1Charles University in Prague, Faculty of Mathematica and Physics, Czech Republic
2Condensed Matter Physics and Materials Science, Brookhaven National Lab. Upton, NY 11973-5000, USA
In presented work, silver and hafnium metallic nanoparticles prepared by the aggregation from the gas phase were studied by Bragg coherent diffraction imaging.
Bragg coherent diffraction imaging (BCDI) is a lens-less technique that enables the reconstruction of the nanocrystal in 3D with high sensitivity to the presence of microstrains in the crystal structure. It is based on the scattering of the coherent beam from monocrystalline nanoparticle and the measurement of a series of 2D reciprocal space cuts around the Bragg diffraction to obtain the 3D diffraction pattern. Afterwards, the phase retrieval algorithm, consisting of the iterations between the reciprocal and real space and constraints applications, is employed to recover the phase information.
Studied nanoparticles were prepared by gas aggregation cluster sources combined with magnetron sputtering of single metallic targets. This physical preparation method is environmentally friendly, scalable to industry demands, provides high cleanness of the process and tunability of nanoparticles structure, and therefore it is highly interesting for industrial applications. The structure of silver nanoparticles was analysed after annealing to 300 °C, i.e., above the temperature of the initial coalescence step. Hafnium nanoparticles were studied as-deposited, and different morphologies were detected. The shape of the strain fields suggests that their presence could be connected with the high complexity of the preparation method. The changes in morphology and inner strain field of Hf nanoparticles were tracked by BCDI in-situ during annealing up to 200 °C in an air atmosphere. BCDI results are combined with outcomes from additional characterization methods, namely in-situ powder x-ray diffraction and electron microscopies, for a complete description of the nanoparticle oxidation process.
TK acknowledges the financial support of this study by the Fulbright U.S. Scholar Program, which is sponsored by the U.S. Department of State and the Czech-American Fulbright Commission.