2,325 research outputs found
Structural and electronic properties of Al nanowires: an ab initio pseudopotential study
The stability and electronic structure of a single monatomic Al wire has been
studied using the ab initio pseudopotential method. The Al wire undergoes two
structural rearrangements under compression, i.e., zigzag configurations at
angles of and . The evolution of electronic structures of the Al
chain as a function of structural phase transition has been investigated. The
relationship between electronic structure and geometric stability is also
discussed. The 2p bands in the Al nanowire are shown to play a critical role in
its stability. The effects of density functionals (GGA and LDA) on cohesive
energy and bond length of Al nanostructures (dimmer, chains, and monolayers)
are also examined. The link between low dimensional 0D structure (dimmer) to
high dimensional 3D bulk Al is estimated. An example of optimized tip-suspended
finite atomic chain is presented to bridge the gap between hypothetical
infinite chains and experimental finite chains.Comment: 11 pages, 5 figure
Raman spectroscopy of epitaxial graphene on a SiC substrate
The fabrication of epitaxial graphene (EG) on SiC substrate by annealing has
attracted a lot of interest as it may speed up the application of graphene for
future electronic devices. The interaction of EG and the SiC substrate is
critical to its electronic and physical properties. In this work, Raman
spectroscopy was used to study the structure of EG and its interaction with SiC
substrate. All the Raman bands of EG blue shift from that of bulk graphite and
graphene made by micromechanical cleavage, which was attributed to the
compressive strain induced by the substrate. A model containing 13 x 13
honeycomb lattice cells of graphene on carbon nanomesh was constructed to
explain the origin of strain. The lattice mismatch between graphene layer and
substrate causes the compressive stress of 2.27 GPa on graphene. We also
demonstrate that the electronic structures of EG grown on Si and C terminated
SiC substrates are quite different. Our experimental results shed light on the
interaction between graphene and SiC substrate that are critical to the future
applications of EG.Comment: 20 pages, 5 figure
Experimental observation of the crystallization of a paired holon state
A new excitation is observed at 201 meV in the doped-hole ladder cuprate
SrCuO, using ultraviolet resonance Raman scattering with
incident light at 3.7 eV polarized along the direction of the rungs. The
excitation is found to be of charge nature, with a temperature independent
excitation energy, and can be understood via an intra-ladder pair-breaking
process. The intensity tracks closely the order parameter of the charge density
wave in the ladder (CDW), but persists above the CDW transition
temperature (), indicating a strong local pairing above .
The 201 meV excitation vanishes in LaCaCuO,
and LaCaCuO which are samples with no holes in the
ladders. Our results suggest that the doped holes in the ladder are composite
bosons consisting of paired holons that order below .Comment: Accepted for publication in Physical Review Letters (4 figures
Oxygen Electromigration and Energy Band Reconstruction Induced by Electrolyte Field Effect at Oxide Interfaces
Electrolyte gating is a powerful means for tuning the carrier density and
exploring the resultant modulation of novel properties on solid surfaces.
However, the mechanism, especially its effect on the oxygen migration and
electrostatic charging at the oxide heterostructures, is still unclear. Here we
explore the electrolyte gating on oxygen-deficient interfaces between SrTiO3
(STO) crystals and LaAlO3 (LAO) overlayer through the measurements of
electrical transport, X-ray absorption spectroscopy (XAS) and photoluminescence
(PL) spectra. We found that oxygen vacancies (Ovac) were filled selectively and
irreversibly after gating due to oxygen electromigration at the amorphous
LAO/STO interface, resulting in a reconstruction of its interfacial band
structure. Because of the filling of Ovac, the amorphous interface also showed
an enhanced electron mobility and quantum oscillation of the conductance.
