Size-selected ag nanoparticles with five-fold symmetry

Abstract

Silver nanoparticles were synthesized using the inert gas aggregation technique. We found the optimal experimental conditions to synthesize nanoparticles at different sizes: 1.3 ± 0.2, 1.7 ± 0.3, 2.5 ± 0.4, 3.7 ± 0.4, 4.5 ± 0.9, and 5.5 ± 0.3 nm. We were able to investigate the dependence of the size of the nanoparticles on the synthesis parameters. Our data suggest that the aggregation of clusters (dimers, trimer, etc.) into the active zone of the nanocluster source is the predominant physical mechanism for the formation of the nanoparticles. Our experiments were carried out in conditions that kept the density of nanoparticles low, and the formation of larges nanoparticles by coalescence processes was avoided. In order to preserve the structural and morphological properties, the impact energy of the clusters landing into the substrate was controlled, such that the acceleration energy of the nanoparticles was around 0.1 eV/atom, assuring a soft landing deposition. High-resolution transmission electron microscopy images showed that the nanoparticles were icosahedral in shape, preferentially oriented with a five-fold axis perpendicular to the substrate surface. Our results show that the synthesis by inert gas aggregation technique is a very promising alternative to produce metal nanoparticles when the control of both size and shape are critical for the development of practical applications.

Keywords: Inert gas aggregation; Nanocrystals and nanoparticles; Silver nanoparticles; Stability and fragmentation of clusters; Structure of nanoscale materials.

Figure 1

HAADF micrograph and histogram of size for Ag nanoparticles of:a,b1.3 ± 0.2 nm;c,d1.7 ± 0.3 nm;e,f2.5 ± 0.4 nm;g,h3.7 ± 0.4 nm;i,j4.5 ± 0.9 nm; andk,l5.5 ± 0.3 nm. Taking into account only the particles dispersed on the sample surface, and leaving the aggregates out of the accountancy

Figure 2

Mass spectrometer profiles (line, before the selection by mass) and HAADF (filled area, alter the selection by mass) of the distribution

Figure 3

AFM image of Ag nanoparticles:a350 × 350 nm image of silver nanoparticles filter with 5.5 nm size selected andbprofile of silver nanoparticles by AFM

Figure 4

HREM micrographs and corresponding FFT for silver nanoparticles:a3.7 nm,b4.5 nm, andc5.5 nm. Caseashows a five-fold orientation,bshow a three-fold orientation, andcshows a two-fold orientation

Figure 5

The profile of Ag nanoparticles in the all the cases indicates a gaussian shape consistent with a 3-D quasispherical shape, consistent with the icosahedral structure:a,d6.0 nm,b,e3.7 nm, andc,f2.0 nm