| Schottky diodes are widely used in integrated circuits due to their unique rectification and limiting characteristics.As the density of electronic components in integrated circuits continues to increase,traditional silicon-based semiconductors are difficult to miniaturize the Schottky diodes due to their poor stability at the nanometer scale and difficult processing.Due to the emergence of microscopic measurement and control technology,molecular electronics has achieved unprecedented development.By switching between the bistable adsorption states of organic molecules on the metal surface,the diode barrier can be changed under positive and negative bias voltage,which provides a new idea for molecular Schottky diode design.A large number of studies have shown that functional groups,as an important part of organic molecules,can change the properties of the interface between the molecule and the electrode,and regulate the performance of molecular devices.In this dissertation,we used density functional theory to study the bistable adsorption structures of p-dichlorobenzene,1,2,4,5-tetrachlorobenzene,hexachlorobenzene,p-difluorobenzene,1,2,4,5-tetrafluorobenzene and hexafluorobenzene on the Pt(111)surface,and designed molecular Schottky diodes based on these bistable adsorption systems.At the same time,the influence of the number of different functional groups and the types of different functional groups on the transport performance of the diodes were studied.The main work of this dissertation is as follows:(1)We studied the adsorption configuration and interface properties of chlorobenzene and fluorobenzene molecules on Pt(111)surface.We compared the structure and electronic properties of the two adsorption states: the chemically adsorbed molecules are deformed with low adsorption height,the physically adsorbed molecules are flat with high adsorption height.There is a large amount of charge transfer at the chemical adsorption interface,,while only local charge transfer occurs at the physical adsorption interface.We compared the adsorption interface of molecules with different functional groups and found that in the chemical adsorption state,the covalent bond between the central carbon ring and the substrate dominates the adsorption height of the carbon ring,so the adsorption height of organic molecules is similar;in the physical adsorption state,as the number of substituted atoms increases,the adsorption height increases due to the increased repulsive force between the molecule and the substrate.Furthermore,we compared the adsorption interface of molecules with different functional groups and found that because the radius of the chlorine atom is larger than that of the fluorine atom,the van der Waals force between the chlorobenzene molecule and the metal is greater,so the adsorption height of the chlorobenzene is higher.(2)Through the energy level arrangement,we calculated the Schottky barriers of the organic molecular adsorption system in the chemical adsorption state and the physical adsorption state.We proposed the actual circuit model and calculated the Schottky barriers between the organic molecules and the left and right electrodes.We found that among the electrodes on both sides,the side with the higher Schottky barrier dominates the transport properties of the circuit.The Schottky barrier that plays a leading role in the chemical adsorption state is higher than that of the physical adsorption state.We calculated the current-voltage curve of the transport model and found that the current in the physical adsorption state is much larger than the current in the chemical adsorption state.We found that as the number of chlorine atoms replaced increases,the switching ratio of the diode decreases.In addition,by calculating the current-voltage curve of the fluorobenzene adsorption systems,we found that the switching ratio of the Schottky diodes designed based on the fluorobenzene molecules are larger than that of the chlorobenzene Schottky diodes,and their signal intensity are more obvious. |
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