66 research outputs found
Phase transitions in two dimensions - the case of Sn adsorbed on Ge(111) surfaces
Accurate atomic coordinates of the room-temperature (root3xroot3)R30degree
and low-temperature (3x3) phases of 1/3 ML Sn on Ge(111) have been established
by grazing-incidence x-ray diffraction with synchrotron radiation. The Sn atoms
are located solely at T4-sites in the (root3xroot3)R30degree structure. In the
low temperature phase one of the three Sn atoms per (3x3) unit cell is
displaced outwards by 0.26 +/- 0.04 A relative to the other two. This
displacement is accompanied by an increase in the first to second double-layer
spacing in the Ge substrate.Comment: RevTeX, 5 pages including 2 figure
Determination of the (3x3)-Sn/Ge(111) structure by photoelectron diffraction
At a coverage of about 1/3 monolayer, Sn deposited on Ge(111) below 550 forms
a metastable (sqrt3 x sqrt3)R30 phase. This phase continuously and reversibly
transforms into a (3x3) one, upon cooling below 200 K. The photoemission
spectra of the Sn 4d electrons from the (3x3)-Sn/Ge(111) surface present two
components which are attributed to inequivalent Sn atoms in T4 bonding sites.
This structure has been explored by photoelectron diffraction experiments
performed at the ALOISA beamline of the Elettra storage ring in Trieste
(Italy). The modulation of the intensities of the two Sn components, caused by
the backscattering of the underneath Ge atoms, has been measured as a function
of the emission angle at fixed kinetic energies and viceversa. The bond angle
between Sn and its nearest neighbour atoms in the first Ge layer (Sn-Ge1) has
been measured by taking polar scans along the main symmetry directions and it
was found almost equivalent for the two components. The corresponding bond
lengths are also quite similar, as obtained by studying the dependence on the
photoelectron kinetic energy, while keeping the photon polarization and the
collection direction parallel to the Sn-Ge1 bond orientation (bond emission). A
clear difference between the two bonding sites is observed when studying the
energy dependence at normal emission, where the sensitivity to the Sn height
above the Ge atom in the second layer is enhanced. This vertical distance is
found to be 0.3 Angstroms larger for one Sn atom out of the three contained in
the lattice unit cell. The (3x3)-Sn/Ge(111) is thus characterized by a
structure where the Sn atom and its three nearest neighbour Ge atoms form a
rather rigid unit that presents a strong vertical distortion with respect to
the underneath atom of the second Ge layer.Comment: 10 pages with 9 figures, added reference
The Impact of Formulation on Lutein, Zeaxanthin, and meso-Zeaxanthin Bioavailability: A Randomised Double-Blind Placebo-Controlled Study
peer-reviewedLutein (L), zeaxanthin (Z), and meso-zeaxanthin (MZ) have been the focus of research and commercial interest for their applications in human health. Research into formulations to enhance their bioavailability is merited. This 6 month randomised placebo-controlled trial involving 81 healthy volunteers compared the bioavailability of different formulations of free L, Z, and MZ in sunflower or omega-3 oil versus L, Z, and MZ diacetates (Ld, Zd, and MZd) in a micromicellar formulation. Fasting serum carotenoids, macular pigment, and skin carotenoid score were analysed at baseline and 6 months. Serum L, Z, and MZ concentrations increased in all active interventions compared to placebo (p < 0.001 to p = 0.008). The diacetate micromicelle formulation exhibited a significantly higher mean response in serum concentrations of Z and MZ compared to the other active interventions (p = 0.002 to 0.019). A micromicellar formulation with solubilised Z and MZ diacetates is a promising technology advancement that enhances the bioavailability of these carotenoids when compared to traditional carotenoid formulations (ISRCTN clinical trial registration number: ISRCTN18206561
Morphometric Cluster Analysis of Sibling NG2-Cells in the Cortex and Proteomic Changes in Two Experimental Models of Multiple Sclerosis
Competing charge ordering and Mott phases in a correlated Sn/Ge(111) two-dimensional triangular lattice
A neuronal migratory pathway crossing from diencephalon to telencephalon populates amygdala nuclei
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