SURFACE AND INTERFACE ANALYSIS Surf. Interface Anal. 2003; 35: 94–98 Published online in Wiley InterScience (www.interscience.wiley.com). DOI: 10.1002/sia.1501 Imaging micropatterned organosilane self-assembled monolayers on silicon by means of scanning electron microscopy and Kelvin probe force microscopy Yunying Wu, 1,2 * Kazuyuki Hayashi, 1 Nagahiro Saito, 1 Hiroyuki Sugimura 1 and Osamu Takai 1 1 Department of Materials Processing Engineering, Graduate School of Engineering, Nagoya University, Chikusa, Nagoya 464-8603, Japan 2 Aichi Science & Technology Foundation, Marunouchi 2-4-7, Naka, Nagoya 460-0002, Japan Received 11 November 2001; Revised 15 December 2001; Accepted 15 December 2001 Field-emission scanning electron microscopy (FE-SEM) and surface potentiometry based on scanning probe microscopy, i.e. Kelvin probe force microscopy (KFM), have been applied to study microstructures consisting of organosilane self-assembled monolayers (SAMs) terminated with -CH 3 or -CF 3 groups. Onto cleaned Si substrates covered with a thin oxide layer of 2 nm thick, SAMs were formed by chemical vapour deposition using n-octadecyltrimethoxysilane (CH 3 (CH 2 / 17 Si(OCH 3 / 3 , ODS) or fluoroalkylsilane (CF 3 (CF 2 / 7 (CH 2 / 2 Si(OCH 3 / 3 , FAS) as a precursor. Through a photolithographic technique employing vacuum ultraviolet light at 172 nm, microstructures composed of ODS, FAS or both were fabricated. Micropatterns of the SAMs on SiO 2 /Si substrates were clearly imaged by FE-SEM at an acceleration voltage of the electron beam below 1 kV, but image contrasts became faint with an increase in the acceleration voltage. At a voltage of 5 kV there was almost no detectable contrast. An FE-SEM image of the ODS–FAS microstructure acquired at an acceleration voltage of 0.8 kV clearly demonstrated that the region covered with ODS was brighter and thus, emitted secondary electrons more efficiently than the region covered with FAS. Furthermore, as indicated in a KFM image, the region covered with FAS had a surface potential ∼180 mV lower than that of the region covered with ODS. The origin of these image contrasts between ODS- and FAS-SAMs was the large difference in electronic states between ODS and FAS owing to the electron negativity of fluorine atoms. Copyright  2003 John Wiley & Sons, Ltd. KEYWORDS: field-emission scanning electron microscopy; Kelvin probe force microscopy; scanning probe microscopy; molecular orbital calculation; organosilane self-assembled monolayer INTRODUCTION Molecular self-assembling and Langmuir–Blodgett tech- niques have been applied successfully to the preparation of organic thin films with well-ordered molecular arrange- ments and have been used frequently to control the phys- ical and chemical properties of solid substrates. 1 Among various organized molecular thin films, monolayers con- structed through chemisorption of organosilane molecules onto hydroxyl (OH)-bearing oxide surfaces 2 attract much attention. Owing to hydrophobic and van der Waals interac- tions between the alkyl chains of the organosilane molecules, the molecules are spontaneously organized into a thin layer of monomolecular thickness in which the molecules are closely packed with each other. 3,4 Such a film belongs to a class of organic film known as self-assembled monolay- ers (SAMs). L Correspondence to: Yunying Wu, Department of Materials Processing Engineering, Nagoya University, Chikusa, Nagoya 464-8603, Japan. E-mail: wu@plasma.numse.nagoya-u.ac.jp Contract/grant sponsor: Japan Society for the Promotion of Science; Contract/grant number: JSPS-RFTF 99R13101. Contract/grant sponsor: Ministry of Education, Culture, Sports, Science and Technology. The self-assembling technique and the organosilane SAMs are expected to play key roles in future microde- vices. Much attention is thus denoted to the micropatterning of such SAMs for constructing future microdevices, par- ticularly in biological applications. 5–14 In order to develop micropatterning technologies for organosilane SAMs, the evaluation of fabricated micropatterns is crucial. Thus, imag- ing techniques for the micropatterned SAMs are of primary importance. Scanning probe microscopes have been applied successfully so far to characterize organic monolayers. The disadvantage of this method at present is its relatively low throughput compared with other techniques, e.g. optical or electron microscopy. Scanning electron microscopy has been widely applied to the characterization of material surfaces, including organic materials. However, it has been adopted rarely to observe organic monolayers owing to the very small topographic contrasts (less than several nanometres) exist- ing in such samples. There have been only a few reports on this issue. 15 – 17 Imaging mechanisms for these results are the differences in chemical properties, orientation and pack- ing of molecules in the monolayers rather than topographic contrasts. For example, Bittermann et al. observed Lang- muir–Blodgett films on a silicon substrate without a metal Copyright  2003 John Wiley & Sons, Ltd.