Xiaobo Yuan

Structural and electronic properties of SiC/AlN core/shell nanowires: a first-principles study

The structural stabilities and electronic properties of passivated and unpassivated SiC/AlN core/shell nanowires (CSNWs) along [0001] direction are investigated by using first-principles calculations with density functional theory. Our calculations demonstrate that thick AlN shell and small ratio of SiC core make the SiC/AlN CSNWs more stable. The band gaps decrease with the increasing of the CSNWs diameters. After passivation at the surface, type of SiC/AlN heterostructure changes and the mobility can be improved by increasing the CSNWs diameter and the SiC core ratio. These results provide an effective way to modulate the electronic properties of SiC/AlN structure, which is useful for fabrications and applications of CSNWs.

Density Functional Theory Calculations of Charge-Induced Spin Polarization in Pentacene

Based on density functional theory (DFT) calculations, we investigate the spin-related properties of spinless-hole injected organic molecule pentacene (Pc). DFT calculations reveal that there is spontaneous spin polarization in Pc when spinless-hole is injected. The charge-induced magnetic moment of Pc increases linearly with the increasing of the extra hole charge amount and its maximum can be up to 1 μB per injected spinless-hole per Pc molecule. The magnetic moment is expected due to the injected unpaired charge. The injected hole will preferably fill the spin-splitted carbon p z orbitals, which makes the Pc molecule spin polarize.

Adsorption properties of chloroform molecule on graphene: Experimental and first-principles calculations

Adsorption properties of chloroform molecule (CHCl3) on graphene surface are studied experimentally and theoretically. Based on the density functional theory (DFT) calculations, effects of different adsorption configurations and different adsorption distances on the system’s conductivity properties are discussed, and the comparisons with the experimental results are made. It is found that band gap appears when the adsorption distance is 1.0 A, which is about 0.32 eV near the Fermi level. However, the band gap is nearly zero when the adsorption distance is increased to 1.5 A, so the conductivity of the system will be increased with the increasing of the adsorption distances. The density of states, the adsorption energy and the effective masses are also calculated and the analyses are consistent with the experimental results. Our results reveal that graphene could be used to build sensors or as a catalyst for molecular adsorption.

Spin polarization properties at the spinterface of thiophene/Fe(100): First principles calculations

Based on density functional theory (DFT), the spin polarization properties of a thiophene molecule which is adsorbed at Fe (100) surface are discussed. A variety of horizontal and vertical adsorption configurations as well as their influences on the spin density distributions are studied in detail. The spin polarization comes from the p-d orbital coupling between the thiophene molecule and the electrode, which leads to the molecules’ energy level shifting and the density of states (DOS) broadening, so the two spin states near the Fermi level are exchange split. It is also found that the interfacial spin polarization is different under different contact configurations, and the biggest one will be obtained when the S atom is directly placed above the Fe atom at the horizontal direction. On the other hand, interface spin inversion can be obtained by adjusting the adsorption position, which will be helpful to build spin sensors.

Adsorption of methanol molecule on graphene: Experimental results and first-principles calculations

Adsorption properties of methanol molecule on graphene surface are studied both theoretically and experimentally. The adsorption geometrical structures, adsorption energies, band structures, density of states and the effective masses are obtained by means of first-principles calculations. It is found that the electronic characteristics and conductivity of graphene are sensitive to the methanol molecule adsorption. After adsorption of methanol molecule, bandgap appears. With the increasing of the adsorption distance, the bandgap, adsorption energy and effective mass of the adsorption system decreased, hence the resistivity of the system decreases gradually, these results are consistent with the experimental results. All these calculations and experiments indicate that the graphene-based sensors have a wide range of applications in detecting particular molecules.

Enhancement of spin injection efficiency in a T-shaped organic device

Considering the special charge-spin relationships of the carries in organic semiconductors,a simple T-shaped model of organic spin injection device is constructed.Based on the spin-diffusion theory,the current-spin polarization of the T-shaped device is theoretically obtained.It is found that by adjusting the branching current the spin polarization in this T-shaped device is enhanced distinctly compared with precious ferromagnetic/organic semiconductor model.The effects of polaron ratio,electric field and conductivity of the organic semiconductor on current spin polarization of the T-shaped device are also discussed.

AMPLIFICATION OF CURRENT SPIN POLARIZATION IN FERROMAGNETIC/ORGANIC SYSTEM WITH SPIN-RELATED INTERFACIAL RESISTANCES

Current spin polarization in ferromagnetic/organic system is theoretically studied based on the spin diffusion theory and Ohms law, and the effects of the spin-related interfacial resistances on the spin-polarized injection are discussed. It is shown that the current spin polarization can be higher than the spin polarization of the ferromagnetic contact and may reach 100% at the interface by modulating the spin-related interfacial resistances. The proposed amplification scheme provides an efficient way to generate a highly spin-polarized current in organic materials because of the easy fabrication of ordered spin-related tunnel barriers at contact structures.