若手のショートレビュー

金属表面上にヘテロ成長したオリゴチオフェン超薄膜の構造
および角度分布関数評価

Evaluation of Structures and Orientation Distribution Function of α-Sexithienyl Ultrathin Films Grown Heteroepitaxially on Metal Substrates

吉川元起
Genki YOSHIKAWA

　金属単結晶基板上にα-sexithienyl (6T)超薄膜を作製し，その面直および面内配向をNEXAFSにより観測した。 Ag，Cu基板上で，6T分子は，分子軸を表面平行方向に揃えた構造で成長し，特にAg(110)，Cu(110)上において，表面の金属原子列と直交する方向に一次元的に並んだ特異な構造をとることを明らかにした。また角度分布関数を導入し，6T分子の面内配向度を定量的に求めた。

　Out-of-plane (perpendicular to the surface) and in-plane (parallel to the surface) orientations of α-sexithienyl (6T) on metal surfaces have been measured by angle dependent near edge X-ray absorption fine structure (NEXAFS), the advantage of which is to determine directly the molecular orientation in the whole thin films. It turns out that, on the atomically clean and flat Ag and Cu single crystal substrates, the 6T molecules grow with their molecular long axes parallel to the substrates (lying mode). The most striking fact is that 6T molecules are arranged on Ag(110) and Cu(110) substrates one-dimensionally. In these systems, the 6T molecular long axes are perpendicular to the atom rows on the metal surfaces. A quantitative analytical method with orientation distribution function is proposed to evaluate the one-dimensionality of 2-fold-symmetry systems. Using this method, it reveals that 6T tends to align more orderly on Ag(110) surface than Cu(110).

Keywords:　α-sexithienyl (6T), Ag, Cu, NEXAFS, 1D structure