We present a systematic investigation of molecule-metal interactions for transition-metal phthalocyanines (TMPc, with TM = Fe, Co, Ni, Cu) adsorbed on Ag(100). Scanning tunneling spectroscopy and ...density functional theory provide insight into the charge transfer and hybridization mechanisms of TMPc as a function of increasing occupancy of the 3d metal states. We show that all four TMPc receive approximately one electron from the substrate. Charge transfer occurs from the substrate to the molecules, inducing a charge reorganization in FePc and CoPc, while adding one electron to ligand pi orbitals in NiPc and CuPc. This has opposite consequences on the molecular magnetic moment: In FePc and CoPc the interaction with the substrate tends to reduce the TM spin, whereas, in NiPc and CuPc, an additional spin is induced on the aromatic Pc ligand, leaving the TM spin unperturbed. In CuPc, the presence of both TM and ligand spins leads to a triplet ground state arising from intramolecular exchange coupling between d and pi electrons. In FePc and CoPc the magnetic moment of C and N atoms is antiparallel to that of the TM. The different character and symmetry of the frontier orbitals in the TMPc series leads to varying degrees of hybridization and correlation effects, ranging from the mixed-valence (FePc, CoPc) to the Kondo regime (NiPc, CuPc). Coherent coupling between Kondo and inelastic excitations induces finite-bias Kondo resonances involving vibrational transitions in both NiPc and CuPc and triplet-singlet transitions in CuPc.
We performed x-ray magnetic circular dichroism (XMCD) measurements on heterostructures comprising topological insulators (TIs) of the ( Bi , Sb ) 2 ( Se , Te ) 3 family and the magnetic insulator ...EuS. XMCD measurements allow us to investigate element-selective magnetic proximity effects at the very TI/EuS interface. A systematic analysis reveals that there is neither significant induced magnetism within the TI nor an enhancement of the Eu magnetic moment at such interface. The induced magnetic moments in Bi, Sb, Te, and Se sites are lower than the estimated detection limit of the XMCD measurements of ∼ 10−3μB/at.
Materials that exhibit ferromagnetism, interfacial stability, and tunability are highly desired for the realization of emerging magnetoelectronic phenomena in heterostructures. Here we present the ...GdAg2 monolayer alloy, which possesses all such qualities. By combining X-ray absorption, Kerr effect, and angle-resolved photoemission with ab initio calculations, we have investigated the ferromagnetic nature of this class of Gd-based alloys. The Curie temperature can increase from 19 K in GdAu2 to a remarkably high 85 K in GdAg2. We find that the exchange coupling between Gd atoms is barely affected by their full coordination with noble metal atoms, and instead, magnetic coupling is effectively mediated by noble metal–Gd hybrid s,p–d bands. The direct comparison between isostructural GdAu2 and GdAg2 monolayers explains how the higher degree of surface confinement and electron occupation of such hybrid s,p–d bands promote the high Curie temperature in the latter. Finally, the chemical composition and structural robustness of the GdAg2 alloy has been demonstrated by interfacing them with organic semiconductors or magnetic nanodots. These results encourage systematic investigations of rare-earth/noble metal surface alloys and interfaces, in order to exploit them in magnetoelectronic applications.
We study the electronic mechanisms underlying the induction and propagation of chirality in achiral molecules deposited on surfaces. Combined scanning tunneling microscopy and ab initio electronic ...structure calculations of Cu-phthalocyanines adsorbed on Ag(100) reveal the formation of chiral molecular orbitals in structurally undistorted molecules. This effect shows that chirality can be manifest exclusively at the electronic level due to asymmetric charge transfer between molecules and substrate. Single molecule chirality correlates with attractive van der Waals interactions, leading to the propagation of chirality at the supramolecular level. Ostwald ripening provides an efficient pathway for complete symmetry breaking and self-assembly of homochiral supramolecular layers.
We investigate the possibility to induce exchange bias between single molecule magnets (SMM) and metallic or oxide antiferromagnetic substrates. Element-resolved X-ray magnetic circular dichroism ...measurements reveal, respectively, the presence and absence of unidirectional exchange anisotropy for TbPc2 SMM deposited on antiferromagnetic Mn and CoO layers. TbPc2 deposited on Mn thin films present magnetic hysteresis and a negative horizontal shift of the Tb magnetization loop after field cooling, consistent with the observation of pinned spins in the Mn layer coupled parallel to the Tb magnetic moment. Conversely, molecules deposited on CoO substrates present paramagnetic magnetization loops with no indication of exchange bias. These experiments demonstrate the ability of SMM to polarize the pinned uncompensated spins of an antiferromagnet during field-cooling and realize metal–organic exchange-biased heterostructures using antiferromagnetic pinning layers.
