ELSEVIER 5 May 1995 Chemical PhysicsLetters 237 (1995) 137-144 CHEMICAL PHYSICS LETTERS A rigorous electrodynamic model for periodic structure formation during UV laser-induced metal atom deposition Andrew C.R. Pipino, George C. Schatz, Richard P. Van Duyne Department of Chemistry, Northwestern University, 2145 Sheridan Road, Evanston, IL 60208-3113, USA Received 9 December1994; in final form 27 February 1995 Abstract A model is presented which describes the time and spatial frequency evolution of periodic structures formed during metal atom deposition arising from UV laser-induced photodissociation of organometallics. In addition to the occurrence of rapid growth of spatial frequencies which allow direct coupling of the incident radiation to the surface-plasmon polariton (SPP), a high-wavevector profile component, associated with the interference of counterpropagating SPP waves, also develops with extremely high gain but without feedback. Pump/probe diffraction methods for verifying the predictions and elucidating the surface modification of photodissociation are briefly proposed. Deposition of aluminum by photolysis of (CH3)3A1 at 257 nm is chosen as the model system. 1. Introduction Laser-induced deposition of metal atoms by pho- todissociation of gas-phase and surface-adsorbed organometallic molecules has been an area of sub- stantial activity in recent years [1]. Interest has been driven in part by applications where spatially re- solved deposition of metal films is required, such as in the fabrication of microelectronic components [2]. These films are typically rough on the nanometer- length scale which can allow excitation of the sur- face-plasmon polariton (SPP) mode. Understanding the influence of a structured metal surface on photol- ysis of organometallics will allow optimization of the technology and provide fundamental insight into the surface modification of photochemistry. Providing a dramatic example of surface-modified photochemistry, the spontaneous formation of peri- odic microstructures during metal atom deposition induced by UV laser photolysis of metal alkyls was first reported by Brueck and Ehrlich [3]. They ob- served the exponential growth of grating structures with mean groove spacings ranging from A/1.2 to A/1.7. Stimulated scattering of the incident radiation into the SPP mode was invoked to explain the phenomenon. To account for the occurrence of feed- back, Brueck and Ehrlich obtained the small-signal gain for that spatial frequency which directly cou- pled the incident radiation into the SPP mode by using explicit expressions from perturbation theory. Jelski and George [4] extended this theoretical analy- sis by incorporating expressions for the surface fields which were expected to be valid at deep corrugations to estimate the limiting grating depth produced dur- ing deposition. Similar to theories for other surface- enhanced phenomena [5], both models assumed that the deposition rate at a point on the surface was proportional to the local intensity, which accounted at least semi-quantitatively for the observations. In- deed, from the surface-enhancement perspective, the 0009-2614/95/$09.50 © 1995 Elsevier Science B.V. All rights reserved SSDI 0009-2614(95)00278-2