AVS 56th International Symposium & Exhibition
    Surface Science Monday Sessions
       Session SS2-MoA

Paper SS2-MoA1
Nanoplasmonic Sensing of Metal Hydride Formation and Catalytic Reactions on Metallic Nanoparticles

Monday, November 9, 2009, 2:00 pm, Room N

Session: Formation & Reactivity of Nanoclusters
Presenter: I.L. Zoric, Chalmers University, Sweden
Authors: E.M. Larsson, Chalmers University, Sweden
C.M. Langhammer, Chalmers University, Sweden
B.H. Kasemo, Chalmers University, Sweden
I.L. Zoric, Chalmers University, Sweden
Correspondent: Click to Email
A novel, nanoplasmonics-based optical sensing platform for real time studies of nanoparticle processes is described. Examples are presented for (i) surface catalytic reaction kinetics on nanoparticles and (ii) formation of a new phase in metal hydride forming nanoparticles. The remarkably sensitive and very versatile sensing platform consists of plasmonic sensing particles (Au nanodisks, D=76nm and h=40 nm, prepared on a transparent substrate), covered by a 10nm dielectric film onto which the nanoparticles to be studied are deposited (in the present case Pd or Pt, with a size range from 2 nm-10nm). The key to the sensing is utilization of localized surface plasmon resonances (LSPR). The LSPR of the sensing nanoparticle sensitively measures changes of the surface coverage (sensitivity <0.05ML) or the formation of the new phase in the studied nanoparticles via shifts in the LSPR extinction spectra. The versatility of this method is illustrated with the following examples:

a) Hydrogen absorption/desorption (hydride formation) studies of Pd nanoparticles in the size range 2-10nm. The main result from these studies includes the size dependent thermodynamics (p-C-T diagram) and kinetics of the H/Pd nanoparticle (1-5 nm) system. The kinetics exhibit a power and power-exponential size dependence of the time scales for the hydrogen uptake and release processes. The uptake is in agreement with Monte Carlo simulations of diffusion controlled hydriding kinetics, while the release (desorption) is explained by the effect of surface tension on the activation energy for hydrogen desorption from the nanoparticle.

b) Kinetic studies of CO and H2 oxidation on Pt nanoparticles with particular emphasis on kinetic phase transition phenomena in these reactions. The latter occur as one varies reactant concentrations but keeps the total amount of reactants constant and are recognized by a sudden transition from oxygen covered nanoparticle surfaces at low CO (H2) concentration, to high CO or H coverage for low O2 concentrations,

c) NO2 storage and conversion to N2 on Pt/BaO. In this case NO2 storage and conversion kinetics is followed via changes in the LSPR resonance of the Au sensing particles, coated with a thin layer of BaO onto which Pt nanoparticles were deposited. Exposure of the sensor to the gas mixture of NO2+O2 leads to a conversion of BaO to Ba(NO3)2 (NOx storage) leading to a change of refractive index of the material surrounding the sensing nanoparticle. This leads to a LSPR peak shift that is monitored. Exposure to H2 converts the stored NO2 to N2. Reversible changes were monitored for such NO2 oxidation/reduction cycles.