Image simulations

Sometimes, indirectly from dififaction and image simulation... 

A special mention is in order of high-resolution electron microscopy (HREM), a variant that permits columns of atoms normal to the specimen surface to be imaged the resolution is better than an atomic diameter, but the nature of the image is not safely interpretable without the use of computer simulation of images to check whether the assumed interpretation matches what is actually seen. Solid-state chemists studying complex, non-stoichiometric oxides found this image simulation approach essential for their work. The technique has proved immensely powerful, especially with respect to the many types of defect that are found in microstructures. 

SWCNTs are imaged as two parallel lines with a separation equal to the tube diameter (Fig. 5). By image simulation it can be shown that under usual observation conditions the black lines correspond to graphene sheets seen edge on in MWCNT as well as in SWCNT tubes [7]. 

Fig. 2 HREM micrograph of a RusPt nanoparticle in PVP showing the twinning (a) and image simulation (b)...

Comparing the 3-D images simulated and the experimental photographs in Fig. 10, it can be seen that the droplet shapes are well reproduced by the present model. During the first 3.5 ms of the impact (frames 1-3), a liquid film with flattened disc shape is formed immediately after the impact. The inertial force drives the liquid to continue spreading on the solid surface, while the surface tension and the viscous forces resist the spreading of the liquid film. As a result, the droplet spreading speed decreases and the fluid mass starts to accumulate at... 

Figure 15. The HRTEM micrograph of three MoS2 nanoparticle with octahedral shape and its image simulation (77).

There are several disadvantages with the image simulation method. A nearly correct structure model is needed beforehand. This is often not available, especially for relatively complicated structures. Images are compared visually and no quantitative figure of merit is used for judging how well images and simulations agree. 

Phase extension proves that the second model gives better and more reasonable results. Fig. 3c shows the final projected potential map of the crystal along [010] with resolution up to 1 A that is obtained after performing the phase extension for two cycles in combination with the diffraction data correction based on the second proposed mode. Hence, it is supposed that, in the examined structure, B atoms replace those Cu atoms sited in the Cu-0 chains. Image simulations based on the multislice theory were performed to confirm the proposed model in Fig. 3e. The simulated image calculated with the crystal thickness of 46 A and defocus value of -650 A is presented in Fig. 3d, which matches the contrast of the averaged experimental image (Fig. 3a) pretty well. 

Based on the model shown in Fig. 5b, image simulation is performed by the multislice method with various defocus values and different crystal thickness. The one shown in Fig.5d was calculated with defocus - 400 A and crystal thickness 61.4 A, which matches quite well with Fig. 5b by contrast. 

In a similar way, Voigt-Martin et al. [14] have solved the structure of [9,9 -bianthryl]-10-carbonitrile in three dimensions using 150 unique diffraction intensities, and independently verified the result with model building and image simulation techniques. As before, the potential maps are difficult to interpret, and independent validation is an important part of the structure solving procedure. 

HREM image simulations are performed using the optical parameters of EM 420-T/EDAX Philips microscope with Cs = 1.0 mm at Scherzer defocus = -57.6 nm at a thickness of 23.3 A along [001] direction and 105.4 A along [021] direction. 

CRYSTAL STRUCTURE DETERMINATION BY MAXIMUM ENTROPY IMAGE DECONVOLUTION IN COMBINATION WITH IMAGE SIMULATION... 

In the present paper, the crystal structure of Ndi ssCcq i5Cu04. has been studied by maximum entropy image deconvolution in combination with image simulation. This work is focused on demonstrating the effectiveness of image deconvolution technique rather than determining the structure itself... 

X-ray topography is the X-ray analogue of transmission election microscopy and as such provides a map of the strain distribution in a crystal. The theory of image formation is well established and image simulation is thus a powerful means of defect identification. Despite a reputation for being a slow and exacting technique, with modem detector technology and care to match spatial resolution of detector and experiment, it can be a powerful and economical quality-control tool for the semiconductor industry. 

In HRTEM studies of complex catalyst structures, complementary multislice image simulations using the dynamical theory of electron diffraction (Cowley 1981) may be necessary for the nanostructural analysis and to match experimental images with theory. 

Examples of image simulations of supported small particles... 

Figure 5.23. (a) HRTEM profile image of a CO-reacted Cu-Pd particle indicating a Pd surface. Inset Pd surface with simulated image. The flat surfaces (at B) are (100) the stepped ones (D) are (110). Away from the surface the structure has equal Cu and Pd (inset enlarged area A with image simulation), (b) Extended unit cell model used for image simulations, (a = 0.3 nm.) It minimizes wrap-around effects. 

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