Nitrogen Adatom Diffusion on a Ga－Rich GaN （0001） Surface

The diffusion of N adatoms on a Ga-rich GaN(O001) surface has been studied using density-functional theory.The configuration of Ga adatoms on a Ga-rich GaN surface has been identified. The first adlayer Ga adatoms are on top of the terminating substrate Ga atoms, and the outmost adlayer Ga adatoms exist randomly at the T4 or H3 sites. A very different diffusivity of N adatoms on a Ga-rich GaN(0001) surface has been found. The excess Ga adatoms on a GaN(0001) surface reduce the diffusion barrier by 0.75eV and influence the migration path. It seems that bilayer Ga adatoms are helpful for N atom diffusion.     

Molecular-beam epitaxy of topological insulator Bi2Se3 （111） and （221） thin films

This paper presents an overview of the growth of Bi2Se3, a prototypical three-dimensional topological insulator, by molecular-beam epitaxy on various substrates. Comparison is made between the growth of Bi2 Se3 （111） on van der Waals （vdW） and non-vdW substrates, with attention paid to twin suppression and strain. Growth along the [221] direction of Bi2Se3 on InP （001） and GaAs （001） substrates is also discussed.     

ATLEED研究6H-SiC(0001)(3~(0.5)×3~(0.5))R30°重构表面

低能电子衍射 (LEED)对 6H SiC(0 0 0 1) (3× 3)R30°表面的研究结果表明 ,该表面有 1/3单层的Si原子吸附在T4 空位上与第一个SiC复合层中的三个Si原子键接 ,它们之间的垂直距离为 0 171nm .通过对该表面 10个非等价垂直入射衍射束的自动张量低能电子衍射 (ATLEED)计算 ,得到“最佳结构”由于表面SiC复合层堆积顺序不同而产生的三种表面终止状态 (surfacetermination)的混合比例为S1∶S2∶S3 =15∶15∶70 ,理论计算与实验I V曲线比较得到可靠性因子RVHT=0 .16 5 ,RP=0 .142 ,表明表面生长符合能量最小化的台阶生长机制     

ATLEED研究6H-SiC(0001)-(√3*√3)R30o重构表面

关键词：     

ATLEED研究6H-SiC(0001)-(3×3)R30°重构表面

低能电子衍射(LEED)对6H-SiC(0001)-(3×3)R30°表面的研究结果表明,该表面有1/3单层的Si原子吸附在T4空位上与第一个SiC复合层中的三个Si原子键接,它们之间的垂直距离为0.171nm.通过对该表面10个非等价垂直入射衍射束的自动张量低能电子衍射(ATLEED)计算,得到“最佳结构”由于表面SiC复合层堆积顺序不同而产生的三种表面终止状态(surface termination)的混合比例为S1∶S2∶S3=15∶15∶70,理论计算与实验I-V曲线比较得到可靠性因子RVHT=0.165,RP=0.142,表明表面生长符合能量最小化的台阶生长机制.     

Charge Density Wave States in 2H-MoTe_2 Revealed by Scanning Tunneling Microscopy

2H-and 1T′-phase monolayer MoTe_2 films on highly oriented pyrolytic graphite are studied using scanning tunneling microscopy and spectroscopy(STM/STS).The phase transition of MoTe_2 can be controlled by a postgrowth annealing process,and the intermediate state during the phase transition is directly observed by STM.For 2H-MoTe2,inversion domain boundaries are presented as bright lines at high sample bias,but as dark lines at lower sample bias.The dI/dV mappings reveal the distinct distributions of electronic states between domain boundaries and interiors of domains.It sihould be noted that a 2×2 periodic structure is clearlfy discernable inside the domains,where the STS measurement shows a small dip of size～150 meV at the vicinity of the Fermi level,indicating that the 2×2 periodic structure may be an incommensurate charge density wave.Moreover,a4×4 periodic structure appears in 2H-MoTe_2 grown at a higher substrate temperature.