Mechanism of formation of curved Kikuchi lines
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RACTION AND SCATTERING OF IONIZING RADIATIONS
Mechanism of Formation of Curved Kikuchi Lines R. K. Karakhanyan and K. R. Karakhanyan Yerevan State University, ul. A. Manukyana 1, Yerevan, 0025 Armenia e-mail: [email protected] Received August 30, 2007
Abstract—The mechanism of formation of curved Kikuchi lines, observed at displacement of point reflections from their normal positions, is proposed. Curving of Kikuchi lines is explained taking into account the participation of diffracted electron beams in the formation of Kikuchi electron diffraction patterns. PACS numbers: 61.14.-x DOI: 10.1134/S1063774508040032
Detection of curved Kikuchi lines in electron diffraction patterns of silicon was reported in [1]. It was also found there that this curving is always observed simultaneously with a displacement of point reflections, and the common reason for this curving and displacement is the presence of limited defects in the investigated samples [2]. The purpose of this study is to determine the correlation between the displacement of point reflections and curving of Kikuchi lines. This fact can be explained by considering the elementary mechanism of formation of Kikuchi patterns based on the phenomenon of double electron diffraction [3], as applied to Kikuchi electron diffraction patterns [4–6]. Obviously, comprehensive analysis of the phenomenon of curving of Kikuchi lines requires application of the dynamic theory of Kikuchi pattern formation [7–9]. As was shown in [4–6], double electron diffraction leads to the formation of forbidden (analogs of kinematically forbidden reflections) and unindexed Kikuchi lines. Double electron diffraction causes also enhancement of excess Kikuchi lines near point reflections with other indices [10] and mutual reversal of the contrast of excess and deficient Kikuchi lines [11]. Thus, the diffracted beams play a significant role in the formation of Kikuchi electron diffraction patterns. On the basis of this fact, we can suggest that, along with the primary beam, diffracted electron beams are also involved in the formation of curved Kikuchi lines. For clarity, we will consider the case where Kikuchi lines and point reflections are simultaneously observed in an electron diffraction pattern. We will assume that, in crystals with limited defects, the primary and diffracted beams form not total Kikuchi lines, as usual [3–6], but only those portions of a given pair of Kikuchi lines that lie in the vicinity of the point reflections corresponding to these beams. Such an approach is in agreement with the fact that the localized deformation fields formed by limited defects decrease the size of the regions where the scattered radiation is described
within the dynamic theory [12]. Therefore, the limited defects should also decrease the length of Kikuchi lines. According to the scheme of formation of Kikuchi patterns [3], the distance between the deficient and excess lines for a given pair is determined by the distance between zero reflection and reflection with indices of the excess line. I
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