Thermal stability of size-selected arrays of gold nanoparticles on (112¯0) sapphire – A thermal desorption spectroscopy study

Exploiting the self-organization of spherical gold salt loaded inverse micelles formed from diblock copolymer poly(styrene)-block-poly(2-vinylpyridine) (PS-b-P2VP) in toluene, arrays of Au nanoparticles were prepared exhibiting narrow size as well as interparticle distance distributions. Starting with such Au nanoparticles (average particle diameters ranging between 1nm and 5nm) deposited on top of (112¯0)-oriented sapphire substrates, thermal desorption spectroscopy (TDS) experiments were performed up to a maximum temperature of 1473K at a standard rate of 5K/s in order to test for size dependent vapor pressures as expected from Kelvin’s equation. Opposite to the expected increase of the vapor pressure for decreasing particle diameters, a split desorption behavior is observed with two peaks. Analyzing the data according to the Polanyi–Wigner equation, from the peak at lower temperature a desorption energy and attempt frequency close to bulk Au is extracted while the peak at higher temperature delivers significantly larger values for both properties. The latter observation is attributed to a substrate–nanoparticle interaction, which becomes dominant for decreasing particle diameters.