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Kim, Hwang-Su
- Applied Microscopy
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- v.35 no.4
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- pp.64-73
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- 2005
In this paper we discussed in details how to determine the nature of dislocations in a crystal such as a Burgers vector, the line vector of dislocation and the associated slip plane, using LACBED and usual imaging techniques. These techniques basically involve the application of Cherns and Prestone s rules, the simulations of LACBED patterns with a certain form of the dynamical diffraction theory. The theoretical aspects including necessary approximations for calculations also were in details discussed. As a test specimen for experiments, the foils of a pure aluminum, containing many dislocations with appropriate density for LACBED experiments, were used..
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Kim, Hwang-Su
- Applied Microscopy
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- v.37 no.2
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- pp.123-133
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- 2007
The strain fields due to precipitates, especially S-phase $(Al_2CuMg)$ particles in Al-2.5Cu-1.5Mg wt.% alloy were first investigated with Large Angle Convergent Beam Electron Diffraction (LACBED) method. The work involves LACBED pattern simulations to estimate possibly the strength of the strain fields. To do this the morphology of S-particle was optimized as a cylindrical shape with $a_s$ axis, and the displacement vector of strain fields was assumed to be perpendicular to $a_s$ axis. With this simple model the reasonable fittings between the observed patterns of the strain fields and simulations were obtained. And in the early aging stage of the alloy the significant strain fields were not observed. As a result of this study it is expected that the strain fields due to S-phase precipitates in the stage with maximum hardness would make a complex networks to possibly contribute to hardiness of the alloy.
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Kim, Hwang-Su
- Applied Microscopy
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- v.33 no.3
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- pp.179-185
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- 2003
The operating accelerating voltage in the electron microscopy may differ from the nominal voltage specified by the manufacture. Thus it is necessary, at least once, to determine the wavelength of electron beam for the nominal accelerating voltage. Particularly in QCBED technique, the wavelength of the incident electron beam on a specimen must be determined as accurately as possible. In this paper we present a simple method to determine accurately the wavelength of electrons from LACBED patterns of a known crystalline materials, which is analogous to a method based on Kikuchi patterns reported previously. This method is to utilize three diffraction lines not belonging to the same zone, which nearly intersect at the same point. For an application of the method, the wavelength of electrons for the 200 kv nominal acceleration voltage of JEM2010 is determined to be 0.002496(3) nm ($201.5{\pm}0.4$ kv) with an uncertainty of 0.12%.
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Kim, Hwang-Su;Kim, Jong-Pil
- Applied Microscopy
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- v.33 no.3
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- pp.187-193
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- 2003
When electron microscope images and selected area diffraction patterns of crystalline materials are being compared, it is important to know for the rotation of the diffraction pattern with respect to the image caused by the magnetic lens in the Electron Microscope. A well-known method to determine this rotation is to use a test crystal of $MoO_3$. But this method of determination of the rotation angle contains an uncertainty of $180^{\circ}$. Thus one has to devise another way to eliminate this uncertainty. In this paper we present a new and simple method of determining this rotation without any complexity. The method involves a process of obtaining LACBED patterns of crystalline materials. For the J2010 electron microscope, the rotation is determined to be $180^{\circ}$ and this angle remains unchanged for changing of the magnification and the camera length.
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Kim, Hwang-Su;Song, Se-Ahn
- Applied Microscopy
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- v.36 no.3
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- pp.155-163
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- 2006
The defects in a synthesized crystal of ${\alpha}-Al_2O_3$ used as substrate for growing of semi-conductor materials such as GaN were examined by the conventional transmission electron microscopy (TEM), Large Angle CBED and High-Angle Annular Dark Field (HAADF) STEM methods. The dominant defects found in the specimen are basal microtwins with the thickness of ${\sim}2\;to\;32 nm$ and the associated strong strain field at the interface of microtwin/matrix, basal dislocations and complex dislocations in the one of {$2\bar{1}\bar{1}3$} pyramidal slip plane. All these basal and pyramidal dislocations seem to be strong related to basal microtwins. It was also found that the density of defects is very uneven. In the certain area with the dimension of a few fm, the dislocation density is quite high as an order of ${/sim}10^{10}/cm^2, but the average density is roughly estimated to be less than ${\sim}10^5/cm^2, as is usually expected in general synthesized crystals.
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