Stm Studies On The Electronic Properties Of Vacancy Defects And C₆₀ Monolayers On Black Phosphorus Surface

The unique electronic properties of 2D materials are essential for their potential utilization in electronic and optoelectronic devices.This blooms tremendous efforts in exploring their fundamental electronic structures.Black Phosphorus（BP）was recently rediscovered from the perspective of a“2D”layered semiconductor for promising applications in nanoelectronics and nanophotonics with its tunable band-gap,high carrier mobility,and intrinsic in-plane anisotropy.Exploring the local electrical properties of BP and its defects is of great importance for both fundamental research and technological applications.In this thesis,we reveal 1)the first observed asymmetric Friedel oscillations around the atomic defects on BP surface;2)How the BP act as a template to modulate the band structure of a molecular monolayer deposited on BP surface,by combining low-temperature scanning tunneling microscopy/spectroscopy（STM/STS）,density functional theory（DFT）calculations,and model simulations.In the thesis,we first give an introduction about the STM and the BP crystals which are synthesized in our group.Then we talk about the research findings in detail.In the second chapter,we characterize the local electronic properties of single atomic P vacancy on BP surface.The scattering of electrons around the vacancy causes a dumbbell-shaped contrast in STM topography image,which is known as Friedel oscillation.Friedel oscillation is often observed on metal surface with atomic defects and is characterized with a symmetric decay length.In our work,we observe an obvious asymmetric oscillation behavior.Combining d I/d V mappings,DFT and tight binding calculations,we suggest that the asymmetry of the Friedel oscillations around the defects on BP surface might be related with different height of the P atoms within the BP atomic plane.In the third chapter,we describe how a BP substrate concatenates a nearly-free-electron（NFE）like conduction band on a C₆₀ monolayer through van der Waals（vd W）forces.STM reveals the C₆₀lowest unoccupied molecular orbital（LUMO）band is strongly delocalized in two-dimension,which is unprecedented for a molecular semiconductor.Experiment and theory show vd W forces between C₆₀ and BP reduce the inter-C₆₀ distance and cause mutual orientation,thereby optimizing the wave function overlap and forming the NFE-like band.Electronic structure and transport calculations predict that the NFE band of C₆₀ acquires an effective mass of 0.53-0.70m_e（m_e is the mass of free electrons）,and achieves unprecedented carrier mobility of hundreds of cm²/（V·s）.The substrate organization of molecular interactions provides a route to enhance charge delocalization in fullerenes and other organic semiconductors.