Abstract Despite the large number of reports on colloidal nanocrystals, very little is known about the mechanistic details in terms of nucleation and growth at the atomistic level. Taking bimetallic core-shell nanocrystals as an example, here we integrate in situ liquid-cell transmission electron microscopy with first-principles calculations to shed light on the atomistic details involved in the nucleation and growth of Pt on Pd cubic seeds. We elucidate the roles played by key synthesis parameters, including capping agent and precursor concentration, in controlling the nucleation site, diffusion path, and growth pattern of the Pt atoms. When the faces of a cubic seed are capped by Br − , Pt atoms preferentially nucleate from corners and then diffuse to edges and faces for the creation of a uniform shell. The diffusion does not occur until the Pt deposited at the corner has reached a threshold thickness. At a high concentration of the precursor, self-nucleation takes place and the Pt clusters then randomly attach to the surface of a seed for the formation of a non-uniform shell. These atomistic insights offer a general guideline for the rational synthesis of nanocrystals with diverse compositions, structures, shapes, and related properties.
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A Mechanistic Study of the Multiple Roles of Oleic Acid in the Oil‐Phase Synthesis of Pt Nanocrystals
Oleic acid (OAc) is commonly used as a surfactant and/or solvent for the oil‐phase synthesis of metal nanocrystals but its explicit roles are yet to be resolved. Here, we report a systematic study of this problem by focusing on a synthesis that simply involves heating of Pt(acac)2in OAc for the generation of Pt nanocrystals. When heated at 80 °C, the ligand exchange between Pt(acac)2and OAc leads to the formation of a PtII–oleate complex that serves as the actual precursor to Pt atoms. Upon increasing the temperature to 120 °C, the decarbonylation of OAc produces CO, which can act as a reducing agent for the generation of Pt atoms and thus formation of nuclei. Afterwards, several catalytic reactions can take place on the surface of the Pt nuclei to produce more CO, which also serves as a capping agent for the formation of Pt nanocrystals enclosed by {100} facets. The emergence of Pt nanocrystals further promotes the autocatalytic surface reduction of PtIIprecursor to enable the continuation of growth. This work not only elucidates the critical roles of OAc at different stages in a synthesis of Pt nanocrystals, but also represents a pivotal step forward toward the rational synthesis of metal nanocrystals.
more » « less- PAR ID:
- 10236169
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Chemistry – A European Journal
- Volume:
- 26
- Issue:
- 67
- ISSN:
- 0947-6539
- Format(s):
- Medium: X Size: p. 15636-15642
- Size(s):
- p. 15636-15642
- Sponsoring Org:
- National Science Foundation
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Abstract Decahedral nanocrystals have received great attention owing to their unique symmetry and strain‐energy distribution. In contrast to other noble metals, it has been difficult to synthesize decahedral Rh nanocrystals. We report a robust, one‐pot method based on polyol reduction for the facile synthesis of Rh decahedral nanocrystals in high purity, with sub‐20 nm sizes. The success of the synthesis relied on our ability to manipulate reduction kinetics by systematically tuning experimental parameters. We found that the yield of Rh decahedral nanocrystals could be maximized by optimizing:
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versus surface) for the formation of completely different products. More significantly, we demonstrate that the speciation, reduction kinetics, and reduction pathway of a Pd(II) precursor can all be manipulated by varying the type and/or amount of halides introduced into a synthesis for the deterministic formation of a specific product. This work represents a critical step forward in achieving a quantitative understanding of the multiple roles of halides involved in the shape‐controlled synthesis of Pd nanocrystals, with the knowledge potentially extendible to other noble metals and their alloys. -
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Ion beam-induced deposition (IBID) using Pt(CO)2Cl2and Pt(CO)2Br2as precursors has been studied with ultrahigh-vacuum (UHV) surface science techniques to provide insights into the elementary reaction steps involved in deposition, complemented by analysis of deposits formed under steady-state conditions. X-ray photoelectron spectroscopy (XPS) and mass spectrometry data from monolayer thick films of Pt(CO)2Cl2and Pt(CO)2Br2exposed to 3 keV Ar+, He+, and H2+ions indicate that deposition is initiated by the desorption of both CO ligands, a process ascribed to momentum transfer from the incident ion to adsorbed precursor molecules. This precursor decomposition step is accompanied by a decrease in the oxidation state of the Pt(II) atoms and, in IBID, represents the elementary reaction step that converts the molecular precursor into an involatile PtX2species. Upon further ion irradiation these PtCl2or PtBr2species experience ion-induced sputtering. The difference between halogen and Pt sputter rates leads to a critical ion dose at which only Pt remains in the film. A comparison of the different ion/precursor combinations studied revealed that this sequence of elementary reaction steps is invariant, although the rates of CO desorption and subsequent physical sputtering were greatest for the heaviest (Ar+) ions. The ability of IBID to produce pure Pt films was confirmed by AES and XPS analysis of thin film deposits created by Ar+/Pt(CO)2Cl2, demonstrating the ability of data acquired from fundamental UHV surface science studies to provide insights that can be used to better understand the interactions between ions and precursors during IBID from inorganic precursors.
