Surface enhanced sum frequency generation of carbon monoxide adsorbed on platinum nanoparticle arrays

Sum frequency generation (SFG) vibrational spectroscopy is used to study th e adsorption of CO at similar to 1 atm pressure on Pt nanoparticle arrays a nd Pt thin films. The SFG signal of CO adsorbed on platinum particles of 45 nm diameter is similar to 10 000 times larger than from CO on smooth Pt fi lms. The large enhancement is explained by plasmon resonance and Maxwell-Ga rnett theory. The Pt arrays are prepared using electron beam lithography to produce particles with uniform spacing and sizes on an oxidized Si(100) wa fer. Further, as the Pt coverage increases the SFG signal shows a polarizat ion dependence that is explained considering the dielectric properties of a metal film on a dielectric surface. In addition, SFG permits investigation of the CO adsorbed on the particles at similar to 1 atm, which is not poss ible with most surface analytical techniques, that will allow for the study of the reaction of small molecules on surfaces relevant in heterogeneous c atalysis. (C) 2000 American Institute of Physics. [S0021-9606(00)70437-5].