Studies On The Spin-dependent Electron Transport Properties Of Chrome-porphyrin Molecular Device

The simulation and regulation of electron transport properties in molecular devices has become one of the main research directions of molecular spintronics.Electronic spin molecular devices with functions of spin filter,spin valve and molecular switch can be designed based on electronic spin characteristics.Porphyrins are widely favored by researchers because of their ring-conjugated planar structure and their inner ring centers can be coordinated with metals to form metalloporphyrins.In this paper,based on the first-principles calculation method,the electron spin transport characteristics of Chrome-porphyrin molecules with molecular linkage configuration and transition metal atom substitution were calculated,analyzed and studied.Some interesting electron transport properties such as spin filtering and switching effect are obtained.The main research content is as follows:The first chapter briefly introduces the limitations of silicon-based semiconductor technology,the research progress of molecular devices,the electron transport properties such as molecular rectification effect,negative differential resistance effect and spin filtration effect.Then the structure and theoretical research status of benzene molecule,porphyrin molecule and phthalocyanine molecule are introduced.In the second chapter,The first principle calculation method is introduced,and the related software is introduced briefly.In the third chapter,the electron spin transport properties of a two-probe system consisting of four connections of Chrome-porphyrin molecules(beta diagonal connection,beta and median dislocation angle connection,beta apex angle connection,and median horizontal connection)with flat gold electrode are studied.The results show that the electron spin polarizability of the diagonally connected Chrome-porphyrin molecule is 87% in the bias interval of 0~0.4V,and even more than 95% in the bias interval of 0~0.2V.The electron spin polarizability of cross-connected Chromeporphyrin molecules was only 85% in the 0~0.34 V bias range,and both of these connection configurations showed that the electron spin-down metal conduction behavior and spin-up were inhibited,and the device presented semi-metallic properties.The electron spins of the Chrome-porphyrin molecules in the horizontal connection configuration all show linear metallic conductivity,and have excellent conductivity compared with other connection configurations.The current is about one order of magnitude higher than that of the diagonal connection.Both the electron spin transport transmission spectrum and the projected state density have wave peaks at similar energy points,indicating that the coupling degree between the molecule and the electrode is similar.It can be seen from the energy and energy difference of the frontier molecular orbital that changing the connection configuration of Chrome-porphyrin molecule will not change the conductive nature of Chrome-porphyrin molecule.The difference of the electron spin transmission coefficient near the Fermi level is large,which leads to the change of the electron spin transport property of the Chrome-porphyrin molecule.The spin filtration effect can be realized by changing the connection configuration of different end atoms of the central molecule and the delocalization degree of the space distribution of frontier molecular orbit,so as to effectively regulate the electron spin transport properties of Chromoporphyrin molecular devices based on different connection configurations.In the fourth chapter,the electron spin transport properties of metalloporphyrin molecular devices(Cobalt porphyrins,Manganese porphyrins,Vanadium porphyrins and Chromium porphyrins)were studied by substituting Chromium atoms with homologous transition metals(Co,Mn,V).The results show that the diagonally connected metalloporphyrins have different degrees of spin filtration at low bias.Projected onto the metal atoms and metal porphyrin molecules all projection state density of wave energy in the basic consistent,illustrate alternative metal atoms center of 3d orbital interaction between porphyrin macrocyclic and cause redistribution molecular orbital energy levels,performance for metal porphyrin molecules of the frontier molecular orbital energy difference is great,the energy difference is different also.Based on the analysis of self-consistent Hamiltonian space distribution of frontier molecular orbital projection,the coupling degree of metalloporphyrins with electrodes is very strong,and the order of coupling degree is Manganese porphyrins,Cobalt porphyrins,Vanadium porphyrins and Chromium porphyrins.When the external bias is 0.2V,the electron spin of Cobalt porphyrin molecule presents a significant switching behavior.The order of the conductivity of metalloporphyrins is Vanadium porphyrins,Manganese porphyrins,Cobalt porphyrins and Chromium porphyrins.By changing the central substitute metal atom,the frontiter molecular orbital energy value and energy difference can be changed to increase the difference value of the transport transmission coefficient near the Fermi level.The spin-up electron and the spin-down electron show different volt-ampere characteristics,so as to effectively regulate the electron spin transport property of the metoporphyrin molecule.The fifth chapter is the summary and prospect of the whole paper.