Roadmap for Modeling RhPt/Pt(111) Catalytic Surfaces

PtRh alloys are used as versatile multipurpose catalysts for a number of industrial applications, including fertilizer production and ammonia slip catalysts for NOx abatement purposes. For the latter, ammonia is oxidized to nitrogen at intermediate temperatures. To optimize the PtRh-alloyed catalysts and explain the role of Pt and Rh for future intermediate-temperature ammonia oxidation operando studies, we prepared a series of distinct RhPt model surfaces. We explore postannealing and high-temperature deposition as two routes for preparation of surface alloys and compare results with literature examples. Scanning tunneling microscopy and X-ray photoelectron spectroscopy provide detailed information on surface morphology and composition and demonstrate excellent temperature stability of RhPt/Pt(111) in the temperature range targeted for operando catalytic studies. A detailed roadmap summarizes preparation conditions to achieve a broad variety of surface structures.Catalysis and Surface Chemistr

Defect ferromagnetism induced by lower valence cation doping:Li-doped SnO(2)nanoparticles

To explore the role of Li in establishing room-temperature ferromagnetism in SnO2, the structural, electronic and magnetic properties of Li-doped SnO(2)compounds were studied for different size regimes, from nanoparticles to bulk crystals. Li-doped nanoparticles show ferromagnetic ordering plus a paramagnetic contribution for particle sizes in the range of 16-51 nm, while pure SnO(2)and Li-doped compounds below and above this particular size range are diamagnetic. The magnetic moment is larger for compositions where the Li substitutes for Sn than for compositions where Li prevalently occupies interstitial sites. The observed ferromagnetic ordering in Li-doped SnO(2)nanoparticles is mainly due to the holes created when Li substitutes at a Sn site. Conversely, Li acts as an electron donor and electrons from Li may combine with holes to decrease ferromagnetism when lithium mainly occupies interstitial sites in the SnO(2)lattice

Defect ferromagnetism in SnO2:Zn2+ hierarchical nanostructures: correlation between structural, electronic and magnetic properties

We report on the ferromagnetism of Sn1-xZnxO2 (x < 0.1) hierarchical nanostructures with various morphologies synthesized by a solvothermal route. A room temperature ferromagnetic and paramagnetic response was observed for all compositions, with a maximum in ferromagnetism for x = 0.04. The ferromagnetic behaviour was found to correlate with the presence of zinc on substitutional Sn sites and with a low oxygen vacancy concentration in the samples. The morphology of the nanostructures varied with zinc concentration. The strongest ferromagnetic response was observed in nanostructures with well-formed shapes, having nanoneedles on their surfaces. These nanoneedles consist of (110) and (101) planes, which are understood to be important in stabilizing the ferromagnetic defects. At higher zinc concentration the nanostructures become eroded and agglomerated, a phenomenon accompanied with a strong decrease in their ferromagnetic response. The observed trends are explained in the light of recent computational studies that discuss the relative stability of ferromagnetic defects on various surfaces and the role of oxygen vacancies in degrading ferromagnetism via an increase in free electron concentration

Endoscopic surgery of pituitary adenomas. Historical overview

Over the past century pituitary surgery has undergone multiple revolutions in surgical technique and technological advancements that have resulted in what is now recognized as modern transsphenoidal surgery. Although the procedure is well established in the current neurosurgical literature, the historical maze that led to its development continues to be of interest because it allows us to appreciate better the unique contributions made by the pioneers of the technique as well as the innovative spirit that continues to fuel neurosurgery

Treatment of intraoperative nasal cerebrospinal fluid leak of patients with hormone active pituitary adenomas

Intraoperative nasal cerebrospinal fluid leak are common during the transnasal transsphenoidal interven tions. In certain cases, it is a feature of these interventions. However, its amplification needs a mandatory treatment. In this article, we describe the technique for closure dural defects that have developed during the transnasal removal of hormone active pituitary adenomas, using thrombin and fibrinogen containing colla genic sponge

Nucleation, alloying, and stability of Co-Re bimetallic nanoparticles on Al2O3/NiAl(110)

This paper reports on the preparation and characterization of nanostructured Re and Co–Re/Al2O3/NiAl(110) surfaces designed as model catalysts for operando studies of Fischer–Tropsch synthesis. Scanning tunneling microscopy on pure Re particles identified strong Re–Al2O3 support interaction, resulting in uniform nucleation and growth on random point defects. X-ray photoelectron spectroscopy confirmed the strong interaction through a shift in the binding energy, in addition to size-dependent final state effects. Co–Re particles were prepared by sequential deposition of the two metals, resulting in core–shell structures in which the shell was (strongly) enriched with the metal deposited second. Annealing of bimetallic particles allowed for elemental redistribution, as was concluded from the XPS data and supported by modeling. The annealing also resulted in sintering of bimetallic clusters. Interestingly, the thermal stability of the Co–Re surfaces prepared by sequential deposition of Co, followed by Re, was better than that of both pure Co and pure Re.Quantum Matter and Optic

Rapid reduction of self-assembled monolayers of a disulfide terminated para-nitrophenyl alkyl ester on roughened Au surfaces during XPS measurements

The application of multiple spectroscopic techniques to the characterisation of self-assembled monolayers (SAMs) is essential for determining whether the desired surface functionalization was achieved, the molecules are integer after self-assembly and well-packed on the substrate. We investigated the use of surface enhanced Raman spectroscopy and X-ray photoelectron spectroscopy to characterise SAMs of a disulfide-functionalised nitrobenzene (i.e. 4-nitrophenyl-5-(1,2-dithiolan-3-yl)pentanoate). We show that electron-induced damage during acquisition of photoemission spectra of the monolayer occurs through reduction of the nitro group. Use of roughened bulk gold substrates to enhance the SERS sensitivity results in an increase in the rate at which the reduction proceeds.