R. K. Soni

Gold/Tin Oxide Nanocomposite by Nanojoining

In this paper we report synthesis of Au-SnO2 nanocomposite by nano-joining. It involves synthesis of Au and SnO2 colloids separately followed by post irradiation of mixed Au-SnO2 colloids. We have used 532 nm and 1064 nm wavelengths of a pulsed Nd:YAG laser and different post irradiation time. The post irradiation by 532 nm laser light results in formation of Au-SnO2 nanocomposite by nanojoining. Distinct gold nanoparticles along with the SnO2 aggregates are observed in case of post irradiation by 1064 nm showing no nanojoining effect. Our results indicate that nanojoining is a wavelength selective process. The X-ray Photoelectron Spectroscopy (XPS) indicates negative binding energy shift of Au 4f peak whereas the position of Sn 3d peak remains unaffected after the post irradiation process. The invariance of Sn 3d peak after post irradiation indicates no change in the valence state of Sn. A red shift with respect to the plasmon resonance peak of gold colloids is observed in Au-SnO2 nanocomposite.

Pulsed-laser-induced photochemical growth of the periodic surface structure on InP

We report the laser-induced surface modification of InP in a HF electrolyte by second harmonic (532 nm) or fourth harmonic (266 nm) wavelengths of a Nd:YAG laser at a constant energy density of 125 mJ cm−2 and by varying the number of laser pulses. Laser-induced periodic surface structures (LIPSS) parallel to laser polarization are fabricated on InP by photochemical surface modification. Atomic force microscopy (AFM) is used to study the surface morphology of the modified InP surface. Photoluminescence (PL), micro-Raman spectroscopy investigations on LIPSS provide clear evidence of the crystalline nature of the fabricated structures. In addition, PL line-shape analysis is used to estimate size and size distribution of nanoscale features in the LIPSS fabricated by UV laser beams.

Laser ablation synthesis of Zn/ZnO core-shell nanoparticles

Zn/ZnO core-shell nanoparticles were synthesized by pulse laser ablation of pure Zn powder in deionised water and aqueous solution of sodium dodecyl sulfate (SDS). The optical absorption spectra show distinct peaks corresponding to the ZnO exciton and Zn metal surface plasmon. These peaks show marked variation with SDS concentration. The High-resolution transmission microscopy (HRTEM) images and optical absorption spectra show laser-induced modification of the nanoparticles size and ZnO shell thickness with SDS concentration.

Femtosecond laser generated gold nanoparticles and their plasmonic properties

The pulsed laser ablation in liquid medium is now commonly used to generate stable colloidal nanoparticles (NPs) in absence of any chemical additives or stabilizer with diverse applications. In this paper, we report generation of gold NPs (Au NPs) by ultra-short laser pulses. Femtosecond (fs) laser radiation (λ = 800 nm) has been used to ablate a gold target in pure de-ionized water to produce gold colloids with smallsize distribution. The average size of the particles can be further controlled by subjecting to laser-induced post-irradiation providing a versatile physical method of size-selected gold nanoparticles. The optical extinction and morphological dimensions were investigated with UV-Vis spectroscopy and Transmission Electron Microscopy measurements, respectively. Finite difference time domain (FDTD) method is employed to calculate localized surface plasmon (LSPR) wavelength and the near-field generated by Au NPs and their hybrids.

Raman scattering from Zn/ZnO core-shell nanoparticles

We have synthesized Zn/ZnO core-shell nanoparticles by pulsed laser ablation in liquid (PLAL) media using nanosecond pulsed Nd:YAG laser. The formation of crystalline core-shell nanoparticles of varying core and shell thickness with varying SDS concentration is confirmed by HRTEM images. The optical absorption shows distinct features corresponding to ZnO exciton and Zn surface plasmon. Raman spectrum from Zn/ZnO core-shell nanoparticles shows E2(high) phonon modes of the bulk which are insensitive to the size and modes unique to the core-shell structures. Moreover, the surface optical mode is dominant feature of the nonresonant spectrum. We have also examined the wavelength dependence of the phonon modes in Zn/ZnO core-shell structure.