(a) Au, (b) AuAg, and (c) Ag. Optical and electrical properties of nanoparticle
deposits subjected to heating The evolution of the UV-vis absorbance spectra for the NP deposits with respect to the heating temperature and corresponding electrical resistance are illustrated in Figure 10. With a higher temperature, the intensity of the SPR (surface plasmon resonance) absorption curves was suppressed and the absorption bands were gradually blue shifted (Figure 10a,c,e). If we determine the wavelength of absorption bands (λ max) from the intersection points of the tangent lines of the curves at both sides of the absorption peak, the quantitative data shown in Figure 10b,d,f indicates that there existed a critical temperature ranging from 125°C to 175°C for the change in absorption band and electrical resistance of the NP deposits. Above this temperature Selleckchem eFT-508 range, the absorption peak value and electrical resistance were depressed significantly, resulting from the coalescence of NPs. Two SC79 supplier opposite tendencies have been observed regarding the plasmon shift caused by heating of nanoparticles.
Anto et al.  reported that upon heating to the percolation transition temperature, which was taken to be the mid-point of the insulator-to-metal transition, the plasmon band redshifts and broadens as a mark of the PF-6463922 manufacturer onset of particle coalescence. On the other hand, other research groups found that plasmon bands become narrower and move to the low wavelength end [20, 21, 36]. Supriya studied the thermal treatment of colloidal Au and suggested that at a lower temperature,
the Au colloids aggregate and the high polydispersity of particle size causes broadened plasmon peaks because of the coupling of the interparticle surface plasmons, while at high temperatures, the colloids coalesce and give rise to a narrowing of peak width due to Forskolin in vitro an increase in interparticle spacing or decrease in aggregation . Prevo et al.  observed the evolution of a uniform, multilayer aggregated nanoparticle structure subject to flame heating. They suggested that a decrease in the average domain size of the metal size results in the spectral blue shift of the SPR absorbance to lower wavelengths. Rast  investigated the thermal decomposition of PVP/Ag nanoparticle composite film and observed a decrease in SPR absorbance and blueshifting, which was ascribed to an initial fragmentation of nanoparticle aggregates and subsequent coalescence of NPs due to diffusion. Figure 10 The evolution of the UV-vis absorbance spectra and electrical resistance. Absorption spectra of NP deposits after heating at different temperatures for 20 min, and wavelength of absorption peaks as well as corresponding electrical resistance: (a, b) Au, (c, d) AuAg3, and (e, f) Ag.