Evidence of microphase separation in controlled pore glasses

The phase separation of a mixture of water and isobutyric acid (iBA) confined in the pore space of Controlled Pore Glass (CPG) 10-75 has been studied by ¹H NMR relaxometry and ¹H-pulsed field gradient (PFG) diffusion measurements. For an acid-rich mixture (mass fraction 54 wt% iBA), evidence of a phase separation process in the pores was obtained, which occurs in a temperature window between 32 and 39 °C, as indicated in the PFG data by an anomalous temperature dependence of the diffusion coefficient and in the relaxation data by a bi-exponential magnetization decay. The phase separation temperature of the mixture in the pore is slightly lower than in the bulk mixture of the same composition (41 °C) and extends over a finite temperature range. A qualitative model of the phase separation process in the pores is developed, which assumes a temperature-dependent domain-like structure of the liquid below the phase transition temperature and a breakdown of these domains upon reaching the transition temperature.     

Formation of ultrathin iron magnetic films on the silicon vicinal surface

Physics of the Solid State - The phase composition, electronic structure, and magnetic properties of ultrathin layers of iron and iron silicides formed upon deposition of 1- to 25-Å-thick Fe...     

Quantum-well states in bilayers of Ag and Au on W(1 1 0)

sp-Like quantum-well states (QWS) in thin monocrystalline bilayer films of Ag and Au on W(1 1 0) and of single Ag films were studied by angle-resolved photoemission. We find that the propagation of the electronic states in the bilayer films along [1 1 1] depends on the energy relative to the band edge of Au metal at the L point of the Brillouin zone. In particular, QWS with binding energies less than this band-edge energy (1.1 eV) are strongly confined to the Ag layer, while for higher binding energies the QWS extend across the whole bilayer film. This clearly demonstrates the weakness of the potential barrier at the Ag/Au interface in the context of QWS formation at energies where electronic states exist in both metals.     

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Medical application of synchrotron radiation (SR) is a fast-growing field of research. Since the advent of the angiography studies at SSRL first and then at NSLS in the U.S. in the 1990s, preclinical and clinical research protocols have been developed at Hasylab (Germany), Photon Factory (Japan), ELETTRA (Italia) and at the ESRF (France). Despite the fact that there are only a few dedicated beamlines in the world (two new ones are under construction at the Australian and Canadian synchrotrons), medical research is carried out in almost all synchrotron facilities.     

Charge order and low frequency spin dynamics in lanthanum cuprates revealed by Nuclear Magnetic Resonance

We report detailed ¹⁷O, ¹³⁹La, and ^63,65Cu Nuclear Magnetic Resonance (NMR) and Nuclear Quadrupole Resonance (NQR) measurements in a stripe ordered La_1.875Ba_0.125CuO₄ single crystal and in oriented powder samples of La_1.8−x Eu_0.2Sr _x CuO₄. We observe a partial wipeout of the ¹⁷O NMR intensity and a simultaneous drop of the ¹⁷O electric field gradient (EFG) at low temperatures where the spin stripe order sets in. In contrast, the ^63,65Cu intensity is completely wiped out at the same temperature. The drop of the ¹⁷O quadrupole frequency is compatible with a charge stripe order. The ¹⁷O spin lattice relaxation rate shows a peak similar to that of the ¹³⁹La, which is of magnetic origin. This peak is doping dependent and is maximal at x ≈ 1/8.     

A comparative study of argon ion irradiated pristine and fluorinated single-wall carbon nanotubes

Effect of Ar(+) ion irradiation on the structure of pristine and fluorinated single-wall carbon nanotubes (SWCNTs) was examined using transmission electron microscopy (TEM), Raman, and x-ray photoelectron spectroscopy (XPS). The TEM analysis revealed retention of tubular structures in both irradiated samples while Raman spectroscopy and XPS data indicated a partial destruction of nanotubes and formation of oxygen-containing groups on the nanotube surface. From similarity of electronic states of carbon in the irradiated pristine and fluorinated SWCNTs observed by XPS, it was suggested that defluorination of nanotubes proceeded with breaking of C-F bonds.     

Controllable p-doping of graphene on Ir(111) by chlorination with FeCl3

The in situ chlorination of graphene on Ir(111) has been achieved by depositing FeCl(3) followed by its thermal decomposition on the surface into FeCl(2) and Cl. This process is accompanied by an intercalation of Cl under graphene and formation of an epitaxial FeCl(2) film on top, which can be removed upon further annealing. A pronounced hole doping of graphene has been observed as a consequence of the annealing-assisted intercalation of Cl. This effect has been studied by a combination of core-level and angle-resolved photoelectron spectroscopies (CL PES and ARPES, respectively), near-edge x-ray absorption fine structure (NEXAFS) spectroscopy and low-energy electron diffraction (LEED). The ease of preparation, the remarkable reproducibility of the doping level and the reversibility of the doping upon annealing are the key factors making chlorination with FeCl(3) a promising route for tuning the electronic properties in graphene.     

Electronic structure of pristine CuPc: Experiment and calculations

The filled and unoccupied electronic states of the organic semiconductor copper-phthalocyanine (CuPc) have been determined by a combination of direct and resonant photoemission, near-edge X-ray absorption and first principles calculations. The experimentally obtained electronic states of CuPc are in very good agreement with results of ab initio density of states, allowing to derive detailed site specific information.     

Formation of sharp metal-organic semiconductor interfaces: Ag and Sn on CuPc

A detailed investigation of the chemistry and electronic structure during the formation of the interfaces between thin films of the archetypal organic molecular semiconductor copper phthalocyanine (CuPc) and Ag or Sn deposited on it was performed using photoemission and near-edge X-ray absorption spectroscopies with synchrotron light. Our study demonstrates the formation of sharp, abrupt interfaces, a behavior which is of particular importance for applications in organic devices. Moreover, for Ag on CuPc we demonstrate that this interface is free from any reaction, whereas there is slight interface reaction for Sn/CuPc.     

Photoemission experiments and density functional calculations for the W(1 1 2) stepped surface with submonolayer Au coverages

Photoemission experiments and theoretical calculations for the system Au-stepped W(1 1 2), have been done at submonolayer coverage region ranging from 0.1 to 0.9 monolayers, for different sample orientations relative to the photon polarization, i.e. parallel and perpendicular to the steps direction. Valence-band photoemission spectra of the Au/W(1 1 2) system demonstrate sharp angular dependent features at 4.5 and 0.3 eV binding energies when the photon polarization is parallel to the steps direction. Density functional theory calculations were performed for the Au/W(1 1 2) system with monolayer and half monolayer Au coverages in order to assign the origin of these features.