Crystalline and electronic structure of single-layer TaS2_2

Single-layer TaS$_2$ is epitaxially grown on Au(111) substrates. The resulting two-dimensional crystals adopt the 1H polymorph. The electronic structure is determined by angle-resolved photoemission spectroscopy and found to be in excellent agreement with density functional theory calculations. The single layer TaS$_2$ is found to be strongly n-doped, with a carrier concentration of 0.3(1) extra electrons per unit cell. No superconducting or charge density wave state is observed by scanning tunneling microscopy at temperatures down to 4.7 K.Comment: 6 pages, 4 figure

Band gap engineering by Bi intercalation of graphene on Ir(111)

We report on the structural and electronic properties of a single bismuth layer intercalated underneath a graphene layer grown on an Ir(111) single crystal. Scanning tunneling microscopy (STM) reveals a hexagonal surface structure and a dislocation network upon Bi intercalation, which we attribute to a $\sqrt{3}\times\sqrt{3}R30{\deg}$ Bi structure on the underlying Ir(111) surface. Ab-initio calculations show that this Bi structure is the most energetically favorable, and also illustrate that STM measurements are most sensitive to C atoms in close proximity to intercalated Bi atoms. Additionally, Bi intercalation induces a band gap ($E_g=0.42\,$eV) at the Dirac point of graphene and an overall n-doping ($\sim 0.39\,$eV), as seen in angular-resolved photoemission spectroscopy. We attribute the emergence of the band gap to the dislocation network which forms favorably along certain parts of the moir\'e structure induced by the graphene/Ir(111) interface.Comment: 5 figure

Interplay between shape and composition in bimetallic nanoparticles revealed by an efficient optimal-exchange optimization algorithm

Despite the large relevance of bimetallic metal nanoparticles for heterogeneous catalysis, the relation between their shape and elemental composition remains elusive. Here, we investigate this relationship by implementing and applying global optimization methods enhanced with a novel optimal-exchange algorithm. In particular, we determine the lowest energy chemical orderings for PtAu nanoparticles, revealing that the most stable shape changes from highly symmetric structures for pure particles to distorted and less symmetric shapes for intermediate compositions. The presented method leverages the local atomic contributions to an empirical surrogate energy expression to identify optimal atom exchanges. This also allows us to pinpoint the origin of the stability of distorted shapes, revealing a favorable energy trade-off when over-coordinating Pt and under-coordinating Au upon distorting the particle shape

Chemical ordering in Pt-Au, Pt-Ag and Pt-Cu nanoparticles from density functional calculations using a topological approach

Bimetallic alloys are actively investigated as promising new materials for catalytic and other energy-related applications. However, the stable arrangements of the two metals in prevailing nanostructured systems, which define their structure and surface reactivity, are seldom addressed. The equilibrium chemical orderings of bimetallic nanoparticles are usually different from those in the corresponding bulk phases and hard to control experimentally, which hampers assessment of the relations between composition, structure, and reactivity. Herewith, we study mixtures of platinum an essential metal in catalysis alloyed with coinage metals gold, silver, and copper. These systems are interesting, for instance, for reducing the costly Pt content and designing improved multifunctional catalysts, but the chemical orderings in such mixtures at the nanoscale are still debated. We therefore explore chemical orderings and properties of Pt-containing nanoalloys by means of a topological method based on density functional calculations. We determine the lowest-energy chemical orderings in 1.4 to 4.4 nm large Pt-Au, Pt-Ag and Pt-Cu particles with different contents of metals. Chemical ordering, bonding, and charge distribution in the nanoparticles are analyzed, identifying how peculiar structural motifs relevant for catalysis and sensing applications, such as monometallic skins and surface single-atom sites, emerge. We compare these results with previous data for the corresponding Pd-based particles, identifying trends in chemical ordering, deepening understanding of the behaviour of catalytically relevant bimetallic compositions, and establishing appropriate models for studying the bimetallic nanoalloys

Spin Structure of K Valleys in Single-Layer WS2 on Au(111)

The spin structure of the valence and conduction bands at the K\u304 and K\u304\u2032 valleys of single-layer WS2 on Au(111) is determined by spin- and angle-resolved photoemission and inverse photoemission. The bands confining the direct band gap of 1.98 eV are out-of-plane spin polarized with spin-dependent energy splittings of 417 meV in the valence band and 16 meV in the conduction band. The sequence of the spin-split bands is the same in the valence and in the conduction bands and opposite at the K\u304 and the K\u304\u2032 high-symmetry points. The first observation explains "dark" excitons discussed in optical experiments; the latter points to coupled spin and valley physics in electron transport. The experimentally observed band dispersions are discussed along with band structure calculations for a freestanding single layer and for a single layer on Au(111)

Multimodality Treatment with Conventional Transcatheter Arterial Chemoembolization and Radiofrequency Ablation for Unresectable Hepatocellular Carcinoma

