[25p-P06-1~5] 15.7 Crystal characterization, impurities and crystal defects

▲ [25p-P06-4] TEM study of structural features of Kanazawa gold leaves

〇(M2)Yuanzhe Xu¹, Kohei Aso¹, Hideyuki Murata¹, Yoshifumi Oshima¹ (1.Japan Adv.Inst.Sci.)

Keywords:gold leaf, TEM, dislocation

Kanazawa gold (Au) leaf is famous for very thin film of ~100 nm in thickness from the 16th century, which is fabricated by hammering. In a previous study, when the thickness of gold leaf was below 200 nm during the fabrication process, the (001) texture was found to appear dominantly. This alignment of the crystal orientation has been thought to be an origin to produce thin gold foil reproducibly (K. Kitagawa and K. Tanimura, Scripta Metall. 20 (1986) 673). Because the other metal films with ~100 nm thickness, which do not show such orientation alignment by hammering, is fragile due to lack of flatness and grains. Interestingly, Kanazawa gold (Au) leaf is not pure gold crystalline but contains small amount of silver (Ag) and copper (Cu), suggesting that such additional elements play a key role in formation of such thin foil. In this study, we investigate the structural difference between Kanazawa gold leaves with Ag atoms of 4.9 wt% and Cu atoms of 0.7 wt% and pure gold (24K) by transmission electron microscopy (TEM) observation to understand the role of additional elements.
Both samples have many crystallographic defects because of the traditional hammering process. We took bright-field (BF) and dark-field (DF) TEM images of these samples under two-beam condition that increases diffraction from a specific lattice plane to clarify the type of the defect in the samples. In detail, BF and DF TEM images were obtained by slightly tilting the incident beam direction from the [001] zone axis to excite a diffraction spot corresponding to either {200} or {220} lattice planes.