Formation and characterization of crystalline iron oxide films on self-assembled organic monolayers and their in situ patterning Hyunjung Shin and Jong Up Jeon Nano System Laboratory, Samsung Advanced Institute of Technology and CRI, P.O. Box 111, Suwon, Korea 440-600 Y. Eugene Pak Micro Electro-Mechanical System (MEMS) Laboratory, Samsung Advanced Institute of Technology, P.O. Box 111, Suwon, Korea Hyejin Im Department of Ceramic Engineering, YonSei University, Seoul, Korea Eung Soo Kim Department of Materials Engineering, Kyonggi University, Suwon, Korea (Received 14 July 2000; accepted 14 November 2000) Crystalline and pore-free films of a–Fe 2 O 3 were prepared on hydrophilic self-assembled organic monolayers (DTT-SAMs) at 80 °C. Subsequently, Fe 3 O 4 and g–Fe 2 O 3 films were synthesized via post annealing of as-deposited a–Fe 2 O 3 . In situ patterning of crystalline iron oxide thin layers was achieved via microcontact printing (mCP) and selective deposition. mCP was used to pattern two different surface moieties of self-assembled organic monolayers (SAMs) on Au–Cr–Si substrates. An elastomeric stamp was used to transfer either hexadecanethiol (HDT) SAMs, which are to sustain deposition of iron oxide precipitates, or hydrophilic SAMs [e.g., dithiothreitol (DTT)]. Selective deposition was realized through precipitation of iron oxide phases. Iron oxide films were deposited onto hydrophilic SAMs, but not onto HDT surfaces. Line (width of <1 mm) patterns in crystalline a–Fe 2 O 3 thin films were obtained. I. INTRODUCTION Magnetic oxides, mainly g–Fe 2 O 3 (maghemite) and Fe 3 O 4 (magnetite), have been used most widely for the last few decades in magnetic recording media. 1–3 Be- cause Fe 2 O 3 is polymorphic and can exist in a thermo- dynamically stable antiferromagnetic form (a–Fe 2 O 3 , hematite), and a metastable ferrimagnetic form (g–Fe 2 O 3 ), the properties of the films are largely depen- dent on film preparation methods and conditions. 4 In most cases a–Fe 2 O 3 is a precursor to Fe 3 O 4 and g–Fe 2 O 3 via reduction in H 2 followed by controlled oxidation at elevated temperatures in air. 5 Our primary interest was in fabrication of crystalline as well as in situ patterned iron oxide film using self- assembled organic monolayers (SAMs) 6 as a promoter and/or inhibitor of its formation. SAMs are functional- ized, siloxane- and/or thiolate-anchored, organic thin films formed spontaneously on surfaces by immersion into solutions of alkyl-chain surfactant molecules. Often the terminal functionality can be chemically modified to dramatically alter the surface’s reactivity and physical characteristics, for example, charge, wetability, and ad- hesion. Substrates derivatized with organic functional groups can be used to control the deposition of inorganic and/or mineral thin films from aqueous solutions, as re- ported by several research groups. 7–9 Deposition and pat- terning of iron oxyhydroxide in the form of FeOOH (goethite) on sulfonic acid terminated SAMs from iron nitrate aqueous solutions has been investigated. 10,11 No reports, however, were found in the literature on the deposition of crystalline iron oxide films onto function- alized SAMs at ambient temperatures (<100 °C). Microcontact printing (mCP) is a broadly applicable technique for derivatizing surfaces. 12–14 Patterns of or- ganic layers having dimensions <0.5 mm can be routinely prepared on metals such as gold, 15,16 silver, 17 or copper and on Si/SiO 2 18 by using an elastomeric stamp [usually polydimethylsiloxane (PDMS)]. In the case of gold sur- faces, alkanethiols are often used. By using different ter- minal groups, it is possible to define areas on the surfaces having well-controlled properties. For example, hydro- phobic surfaces can be generated with hexadecanethiols (HDT), hydrophilic surfaces with dithiothreitol (DTT), and so on. Our strategy for the fabrication of patterned iron oxide films was to combine two key technologies: mCP to gen- erate mixed surface moieties and selective deposition of crystalline iron oxide films onto specific areas. There are significant advantages in our strategy. First, patterned oxide films can be generated directly without any post- J. Mater. Res., Vol. 16, No. 2, Feb 2001 © 2001 Materials Research Society 564