Transition metal dichalcogenides (TMDs) possess spin-valley locking and spin-split K/K′ valleys, which have led to many fascinating physical phenomena. However, the electronic structure of TMDs also ...exhibits other conduction band minima with similar properties, the Q/Q′ valleys. The intervalley K–Q scattering enables interesting physical phenomena, including multivalley superconductivity, but those effects are typically hindered in monolayer TMDs due to the large K–Q energy difference (ΔE KQ). To unlock elusive multivalley phenomena in monolayer TMDs, it is desirable to reduce ΔE KQ, while being able to sensitively probe the valley shifts and the multivalley scattering processes. Here, we use high pressure to tune the electronic properties of monolayer MoS2 and WSe2 and probe K–Q crossing and multivalley scattering via double-resonance Raman (DRR) scattering. In both systems, we observed a pressure-induced enhancement of the double-resonance LA and 2LA Raman bands, which can be attributed to a band gap opening and ΔE KQ decrease. First-principles calculations and photoluminescence measurements corroborate this scenario. In our analysis, we also addressed the multivalley nature of the DRR bands for WSe2. Our work establishes the DRR 2LA and LA bands as sensitive probes of strain-induced modifications to the electronic structure of TMDs. Conversely, their intensity could potentially be used to monitor the presence of compressive or tensile strain in TMDs. Furthermore, the ability to probe K–K′ and K–Q scattering as a function of strain shall advance our understanding of different multivalley phenomena in TMDs such as superconductivity, valley coherence, and valley transport.
Despite the advanced stage of diamond thin-film technology, with applications ranging from superconductivity to biosensing, the realization of a stable and atomically thick two-dimensional diamond ...material, named here as diamondene, is still forthcoming. Adding to the outstanding properties of its bulk and thin-film counterparts, diamondene is predicted to be a ferromagnetic semiconductor with spin polarized bands. Here, we provide spectroscopic evidence for the formation of diamondene by performing Raman spectroscopy of double-layer graphene under high pressure. The results are explained in terms of a breakdown in the Kohn anomaly associated with the finite size of the remaining graphene sites surrounded by the diamondene matrix. Ab initio calculations and molecular dynamics simulations are employed to clarify the mechanism of diamondene formation, which requires two or more layers of graphene subjected to high pressures in the presence of specific chemical groups such as hydroxyl groups or hydrogens.The synthesis of two-dimensional diamond is the ultimate goal of diamond thin-film technology. Here, the authors perform Raman spectroscopy of bilayer graphene under pressure, and obtain spectroscopic evidence of formation of diamondene, an atomically thin form of diamond.
We apply first-principles calculations to address the problem of the formation and characterization of covalently linked porphyrin-like structures. We show that upon pressure a rehybridization ...process takes place which leads to one-dimensional compounds resembling nanothreads, in which carbon atoms are all 4-fold coordinated. We also show that the resulting nanostructures have metallic character and possess remarkable mechanical properties. Moreover, in the case of porphyrin–metal complexes, we find that the covalently linked structures may be a platform for the stabilization of straight metallic wires.
FOCUS (Fast Monte CarlO approach to Coherence of Undulator Sources) is a new GPU‐based simulation code to compute the transverse coherence of undulator radiation from ultra‐relativistic electrons. ...The core structure of the code, which is written in the language C++ accelerated with CUDA, combines an analytical description of the emitted electric fields and massively parallel computations on GPUs. The combination is rigorously justified by a statistical description of synchrotron radiation based on a Fourier optics approach. FOCUS is validated by direct comparison with multi‐electron Synchrotron Radiation Workshop (SRW) simulations, evidencing a reduction in computation times by up to five orders of magnitude on a consumer laptop. FOCUS is then applied to systematically study the transverse coherence in typical third‐ and fourth‐generation facilities, highlighting peculiar features of undulator sources close to the diffraction limit. FOCUS is aimed at fast evaluation of the transverse coherence of undulator radiation as a function of the electron beam parameters, to support and help prepare more advanced and detailed numerical simulations with traditional codes like SRW.
FOCUS (Fast Monte CarlO approach to Coherence of Undulator Sources), a new GPU‐based code to compute the transverse coherence of X‐ray radiation from undulator sources as a function of the electron beam parameters, is described. FOCUS is validated with the Synchrotron Radiation Workshop (SRW) and SPECTRA codes. Examples of application to coherence studies in third‐ and fourth‐generation light sources are shown.
