AVS 52nd International Symposium
    Applied Surface Science Monday Sessions
       Session AS+BI+NS-MoM

Paper AS+BI+NS-MoM7
Scanning Atom Probe Study of Fragmentation of Organic Molecules

Monday, October 31, 2005, 10:20 am, Room 206

Session: Nanoscale Analysis: Biomaterial and Other Applications
Presenter: O. Nishikawa, Kanazawa Institute of Technology, Japan
Authors: O. Nishikawa, Kanazawa Institute of Technology, Japan
M. Taniguchi, Kanazawa Institute of Technology, Japan
Correspondent: Click to Email
Fragmentation of two organic molecules, crystal violet [(C@sub25@N@sub3@H@sub30@)@super+@Cl@super-@: 408 amu] and tetra-n-butyl-ammonium hydroxide [N(C@sub4@H@sub9@)@sub4@@super+@OH@super-@: 259 amu], was studied at atomic level by mass analyzing the dissociated fragments with the scanning atom probe (SAP). In the SAP analysis the molecules and their fragments are field evaporated as positive ions and detected one by one. Since the field evaporation is a static process, it does not disorder surface structure breaking atomic bonds by external energy. Accordingly, evaporated positive ions reflect the binding state in the molecules. For example, the radical of polythiophene, SC@sub4@H@sub2@, is field evaporated as doubly charged ions indicating that the atoms forming the radical are strongly bound. A thin layer of crystal violet was deposited on a tungsten substrate. Since the crystal violet is non conductive, the molecules are field evaporated applying a DC high voltage to the tungsten substrate and irradiating the specimen with a pulsed laser beam, 2nd harmonic of YAG laser, 532 nm. Although non-dissociated molecule ions are detected, most molecules are dissociated showing the ions such as C@sub13@H@sub2@, C@sub13@NH@sub4@ and C@sub8@NH@subn@. The detected fragments suggest that no double bonds are broken. When the molecule layer was deposited on a titanium oxide layer, all molecules were dissociated possibly due to the photo-catalytic function of titanium oxide. The most abundant fragment is C@sub4@NH@subn@. The ratio of the number of carbon atoms to that of nitrogen atom was found to be nearly 8:1 as expected. Although the dissociation of tetra-n-butyl-ammonium hydroxide molecules at the boundary with the tungsten substrate is noticeable, the dissociation is insignificant at non-boundary areas. It was also found that hydroxide of the molecules is dissociated and oxygen atoms are bound with tungsten. This may suggest that tungsten also have catalytic function.