Direct observation of a surface resonance state and surface band inversion control in black phosphorus

We report a Cs-doping-induced band inversion and the direct observation of a surface resonance state with an elliptical Fermi surface in black phosphorus (BP) using angle-resolved photoemission spectroscopy. By selectively inducing a higher electron concentration (1.7 × 1014 cm−2) in the topmost layer, the changes in the Coulomb potential are sufficiently large to cause surface band inversion between the parabolic valence band of BP and a parabolic surface state around the point of the BP Brillouin zone. Tight-binding calculations reveal that band gap openings at the crossing points in the two high-symmetry directions of the Brillouin zone require out-of-plane hopping and breaking of the glide mirror symmetry. Ab initio calculations are in very good agreement with the experiment if a stacking fault on the BP surface is taken into account. The demonstrated level of control over the band structure suggests the potential application of few-layer phosphorene in topological field-effect transistors

Core level shifts of undercoordinated Pt atoms

We present the results of high-energy resolution core level photoelectron spectroscopy experiments paralleled by density functional theory calculations to investigate the electronic structure of highly undercoordinated Pt atoms adsorbed on Pt(111) and its correlation with chemical activity. Pt4f(7/2) core level binding energies corresponding to atoms in different configurations are shown to be very sensitive not only to the local atomic coordination number but also to the interatomic bond lengths. Our results are rationalized by introducing an indicator, the effective coordination, which includes both contributions. The calculated energy center of the valence 5d-band density of states, which is a well known depicter of the surface chemical reactivity, shows a noteworthy correlation with the Pt4f(7/2) core level shifts and with the effective coordination

O- and H- induced surface core level shifts on Ru(0001): Prevalence of the additivity rule

In previous work on adsorbate-induced surface core level shifts (SCLSs), the effects caused by O atom adsorption on Rh(111) and Ru(0001) were found to be additive: the measured shifts for first layer Ru atoms depended linearly on the number of directly coordinated O atoms. Density-functional theory calculations quantitatively reproduced this effect, allowed separation of initial and final state contributions, and provided an explanation in terms of a roughly constant charge transfer per O atom. We have now conducted similar measurements and calculations for three well-defined adsorbate and coadsorbate layers containing O and H atoms: (1 x 1)-H, (2 x 2)-(O+H), and (2 x 2)-(O+3H) on Ru(0001). As H is stabilized in fcc sites in the prior two structures and in hcp sites in the latter, this enables us to not only study coverage and coadsorption effects on the adsorbate-induced SCLSs, but also the sensitivity to similar adsorption sites. Remarkably good agreement is obtained between experiment and calculations for the energies and geometries of the layers, as well as for all aspects of the SCLS values. The additivity of the next-neighbor adsorbate-induced SCLSs is found to prevail even for the coadsorbate structures. While this confirms the suggested use of SCLSs as fingerprints of the adsorbate configuration, their sensitivity is further demonstrated by the slightly different shifts unambiguously determined for H adsorption in either fcc or hcp hollow sites.Comment: 9 pages including 4 figures; related publications can be found at http://www.fhi-berlin.mpg.de/th/th.htm

Metallization of the C-60/Rh(100) interface revealed by valence photoelectron spectroscopy and density functional theory calculations

The electronic structure of single and multiple layers of C(60) molecules deposited on a Rh(100) surface is investigated by means of valence photoemission spectroscopy and density functional theory calculations. The binding of the fullerene monolayer to the metal surface yields the appearance of a new state in the valence band spectrum crossing the Fermi level. Insight into the metallization of the metal/fullerene interface is provided by the calculated electronic structure that allows us to correlate the measured interface state with a strong hybridization between the Rh metal states and the highest and lowest molecular orbitals. This results in a net charge transfer of approximate to 0.5e-0.6e from the metal to the p states of the interfacial C atoms. The charge transfer is shown to be very short range, involving only the C atoms bound to the metal. The electronic structure of the second C(60) layer is already insulating and resembles the one measured for C(60) multilayers supported by the same substrate or calculated for fullerenes isolated in vacuum. The discussion of the results in the context of other C(60)/metal systems highlights the distinctive electronic properties of the molecule/metal interface determined by the Rh support

Inclusion of new 5-fluorouracil amphiphilic derivatives in liposome formulation for cancer treatment

Correction for 'Inclusion of new 5-fluorouracil amphiphilic derivatives in liposome formulation for cancer treatment' by M. Petaccia et al., Med. Chem. Commun., 2015, 6, 1639–1642

Observation of Dirac-like surface state bands on the top surface of BiSe

Two quintuple layers of strong topological insulator Bi2Se3 are coupled by a Bi bilayer in BiSe crystal. We investigated its electronic structure using angle resolved photoelectron spectroscopy to study its topological nature. Dirac like linearly dispersive surface state bands are observed on the 001 surface of BiSe and Sb doped BiSe, similar to Bi2Se3. Moreover, the lower part of the SSBs buries deep in the bulk valence band. Overlap region between the SSBs and BVB is large in Sb doped system and the SSBs deviate from the Dirac like linear dispersion in this region. These results highlight the role of interlayer coupling between the Bi bilayer and the Bi2Se3 QLs. Furthermore, we observed a large intensity imbalance in the SSBs located at the positive and negative k parallel directions. This asymmetry pattern gradually reverses as the excitation energy scans from low 14eV to high 34eV value. However, we did not observe signal of surface magnetization resulting from the intensity imbalance in SSBs due to hole-generated uncompensated spin accumulation in the photoexcitation process. The main reason for this could be the faster relaxation process for photo hole due to the presence of the Bi bilayer between the adjacent Bi2Se3 QLs. The observed photon energy dependent intensity variation could be a signature of the mixing between the spin and the orbit texture of the SSBs

Clarifying the apparent flattening of the graphene band near the van Hove singularity

Graphene band renormalization near the van Hove singularity (VHS) has been investigated by angle-resolved photoemission spectroscopy (ARPES) on Li-doped quasifreestanding graphene on a cobalt (0001) surface. The absence of graphene band hybridization with the substrate, the doping contribution well represented by a rigid energy shift, and the excellent electron-electron interaction screening ensured by the metallic substrate offer a privileged point of view for such an investigation. A clear ARPES signal is detected along the KMK direction of the graphene Brillouin zone, giving rise to an apparent flattened band. By simulating the graphene spectral function from the density functional theory calculated bands, we demonstrate that the photoemission signal around the M point originates from the "tail"of the spectral function of the unoccupied band above the Fermi level. Such an interpretation puts forward the absence of any additional strong correlation effects near the VHS, reconciling the mean-field description of the graphene band structure even in a highly doped scenario