Title
Damage and molecular changes under a laser beam in SEM-EDX/MRS interface : a case study on iron-rich particles
Author
Faculty/Department
Faculty of Sciences. Chemistry
Faculty of Medicine and Health Sciences
Publication type
article
Publication
Dordrecht ,
Subject
Chemistry
Source (journal)
Journal of Raman spectroscopy. - Dordrecht
Volume/pages
42(2011) :4 , p. 808-814
ISSN
0377-0486
ISI
000290484700033
Carrier
E
Target language
English (eng)
Full text (Publishers DOI)
Affiliation
University of Antwerp
Abstract
The control of damage to individual environmental particles by a laser beam during Raman spectroscopy carried out in ambient air is generally well understood. The nature and control of damage under vacuum conditions (e.g. in the scanning electron microscopy with energy X-ray detection combined with micro-Raman spectroscopyinterfaced SEM-EDX/MRS) are more complex and less well comprehended. The physical and chemical processes that affect the damage caused to small particles by lasers still remain somewhat unclear, but certainly the atmosphere (vacuum/air) and the beam intensity have very significant influences. Furthermore, it has been determined that some particles (e.g. haematite), although stable under an electron beam, are damaged by the laser beam, hampering their analysis. Additionally, when simultaneous analyses by SEM/EDX and MRS are considered, the correct choice of the collection surface plays a crucial role. As a result, the following collection substrates were tested to determine their influence on the laser beam damage process to the particle: silver and aluminium foils and silicon wafers. A test study was performed using artificial examples of haematite (Fe2O3) particles. Exposure of Fe2O3 particles in vacuum to 514- and 785-nm laser radiation often leads to their melting, transformation and evaporation. The dependence of the damage caused by the laser beam on the particle structure is reported here. Molecular and crystallographic changes have also been revealed. Formation of magnetite (as an effect of re-crystallisation) and Raman inactive structures was detected.
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