Morphology faceted particles

Fig. 26. Surface morphology of a platinum sample after 4 h of oxygen plasma treatment. The platinum surface is partially covered by faceted particles 5 pm in diameter (245).

Figure 4.29. Experimental images of a (5%)Pt/Ceo.gTbo.20i, catalyst reduced at 1173 K registered in profile view a) and planar view c). Simulated images obtained using n els considering well faceted (beryl type morphology) CePts particles supported on a mixed oxide crystal b) and d). Model of a supported intermetallic particle used to obtain the simulated images e) (155).

The shape control of nanoparticles is a very important aspect in nanotechnology, due to the spectacular effects that structural anisotropy may have on many of the material s physical properties. Because of these size- and shape-dependent properties, much effort has been expended in controlling the morphology and assembly of nanoparticles [68-69]. The most common architecture of these nanocrystals is isotropic particles, ranging from spherical to highly faceted particles, such as cubic and octahedral. One-dimensional (1-D) anisotropic nanoparticles include uniform rods and wires, whereas two-dimensional (2-D) nanoparticles consists of nanodiscs, plates and other advanced shapes such as rod-based multipods and nanostars. 

How does a support affect the morphology of a particle on top of it Which surface planes does the metal single crystal expose The thermodynamically most stable configuration of such small crystallites is determined by the free energy of the surface facets and the interface with the support, and can be derived by the so-called Wulff construction, which we demonstrate for a cross section through a particle-support assembly in two dimensions (Fig. 5.13). 

The potential of morphologically controlled metal nanoparticles should be expanded by further improvement of their preparation method. It is highly required to develop preparation methods to obtain a better morphological control, i.e., perfect facet control on the particles of optional size. Better morphological control of metal nanoparticles is expected to be achieved in near future and the obtained metal particles will find new exciting applications, not only in catalysis but also in other technically important fields. 

The structure of 3 was confirmed by X-ray crystallography (Fig. 1). The morphology of the nanoparticles was examined by transmission electron microscopy (TEM). The two sp2-C palladacycles 1 and 4 gave what appeared to be triangular nanoparticles, in 2D, from 2-12 nm in size while the sp3-C PdCys 5 and 6 and Pd(OAc)2 exhibited more conventional morphology and were faceted palladium particles from 3-10 nm (Fig. 2). 

The microscopy results characterizing the Cu/ZnO catalyst are in accord with EXAFS data representing the dynamic morphology changes (39—41), and they also provide an important additional insight On the basis of the lattice-resolved images, the nature of the exposed facets of the projected copper nanoclusters and the epitaxial relationship between the copper and ZnO can be identified. The majority of the copper nanocrystals appear to be in contact with the ZnO support with their (111) facets, as was also observed for copper particles prepared by vapor... 

The Pt particles were formed by physical vapor deposition onto 10 nm thick Fe304(lll) films grown on Pt(lll). The particles become more uniform in size and well-faceted upon heating to elevated temperatures. Figure 4.4.6 shows typical morphology of the Pt nanoparticles vacuum-annealed at temperatures above 800 K. The particles, about 1 nm in height and 5 nm in width, expose atomically... 

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