Characterization of surface and layered films with cluster secondary ion mass spectrometry

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Title: Characterization of surface and layered films with cluster secondary ion mass spectrometry
Author: Li, Zhen
Abstract: 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 .
URI: http : / /hdl .handle .net /1969 .1 /ETD -TAMU -2028
Date: 2009-05-15

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Characterization of surface and layered films with cluster secondary ion mass spectrometry. Available electronically from http : / /hdl .handle .net /1969 .1 /ETD -TAMU -2028 .

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