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Ion beam-induced shaping of Ni nanoparticles embedded in a silica matrix: from spherical to prolate shape.

Kumar H, Ghosh S, Avasthi DK, Kabiraj D, Mücklich A, Zhou S, Schmidt H, Stoquert JP - Nanoscale Res Lett (2011)

Bottom Line: The Ni NPs embedded in silica matrix have been prepared by atom beam sputtering technique and subsequent annealing.Irradiation induces a change from single crystalline nature of spherical particles to polycrystalline nature of elongated particles.Magnetization measurements indicate that changes in coercivity (Hc) and remanence ratio (Mr/Ms) are stronger in the ion beam direction due to the preferential easy axis of elongated particles in the beam direction.

View Article: PubMed Central - HTML - PubMed

Affiliation: Nanostech Laboratory, Department of Physics, Indian Institute of Technology Delhi, New Delhi 110016, India. hsehgal_007@yahoo.com.

ABSTRACT
Present work reports the elongation of spherical Ni nanoparticles (NPs) parallel to each other, due to bombardment with 120 MeV Au+9 ions at a fluence of 5 × 1013 ions/cm2. The Ni NPs embedded in silica matrix have been prepared by atom beam sputtering technique and subsequent annealing. The elongation of Ni NPs due to interaction with Au+9 ions as investigated by cross-sectional transmission electron microscopy (TEM) shows a strong dependence on initial Ni particle size and is explained on the basis of thermal spike model. Irradiation induces a change from single crystalline nature of spherical particles to polycrystalline nature of elongated particles. Magnetization measurements indicate that changes in coercivity (Hc) and remanence ratio (Mr/Ms) are stronger in the ion beam direction due to the preferential easy axis of elongated particles in the beam direction.

No MeSH data available.


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Micro-structural study of irradiated Ni-SiO2 film. (a) Cross-sectional TEM micrograph of irradiated Ni-SiO2 nanogranular film, (b) high-resolution TEM micrograph of an elongated Ni particle, and (c), (d) histogram of minor and major axis lengths of elongated particles, respectively
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Figure 2: Micro-structural study of irradiated Ni-SiO2 film. (a) Cross-sectional TEM micrograph of irradiated Ni-SiO2 nanogranular film, (b) high-resolution TEM micrograph of an elongated Ni particle, and (c), (d) histogram of minor and major axis lengths of elongated particles, respectively

Mentions: Figure 1a shows the cross-sectional TEM micrograph of pristine Ni-SiO2 film and the corresponding histogram of particle sizes is shown in Figure 1b. It is clear from Figures 1a,b that the pristine film contains nearly spherical particles with a broad size distribution ranging from 3.8-60 nm with a mean particle size of ~25 nm. Figure 1c shows the high-resolution TEM micrograph of a particle evidencing its single crystalline nature and the measured lattice spacing of 0.202 nm corresponding to (111) plane of fcc Ni. Figure 2a shows the cross-sectional TEM micrograph of the irradiated film taking the direction of ion irradiation from top to bottom. It is clear from Figure 2a that most of the Ni NPs change from spherical to prolate shape with their major axis aligned along the direction of ion beam at a fluence of 5 × 1013 ions/cm2. The elongated particles exhibit polycrystalline morphology, as apparent from high-resolution TEM micrograph (see Figure 2b). Figure 2c,d shows the histogram of major and minor axis length for prolate shape Ni particles. The mean major and minor axis lengths are 28.8 and 14.7 nm, respectively, estimated by considering all particles in Figure 2a. The mean aspect ratio for prolate-shaped particles is ~2. On comparing Figures 1a and 2a, it is observed that the smallest particles disappear after irradiation and shape deformation is completely suppressed for particles of size >14 nm. This confirms that the previous observations of shape deformation process is somewhat related to initial size of the nanoparticles, i.e., the bigger the particle the larger is its inertia against deformation/bigger particles require higher electronic stopping power for deformation [14-16]. Further, no deformation is observed for the free-standing Ni particles present at the surface of film (indicated by 1-3 in Figure 2a) and also those which are not surrounded by silica matrix completely (indicated by 4 in Figure 2a). This confirms previous observation by Pennikof et al. [38], which demonstrated the need of the surrounding matrix for shape deformation process upon comparison with free-standing particles. SHI irradiation is known for modification of materials due to removal of atoms from the surface of a material. This process is called electronic sputtering as it is governed by electronic stopping power at higher energies. Generally, a higher sputtering yield is observed for insulators (particularly silica) than metals [39-42], and this may be responsible for the removal of silica surrounding the surface Ni NPs in the irradiated film. TEM results indicate the dissolution of Ni particles much smaller than ion track in silica matrix (of which diameter will be discussed later), whereas the growth and elongation of relatively bigger particles by 120 MeV Au+9 ions at a fluence of 5 × 1013 ions/cm2 and also a threshold size (14 nm) exists above which no shape deformation occurs under the studied beam parameters.


