COMBINED FIB–SEM TECHNIQUES: ADVANCED TOOLS TO RESOLVE MICROSTRUCTURES AND MINERALS PHASES IN SEDIMENTARY ROCKS

based on Richard Wirth and Luiz Morales

FIB the principle

FIB= focused ion beam

A FIB device basically resembles a SEM consisting of an ion source instead of an electron source, an ion column to focus and to scan the beam and a sample stage to position the target material

The interaction of the accelerated ions with the target material produces both backscattered and secondary electrons that can be detected with suitable electron detectors and used for imaging.

FIB the principle

FIB can be used as a machining tool to sputter cavities with exact dimensions

At the beginning, FIB was operated as a single beam device.

FIB the principle

Next logical step: the combination of an ion column FIB with an electron column SEM creating a DualBeam™ machine FIB/SEM.

The assembly of FIB and SEM extended the utilization of such a device tremendously because it combines the capabilities of an SEM such as imaging, X-ray analysis and BSE with sputtering of material from the target.

FIB nanotomography, Slice&View3D FIB/SEM, FIB Serial sectioning,…

FIB-nt: now possible to prepare a new surface normal to the sample surface => access to the third dimension of a sample.

FIB nanotomography / Slice&View

FIB-nt: now possible to prepare a new surface normal to the sample surface => access to the third dimension of a sample.

FIB nanotomography / Slice&View

The ion-polished front wall can be imaged and analyzed with EDS

Serial sectioning of the surface generates an image stack

=> 3D volume analysis

Principle of a FIB/SEM DualBeam

FIB-nanotomography / slice&view

Resolution same as SEM

Spatial resolution in z-direction limited to +/- 10 nm

Very small volumes (less than 50 x 50 x 50 µm³) (usually less)

Sectioning and polishing is the time-consuming step

example: 100 nm slice thickness x 200 slices = 20 µm, Aquisition time = +3 hours

FIB/SEM: Cross-Sectioning 3D Analysis

FIB/SEM applications

Drawbacks

Working with geological materials, there are some important disadvantages to the technique:

1. Representative volume?

Drawbacks

2. Unequal milling depth due to non-uniform material composition -> increased milling times

-> increased milling times

Drawbacks

3. Charge build-up due to non-conductive samples as no coating is possible between different image steps

-> low voltage, backscattered imaging

FIB-SEM @ugent

Intec

First experiments @UGent

Analysis of regions with clay minerals in 3D

To fill in the gaps that High Resolution CT cannot capture

First experiments @UGent

Other applications of FIB/SEM

Preparation of micro-pilars for nano-tomography

Other applications of FIB/SEM

Linking X-ray and FIB-SEM tomographies

3D porosity - µCT

Resolution of X-ray computed µCT is not sufficient to describe connected pore space

Where are the pores ?

Surface preparation

Damages due to drying

Porosity down to the state-of-the-art-SEM resolution

FIB-SEM tomography on selected ROI from large BIB image

3D porosity – FIB-SEM

Connected pore space down to 20 nm pore throat is accessible with FIB-SEM

Boom Clay (HADES), Voxel size 20 x 20 x 20 nm³

Pore cross section area sizes distribution from images

3D-FIB-SEM characterization of representative islands

Focused Ion Beam (FIB)-TEM: Exploring Earth Materials with ions and electrons.

Richard Wirth

Helmholtz Centre Potsdam

GFZ German Research Centre for Geosciences

How to explore the Geosciences “Nano-world”?

Diamonds

Focused Ion Beam (FIB): site-specific TEM sample preparation

FIB systems operated at GFZ Potsdam

Focused Ion Beam (FIB): site-specific TEM sample preparation

Ex-situ lift-out technique

TEM Micro- and Nanoanalysis

FIB/TEM Applications in Geosciences

Meteorites

FIB/TEM Applications in Geosciences

Meteorites: Microstructure

FIB/TEM Applications in Geosciences

Meteorites: Microstructure “barred olivine”

FIB/TEM Applications in Geosciences

Meteorites: Microstructure “shock-induced melt vein”

FIB/TEM Applications in Geosciences

Meteorites: Microstructure “Phase analysis” in melt veins

FIB/TEM Applications in Geosciences

Meteorites: Microstructure “Phase analysis” in melt veins

Nanoinclusions in diamond from the lower Transition Zone

Inclusion in diamond (Juina, Brazil)

Inclusions of “Phase Egg” (AlSiO3 (OH) + fluid (porosity) + nanocrystals of stishovite

Nanoinclusions in diamond from the upper mantle

Inclusions in microdiamond, Samotkan Placer, Ukraine

Nanoinclusions in diamond from the upper mantle

FIB/TEM Applications in Geosciences

Partially open grain boundaries in Carrara marble: 3D imaging

FIB/TEM Applications in Geosciences

Partially open grain boundaries in Carrara marble

Implications of partially open grain boundaries:

• Enhanced weathering of marble because of interconnected pore space.
• Rapid desintegration of marble when exposed to weather and temperatures below freezing point.

FIB/TEM Applications in Geosciences

TEM element mapping after using the foil for STXM and XANES

FIB/TEM Applications in Geosciences

Geobiology: Deep sea sponge monorhaphis chuni

FIB/TEM Applications in Geosciences

Geobiology: Deep sea sponge monorhaphis chuni

FIB/TEM Applications in Geosciences

Geobiology: Fossil Acritarch

Fossil Acritarch cell walls from 650 my old Chichkan Formation, Kazakhstan

FIB/TEM Applications in Geosciences

Geobiology: Precambrian Acrtitarch

FIB/TEM Applications in Geosciences

Sedimentary rocks: porosity

Ultracataclastic core samples recovered from 3194 m and 3294 m depth of the main bore hole of the San Andreas Fault Observatory at Depth (SAFOD).

Summary

• FIB is a site-specific preparation technique that allows cutting foils from precisely the location we are interested in.
• FIB/SEM is a site-specific 3D imaging technique that provides an insight in the 3D microstructure of a sample even on the nanometre scale.
• 3D EBSD as well as 3D EDX analysis is also technically feasible. However, time consuming and huge data files.
• TEM is an ideal tool for studying the “nanoworld” because it allows to get chemical and structural information from the same tiny little object. Structure and chemical composition identify a phase – even a nanometre-sized phase- unambiguously.