Optical Tracking of Single Ag Clusters in Nanostructured Water Films

Abstract

The spatial diffusion and size distribution of monodisperse silver nanoclusters synthesized via Ag(I) carboxylate in zeolite Y cages are investigated in nanostructured water films on silicon dioxide (SiO 2 ) and mica surfaces with optical and atomic force techniques. Subnanometer clusters escaping the zeolite Y cage show a strong and photostable fluorescence emission in the visible range and allow for optical singlecluster tracking. Heterogeneous diffusion dynamics reflect the transition from an ice-like to a liquid-like water film as a function of film thickness. The contributions of the different diffusion coefficients strongly correlate with the water film thickness and the chemical composition of the interface. The heterogeneity of the diffusion is caused by ad-and desorption of Ag clusters to silanol groups at the SiO 2 interface which couple vibronically to the Ag clusters as can be seen from single cluster fluorescence spectra.

Optical investigation of diffusion of single Ag markers in confined water films

“…Blinking provides additional confidence that we are dealing with the emission of single Ag clusters and will also influence the determination of the length of diffusion trajectories. (ii) Some of the Ag clusters diffuse in space as has been reported previously (Krause et al 2013) and will be discussed in the main part of the results. Figure 4 shows the typical fluorescence of a single Ag cluster in comparison to the broad fluorescence of an ensemble of Ag particles excited in the UV.…”

“…Spectroscopic results shown in the supplement agree with recently published data (Pyatenko et al 2004;Ozin and Hugues 1983;Hartmann 2012;Lecoultre et al 2011;Mitchell et al 1980) and confirm typical properties of Ag clusters. From the overall comparison with published spectroscopic data, we recently concluded that the presently investigated clusters consist of (n = 8-15) Ag atoms (Krause et al 2013).…”

“…We have reported recently that about 50 % of single Ag particles are subject to spatial diffusion as can be easily detected at a wide-field frame rate of 200 ms (Krause et al 2013;Kahle et al 2014). We have shown that the diffusion occurs in an ultrathin water film, the thickness of which can be controlled by regulating the humidity in an appropriate chamber.…”

“…The mean diameter of 40 Ag particles is 0.9 nm. The width of the distribution of diameters (as determined from heights) is ±0.6 nm (Krause et al 2013). This diameter is close to the diameter of 0.78 nm for the zeolite channel (see Fig.…”

“…Recently, we have reported on spatial diffusion of Ag nanoparticles in ultrathin water films (Krause et al 2013). Since the structure of ultrathin water films has been investigated by various static techniques (Asay and Kim 2005;Verdaguer et al 2007), it is of special interest whether the structure influences dynamics such as spatial diffusion within films of a thickness less than 2 nm.…”