Water as Buffer Material for Gold Nanocluster Growth

Abstract

Water molecules adsorbed on SiO2/Si(100) at 140 K to form amorphous solid water (ASW) layers were utilized as a buffer for assisting the growth of gold nanoclusters. It was shown that the average height and diameter of the clusters deposited on the silicon oxide substrate following the buffer annealing/desorption increase as the buffer layer becomes thicker and as more gold is deposited. The clusters' height and diameter were determined by tapping mode AFM and high-resolution SEM imaging, respectively. Typical heights were between 0.5 and 4.5 nm, and the diameters were in the range of 3-9 nm for ASW layer thickness of 7-100 ML and gold deposition in the range of 0.2-1.2 A. The density of the clusters decreased from 65 x 10(10) to 8 x 10(10) cm (-2) in the same buffer layer thickness range. Significantly different morphology of the clusters is obtained when compared to those formed by direct deposition of gold on the silicon oxide surface and to those grown on top of Xe as buffer material.

Gold Nanoclusters Deposited on SiO2 via Water as Buffer Layer: CO-IRAS and TPD Characterization

“…To isolate the role of cluster morphology and size on the IR peak position and intensity, the IRAS spectrum of CO adsorbed on BLAG clusters (1.5 Å Au on 10 monolayers of H 2 O, Figure 4, inset b) was compared with that from clusters made by direct deposition of 1.5 Å Au on SiO 2 ( Figure 4, inset a). The DD clusters are three times denser than a single cycle of BLAG clusters, 17 while the BLAG clusters are larger. Furthermore there is a clear difference in the cluster morphology, since the BLAG clusters have an aspect ratio (height/diameter) of ∼0.4, while the DD clusters have an aspect ratio of ∼0.2.…”

“…The TPD peak attributed to CO adsorbed on bare SiO 2 has shifted to 113 K, and a new high-temperature peak emerged at 240 K. This broad peak is assigned to CO molecules adsorbed on gold clusters. CO-TPD spectra from BLAG clusters (0.5 Å gold on top of 40 monolayers of H 2 O, 6 nm average cluster diameter 17 ) resulted in a shift of the high-temperature peak to 190 K, while the lowtemperature peak location did not change (Figure 6c). This shift is associated with the size of the gold clusters: Higher desorption temperature pertains to the smaller clusters ( Figure 7).…”

Chemical Reactivity of Pd−Au Bimetallic Nanoclusters Grown via Amorphous Solid Water as Buffer Layer

“…Ex-situ AFM and HR-SEM were used to determine clusters height and diameter, respectively. 22 BLAG metallic nanoclusters were grown also on top of a standard amorphous carbon (a-C) TEM sample holder grid attached in place of the silicon samples. Their structure and elemental composition were determined using HR-TEM (Tecnai F20 G 2 , nominal line resolution 0.1 nm with EDX capability).…”

“…[16][17][18][19][20] Introduction of weakly bound buffer layers to assist the growth of clusters by Weaver and co-workers 21 (buffer layer assisted growthsBLAG) has enabled better control over size and density of particles to obtain more 3D clusters. [21][22][23] Here we report on the preparation and initial chemical reactivity of bimetallic clusters, for the first time via the BLAG procedure, manipulating Pd-Au clusters morphology and composition. We were able to demonstrate that the deposition and growth procedure of bimetallic Pd-Au alloy clusters significantly affect their chemical reactivity.…”

Patterning thin metallic film via laser structured weakly bound template

“…The utilization of other buffer materials such as water [19] and carbon dioxide [21] have recently been demonstrated for the growth of metallic and oxide clusters. This is of practical importance allowing liquid nitrogen instead of liquid helium level of sample cooling.…”