Ion beam-induced shaping of Ni nanoparticles embedded in a silica matrix: from spherical to prolate shape.

Kumar H, Ghosh S, Avasthi DK, Kabiraj D, Mücklich A, Zhou S, Schmidt H, Stoquert JP - Nanoscale Res Lett (2011)

Micro-structural study of irradiated Ni-SiO2 film. (a) Cross-sectional TEM micrograph of irradiated Ni-SiO2 nanogranular film, (b) high-resolution TEM micrograph of an elongated Ni particle, and (c), (d) histogram of minor and major axis lengths of elongated particles, respectively
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3211206&req=5

Figure 2: Micro-structural study of irradiated Ni-SiO2 film. (a) Cross-sectional TEM micrograph of irradiated Ni-SiO2 nanogranular film, (b) high-resolution TEM micrograph of an elongated Ni particle, and (c), (d) histogram of minor and major axis lengths of elongated particles, respectively
Mentions: Figure 1a shows the cross-sectional TEM micrograph of pristine Ni-SiO2 film and the corresponding histogram of particle sizes is shown in Figure 1b. It is clear from Figures 1a,b that the pristine film contains nearly spherical particles with a broad size distribution ranging from 3.8-60 nm with a mean particle size of ~25 nm. Figure 1c shows the high-resolution TEM micrograph of a particle evidencing its single crystalline nature and the measured lattice spacing of 0.202 nm corresponding to (111) plane of fcc Ni. Figure 2a shows the cross-sectional TEM micrograph of the irradiated film taking the direction of ion irradiation from top to bottom. It is clear from Figure 2a that most of the Ni NPs change from spherical to prolate shape with their major axis aligned along the direction of ion beam at a fluence of 5 × 1013 ions/cm2. The elongated particles exhibit polycrystalline morphology, as apparent from high-resolution TEM micrograph (see Figure 2b). Figure 2c,d shows the histogram of major and minor axis length for prolate shape Ni particles. The mean major and minor axis lengths are 28.8 and 14.7 nm, respectively, estimated by considering all particles in Figure 2a. The mean aspect ratio for prolate-shaped particles is ~2. On comparing Figures 1a and 2a, it is observed that the smallest particles disappear after irradiation and shape deformation is completely suppressed for particles of size >14 nm. This confirms that the previous observations of shape deformation process is somewhat related to initial size of the nanoparticles, i.e., the bigger the particle the larger is its inertia against deformation/bigger particles require higher electronic stopping power for deformation [14-16]. Further, no deformation is observed for the free-standing Ni particles present at the surface of film (indicated by 1-3 in Figure 2a) and also those which are not surrounded by silica matrix completely (indicated by 4 in Figure 2a). This confirms previous observation by Pennikof et al. [38], which demonstrated the need of the surrounding matrix for shape deformation process upon comparison with free-standing particles. SHI irradiation is known for modification of materials due to removal of atoms from the surface of a material. This process is called electronic sputtering as it is governed by electronic stopping power at higher energies. Generally, a higher sputtering yield is observed for insulators (particularly silica) than metals [39-42], and this may be responsible for the removal of silica surrounding the surface Ni NPs in the irradiated film. TEM results indicate the dissolution of Ni particles much smaller than ion track in silica matrix (of which diameter will be discussed later), whereas the growth and elongation of relatively bigger particles by 120 MeV Au+9 ions at a fluence of 5 × 1013 ions/cm2 and also a threshold size (14 nm) exists above which no shape deformation occurs under the studied beam parameters.

Bottom Line: The Ni NPs embedded in silica matrix have been prepared by atom beam sputtering technique and subsequent annealing.Irradiation induces a change from single crystalline nature of spherical particles to polycrystalline nature of elongated particles.Magnetization measurements indicate that changes in coercivity (Hc) and remanence ratio (Mr/Ms) are stronger in the ion beam direction due to the preferential easy axis of elongated particles in the beam direction.

View Article: PubMed Central - HTML - PubMed

Affiliation: Nanostech Laboratory, Department of Physics, Indian Institute of Technology Delhi, New Delhi 110016, India. hsehgal_007@yahoo.com.

ABSTRACT
Present work reports the elongation of spherical Ni nanoparticles (NPs) parallel to each other, due to bombardment with 120 MeV Au+9 ions at a fluence of 5 × 1013 ions/cm2. The Ni NPs embedded in silica matrix have been prepared by atom beam sputtering technique and subsequent annealing. The elongation of Ni NPs due to interaction with Au+9 ions as investigated by cross-sectional transmission electron microscopy (TEM) shows a strong dependence on initial Ni particle size and is explained on the basis of thermal spike model. Irradiation induces a change from single crystalline nature of spherical particles to polycrystalline nature of elongated particles. Magnetization measurements indicate that changes in coercivity (Hc) and remanence ratio (Mr/Ms) are stronger in the ion beam direction due to the preferential easy axis of elongated particles in the beam direction.

No MeSH data available.


Related in: MedlinePlus