Nanometer-scale imaging and pore-scale fluid flow modeling inchalk Page: 3 of 16
This article is part of the collection entitled: Office of Scientific & Technical Information Technical Reports and was provided to Digital Library by the UNT Libraries Government Documents Department.
The following text was automatically extracted from the image on this page using optical character recognition software:
ports present allows for installation of various other instruments (element analysis, platinum deposition,
micromanipulator, etc.) (Fig. 2).
Figure 2. FIB Sample chamber with sample mounted on 45 deg stage
To perform 3D imaging using FIB technology, the samples are prepared using standard SEM procedures, i.e.
cleaning, cutting, polishing, mounting and carbon coating. Good sample cleaning is important to minimize
hydrocarbon contamination of the instrument and interference with the high vacuum. Because the FIB mills
submicron layers, the sample surface has to be flat at the micron scale. High roughness of the sample surface
can significantly increase the time required for the FIB to mill the surface to the flatness required for serial
sectioning. For soft materials, such as diatomite, a microtome can be used while for harder materials or epoxy
impregnated samples, diamond saw cutting and standard thin section procedures for polishing is recommended.
The prepared sample is mounted on a 45 degrees SEM stub using conducting adhesive (Fig. 3). As seen in
Figure 3, ion milling and SEM imaging can be performed without moving the sample, except for minor
refocusing. The SEM approach is the preferred mode of operation from the point of view of increased
productivity and improved registration of images if there is a good contrast between the pore space and the
matrix, and the charge build up on the sample is not too rapid. The ion beam imaging yields better quality
images than the electron beam imaging, due to less charging of the surface, but it is significantly more time
consuming to implement due to sample repositioning and refocusing between the milling and imaging steps.
Once the region to be milled has been defined (Fig. 4), the depth milled is proportional with the time elapsed.
Thus, images captured at equal time intervals display equidistant surfaces at increasing depths within the sample
volume. The time required to mill a certain quantity of material depends on the ion current and the sample
material. For example, the time required to mill a volume 50x50x0.1 pm in chalk is of the order of minutes, for
30 kV, 3000 pA Ga+ ions beam. Higher currents (7000-20,000 pA) will cut faster, but also will yield rougher
surfaces, and negatively affect the image quality.
Very clean flat surfaces, in which the pore-grain boundaries appear in high contrast, can be generated with no
apparent distortion of the pore boundaries. The pore/matrix contrast is more pronounced in an epoxy-
impregnated sample than in samples not impregnated. After each milling episode, images are acquired at a
selected magnification such that each view captures the desired number of pores with the adequate resolution.
Here’s what’s next.
This article can be searched. Note: Results may vary based on the legibility of text within the document.
Tools / Downloads
Get a copy of this page or view the extracted text.
Citing and Sharing
Basic information for referencing this web page. We also provide extended guidance on usage rights, references, copying or embedding.
Reference the current page of this Article.
Tomutsa, Liviu; Silin, Dmitriy & Radmilovich, Velimir. Nanometer-scale imaging and pore-scale fluid flow modeling inchalk, article, August 23, 2005; Berkeley, California. (https://digital.library.unt.edu/ark:/67531/metadc893671/m1/3/: accessed April 22, 2019), University of North Texas Libraries, Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.