1. What is XPS?
XPS (x-ray photoelectron spectroscopy) is also known as ESCA (electron spectroscopy for chemical analysis).
XPS provides chemical information via binding energy measurements.
XPS is a surface analysis technique with an average analysis depth of 50Å.
XPS has an average detection limit of 0.05 atom percent.
XPS is highly quantitative.
XPS provides spatial distribution information via mapping or depth profiling.
Ejected Photoelectron
X-ray Excitation

2. Electron Spectroscopy for Chemical Analysis
ESCA is an analytical technique that obtains compositional information from the top few monolayers of a material by probing the sample with a mono-energetic X-ray beam. ESCA is also known as XPS (X-ray Photoelectron Spectroscopy).
Detect: all elements above He
Detection limits: atomic %
Analysis depth: nm
Spatial resolution: <10µm probe size

3. ESCA Provides Surface Sensitivity Detection of all Elements above He
Quantification
Chemical State Identification
Chemical State Distributions
Mapping
Sputter Depth Profiling
Angle Dependant Depth Profiling

4. Binding Energy = X-ray Energy - Photoelectron Kinetic Energy
ESCA Process
Photoelectron
Efermi level
3/2 2p
1/2
X-ray (photon)
Binding Energy 2s 1s
Binding Energy = X-ray Energy - Photoelectron Kinetic Energy

5. ESCA System Schematic Energy Analyzer (SCA) Quartz Crystal
Monochromator
Electron Source
Al ka x-rays
15-20 kv electrons
Input Lens
Multi-channel
Detector
Rowland
Circle
Photoelectrons
Al Anode
Sample

6. Application Areas for XPS
Surface chemistry:
Adhesion, corrosion, bio-compatibility, lubrication, catalysis, surface cleanliness,
processing residues, composition of thin layers, migration of impurities or additives
from the bulk, etc..
Interface chemistry:
Contamination, migration of impurities or low level bulk components, interdiffusion of layers.
Construction analysis:
Thin film chemical analysis, imaging and cross-section analysis.
Particle analysis:
Micro analysis of small particulates, defects or features.

7. ESCA Spectra from Poly(ethylene terephthalate)
Atom % C O
PET
-O1s
C 1s O O
-C1s O C C O
CH2
CH2
% of C 1s CH
C-O
O=C-O 17.1
c/s
c/s
C-O=O
C-O CH
-O KLL
-O2s
1000
800
600
400
200
300
295
290
285
280
Binding Energy (eV)
Binding Energy (eV)
ESCA survey spectra provide quantitative elemental information.
High resolution ESCA spectra provide quantitative chemical state information.

8. ESCA Sputter Depth Profile
185 20 40 60 80
100
Sputter Depth (nm)
Atomic Concentration (%)
Si 2p
O 1s
Cr 2p
Ni 2p
The analysis of thin film structures to verify composition or search for impurities at interfaces is a routine task for PHI ESCA instruments.

9. SPS Photo of Paint System Cross-section Showing area defined for ESCA maps
Polyethylene
Mapping Area
Substrate
Adhesion Layer
Base Coat
Clear Coat
695 x 320µm
1072 x 812mm

10. ESCA Maps of an Automotive Paint Cross-section
695 x 320mm

11. Chemical State Maps for Carbon
C 1s
Chemical state maps are generated by examining the C 1s spectra stored at each pixel of the map.

12. Angle Resolved Analysis
XPS ESCA/
Angle Resolved Analysis
Sample is tilted with respect to x-ray source and analyzer
Angle determines sampling depth (d)
Analyzer
Analyzer
X-ray Source
X-ray Source
Q = 10o
Q = 90o d1 L1 L2
d = lsinq = Sampling Depth d1 > d2 L1 = L2 d2
ECA-FP-06-01A

13. Plasma Treated Polymer, Angle Resolved Analysis
XPS ESCA/
Plasma Treated Polymer, Angle Resolved Analysis
High Sensitivity Mode
90º Take Off Angle
C 1s
Greater sampling depth
More surface sensitive
N (E)/E
C AUGER
O 1s
O AUGER
1000.0
500.0
0.0
O 1s
10º Take Off Angle
C AUGER
N (E)/E
O AUGER
C 1s
1000.0
500.0
0.0
Binding Energy (eV)
ECA-AP-08-01C

14. Ion Beam Depth Profiling
XPS ESCA/
Ion Beam Depth Profiling
Depth profiling features
Energetic (1–4 keV) Ar+ ion beam
1–50 nm/min sputter rates
Alternating sputter/spectral data acquisition
High resolution elemental windows
Zalar™ rotation for enhanced depth resolution
Issues
Energetic ion beam can change sample chemistry
All organic information lost
Preferential sputtering may change observed stoichiometry
Ion Milling with XPS is fundamentally the same as milling with Auger. However, because of the larger spot size (in some cases) and the desire for chemical state information, there are some important differences.
ECA-AP-18-08A

15. Quantification
In contrast to other surface analysis techniques the mechanisms for quantification of XPS data are relatively well understood.
PHI is a leader in applying current methodology and obtaining the empirical data needed to provide accurate quantification.
PHI uses the following building blocks to provide accurate quantification:
A standardized set of sensitivity factors based on PHI’s library of empirical data.
Algorithms to model the transmission function of the spectrometer.
Corrections for geometric asymmetry related to the angle between the X-ray source and the analyzer input lens
Key information including transmission function parameters are stored with data files to allow accurate quantification at any data reduction station.

16. Application Areas for XPS
Surface Sensitivity
X-rays
Escaping photoelectrons
Application Areas for XPS
X-rays penetrate deep into the sample surface, exciting photoelectrons. However, photoelectrons can travel only a short distance before their energy is modified due to interaction with another atom. Only photoelectrons that escape at their original energy contribute to a peak in a spectrum. This phenomena makes ESCA a very surface sensitive technique, with an average depth of analysis of 5 nm or less.

17. Which System Meets Your Needs?
PHI
5800
MultiTechnique
ESCA
PHI
Quantum 2000
Scanning ESCA
Microprobe
low
medium
high