THE ROLE OF AFM, HRTEM, SAXS AND OPTICAL SPECTROSCOPY IN SIZING Cu, Ag, Fe AND Ni NANOPARTICLES GENERATED BY ULTRAFAST LASER ABLATION OF SOLID TARGETS IN DIFFERENT LIQUID MEDIA

MARCELA B. FERNÁNDEZ VAN RAAP ; JESICA M. J. SANTILLÁN ; DIEGO MURACA ; DAVID MUÑETÓN ARBOLEDA ; PEDRO MENDOZA ZÉLIS ; D. F. CORAL ; DANIEL C. SCHINCA ; LUCÍA B. SCAFFARDI

Bariloche

Conferencia; Acta Microscopica, Vol. 25 Supp. A., 2016, 4° Congreso de la Asociación Argentina de Microscopía (SAMIC 2016); 2016

SAMIC 2016

This work deals with the generation of Cu, Ag, Fe and Ni nanoparticles (NPs) by femtosecond laser ablation in different media and the characterization of their structures, configurations and sizes using Atomic Force Microscopy (AFM), High Resolution Transmission Electron Microscopy (HRTEM), Optical Extinction Spectroscopy (OES) and Small Angle X-Ray Scattering (SAXS). Colloidal suspensions receive nowadays considerable attention due to their attractive physicochemical properties, which boost applications in catalysis, optics, electronics and biomedical areas based on their unique size-dependent optical, electrical and magnetic properties. Over the last few years, we have carried out a systematic work in producing, by top down methods, noble-metal (Cu and Ag) metallic NPs colloids [1], [2] and more recently magnetic NPs such as Fe and Ni [3]. In laser ablation, energy is deposited in a bulk material at a sufficient fast rate so that it breaks up and forms particles in the nanometric scale. The structure of the so-produced colloids includes a variety of morphologies like bare-core, core?shell and hollows NPs as well as aggregates including fractals. AFM appears as a suitable tool for 3D characterization with sub-nanometric resolution. AFM and TEM characterize dried samples while OES and SAXS characterize the NPs structuring in the colloid state. The observation of isolated NPs is shown in Fig. 1 for Ag. The formation of fractal structure is shown in Fig. 2 for Fe colloid. Self-similarity property of fractal Fe colloid is demonstrated through the invariance under scale transformation comparing AFM with optical microscopy images shown in Fig. 3. Complementarily, TEM technique images a hollow Ni NP, as shown in Fig. 4. The size distribution and composition of the colloidal suspensions were derived from OES by fitting experimental extinction spectra using Mie theory, taking into account specific modifications of the complex metal dielectric function with size for free and bound electron contributions, as shown for Cu colloid in Fig. 5. We discuss the advantages, limits and complementarity of AFM and TEM techniques with OES optical spectroscopy and SAXS to characterize nanometric size colloids produced by femtosecond laser ablation. REFERENCES[1] J. M. J. Santillán, F. A. Videla, M. B. Fernández van Raap, D. C. Schinca and L. B. Scaffardi. (2013) ?Analysis of the structure, configuration, and sizing of Cu and Cu oxide nanoparticles generated by fs laser ablation of solid target in liquids? J. Appl. Phys. 113, 134305. DOI:10.1063/1.4798387 [2] . J. M. J. Santillán, M. B. Fernández van Raap, D. Muraca, D. Coral, P. Mendoza Zelis, D. C. Schinca,and L. B. Scaffardi. (2015) ?Ag nanoparticles formed by femtosecond pulse laser ablation in water: self-assembled fractal structures? Journal of Nanoparticle Research. 17(2), DOI: 10.1007/s11051-015-2894-8[3] D. Muñeton Arboleda, J. M. J. Santillan, L. J. Mendoza Herrera, M. B. Fernández van Raap, P. Mendoza Zelis, D. Muraca, D. C. Schinca and L. B. Scaffardi (2015) ? Synthesis of Ni nanoparticles by fs laser ablation in liquids: structure and sizing?. J. Phys. Chem. C, 119 (23), 13184 DOI: 10.1021/acs.jpcc.5b03124ACKNOWLEDGMENTSThis work was granted by PIP 0394 and PIP 0720 of CONICET, PME2006-00018 of ANPCyT, grant11/I151 of Facultad de Ingeniería Universidad Nacional de La Plata and 11/X680 of Facultad de Ciencias Exactas Universidad Nacional de La Plata, Argentina. We thank C2NANO-Brazilian Nanotechnology National Laboratory (LNNano) at Centro Nacional de Pesquisa em Energia e Materiais (CNPEM)/MCT (#14825 and 14827). AFM was carried out at LFAyM of Instituto de Física La Plata (IFLP-CONICET). FIGURES Fig. 1: AFM data analysis of a single Ag nanoparticle of 2.5 nm diameter. Upper panel height profile of topographic image. Left: semicontact topography image. Right: second pass phase contrast image. Fig. 2: 50 x 50 microm AFM image of Fe fractal structure acquired using semicontact mode. Right bar color scale from 0 to 25 nm. Fig. 3: Upper panel: optical microscopy bright field image of a fractal structure produced dropping Fe colloid into a mica sheet. Lower panel: dark field image of other region of the sample. Field of view diameter: 200 m Fig. 4: TEM image of hollow Ni nanoparticle. Fig. 5: Experimental spectra and theoretical fit of colloidal suspension in acetone with pulse energy E = 500 mJ. The fit is based on a combination of Cu bare-core and Cu-Cu2O structures.