Development of angle-resolved spectroscopy system of electrons emitted from a surface with negative electron affinity state.

We developed an angle-resolved photoemission spectroscopy system for the analysis of conduction-band electrons. By forming a negative electron affinity surface on a semiconductor surface, electrons in conduction bands are emitted into a vacuum and measured by using an analyzer. This method enables us to determine the energy and momentum of the conduction electrons. Furthermore, it can be used to determine unoccupied conduction band structures. The main challenges of this method are that the energies of the emitted electrons are extremely low and the trajectories of the electrons change due to various influences. We overcame these problems by placing the shielding mesh close to the sample and parallel to the sample surface. The entire chambers, including the shielding mesh, were grounded, and a negative bias voltage was applied only to the sample. This configuration realizes the acceleration of electrons while preserving the momentum component parallel to the sample surface. Another problem is the establishment of a method for converting a detected angle into the corresponding wavevector. We focused on the emission angle of electrons emitted from a sample and their minimum energy and then established an analytical method for converting detected angles into corresponding wavevectors on the basis of the minimum energy.

Magnetic-field-induced phase separation via spinodal decomposition in epitaxial manganese ferrite thin films.

In this study, we report about the occurrence of phase separation through spinodal decomposition (SD) in spinel manganese ferrite (Mn ferrite) thin films grown by Dynamic Aurora pulsed laser deposition. The driving force behind this SD in Mn ferrite films is considered to be an ion-impingement-enhanced diffusion that is induced by the application of magnetic field during film growth. The phase separation to Mn-rich and Fe-rich phases in Mn ferrite films is confirmed from the Bragg's peak splitting and the appearance of the patterned checkerboard-like domain in the surface. In the cross-sectional microstructure analysis, the distribution of Mn and Fe-signals alternately changes along the lateral (x and y) directions, while it is almost homogeneous in the z-direction. The result suggests that columnar-type phase separation occurs by the up-hill diffusion only along the in-plane directions. The propagation of a quasi-sinusoidal compositional wave in the lateral directions is confirmed from spatially resolved chemical composition analysis, which strongly demonstrates the occurrence of phase separation via SD. It is also found that the composition of Mn-rich and Fe-rich phases in phase-separated Mn ferrite thin films deposited at higher growth temperature and in situ magnetic field does not depend on the corresponding average film composition.