Changes

effects of higher landing energy and deeper specimen interaction, including more compositional and less topographical information.

effects of higher landing energy and deeper specimen interaction, including more compositional and less topographical information.

[[:file:M102Ch1Fg4.jpg|Figure 4]]a shows an SE2 image of a cross section of a shale sample that has been polished by argon-ion milling, a sample preparation technique that consists of using one or more beams of argon ions to gently polish the surface of a sample by sputtering away material, thus providing an extremely smooth surface for SEM investigation. The image was acquired with an Everhart-Thornley type secondary electron detector.

[[:file:M102Ch1Fg4.jpg|Figure 4]]a shows an SE2 image of a [[cross section]] of a shale sample that has been polished by argon-ion milling, a sample preparation technique that consists of using one or more beams of argon ions to gently polish the surface of a sample by sputtering away material, thus providing an extremely smooth surface for SEM investigation. The image was acquired with an Everhart-Thornley type secondary electron detector.

The SE2 image contrast reveals both topographical and compositional information due to the greater sample interaction depth of SE2 electrons. High SE yield is scaled as lighter shades of gray, and low SE yield is scaled as dark shades of gray in SEM images. Pores and [[fracture]]s appear dark in the SE2 image, reflecting lower secondary electron yield from negative depressions than from elsewhere on the sample surface. Therefore, [[porosity]] information can be readily characterized with the SE2 electrons.

The SE2 image contrast reveals both topographical and compositional information due to the greater sample interaction depth of SE2 electrons. High SE yield is scaled as lighter shades of gray, and low SE yield is scaled as dark shades of gray in SEM images. Pores and [[fracture]]s appear dark in the SE2 image, reflecting lower secondary electron yield from negative depressions than from elsewhere on the sample surface. Therefore, [[porosity]] information can be readily characterized with the SE2 electrons.

==Focused ion beam applications==

==Focused ion beam applications==

Focused ion beam (FIB) systems also find a growing number of applications in geology.<ref name=Goldsteinetal_2003 /> In a typical FIB-SEM system, an extraction field is applied to a gallium (Ga) liquid metal ion source to field emit Ga ions and form a Ga beam. Due to the higher atomic mass, the Ga beam not only can be used to generate electron and ion images, but also may be used to mill samples to remove material. [[:file:Figure-9.jpg|Figure 9a]] shows the schematic diagram of an FIB-SEM system where a cross section of the sample is milled by a Ga FIB beam and is imaged simultaneously by the SEM. This milling and imaging process can be automated in a serial fashion to acquire a stack of two-dimensional images, from which a 3-D image volume can be constructed from the data set. This technique is particularly useful in revealing the 3-D distribution of mineral types, organic matter, porosity, and the like in shale (and other rock) samples.

Focused ion beam (FIB) systems also find a growing number of applications in geology.<ref name=Goldsteinetal_2003 /> In a typical FIB-SEM system, an extraction field is applied to a gallium (Ga) liquid metal ion source to field emit Ga ions and form a Ga beam. Due to the higher atomic mass, the Ga beam not only can be used to generate electron and ion images, but also may be used to mill samples to remove material. [[:file:Figure-9.jpg|Figure 9a]] shows the schematic diagram of an FIB-SEM system where a [[cross section]] of the sample is milled by a Ga FIB beam and is imaged simultaneously by the SEM. This milling and imaging process can be automated in a serial fashion to acquire a stack of two-dimensional images, from which a 3-D image volume can be constructed from the data set. This technique is particularly useful in revealing the 3-D distribution of mineral types, organic matter, porosity, and the like in shale (and other rock) samples.

Scanning electron microscopy provides different modes and techniques for acquiring high-quality images of shale and other rock samples. The images in this chapter demonstrate their fine resolution and their applicability for the characterization of shale reservoirs.

Scanning electron microscopy provides different modes and techniques for acquiring high-quality images of shale and other rock samples. The images in this chapter demonstrate their fine resolution and their applicability for the characterization of shale reservoirs.