The optical and catalytic properties of metallic nanoparticles (NPs) are currently of considerable interest and subject of recent investigation. In particular, the possibility of forming alloy NPs is very promising because the alloy composition can be a parameter to further control the optical properties of these systems. Specifically, the optical properties of bimetallic NPs synthesized from free-electron like metals, such as Au and Cu are greatly interest and important.
In this work, we report preparation and characterization of Au-Cu alloy NPs in SiO2 thin film matrix. Transparent SiO2thin films containing Au-Cu alloy particles were deposited on quartz, soda lime and glass substrates by reactive RF magnetron co-sputtering technique. Two pieces of Au and Cu strips (1mm in length) were placed symmetrically on Si target with 50 mm in diameter. The prepared target was sputtered using a 50 W power at pressure of 20 mTorr in a mixed Ar+O2(60%-40%) environment. The as deposited films were annealed at temperature of 400, 600 and 800°C for 1h in an Ar+H2 (80%-20%) atmospheres.
The optical UV-visible analysis of Au-Cu bimetallic showed one absorption peak located between the absorption bands of pure Au and Cu at 540 nm for the Au-Cu-SiO2annealed (600 and 800°C ) thin films indicating formation of Au-Cu alloy. While for the samples annealed at 400°C no absorption peak was observed. X-ray photoelectron spectroscopy (XPS) results showed that the alloys are in metallic state, and they have greater tendency to lose electrons as compared to their monometallic state. Positive shift of Au(4f) core level binding energy to higher values relative to monometallic state suggests formation of alloying Cu with Au. Also, it was found that the Au-Cu alloying resulted in a negative shift of Cu(3d) binding energy. Using atomic force microscopy (AFM) and lateral force microscopy (LFM) analyses, we have found that the some particle like features uniformly distributed on the surface with average grain size of about 25 nm. Therefore, observations of these surface topographics along with our XPS and UV-visible analyses confirm these features are Au-Cu alloy NPs. |