Annealing of focused ion beam damage in gold microcrystals: an in situ Bragg coherent X-ray diffraction imaging study

Focused ion beam (FIB) techniques are commonly used to machine, analyse and image materials at the micro- and nanoscale. However, FIB modifies the integrity of the sample by creating defects that cause lattice distortions. Methods have been developed to reduce FIB-induced strain; however, these protocols need to be evaluated for their effectiveness. Here, non-destructive Bragg coherent X-ray diffraction imaging is used to study the in situ annealing of FIB-milled gold microcrystals. Two non-collinear reflections are simultaneously measured for two different crystals during a single annealing cycle, demonstrating the ability to reliably track the location of multiple Bragg peaks during thermal annealing. The thermal lattice expansion of each crystal is used to calculate the local temperature. This is compared with thermocouple readings, which are shown to be substantially affected by thermal resistance. To evaluate the annealing process, each reflection is analysed by considering facet area evolution, cross-correlation maps of the displacement field and binarized morphology, and average strain plots. The crystal's strain and morphology evolve with increasing temperature, which is likely to be caused by the diffusion of gallium in gold below ∼280°C and the self-diffusion of gold above ∼280°C. The majority of FIB-induced strains are removed by 380–410°C, depending on which reflection is being considered. These observations highlight the importance of measuring multiple reflections to unambiguously interpret material behaviour.

Solution synthesis of anisotropic gold microcrystals

Amplification of pentahedrally twinned gold nanorods with Au(i)/AA results in the formation of very well-defined anisotropic microcrystals of gold referred to as gold microrods.

Phase Separation of Gold Microcrystals in Glass with an Electric Field

Based on static electromagnetics theory and thermodynamics theory, a new model is proposed to describe the phase separation from the glass doped with metal particles in a static electric field. This model is proved by a heat-treatment experiment of boracic silicate glass doped with gold. The results indicate that the externally applied electric field promotes the phase separation of the glass and leads to a different size of the droplet phase just as this new model has predicted.

Lattice Images of Non-Integer Planes in Gold

A common growth habit for gold microcrystals is a thin (111) platelet of hexagonal or trigonal symmetry. It has been shown that such microcrystals contain coherent faults in the ABCABC stacking sequence giving rise to non-zero structure factors for lattice planes of index 1/3(422). Transmission electron diffraction patterns from these crystals such as shown in Figure 2 confirm the existence of this non-zero structure factor by exhibiting reflections whose spacing and orientation correspond to lattice planes of the type 1/3(422). The diffraction pattern in Figure 2 has been superimposed on the polycrystalline ring pattern of gold for reference and the spacings of the inner-most spots is equal to the 2.497Å of the 1/3(422) planes to within the experimental error. Additional confirmation of the indexing of these spots has been obtained by electron diffraction at various angles of tilt.Phase contrast lattice images of the non-integer planes shown in Figure 1 were obtained with axial illumination of the sample by defocusing the objective lens of a Philips EM-300 electron microscope.

High Resolution Replication of Metallic Microcrystals

Bradley's well known direct carbon replication technique with Pt-C shadowing offers the best resolution of any method currently in use. In the present study variations of this technique were applied to a system of gold microcrystals in an effort to obtain replicas of the highest possible resolution. Crystals with diameter on the order of 1000Å and thickness ∼100 Å have been examined for surface defects which might effect the growth process. This requires replication with higher resolution than is normally obtained.The basic technique consists of evaporating a suspension of the particles onto a clean glass slide, depositing 100-200 angstroms of carbon by vacuum evaporation, floating the carbon film on a solvent to remove the particles, and mounting the replica on support grids for shadowing. The factors limiting the resolution of the replica are:The accuracy in the reproduction of the surface topography by the carbon film.“Pile-up” effects due to the physical thickness of the carbon and Pt-C in the shadowing direction.Contamination of the specimen and replica surfaces by a layer of hydrocarbons.Granularity of the shadowing material.