Characterising the surface and interior chemistry of core–shell nanoparticles using scanning transmission electron microscopy

Mendis, Budhika G.; Craven, A. J.

doi:10.1016/j.ultramic.2010.11.002

Cited by 7 publications

(8 citation statements)

References 24 publications

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“…However, that multiple splitting was not observed in our EELS data. This fact suggests that the crystal field effect is smaller, probably due to a decreasing of crystallinity, leading to broadening of the spectrum for TiO 2 nanoparticles as reported by other authors. , …”

supporting

confidence: 70%

Room-Temperature Ferromagnetism in Reduced Rutile TiO_2−δ Nanoparticles

Parras¹,

Varela²,

Cortés‐Gil³

et al. 2013

J. Phys. Chem. Lett.

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We report a synthesis method to stabilize TiO 2 rutile nanoparticles (around 10 nm) and keep the particle size when reduced down to TiO 1.84 . TiO 2−δ nanoparticles exhibit room-temperature ferromagnetism that becomes stronger for TiO 1.84 . The reduction mechanism to stabilize Magneli phases excludes a relevant influence of oxygen vacancies in the modification of the magnetic properties. The arrangement of Ti 3+ could give rise to hopping of the single 3d electron inducing local ferromagnetic-like behavior.

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supporting

confidence: 70%

Room-Temperature Ferromagnetism in Reduced Rutile TiO_2−δ Nanoparticles

Parras¹,

Varela²,

Cortés‐Gil³

et al. 2013

J. Phys. Chem. Lett.

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“…However, the amount and accuracy of the information extracted depends strongly on the elemental composition of the particles and also on the quality of the instrument itself. Moreover, due to the fact that the electrons penetrate deep into if not through the sample, the response will inevitably contain mixed information from both the core and the shell phases [35], hence lacking the sensitivity to surface structure. The sub-nanometer resolution of some high resolution TEMs opens up the possibility to come close to spotting individual atoms within the nanoparticle [4,36,37].…”

Section: Electron Microscopy and Spectroscopymentioning

confidence: 99%

“…One example is the study of silver-core platinum-shell type particles by Wojtysiak et al, where profiling could help distinguishing core-shell particles from hollow Pt particles [29]. Even more impressive step resolution profiling is achieved with STEM-EELS setups [10,11,24,35] with examples for particles not more than 2 nm in diameter [38]. Although this kind of profiling struggles to exclude the presence of pores through the shell, which could only be estimated visually, standard EDX has been used as a tool to investigate the intactness of the shell.…”

Section: Electron Microscopy and Spectroscopymentioning

confidence: 99%

“…Further TEM compositional profiling methods are limited in determining possible alloying of two metals in bimetallic core-shell particles. An attempt to resolve the issue with inevitably combined signals from the core and shell was made by Mendis et al [35]. By using STEM fitted with EELS and HAADF in combination with linear regression analysis, compositional profiles were made with resolution steps as small as 0.1 nm for a set of TiN-core Ti-oxide-shell and Cu-core Cu-oxide-shell particles.…”

Section: Electron Microscopy and Spectroscopymentioning

confidence: 99%

“…Although image contrast in TEM is specific to the type of element, TEM is usually complemented with spectroscopic detectors enabling compositional analysis, such as Energy Dispersive X-ray (EDX) spectroscopy. On the high end of the spectrum, STEM accompanied with Electron Energy Loss Spectroscopy (EELS) or High-Angle Annular Dark Field (HAADF) imaging, composition profiling can be made across the particles taking advantage of the close-to-atomic resolution [10,29,35]. In Electron Energy Loss Spectroscopy (EELS) the energy distribution of initially mono-energetic electrons, after they have interacted with the sample, is being measured using an energy loss filter [36,38].…”

Section: Electron Microscopy/spectroscopymentioning

confidence: 99%

See 2 more Smart Citations

How to Determine the Core-Shell Nature in Bimetallic Catalyst Particles?

Westsson

Koper

2014

Catalysts

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Nanometer-sized materials have significantly different chemical and physical properties compared to bulk material. However, these properties do not only depend on the elemental composition but also on the structure, shape, size and arrangement. Hence, it is not only of great importance to develop synthesis routes that enable control over the final structure but also characterization strategies that verify the exact nature of the nanoparticles obtained. Here, we consider the verification of contemporary synthesis strategies for the preparation of bimetallic core-shell particles in particular in relation to potential particle structures, such as partial absence of core, alloying and raspberry-like surface. It is discussed what properties must be investigated in order to fully confirm a covering, pinhole free shell and which characterization techniques can provide such information. Not uncommonly, characterization strategies of core-shell particles rely heavily on visual imaging like transmission electron microscopy. The strengths and weaknesses of various techniques based on scattering, diffraction, transmission and absorption for investigating core-shell particles are discussed and, in particular, cases where structural ambiguities still remain will be highlighted. Our main conclusion is that for particles with extremely thin or mono-layered shells-i.e., structures outside the limitation of most imaging techniques-other strategies, not involving spectroscopy or imaging, are to be employed. We will provide a specific example of Fe-Pt core-shell particles prepared in bicontinuous microemulsion and point out the difficulties that arise in the characterization process of such particles. OPEN ACCESSCatalysts 2014, 4 376

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