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Some aspects of formation and tribological properties of silver nanodumbbells.

Polyakov B, Vlassov S, Dorogin LM, Novoselska N, Butikova J, Antsov M, Oras S, Lohmus R, Kink I - Nanoscale Res Lett (2014)

Bottom Line: The mechanism of ND formation is proposed and illustrated with finite element method simulations.The geometry of NDs enables to distinguish between different types of motion, i.e. rolling, sliding and rotation.Real contact areas are calculated from the traces left after the displacement of NDs and compared to the contact areas predicted by the contact mechanics and frozen droplet models. 81.07.-b; 62.25.-g; 62.23.Hj.

View Article: PubMed Central - HTML - PubMed

Affiliation: Institute of Solid State Physics, University of Latvia, Kengaraga str. 8, Riga LV-1063, Latvia.

ABSTRACT

Unlabelled: In this paper, metal nanodumbbells (NDs) formed by laser-induced melting of Ag nanowires (NWs) on an oxidized silicon substrate and their tribological properties are investigated. The mechanism of ND formation is proposed and illustrated with finite element method simulations. Tribological measurements consist in controllable real-time manipulation of NDs inside a scanning electron microscope (SEM) with simultaneous force registration. The geometry of NDs enables to distinguish between different types of motion, i.e. rolling, sliding and rotation. Real contact areas are calculated from the traces left after the displacement of NDs and compared to the contact areas predicted by the contact mechanics and frozen droplet models.

Pacs: 81.07.-b; 62.25.-g; 62.23.Hj.

No MeSH data available.


Related in: MedlinePlus

Schematics of ND formation. Laser treatment (a). NW ends are melting, and the NW length decreases (b). Surface tension detaches a part of NW near the end bulbs from the substrate (c). Crystallization and elastic straightening of NW connecting two end bulbs of ND (d). Complete solidification of ND (e).
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Figure 2: Schematics of ND formation. Laser treatment (a). NW ends are melting, and the NW length decreases (b). Surface tension detaches a part of NW near the end bulbs from the substrate (c). Crystallization and elastic straightening of NW connecting two end bulbs of ND (d). Complete solidification of ND (e).

Mentions: Let us propose a mechanism of ND formation using SEM images of NDs frozen at different stages of formation. After absorption of laser pulse energy, a NW starts to melt; liquid droplets grow in volume and move towards the centre of a NW (Figure 2a,b). Surface tension tends to minimize the surface area of a droplet and makes it spherical. The temperature of the parts of a NW close to the liquid bulbs approaches the melting point, causing a local decrease of Young's modulus and resulting in the detachment of the parts from the substrate pulled by the growing droplet (Figure 2c). Adhesion of the central part of a NW resting on the substrate is significantly reduced due to inverse dependence of surface free energy on temperature [16]. However, the temperature in the central part of a NW is below the melting point, since the NW preserves its original crystalline structure (Additional file 1: Figure S2). When the ND is cooled down, the middle part becomes a crystallization nucleus and defines the epitaxial crystallization of the melted part of the wire towards the end bulbs. After solidification, there is an elastic stress tending to restore the straight profile of the bent part connecting two bulbs. Restoring force is also enhanced by the axial stress that originated from the thermal contraction of cooling wire (Figure 2d). If the part of the NW adhered to the substrate is short enough, and adhesion force is less than restoring elastic forces, the middle part of the NW can get detached from the substrate, and the ND will rest on the end bulbs only (Figure 2e). It is worth to note that in spite of rapid cooling, the end bulbs are crystalline as it was demonstrated by Liu et al. [13].


Some aspects of formation and tribological properties of silver nanodumbbells.

Polyakov B, Vlassov S, Dorogin LM, Novoselska N, Butikova J, Antsov M, Oras S, Lohmus R, Kink I - Nanoscale Res Lett (2014)

Schematics of ND formation. Laser treatment (a). NW ends are melting, and the NW length decreases (b). Surface tension detaches a part of NW near the end bulbs from the substrate (c). Crystallization and elastic straightening of NW connecting two end bulbs of ND (d). Complete solidification of ND (e).
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4022052&req=5

Figure 2: Schematics of ND formation. Laser treatment (a). NW ends are melting, and the NW length decreases (b). Surface tension detaches a part of NW near the end bulbs from the substrate (c). Crystallization and elastic straightening of NW connecting two end bulbs of ND (d). Complete solidification of ND (e).
Mentions: Let us propose a mechanism of ND formation using SEM images of NDs frozen at different stages of formation. After absorption of laser pulse energy, a NW starts to melt; liquid droplets grow in volume and move towards the centre of a NW (Figure 2a,b). Surface tension tends to minimize the surface area of a droplet and makes it spherical. The temperature of the parts of a NW close to the liquid bulbs approaches the melting point, causing a local decrease of Young's modulus and resulting in the detachment of the parts from the substrate pulled by the growing droplet (Figure 2c). Adhesion of the central part of a NW resting on the substrate is significantly reduced due to inverse dependence of surface free energy on temperature [16]. However, the temperature in the central part of a NW is below the melting point, since the NW preserves its original crystalline structure (Additional file 1: Figure S2). When the ND is cooled down, the middle part becomes a crystallization nucleus and defines the epitaxial crystallization of the melted part of the wire towards the end bulbs. After solidification, there is an elastic stress tending to restore the straight profile of the bent part connecting two bulbs. Restoring force is also enhanced by the axial stress that originated from the thermal contraction of cooling wire (Figure 2d). If the part of the NW adhered to the substrate is short enough, and adhesion force is less than restoring elastic forces, the middle part of the NW can get detached from the substrate, and the ND will rest on the end bulbs only (Figure 2e). It is worth to note that in spite of rapid cooling, the end bulbs are crystalline as it was demonstrated by Liu et al. [13].

Bottom Line: The mechanism of ND formation is proposed and illustrated with finite element method simulations.The geometry of NDs enables to distinguish between different types of motion, i.e. rolling, sliding and rotation.Real contact areas are calculated from the traces left after the displacement of NDs and compared to the contact areas predicted by the contact mechanics and frozen droplet models. 81.07.-b; 62.25.-g; 62.23.Hj.

View Article: PubMed Central - HTML - PubMed

Affiliation: Institute of Solid State Physics, University of Latvia, Kengaraga str. 8, Riga LV-1063, Latvia.

ABSTRACT

Unlabelled: In this paper, metal nanodumbbells (NDs) formed by laser-induced melting of Ag nanowires (NWs) on an oxidized silicon substrate and their tribological properties are investigated. The mechanism of ND formation is proposed and illustrated with finite element method simulations. Tribological measurements consist in controllable real-time manipulation of NDs inside a scanning electron microscope (SEM) with simultaneous force registration. The geometry of NDs enables to distinguish between different types of motion, i.e. rolling, sliding and rotation. Real contact areas are calculated from the traces left after the displacement of NDs and compared to the contact areas predicted by the contact mechanics and frozen droplet models.

Pacs: 81.07.-b; 62.25.-g; 62.23.Hj.

No MeSH data available.


Related in: MedlinePlus