Ž . Applied Surface Science 157 2000 244–250 www.elsevier.nlrlocaterapsusc High-resolution imaging of organic monolayers using noncontact AFM T. Uchihashi a, ) , T. Ishida b , M. Komiyama c , M. Ashino a , Y. Sugawara a,d , W. Mizutani b , K. Yokoyama d , S. Morita d , H. Tokumoto b , M. Ishikawa a a Joint Research Center for Atom Technology, Angstrom Technology Partnership, 1-1-4 Higashi, Tsukuba, Ibaraki 305-0046, Japan b Joint Research Center for Atom Technology, National Institute for AdÕanced, Interdisciplinary Research, 1-1-4 Higashi, Tsukuba, Ibaraki 305-8562, Japan c Institute of Inorganic Synthesis, Yamanashi UniÕersity, Takeda, Kofu 400-8511, Japan d Department of Electronic Engineering, Graduate School of Engineering, Osaka UniÕersity, 2-1 Yamada-Oka, Suita, Osaka 565-0871, Japan Abstract Ž . Noncontact atomic force microscopy AFM provides useful technique for imaging organic molecules in high resolution. Ž. Here we present our recent advances in the noncontact AFM imaging of organic materials. I Molecular packing structures, defects and domain boundaries were clearly observed on adenine and thymine films. The noncontact AFM images revealed detailed features of the individual nucleic acid base molecules, thus allowing us to distinguish between adenine and thymine. Ž . Ž . Ž . II Both 63 =63 R308 structures and c 4 =2 superlattice structures were resolved on alkanethiolate self-assembled Ž . w Ž . x Ž . Ž . Ž . monolayer SAM CH CH SH nonanethiol on Au 111 . We found that the c 4 =2 superlattice structures changed 3 28 Ž . into 63 =63 R308 structures when the tip–surface distance decreased. q 2000 Elsevier Science B.V. All rights reserved. PACS: 87.64.Dz Keywords: Noncontact atomic force microscopy; Molecular imaging; Nucleic acid base; Alkanethiol 1. Introduction High-resolution imaging of organic materials is of high interest in surface chemistry and physics. Al- Ž . though scanning tunneling microscopy STM has a sufficient resolution of imaging conductive samples at an atomic scale, an STM tip often penetrates poor conductive samples such as thick organic films to w x sustain a tunneling current 1,2 . Thus, deformation ) Corresponding author. Tel.: q 81-298-54-2708; fax: q 81-298- 54-2784. Ž . E-mail address: uchi@jrcat.or.jp T. Uchihashi . and damage of the sample surfaces and even the motion of isolated molecules occur during the scan- ning. On the other hand, atomic force microscopy Ž . AFM offers the possibility of imaging nonconduc- tive samples. Contact or tapping AFM cannot avoid the damage of both the tip apex and the sample surface due to a large loading force, and hence, the true atomic resolution has not been achieved. Fur- thermore, contact AFM sometimes causes local de- formation of soft materials and the motion of w x molecules adsorbed on substrates 3,4 . Noncontact AFM can reduce the damage of the tip apex and the sample surface because the loading 0169-4332r00r$ - see front matter q 2000 Elsevier Science B.V. All rights reserved. Ž . PII: S0169-4332 99 00534-6