Sudipto Pal

Oriented Au–Cu nanoalloy particle incorporated SiO2 films using a new layer by layer deposition technique

Oriented Au–Cu nanoalloys have been generated in SiO2 films using a new two-layer (TL) coating approach. Two successive overlapping coating layers were deposited on silica glass substrate using Au- and Cu-incorporated inorganic–organic hybrid silica sols. The concentrations of the Au and Cu (3 equivalent mol% metal–97% SiO2 in each case) in the respective layers and their individual coating thicknesses were kept similar for the generation of Au–Cu alloys of an approximate atomic ratio 1 : 1. The UV-visible and X-ray diffraction (XRD) spectra of the TL films show the formation of nanoalloys with a gradual increase of Cu content with increasing heat-treatment temperature up to 750 °C in 10% H2–90% Ar. The XRD patterns reveal that the Au and Cu gradually formed Au–Cu nanoalloys of different ratios with a orientation. Estimation shows that the final nanoalloy composition reaches Au0.58Cu0.42. The transmission electron microscope (TEM) image obtained from an Au0.58Cu0.42 nanoalloy containing film shows the presence of mainly oriented plate-like circular nanoalloys of diameter 9–14 nm. XRD and TEM confirm that the alloy formation took place mainly through the diffusion and gradual dissolution of Cu atoms onto the planes of Au and intermediate Au–Cu nanoalloy crystals.

Metal nanoparticle-doped coloured films on glass and polycarbonate substrates

In a program on the development of metal (e.g. Au, Ag, Cu and their alloy) nanoparticles in sol-gel derived films, attempts were made to synthesize different coloured coatings on glasses and plastics. The absorption position of surface plasmon resonance (SPR) band arising from the embedded metal nanoparticles was tailored by controlling the refractive index of the matrix for the development of different colours. Thus different coloured (pink to blue) coatings on ordinary sheet glasses were prepared by generating Au nanoparticles in mixed SiO2-TiO2 matrices having refractive index values ranging from about 1.41 to 1.93. In another development,in situ generation of Ag nanoparticles in the inorganic-organic hybrid host leads to the formation of different abrasion resistant coloured coatings (yellow to pink) on polycarbonate substrates after curing. As expected, the SPR peak of Ag or Au is gradually red-shifted due to the increase of refractive index of the coating matrices causing a systematic change of colour