65 research outputs found
Evolution of the interfacial structure of LaAlO3 on SrTiO3
The evolution of the atomic structure of LaAlO3 grown on SrTiO3 was
investigated using surface x-ray diffraction in conjunction with
model-independent, phase-retrieval algorithms between two and five monolayers
film thickness. A depolarizing buckling is observed between cation and oxygen
positions in response to the electric field of polar LaAlO3, which decreases
with increasing film thickness. We explain this in terms of competition between
elastic strain energy, electrostatic energy, and electronic reconstructions.
The findings are qualitatively reproduced by density-functional theory
calculations. Significant cationic intermixing across the interface extends
approximately three monolayers for all film thicknesses. The interfaces of
films thinner than four monolayers therefore extend to the surface, which might
affect conductivity
Unit cell of graphene on Ru(0001): a 25 x 25 supercell with 1250 carbon atoms
The structure of a single layer of graphene on Ru(0001) has been studied
using surface x-ray diffraction. A surprising superstructure has been
determined, whereby 25 x 25 graphene unit cells lie on 23 x 23 unit cells of
Ru. Each supercell contains 2 x 2 crystallographically inequivalent subcells
caused by corrugation. Strong intensity oscillations in the superstructure rods
demonstrate that the Ru substrate is also significantly corrugated down to
several monolayers, and that the bonding between graphene and Ru is strong and
cannot be caused by van der Waals bonds. Charge transfer from the Ru substrate
to the graphene expands and weakens the C-C bonds, which helps accommodate the
in-plane tensile stress. The elucidation of this superstructure provides
important information in the potential application of graphene as a template
for nanocluster arrays.Comment: 9 pages, 3 figures, paper submitted to peer reviewed journa
Electronic and Geometric Corrugation of Periodically Rippled, Self-nanostructured Graphene Epitaxially Grown on Ru(0001)
Graphene epitaxially grown on Ru(0001) displays a remarkably ordered pattern
of hills and valleys in Scanning Tunneling Microscopy (STM) images. To which
extent the observed "ripples" are structural or electronic in origin have been
much disputed recently. A combination of ultrahigh resolution STM images and
Helium Atom diffraction data shows that i) the graphene lattice is rotated with
respect to the lattice of Ru and ii) the structural corrugation as determined
from He diffraction is substantially smaller (0.015 nm) than predicted (0.15
nm) or reported from X-Ray Diffraction or Low Energy Electron Diffraction. The
electronic corrugation, on the contrary, is strong enough to invert the
contrast between hills and valleys above +2.6 V as new, spatially localized
electronic states enter the energy window of the STM. The large electronic
corrugation results in a nanostructured periodic landscape of electron and
holes pockets.Comment: 16 pages, 6 figure
Oxidation of graphene on metals
We use low-energy electron microscopy to investigate how graphene is removed
from Ru(0001) and Ir(111) by reaction with oxygen. We find two mechanisms on
Ru(0001). At short times, oxygen reacts with carbon monomers on the surrounding
Ru surface, decreasing their concentration below the equilibrium value. This
undersaturation causes a flux of carbon from graphene to the monomer gas. In
this initial mechanism, graphene is etched at a rate that is given precisely by
the same non-linear dependence on carbon monomer concentration that governs
growth. Thus, during both growth and etching, carbon attaches and detaches to
graphene as clusters of several carbon atoms. At later times, etching
accelerates. We present evidence that this process involves intercalated
oxygen, which destabilizes graphene. On Ir, this mechanism creates observable
holes. It also occurs mostly quickly near wrinkles in the graphene islands,
depends on the orientation of the graphene with respect to the Ir substrate,
and, in contrast to the first mechanism, can increase the density of carbon
monomers. We also observe that both layers of bilayer graphene islands on Ir
etch together, not sequentially.Comment: 15 pages, 10 figures. Manuscript revised to improve discussion,
following referee comments. Accepted for publication in Journal of Physical
Chemistry C, Feb. 11, 201
Graphene on Ru(0001): A corrugated and chiral structure
We present a structural analysis of the graphene/Ru(0001) system obtained by
surface x-ray diffraction. The data were fit using Fourier-series expanded
displacement fields from an ideal bulk structure, plus the application of
symmetry constraints. The shape of the observed superstructure rods proves a
reconstruction of the substrate, induced by strong bonding of graphene to
ruthenium. Both the graphene layer and the underlying substrate are corrugated,
with peak-to-peak heights of (0.82 +/- 0.15) A and (0.19 +/- 0.02) A for the
graphene and topmost Ru-atomic layer, respectively. The Ru-corrugation decays
slowly over several monolayers into the bulk. The system also exhibits
chirality, whereby in-plane rotations of up to 2.0 degrees in those regions of
the superstructure where the graphene is weakly bound are driven by elastic
energy minimization
B-TURP versus HoLEP. Peri-operative outcomes and complications in frail elderly (>75 y.o.) patients. A prospective randomized study
