TY - JOUR
T1 - Specimen thickness dependence of hydrogen evolution during cryo-transmission electron microscopy of hydrated soft materials
AU - Yakovlev, S.
AU - Misra, M.
AU - Shi, S.
AU - Libera, M.
PY - 2009/12
Y1 - 2009/12
N2 - The evolution of hydrogen from many hydrated cryo-preserved soft materials under electron irradiation in the transmission electron microscope can be observed at doses of the order of 1000 e nm-2 and above. Such hydrogen causes artefacts in conventional transmission electron microscope or scanning transmission electron microscopy (STEM) imaging as well as in analyses by electron energy-loss spectroscopy. Here we show that the evolution of hydrogen depends on specimen thickness. Using wedge-shaped specimens of frozen-hydrated Nafion, a perfluorinated ionomer, saturated with the organic solvent DMMP together with both thin and thick sections of frozen-hydrated porcine skin, we show that there is a thickness below which hydrogen evolution is not detected either by bubble observation in transmission electron microscope image mode or by spectroscopic analysis in STEM electron energy-loss spectroscopy mode. We suggest that this effect is due to the diffusion of hydrogen, whose diffusivity remains significant even at liquid nitrogen temperature over the length scales and time scales relevant to transmission electron microscopy analysis of thin specimens. In short, we speculate that sufficient hydrogen can diffuse to the specimen surface in thin sections so that concentrations are too low for bubbling or for spectroscopic detection. Significantly, this finding indicates that higher electron doses can be used during the imaging of radiation-sensitive hydrated soft materials and, consequently, higher spatial resolution can be achieved, if sufficiently thin specimens are used in order to avoid the evolution of hydrogen-based artefacts.
AB - The evolution of hydrogen from many hydrated cryo-preserved soft materials under electron irradiation in the transmission electron microscope can be observed at doses of the order of 1000 e nm-2 and above. Such hydrogen causes artefacts in conventional transmission electron microscope or scanning transmission electron microscopy (STEM) imaging as well as in analyses by electron energy-loss spectroscopy. Here we show that the evolution of hydrogen depends on specimen thickness. Using wedge-shaped specimens of frozen-hydrated Nafion, a perfluorinated ionomer, saturated with the organic solvent DMMP together with both thin and thick sections of frozen-hydrated porcine skin, we show that there is a thickness below which hydrogen evolution is not detected either by bubble observation in transmission electron microscope image mode or by spectroscopic analysis in STEM electron energy-loss spectroscopy mode. We suggest that this effect is due to the diffusion of hydrogen, whose diffusivity remains significant even at liquid nitrogen temperature over the length scales and time scales relevant to transmission electron microscopy analysis of thin specimens. In short, we speculate that sufficient hydrogen can diffuse to the specimen surface in thin sections so that concentrations are too low for bubbling or for spectroscopic detection. Significantly, this finding indicates that higher electron doses can be used during the imaging of radiation-sensitive hydrated soft materials and, consequently, higher spatial resolution can be achieved, if sufficiently thin specimens are used in order to avoid the evolution of hydrogen-based artefacts.
KW - Cryo-TEM
KW - EELS
KW - Electron energy-loss spectroscopy
KW - Nafion
KW - STEM
KW - Scanning transmission electron microscopy
KW - Skin
KW - Water mapping
UR - http://www.scopus.com/inward/record.url?scp=70450207195&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=70450207195&partnerID=8YFLogxK
U2 - 10.1111/j.1365-2818.2009.03215.x
DO - 10.1111/j.1365-2818.2009.03215.x
M3 - Article
C2 - 19941557
AN - SCOPUS:70450207195
SN - 0022-2720
VL - 236
SP - 174
EP - 179
JO - Journal of Microscopy
JF - Journal of Microscopy
IS - 3
ER -