CHEM02200704003 Nilamadhab Pandhy - Homi Bhabha National ...

Chapter 3
repeated over three different places on the surface, and the data presented is a representative of the
whole surface. The pressure inside the chamber during measurement was around 10 -7 Pa.
3.1.4.3 X-ray Photoelectron Spectroscopy
X-ray Photoelectron Spectroscopy (XPS) or Electron Spectroscopy for Chemical Analysis
(ESCA) is a surface analysis technique that is unique in providing the information regarding the
bonding in different chemical states of elements. Its application is wide spread involving oxidation
state determination of elements, identification of the chemical state of the metal oxide films,
surface analysis of semi-conducting and insulating materials, and elemental depth profiling etc
[85-87]. XPS in combination with traditional electrochemical techniques has long been used for
understanding and solution of different types of corrosion problems. It is invaluable in the field of
corrosion science, and the areas of corrosion research which are finding major applications are (a)
for understanding the phenomenon of passivity, (b) compositional analysis at interface, (c)
selective oxidation phenomenon, (d) assessment of mass transport process, and (e) the interaction
of materials in different electrochemical environment [88-90]. However, the inability to detect
hydrogen is one of the limitations in understanding greater details of overlapping mechanism of
various corrosion phenomena [91].
XPS involves irradiating a sample with X-rays of a characteristic energy and measuring the
energy of flux of electrons leaving the surface [92]. The energy spectrum for the ejected electrons
is a combination of an overall trend due to energy loss processes within the sample, transmission
characteristics of the spectrometer, and resonance structures that derive from electronic states of
the material under analysis. In principle it consists of (a) X-ray source, (b) electronic focusing
system, (c) electron energy analyzer, and (d) detector. The schematic of X-ray photoelectron
spectroscopy is shown in Fig. 3.7 [92].