Background: The aim of this study was to compare the peri-operative and functional results between trans-urethral resection of the prostate (TURP) and holmium laser enucleation of the prostate (HoLEP) in the treatment of benign prostatic hyperplasia (BPH) associated with lower urinary tract symptoms (LUTS) in middle-old patients. Materials and methods: This prospective single-center study included patients over 75 years old treated with B-TURP or HoLEP for BPH associated with LUTS with prostate volume (PV) <100 mL. Primary endpoints were the intra-operative blood loss, percentage of loss of hemoglobin, blood transfusion, complications, and the comparison of functional outcomes. All patients were evaluated at 1, 3, 6, and 12 months of follow-up. Results: Overall, 96 patients undergoing HoLEP and 104 B-TURP were eligible and enrolled for the study. Post-operative results showed statistically significant differences between the two groups, all in favor of HoLEP group, specifically in terms of removed prostate tissue, PV reduction rate, hemoglobin values at 24 h, hemoglobin loss, operative time, length of hospitalization, days of catheterization, and urinary flow rates. There was no significant difference in terms of postvoid residual urine volume, perioperative complication, blood transfusion, International Prostate Symptom Score (IPSS), and IPSS quality of life scores. Conclusions: In middle-old patients, the HoLEP technique represents a prostate size-independent treatment option with a more favorable safety profile defined by less bleeding, lower blood transfusions, and a significantly lower hemoglobin drop than B-TURP
Laser-induced etching of few-layer graphene synthesized by Rapid-Chemical Vapour Deposition on Cu thin films
The outstanding electrical and mechanical properties of graphene make it very
attractive for several applications, Nanoelectronics above all. However a
reproducible and non destructive way to produce high quality, large-scale area,
single layer graphene sheets is still lacking. Chemical Vapour Deposition of
graphene on Cu catalytic thin films represents a promising method to reach this
goal, because of the low temperatures (T < 900 Celsius degrees) involved during
the process and of the theoretically expected monolayer self-limiting growth.
On the contrary such self-limiting growth is not commonly observed in
experiments, thus making the development of techniques allowing for a better
control of graphene growth highly desirable. Here we report about the local
ablation effect, arising in Raman analysis, due to the heat transfer induced by
the laser incident beam onto the graphene sample.Comment: v1:9 pages, 8 figures, submitted to SpringerPlus; v2: 11 pages,
PDFLaTeX, 9 figures, revised peer-reviewed version resubmitted to
SpringerPlus; 1 figure added, figure 1 and 4 replaced,typos corrected,
"Results and discussion" section significantly extended to better explain
etching mechanism and features of Raman spectra, references adde
Size Quantization in Planar Graphene-Based Heterostructures: Pseudospin Splitting, Interface States, and Excitons
A planar quantum-well device made of a gapless graphene nanoribbon with edges
in contact with gapped graphene sheets is examined. The size-quantization
spectrum of charge carriers in an asymmetric quantum well is shown to exhibit a
pseudospin splitting. Interface states of a new type arise from the crossing of
dispersion curves of gapless and gapped graphene materials. The exciton
spectrum is calculated for a planar graphene quantum well. The effect of an
external electric field on the exciton spectrum is analyzed.Comment: 15 pages, 14 figure
Characteristics and patterns of care of endometrial cancer before and during COVID-19 pandemic
Objective: Coronavirus disease 2019 (COVID-19) outbreak has correlated with the disruption of screening activities and diagnostic assessments. Endometrial cancer (EC) is one of the most common gynecological malignancies and it is often detected at an early stage, because it frequently produces symptoms. Here, we aim to investigate the impact of COVID-19 outbreak on patterns of presentation and treatment of EC patients. Methods: This is a retrospective study involving 54 centers in Italy. We evaluated patterns of presentation and treatment of EC patients before (period 1: March 1, 2019 to February 29, 2020) and during (period 2: April 1, 2020 to March 31, 2021) the COVID-19 outbreak. Results: Medical records of 5,164 EC patients have been retrieved: 2,718 and 2,446 women treated in period 1 and period 2, respectively. Surgery was the mainstay of treatment in both periods (p=0.356). Nodal assessment was omitted in 689 (27.3%) and 484 (21.2%) patients treated in period 1 and 2, respectively (p<0.001). While, the prevalence of patients undergoing sentinel node mapping (with or without backup lymphadenectomy) has increased during the COVID-19 pandemic (46.7% in period 1 vs. 52.8% in period 2; p<0.001). Overall, 1,280 (50.4%) and 1,021 (44.7%) patients had no adjuvant therapy in period 1 and 2, respectively (p<0.001). Adjuvant therapy use has increased during COVID-19 pandemic (p<0.001). Conclusion: Our data suggest that the COVID-19 pandemic had a significant impact on the characteristics and patterns of care of EC patients. These findings highlight the need to implement healthcare services during the pandemic
h-BN on Rh(1 1 1): Persistence of a commensurate 13-on-12 superstructure up to high temperatures
We present a high-resolution surface X-ray diffraction study of hexagonal boron nitride (h-BN) on the surface of Rh(1 1 1). The previously observed commensurate 13-on-12 superstructure for this system is stable in the temperature range between room temperature and 830 °C. Surface X-ray diffraction measurements up to 830 °C on the superstructure show no sign of a shift towards a different superstructure, demonstrating the high thermal stability and strong bonding between film and substrate. At lower temperatures, an anomalous thermal expansion behaviour of the topmost surface region of rhodium is observed, where the rhodium in-plane lattice constant remains invariant. This can be explained by the (h-BN) single-layer being compressively strained, whereby the strong bonding to the substrate causes the latter to be tensile strained
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