X-ray Photoelectron Spectroscopy, Paper Surface Analysis By

X-ray photoelectron spectroscopy (XPS) also popularly known as electron spectroscopy for chemical analysis (ESCA) involves the irradiation of a solid surface in ultrahigh vacuum with monoenergetic soft X-rays. The X-rays cause electrons of an atom to be ejected and to be ionized as photoelectrons. The number of electrons and their kinetic energies are then measured. The energy of the emitted electron is very characteristic of the atom from which the electron originated and its environment. The XPS spectrum is a plot of the number of emitted electrons per energy interval versus their binding energies. Quantitation can be achieved either by fundamental parameter calculation or comparison with appropriate standards. In the pulp and paper industry, XPS has successfully been used to study migration of binder in coated paper, the surface chemistry of pulps and its effect on the properties of the final products; the adhesion between paper and polymer, toner or ink; and the chemical additives on the paper surface.

As with most analytical instrumentation, XPS has its limitations and disadvantages and is often used in conjunction with other, complementary techniques such as SIMS (secondary ion mass spectrometry) and FTIR (Fourier transform infrared) spectroscopy for the identification of organic compounds on paper surfaces. XPS is surface sensitive which renders it useless if the underlying cause of the problem might be other than surface related. XPS provides only semiquantitative information. A more precise quantification of the elements is possible, but requires exhaustive calibration.