AVS 60th International Symposium and Exhibition
    Surface Science Thursday Sessions
       Session SS1-ThA

Paper SS1-ThA10
Passivation of Metallic Al Surface with Monolayer Organic Adsorbates

Thursday, October 31, 2013, 5:00 pm, Room 201 A

Session: Organic Layers on Surfaces
Presenter: T. Yamada, RIKEN, Japan
Authors: T. Yamada, RIKEN, Japan
R. Sato, RIKEN, Japan
K. Watanabe, Science University of Tokyo, Japan
M. Kawai, The University of Tokyo, Japan
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We performed a surface-scientific investigation on adsorption of hydrocarbon thiols and fluorocarbon thiols on clean aluminum (111) in order to realize passivation of metallic Al towards air oxidation. Passivation of Al surfaces with oxide-free ultimately thin layers, that is, molecular monolayers, is a prerequisite in nanofabrication with Al entities, such as planer nano-patterned devices and nano-particles. We newly surveyed the adsorption of organic thiol molecules to form densely-packed monolayers, which are suitable for blocking O2 gas molecules. We found hydrocarbon thiols can readily adsorb on clean Al(111) and form monolayers at room temperature by exposure to vapor from liquid (n-CnH2n+1SH, (n≤12)) or by sublimation ((n-CnH2n+1SH, (n>12) and 4-biphenylthiol). The hydrocarbon parts were proven to be intact after adsorption by the electron spectroscopies (XPS and vibrational analysis byHREELS). The SH species was not detected vibrationally, indicating that S is anchoring the hydrocarbon part on Al. Blocking of O2 oxidation of Al substrate was effective in the O2 pressure range below 10-5 Torr. At higher pressures ranging up to 1000 Torr, a multilayer of Al2O3 was formed underneath the organic monolayer, even for n-C18H37SH monolayer. The ability to block O2 oxidation was remarkably enhanced by curing these organic monolayers with electron beam. We irradiated a shower of 100 eV electron (~1 mC cm-2) onto these monolayers, and the rate of Al substrate oxidation decreased to less than one tenth of that of the clean Al(111) in the atmospheric pressure of O2. It was seen that the irradiation of electron beam introduces unsaturated C-C bonds with a neary compleet loss of C-H bonds from the monolayer, both from alkane and aromatic thiols. A quasi-graphitic monolayer is anticipated to be formed by electron irradiation. The thickness of this layer is ~ 1 nm. The electron-bombarded monolayers of this type exhibited a substantial robustness towards oxidation in ambient O2.[1,2] Linear fluoroalkanethiols, n-CnF2n+1C2H4SH (n=4,8), form monolayers at room temperature with a full coverage smaller than the alkanethiols. When the adsorption process was made at substrate temperatures higher than 100°C, the uptake of carbon exceeded the monolayer amount of the precursor molecule, and substantial loss of F from the adlayer was observed. The adlayer seemed to be composed of polymerized fluorohydrocarbon, and exhibited a substantial strength against oxidation. These robust monolayers will bring about a better utility of metallic Al in nanotechnology in general. [1] S. Nomura et al., Chem. Lett.39 (2010) 1297. [2] T. Yamada, Japan Patent Application 2011-168725.