Selective Depositions of Fe-Containing Oxide Films on Mixed Selfassembled Organic Monolayers using Microcontact Printing

Abstract

In situ patterning of crystalline iron oxide thin layers has been achieved via microcontact printing (μCP) and selective deposition. μCP was used to pattern two different surface moieties of selfassembled organic monolayers (SAMs) on Au/Cr/Si substrates. An elastomeric stamp (poly(dimethylsiloxane); PDMS) having a submicron-size patterned relief structure 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 is realized through precipitation of iron oxide phases from aqueous solutions at ambient temperature (<100°C). Aqueous solutions of 0.05 M of iron nitrate (Fe(NO3)2•9H20) containing urea under nitric acid (pH < 2) were prepared for selective depositions. X-ray photoelectron spectroscopic (XPS) results showed that iron oxide precipitates were deposited onto hydrophilic SAMs, but not onto HDT surfaces. As-deposited films onto DTT-SAM surfaces at 80°C were crystalline α-Fe2O3 (hematite). Fe3O4 and γ-Fe2O3 films were synthesized via annealing of as-deposited α-Fe2O3. Scanning electron microscopy, x-ray diffractometry, vibrating sample magnetometry, and optical microscopy were used to characterize the films' microstructures and properties.