Microstructure of the Native Oxide Layer on Ni and Cr-doped Ni Nanoparticles
Metallic or alloy nanoparticles exposed to air at room temperature will be instantaneously oxidized and covered by an oxide layer. However, for most cases, the true structural nature of the oxide layer formed at this stage is hard to determine. In this paper, we report the structure, morphology, and electronic structure (the density of state of both valence and conduction bands measured by a combination of XPS and EELS) of pure Ni and Cr-doped Ni nanoparticles synthesized using a cluster deposition process. Structural characterization carried out at the atomic level using aberration corrected high resolution transmission electron microscopy (HRTEM) in combination with electron and x-ray diffractions reveals that both pure Ni and Cr-doped Ni particles exposed to air at room temperature similarly possesses a core-shell structure of metal core covered by an oxide layer of typically 1.6 nm in thickness. There exists a critical size of ~ 6 nm, below which the particle is fully oxidized. The oxide particle corresponds to the rock-salt structured NiO and is faceted on the (001) planes. XPS of O-1s shows a strong peak that is attributed to (OH)-, which in combination with the atomic level HRTEM imaging indicates that the very top layer of the oxide is hydrolyzed as Ni(OH)2. Chemical composition analysis using EDS, EELS, and XPS indicates that the Cr dopant at the level of ~ 5at% forms solid solution with the Ni lattice. The Cr shows no segregation on the surface or preferential oxidation during the initial oxidation.
- Research Organization:
- Pacific Northwest National Lab. (PNNL), Richland, WA (United States). Environmental Molecular Sciences Lab. (EMSL)
- Sponsoring Organization:
- USDOE
- DOE Contract Number:
- AC05-76RL01830
- OSTI ID:
- 1034584
- Report Number(s):
- PNNL-SA-76189; 39399; KP1704020; KC0201020; TRN: US201203%%634
- Journal Information:
- Journal of Nanoscience and Nanotechnology, 11(10):8488-8497, Vol. 11, Issue 10
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
ALLOYS
CHEMICAL COMPOSITION
CRITICAL SIZE
DEPOSITION
ELECTRONIC STRUCTURE
ELECTRONS
LASERS
MICROSTRUCTURE
MORPHOLOGY
OXIDATION
OXIDES
RESOLUTION
SALT DEPOSITS
SEGREGATION
SOLID SOLUTIONS
TRANSMISSION ELECTRON MICROSCOPY
VALENCE
X-RAY DIFFRACTION
X-RAY PHOTOELECTRON SPECTROSCOPY
Core-shell
structure
Ni nanoparticles
Cr-doped Ni nanoparticles
electronic structure
HRTEM
surface
layer
Environmental Molecular Sciences Laboratory