Ir(111) surface state with giant Rashba splitting persists under graphene in air

We reveal a giant Rashba effect (α(R)≈1.3 eV??) on a surface state of Ir(111) by angle-resolved photoemission and by density functional theory. It is demonstrated that the existence of the surface state, its spin polarization, and the size of its Rashba-type spin-orbit splitting remain unaffected when Ir is covered with graphene. The graphene protection is, in turn, sufficient for the spin-split surface state to survive in ambient atmosphere. We discuss this result along with indications for a topological protection of the surface state.     

The Tamm surface state on Cu(111) and Ag(111)

It is shown, that the well-known d-electron Tamm surface-state emission observed in photoelectron spectra from Cu(111) at the M̄ point in the surface Brillouin zone, is indeed due to such a surface state and not a bulk band transition as recently suggested L. Wallden, Solid State Commun. 59, 205 (1986). A similar surface state on Ag(111) is reported.     

点缺陷扶手型石墨烯量子点的电子性质研究

基于有限差分方法, 数值求解了Dirac方程, 研究了垂直磁场下的点缺陷扶手型 石墨烯 量子点的能谱结构, 分析了尺寸大小对带隙的影响. 与无磁场时具有一定带隙 (带隙的大小与半径成反比) 的量子点相比, 在外加有限磁场下, 能谱中出现朗道能级, 最低朗道能级能量为零并与磁场强度无关, 并且朗道能级的简并度随着磁场的增加而增加. 进一步的计算表明, 最低朗道能级的简并度与磁场成线性关系, 与半径的平方成线性关系. 本文工作对基于石墨烯量子点的器件设计具有一定的指导意义.     

单层正三角锯齿型石墨烯量子点的电子结构和磁性

采用基于密度泛函理论的广义梯度近似(GGA),对不同尺寸(N=2—11)的单层正三角锯齿型石墨烯量子点(Z_N -GNDs)的结构进行优化,得到与实验数据较好符合的晶格常数,进一步计算得到不同尺寸下体系的自旋多重度、磁矩、电子态密度以及自旋电子密度.结果表明:所有体系都呈现金属性,在尺寸较小的体系中量子尺寸效应对电子结构的影响比较明显;与单层石墨烯片一样,sp²杂化作用和非键态电子在量子点中仍起到非常重要的作用;费米能级上有自旋向上的电子分布,体系的 关键词： 石墨烯 量子点 电子结构 磁性     

边界对石墨烯量子点非线性光学性质的影响

石墨烯作为一种新型非线性光学材料,在光子学领域具有重要的应用前景,引起研究人员的极大兴趣.本文运用量子化学计算方法研究了边界引入碳碳双键(C=C)和掺杂环硼氮烷(B3N3)环对石墨烯量子点非线性光学性质和紫外-可见吸收光谱的影响.研究发现,扶手椅边界上引入C=C双键后,六角形石墨烯量子点分子结构对称性降低,电荷分布对称...     

A rigorous proof for non-existence of edge state in the semi-infinite armchair edged graphene

Within the transfer matrix method, we study the conditions for the existence of the edge states in the semi-infinite armchair edged graphene. We discuss zero-energy and non-zero-energy edge states, respectively, and show the non-existence of the edge states in the model analytically and rigorously.     

Si(111)-(7×7)表面上Ge量子点的自组织生长

用扫描隧道显微镜研究了Si(111)(7×7)表面上Ge量子点的自组织生长.室温下用固相外延法在硅基底上沉积亚单层的Ge,然后在适当的温度下退火可以聚集形成有序的Ge量子点.由于Ge在Si(111)(7×7)表面选择性的吸附而形成有序的Ge量子点. 关键词： 锗 硅 扫描隧道显微镜 自组织生长     

Triphenylene adsorption on Cu(111) and relevant graphene self-assembly

Investigations on adsorption behavior of triphenylene(TP) and subsequent graphene self-assembly on Cu(111) were carried out mainly by using scanning tunneling microscopy(STM).At monolayer coverage,TP molecules formed a longrange ordered adsorption structure on Cu(111) with an uniform orientation.Graphene self-assembly on the Cu(111) substrate with TP molecules as precursor was achieved by annealing the sample,and a large-scale graphene overlayer was successfully captured after the sample annealing up to 1000 K.Three different Moire patterns generated from relative rotational disorders between the graphene overlayer and the Cu(111) substrate were observed,one with 40 rotation between the graphene overlayer and the Cu(111) substrate with a periodicity of 2.93 nm,another with 70 rotation and 2.15 nm of the size of the Moire supercell,and the third with 100 rotation with a periodicity of 1.35 nm.     

