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Microscopic characterization of Fe nanoparticles formed on SrTiO 3 (001) and SrTiO 3 (110) surfaces

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ABSTRACT

Fe nanoparticles grown on SrTiO3 (STO) {001} and {110} surfaces at room temperature have been studied in ultrahigh vacuum by means of transmission electron microscopy and scanning tunnelling microscopy. It was shown that some Fe nanoparticles grow epitaxially. They exhibit a modified Wulff shape: nanoparticles on STO {001} surfaces have truncated pyramid shapes while those on STO {110} surfaces have hexagonal shapes. From profile-view TEM images, approximate values of the adhesion energy of the nanoparticles for both shapes are obtained.

No MeSH data available.


Schematic models of the nanoparticles with Wulff shapes. a) A truncated pyramid with OR1 and b) a distorted hexagon with OR2; c–f) corresponding top and side views. Top surfaces are shaded.
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Figure 2: Schematic models of the nanoparticles with Wulff shapes. a) A truncated pyramid with OR1 and b) a distorted hexagon with OR2; c–f) corresponding top and side views. Top surfaces are shaded.

Mentions: As mentioned above, there are nanoparticles with ideal interfaces. These nanoparticles may well be assumed to have nearly thermodynamically stable shapes, since surface self-diffusion lengths of iron atoms on both Fe(100) and (110) surfaces are reported to be larger than the nanoparticle sizes observed here [56–57]. Although a more precise evaluation of kinetic factors and of the possibility of anisotropic growth should be made, it is not unreasonable to suppose that ideal nanoparticles have a simple Wulff shape. And nanoparticles with OR1 and OR2 can be illustrated as shown in Fig. 2. Fig. 2,b present the same schematic model being cut along different planes. They are drawn using only the least-energy surface and the second-least-energy surface, namely {110} and {100}, respectively. The surface free energy values are taken from the literature with γFe{110}/γFe{100} of 0.92 [51]. The nanoparticle in Fig. 2 has Fe(001) top and bottom surfaces, and the nanoparticle in Fig. 2 has Fe (110) top and bottom surfaces. Actual nanoparticles are located on a substrate so they do not possess a complete Wulff shape but are cut along a certain plane. This type of modified Wulff construction, which takes into account the particle–substrate interaction, is denominated as the Winterbottom construction [58]. The Winterbottom theory describes the dependence of the particle shape upon the anisotropy of the surface energy of the particle and upon the binding between the particle and the substrate. Fig. 2–f shows the top and side views of the Winterbottom constructions of the nanoparticles in Fig. 2,b. In the image the Wulff shapes are cut along the planes that contain the Wulff points (the centre of mass). Hereafter, we call nanoparticles with a configuration modelled in Fig. 2,d truncated pyramids and those in Fig. 2,f distorted hexagons.


Microscopic characterization of Fe nanoparticles formed on SrTiO 3 (001) and SrTiO 3 (110) surfaces
Schematic models of the nanoparticles with Wulff shapes. a) A truncated pyramid with OR1 and b) a distorted hexagon with OR2; c–f) corresponding top and side views. Top surfaces are shaded.
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Related In: Results  -  Collection

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Figure 2: Schematic models of the nanoparticles with Wulff shapes. a) A truncated pyramid with OR1 and b) a distorted hexagon with OR2; c–f) corresponding top and side views. Top surfaces are shaded.
Mentions: As mentioned above, there are nanoparticles with ideal interfaces. These nanoparticles may well be assumed to have nearly thermodynamically stable shapes, since surface self-diffusion lengths of iron atoms on both Fe(100) and (110) surfaces are reported to be larger than the nanoparticle sizes observed here [56–57]. Although a more precise evaluation of kinetic factors and of the possibility of anisotropic growth should be made, it is not unreasonable to suppose that ideal nanoparticles have a simple Wulff shape. And nanoparticles with OR1 and OR2 can be illustrated as shown in Fig. 2. Fig. 2,b present the same schematic model being cut along different planes. They are drawn using only the least-energy surface and the second-least-energy surface, namely {110} and {100}, respectively. The surface free energy values are taken from the literature with γFe{110}/γFe{100} of 0.92 [51]. The nanoparticle in Fig. 2 has Fe(001) top and bottom surfaces, and the nanoparticle in Fig. 2 has Fe (110) top and bottom surfaces. Actual nanoparticles are located on a substrate so they do not possess a complete Wulff shape but are cut along a certain plane. This type of modified Wulff construction, which takes into account the particle–substrate interaction, is denominated as the Winterbottom construction [58]. The Winterbottom theory describes the dependence of the particle shape upon the anisotropy of the surface energy of the particle and upon the binding between the particle and the substrate. Fig. 2–f shows the top and side views of the Winterbottom constructions of the nanoparticles in Fig. 2,b. In the image the Wulff shapes are cut along the planes that contain the Wulff points (the centre of mass). Hereafter, we call nanoparticles with a configuration modelled in Fig. 2,d truncated pyramids and those in Fig. 2,f distorted hexagons.

View Article: PubMed Central - HTML - PubMed

ABSTRACT

Fe nanoparticles grown on SrTiO3 (STO) {001} and {110} surfaces at room temperature have been studied in ultrahigh vacuum by means of transmission electron microscopy and scanning tunnelling microscopy. It was shown that some Fe nanoparticles grow epitaxially. They exhibit a modified Wulff shape: nanoparticles on STO {001} surfaces have truncated pyramid shapes while those on STO {110} surfaces have hexagonal shapes. From profile-view TEM images, approximate values of the adhesion energy of the nanoparticles for both shapes are obtained.

No MeSH data available.