Using time-of-flight secondary ion mass spectrometry to investigate behavior of vapor-deposited metal on alkanethiol self-assembled monolayers

Metal behavior on alkanethiol self-assembled monolayers (SAMs) has been studied for more than ten years. Our group has employed time-of-flight secondary ion mass spectrometry (ToF-SIMS) to characterize the SAM/top metal contact for many years, and it has proven to be a very powerful technique. Analysis of the mass spectra yields direct information about chemical reactions, metal penetration, and metal nucleation.; In this thesis, ToF-SIMS is applied to study the behavior of K Au and Ti atoms on several alkanethiol SAMs. Au and Ti are the most commonly used contact metals in molecular electronic studies. The structure of the SAM/Ti interfaces and SAM/Au interfaces are important for measurements of electronic properties of functional molecules. K is an active metal and may be a potential reducing reagent to modify the surface of alkanethiol SAMs. It is also of interest to compare the difference between the chemical activity of K atoms on organic surfaces to that found in organic solvents.; In Chapter 2, the K behavior on C15CH3 (-S(CH 2)15CH3), C15CO2H, C 15CO2CH3, C16OH, and C16OCH 3 SAMs is investigated. It is found that K atoms react with -CO 2H, -CO2CH3 and OH groups, forming -CO2K or OK. The K atoms only form complexes with OCH3 groups, whereas no chemical reaction is observed on the -CH3 surface. The activity of these organic functional groups can be ranked as CO2 H > CO2CH3 > OH > OCH3 > CH3.; In Chapter 3, the relationship between metal penetration and inter-molecular interactions is studied via the Au/SAM system. It is found that weak inter-molecular interactions lead to high penetration, and strong inter-molecular interactions lead to low penetration. For example, Au atoms continuously penetrate through C15CH3 and C15CO2CH3 films, forming smooth buried layers under organic thin films.; In Chapter 4, SAM/Ti top contact interfaces are investigated. Ti/organic functional group interactions can be ranked as Ti/CO2H > Ti/CO 2CH3 > Ti/CH3. Vapor deposited Ti atoms are so active that they damage all surface organic functional groups and the (CH2)n chain. At the same time, penetration of Ti atoms through the SAMs is weak. The temperature effect on metal penetration through the SAMs is studied in Chapter 5. Decreasing sample temperature is found to reduce metal penetration. However, at low temperature, H2O molecules can be condensed on the sample surface. The effect of H2O molecules on the structure of metal overlayers is not clear. (Abstract shortened by UMI.)...