Theoretical Study On The Effect Of Molecular Adsorption To The Electrical Transport Properties Of OPE Molecule

With the development of science and technology,people began to design and preparation electronic devices at the molecular level.Therefore,the investigated of molecular electronics has attracted wide attention.In addition to the intrinsic transport properties of molecular devices,their properties are also affected by external conditions,such as temperature,magnetic field,electric field and molecular adsorption,etc.It has been found that the modification of the side group,the bridging of the atom and the adsorption of gas molecules have an influence on the electronic transport properties of the molecular devices.We have studied the electrical transport properties of Oligo?phenylene ethynylene??OPE?and Al₁₂N₁₂ systems.By using the density–functional theory?DFT?and non-equilibrium Green's function?NEGF?,we investigated the electronic transport characteristics of OPE molecule under bridging effect with S atom and modification effects with NH₂ and CH3 groups.The effects of the OPE molecule as the H₂ sensing device and the adsorption of CO,CO₂,H₂ O,H₂S on the electrical transport properties of Al₁₂N₁₂ were studied.Firstly,The modification effects of the groups?CH₃?₂ and?NH₂?₂ on the OPE molecules with single and double S atoms connected to the two electrodes are investigated by the density functional theory and non-equilibrium Green's function.The calculation results show that both the modified groups and the bridge atoms can lead to the switch effect,the negative differential resistance behavior,and the rectifying behavior for the two-probe system.When molecules are connected with single S atom at one end,both the?NH₂?₂–OPE and the?CH₃?₂–OPE molecules show the rectifying behavior.However,the?NH₂?₂–OPE also shows a switch effect,while the?CH₃?₂–OPE molecule demonstrates a complete rectifying behavior.For the case of the molecule connected with S atoms at both ends,the?NH₂?₂–OPE?S?and?CH₃?₂–OPE?S?models show negative differential resistance behaviors in the negative bias range.These phenomena were analyzed by using the molecular projected self-consistent Hamiltonian?MPSH?,and transmission spectra.To expand the application of the OPE molecule,we investigated the changes in the electronic transport characteristics of the adsorbed hydrogen molecules on OPE molecule using density–functional theory?DFT?and non-equilibrium Green'sfunction?NEGF?.We also obtained the current–voltage?I–V?curves of the molecular junction with different numbers of hydrogen molecules.These curves were analyzed by using the projected density of states?PDOS?,molecular projected self-consistent Hamiltonian?MPSH?,and transmission spectra.Six adsorption configurations,including 4,6?two configurations?,8?two configurations?,and 10 hydrogen molecules,are considered;Results show that the current of the OPE junction significantly changes when H₂ molecules are adsorbed on the OPE molecule.Moreover,a notable NDR behavior weakens or disappears after the H₂ molecules are adsorbed,regardless of the number.Finally,we investigated the effects of the electronic transport characteristics of the adsorbed CO,CO₂,H₂ O,H₂S gas molecules on Al₁₂N₁₂ molecular.We also obtained the I–V curves of the molecular junction with different types of gas molecules.These curves were analyzed by using the molecular projected self-consistent Hamiltonian and transmission spectra.