Structure and stability of nickel/nickel oxide core–shell nanoparticles

Abstract

The results of a combined x-ray photoelectron spectroscopy (XPS) and high resolution transmission electron microscopy (HR-TEM) study of Ni nanoparticles (NP), before and after oxidation, are presented. An experimental set-up was realized for the preparation and study of pre-formed NP films, concentrating the attention on Ni NP in the diameter range between 4 and 8 nm. The XPS data were taken in situ from NPs after different stages of oxidation, including controlled dosing of O(2) gas in the experimental system and exposure to the atmosphere. The Ni 2p structure is a combination of spectra from metallic Ni in the NP core and from the oxide shell. The signal from the NP core was observed even for samples after exposure to air. From the comparison of HR-TEM experimental images with theoretical simulations, it was found that the Ni NP core has a regular multitwinned icosahedral structure, composed of single-crystal tetrahedra with (111) faces. The NiO phase is clearly observed forming islands on the NP surface.

Influence of size, shape and core–shell interface on surface plasmon resonance in Ag and Ag@MgO nanoparticle films deposited on Si/SiOx

“…Aggregation of the NPs was also observed with scanning TEM-high angle annular dark field (STEM-HAADF) ( Figure 2a) and TEM (see also Supporting Information File 1). Areas with different crystal domains were observed and are evidently caused by crystal twinning, which occurs during the NP growth process [28] or by formation of NP agglomerates with different crystal orientations after deposition and diffusion on the substrate [29][30][31]. Figure 2b shows an atomic resolution TEM image of a single NP.…”

“…Figure 2b shows an atomic resolution TEM image of a single NP. The image corresponds to a McKay icosahedral geometry, where the icosahedron is assembled from single crystal tetrahedra with (111) faces [28,32] (see Figure 2c). This type of structure, as previously observed in other fcc metal NPs [22,23,28,33], can be ascribed to the dynamics of NP growth.…”

“…The image corresponds to a McKay icosahedral geometry, where the icosahedron is assembled from single crystal tetrahedra with (111) faces [28,32] (see Figure 2c). This type of structure, as previously observed in other fcc metal NPs [22,23,28,33], can be ascribed to the dynamics of NP growth. In particular, it was found that formation of icosahedra is favoured at fast quenching rates for fcc metal NPs [33][34][35].…”

“…In these conditions we could obtain Ag NP with a linear size distribution between 3 and 10 nm, as measured by the QMF and directly verified by the SEM and TEM images. The size distribution of the deposited particles was always checked ex situ with SEM and with TEM [22][23][24]27,28]. The quantity of deposited Ag NPs and the resulting MgO (see the Results and Discussion section) are given in this work in terms of nominal thickness of an equivalent continuous film with the same density as bulk fcc Ag and rock salt MgO.…”

A Structural Characterization of GaAs MBE Grown on Si Pillars

“…Defect analysis was performed on cross-section specimens by TEM at 200 keV (STEM/TEM JEOL 2200 FS) operated in the two beam diraction contrast, high resolution (HR-TEM) and high angle annular dark eld (HAADF) modes. Strain maps to locate the dislocations at the interface were obtained by geometric phase analysis (GPA) [23,24] processing of HR-TEM images using the STEM--CELL software package [25,26]. The 110 cross-section specimens were prepared by sandwiching a piece of the sample between two slabs of Si, followed by mechanical grinding down to 30 µm.…”