Plasmonic Nanostructures Induced Surface Photochemistry

Gil Toker Chemistry, The Hebrew University of Jerusalem, Jerusalem, Israel Liat Zilberberg Chemistry, The Hebrew University of Jerusalem, Jerusalem, Israel Alex Bespaly Chemistry, The Hebrew University of Jerusalem, Jerusalem, Israel Serge Mitlin Chemistry, The Hebrew University of Jerusalem, Jerusalem, Israel Micha Asscher Chemistry, The Hebrew University of Jerusalem, Jerusalem, Israel

The search for direct evidence of plasmon enhanced photochemistry and catalysis at the vicinity of metal nanostructures is at the focus of interest in recent years due to its potential importance in solar energy related applications1,2. Such enhancement has been predicted theoretically more than 3 decades ago3, during the early reports on Surface Enhanced Raman Spectroscopy (SERS) but has not yet been demonstrated under well controlled UHV environment.

In this report we present the first attempt to address this issue under well-defined ultra-high vacuum conditions, on top of clean (non-colloidal) silver nanoparticles at the size range of 10-120nm. Ethyl chloride molecules adsorbed at 45K on silver clusters decorated SiO2/Si(100) substrate were used as our probe molecule for photo-reactivity and selectivity studies.

Experimental parameters included gradual increase of the silver particles size and total coverage, excitation laser wavelength and in particular varying the distance of the probe molecule from the silver particle`s surface via Xe spacer layers (see figure 1 below). Pump-probe experiments employing two laser wavelengths were used to dissociate the molecule (355nm) and to excite the TiO2 film modified surface plasmon resonance of the silver particles (532nm). This experiment has revealed that no observable enhancement of photo-reactivity could be detected when the two nsec laser pulses overlap in time. The overall list of observations has led us to conclude that energetic photo-induced electrons, affected by work function modifications, transiently scatter from the adsorbed ethyl chloride affinity level, leading to dissociative electron attachment (DEA).

Another hybrid system composed of silver nano-particles embedded within vacuum prepared titania thin film (20nm thick) has been tested for its photo-catalytic activity, via degradation of methylene blue (MB) dye molecule at 355nm. Enhanced activity has been observed and will be discussed.

  1. N. J. Halas et. al., JACS, 136, 64 (2014)
  2. P. Christopher et. al., ACS Catalysis, 4, 116 (2014)
  3. A. Nitzan and L. E. Brus, J. Chem. Phys., 75, 2205 (1981)

Micha.Asscher@mail.huji.ac.il









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