Dark-field transmission electron microscopy for a tilt series of ordering alloys: toward electron tomography

Here we show a technique to obtain a tilt series of dark-field (DF) transmission electron microscopy (TEM) images in ordering alloys for tomographic three-dimensional (3D) observations. A tilt series of DF TEM images of D1(a)-ordered Ni4Mo precipitates in a Ni-Mo alloy was successfully obtained by adjusting a diffraction condition for a superlattice reflection from the Ni4Mo precipitates. Since the superlattice reflection usually has a long extinction distance, dynamic diffraction effects such as thickness fringes can be suppressed to some extent with precise realignment of the diffraction condition. By using the tilt series of the DF TEM images, we attempted a computed TEM tomography to visualize 3D shapes and positions of the precipitates.