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We studied the self-assembly of n-alkanethiols CH3(CH2) m SH (m = 5, 7, 9, 11, 13, 15, 17, 19, 21) onto platinum thin films with two different surface properties:  metallic and oxide. Water contact angle, ellipsometry, and reflection−absorption infrared spectroscopy (RAIRS) measurements suggested that well-organized, methyl-terminated monolayer films formed on the metallic platinum surface. On the other hand, the molecular films formed with the alkanethiol molecules on platinum oxide surfaces were loosely packed and poorly ordered. For the monolayer films formed with alkanethiols of different chain lengths on metallic Pt surfaces, a transition from slightly disordered to crystalline-like structure was observed with increasing chain length. Based on the intensities of the methylene and methyl C−H vibration modes in the RAIRS, the tilt angle of the alkyl chain in the monolayers on Pt surfaces was estimated to be less than 15° with respect to the surface normal. X-ray photoelectron spectroscopy revealed the formation of metal−thiolate bonding of the thiol headgroups in the alkanethiol molecules with Pt atoms on the surfaces.

Molecular-electronic devices are usually fabricated by sandwiching organic monolayers between electrodes. Questions arise about whether the molecules react with a deposited metal. We investigated a self-assembled monolayer (SAM) of alkoxynaphthalene thiol (I) on Pt before and after Ti film deposition. The SAM on Pt was highly ordered. Ti deposition resulted in some reaction with the alkyl chains and disordering, but the napthelenes remained intact. Pinhole free films of the monolayers were characterized by current–voltage measurements, revealing that a rectification ratio as high as 5×105 was achieved.

Monomolecular films with well-defined structure were prepared by self-assembling of n-alkanoic acids on an evaporated silver surface. Here we report the structural studies of thin films of acids containing aromatic chromophores of varied size and polarity. Informationregarding the packing, orientation and conformation of the structural units within the assembly were deduced from ellipsometnc thickness measurement, polarized reflection absorption infrared spectra and wetting property measurement. Implications of results to the design of functional thin films are discussed. 659

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