Graphene growth by chemical vapor deposition (CVD) was studied on three types of epitaxial metal films with different crystal structures on sapphire. Nickel (face-centered-cubic: fcc), Ru (hexagonal-closed-pack: hcp), and Co (fcc at temperature for graphene growth and hcp at R.T.) were deposited on c-face sapphire substrates and annealed in a furnace for solid phase epitaxial growth. Graphene layers were grown by CVD with methane gas on the epitaxial metal film. The graphene layer uniformity was consistent with the structural simplicity of the metal film. The Ru sample had a single domain in the metal film and the highest graphene uniformity. The Co sample had a very complex crystal structure in the metal film and the poorest uniformity in graphene. The Ni sample had two types of stacking domains in the metal film and the graphene layer was uniform on each domain, but inhomogeneity was observed at domain boundaries.

Change of the charge ordered (CO) structure by substituting Cu2+ for Fe2+ in LuFe2O4 was investigated by means of the transmission electron microscopy. The CO structure in LuFe2O4 is characterized by the modulated structure with the wave vector of q=1/3[1-13/2] and the average size of the CO domains can be estimated to be about 10-20nm. On the contrary, the Cu2+ substitution in LuFe2O4 destroyed the CO structure drastically and induced characteristic local lattice distortion, which gives rise to characteristic diffuse scattering in the reciprocal space. High-resolution lattice images revealed that there exist nano-scale clusters, which are characterized as the short-range ordering of the Fe3+ and Cu2+ ions on the triangular lattice. In addition, the magnetic measurement revealed that LuFeCuO4 exhibits an antiferromagnetic transition around 50K, which is lower than the Neel temperature of 250K in LuFe2O4.

We report ferroelectricity in triangular mixed valence material RFe2O4 (R=Y, Dy, Ho, Er, Tm, Yb, Lu). This ferroelectricity originates from the polar ordering of Fe3+ and Fe2+ or the polar ordering of electrons on Fe3+.