Further, the filling effect could be controlled by the degree of the
crystallinity of the LAO overlayer by varying the growth temperatures. Our
results reveal the different effects induced by electrolyte gating, providing
further clues to understand the mechanism of electrolyte gating on buried
interfaces and also opening a new avenue for constructing high-mobility oxide
interfaces.Comment: 5 figures; Supplementary materials included at the end of the main
tex
EUS assessment for intermediate risk of choledocholithiasis after a negative magnetic resonance cholangiopancreatography
© 2020 SPRING MEDIA PUBLISHING CO. LTD | PUBLISHED BY WOLTERS KLUWER - MEDKNOW 291. Background and Aims: Guidelines recommend either EUS or magnetic resonance cholangiopancreatography (MRCP) for intermediate risk of choledocholithiasis. There is a lack of evidence that supports proceeding with EUS if the MRCP is negative and if clinical suspicion still exists. Methods: This is a retrospective study of all patients who underwent EUS to assess for choledocholithiasis at a tertiary care referral center from July 2013 to October 2019. Results: A total of 593 patients underwent EUS for evaluation for choledocholithiasis. Of the 593 patients, 35.2% (209/593) had an MRCP. 73.2% (153/209) had a negative MRCP while 26.8% (56/209) had a positive MRCP. Of the group of patients who underwent EUS with a negative MRCP, 15% (23/153) were positive for choledocholithiasis on EUS. Of these, 91% (21/23) were also positive for sludge or stones on endoscopic retrograde cholangiopancreatography and thus 14% (21/153) of the EUS were \u27true positives.\u27 There were no clinical or laboratory factors predictive of choledocholithiasis on univariate analysis in the EUS plus negative MRCP group. When further analyzing the MRCP negative group into MRCP-/EUS+ and MRCP-/EUS-subgroups, a total bilirubin \u3e3 mg/dL predicted a bile duct stone (55% vs. 32%, P = 0.05). Conclusion: The diagnostic yield of EUS for suspected choledocholithiasis in the setting of a negative MRCP is 14% in our cohort. EUS should be considered in patients with intermediate risk of choledocholithiasis with a negative MRCP if the clinical suspicion is still present, and especially if the total bilirubin is above 3 mg/dL
Cationic vacancy induced room-temperature ferromagnetism in transparent conducting anatase Ti_{1-x}Ta_xO_2 (x~0.05) thin films
We report room-temperature ferromagnetism in highly conducting transparent
anatase Ti1-xTaxO2 (x~0.05) thin films grown by pulsed laser deposition on
LaAlO3 substrates. Rutherford backscattering spectrometry (RBS), x-ray
diffraction (XRD), proton induced x-ray emission (PIXE), x-ray absorption
spectroscopy (XAS) and time-of-flight secondary ion mass spectrometry
(TOF-SIMS) indicated negligible magnetic contaminants in the films. The
presence of ferromagnetism with concomitant large carrier densities was
determined by a combination of superconducting quantum interference device
(SQUID) magnetometry, electrical transport measurements, soft x-ray magnetic
circular dichroism (SXMCD), XAS, and optical magnetic circular dichroism (OMCD)
and was supported by first-principle calculations. SXMCD and XAS measurements
revealed a 90% contribution to ferromagnetism from the Ti ions and a 10%
contribution from the O ions. RBS/channelling measurements show complete Ta
substitution in the Ti sites though carrier activation was only 50% at 5% Ta
concentration implying compensation by cationic defects. The role of Ti vacancy
and Ti3+ was studied via XAS and x-ray photoemission spectroscopy (XPS)
respectively. It was found that in films with strong ferromagnetism, the Ti
vacancy signal was strong while Ti3+ signal was absent. We propose (in the
absence of any obvious exchange mechanisms) that the localised magnetic
moments, Ti vacancy sites, are ferromagnetically ordered by itinerant carriers.
Cationic-defect-induced magnetism is an alternative route to ferromagnetism in
wide-band-gap semiconducting oxides without any magnetic elements.Comment: 21 pages, 10 figures, to appear in Philosophical Transaction - Royal
Soc.
Direct observation of anisotropic small-hole polarons in an orthorhombic structure of BiVO₄ films
Here, we report an anisotropic small-hole polaron in an orthorhombic structure of BiVO₄ films grown by pulsed-laser deposition on yttrium-doped zirconium oxide substrate. The polaronic state and electronic structure of BiVO₄ films are revealed using a combination of polarization-dependent x-ray absorption spectroscopy at VL[subscript 3,2] edges, spectroscopic ellipsometry, x-ray photoemission spectroscopies, and high-resolution x-ray diffraction with the support of first-principles calculations. We find that in the orthorhombic phase, which is slightly different from the conventional pucherite structure, the unoccupied V 3d orbitals and charge inhomogeneities lead to an anisotropic small-hole polaron state. Our result shows the importance of the interplay of charge and lattice for the formation of a hole polaronic state, which has a significant impact in the electrical conductivity of BiVO₄, hence its potential use as a photoanode for water splitting
Using Tracker as a Pedagogical Tool for Understanding Projectile Motion
This paper reports the use of Tracker as a pedagogical tool in the effective
learning and teaching of projectile motion in physics. When computer model
building learning processes is supported and driven by video analysis data,
this free Open Source Physics (OSP) tool can provide opportunities for students
to engage in active inquiry-based learning. We discuss the pedagogical use of
Tracker to address some common misconceptions of projectile motion by allowing
students to test their hypothesis by juxtaposing their mental models against
the analysis of real life videos. Initial research findings suggest that
allowing learners to relate abstract physics concepts to real life through
coupling computer modeling with traditional video analysis could be an
innovative and effective way to learn projectile motion. 2015 Resources:
http://iwant2study.org/ospsg/index.php/interactive-resources/physics/02-newtonian-mechanics/01-kinematics/174-projectile-motionComment: 9 pages, 9 figures; http://iopscience.iop.org/0031-9120/47/4/44
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