The field of nanoparticle research has drawn much attention in the past decade as a result of the search for new materials. Size confinement results in new electronic and optical properties, possibly suitable for many electronic and optoelectronic applications. A characteristic feature of noble metal nanoparticles is the strong color of their colloidal solutions, which is caused by the surface plasmon absorption. This article describes our studies of the properties of the surface plasmon absorption in metal nanoparticles that range in size between 10 and 100 nm. The effects of size, shape, and composition on the plasmon absorption maximum and its bandwidth are discussed. Furthermore, the optical response of the surface plasmon absorption due to excitation with femtosecond laser pulses allowed us to follow the electron dynamics (electron−electron and electron−phonon scattering) in these metal nanoparticles. It is found that the electron−phonon relaxation processes in nanoparticles, which are smaller than t...

Spectral properties and relaxation dynamics of surface plasmon electronic oscillations in gold and silver nanodots and nanorods

The physical and chemical properties of nanophase materials rely on their crystal and surface structures. Transmission electron microscopy (TEM) is a powerful and unique technique for structure characterization. The most important application of TEM is the atomic-resolution real-space imaging of nanoparticles. This article introduces the fundamentals of TEM and its applications in structural determination of shape-controlled nanocrystals and their assemblies. By forming a nanometer size electron probe, TEM is unique in identifying and quantifying the chemical and electronic structure of individual nanocrystals. Electron energy-loss spectroscopy analysis of the solid-state effects and mapping the valence states are even more attractive. In situ TEM is demonstrated for characterizing and measuring the thermodynamic, electric, and mechanical properties of individual nanostructures, from which the structure−property relationship can be registered with a specific nanoparticle/structure.

Transmission Electron Microscopy of Shape-Controlled Nanocrystals and Their Assemblies

The structural properties of free nanoclusters are reviewed. Special attention is paid to the interplay of energetic, thermodynamic, and kinetic factors in the explanation of cluster structures that are actually observed in experiments. The review starts with a brief summary of the experimental methods for the production of free nanoclusters and then considers theoretical and simulation issues, always discussed in close connection with the experimental results. The energetic properties are treated first, along with methods for modeling elementary constituent interactions and for global optimization on the cluster potential-energy surface. After that, a section on cluster thermodynamics follows. The discussion includes the analysis of solid-solid structural transitions and of melting, with its size dependence. The last section is devoted to the growth kinetics of free nanoclusters and treats the growth of isolated clusters and their coalescence. Several specific systems are analyzed.

/pdf/structural-properties-of-nanoclusters-energetic-56vj4t3ucw.pdf

Structural properties of nanoclusters: Energetic, thermodynamic, and kinetic effects

Gold−silver alloy nanoparticles with varying mole fractions are prepared in aqueous solution by the co-reduction of chlorauric acid HAuCl4 and silver nitrate AgNO3 with sodium citrate. As the optical absorption spectra of their solutions show only one plasmon absorption it is concluded that mixing of gold and silver leads to a homogeneous formation of alloy nanoparticles. The maximum of the plasmon band blue-shifts linearly with increasing silver content. This fact cannot be explained by a simple linear combination of the dielectric constants of gold and silver within the Mie theory. On the other hand, the extinction coefficient is found to decrease exponentially rather than linearly with increasing gold mole fraction xAu. Furthermore, the size distribution of the alloy nanoparticles is examined using transmission electron microscopy (TEM). High-resolution TEM (HRTEM) also confirms the formation of homogeneous gold−silver alloy nanocrystals.

http://www.nanoscience.gatech.edu/zlwang//paper/1999/99_JPCB_1.pdf

Alloy Formation of Gold−Silver Nanoparticles and the Dependence of the Plasmon Absorption on Their Composition

Ordered magnetic nanostructures: fabrication and properties

The structure of asymmetric [110] tilt boundaries developed during creep of pure aluminium single crystals is studied using high-resolution electron microscopy. The small- and moderate-misorientation boundaries are composed of Lomer and 60° dislocations. Extensive image simulation is used to deduce the detailed core structures of these two dislocations. Comparisons with calculated elastic displacements indicate that the Lomer dislocation is not detectably dissociated in its (001) glide plane, or into the sessile Lomer-Cottrell configuration. The agreement between the observed atomic column positions and continuum elasticity is excellent, except for the innermost positions near the core of the Lomer dislocation. The core structure of these discrete Lomer dislocations also correlates well with previous atomistic calculations for a larger-misorientation Σ = 19 boundary. A similar analysis of the displacements around 60° dislocations using isotropic elasticity indicates a slight dissociation of about...

A study of the structure of Lomer and 60° dislocations in aluminium using high-resolution transmission electron microscopy

Reference CIME-ARTICLE-1995-003doi:10.1103/PhysRevLett.75.4630View record in Web of Science Record created on 2007-02-15, modified on 2017-05-12

Flux quantization in magnetic nanowires imaged by electron holography.

ince high-resolution electron micrographs of dodecagonal Ni-Cr quasicrystals are similar in contrast to those of several closely related periodic phases, it has been argued that dodecagonal quasicrystals can be described as a decoration of a dodecagonal quasiperiodic tiling with the same structural units as occur in these periodic phases. In order to corroborate this hypothesis, electron microscopic contrast simulations using such model structures are presented. The models considered are based on different quasiperiodic, twelvefold-symmetric tilings as well as on several periodic tilings leading to the structures of the periodic phases mentioned above. The simulated contrast is in excellent agreement with the experimental electron microscopic images, both for the periodic and for the quasiperiodic structures. It essentially reflects the structure of the underlying tiling, also for the quasiperiodic structures. It is therefore concluded that the usual interpretation of high-resolution structure images is valid not only for periodic but also for the nonperiodic dodecagonal structures, and that therefore the decoration scheme used correctly describes the atomic structure of the dodecagonal quasicrystal.

/pdf/comparison-of-hrem-images-and-contrast-simulations-for-4tjiw6q04n.pdf

Comparison of HREM images and contrast simulations for dodecagonal Ni-Cr quasicrystals

Wedge Transmission Electron Microscopy has many advantages, one of which is the concentration determination in III–V semiconductors with a fairly good accuracy. This allows us to determine the concentration variation during the growth of GaInAs/InP multilayered structures and to deduce the concentration grading at the interface GaInAs/InP (As in InP) and the abruptness of the InP/GaInAs interface.

Wedge Tem Characterization of Movpe GaInAs/InP Layers, Concentration Grading at Interfaces

The growth by molecular beam epitaxy of III-V layers with reduced thickness permits the synthesis of new materials. The optical and electrical properties of these structures are strongly related to the roughness of the hetero-interfaces, the chemical composition and the accurate thickness of the layers. Electron microscopy is a direct way to get local information. Despite its rather limited resolution power, SEM is quite commonly used. Routine TEM applications are limited due to the time consuming nature of the thin foils preparation process and the artefacts associated. Our observations on cleaved samples demonstrate that Wedge Transmission Electron Microscopy (WTEM) and Reflection Electron Microscopy (REM) offer some unique advantages on the previous methods in terms of specimen preparation, layer thickness determination, estimation of interface abruptness, chemical composition information and parallelism of the epilayers.

Transmission and Reflection Electron Microscopy on Cleaved Edges of III-V Multilayered Structures

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