AVS 45th International Symposium
    Applied Surface Science Division Thursday Sessions
       Session AS-ThM

Paper AS-ThM9
Quantitative Detection of Metals in Organic Matrices by Laser-SNMS

Thursday, November 5, 1998, 11:00 am, Room 307

Session: Gaede-Langmuir Award Address and Quantitative Surface Analysis
Presenter: A. Schnieders, Universität Münster, Germany
Authors: A. Schnieders, Universität Münster, Germany
H.F. Arlinghaus, Universität Münster, Germany
A. Benninghoven, Universität Münster, Germany
Correspondent: Click to Email
TOF-SIMS and Laser-SNMS have been established as powerful tools for high sensitive trace analysis of elements in inorganic materials, like alloys and semiconductors. Detection limits for almost all elements are in the range of 10@super 8@ - 10@super 9@ particles/cm@super 2@ of a single monolayer. For many analytical applications comparable sensitivities for the detection of metals in organic matrices are required, e. g. in life sciences. Unfortunately, TOF-SIMS is limited by the low secondary ion yields for metals in these matrices. The sensitivity is several decades lower than for the same metals on semiconductor surfaces. Because of the decoupling of the desorption and ionization processes, the use of Laser-SNMS is a promising approach to get rid of this limitation. Laser-SNMS combines the advantages of ion beam induced desorption with the possibility to optimize the ionization efficiency. For our investigations we applied nonresonant multiphoton ionization allowing a nonselective and highly efficient postionization of sputtered neutrals. As a model system for metals in organic matrices we prepared submonolayer coverages of several metals (Be, Cr, Mn, Fe, Co, Ni, Mo, W) on different polymer foils (polycarbonate, polyimide, and polyvinylidenechloride) by sputter deposition. We used these standards for quantification. Relative sensitivity factors of the respective elements are found to be similar to those for material sputtered from alloys or semiconductors within a factor of 3. The detection limits are in the range of 10@super 8@ to 10@super 9@ particles/cm@super 2@. We also used Laser-SNMS for the identification of the active center of a purple acid phosphatase. Our results demonstrate the detection and identification of single metal atoms in organic macromolecules with an atom concentration down to < 100 ppm. The use of resonant photoionization lowers the detection limits for similar systems by further decades.