Theoretical Study Of One-dimensional Metallacarboranes Sandwich Nanowires

Sandwich nanowire complexes constructed by transition metal atoms and aromatic ligands exhibit prolific electronic and magnetic properties. These properties make them potential candidates in the application of electronic and spintronic devices.In this thesis, using first principles calculations based on density functional theory,we systematically study the electronic and magnetic properties of two kinds new type of ionic metallic sandwich nanowires((Mt C2B10H12)∞ and(Mt C4B8H12)∞) based on the carborane and organometallic sandwich nanowire(VCp)∞. The modulation to change their electronic properties is also discussed. According to these studies, we propose a new type of charge-transfer modification which can be applied to explain the half-metallicity in carborane and aromatic metallic sandwich nanowires. This modification can give good explanation about the relationship between charge-transfer in ions and magnetic exchange interaction. It also greatly enhance the investigation of covalent-ion complex. The main results are listed below:We systematically investigate the structural, electronic and magnetic properties of(Mt C2B10H12)∞(Mt=Sc, Ti, V, Fe, Co, Al, Ru, Co Ru) nanowires. They have low structural symmetries. Firstly, we disscuss torsion angle’s effect on electronic property and stability of the nanowires. The result show that it can be negligible compare with the total energy. Their combine energy are bigger than organometallic sandwich nanowires.(Sc C2B10H12)∞ is ferromagnetic semiconductor with indirect gap of 0.289 e V and magnetic moment of 1 μB. We modulate the electronic properties of(Sc C2B10H12)∞on its active sites as its application in spintronic. We find that the introduction of electron donor such as methyl and amino on cage carbons can reduce band gap effectively, while their introduction on cage boranes would increase band gap.Introduction of electron acceptor on active site has opposite effect compare with the donor.We systematically investigate the stability, electronic and magnetic properties of Mt TCDC(Mt = V, Cr, Mn, Co, Ni. TCDC = C4B8H12). The nanowires adopt normal sandwich conformations with D2 d symmetry. The binding energy of Co TCDC is 9.3e V/Co, which is consistent with the calculation of similar metallacarborane cluster. The Co TCDC is half-metal and the band gap in the semiconducting channel is approximately equal to 2.5 e V. We propose a new type of charge-transfer modification based on analyze of Mt TCDC and Mc Connell’s study. It can give a brief explanationfor ferromagnetic half-metallicity in nanowires by three aspects. First, the symmetry which adopted in structure should be high, so the overlap interactions between donor and accepter are very strong. Second, after electrons transferring, single electron occupied in the degenerate HOMO of donor, which provide magnetic moment for the nanowire. Third, after accepting electrons from donor, the accepter can maintain high chemical stability. The strong electrostatic interactions between them and the single electron in different spin channel will result in high spin polarization, which make nanowire half-metal. This modification has a good prediction of farromagnetic half-metallicity in organometallic and carborane nanowires. And can help us design new half-metal structure in experiment.As the new modification cannot give an explanation of the half-metallicity in(VCp)∞, we carry out further research on(VCp)∞. We firstly propose that there are direct and indirect exchange interaction in(VCp)∞ by our investigation. Take use of external electric fields, pressure, injecting electrons or holes on(VCp)∞, we find the last one is the most useful way to change its properties. Its half-metallicity can be switched to metal while injecting one or two electrons, whereas injecting one or two holes, the nanowires can be semiconductor.