We investigate the interaction of TbPc(2) single molecule magnets (SMMs) with ferromagnetic Ni substrates. Using element-resolved x-ray magnetic circular dichroism, we show that TbPc(2) couples ...antiferromagnetically to Ni films through ligand-mediated superexchange. This coupling is strongly anisotropic and can be manipulated by doping the interface with electron acceptor or donor atoms. We observe that the relative orientation of the substrate and molecule anisotropy axes critically affects the SMM magnetic behavior. TbPc(2) complexes deposited on perpendicularly magnetized Ni films exhibit enhanced magnetic remanence compared to SMMs in the bulk. Contrary to paramagnetic molecules pinned to a ferromagnetic support layer, we find that TbPc(2) can be magnetized parallel or antiparallel to the substrate, opening the possibility to exploit SMMs in spin valve devices.
Obstructive sleep apnoea is associated with increased blood pressure and other features of the metabolic syndrome. The aim of the present study was to determine the relative effectiveness of ...continuous positive airway pressure (CPAP) in modifying these outcomes. A randomised placebo-controlled blinded crossover trial comparing cardiovascular and metabolic outcomes after 6 weeks of therapeutic and sham CPAP was performed in 34 CPAP-naïve patients (mean+/-SD body mass and respiratory disturbance indices were 36.1+/-7.6 and 39.7+/-13.8, respectively). Mean waking systolic and diastolic blood pressure fell by 6.7 and 4.9 mmHg, respectively, when compared with sham CPAP. No change was observed in glucose, lipids, insulin resistance or the proportion of patients with metabolic syndrome. In CPAP-compliant patients the fall in blood pressure was greater and the baroreceptor sensitivity improved significantly but no metabolic variable changed. In obese Caucasians with untreated obstructive sleep apnoea, continuous positive airways pressure can improve baroreceptor responsiveness and reduce waking blood pressure within 6 weeks, but this treatment period was insufficient to modify insulin resistance or change the metabolic profile. The mechanisms underlying this difference in the time course of blood pressure and metabolic response to continuous positive airway pressure in obstructive sleep apnoea requires further exploration.
Heavy metal surface alloys represent model systems to study the correlation between electron scattering, spin-orbit interaction, and atomic structure. Here, we investigate the electron scattering ...from the atomic steps of monolayer BiAg_{2} on Ag(111) using quasiparticle interference measurements and density functional theory. We find that intraband transitions between states of opposite spin projection can occur via a spin-flip backward scattering mechanism driven by the spin-orbit interaction. The spin-flip scattering amplitude depends on the chemical composition of the steps, leading to total confinement for pure Bi step edges, and considerable leakage for mixed Bi-Ag step edges. Additionally, the different localization of the occupied and unoccupied surface bands at Ag and Bi sites leads to a spatial shift of the scattering potential barrier at pure Bi step edges.
Aims Obstructive sleep apnoea (OSA) is associated with increased cardiovascular morbidity and mortality. Although it was previously assumed that this was due to its relation with obesity, recent data ...suggest that OSA is independently associated with the cardiovascular risk factors that comprise metabolic syndrome, including hypertension, insulin resistance, impaired glucose tolerance, and dyslipidaemia. However, as previous studies have only considered these variables individually, it has not been possible to determine the overall association of OSA with this syndrome. Methods and results We recruited 61 male subjects with OSA and 43 controls. Glucose, insulin, lipids, and blood pressure (BP) were measured following an overnight fast. Insulin resistance was estimated using homeostasis model assessment (HOMA). Metabolic syndrome was diagnosed according to National Cholesterol Education Program (NCEP) criteria. Subjects with OSA were more obese, had higher BP and fasting insulin, were more insulin resistant, had lower HDL cholesterol, and an increased incidence of metabolic syndrome (87% vs. 35%, \batchmode \documentclassfleqn,10pt,legalpaper{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} \(p{<}0.0001\) \end{document}). In order to determine whether these associations were independent of obesity and other known covariates, a regression analysis adjusted for age, BMI, smoking, and alcohol consumption was performed. This demonstrated that OSA was independently associated with increased systolic and diastolic blood pressure, higher fasting insulin and triglyceride concentrations, decreased HDL cholesterol, increased cholesterol:HDL ratio, and a trend towards higher HOMA values. Metabolic syndrome was 9.1 (95% confidence interval 2.6, 31.2: \batchmode \documentclassfleqn,10pt,legalpaper{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} \(p{<}0.0001\) \end{document}) times more likely to be present in subjects with OSA. Conclusions OSA is independently associated with an increase in the cardiovascular risk factors that comprise the metabolic syndrome and its overall prevalence. This may help explain the increased cardiovascular morbidity and mortality associated with this condition.
PDF
