Design Of Nanostructures Based On The Ti And C Compounds And Their Electronic Transport Properties

During the past decades,self-assembled molecular devices have attracted much attention due to their small volume,good performance and strong scalability.There are several categories of self-assembled molecular devices that are fabricated through different self-assembly methods and materials,including molecular wires,molecular switches,molecular rectifiers,molecular diodes,molecular memory and molecular field effect transistors.In recent years,with the introduction of a variety of self-assembly systems and the application of new materials,the performance records in self-assembled molecular devices are constantly being refreshed.However,the poor stability and repeatability have been considered to be critical hurdles for commercialization of self-assembled molecular devices.Therefore,exploring novel molecules,exploring the interface configuration between molecules and electrodes,and analyzing electronic transport mechanisms are urgent problems in molecular electronics.How to regulate the electronic transport of molecular devices and design functional molecular devices are the main research contents of this thesis.In this thesis,the first principles method combining density functional theory(DFT)and nonequilibrium Green’s function(NEGF)is used to study the effects of different interface configurations between different TiC clusters and electrodes on the electronic transport properties.The electronic transport properties of MXenes(M=Ti)and their surface after adsorption of fluorine and chlorine are also studied.Finally,the electronic transport properties of N-heteropentacenes consisting of different numbers,positions,and valence states of N atoms are analyzed.The main research contents of this thesis are as follows:(1)The electronic transport properties of the TiC clusters attached to the gold electrodes are investigated.It is found that the current-voltage curves of molecular devices composed of the same clusters showed symmetry in the low bias region before and after rotating the clusters by 90° along the electronic transport direction.Among these TiC clusters,the Device Ti9C13 has a superior transport performance and switching effect.Compared with Ti9C13(containing C2 dimer),Ti9C9 with cubic structure exhibits poor transport performance due to the different molecular orbital coupling,but also shows a unique negative differential resistance effect.These results contribute to select molecular connecting and control the coupling between molecules and electrodes,and design molecular devices with unique properties.(2)The electronic transport properties of pristine MXenes devices(M=Ti)and its surface fluorinated and chlorinated devices are investigated.It is obtained that the devices Ti2C,Ti2N,and Ti4N3 all show negative differential resistance effect,and the electronic transport properties of the devices MXenes can be regulated by surface functionalization,which can be greatly improved by surface fluoridation and chlorination.(3)The electronic transport properties of N-heteropentacenes,which consists of different numbers,positions and valence states of N atoms,are investigated.It is found that the transport properties of N-heteropentacenes depend strongly on the valence state of N atoms.For devices with C-N double bonds,the behavior of the current with voltage is consistent,and the electronic transport properties are less dependent on the number and position of N atoms.Compared with the devices with C-N double-bond,the devices with C-N single-bond exhibit negative differential resistance effects earlier and show significant rectification effects.Manipulating the structure of N-heteropentacenes molecule can produce unique electronic transport properties to meet some specific requirements of microelectronic applications.Manipulating the structure of N-heteropentacenes molecules can yield unique electronic transport properties to meet some specific requirements of microelectronics applications.