| Both graphene and quantum dots (QDs) possess perpestiveaplication potentional in the magnetics, electronics optical andnew energy electronic properties. For the graphene, thetwo-dimensional (2D) single-atom carbon sheet has attractedtremendous research interest due to its large surface area, highcarrier transport mobility, superior mechanical flexibility andexcellent thermochemistry stability.Spintronics need to manipulateboth charge and spinpolarization of electron. The Graphene hasthe execlent charge transport proporties, however the spinpolarization hamper the graphene applications in spintronics.Development of graphene-based spintronics necessitates theintroduction of magnetic ordering, or more specifically, long-rangeferromagnetism in graphene. In the past few years, several methods including formation of zigzag edges in graphene nanoribbons ornanoislands, carbon vacancies, hydrogenation, and doping withmagnetic transition metal (TM) atoms have been proposed aimingtowards the realization magnetic graphene. Nevertheless, aninescapable fact is that the linear energy disappears whenmagnetism appears in graphene. In simple terms, magneticgraphene tends to lose its exceptional physical properties, forwhich they are highly sought in various applications. It has beendemonstrated that n-p co-doping method can be used to achievep-doping of ZnO. We demonstrate that Fe/NO2co-doped graphenepreserves the unique linear dispersion of the charge carriers, andthe n-p pairs exist long-range and ferromagnetic coupling with greatmagnetic momentWith the development of nanotechnology, nanoscale device maybe used anywhere, include the molecular scale the Dye-sensitizedsollar cell（DSSC）. In experiment we can find that the properties ofabsorption and transport of molecular increased with theincreasing of size of molecular. The size effect change the energygrade, especially the HOMO and LUMO, the all kinds of properties ofthe molecular would be affected by the size effect. Through thecalculation we found that the HOMO and LUMO play the differentrole in the absorption, we think that the size effect plays differentrole in the nanodevice. In the nano scale, the size effect will be much more important for the materials; at the same time shapeeffect also have great effect on physical properties, which willfurther allow new devices to be developed with distinctiveproperties and functions for numerous applications.Graphene quantum dots (GQDs), single-or few-layer graphenewith a tiny size of only several nanometers, there is the remarkablequantum-confinement and edge effects in the GQDs. Therefore,many interesting phenomena that are different from those in normalQDs are highly expected. Recently peoples have been revealed theirimportant potentials in solar cells, fuel cells and so on. Especially inthe magnetic graphene which provide a new materials forapplication of spintronics. In the paper, we discussed the newquantum-confined system of GQDs in which exist both the excitingdevelopment and great challenges.The First-principles calculation software Vasp usingpseudopotential and plane wave basis set processing the periodicsystem, there are obvious advantages in magnetic calculations.The magnetic discovery in graphene paves the way for theapplication of magical graphene in spintronics. Gaussian with highaccuracy, there are a lot of functional and basis set method couldbe used in the calculation progress. We calculate the magneticgraphene and both shape and size effects in the visible lightabsorption process. The main contents are as follows：1Through the first principal calculation， we have studied theelectronic structures and magnetic properties of Fe/NO2co-dopedgraphene using first-principles calculations. First, we confirmed thatthe linear energy relationship of graphene is preserved after NO2 co-doping, although there is a little gap near the Fermi energy. The transport property of electron in the Fe/NO2co-doped graphene is almost not affected. Second, it was shown that the FM and long-range FM coupling are largely improved in this case of Fe/NO2co-doped graphene. This study substantiates that the n-p co-doping method is an effective way to realize the long-range ferromagnetism in graphene, especially preserve the extraordinary properties of graphene.2Based on Times Dependent Density Functional Theory (TDDFT) calculations, the size effects and the edge-shape effect of GQDs are confirmed to be significant for the visible light absorption properties of GQDs. The edge-shape effect is intertwined with the size effect, and is enhanced with an increase in size of square GQDs. The shifting of the strongest absorption peak with the total atomic number Na can be fitted by using37×(?). The atomic number includes both carbon and hydrogen atoms in the GQD. The percentage of zigzag (ZZ) edge state in HOMO increased monotonically with Ns increasing. The change of the percentage can be fitted very well by using where Ns represent the edge size of square GQDs and Ns change from3to7. The edge-shape effect is accompanied with size effects and vary with dimension. So the zigzag edge will greatly affect the properties related with the HOMO, such as catalysis, magnetism and optoelectronic process. These results could be used to explain the experiment phenomen:high molecular weight high performance.3Using the ab initio density-functional theory method, we found that the seam atoms, which belong to the armchair (AC) side and occupy the junction sites between the discontinuous sides, hardlycontribute to the strongest visible light absorption. This refinementedge-shape effect can be found in rectangular, triangular andhexagonal GQDs, and has not been considered before. The seamatoms are inactive in the strongest transition peak within the300nmto800nm range. In designing optoelectronic devices using GQDs, thisrefinement edge-shape effect, should be considered because theSeam atoms occupy a large proportion of arbitrarily shaped GQDs.The effects of Seam atoms should be minimized to enhance the lightabsorption in GQDs by accurately controlling the shape.4Using the time dependent density functional theory calculate thestructure and optical absorption properties of the Coumarin baseddyes: C343、NKX-2388、NKX-2311and NKX-2586. The short-circuitcurrent density is mainly determined by the HOMO、 LUMO、LUMO-HOMO and absorption. The LUMO is the key parameteraffecting the electron injection efficiency, HOMO has enormous effecton the charge collection efficiency, and the LUMO-HOMO are keyparameters affecting the absorption. The variation of short-circuitcurrent density from C343to NKX-2586could be explained byCombining the three factors. According to the calculating results theHOMO and LUMO both be affected by CN and–C=C–unit. We alsoindicate that the influence of the size effect on the short-circuitcurrent density with the increasing of size of molecular. Theincreasing of short-circuit density does not increasing proportional tothe increasing of size. Large size corresponding to the absorption willbe more, but lowering the LUMO and raising the HOMO have negativeeffect on the efficiency of electron injection and electron collect respectively. According to these results we can find the bottleneck ofimproving the efficiency of dye sensized solar cells.5We calculated the hysteresis loop of spin valve by OOMMF，it isfound that the structure of the tunnel junction withbroad linearity range in-1.8~1.8T. Strong magnetocrystallineanisotropy energy and the shape anisotropy energy supressthe exchange interaction, so the remanent magnetization changelittle compared with the value of start point when the externalfield drops to zero. Then we got a good linear hysteresis loop. Whenreducing the magneto crystalline anisotropy energy of softmagnetic layer the pinning effect will gradually appear, but the lineardetection range of linear sensor will reduce for the linear sensor， ifthe pinning effect of the proportion increased significantly. Ourcalculation results provide a good idea for the design of a wide rangelinear sensor, and a few of defect in soft magnetic layer nearly haveno effect on the performance of the device, so the growth of softmagnetic layer does not require harsh conditions. |
PDF Full Text Request