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Description:
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Cluster secondary ion mass spectrometry (SIMS ) analyses of layer -by -layer thin
films were performed to investigate the depth /volume of SI emission and accuracy of
the SI signal . The thin -layered samples were assembled by alternate adsorption of
polyethylenimine (PEI ) , polystyrene sulfonate (PSS ) , polydiallyldimethylammonium
chloride (PDDA ) and clay nanoparticles . The films have controlled 3 -D structure to
test the depth of secondary ion (SI ) emission and evaluate planar homogeneity .
The SI emission depth is ~ 6 -9 nm with 136 keV Au400
4+ (340 eV /atom ) and 26
keV C60
+ (433 eV /atom ) projectile impacts . The diameter of the SI emission area is ~
15 nm by assuming a semispherical emission volume . The SI yields oscillate with the
alternation of the compositions of the topmost layers , which was observed with small
cluster projectiles (CsICs+ and Au3
+ ) as well as with the large cluster projectiles (C60
+
and Au400
4+ ) .
The SI signals of C - and CH - are enhanced in the presence of metal atoms in the
expanding plume . Recoiled C60 projectile fragments (m /z=12 , 13 , 36 ) are observed in
the SI mass spectra . Caution must be taken when monitoring the yields of such
carbon cluster ions from organic surfaces because their yields don't reflect the true
surface concentration .
The Au400
4+ projectile impacts produce abundant co -emission . The correlation
coefficient between the co -emitted SIs can be used to evaluate the planar homogeneity . The results show that the PSS layer is more uniform than the clay
layers .
The effect of alkali metal ion implantation on the nature and abundance of SI
emission was investigated on Cs+ or Na+ implanted glycine samples . The alkali metal
implantation induces surface damage and decreases the glycine molecular ion yields .
Glycine molecular ions and fragment ions (CN - , CNO - ) are emitted from different
depths and locations of the emission volume . The same implanted glycine sample
analyzed with different cluster projectiles (Au400
4+ and C60
+ ) shows different trends in
the yields of molecular and fragment ions , which suggest a different mechanism of SI
emission with different projectile impacts . The Na+ beam induces more surface
damage compared with the Cs+ at equal impact energy . |