[Todos] PROXIMO SEMINARIO

[Fernando V. Molina]

Lunes 12 de noviembre - 13 hs

Aula de Seminarios del INQUIMAE, 3er piso Pab. II


Michel J. Genet
Unité de chimie des interfaces
Université catholique de Louvain
Louvain-la-Neuve (Belgium)


"X-ray photoelectron spectroscopy: a powerful 
tool applicable to all types of surfaces"

Abstract:

Most materials, but also living systems, are made 
of many constituents between which are 
boundaries: surfaces and interfaces. There is a 
growing interest in characterizing the surface of 
materials: atomic and molecular composition, 
properties, organisation of their constituents in 
space. This presentation will be focused on X-ray 
photoelectron spectroscopy (XPS - ESCA). This 
technique, developed in the 1960's, is applicable 
to all kinds of materials and in all research 
areas. The number of papers, in which XPS is 
involved, continues to progress from year to year.

A survey of the principles of XPS as well as on 
the instrumentation will be proposed, 
concomitantly with an overview of its qualitative 
and quantitative potentialities. A sample, 
introduced in an ultra high vacuum chamber, is 
irradiated with an X-ray beam. The kinetic energy 
of emitted electrons of all elements (except H 
and He) present at the surface (analyzed depth 
between 1 and 10 nm) is measured with a precision 
of about 0.2 eV. Shape and position of peaks 
depend on the chemical state of the element (the 
so-called "chemical shift" effect). Area of peaks 
used in combination with elemental sensitivity 
factors allow to calculate elements 
concentrations with a detection limit of a few 
tenths of mole percent. A detailed analysis of 
certain well-resolved peaks allows quantifying 
the chemical functions present at the surface. On 
most recent systems the lateral resolution is 
about 15 µm and 5 µm in spectroscopic and imaging modes, respectively.

Data interpretation will be illustrated by some 
recent results obtained in very different areas: 
from steel corrosion to bio materials, from minerals to food products.

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