Impact Of Heteroatom Substitution On Thin Film Growth And Energetics At Organic/Metal Interfaces

The development of organic devices has made a qualitative leap during the past decades due to the great efforts of numerous researchers.Organic devices possess incomparable advantages such as low cost or,flexibility compared to inorganic devices,and are easy to prepare in a larger area.However,some problems limit further development of organic devices,such as low efficiency or,instability.Therefore,diligent exploration has to be made to improve efficiency and achieve the sustainable development standard.Generally,the performance of devices is largely affected by interfaces.Although interfaces between organic materials and metals have been studied deeply,still fundamental properties are not well understood.In particular,the energy-level alignment cannot be predicted based on a few parameters like the work function of the metal and the ionization energy and the electron affinity of the organic thin films.Therefore,our research focuses on interface characteristics,including the coupling strength at the interface,whether charge transfer complex formation exists at the contact layer,the adsorption modes at the interface,etc.Ultraviolet photoelectron spectroscopy(UPS),X-ray photoelectron spectroscopy(XPS),low energy electron(LEED)and the X-ray standing wave(XSW)technique have been used to characterize interfaces between organic materials and metal substrates.In the first experiment,we mainly study the interface between 1,2,5,6,9,10-coronenehexone(COHON)molecules and Au(111),Ag(111),Cu(111)and 1,2,6,7-pyrenetetrone(PYTON)molecules on Cu(111).We found that the coupling strength of COHON on Au(111)is weak chemisorption but strong chemisorption prevails on Ag(111)and Cu(111).Besides,PYTON molecules are chemisorbed on Cu(111).The chemisorption involves charge transfer complex formation at the contact layer and we can clearly observe a filled former lowest unoccupied molecular orbitals(F-LUMO)at substrates.Besides,COHON molecules on all three substrates are Fermi level pinned.In the second experiment,we mainly study the electronic structure and growth modes of 2,3,9,10-Tetrafluoropentacene(F4PEN)molecules adsorbed on Ag(111).We found that the coupling strength between F4PEN molecules and Ag(111)is weak chemisorption.As for growth modes,F4PEN monolayer are flat-lying on the substrate and multilayers exhibit a ?-stacking packing motif.In the third experiment,we mainly study the interface of 2-4:6-8-bis(3,3,3,4,4-tetramethyldihydropyrrolo)-10-15-(2,2'-biquinazolino)-[15]-1,3,5,8,10,14-hexaene-1,3,7,9,11,14-N6(Mabiq)adsorbed on Au(111)and Cu We found that the coupling strength of Mabiq on both substrates is weak chemisorption,and Mabiq adsorbed on the metals leads to interface dipole and molecular band bending.By means of XPS,UPS,LEED and XSW measurements,we analyze the interface characteristics of four organic molecules adsorbed on metals.Through our research,we have more choices of organic material layer and interface characteristics in organic devices,which offer a significant basis for future organic photoelectron devices development.