Column ratio mapping: A processing technique for atomic resolution high-angle annular dark-field (HAADF) images

Robb, Paul D.; Craven, A. J.

doi:10.1016/j.ultramic.2008.08.001

Cited by 44 publications

(45 citation statements)

References 29 publications

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“…A useful way to quantify the shape of a dumbbell is to calculate the column ratio [33]. This is defined as (I III -I BIII ) / (I V -I BV ) and provides an estimate of the average scattering strength of the channelled region of the Group III column relative to that of the neighbouring Group V column.…”

Section: Dumbbell Signalsmentioning

confidence: 99%

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Experimental evaluation of interfaces using atomic-resolution high angle annular dark field (HAADF) imaging

et al. 2012

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Section: Dumbbell Signalsmentioning

confidence: 99%

“…The processing technique of column ratio mapping was developed in order to convert a HAADF image into a map that shows the column ratio value of every dumbbell present, thereby allowing the local composition to be estimated at a glance [33]. In a similar way, maps of the total, column and background signals can also be produced.…”

Section: Dumbbell Signalsmentioning

confidence: 99%

Experimental evaluation of interfaces using atomic-resolution high angle annular dark field (HAADF) imaging

et al. 2012

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“…I III and I V are the total HAADF signals at the Group III and Group V columns of a particular dumbbell, respectively, and I BD is the background signal for each column in the dumbbell. The automated image processing technique that was employed is described in detail by Robb and Craven (2008) and Robb et al (2012). In the first step of the process, an image sub-section around a dumbbell is identified and a variable reference area is overlaid and compared.…”

Section: Experiments and Simulation Detailsmentioning

confidence: 99%

“…The level of sharpness is then defined by the distance over which the column ratio switches in value across the boundary. The processing technique of column ratio mapping was developed for <110> oriented III-V semiconductors (Robb and Craven, 2008;Robb et al, 2012). This automated procedure separates the high-spatial resolution information from the background signal and provides an objective and consistent measurement of the column ratio of all of the dumbbells in an image.…”

Section: Introductionmentioning

confidence: 99%

Characterisation of InAs/GaAs short period superlattices using column ratio mapping in aberration-corrected scanning transmission electron microscopy

Robb

Finnie

Craven

2012

Micron

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. (2012) Characterisation of InAs/GaAs short period superlattices using column ratio mapping in aberration-corrected scanning transmission electron microscopy. Micron, 43 (10 AbstractThe image processing technique of column ratio mapping was applied to aberration-corrected high angle annular dark field (HAADF) images of short period MBE (molecular beam epitaxy) grown InAs/GaAs superlattices. This method allowed the Indium distribution to be mapped and a more detailed assessment of interfacial quality to be made. Frozen-phonon multislice simulations were also employed to provide a better understanding of the experimental column ratio values. It was established that ultra-thin InAs/GaAs layers can be grown sufficiently well by MBE. This is despite the fact that the Indium segregated over 3-4 monolayers. Furthermore, the effect of the growth temperature on the quality of the layers was also investigated. It was demonstrated that the higher growth temperature resulted in a better quality superlattice structure.

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“…However the complexity of interface structure makes it desirable to seek further information, such as the dopant distribution. Image quantification may provide one approach [5][6][7], and depth sectioning in aberration corrected machines may provide another [8]. However, the most direct approach is to observe the specimen from multiple directions, provided the images can be interpreted equally well.…”

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Prospects for 3D Imaging of Dopant Atoms in Ceramic Materials

et al. 2009

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High angle annular dark field (HAADF) imaging in scanning transmission electron microscopy (STEM) is well suited to identifying heavy elements in lighter surrounds [1,2]. This has been used recently to explore the detailed configuration of impurity atoms segregated at grain boundaries in ceramic materials [3], where such dopant addition can significantly change the physical properties of the material, particularly its resistance to creep deformation [4]. At best, a single image only gives a clear indication of the projected structure along one direction. However the complexity of interface structure makes it desirable to seek further information, such as the dopant distribution. Image quantification may provide one approach [5][6][7], and depth sectioning in aberration corrected machines may provide another [8]. However, the most direct approach is to observe the specimen from multiple directions, provided the images can be interpreted equally well. A spherical aberration corrector allows the formation of an atomically fine probe on the crystal surface, but, depending on the specimen orientation, it becomes important to describe in detail how the probe spreads through the sample in order to best interpret the experimental images. We will explore the effects of sample orientation, defocus selection, and probe spreading on atomic resolution HAADF STEM imaging using rare earth segregation in an alumina (α-Al 2 O 3 ) grain boundary as a test case.We explore imaging of the dopant distribution in the interface plane via imaging from three orthogonal directions with a view to determining as much three-dimensional structure information as possible. Fig. 1 shows the projected structure model and corresponding simulated HAADF images for a Y-doped α-Al 2 O 3 grain boundary between two single crystals in the Σ13 orientation relationship. Figs. 1A and B have the crystals viewed along the <12 _ 10> direction while Figs. 1Cand D have it viewed along the <2 _ 021> direction. In both cases the <505 _ 4> direction is vertical in the images. As the matrix is fairly light and the <505 _ 4> direction is not a strong channelling direction, it may be possible to image the interface from the <505 _ 4> direction as well. Fig. 2A shows the intensity profile, projected along the <2 _ 021> direction, of the electron probe wavefunction travelling along the <505 _ 4> direction through the two crystals of total thickness 325 Å. Fig. 2B shows the corresponding profile in vacuum. The differences between the profiles are small, suggesting that the crystal does not cause much perturbation of the intensity distribution and that the probe retains its atomic sized beam waist at the interface. Fig. 2C shows the simulated HAADF STEM image of the model Y-doped α-Al 2 O 3 grain boundary from this third orthogonal orientation, and despite the thickness of the sample the individual Y atoms are clearly visible: in this specimen it should be possible to image the buried interface in plan-view.

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Column ratio mapping: A processing technique for atomic resolution high-angle annular dark-field (HAADF) images

Cited by 44 publications

References 29 publications

Experimental evaluation of interfaces using atomic-resolution high angle annular dark field (HAADF) imaging

Experimental evaluation of interfaces using atomic-resolution high angle annular dark field (HAADF) imaging

Characterisation of InAs/GaAs short period superlattices using column ratio mapping in aberration-corrected scanning transmission electron microscopy

Prospects for 3D Imaging of Dopant Atoms in Ceramic Materials

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