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Free keywords:
PEEM; UHV; Resonance Forcing; Entrainment; CO-oxidation on Pt(110)
Abstract:
Pattern formation is a subfield of nonlinear science. In the last few decades pattern-forming processes in non-equilibrium systems have been extensively studied. A well known example of pattern-forming non-equilibrium systems is CO oxidation on Pt(110). The dynamics of the reaction are widely understood. Thus, CO oxidation on Pt(110) is utilized as a well-suited model system for the analysis of spatial and temporal pattern formation.
A large part of the present work is focused on the effects of periodic external forcing on chemical turbulence in CO oxidation on Pt(110), investigated both experimentally and theoretically.
Experiments are performed in an UHV chamber with a base pressure of 10−10 mbar. Photoemission electron microscopy (PEEM) is used to obtain spatially resolved images of adsorbate patterns on the catalytic Pt(110) surface. A compressor driven reactor, which allows global gas-phase forcing for frequency modulations up to 4 Hz, was specifically designed.
Experiments are performed in different resonant forcing regimes such as 2:1, 3:1, and 4:1. Under 2:1 forcing, experiments show that periodic forcing on chemical turbulence may suppress spatial turbulence and could lead to a chaotic response of the system. The path to chaos is given by a period doubling cascade, which could be experimentally followed by the subsequent increase of the forcing amplitude. Two different types, phase clusters and amplitude clusters, are found.
At 3:1 forcing, two, three, and six phase clusters are found at 2:1, 3:1, and 6:1 entrainment respectively.
4:1 resonance forcing is performed in turbulent and nonturbulent regimes. In turbulent regime, four phase clusters are observed while in nonturbulent regime, two phase clusters are observed.
The experimental results are compared with numerical simulations by using the realistic Krischer, Eiswirth, and Ertl (KEE) model. An analysis of the KEE model reveals significant differences between the oscillation frequency of the single oscillator and the mean frequency of the extended system, which appears to be higher in the turbulent state.
Numerical simulations support the findings of experimental results with only small deviations found. Under 2:1 forcing, only phase clusters are observed numerically, while under 4:1 forcing in nonturbulent regime, the four phase patterns could not be observed experimentally.
Thus, the results of this work demonstrate that by means of periodic forcing, turbulence can be effectively controlled and manipulated. Furthermore, the statistical properties of chemical turbulence are determined with increasing order of CO pressure experimentally.