Background/Aims: To evaluate the efficacy of multimodality treatment consisting of conventional transcatheter arterial chemoembolization (TACE) and radiofrequency ablation (RFA) in patients with non-resectable and non-ablatable hepatocellular carcinoma (HCC). Methods: In this retrospective study, 85 consecutive patients with HCC (59 solitary, 29 multifocal HCC) received TACE followed by RFA between 2001 and 2010. The mean number of tumors per patient was 1.6 +/- 0.7 with a mean size of 3.0 +/- 0.9 cm. Both local efficacy and patient survival were evaluated. Results: Of 120 treated HCCs, 99 (82.5%) showed a complete response (CR), while in 21 HCCs (17.5%) a partial response was depicted. Patients with solitary HCC revealed CR in 91% (51/56); in patients with multifocal HCC (n = 29) CR was achieved in 75% (48 of 64 HCCs). The median survival for all patients was 25.5 months. The 1-, 2-, 3- and 5-year survival rates were 84.6, 58.7, 37.6 and 14.6%, respectively. Statistical analysis revealed a significant difference in survival between Barcelona Clinic Liver Cancer (BCLC) A (73.4 months) and B (50.3 months) patients, while analyses failed to show a difference for Child-Pugh score, Cancer of Liver Italian Program (CLIP) score and tumor distribution pattern. Conclusion: TACE combined with RFA provides an effective treatment approach with high local tumor control rates and promising survival data, especially for BCLC A patients. Randomized trials are needed to compare this multimodality approach with a single modality approach for early-stage HCC. Copyright (C) 2011 S. Karger AG, Base

Aromatic polymers obtained by precipitation polycondensation: 4*. Synthesis of poly(ether ketone ketone)s

High molecular weight aromatic poly(ether ketone ketone)s were synthesized by the Friedel-Crafts polyacylation condensation of iso- and terephthaloyl chlorides with diphenyl ether, 1,4- and 1,3-bis(4- phenoxybenzoyl)benzenes. Depending on the monomers used for polycondensation, polyketones of regular structure with different iso-/tereisomer repeating unit ratio (100/0, 50/50, 0/100) in the main chain were obtained. Polymers of each repeating isomer unit were prepared in two different ways. All the polymer syntheses were performed as precipitation polycondensations and the resulting polymers were obtained in particle form. The influence of reaction conditions and preparation route on the polymer properties were examined. The monomer concentration and monomer stoichiometric ratio were found to affect the polymer viscosity. The size and shape of the polyketone particles obtained were also found to be governed by reaction conditions and preparation route.Peer reviewe

Charting the Atomic C Interaction with Transition Metal Surfaces

Carbon interaction with transition metal (TM) surfaces is a relevant topic in heterogeneous catalysis, either for its poisoning capability, for the recently attributed promoter role when incorporated in the subsurface, or for the formation of early TM carbides, which are increasingly used in catalysis. Herein, we present a high-throughput systematic study, adjoining thermodynamic plus kinetic evidence obtained by extensive density functional calculations on surface models (324 diffusion barriers located on 81 TM surfaces in total), which provides a navigation map of these interactions in a holistic fashion. Correlation between previously proposed electronic descriptors and ad/absorption energies has been tested, with the d-band center being found the most suitable one, although machine learning protocols also underscore the importance of the surface energy and the site coordination number. Descriptors have also been tested for diffusion barriers, with ad/absorption energies and the difference in energy between minima being the most appropriate ones. Furthermore, multivariable, polynomial, and random forest regressions show that both thermodynamic and kinetic data are better described when using a combination of different descriptors. Therefore, looking for a single perfect descriptor may not be the best quest, while combining different ones may be a better path to follow

NMR characterisation of the minimal interacting regions of centrosomal proteins 4.1R and NuMA1: effect of phosphorylation

<p>Abstract</p> <p>Background</p> <p>Some functions of 4.1R in non-erythroid cells are directly related with its distinct sub-cellular localisation during cell cycle phases. During mitosis, 4.1R is implicated in cell cycle progression and spindle pole formation, and co-localizes with NuMA1. However, during interphase 4.1R is located in the nucleus and only partially co-localizes with NuMA1.</p> <p>Results</p> <p>We have characterized by NMR the structural features of the C-terminal domain of 4.1R and those of the minimal region (the last 64 residues) involved in the interaction with NuMA1. This subdomain behaves as an intrinsically unfolded protein containing a central region with helical tendency. The specific residues implicated in the interaction with NuMA1 have been mapped by NMR titrations and involve the N-terminal and central helical regions. The segment of NuMA1 that interacts with 4.1R is phosphorylated during mitosis. Interestingly, NMR data indicates that the phosphorylation of NuMA1 interacting peptide provokes a change in the interaction mechanism. In this case, the recognition occurs through the central helical region as well as through the C-terminal region of the subdomain meanwhile the N-terminal region do not interact.</p> <p>Conclusions</p> <p>These changes in the interaction derived from the phosphorylation state of NuMA1 suggest that phosphorylation can act as subtle mechanism of temporal and spatial regulation of the complex 4.1R-NuMA1 and therefore of the processes where both proteins play a role.</p