LDI-FTMS Analysis of Polyacetylene Thin Films Deposited on Silicon by Plasma Polymerization
by Miladinovic, Sasa; Robotham, Scott A.; De Vriendt, Valerie; Lucas, Stephane; Wilkins, Charles L.
The work presented here demonstrates LDI-FTMS anal. of thin films deposited on silicon by plasma polymn. of acetylene. LDI enables ionization of intact thin film oligomers deposited on silicon, while FTMS anal. of the ions produced gives information about the compn. of oligomers. In the pos. ion mode spectra, carbon clusters are the most abundant component of the sample, differing from one another by two carbons. In all pos. ion spectra C60 and C70 are found in high abundance because of their stability as pos. ions. We believe that clusters are not formed by LDI since a no. of samples did not produce cluster signals. The neg. ion mode spectra also show carbon clusters as more abundant. However, there is a much larger abundance of hydrocarbons present. These hydrocarbons have a much higher no. of carbons than hydrogens in the structures, and the oligomers show a pattern of having either an even no. of carbons and hydrogens, or an odd no. of carbons and hydrogens. The results indicate that bipolar discharge leads to a greater formation of hydrocarbons in the plasma polymn. than the products of unipolar and continuous discharges. The continuous discharge film shows a broader mass range then the other two films since the thickness of this film is approx. 3× thicker then the other films. The unipolar discharge film neg. ion mode spectrum also shows less hydrocarbon formation compared to that of the bipolar discharge film, but is similar to that from the continuous discharge film.