XANES microspectroscopy of biominerals with photoconductive charge compensation

Citation
B. Gilbert et al., XANES microspectroscopy of biominerals with photoconductive charge compensation, J ELEC SPEC, 114, 2001, pp. 1005-1011
Citations number
14
Language
INGLESE
art.tipo
Article
Categorie Soggetti
Spectroscopy /Instrumentation/Analytical Sciences
Journal title
JOURNAL OF ELECTRON SPECTROSCOPY AND RELATED PHENOMENA
ISSN journal
0368-2048 → ACNP
Volume
114
Year of publication
2001
Pages
1005 - 1011
Database
ISI
SICI code
0368-2048(200103)114:<1005:XMOBWP>2.0.ZU;2-D
Abstract
Specimen charging under X-ray illumination is a well known phenomenon that can seriously obstruct the analysis of insulating samples. Synchrotron X-PE EM spectromicroscopy can reach a lateral resolution of 20 nm, 1-2 orders of magnitude larger than electron microscopies, but has the added capacity to probe oxidation state through total yield X-ray absorption near edge struc ture (XANES) spectroscopy. This capability may be compromised, however, if specimen charging restricts electron emission, as was encountered in the st udy of silicified bacteria from an Icelandic hot spring microbial mat. Bact eria living in an environment containing a high concentration of dissolved silica provide nucleation sites for amorphous silicate precipitation, a pro cess which may lead to the preservation of the cellular structure, i.e. fos silization. TEM studies of bacteria in progressive stages of mineralization showed that mineral formation was initiated in the extracellular sheath, r eaching the cell interior after death. Spectromicroscopy at the Si L-edge o f sectioned mineralized bacteria encountered major charging difficulties, w hich were relieved by simultaneously illuminating the specimen with 325 nm HeCd laser light during the analysis. The low energy light excites mobile f ree electrons below the work function threshold, which can offset surface p ositive charge. This approach allowed spectroscopy to be performed from mic roscopic areas, and may be applicable to a wider range of insulating sample s. (C) 2001 Elsevier Science B.V. All rights reserved.