Orientated, very thin structures in TEM specimens can cause streaking of electron diffraction spots. For instance, for the T₁ (Al₂CuLi) alloys, the orientation relationship between the T1 and the Al matrix is (0001)_T1||(111)_Al and [10-10]_T1||[-110]_Al [1]. The T1 precipitates form as extremely thin (< ~2 nm thick) hexagonal-shaped plates which induce alterations in the shape of reciprocal lattice points, resulting in streaking of diffraction spots in the selected-area electron diffraction (SAED) patterns [2].

Figure 1604 shows HRTEM and HAADF images taken from an Mg₉₇Zn₁Y₂ crystalline alloy. The extra diffraction spots along the c*-direction with strong streaks indicate a correlation length of 6 x d_(002)Mg as marked by the arrow in the diffraction pattern. The HAADF-STEM image shows that the heavy Zn and/or Y atoms, indicated by the bright lines with an interval of ~1.56 nm (= 6 x d_(002)Mg), are located at the specific positions of the lamellar structure due to chemical ordering.

[1] H.K. Hardy and J.M. Silcock: J. Inst. Met., 1955-56, vol. 84, pp. 423-28.
[2] B. Noble and G. E. Thompson: Met. Sci. Jour., 1972, vol. 6, pp. 167-74.
[3] Eiji Abe, Atomic-Scale Characterization of Nanostructured Metallic Materials by HAADF/Z-contrast STEM, Materials Transactions, 44(10), 2035-2041, (2003).