Surface plasmon eects on surface second harmonic generation during Au nanoparticle deposition onto H±Si1 1 1) Ramanathan Srinivasan, Yuan Tian, Ian Ivar Suni * Department of Chemical Engineering, Clarkson University, Potsdam, NY 13699-5705, USA Received 8 November 2000; accepted for publication 7 May 2001 Abstract Deposition of Au nanoparticles from aqueous HF onto H±Si1 1 1) was studied in situ by surface second harmonic generation SHG) and ex situ by extinction spectroscopy and non-contact atomic force microscopy AFM). AFM measurements indicate that the maximum SHG intensities occur at lateral particle diameters of approximately 90±100 nm independent of solution phase composition, but with an intensity that depends on solution phase composition. Employing the evolution of SHG intensity to monitor lateral cluster growth, simultaneous Au deposition and Si oxidation exhibit apparent kinetic reaction orders of 1=2 and zero with respect to HF and AuCN)  2 , respectively. These results are similar to those obtained purely from ex situ AFM analysis. The variations in SHG intensity with AuCN)  2 concentration can be related to particle nucleation densities. These results demonstrate the utility of SHG as an in situ probe of particle growth. Ó 2001 Published by Elsevier Science B.V. Keywords: Models of non-linear phenomena; Models of surface kinetics; Atomic force microscopy; Non-linear optical methods; Second harmonic generation methods; Second harmonic generation; Surface chemical reaction; Gold; Silicon; Single crystal surfaces; Solid±liquid interfaces 1. Introduction Due to their low resistivity and good corrosion resistance, noble metal thin ®lms have a variety of applications as contacts and conductors in the electronics industries [1±5]. When feasible, no- ble metal deposition by electrochemical means is usually desirable as it is less expensive than vac- uum methods. On the other hand, direct noble metal deposition onto Si during wafer cleaning and preparation prior to semiconductor device fabrication is undesired and must be prevented to maintain high device yields. Following dissolution of the native SiO x oxide in aqueous HF, noble metals may be reduced and deposited onto bare Si, which is a strong reducing agent [6]. Metal deposition from aqueous HF initially forms nm-sized particles that are approximately oblate hemispheroids, as seen by scanning probe microscopy [7±11]. Such noble and alkali metal nanoparticles exhibit strong resonant electric ®eld enhancements associated with the surface plasmon resonance, producing highly colored colloidal so- lutions [12,13]. Electric ®eld enhancements in surface ensembles of noble and alkali metal nanoparticles can also Surface Science 490 2001) 308±314 www.elsevier.com/locate/susc * Corresponding author. Tel.: +1-315-268-5705/4471; fax: +1-315-268-6654. E-mail address: isuni@clarkson.edu I.I. Suni). 0039-6028/01/$ - see front matter Ó 2001 Published by Elsevier Science B.V. PII:S0039-602801)01350-4