AUGER AND XPS SPECTROSCOPY

 

THE LABORATORY

         Objectives

         Contacts

         Conditions


 
INFORMATION ABOUT THE TECHNIQUES

        The Name

        The Background   

        The Information

        The System (Microlab  310F)       


APPLICATIONS NOTE

         Auger analysis

         XPS analysis

LINKS

 

 

THE LABORATORY:

The Auger and XPS laboratory is located at "Edifício Ciência", Level 01 - Room 5.01

The Objectives:

The Auger and XPS laboratory is part of the facilities existing at Instituto Superior Técnico (ICEMS) and the aim of the laboratory is to provide scientific support in surface engineering research. The laboratory provides services to: research groups from IST, from other universities, from research laboratories and from industry.

Contacts: 
For details or utilisation of the techniques please contact:
M. F. Montemor
(mfmontemor@ist.utl.pt)

Conditions for utilisation of the laboratory:

The conditions and prices of utilisation are described elsewhere.
To access the laboratory users must fill the "user file".

 

INFORMATION ABOUT THE TECHNIQUES

The name

Auger Electron Spectroscopy (usually defined as AES) was developed in the late 1960’s, deriving its name from Pierre Auger (a French physicist), who first observed the Auger effect in the mid 1920´s. From that time to nowadays, AES became one of the most powerful analytical techniques for surface analysis.

The Background

The basic Auger process involves four steps (Figure 1)

Removal of an inner shell electron and formation of a vacancy. Several excitation sources are able to produce this vacancy, but bombardment with an electron beam is the most common.

A second electron from a higher shell fills the inner shell vacancy. However, energy must be released in order to balance the process.

A third electron, the Auger electron escapes from the atom carrying the excess energy in a radiation less process - the Auger process. Alternatively, an X-ray photon can also remove the excess of energy.

Analysis of the emitted Auger electrons. This stage is a technical step, which allows detection of the charged particles with high sensitivity and measurement of their kinetic energies.

The information

The kinetic energy of the Auger electrons allows identification of the elements present on the surface under analysis. The area of the Auger peaks is proportional to elemental concentration. During the process, the electrons must leave the surface without energy losses. The electron beam penetrates into a depth of about one cubic micron, however the Auger electrons escape from much smaller volumes . The distance that an electron can travel without energy losses is defined as the escape depth and depends on the electron energy and beam diameter. The minimum escape depth occurs around 80 - 100 eV, and increases for lower and higher kinetic energies.

The System available at ICEMS (Instituto Superior Técnico)

Microlab 310 F Capabilities

Elemental composition in a sampling depth that can attain 20 Å.

Detection of elements heavier than Li. Very good sensitivity for light elements.

Depth profiling, with depth resolution around 20 Å.

Spatial distribution of the elements (Auger maps or analysis in lines, points and areas)

Secondary electron images with spatial resolution down to 200 nm.

Backscattered electrons imaging.

XPS facilities. Non-monochromatic Mg and Al anodes are available. Best energy resolution ~ 0.9 eV.

Limitations:

Samples must be conductive.

Possibility of beam damage of some surfaces

Hydrogen and helium are not detectable.

Quantitative detection is dependent on the element: light elements > 0.1%; heavier elements > 1%.

Accuracy of quantitative analysis depending on the availability of adequate sensitivity factors. Best accuracy ± 10%.

Analysis requirements:

AES - Conductive materials. Cylindrical specimens: max. diameter 1 cm and max. height 1 cm; other shapes: max. largest side 1 cm and max. height 0.3 cm.

XPS – Conductive or non-conductive materials with the same dimensions as above.

Specimen surface not handled. Samples must be clean and free of organics or high vapour pressure contaminants.

Samples are first analysed “as received” and after a short etching to ensure that all contaminants are removed.

Surface elemental composition and quantification takes less than 1 hour.

Depth profiling, Auger imaging and XPS with high-resolution curve fitting require analysis time between 1 and 5 hours.

 

APPLICATIONS NOTE:

  1 - Auger Analysis

A - Chemical composition, thickness and spatial distribution of the elements on cerium conversion layers deposited on galvanised steel. Effect of the treatment time (30 minutes and 24 hours)

B - Characterisation of passive films formed on stainless steels.

C - Study of Cr-free pre-treatments for aluminium alloys

 2 - XPS Analysis

A - Composition of cerium conversion layers deposited on galvanised steel.

B - Characterisation of alkali germanate glasses.

C - Degradation of temperature aged coatings.