Monochromatic X-ray sources provide significant advantages over conventional Mg/Al dual mode sources with narrower excitation lines and lower backgrounds due to the removal of the Bremsstrahlung radiation. These features make it an ideal X-ray source for chemical characterization of sensitive materials such as polymer surfaces.

A major benifit to using a monochromatic source is the ability to identify differant chemical species located at the surface. This capability is suitably illustrated using an material such as Polyethylene terephthalate (PET), whose structure is shown below. This material has 3 distinct and easily identifiable carbon species. In addition a fourth species can be detected as an asymmetry on the main C-C peak. This asymmetry can only be observed under high resolution conditions. (This peak was postulated by Pijpers and Donners¹ to account for secondary substituent effects induced by the carboxyl group).

C 1s spectrum acquired with monochromatic x-ray source

The above spectrum illustrates the capability of the AXIS spectrometers to obtain high resolution data from polymeric materials. The FWHM of the ester C 1s peak in the above example is 0.68eV which was obtained using 10eV pass energy and 450W Al Kα monochromatic X-rays. No special sample mounting techniques were used (such as a mask).

1) A.P. Pijpers & W.A.B. Donners, J. Polym. Sci. Chem. Ed'n. 23, (1985), 453

Neutralisation of insulating samples - specifications

XPS peformance on insulators for the AXIS spectrometers is guaranteed by specification defined using a polymer. The standard used is PET (polyethylene terephthalate) which has the chemical stucture shown. The specifications are defined as the cps from the CC,CH component at 285eV and the FWHM of the ester component C-C(=O)-O- ) at ca.289 eV.

PET Specification

ARXPS of Insulating Materials

During an angle resolved experiment the sample is rotated with respect to the x-ray source and the collection lens column. For an  insulating sample this can challenge the neutralisation system as the x-ray illuminated area and the collection areas are changing. With the co-axial system such experiments pose no problem as demonstrated by the following example:

C 1s region acquired at normal and grazing emission