Abstract
Silver nanoparticles (NPs) are known to exhibit strong interaction with light photons because their surface conduction electrons undergo collective oscillations once photo-excited at specific wavelengths; the so-called surface plasmon resonance (SPR). Their incorporation into carbon-based material is shown to greatly influence the overall optical response of the matrix due to aggregation. In this paper, we studied the optical response of silver-irradiated amorphous carbon films due to varying fluence of 25 keV Ag ions in the range 2.5–3.4 × 1016 ions/cm2. Raman spectroscopy provided an insight into the microstructural details of the Ag:a-C nanocomposites such that access to bond characteristics of the films is enabled by directly linking the Raman information with sp2/sp3 configurations. Atomic force microscopy (AFM) analysis show significant increase in particle grain size and surface roughness of the films with increasing fluence while transmission electron microscopy (TEM) confirmed fluence-induced particle aggregation due to irradiation. Optical absorption studies revealed that the SPR of Ag NPs occurs in the wavelength range 418–395 nm in the irradiated films. The blue shift in plasmonic wavelength response is explained with respect to the fluence-induced increase in the particulate grain size and particle density as confirmed by AFM and TEM. The optical band gap energy ( E g ) of the pristine carbon film decreased from 1.79 eV to 1.41 eV while Urbach parameter ( E u ) increased from 0.01 eV to 12.0 eV, respectively with increasing fluence. These tunable optical parameters can be tailored into applications in surface coatings and as functional materials for solar cell efficiency enhancement.
Highlights
Carbon as a unique material generally exists in two main isotopes (12 C and 13 C) and is, under normal conditions, highly unreactive despite its versatility in compound formation [1]
Other Raman studies on amorphous carbon films have shown that the 1575 cm−1 is typically referred to as the G band and commonly attributed to the Raman active mode of graphite-like carbon [32,33,34,35,36,37]
Ferrari and Robertson [37] relate the D band (~1355 cm−1 ) to a breathing mode, involving phonons, that is only active in carbon films with relative disorder and which is absent in perfect graphite materials
Summary
Carbon as a unique material generally exists in two main isotopes (12 C and 13 C) and is, under normal conditions, highly unreactive despite its versatility in compound formation [1]. Noble metals-containing nanostructured materials have attracted great attention of researchers in the past few decades [14,15,16,17,18,19,20,21] because the metal nanoparticles exhibit a pronounced resonance extinction of visible light due to the collective excitation of quasi free electrons of the metallic system [22,23,24] This phenomenon causes the absorption and scattering intensities of the metal nanoparticles to be much higher than that of identically sized non-plasmonic nanoparticles [25]. We confirm the effects of the particle aggregation/size increase on the overall optical response of the nanocomposites in relation to the observed blue shift in the surface plasmon resonance wavelength
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