We report electron-microscopy and high-resolution x-ray-scattering measurements of rapidly quenched ${\mathrm{Al}}_{6}$Mn. The electron-diffraction pattern shows icosahedral symmetry. Peaks in the x-ray-diffraction pattern can be indexed to a mixture of fcc Al and a phase whose reciprocal lattice is described by a sum of icosahedral vectors. The half-width of the sharpest x-ray peak is 0.01 ${\mathrm{\AA{}}}^{\ensuremath{-}1}$. A comparison is made with current theories of quasicrystalline order.

Structure of rapidly quenched Al-Mn.

Nanoparticles are a state of matter that has properties different from either molecules or bulk solids. In the present work, we review the shape and structure of nanometer-sized particles; several shapes are discussed, such as the octahedron and truncated octahedron, the icosahedron, the Marks decahedron, the truncated “star-like” decahedron, the rounded decahedron and the regular decahedron. Experimental high-resolution transmission electron microscopy (TEM) images of each type of particle are presented together with the Fast Fourier Transform and a model of the particle. We consider only gold particles grown by vapor deposition or by colloidal methods. High-resolution TEM images of the particles in different orientations are shown. We discuss two basic types of particles uncapped and capped. Data for other metals and semiconductors are reviewed. We have also performed very extensive simulations obtaining the total energy and pair correlation functions for each cluster under study. Furthermore, distributions of single atom energy for every cluster are displayed in order to reveal the effect of surface on the stability of different types and sizes of clusters. We discuss the structure of the particles from ∼1 to ∼100 nm. The mechanisms for stress release as the particles grow larger are reviewed and a mechanism is suggested. Finally, we discuss the parameters that define the shape of a nanoparticle and the possible implications in technological applications.Nanoparticles are a state of matter that has properties different from either molecules or bulk solids. In the present work, we review the shape and structure of nanometer-sized particles; several shapes are discussed, such as the octahedron and truncated octahedron, the icosahedron, the Marks decahedron, the truncated “star-like” decahedron, the rounded decahedron and the regular decahedron. Experimental high-resolution transmission electron microscopy (TEM) images of each type of particle are presented together with the Fast Fourier Transform and a model of the particle. We consider only gold particles grown by vapor deposition or by colloidal methods. High-resolution TEM images of the particles in different orientations are shown. We discuss two basic types of particles uncapped and capped. Data for other metals and semiconductors are reviewed. We have also performed very extensive simulations obtaining the total energy and pair correlation functions for each cluster under study. Furthermore, distribut...

Structure shape and stability of nanometric sized particles

Experimental results from thermally annealed particles of silver and gold in the size range 10–50 nm show the presence of re-entrant surfaces on the decahedral multiply twinned particles (MTPs). A theoretical model is developed to explain these results based on the Wulff construction modified to include twin-boundaries. In addition to reproducing the re-entrant surfaces, the theory suggests that the total surface energy of the decahedral form is sandwiched between those of a single crystal and an icosahedral MTP. Consequently the stability of the decahedral particles (in a certain size range) relative to single crystals can now be explained. A useful perturbation modification is also outlined which enables qualitative comparisons of the surface energies to be made, and shows that the twin boundaries in MTPs limit the possible surface facets. Explicit shapes and energies are presented for two extreme models of the faceting. Finally, a model is outlined to justify the difference between the structu...

/pdf/surface-structure-and-energetics-of-multiply-twinned-3s4242c5zh.pdf

Surface structure and energetics of multiply twinned particles

The diffusion and coalescence of metal nanoparticles play important roles in many phenomena. Here, we offer a new integrated overview of the main factors that control the nanoparticle coalescence process. Three factors are considered in our description of the coalescence process: nanoparticle diffusion across the surface, their physical and thermodynamic properties, and the mechanism of coalescence. We demonstrate that the liquid-like properties of the surface layers of the nanoparticles play an essential role in this process. We present experimental evidence for our opinion, based on the high-resolution electron microscopic analysis of several different types of nanoparticles.

Surface diffusion and coalescence of mobile metal nanoparticles.

The energetics of nickel clusters over a broad size range are explored within the context of the many‐body potentials obtained via the embedded atom method. Unconstrained local minimum energy configurations are found for single crystal clusters consisting of various truncations of the cube or octahedron, with and without (110) faces, as well as some monotwinnings of these. We also examine multitwinned structures such as icosahedra and various truncations of the decahedron, such as those of Ino and Marks. These clusters range in size from 142 to over 5000 atoms. As in most such previous studies, such as those on Lennard‐Jones systems, we find that icosahedral clusters are favored for the smallest cluster sizes and that Marks’ decahedra are favored for intermediate sizes (all our atomic systems larger than about 2300 atoms). Of course very large clusters will be single crystal face‐centered‐cubic (fcc) polyhedra: the onset of optimally stable single‐crystal nickel clusters is estimated to occur at 17 000 atoms. We find, via comparisons to results obtained via atomistic calculations, that simple macroscopic expressions using accurate surface, strain, and twinning energies can usefully predict energy differences between different structures even for clusters of much smaller size than expected. These expressions can be used to assess the relative energetic merits of various structural motifs and their dependence on cluster size.

The energetics and structure of nickel clusters: Size dependence

The structure of small, vapor-deposited particles: I. Experimental study of single crystals and particles with pentagonal profiles

The structure of small, vapor-deposited particles: II. Experimental study of particles with hexagonal profile

Crystallography of decahedral and icosahedral particles. II - High symmetry orientations

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The structure of small, vapor-deposited particles: I. Experimental study of single crystals and particles with pentagonal profiles

The structure of small, vapor-deposited particles: II. Experimental study of particles with hexagonal profile

Crystallography of decahedral and icosahedral particles. II - High symmetry orientations