A First Principle Study Of Low-Dimensional Thin-film Materials

Low-dimensional thin-film materials provide rich resources for the design and development of new semiconductor devices.At present,self-assembly of organic molecules on solid surfaces has been demonstrated as an efficient approach in manufacturing such low-dimensional nanostructures.Self-assembled organic films can modify the semiconductor surface through the surface/interface effect,or in a sense,can be treated as good semiconductor materials.More importantly,due to its superior capabilities such as well-controlled,tailor-made properties to meet the special demand,as well as high flexibility in the modulation of semiconductor materials’ performance,a broad range of applications have been proposed for the self-assembled organic thin-film materials in the field of semiconductor devices.In addition to the self-assembled organic thin-film materials,two-dimensional(2D)materials as well as their derivatives of van der Waals heterostructures and nanoribbons can also be considered as a special kind of low-dimensional thin-film materials.Generally,owing to the dramatic changes in dimension and symmetry,2D materials tend to exhibit unique optical,electrical,magnetic,thermal,mechanical,and other physical and chemical properties,which are totally different from their bulk phases,therefore receive extensive attentions.The past few years have seen great progress made by the first principle method based on density functional theory in this field,especially for the prediction of the structures and properties of new 2D materials.In this article,we perform first principle studies based on density functional theory on two kinds of low-dimensional thin-film materials: CoPc/Bi(111)adsorption system and one-dimensional Te nanoribbons,mainly concentrating on their geometric configurations and electronic properties.In the first chapter,we introduce the surface science which is closely related to the low-dimensional thin film material,mainly describes the concept and application of surface/interface effect.In addition,the recent progresses and applications of the self-assembled organic thin-film materials and two-dimensional materials are also summarized.The second chapter mainly introduces the basic knowledge and methods of density functional theory(DFT),including the Hohenberg-Kohn theorem and the Kohn-Sham equations,as well as the core issue of DFT: exchange-correlation energy functional.Moreover,we also briefly introduce several van der Waals correction methods developed in recent years.Finally,we introduce the most common first-principle package based on DFT.In the third chapter,we presented a comprehensive study of the CoPc molecule adsorbed on a semimetal Bi(111)surface by means of first principle calculations and photoemission spectroscopy.Firstly,the adsorption energy was calculated to establish the most stable adsorption configuration of CoPc/Bi(111)adsorption system.The electronic density of states of CoPc molecule before and after the adsorption,the charge density difference combined with Bader charge were also calculated and analyzed to reveal the interfacial electronic structures and mechanism of charge transfer.Finally,the calculation results are verified by the photoelectron spectroscopy studies.In the fourth chapter,we studied the structural stabilities and electronic properties of the single-layer and double-layer tellurium nanoribbons using first principle calculations.Firstly,the formation energy of tellurium nanoribbons was calculated to determine the factors that affect the thermodynamic stability.Then the band structures for each type of tellurium nanoribbons were also calculated and analyzed.In the fifth chapter,we summarize the main work of this article and puts forward the prospect about the future research work.