Tellurium (Te) films with monolayer and few-layer thickness are obtained by molecular beam epitaxy on a graphene/6H-SiC(0001) substrate and investigated by in situ scanning tunneling microscopy and ...spectroscopy (STM/STS). We reveal that the Te films are composed of parallel-arranged helical Te chains flat-lying on the graphene surface, exposing the (1 × 1) facet of (101̅0) of the bulk crystal. The band gap of Te films increases monotonically with decreasing thickness, reaching the near-infrared band for the monolayer Te. An explicit band bending at the edge between the monolayer Te and graphene substrate is visualized. With the thickness controlled in the atomic scale, Te films show potential applications of electronics and optoelectronics.
The concept of a charge density wave (CDW) permeates much of condensed matter physics and chemistry. CDWs have their origin rooted in the instability of a one-dimensional system described by Peierls. ...The extension of this concept to reduced dimensional systems has led to the concept of Fermi surface nesting (FSN), which dictates the wave vector (
q
→
CDW
) of the CDW and the corresponding lattice distortion. The idea is that segments of the Fermi contours are connected by
q
→
CDW
, resulting in the effective screening of phonons inducing Kohn anomalies in their dispersion at
q
→
CDW
, driving a lattice restructuring at low temperatures. There is growing theoretical and experimental evidence that this picture fails in many real systems and in fact it is the momentum dependence of the electron–phonon coupling (EPC) matrix element that determines the characteristic of the CDW phase. Based on the published results for the prototypical CDW system 2H-NbSe₂, we show how well the
q
→
-dependent EPC matrix element, but not the FSN, can describe the origin of the CDW. We further demonstrate a procedure of combing electronic band and phonon measurements to extract the EPC matrix element, allowing the electronic states involved in the EPC to be identified. Thus, we show that a large EPC does not necessarily induce the CDW phase, with Bi₂Sr₂CaCu₂O8+δas the example, and the charge-ordered phenomena observed in various cuprates are not driven by FSN or EPC. To experimentally resolve the microscopic picture of EPC will lead to a fundamental change in the way we think about, write about, and classify charge density waves.
Monolayer molybdenum disulfide (MoS2) has attracted great interest due to its potential applications in electronics and optoelectronics. Ideally, single-crystal growth over a large area is necessary ...to preserve its intrinsic figure of merit but is very challenging to achieve. Here, we report an oxygen-assisted chemical vapor deposition method for growth of single-crystal monolayer MoS2. We found that the growth of MoS2 domains can be greatly improved by introducing a small amount of oxygen into the growth environment. Triangular monolayer MoS2 domains can be achieved with sizes up to ∼350 μm and a room-temperature mobility up to ∼90 cm2/(V·s) on SiO2. The role of oxygen is not only to effectively prevent the poisoning of precursors but also to eliminate defects during the growth. Our work provides an advanced method for high-quality single-crystal monolayer MoS2 growth.
Abstract
Enormous enhancement of superconducting pairing temperature (
T
g
) to 65 K in FeSe/SrTiO
3
has made it a spotlight. Despite the effort of interfacial engineering, FeSe interfaced with TiO
x
...remains the unique case in hosting high
T
g
, hindering a decisive understanding on the general mechanism and ways to further improving
T
g
. Here we constructed a new high-
T
g
interface, single-layer FeSe interfaced with FeO
x
-terminated LaFeO
3
. Large superconducting gap and diamagnetic response evidence that the superconducting pairing can emerge near 80 K, highest amongst all-known interfacial superconductors. Combining various techniques, we reveal interfacial charge transfer and strong interfacial electron-phonon coupling (EPC) in FeSe/LaFeO
3
, showing that the cooperative pairing mechanism works beyond FeSe-TiO
x
. Intriguingly, the stronger interfacial EPC than that in FeSe/SrTiO
3
is likely induced by the stronger interfacial bonding in FeSe/LaFeO
3
, and can explain the higher
T
g
according to recent theoretical calculations, pointing out a workable route in designing new interfaces to achieve higher
T
g
.
The d-band-filling of transition metals in complex oxides plays an essential role in determining their structural, electronic and magnetic properties. Traditionally, at the oxide heterointerface, ...band-filling control has been achieved via electrostatic modification in the structure of field-effect transistors or electron transfer, which is limited to the quasi-two-dimension at the interface. Here we report a three-dimensional (3D) band-filling control by changing the local lattice coordination in a designed oxide heterostructure. At the LaCoO
/LaTiO
heterointerface, due to the Fermi level mismatch, electrons transfer from LaTiO
to LaCoO
. This triggers destabilisation of the CoO
octahedrons, i.e. the formation of lattice configurations with a reduced Co valence. The associated oxygen migration results in the 3D topotactic phase transition of LaCoO
. Tuned by the thickness of LaTiO
, different crystalline phases and band-fillings of Co occur, leading to the emergence of different magnetic ground states.
