TEM foil preparation of sub-micrometre sized individual grains by focused ion beam technique

Transmission electron microscopy sample preparation method for micrometer-sized powder particles using focused ion beam

A TEM sample preparation technique for micrometer-sized powder particles in the 1-10 μm size range is proposed, using a focused ion beam (FIB) system. It is useful for characterizing elemental distributions across an entire cross-section of a particle. It is a simple and universal method without using any embedding agent, enabling the powder particles with different size, shape or orientation to be easily selected based on the SEM observations. The suitable particle is covered with Pt coating layers through an ion-beam-assisted deposition. The Pt coating layers provide sufficient support for the TEM lamella. A small piece of tungsten needle is used as a support under the particle by taking a series of operations using a micromanipulator. The particle can be precisely thinned by the ion beam to be suitable for both TEM observation and EDX elemental mapping. This novel technique reduces the TEM sample preparation time to a few hours, allowing much higher efficiency compared to complicated and time-consuming embedding methods.

Rock mechanics. Superplastic nanofibrous slip zones control seismogenic fault friction

Understanding the internal mechanisms controlling fault friction is crucial for understanding seismogenic slip on active faults. Displacement in such fault zones is frequently localized on highly reflective (mirrorlike) slip surfaces, coated with thin films of nanogranular fault rock. We show that mirror-slip surfaces developed in experimentally simulated calcite faults consist of aligned nanogranular chains or fibers that are ductile at room conditions. These microstructures and associated frictional data suggest a fault-slip mechanism resembling classical Ashby-Verrall superplasticity, capable of producing unstable fault slip. Diffusive mass transfer in nanocrystalline calcite gouge is shown to be fast enough for this mechanism to control seismogenesis in limestone terrains. With nanogranular fault surfaces becoming increasingly recognized in crustal faults, the proposed mechanism may be generally relevant to crustal seismogenesis.

Fluid-induced organic synthesis in the solar nebula recorded in extraterrestrial dust from meteorites

Isotopically anomalous carbonaceous grains in extraterrestrial samples represent the most pristine organics that were delivered to the early Earth. Here we report on gentle aberration-corrected scanning transmission electron microscopy investigations of eight (15)N-rich or D-rich organic grains within two carbonaceous Renazzo-type (CR) chondrites and two interplanetary dust particles (IDPs) originating from comets. Organic matter in the IDP samples is less aromatic than that in the CR chondrites, and its functional group chemistry is mainly characterized by C-O bonding and aliphatic C. Organic grains in CR chondrites are associated with carbonates and elemental Ca, which originate either from aqueous fluids or possibly an indigenous organic source. One distinct grain from the CR chondrite NWA 852 exhibits a rim structure only visible in chemical maps. The outer part is nanoglobular in shape, highly aromatic, and enriched in anomalous nitrogen. Functional group chemistry of the inner part is similar to spectra from IDP organic grains and less aromatic with nitrogen below the detection limit. The boundary between these two areas is very sharp. The direct association of both IDP-like organic matter with dominant C-O bonding environments and nanoglobular organics with dominant aromatic and C-N functionality within one unique grain provides for the first time to our knowledge strong evidence for organic synthesis in the early solar system activated by an anomalous nitrogen-containing parent body fluid.

Laboratory analysis of stardust

Tiny dust grains extracted from primitive meteorites are identified to have originated in the atmospheres of stars on the basis of their anomalous isotopic compositions. Although isotopic analysis with the ion microprobe plays a major role in the laboratory analysis of these stardust grains, many other microanalytical techniques are applied to extract the maximum amount of information.