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The electrical and magnetic properties of Mn-doped GaN were investigated by the density functional theory of spin polarization. The results indicate that Mn-doped GaN is still a direct band...

Cathode samples of titanium-based nanodiamond field emission were prepared by electrophoresis dispersed solutions in different formulas. Observe the surface and structure of the coating by using metaloscope, microscopy, scanning electron microscopy (SEM) and X-ray diffraction (XRD); Test the field emission characteristic after annealing; Analyze the relation between the samples’ light photos and the uniformity of coating; Discuss the mechanism of the improved field emission characteristic after annealing. Under the same conditions the surface uniformity of diamond coating prepared by isobutyl alcohol is best,it is the minimum threshold electric field emission, 5.5 V/μm, the current density can reach to 85μA/cm2 at the field of 15V/μm. Field emission characteristic and luminescence could be best after annealing.

To study the geometrical and electronic structure of 15R-SiC polytypes, the lattice parameter, band structure, density of states (DOS) and charge density of 15R-SiC are calculated by using density functional theory based on the plane wave pseudopotential approach, and electronic structure and ground properties of 15R-SiC are investigated by the calculated band structure and DOS, the results show that 15R-SiC is an indirect band gap semiconductor, with calculated indirect band gap width being 2.16 eV and band gap dependent on Si 3p and C 2p states. While charge density results show that Si-C bond is a hybrid bond semiconductor strong in covalent bond and weak in ionicity, characterized by intense sp3 hybrid characteristics, which is in accordance with the experimental results. The above mentioned results are considered as theoretical reference for design and application of SiC polytype materials.

Geometric structure and electronic structure of wurtzite ZnO have been calculated adopting first principle plane wave ultrosoft pseudo potential method based on density functional theory, and band structure, electronic state density, differential charge distribution of ZnO have been subjected to systematic analysis, the results of which show that ZnO is a type of wide gap and direct gap semiconductor, with conduction band bottom and valence band top at the point Γ of Brillouin zone and valence band top showing obvious triply degenerateΓ7、Γ9、Γ7,while conduction band bottom beingΓ7. electronic structure calculation shows that Zn 3d narrow orbit between-6 and-4 eV has been fully filled with electrons and that O 2p wide orbit between-4 and 0 eV has also been fully filled with electron. In addition, charge density calculation shows that ZnO is metal oxide semiconductor with hybrid bond characterized by high ionicity and low covalent bond, accordingly, the above mentioned findings are superior to value of calculation mentioned in some documents.

SiC poly-type geometric structure, electronic structure and energy have been subjected to systematic study based on first principle calculation method given in density functional theory. After calculation, the energy results show that 4H-SiC system energy is the lowest and stablest, while 2H-SiC system energy is the highest and unstablest; the calculation results of the band structure show that six SiC poly-types are indirect wide band gap semiconductor, with valence band top on point Γ of Brillouin zone, conduction band bottom on point M of Brillouin zone; with the increase of hexagonality, the energy gap and valence band width are gradually getting smaller, with largest splitting of orbital energy level on 2H-SiC valence band top, reaching to 0.122 eV, while the splitting of orbital energy level on 8H-SiC valence band top is the smallest, with 0.027 eV only.

Electronic structure and optical properties of 2H-SiC are calculated by the first-principles calculation based on density functional theory, thus to give out the relation of electronic structure and optical properties of 2H-SiC material in theory. It is theoretically predicated that the 2H-SiC is an indirect band gap semiconductor with all valence band maximum located at Γ point in Brillouin zone and conduction band bottom located at M point of Brillouin zone. The optical property of the 2H-SiC for the band-to-band transition is analyzed by using the calculated band structure and density of state. The result of optical properties shows that obvious dielectric peaks appear in 0~10eV which absorb the band edge to correspond to the ultraviolet band. Therefore, 2H-SiC material maybe become the excellent ultraviolet semiconductor material.

Geometric structure and electronic structures of Zn1-xMgxO alloy under different Mg doped concentrations have been investigated by performing the first-principle calculations based on density functional theory under the generalized gradient approximation (GGA). The calculated results show that there is substantial change in electronic structure of Mg doped MgxZn1-xO alloy, with the constant increase of Mg content, cell parameter a shall be on the gradual increase, with c on gradual decrease and band gap width of MgxZn1-xO alloy on the increase. The research findings show that the position of conduction band bottom is dependent on Mg 2p and Zn 4s. Mg doping results in drift of Mg 2p and Zn 4s toward high energy region, being the root cause for the increase in band gap width,the research results in the paper are in accordance with other experimental results. The above results provide theoretical guidance to the preparation of Zn1-xMgxO alloy in experiment.

A detailed theoretical study of electronic structure and optical properties of GaN under pressure was performed by the first-principles calculations of plane wave ultra-soft pseudo-potential method based on the density functional theory (DFT). The results indicate that Ga-N bond length becomes shorter and the valence bonds shift towards the low energy while the conduction bands towards high energy, the band gap becomes wider with the pressure increasing, and theoretical studies explained the relationship between the band edges, energy gap of GaN and pressure. In addition, the peak in band was cracked slightly, and the Ga 3d-N 2p hybridization was enhanced.

The cell structures, locally micro-structures, combinations, electronic states as well as carrier transports induced by Oxygen vacancy for the CaMnO3 compound have been systematically investigated by pseudo-potential plane wave functions within the framework of density functional theory calculational method. The results reveal that the Oxygen vacant CaMnO2.75 has larger formation enthalpy than that of the intrinsic CaMnO3 and the Oxygen vacancy formation energy of CaMnO3 is as large as 7.10 eV. The Oxygen vacant CaMnO2.75 is harder to form than the intrinsic CaMnO3. The cubical orthorhombic structure tends to be rhombohedral. The lattice parameters a, b and c decrease simultaneously. The α and γ shrinks, the β increases. The lattice shrinkage induced by oxygen vacancy is anisotropic. The MnO6 octahedrons is twisted and it is shrinked along c and expanded along a. The bond strengths of Mn-O are all enhanced. There are six energy bands and the band gap is narrowed, the Fermi level is heightened and the electrons tend to occupy high energy bands. At the same time, the work function of electrons is lowered from 4.69872 eV to 4.00048 eV. The conductivity should be enhanced for Oxygen vacant CaMnO2.75, the O p and Mn d state electrons contribute most to the upper valance bands as well as the lower conduction bands, they jointly realize the conduction process. Keywords: CaMnO3, Oxygen vacancy, Formation, Electronic states

The transport properties in ultrasmall single-wall carbon nanotubes (SWCNTs) under tensile strain have been theoretically investigated. The regular negative differential resistance (NDR) induced by the strain undergoes a process from enhancement to weakening in the zigzag (3,[Formula: see text]0) SWCNT. The NDR achieves maximum with applying 4% tensile strain. Compared to the case of (3,[Formula: see text]0) SWCNT, that NDR cannot be manipulated by applying strain clearly in (4,[Formula: see text]0) and (5,[Formula: see text]0) ultrasmall SWCNTs with tensile strain lower than 10%. It proposes this strain-induced NDR effect to demonstrate the possibility of finding potential applications in SWCNT-based NDR nanodevices such as in memory devices, oscillators and fast switching devices.