| Two-dimensional nanomaterials,such as graphene and hexagonal boron nitride(h-BN),have a large number of development opportunities in device applications since they were found,due to their unique 2D structural features and outstanding electronic properties.Two-dimensional layered nanomaterials combine with Van der Waals force so that they can be easily exfoliated and be applied to the heteroepitaxy as substrate with other layered materials.On the other hand,organic semiconductor materials have widespread applications in the flexible devices and the display market due to their outstanding electronic properties and unique advantage of flexibility.As an emerging field in electronic field,organic semiconductor materials offers a variety of structures and the advantages of molecular diversity,ease of processing and low cost.Therefore,it is necessary to combine two-dimensional nanomaterials with organic semiconductor materials with Van der Waals force by taking advantages of the structure two-dimensional nanomaterials.While developing precise growth,the height of organic semiconductor film can be effectively controlled,making preparation for the research of unique properties in organic semiconductor film.In this thesis,we chose organic molecular material Perylene-3,4,9,10-tetracarboxylic dianhydride(PTCDA).We developed Van der Waals epitaxy for the growth of organic molecular film while using two-dimensional nanomaterials as substrate.Moreover,we developed detailed characterizations and carried out applications on the basis of the epitaxy growth.The main works in this thesis are listed as follows:In Chapter 1,typical two-dimensional nanomaterials and organic semiconductor materials are introduced and some common preparation methods of organic molecular films are also summarized.By analyzing the several growth modes of epitaxy,we summarized the characteristics of the combination of organic molecular materials and two-dimensional nanomaterials.It is defined as Van der Waals epitaxy in the combination of the selected material PTCDA and the substrate BN.And the related epitaxy methods of PTCDA are introduced.In Chapter 2,we developed the vapor phase epitaxy of PTCDA on BN by experiment.While using Van der Waals force,PTCDA was deposited on BN by physical transfer for large-area thin-film crystal,whose size was about tens of microns.By changing the specific growth conditions such as temperature and relative positions,the crystal thickness was greatly controlled.The limit of the thickness was explored and even could be down to monolayer.The thickness of each layer is about 0.3nm.The law in the growth of organic material was learned experimentally.We characterized the morphology and optical properties of the film by optical microscope,atomic force microscope(AFM),fluorescence microscope,test of fluorescence spectra,etc.At the same time,we performed molecular dynamics simulations of the epitaxy growth,which effectively supported the experimental results and helped us to understand the features of organic molecular growth.In Chapter 3,on the basis of the growth characteristics of organic molecule PTCDA,we adjusted the growth method and growth mechanism.By using’High-temperature growth’,we obtained large-area and completely monolayer.The thickness was 0.3nm and the film in high quality was highly homogeneous on the substrate BN.We performed simulations of the high-temperature growth and compared the monolayer in this chapter with the film in Chapter 2.The morphology of monolayer was characterized by AFM and fluorescence microscope,while the optical properties were characterized by fluorescence spectra.Furthermore,the high-temperature growth was applied on other two-dimensional materials like graphene,on which PTCDA can grow monolayer steadily.We characterized the film by AFM and Raman spectrum,to prove the stability of the high-temperature growth.In Chapter 4,there is a summary of this thesis and an outlook of the future research. |
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