Engineering negative differential conductance with the Cu(111) surface state

Low-temperature scanning tunneling microscopy and spectroscopy are employed to investigate electron tunneling from a C60-terminated tip into a Cu(111) surface. Tunneling between a C60 orbital and the Shockley surface states of copper is shown to produce negative differential conductance (NDC) contrary to conventional expectations. NDC can be tuned through barrier thickness or C60 orientation up to complete extinction. The orientation dependence of NDC is a result of a symmetry matching between the molecular tip and the surface states.     

Link between adatom resonances and the Cu(111) Shockley surface state

Low-temperature scanning tunneling microscopy and spectroscopy at 7 K was used to assemble and characterize native adatom islands of successive size on the Cu(111) surface. Starting from the single adatom we observe the formation of a series of quantum states which merge into the well known two-dimensional Shockley surface state in the limit of large islands. Our experiments reveal a natural physical link between this fundamental surface property and the sp(z) hybrid resonance associated with the single Cu/Cu(111) adatom.     

Optical phonons in Ge quantum dots obtained on Si(111)

The Raman light scattering from optical phonons of Ge quantum dots grown by molecular beam epitaxy on a Si(111) surface is studied. A series of Raman lines related to the quantization of phonon spectrum is observed. It is shown that phonon frequencies are adequately described in terms of the elastic properties and the dispersion of the optical phonons of bulk Ge. The strain experienced by the Ge quantum dots is estimated.     

Angle-resolved photoemission studies of a surface state for Ag overlayers on Cu(111)

We have performed an angle-resolved photoemission study of a surface state on Cu(111) covered by various thicknesses of Ag. The growth mode of Ag on Cu(111) was determined to be layer-by-layer despite the large mismatch between the two lattices. The Cu(111) surface state was observed to evolve monotonically for increasing Ag overlayer thickness to eventually become the Ag(111) surface state. The measured rate of shift of the surface state binding energy can be explained qualitatively in terms of the degree of localization of the surface-state wave functions.     

Surface state energy shifts by molecular adsorption: CO ON Cu(111)

Molecular adsorption induced energy shifts of a surface state is observed for the Cu(111)/CO system. Angle resolved photoelectron energy spectra show that a zone center surface state shifts to higher energy relative to the Cu bulk bands. The effects is discussed in terms of charge transfer, molecular interaction range and absorption site.     

Morphological modifications of Ag/Cu(111) probed by photoemission spectroscopy of quantum well states and the Shockley surface state

Epitaxial ultra-thin Ag films grown on Cu(111) have been investigated by angle-resolved photoemission spectroscopy. The thickness dependence of the binding energy for the Shockley surface state at 300 K could be determined accurately in films up to 5 ML thick. Furthermore, we observe drastic changes in the film morphology after annealing to 450 K. Spectral modifications in the shape of the quantum-well states (QWS), characteristic for these ultra-thin silver films, prove that the surface morphology is homogeneous. The photoemission spectra also indicate that the silver film bifurcates to form a film exhibiting two distinct film thicknesses. For all levels of silver coverage, we identify surface regions that are 2 ML thick, while the thickness of the remaining surface depends on the amount of deposited silver. The almost purely Lorentzian line-shape of the spectral features corresponding to the two different surface regions show that both surface areas are atomically flat. PACS 68.55.Jk; 73.20.At; 73.21.Fg; 79.60.Dp     

Surface state like bulk band emission in the photoelectron energy spectra of Cu(111)

Using a relativistically calculated band structure the presence in Cu(111) UV photoemission spectra of a prominent 3d peak, previously ascribed to a Tamm type surface state, is explained in terms of bulk band transitions.