Disordering of small metal particles in a scanning transmission electron microscope

Small metal particles in the range of a few nanometers in diameter are seen to progressively disorder when the 100 keV electron beam of a Scanning Transmission Electron Microscope (STEM) is held stationary on the particle. The diffraction pattern of the individual particle is seen to progress from an initial array of indexable diffraction spots to a mixture of diffraction spots and amorphous-like rings and finally to rings with no persistent diffraction spots. Only particles below a critical size are seen to fully disorder. We have observed this disordering in Platinum, Palladium, Rhodium, and Iridium and have developed a model for the disordering process. In this model, electrons scattering from surface atoms transfer enough energy to break the surface atoms from their binding site. A competing process of disordered atoms rebinding to crystalline sites is also included. Because small particles have large fractions of their atoms on the surface, the beam driven disorder, under certain conditions, is able to propagate into the core of the particle. For Platinum, surface disordering requires energy transfers from the electrons to the Platinum atoms of0.54 eV.U of I Onlydissertation/thesi

Characterization Of Individual L10 Fept Nanoparticles

The long-range order parameter of [001]-oriented FePt L10 nanoparticles has been determined by measurement of convergent-beam electron diffraction (CBED) intensities of single particles using scanning transmission electron microscopy (STEM) and comparison of the measured intensities to simulations of diffracted-beam intensities. The nanoparticles were fabricated by co-sputtering high-purity Fe and Pt targets onto SiO2-Si substrates and annealing the deposited material. © 2005 IEEE

Synthesis of V, Pt and Pt-V nanoparticles

Bimetallic platinum-vanadium nanoparticles have been successfully synthesised by high temperature thermal decomposition of metal precursor salts. Vanadium is a highly reactive metal and poses considerable difficulty in synthesising metallic nanoparticles, while platinum has low reactivity where nanoparticles are easily synthesised. The difficulties associated with the reduction of vanadium salt were circumvented by the use of high boiling point solvents and selected surfactants. Co-reduction using platinum precursors compatible with the high temperature processes was required for bimetallic nanoparticle synthesis. The chemical synthesis route described is novel, robust and highly reproducible. Microstructural characterisation of nanoparticles synthesised as described, using transmission electron microscopy, reveals single-crystal particles.14 page(s

Amorphous Silica Nanowires Grown By The Vapor-Solid Mechanism

Silica nanowires were synthesized by using silica nanoparticles as a growth catalyst using a gas composed of CH4 and H2 at 1050°C. Silica nanoparticles provide silicon and oxygen atoms for the formation of the nanowires, as well acting as a growth site. The nanowires nucleated on graphitic carbon layers formed around the seed particles, indicating that the nanowires grow by the vapor-solid mechanism. Photoluminescence spectra of the nanowires normally showed strong blue emission peaked at 3.1 and 2.8 eV under 3.8 eV laser excitation. Post-hydrogen annealing resulted in the appearance of longer wavelength photoluminescence band. © 2003 Elsevier B.V. All rights reserved

A Modified Back-Etch Method For Preparation Of Plan-View High-Resolution Transmission Electron Microscopy Samples

A modified back-etch method is described that has been successfully used to prepare samples of thin films and nanoparticles on Si wafer substrates for examination by high-resolution transmission electron microscopy (HRTEM). This process includes ultrasonic cutting, abrasive pre-thinning and a two-stage etching procedure. Unlike previous reports of back-etching methods, tetramethyl ammonium hydroxide, which has a very high-etching selectivity of Si to SiO 2, is used for the final etching to allow removal of the Si without degradation of the SiO2 membrane. An innovative wrapping method is also described. This novel approach reduces the preparation time for HRTEM samples to \u3c1 h per sample for groups of 10 or more samples. As an example, the preparation of FePt nanoparticle samples for HRTEM imaging is described. © The Author 2006. Published by Oxford University Press on behalf of Japanese Society of Microscopy. All rights reserved

Direct Growth Of Amorphous Silica Nanowires By Solid State Transformation Of Sio2 Films

Amorphous silica nanowires (a-SiONWs) were produced by direct solid state transformation from silica films. The silica nanowires grow on TiN/Ni/SiO 2/Si substrates during the annealing in H2 or a H 2:CH4 mixture at 1050°C. Titanium nitride (TiN) films were used to induce a solid state reaction with silica (SiO2) films on silicon wafers to provide silicon atoms into growing nanowires. The TiN layers induce the diffusion of silicon and oxygen to the surface by a stress gradient built inside the films. The nickel diffuses to the surface during the TiN deposition and acts as a nucleation site for the a-SiONWs. © 2003 Elsevier B.V. All rights reserved

Revisiting the CuPt₃ prototype and the L1₃ structure

Experimentally and computationally, the structure of Pt-Cu at 1:3 stoichiometry has a convoluted history. The L1₃ structure has been predicted to occur in binary alloy systems, but has not been linked to experimental observations. Using a combination of electron diffraction, synchrotron X-ray powder diffraction, and Monte Carlo simulations, we demonstrate that it is present in the Cu-Pt system at 1:3 stoichiometry. We also find that the 4-atom, fcc superstructure L1₃ is equivalent to the large 32-atom orthorhombic superstructure reported in older literature, resolving much of the confusion surrounding this composition. Quantitative Rietveld analysis of the X-ray data and qualitative trends in the electron-diffraction patterns reveal that the secondary X₁+(a,0,0) order parameter of the L1₃ phase is unexpectedly weak relative to the primary L₁+(a,a,0,0) order parameter, resulting in a partially-ordered L1₃ ordering, which we conclude to be the result of kinetic limitations. Monte Carlo simulations confirm the formation of a large cubic superstructure at high temperatures, and its eventual transformation to the L1₃ structure at lower temperature, but also provide evidence of other transitional orderings.11 page(s