title: Comparison of fullerene and large argon clusters for the molecular depth profiling of amino acid multilayers.
abstract: A major challenge regarding the characterization of multilayer films is to perform high-resolution molecular depth profiling of, in particular, organic materials. This experimental work compares the performance of C60(+) and Ar1700(+) for the depth profiling of model multilayer organic films. In particular, the conditions under which the original interface widths (depth resolution) were preserved were investigated as a function of the sputtering energy. The multilayer samples consisted of three thin δ-layers (~8 nm) of the amino acid tyrosine embedded between four thicker layers (~93 nm) of the amino acid phenylalanine, all evaporated on to a silicon substrate under high vacuum. When C60(+) was used for sputtering, the interface quality degraded with depth through an increase of the apparent width and a decay of the signal intensity. Due to the continuous sputtering yield decline with increasing the C60(+) dose, the second and third δ-layers were shifted with respect to the first one; this deterioration was more pronounced at 10 keV, when the third δ-layer, and a fortiori the silicon substrate, could not be reached even after prolonged sputtering. When large argon clusters, Ar1700(+), were used for sputtering, a stable molecular signal and constant sputtering yield were achieved throughout the erosion process. The depth resolution parameters calculated for all δ-layers were very similar irrespective of the impact energy. The experimental interface widths of approximately 10 nm were barely larger than the theoretical thickness of 8 nm for the evaporated δ-layers.
authors.affiliation: Research Centre in Physics of Matter and Radiation (PMR), University of Namur (FUNDP), 61, rue de Bruxelles, 5000, Namur, Belgium, wehbe@lippmann.lu.
authors.forename: N
authors.initials: N
authors.lastname: Wehbe
authors.forename: T
authors.initials: T
authors.lastname: Mouhib
authors.forename: A
authors.initials: A
authors.lastname: Delcorte
authors.forename: P
authors.initials: P
authors.lastname: Bertrand
authors.forename: R
authors.initials: R
authors.lastname: Moellers
authors.forename: E
authors.initials: E
authors.lastname: Niehuis
authors.forename: L
authors.initials: L
authors.lastname: Houssiau
mesh_terms: D001128:Argon / Q000737:chemistry*; D037741:Fullerenes / Q000737:chemistry*; D010649:Phenylalanine / Q000737:chemistry*; D012825:Silicon / Q000737:chemistry; D013499:Surface Properties; D013816:Thermodynamics; D014443:Tyrosine / Q000737:chemistry*; D014835:Volatilization
chemical_list: D037741:Fullerenes; D014443:Tyrosine; D010649:Phenylalanine; D001128:Argon; D012825:Silicon