Self-assembly And Monoclinic Crystals Of Rubrene On The Cd Surface

In the past decades,the nanomaterials has already caused wide attention,Nano-materials and nano-devices have strong applications in the electronics industry.The current organic materials are a hot topic in nanomaterials.Organic materials have many advantages over traditional materials,such as lower energy consumption,faster transfer speeds,and smaller volumes.However,organic materials still have many problems to be solved at present,such as service life and production process.Our laboratory is mainly to study the growth mechanism of organic thin films and the surface properties of thin films.Rubrene has great applications in organic light-emitting diodes,organic field-effect transistors,and organic solar cells.Scanning tunneling microscopy considered to be a very beneficial characterization technique in the research field of Nanomaterials and nano-devices.In this work,the method of growing samples in this paper is organic molecular beam deposition.Firstly,a flat Cd film is grown on a Si(111)-7×7 substrate at a high temperature,and the generally grown Cd film is controlled between 15 to 20 layers.Such a number of layers can make the surface more flat and also facilitate the characterization of the STM.We used a scanning tunneling microscope to observe the surface imaging of the Cd film at the atomic scale on Si(111)and observe the Uniformity of the morphology,The rubrene molecule was grown on the surface of Cd(0001).We found a rubrene monomer when the substrate was kept at a low temperature,and a small amount of rubrene molecule was first deposited.The rubrene monomer was found and the monomer was lying on the surface of Cd(0001),When the coverage of rubrene is continuously increased,the single layer structure of rubrene is observed by LT-STM.The morphology of the rubrene molecule under this structure is very dependent on the bias voltage,and the structure difference under different bias is large..When we continued to increase the coverage,we observed a single layer structure of rubrene,the single layer structure of rubrene was arranged in fish scales,and scanning in different areas,we found some very strange structures,various topography They all have their own characteristics,but some of them cannot explain them clearly.Japanese physicist Obata et al.calculated the predicted monoclinic phase I of rubrene monoclinic crystal by the CONFLEX program.When verifying the results,the group obtained the orthorhombic phase,the triclinic phase,the monoclinic phase I,and the monoclinic phase II according to the stability level.When verifying the results,the group obtained the orthorhombic phase,the triclinic phase,the monoclinic phase I,and the monoclinic phase II according to the stability level.When increasing the coverage to 1.5ML,we obtained rubrene monoclinic crystal I in the case of low temperature growth and controlled growth rate,which is in good agreement with the predicted structure and lattice constant of Obata.This structure was observed by STM,and the rubrene molecule was exemplified by one end of a phenyl group and a tetracene.Under this coverage,we also found a structure which is a chain structure.Compared with the molecular structure of rubrene,we found that the molecule is supported by two phenyl groups and stands on the surface of the substrate.