Silver nanoparticles were spontaneously formed on pristine and oxidized single-wall nanotubes. Nanoparticles were observed on carbon nanotubes with AFM, and the presence of Ag nanoparticles were confirmed by ESR experiments. Raman spectroscopy of the Ag-treated carbon nanotubes had a 4–10X enhancement of intensity compared to untreated carbon nanotubes. Ag nanoparticles formed at defect sites on the CNT surface, where free electrons located at the defect sites reduced Ag+ to Ag. A mechanism for the propagation of the nanoparticles is through a continual negative charge generation on the nanoparticle by electron transfer from doublet oxygen (O2？). 1. Introduction Since the discovery of carbon nanotubes was first published in 1991, their unique chemical and physical properties have since attracted interest in a wide spectrum of fields, including materials science, engineering, physical sciences, and medical/health sciences [1–5]. In its simplest form, single-walled carbon nanotubes (SWCNTs) are composed of a single graphene layer rolled into a cylindrical shape, having dimensions of 0.4–1？nm diameter and lengths on the order of 103？nm. Multi walled carbon nanotubes (MWCNTs), on the other hand, are composed of an array of concentric cylinders with diameters up to 50？nm. In addition, the orientation of the graphitic rings along the tubular surface result in the CNTs exhibiting metallic or semiconducting properties [6]. Similar to CNTs, metal nanoparticles have also generated interest, especially in regards to sensors, catalysis, and fuel cell research. Integrating nanoparticles with CNTs is an attractive feature that has potential application in catalysis, sensors, and fuel cells due to the enhanced dispersion and performance [7–9]. There are many strategies for incorporating metal nanoparticles onto CNT surfaces. One of the most straight forward methods is vapor deposition of a metal layer onto the CNT surface [10]. However, this method requires the deposition of the CNTs onto a substrate, followed by depositing a metal film under vacuum. Electrodepositing Ag through electrolysis reduction [11, 12], or through a η2-coordination, where a Sn2+-activated surface reduces Ag+ onto the CNT surface [13]. Irradiating CNTs with γ-rays in the presence of Ag+ as well as some type of hydrophilic polymer has also produced Ag-decorated CNTs, presumably through the attachment of the polymer onto the CNT surface [14–16]. Here, we report the spontaneous formation of Ag nanoparticles onto freshly sonicated SWCNT surfaces. Raman spectroscopy measurements revealed signal
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