analytica chimica acta 602 ( 2 0 0 7 ) 236–243 available at www.sciencedirect.com journal homepage: www.elsevier.com/locate/aca Surface enhanced Raman scattering from layered assemblies of close-packed gold nanoparticles Hye Young Jung a , Yong-Kyun Park a , Sungho Park a,b,∗ , Seong Kyu Kim a,∗ a Department of Chemistry and BK School of Chemical Materials Science, Sungkyunkwan University, Suwon 440-746, Republic of Korea b SKKU Advanced Institute of Nanotechnology, Sungkyunkwan University, Suwon 440-746, Republic of Korea article info Article history: Received 27 July 2007 Received in revised form 30 August 2007 Accepted 8 September 2007 Published on line 19 September 2007 Keywords: Surface enhanced Raman scattering Enhancement factor Gold Au Nanoparticle Surface plasmon Benzenethiol Thiophenol Electromagnetic effect Chemical effect abstract A synthetic method of ordering hydrophilic gold nanoparticles into a close-packed two- dimensional array at a hexane–water interface and subsequent transferring of such structure onto a solid substrate is described. By repeating the transfer process, multilay- ered gold nanoparticle films are formed without need of linker molecules. Their surface enhanced Raman scattering (SERS) efficiencies are compared as a function of the number of layers. It is shown that both the number of layers and the particle size contribute to SERS phenomenon. Judging from the noticeable dependence of SERS efficiency on the nanome- ter scale architecture, the close-packed nanoparticle formation at an immiscible interface presents a facile route to the preparation of highly active and relatively clean SERS substrates by controlling both the particle size and the film thickness. Among the investigated sam- ples, the gold nanoparticle film assembled with quintuple layers of 30 nm diameter particles showed the maximum SERS efficiency. © 2007 Elsevier B.V. All rights reserved. 1. Introduction The elucidation of the microscopic processes, such as molec- ular adsorption, catalysis, and corrosion, is of fundamental interest for solving challenging problems in surface chemistry. One of the primary objectives in the study of surface science is the understanding of adsorbate–surface interactions at the molecular level. In order to investigate surface adsorption and its dynamics, a myriad of surface-characterization techniques ∗ Corresponding authors. Tel.: +82 31 299 4562 (S. Park), +82 31 290 7069 (S.K. Kim); fax: +82 31 290 7075. E-mail addresses: spark72@skku.edu (S. Park), skkim@skku.edu (S.K. Kim). have been utilized. In particular, surface enhanced Raman scattering (SERS) has been extensively utilized as a major tool for unveiling the vibrational characteristics of adsor- bates on noble metal surfaces owing to its enormous signal enhancement effect. It is a general understanding that the SERS from noble metal nanostructures has two major contri- butions: one is a local field enhancement induced by localized surface plasmon resonance, and the other is a charge-transfer resonance between an analyte and a metal surface [1]. The 0003-2670/$ – see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.aca.2007.09.026