Kinetic energy and angular distributions of sputtered molecules studied by ion-beam desorption and laser postionization

Conference · Sun Dec 31 04:00:00 EST 1995

OSTI ID:258308

Riederer, D E; Chatterjee, R; Rosencrance, S W ^[1]

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1. Pennsylvania State Univ., University Park, PA (United States); and others

Ion beam induced desorption of atoms and molecules continues to evolve and find new uses in surface chemical analysis. Secondary ion mass spectrometry (SIMS), an established analysis method for metallic and semiconductor surfaces, has also proven to be useful in the analysis of organic and biological surfaces. The use of lasers to ionize sputtered neutrals has added an additional degree of usefulness to this methodology since in many instances the majority of the desorbed species are neutral. While the mechanisms leading to the desorption of atoms are well understood, significantly less is known about the processes which lead to molecular desorption during keV surface bombardment. In this study, the authors present initial findings of experiments aimed at understanding the mechanisms which lead to molecular desorption from organic surfaces. The kinetic energy and angular distributions of sputtered surface molecules have been measured subsequent to bombardment with 8 keV argon ions using laser postionization combined with a position sensitive detector. The peak in the kinetic energy distributions of pyrene butyric acid and tryptophan sputtered from surfaces containing multilayers of these compounds are extremely low (ca. 0.1 eV) and more than 95% of the molecules have kinetic energies <0.5 eV. Self-assembled monolayers consisting of phenethylmercaptan on gold exhibit similar behavior. This is in sharp contrast to the behavior of metal atoms sputtered from clean metal surfaces which have most probable kinetic energies ranging from 1-5 eV. The shape of the angular distribution from a disordered layer of pyrene butyric acid surface approximates cos{sup n}{theta}.

• OSTI ID: 258308
• Report Number(s): CONF-9506225--
• Country of Publication: United States
• Language: English

Related Subjects

40 CHEMISTRY
66 PHYSICS
ANGULAR DISTRIBUTION
BUTYRIC ACID
DESORPTION
KINETIC ENERGY
MASS SPECTROSCOPY
ORGANIC SULFUR COMPOUNDS
PYRENE
SPUTTERING
TRYPTOPHAN