4,628 research outputs found
The Mn site in Mn-doped Ga-As nanowires: an EXAFS study
We present an EXAFS study of the Mn atomic environment in Mn-doped GaAs
nanowires. Mn doping has been obtained either via the diffusion of the Mn used
as seed for the nanowire growth or by providing Mn during the growth of
Au-induced wires. As a general finding, we observe that Mn forms chemical bonds
with As but is not incorporated in a substitutional site. In Mn-induced GaAs
wires, Mn is mostly found bonded to As in a rather disordered environment and
with a stretched bond length, reminiscent of that exhibited by MnAs phases. In
Au-seeded nanowires, along with stretched Mn-As coordination we have found the
presence of Mn in a Mn-Au intermetallic compound.Comment: This is an author-created, un-copyedited version of an article
accepted for publication in Semiconductor Science and Technology. IOP
Publishing Ltd is not responsible for any errors or omissions in this version
of the manuscript or any version derived from it. The definitive
publisher-authenticated version is available online at
doi:10.1088/0268-1242/27/8/08500
Step by step capping and strain state of GaN/AlN quantum dots studied by grazing incidence diffraction anomalous fine structure
The investigation of small size embedded nanostructures, by a combination of
complementary anomalous diffraction techniques, is reported. GaN Quantum Dots
(QDs), grown by molecular beam epitaxy in a modified Stranski-Krastanow mode,
are studied in terms of strain and local environment, as a function of the AlN
cap layer thickness, by means of grazing incidence anomalous diffraction. That
is, the X-ray photons energy is tuned across the Ga absorption K-edge which
makes diffraction chemically selective. Measurement of \textit{hkl}-scans,
close to the AlN (30-30) Bragg reflection, at several energies across the Ga
K-edge, allows the extraction of the Ga partial structure factor, from which
the in-plane strain of GaN QDs is deduced. From the fixed-Q energy-dependent
diffracted intensity spectra, measured for diffraction-selected iso-strain
regions corresponding to the average in-plane strain state of the QDs,
quantitative information regarding composition and the out-of-plane strain has
been obtained. We recover the in-plane and out-of-plane strains in the dots.
The comparison to the biaxial elastic strain in a pseudomorphic layer indicates
a tendency to an over-strained regime.Comment: submitted to PR
Archaeometric studies at the GILDA beamline at the European Synchrotron Radiation Facility
In the latest years archaeometry scientists have directed a growing interest to synchrotron radiation techniques. The Italian CRG beamline GILDA at the European Synchrotron Radiation Facility provides to the users the access to
experimental techniques like X-ray absorption spectroscopy and diffraction that are of great potential usefulness in this field. Here we give a technical overview of the
instrumentation available as well as some examples among the archaeometry studies presently in progress on the beamline
Ab initio analysis of the x-ray absorption spectrum of the myoglobin-carbon monoxide complex: Structure and vibrations
We present a comparison between Fe K-edge x-ray absorption spectra of
carbonmonoxy-myoglobin and its simulation based on density-functional theory
determination of the structure and vibrations and spectral simulation with
multiple-scattering theory. An excellent comparison is obtained for the main
part of the molecular structure without any structural fitting parameters. The
geometry of the CO ligand is reliably determined using a synergic approach to
data analysis. The methodology underlying this approach is expected to be
especially useful in similar situations in which high-resolution data for
structure and vibrations are available.Comment: 13 pages, 3 figure
Ferromagnetism in 2p Light Element-Doped II-oxide and III-nitride Semiconductors
II-oxide and III-nitride semiconductors doped by nonmagnetic 2p light
elements are investigated as potential dilute magnetic semiconductors (DMS).
Based on our first-principle calculations, nitrogen doped ZnO, carbon doped
ZnO, and carbon doped AlN are predicted to be ferromagnetic. The ferromagnetism
of such DMS materials can be attributed to a p-d exchange-like p-p coupling
interaction which is derived from the similar symmetry and wave function
between the impurity (p-like t_2) and valence (p) states. We also propose a
co-doping mechanism, using beryllium and nitrogen as dopants in ZnO, to enhance
the ferromagnetic coupling and to increase the solubility and activity
GaAs:Mn nanowires grown by molecular beam epitaxy of (Ga,Mn)As at MnAs segregation conditions
GaAs:Mn nanowires were obtained on GaAs(001) and GaAs(111)B substrates by
molecular beam epitaxial growth of (Ga,Mn)As at conditions leading to MnAs
phase separation. Their density is proportional to the density of catalyzing
MnAs nanoislands, which can be controlled by the Mn flux and/or the substrate
temperature. Being rooted in the ferromagnetic semiconductor (Ga,Mn)As, the
nanowires combine one-dimensional properties with the magnetic properties of
(Ga,Mn)As and provide natural, self assembled structures for nanospintronics.Comment: 13 pages, 6 figure
The effect of long-range order on intermolecular interactions in organic semiconductors: Zinc octaethyl porphyrin molecular thin film model systems
Domestication, diversity and use of Brassica oleracea L., based on ancient Greek and Latin texts
The domestication process of Brassica oleracea L. has not been fully clarified, either regarding its initial location or the progenitor species involved. Two alternative hypotheses proposed so far point to either a northwest European or a Mediterranean location. Previous studies to clarify the domestication process focused on linguistic aspects and on the earliest occurrences in ancient literature of words referring to B. oleracea. Those studies are here extended to offer a comprehensive account of literary occurrences of the brassica vegetables in ancient Greek and Latin texts, between the VI century B.C.E. and the IV century C.E. This study offers a contribution to ancient ethnobotanical knowledge in the Mediterranean, including agricultural practices and culinary and medicinal uses. It also defines the time when increasing diversity of crop varieties is documented and it adds weight to the hypothesis of a Mediterranean location of the domestication of B. oleracea
Measurement of charged and neutral current e-p deep inelastic scattering cross sections at high Q2
Deep inelastic e-p scattering has been studied in both the charged current (CC) and neutral current (NC) reactions at momentum transfers squared Q2 above 400 GeV2 using the ZEUS detector at the HERA ep collider. The CC and NC total cross sections, the NC to CC cross section ratio, and the differential cross sections d/dQ2 are presented. From the Q2 dependence of the CC cross section, the mass term in the CC propagator is determined to be MW=76 16 13 GeV. © 1995 The American Physical Society
Measurement of Elastic Υ Photoproduction at HERA
The photoproduction reaction γp → μ+ μ-p has been studied in ep interactions using the ZEUS detector at HERA. The data sample corresponds to an integrated luminosity of 43.2pb-1. The Υ meson has been observed in photoproduction for the first time. The sum of the products of the elastic Υ(1S), Υ(2S),Υ(3S) photoproduction cross sections with their respective branching ratios is determined to be 13.3 ± 6.0(stat.)-2.3+2.7(syst.) pb at a mean photon-proton centre of mass energy of 120 GeV. The cross section is above the prediction of a perturbative QCD model. © 1998 Elsevier Science B.V. All rights reserved
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