Crossed Nanotube Junctions Fuhrer, M. S.; Nygård, J.; Shih, L. ...
Science (American Association for the Advancement of Science),
04/2000, Letnik:
288, Številka:
5465
Journal Article
Recenzirano
Junctions consisting of two crossed single-walled carbon nanotubes were fabricated with electrical contacts at each end of each nanotube. The individual nanotubes were identified as metallic (M) or ...semiconducting (S), based on their two-terminal conductances; MM, MS, and SS four-terminal devices were studied. The MM and SS junctions had high conductances, on the order of 0.1 e2/h (where e is the electron charge and h is Planck's constant). For an MS junction, the semiconducting nanotube was depleted at the junction by the metallic nanotube, forming a rectifying Schottky barrier. We used two- and three-terminal experiments to fully characterize this junction.
We probe electron and hole mobilities in bilayer graphene under exposure to molecular oxygen. We find that the adsorbed oxygen reduces electron mobilities and increases hole mobilities in a ...reversible and activated process. Our experimental results indicate that hole mobilities increase due to the screening of long-range scatterers by oxygen molecules trapped between the graphene and the substrate. First principle calculations show that oxygen molecules induce resonant states close to the charge neutrality point. Electron coupling with such resonant states reduces the electron mobilities, causing a strong asymmetry between electron and hole transport. Our work demonstrates the importance of short-range scattering due to adsorbed species in the electronic transport in bilayer graphene on SiO2 substrates.
In this work we apply first principles calculations to investigate the flat band phenomenology in twisted antimonene bilayer. We show that the relatively strong interlayer interactions which ...characterize this compound have profound effects in the emergence and properties of the flat bands. Specifically, when the moiré length becomes large enough to create well defined stacking patterns along the structure, out-of-plane displacements take place and are stabilized in the regions dominated by the AB stacking, leading to the emergence of flat bands. The interplay between structural and electronic properties allows for detection of flat bands in higher twist angles comparable to other two-dimensional materials. We also show that their energy position may be modulated by noncovalent functionalization with electron acceptor molecules.
Strong interlayer interactions allows for electron localization and emergence of flat bands in relatively higher twist angles in Sb bilayer. Noncovalent functionalization with electron acceptor molecules may modulate their energy position.
The goal of the first phase of the AWAKE 1,2 experiment at CERN is to measure the self-modulation 3 of the σz=12cm long SPS proton bunch into microbunches after traversing 10m of plasma with a plasma ...density of npe=7×1014electrons/cm3. The two screen measurement setup 4 is a proton beam diagnostic that can indirectly prove the successful development of the self-modulation of the proton beam by imaging protons that got defocused by the transverse plasma wakefields after passing through the plasma, at two locations downstream the end of the plasma. This article describes the design and realization of the two screen measurement setup integrated in the AWAKE experiment. We discuss the performance and background response of the system based on measurements performed with an unmodulated Gaussian SPS proton bunch during the AWAKE beam commissioning in September and October 2016. We show that the system is fully commissioned and adapted to eventually image the full profile of a self-modulated SPS proton bunch in a single shot measurement during the first phase of the AWAKE experiment.
This paper describes a new protocol for mandibular reconstruction. Computer-aided design/computer-aided manufacturing (CAD/CAM) technology was used to manufacture custom-made cutting guides for tumor ...ablation and reconstructive plates to support fibula free flaps. CT scan data from a patient with an odontogenic keratocyst on the left mandibular ramus were elaborated to produce a virtual surgical plan of mandibular osteotomy in safe tissue for complete ramus resection. The CAD/CAM procedure was used to construct a customized surgical device composed of a cutting guide and a titanium reconstructive bone plate. The cutting guide allowed the surgeon to precisely transfer the virtual planned osteotomy into the surgical environment. The bone plate, including a custom-made anatomical condylar prosthesis, was designed using the outer surface of the healthy side of the mandible to obtain an ideal contour and avoid the bone deformities present on the side affected by the tumor. Operation time was reduced in the demolition and reconstruction phases. Functional and aesthetic outcomes allowed patients to immediately recover their usual appearance and functionality. This new protocol for mandibular reconstruction using CAD/CAM to construct custom-made guides and plates may represent a viable way to reproduce the patient’s anatomical contour, give the surgeon better procedural control, and reduce operation time.
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