Directed C–H functionalization of heterocycles through an exocyclic directing group (DG) is challenging due to the interference of the endocyclic heteroatom(s). Recently, the “heteroatom problem” was ...circumvented with the development of the protection-free Pd-catalyzed aerobic C–H functionalization of heterocycles guided by an exocyclic CONHOMe DG. We herein provide DFT mechanistic insights to facilitate the expansion of the strategy. The transformation proceeds as follows. First, the Pd2(dba)3 precursor interacts with t-BuNC (L, one of the substrates) and O2 to form the L2Pd(II)-η2-O2 peroxopalladium(II) species that can selectively oxidize N-methoxy amide (e.g., PyCONHOMe) substrate, giving an active L2Pd(II)X2 (X = PyCONOMe) species and releasing H2O2. After t-BuNC ligand migratory insertion followed by a 1,3-acyl migration and association with another t-BuNC, L2Pd(II)X2 converts to a more stable C-amidinyl L2Pd(II)XX′ (X′ = PyCON(t-Bu)CNOMe) species. Finally, L2Pd(II)XX′ undergoes C–H activation and C–C reductive elimination, affording the product. The C–H activation is the rate-determining step. The success of the strategy has three origins: (i) the N-methoxy amide DG can be easily oxidized in situ to generate the active L2Pd(II)X2 species via the oxidase pathway, thus preventing the destructive oxygenase pathway leading to stable t-BuNCO or the O-bridged dimeric Pd(II) species. The methoxy group in this amide DG greatly facilitates the oxidase pathway, and the tautomerization of N-methoxy amide to its imidic acid tautomer makes the oxidation of the substrate even easier. (ii) The X group in L2Pd(II)X2 can serve as an internal base to promote the C–H activation via CMD (concerted metalation-deprotonation) mechanism. (iii) The strong coordination ability of t-BuNC substrate/ligand suppresses the conventional cyclopalladation pathway enabled by the coordination of an endocyclic heteroatom to the Pd-center.
Charge density wave (CDW) is an important concept in condensed matter physics, germane to a number of physical phenomena. But the origin of CDW is still under debate, partly because the origin and ...properties of CDW are highly material-dependent. The concept of a CDW has been applied to many materials without a clear definition of the fundamental nature of CDW. As a result, misconceptions about CDW can be seen in the literature. In this review, we will try to describe and explain the possible existing misconceptions associated with the origin of CDWs.
To investigate the individualized survival benefit of hepatic arterial infusion chemotherapy (HAIC) and sequential ablation treatment in large hepatocellular carcinoma (HCC) patients.
Between ...February 2016 and December 2020, a total of 228 HCC patients (diameter > 5 cm) who underwent HAIC alone (HAIC group, n = 135) or HAIC and sequential ablation (HAIC-ablation group, n = 93) treatment were reviewed. We applied the inverse probability of treatment weighting (IPTW) to adjust for potential bias of two treatment groups. The overall survival (OS) and progression-free survival (PFS) were compared with Kaplan-Meier curves. The Cox regression model was used to identify independent prognostic factors. And a prediction nomogram based on these independent prognostic factors was built, aiming to make probabilistic survival predictions and estimate personalized ablation benefits.
After a median follow-up of 17.9 months, HCC patients in the HAIC-ablation group have longer significantly OS and PFS than those in the HAIC alone group (median OS: 22.2 months vs. 14.5 months; median PFS: 8.5 months vs. 4.6 months; both, p < 0.001). The IPTW-adjusted analysis revealed similar findings (both, p < 0.001). Tumor size, tumor number, and treatment modality were identified as independent prognostic factors for OS. The nomogram based on these factors showed favorable discrimination and well calibration.
HAIC and sequential ablation provided significant survival benefits in patients with large HCC. The nomogram could help predict individual survival probabilities and estimate personalized sequential ablation benefits.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
In many realistic topological materials, more than one kind of fermions contribute to the electronic bands crossing the Fermi level, leading to various novel phenomena. Here, using momentum-resolved ...inelastic electron scattering, we investigate the plasmons and their evolution across the phase transition in a type-II Weyl semimetal MoTe2, in which both Weyl fermions and trivial electrons contribute to the Fermi surface in the Td phase. One plasmon mode in the 1T′ phase at high temperature and two plasmon modes in the topological Td phase at low temperature are observed. Combining with first-principles calculations, we show that all the plasmon modes are dominated by the interband correlations between the inverted bands of MoTe2. Especially in the Td phase, since the electronic bands split due to inversion symmetry breaking and spin-orbit coupling, the plasmon modes manifest the interband correlation between the topological Weyl fermions and the trivial electrons. Our work emphasizes the significance of the interplay between different kinds of carriers in plasmons of topological materials.
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