AVS 49th International Symposium
    Applied Surface Science Tuesday Sessions
       Session AS-TuA

Paper AS-TuA2
Molecular Imaging Using Atomic and Molecular Primary Ions

Tuesday, November 5, 2002, 2:20 pm, Room C-106

Session: Imaging in Surface Analysis
Presenter: F. Kollmer, ION-TOF GmbH, Germany
Authors: F. Kollmer, ION-TOF GmbH, Germany
R. Moellers, ION-TOF GmbH, Germany
D. Rading, ION-TOF GmbH, Germany
R. Kersting, TASCON GmbH, Germany
E. Niehuis, ION-TOF GmbH, Germany
Correspondent: Click to Email
The secondary ion yield Y of organic materials increases considerably with the mass of the primary ion. A further yield enhancement can be achieved when changing from atomic to polyatomic primary ions. As the corresponding increase in damage cross section @sigma@ is much smaller, the ion formation efficiency E:= Y/@sigma@ also increases significantly. The efficiency E not only determines the achievable detection limits in surface spectrometry but also influences the useful lateral resolution @Delta@l in organic imaging via @Delta@l ~ (1/E)@super ½@. In order to investigate the influence of the primary ion bombardment conditions in imaging of real world samples we applied both monoatomic as well as polyatomic primary ions including Ga@super +@, In@super +@, Au@sub 1@@super +@, Au@sub 2@@super +@ and Au@sub 3@@super +@. The application of a Au LMIS combines capabilities such as high brightness and high lateral resolution with the advantages of molecular primary ion bombardment. The investigated samples consisted of various thick organic materials with analyte molecules in the mass range > 500 u. The results confirm the dependence of the useful lateral resolution on E and show that imaging of organic materials can best be performed with polyatomic primary ion bombardment. If monoatomic bombardment is used high mass ions are preferable compared to low mass ions. Enhancement factors (E compared to E@sub Ga@) for polyatomic primary ions reach several orders of magnitude whereas at maximum an enhancement factor of 10 can be achieved with monoatomic primary ions.