Atomic Fabrication Based On Scanning Tunneling Microscopy

Moore’s Law is gradually approaching its limits with the rapid development of semiconductor and chip manufacturing.As the device size is shrinking to the atomic scale,the quantum effect in electronic devices starts to dominate and the functionality may depend on structures with sub-nanometer precision.The traditional "top-down" fabrication method encounters tremendous challenges in fabrication of atomic devices,including spatial resolution,control precision,and complexity of the device.The "bottom-up" method for the design and fabrication of functional devices at the singleatom/molecular level,the atomic fabrication,is a new path for the development of device fabrication and is it is gradually receiving more and more attention.Scanning tunneling microscopy(STM)has demonstrated great potential in atomic fabrication with its unique functionalities including topographic imaging with atomic spatial resolution,detection of local electronic density of states,and atomic manipulation using the interaction between tip and atom/molecule on surface.Development of single atom/molecule manipulation technique based on scanning probes has been one of the research frontiers in condensed matter physics.The employment of automation and artificial intelligence technique in STM recent years has been pushing forward the autonomous atomic manipulation technology rapidly.In this thesis,we developed the autonomous atomic manipulation system based on a home-built STM,and investigated the automated single atom/molecule manipulation on surface and the tip-induced chemical reactions in single molecules.The dynamics of the reaction is investigated by first-principles density functional theory(DFT)calculations to understand the underlying mechanism and to enhance the controllability of the tip-induced reactions.The details of the study are as follows:1.An FPGA-based autonomous atom/molecule manipulation system has been developed.Stable and fast digital feedback control,multiple atom manipulation modes,real-time signal process and analysis,and fast decision and execution during atom/molecule manipulation have been realized,which reveals strong flexibility and expandability of the control system.2.Investigation in automated manipulation of CO molecules on the Cu(111)surface has been carried out to explore reliable method for manipulation with high efficiency.The anisotropic interaction between the tip of and the molecule on the surface has been discovered,which demonstrates and reveals the critical role of tip quality for atom manipulation.Suggestion and solution have been proposed in order to increase the efficiency of atom manipulation on surface.3.An automated program has been developed for the tip-induced chemical reaction in single molecules on surface.The debromination in single 9,10-dibromoanthracene(DBA)molecules on surface as stimulated by the voltage pulse through the tip of a scanning tunneling microscopy(STM)has been explored.A voltage threshold is obtained and the nature of single-electron process is revealed by the map of debromination yield as a function of tunneling current,pulse amplitude,and excitation position.Strong asymmetry in debromination yield for the two C-Br bonds has been evident.The asymmetric adsorption configuration of the DBA molecule on Cu(111)surface and the distinct dynamics in dissociation of the two bonds have been illustrated by the first-principles density functional theory(DFT)calculations.The influence by the local electric field in STM tunneling junction on the dissociation of the C-Br bond has also been discussed.