TOTAL YIELD AND POLAR-ANGLE DISTRIBUTIONS OF BIOMOLECULES SPUTTERED BY FAST HEAVY-IONS

Direct measurements of the number of peptide molecules ejected per fas t heavy ion impact (total yield) and data on polar-angle distributions of the total amount of sputtered bioorganic material are presented. T hese data allow direct comparisons with sputtering models and provide information complementary to that obtained by conventional experiments on the fraction of sputtered material ejected in the form of molecula r ions. Solid targets composed of the peptide tri-leucine (m=357 u) we re irradiated by 55-MeV(127) I ions incident at an angle of 51 degrees with respect to the target surface normal. The sputtered material was collected on silicon plates placed in various configurations in front of the target. The collectors were subsequently analyzed by two diffe rent methods: time-of-flight mass spectrometry and amino acid analysis . A total yield of (3.5+/-0.7)x10(3) tri-leucine molecules per inciden t ion was measured, which corresponds to a volume of about 2x10(3) nm( 3) of target material removed in a single ion impact. In the plane of ion incidence, i.e., the plane encompassing the ion incidence directio n and the surface normal, the polar-angle distribution was asymmetric with respect to the surface normal and peaked away from the direction of the incoming ions. In the plane containing the surface normal and p erpendicular to the plane of incidence, the ejected material displayed a symmetric and normally peaked polar-angle distribution. Comparisons of data from the two methods of collector analysis suggest that the t otal sputtering yield is dominated by clusters of molecules. Asymmetri c angular distribution and extensive cluster ejection support hydrodyn amic-type sputtering models which assume impulsive radial expansion of the solid around the incident ion path.