Exposure of mass-selected bimetallic Pt-Ti nanoalloys to oxygen explored using scanning transmission electron microscopy and density functional theory

• Published in: RSC advances Vol. 8; no. 48; pp. 27276 - 27282
• Main Authors: Gholhaki, Saeed, Hung, Shih-Hsuan, Cant, David J. H, Blackmore, Caroline E, Shard, Alex G, Guo, Quanmin, McKenna, Keith P, Palmer, Richard E
• Format: Journal Article
• Language: English
• Published: England Royal Society of Chemistry 01.01.2018; The Royal Society of Chemistry
• Subjects: Bimetals; Chemistry; Density functional theory; Electron beams; Exposure; First principles; Magnetron sputtering; Mathematical analysis; Morphology; Nanoalloys; Nanoparticles; Nanotechnology; Oxidation; Oxygen; Platinum; Scanning electron microscopy; Scanning transmission electron microscopy; Titanium; Transmission electron microscopy
• ISSN: 2046-2069; 2046-2069
• DOI: 10.1039/c8ra02449a

The response of nanoparticles to exposure to ambient conditions and especially oxidation is fundamental to the application of nanotechnology. Bimetallic platinum-titanium nanoparticles of selected mass, 30 kDa and 90 kDa, were produced using a magnetron sputtering gas condensation cluster source and deposited onto amorphous carbon TEM grids. The nanoparticles were analysed with a C s -corrected Scanning Transmission Electron Microscope (STEM) in High Angle Annular Dark Field (HAADF) mode. It was observed that prior to full Ti oxidation, Pt atoms were dispersed within a Ti shell. However, after full oxidation by prolonged exposure to ambient conditions prior to STEM, the smaller size 30 kDa particles form a single Pt core and the larger size 90 kDa particles exhibit a multi-core structure. Electron beam annealing induced a single core morphology in the larger particles. First principles density functional theory (DFT) calculations were employed to calculate the lowest energy structure of the Pt-Ti nanoparticles with and without the presence of oxygen. It was demonstrated that, as the concentration of oxygen increases, the lowest energy structure changes from dispersed Pt to multiple Pt cores and finally a single Pt core, which is in good agreement with the experimental observations. Theoretical and experimental morphology induced by oxidation of the Ti element.