## 2 Materials and Methods  
The colloidal solutions of metallic gold and silver were separately produced by pulsed laser ablation (PLA) in Millipore water, using the second harmonic (532 nm) output of a Nd:YAG laser operating at 10 Hz [33; 34]. In a second step, Au and Ag colloids were mixed at the volume ratio of 50/50. The as mixed dispersions were obtained from the same parental solutions and irradiated with the same laser source at constant power density (0.2 J/cm\({}^{2}\)) and at different irradiation times. The irradiations were performed in order to illuminate the entire system with the same beam. Linear carbon chains (LCCs) containing sp-hybridization as alternating triple and single bonds (polyenes, (-C\(\equiv\)C-)n) were synthesized by arcing between two graphite electrodes in water. Two cylindrical graphite rods (99.995%) with a diameter of about 6 mm were connected to a DC supplier. The voltage was set at 30 V and the measured current was about 10 A. The discharge time was 10 min. The solution of LCCs was filtered with a 0.22 mm filter (Millipore Millex in PES) to remove the large amount of carbon dust formed during the discharge process. To test the formation of Au-Ag nanoalloys the optical transmittance spectrum was immediately recorded, with a double beam spectrophotometer (Perkin-Elmer Lambda750) through their characteristic absorption peak (400-520 nm). Scanning Transmission Electron Microscopy (STEM) images of kV are shown in Figure 1. Besides coalescence, the lack of an apparent core-shell structure in the STEM picture strongly suggests that the nanoparticles are alloys rather than core-shell composites. Recently [PERSON] et al. [35] simulated the extinction spectra of Ag-Au alloyed nanoparticles produced by pulsed laser ablation in liquid of elemental targets followed by reirradiation of suitable mixtures of the obtained colloidal suspensions. When we make use of the optical constants of Ag-Au alloys, our theoretical approach, developed in the framework of the T-matrix formalism, accurately reproduces the experimental features of the extinction spectra of laser-produced nanoalloys with compositions that span the entire composition range. Additionally, thanks to the simulation of the optical absorption data, [PERSON] et al. [35] excluded the formation of core-shell structures and validated the formation of Au-Ag alloys. As seen from the histogram (Figure 2) the size of the rounded nanoparticles is about 8 nm and tails down to 2 nm and up to 13 nm. The XPS core-level and valence band (VB) measurements were performed using a PHI 5000 Versa Probe XPS spectrometer (ULVAC Physical Electronics, Chanhassen, MN,  
Figure 1: STEM image of the alloy (50:50): (**a**) Au-Ag NPs, (**b**) and (**c**) Au-Ag)@LCC. Figure 2: The histogram of Ag/Au@LCC nanoparticles size distribution. USA) based on a classic X-ray optic scheme with a hemispherical quartz monochromator and an energy analyzer working in the range of binding energies from 0 to 1500 eV. This equipment uses electrostatic focusing and magnetic screening to achieve an energy resolution of \(\Delta\)E \(\leq\) 0.5 eV for Al K\(\alpha\) radiation (1486.6 eV). Pumping of analytical chamber was carried out using an ion pump providing pressure better than 10\({}^{-7}\) Pa. The XPS spectra were recorded using Al K\(\alpha\) X-ray emission; the spot size was 200 \(\upmu\)m, and the X-ray power load delivered to the sample was less than 50 W. Typical signal-to-noise ratios were greater than 10,000:3. XPS spectra were processed using MultiPak 9.9.0.8 software. Finally, the background was taken into account using the Shirley method. A few drops from the nanoparticle suspension was deposited and dried on a monocrystalline silicon substrate to record XPS of the core-levels and valence bands. The presence of metal-carbon bonds is of crucial importance in the solid state analysis since free _sp_ chains air-exposed easily degrade as a consequence of their interaction with atmospheric gases [36].