High-Resolution TOF-SIMS Study of Varying Chain Length Self-Assembled Monolayer Surfaces

Abstract

A high-resolution time-of-flight secondary ionization mass spectrometer (TOF-SIMS) has been used to investigate chain length effects in hydrocarbon seff-assembled monolayer (SAM) surfaces on gold substrates. A wide range of n-alkanethiols was used to make homogeneous SAM surfaces, which included both odd and even hydrocarbon chain length thiols. Variations in coverage, extent of oxidation, and high-mass cluster formation as a function of hydrocarbon chain length of the alkanethiol SAM surfaces were investigated. Long-short chain length effects were observed for the relative coverage of the SAM surfaces, which directly influences the extent of oxidation for the thin films. The formation of gold-sulfur and gold-adsorbate cluster ions was also observed, since the mass range of the TOF-SIMS made it possible to monitor all of the cluster ions that were formed following the high-energy ion/surface interactions.

Formation and electrochemical desorption of self‐assembled monolayers as studied by ToF‐SIMS

“…Time‐of‐flight secondary ion mass spectrometry (ToF‐SIMS)23 evolved in recent years as a fast semiquantitative tool for surface analysis24–26 which found applications in the area of thiol SAMs on Au,25, 27–39 and whose results agree well with other analytical techniques,25, 29 and as such, is suitable for the analysis of the composition of mixed SAMs.…”

Self‐assembled monolayers of octadecylphosphonic acid and polymer films: Surface chemistry and chemical structures studied by time‐of‐flight secondary ion mass spectrometry

“…The TOF‐SIMS, due to its surface sensitivity, has proven powerful in exploring organic molecular monolayer systems including alkanethiols, fatty acids, and organophosphonic acids, whose thickness is on an order of 2 nm. Therefore, TOF‐SIMS probes both the hydrocarbon chains of the molecules in the SAMs and the interactions between their headgroups and the substrate, which is either a metal or metal oxide.…”

“…Alkane thiol monolayers and multilayers have been used as a model system for TOF‐SIMS to investigate ion yields of atomic and cluster ions associated with the molecules and the gold substrate as a function of number of layers . Thiol SAMs prepared on a gold substrate were found to degenerate in air as evidenced by detection of alkanesulfonate ions, which was dependent on the length of the hydrocarbon chain . The TOF‐SIMS investigations on OPA SAMs on tantalum oxide, with the help of some other analytical techniques, revealed the bonding configuration of the molecular headgroups and the substrate .…”

Direct metal-to-metal thermocompression bonding studies

“…Here, we report an enhancement in the tensile bond strength of gold joints that were coated with a layer of dodecanethiol (C12) prior to bonding at a temperature range of 80°C to 180°C. Since it is known that the properties of alkanethiols vary as a function of their chain length [82][83][84], this chapter also reports the chain length dependence in SAMs-assisted bonding whereby shorter chain alkanethiol, C6 exhibits better strength improvement at very low temperatures compared to the longer ones. Further discussion to explain the superior strength improvement by C6 will be reported in the next chapter.…”

“…This chapter explains how bond enhancement varies according to the structural integrity (thermal and mechanical) of the monolayer coating which is a function of the thickness of the monolayer. Gathered with the findings, we have evaluated on the bonding mechanism between two metallic surfaces and coated surfaces in Chapters 3 and 4, a working hypothesis is derived which highlights three key factors enabling low temperature direct metal thermocompression bonding, namely: (1) surface passivation,(2) thermal activation through bond-weakening or desorption of SAMs and(3)mechanical displacement of the weakened SAMs layer.Self-assembled monolayers on planar substrates such as thin metallic films on silicon wafers, mica or glass are most commonly characterized due to the ease of preparation as well as its compatibility with several surface analytical techniques such as X-ray photoelectron spectroscopy (XPS)[76,90,91] , contact angle measurements[76,92], surface plasmon resonance spectroscopy (SPRS)[93], time-offlight secondary ions mass spectroscopy (TOF-SIMS)[84,94,95]and many more. This chapter presents several surface studies to evaluate the passivating properties of alkanethiols at various chain length on gold metal by comparing the amount of carbon…”