin film composition and depth analysis 
XPS can be used to detect the composition of thin films. By combining argon ion source sputtering, it is able to produce high quality depth profiles with excellent resolution.

• The determination of the oxide thickness and oxidation degree for metal surfaces 
XPS can provide the composition of metal alloy and surface oxide and thus reflects surface oxidation degree. In addition, the surface oxide thickness of samples can be determined either by non-destructive (film thickness is less than 10nm) or destructive depth profiling.

• Work function analysis of metal materials
XPS measurement can be used to detect the work function of metal materials.

Technical Specifications

• Twin anode Non-Monocromated XPS facility
• Dual anode Mg Kα/Al Kα Micro focused monochromated Al Kα X-ray sources and dual anode Al/Mg K α source
• Double focusing full 180 degree hemispherical analyzer with magnetic and multielement electrostatic input lenses for spectroscopy.
• 10 eV Auger Electron Source.
• UHV Mu-Metal chamber and sample preparation chamber for the XPS system along with standard Preploc chamber
• Mini view point with a computer controlled LED light sources
• Preloc Chamber Vacuum: 7x10^-9 mbar 
• Vacuum level in analysis chamber: ≤5x10^-10 mbar
• Flood gun- charge neutraliser system.
• Source-defined area selection: The monochromated X-ray beam can be focused to spot sizes ranging from 900 µm to 200 µm
• Lens-defined area selection: Computer-controlled irises in the transfer lens can be set to provide a lateral resolution down to 20 µm. Performed to scan with a larger area which coveran area of 8 mm x 8mm
• Source for Depth profiling: Ion source (Argon ion) and Argon ion cluster