Graphene on ferromagnetic surfaces and its functionalization with water and ammonia

Here we present an angle-resolved photoelectron spectroscopy (ARPES), x-ray absorption spec-troscopy (XAS), and density-functional theory (DFT) investigations of water and ammonia ad-sorption on graphene/Ni(111). Our results on graphene/Ni(111) reveal the existence of interface states, originating from the strong hybridization of the graphene {\pi} and spin-polarized Ni 3d valence band states. ARPES and XAS data of the H2O (NH3)/graphene/Ni(111) system give an information about the kind of interaction between adsorbed molecules and graphene on Ni(111). The presented experimental data are compared with the results obtained in the framework of the DFT approach.Comment: accepted in Nanoscale Research Letters; 16 pages, 4 figures, 2 table

Structural and electronic properties of the graphene/Al/Ni(111) intercalation-like system

Decoupling of the graphene layer from the ferromagnetic substrate via intercalation of sp metal has recently been proposed as an effective way to realize single-layer graphene-based spin-filter. Here, the structural and electronic properties of the prototype system, graphene/Al/Ni(111), are investigated via combination of electron diffraction and spectroscopic methods. These studies are accompanied by state-of-the-art electronic structure calculations. The properties of this prospective Al-intercalation-like system and its possible implementations in future graphene-based devices are discussed.Comment: 20 pages, 8 figures, and supplementary materia

Induced magnetism of carbon atoms at the graphene/Ni(111) interface

We report an element-specific investigation of electronic and magnetic properties of the graphene/Ni(111) system. Using magnetic circular dichroism, the occurrence of an induced magnetic moment of the carbon atoms in the graphene layer aligned parallel to the Ni 3d magnetization is observed. We attribute this magnetic moment to the strong hybridization between C $\pi$ and Ni 3d valence band states. The net magnetic moment of carbon in the graphene layer is estimated to be in the range of $0.05-0.1 \mu_B$ per atom.Comment: 10 pages, 3 figure

Pacific sea surface temperature associations with southwestern United States summer rainfall and atmospheric circulation

Pacific sea surface temperatures (SSTs) are examined for their associations with (1) summer rainfall, and (2) the latitude location of the mid-tropospheric subtropical high pressure ridge (STR) in the southwestern United States during 1945 to 1986. Extreme northward (southward) displacements of STR are associated with wet (dry) summers over Arizona and an enhanced (weakened) gradient of SST off the California and Baja coasts. These tend to follow winters marked by positive (negative) phases of the PNA, Pacific/North America, teleconnection pattern. Recent decadal variations of Arizona summer rainfall (1950s wet; 1970s dry) appear similarly related to southwestern United States synoptic circulation and eastern Pacific SSTs

The Sweetest Girl of All / music by Otto M. Hensman; words by John A. Hensman

Cover: a drawing of a woman in a garden; photo inset of Miss Edna Wallage Hopper; Publisher: Weser Bros. (New York)https://egrove.olemiss.edu/sharris_b/1028/thumbnail.jp

The complexity of surface acoustic wave fields used for microfluidic applications

Using surface acoustic waves (SAW) for the agitation and manipulation of fluids and immersed particles or cells in lab-on-a-chip systems has been state of the art for several years. Basic tasks comprise fluid mixing, atomization of liquids as well as sorting and separation (or trapping) of particles and cells, e.g. in so-called acoustic tweezers. Even though the fundamental principles governing SAW excitation and propagation on anisotropic, piezoelectric substrates are well-investigated, the complexity of wave field effects including SAW diffraction, refraction and interference cannot be comprehensively simulated at this point of time with sufficient accuracy. However, the design of microfluidic actuators relies on a profound knowledge of SAW propagation, including superposition of multiple SAWs, to achieve the predestined functionality of the devices. Here, we present extensive experimental results of high-resolution analysis of the lateral distribution of the complex displacement amplitude, i.e. the wave field, alongside with the electrical S-parameters of the generating transducers. These measurements were carried out and are compared in setups utilizing travelling SAW (tSAW) excited by single interdigital transducer (IDT), standing SAW generated between two IDTs (1DsSAW, 1D acoustic tweezers) and between two pairs of IDTs (2DsSAW, 2D acoustic tweezers) with different angular alignment in respect to pure Rayleigh mode propagation directions and other practically relevant orientations. For these basic configurations, typically used to drive SAW-based microfluidics, the influence of common SAW phenomena including beam steering, coupling coefficient dispersion and diffraction on the resultant wave field is investigated. The results show how tailoring of the acoustic conditions, based on profound knowledge of the physical effects, can be achieved to finally realize a desired behavior of a SAW-based microacoustic-fluidic system. © 2020 Elsevier B.V

Electronic structure and magnetic properties of the graphene/Fe/Ni(111) intercalation-like system

The electronic structure and magnetic properties of the graphene/Fe/Ni(111) system were investigated via combination of the density functional theory calculations and electron-spectroscopy methods. This system was prepared via intercalation of thin Fe layer (1 ML) underneath graphene on Ni(111) and its inert properties were verified by means of photoelectron spectroscopy. Intercalation of iron in the space between graphene and Ni(111) changes drastically the magnetic response from the graphene layer that is explained by the formation of the highly spin-polarized $3d_{z^2}$ quantum-well state in the thin iron layer.Comment: Manuscript and supplementary material

Electronic correlations and magnetic interactions in infinite-layer NdNiO2

The large antiferromagnetic exchange coupling in the parent high-Tc cuprate superconductors is believed to play a crucial role in pairing the superconducting carriers. The recent observation of superconductivity in hole-doped infinite-layer (IL-) NdNiO2 brings to the fore the relevance of magnetic coupling in high-Tc superconductors, particularly because no magnetic ordering is observed in the undoped IL-NdNiO2, unlike in parent copper oxides. Here, we investigate the electronic structure and the nature of magnetic exchange in IL-NdNiO2 using state-of-the-art many-body quantum chemistry methods. From a systematic comparison of the electronic and magnetic properties with isostructural cuprate IL-CaCuO2, we find that the on-site dynamical correlations are significantly stronger in IL-NdNiO2 compared to the cuprate analog. These dynamical correlations play a critical role in the magnetic exchange resulting in an unexpectedly large antiferromagnetic nearest-neighbor isotropic J of 77 meV between the Ni1+ ions within the ab plane. While we find many similarities in the electronic structure between the nickelate and the cuprate, the role of electronic correlations is profoundly different in the two. We further discuss the implications of our findings in understanding the origin of superconductivity in nickelates. © 2020 authors

Dispersion of a single 4f4f impurity state in photoemission spectra of Yb/W(110)

Angle-resolved photoemission spectra of a monolayer of Yb on W(110) reveal energy splittings and dispersion of the Yb 4f states that are obviously due to their hybridization with W-derived valence bands. These effects occur at well defined points of the surface Brillouin zone although a smearing over reciprocal space is expected from the structural incoherence of the Yb and W lattices. We conclude therefore that dispersion is not related to the periodic arrangement of the $4f$ states but reflects the k-dependent interaction of a single Yb 4f impurity with W bands.Comment: 7 pages, 4 figure