Ion-irradiation-induced amorphization of cobalt nanoparticles

Journal Article · Thu Apr 15 00:00:00 EDT 2010 · Physical Review. B, Condensed Matter and Materials Physics

DOI:https://doi.org/10.1103/PHYSREVB.81.155414· OSTI ID:21366727

Sprouster, D J; Giulian, R; Araujo, L L; Kluth, P; Johannessen, B; Kirby, N; Nordlund, K; Ridgway, M C ^[1]

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1. Department of Electronic Materials Engineering, Research School of Physics and Engineering, Australian National University, Canberra, Australian Capital Territory 0200 (Australia)

The amorphization of Co nanoparticles embedded in SiO{sub 2} has been investigated by measuring their structure and size, before and after ion irradiation, by x-ray absorption spectroscopy and small-angle x-ray scattering, respectively. Compared to bulk material, unirradiated crystalline nanoparticles exhibited increased structural disorder and a decreased average coordination number as a result of finite-size effects. Upon irradiation, there was no variation in nanoparticle size yet significant structural change. The coordination number decreased further while the mean value (bondlength), variance (Debye-Waller factor), and asymmetry (third cumulant) of the interatomic distance distribution all increased, as consistent with theoretical predictions for an amorphous elemental metal. Furthermore, the interatomic distance distribution for irradiated Co nanoparticles was in excellent agreement with our molecular dynamics simulations for bulk amorphous Co, and we have thus attributed the observed structural changes to the formation of an amorphous phase. Though such a crystalline-to-amorphous phase transformation is not readily achievable in bulk material by ion irradiation, we suggest that the perturbed structural state prior to irradiation and the amorphous surrounding matrix both contribute to nucleating and stabilizing the amorphous phase in irradiated Co nanoparticles. In addition to the structural properties, the vibrational properties of the amorphous phase were also probed, using temperature-dependent x-ray absorption spectroscopy measurements. The Einstein temperature of the unirradiated crystalline nanoparticles was lower than that of bulk material due to loosely bonded surface/interfacial atoms. In contrast, that of the irradiated amorphous nanoparticles was substantially higher than the bulk value. We attribute this apparent bond stiffening to the influence of the rigid surrounding matrix.

• OSTI ID: 21366727
• Journal Information: Physical Review. B, Condensed Matter and Materials Physics, Vol. 81, Issue 15; Other Information: DOI: 10.1103/PhysRevB.81.155414; (c) 2010 The American Physical Society; ISSN 1098-0121
• Country of Publication: United States
• Language: English

Related Subjects

75 CONDENSED MATTER PHYSICS
SUPERCONDUCTIVITY AND SUPERFLUIDITY
ABSORPTION SPECTROSCOPY
AMORPHOUS STATE
ASYMMETRY
ATOMS
COBALT
DEBYE-WALLER FACTOR
FORECASTING
INTERATOMIC DISTANCES
IONS
IRRADIATION
MOLECULAR DYNAMICS METHOD
NANOSTRUCTURES
PARTICLES
PHYSICAL RADIATION EFFECTS
SILICON OXIDES
SIMULATION
SMALL ANGLE SCATTERING
SURFACES
TEMPERATURE DEPENDENCE
TRANSFORMATIONS
X-RAY DIFFRACTION
X-RAY SPECTROSCOPY
CALCULATION METHODS
CHALCOGENIDES
CHARGED PARTICLES
COHERENT SCATTERING
DIFFRACTION
DISTANCE
ELEMENTS
METALS
OXIDES
OXYGEN COMPOUNDS
RADIATION EFFECTS
SCATTERING
SILICON COMPOUNDS
SPECTROSCOPY
TRANSITION ELEMENTS