Paper EM-TuM12
New Methods for Metal Deposition on Self-Assembled Monolayers: Towards Molecular Electronic Circuitry

Tuesday, October 16, 2007, 11:40 am, Room 612

We have investigated the deposition of metals on alkanethiolate self-assembled monolayers (SAMs) adsorbed on Au using chemical vapor deposition (CVD) and electroless deposition. This work has important applications in molecular and organic electronics, sensing, biotechnology, photonics and other technologies. Chemical vapor deposition (CVD) is a widely employed technique for the deposition of metals on semiconductor substrates. CVD has not been widely employed to deposit films on organic materials because high temperatures (Tsubstrate > 200 °C) are often required that are not compatible with most organic thin films. However, by exploiting the chemical reactivity of functional groups at the SAM surface it is possible to deposit thin metallic films at room temperature. We demonstrate this method using trimethyl aluminum (TMA). TMA reacts at room temperature with a -COOH terminated SAM to form an Al overlayer, whereas TMA does not react with a -CH₃ terminated SAM. We have also investigated the mechanism of electroless deposition of copper on functionalized SAMs using a copper sulphate/formaldehyde reaction. Copper is deposited on -CH₃ and -COOH terminated SAMs but not on -OH terminated SAMs. For -CH₃ and -COOH SAMs, the deposited Cu is weakly stabilized at the SAM/vacuum interface and so slowly penetrates through the SAMs to the Au/S interface. Further, Cu does not deposit on -OH terminated SAMs because the formaldehyde reacts with the -OH terminal groups rather than reducing the copper.