红荧烯薄膜在Bi(0001)表面从高阶公度相到非公度相转变

Transition from high-order commensurate to incommensurate phase in organic films:rubrene on Bi(0001)

在红荧烯薄膜中发现了一类新的相变:分子从高阶的公度相转变到弱的非公度相。前者表现出"格点位于线上"(point-on-line)关系;后者是一种混合相,包含红荧烯的晶态畴和自组装的畴壁。相比于红荧烯晶体的a-b面,晶态畴中存在着极大的各向异性应变。通过改变衬底的温度,发现在室温下畴壁呈现出"之"字型网状结构;而在高温下转变为条状结构。形成不同形状畴壁的原因可以认为是应力释放和转动外延的相互作用力所导致的。

A transition from high-order commensurate phase to weak incommensurate phase（HC-WI） has been found in rubrene films grown on Bi（0001） surface.The HC phase corresponds to a self-assembled rubrene bilayer with point-on-line coincident match with Bi（0001）.The WI phase can be described as a collection of incommensurate domains separated by commensurate domain walls with well-developed patterns.A large anisotropic strain has been found in the incommensurate domains,which exhibits orthorhombic lattices resembling the a-b plane of crystalline rubrene.Depending on the substrate temperature,the domain walls may exhibit zigzagged networks at room temperature,or linear stripe patterns at elevated temperature.The formation of different domain wall patterns can be regarded as the result of complicated interplay of the anisotropic strain relief and rotational epitaxy.