Search

Coupling Weyl quasiparticles and charge density waves (CDWs) can lead to fascinating band renormalization and many-body effects beyond band folding and Peierls gaps. For the quasi-one-dimensional chiral compound (TaSe4)2I with an incommensurate CDW transition at TC= 263 K, photoemission mappings thus far are intriguing due to suppressed emission near the Fermi level. Models for this unconventional behavior include axion insulator phases, correlation pseudogaps, polaron subbands, bipolaron bound states, etc. Our photoemission measurements show sharp quasiparticle bands crossing the Fermi level at T> TC, but for T< TC, these bands retain their dispersions with no Peierls or axion gaps at the Weyl points. Instead, occupied band edges recede from the Fermi level, opening a spectral gap. Our results confirm localization of quasiparticles (holes created by photoemission) is the key physics, which suppresses spectral weights over an energy window governed by incommensurate modulation and inherent phase defects of CDW.

In recent years, the interest for narrow band gap colloidal quantum dots (CQDs) has shifted from materials optimized for solar cells (with EG≈ 1.2 eV) to materials with properties at longer wavelengths. This shift necessitates a systematic investigation of their electronic properties to optimize photodiode designs effectively. In this study, we utilized X-ray photoemission to systematically determine how the band gap (with absorption maximum wavelengths of 1000, 1200, 1400, and 1550 nm) and surface chemistry (short halides and thiols) influence the band alignment and the core levels in PbS nanocrystals. Our research provides evidence for a shift from a quasi-intrinsic behavior for the narrowest band gap to an exclusively n-type nature for the particles with the largest size, potentially indicating the emergence of degenerate doping. Core-level analysis reveals that the effect of ligands extends beyond dipole behavior, also inducing charge transfer leading to the formation of metallic islands, which might be detrimental to photodetection. Furthermore, by employing scanning photoemission microscopy, we gained direct access to the photodiode’s built-in potential, a parameter typically obtained through indirect modeling. We then discussed how the particle size influences this property. This study lays the foundation for a more rational design of PbS CQD-based photodiodes operating in the short-wave infrared spectrum.

Controllable growth, band-alignment engineering, and accurate electronic-structure evaluation are very important for manipulating the physical properties and customizing the potential optoelectronic applications of two-dimensional heterostructures. Herein, a series of lateral WS2–WS2(1–x)Se2x–WSe2multiheterostructures having atomically sharp interfaces and tunable band alignments were synthesized using a well-designed one-step source-switched physical vapor deposition method. By controlling the chemical composition of the WS2(1–x)Se2xalloy at the middle region, the band alignments and conduction types of the WS2–WS2(1–x)Se2x–WSe2multiheterostructures could be effectively modulated. The sharp one-dimensional junction interfaces of the WS2–WS2(1–x)Se2x–WSe2multiheterostructures were characterized by using microphotoluminescence and scanning transmission electron microscopy. Furthermore, the work function differences, energy band gaps, and electronic-structure of the lateral WS2–WS2(1–x)Se2x–WSe2multiheterostructure were accurately measured using nanoangle-resolved photoemission spectroscopy. Based on our experimental results, an accurate and reliable type-II band-alignment diagram was depicted for the WS2–WS2(1–x)Se2x–WSe2multiheterostructure. This work confirms the possibility for controlling band alignments in two-dimensional lateral multiheterostructures, which represents a key feature for designing optoelectronic devices.

As the field of nanocrystal-based optoelectronics matures, more advanced techniques must be developed in order to reveal the electronic structure of nanocrystals, particularly with device-relevant conditions. So far, most of the efforts have been focused on optical spectroscopy, and electrochemistry where an absolute energy reference is required. Device optimization requires probing not only the pristine material but also the material in its actual environment (i.e., surrounded by a transport layer and an electrode, in the presence of an applied electric field). Here, we explored the use of photoemission microscopy as a strategy for operandoinvestigation of NC-based devices. We demonstrate that the method can be applied to a variety of materials and device geometries. Finally, we show that it provides direct access to the metal–semiconductor interface band bending as well as the distance over which the gate effect propagates in field-effect transistors.

Electron doping of graphene has been extensively studied on graphene-supported surfaces, where the metallicity is influenced by the substrate. Herewith we propose potassium adsorption on free-standing nanoporous graphene, thus eluding any effect due to the substrate. We monitor the electron migration in the π* downward-shifted conduction band. In this rigid band shift, we correlate the spectral density of the π* state in the upper Dirac cone with the associated plasmon, blue-shifted with increasing K dose, as deduced by electron energy loss spectroscopy. These results are confirmed by the Dirac plasmon activated by the C 1s emitted electrons, thanks to spatially resolved photoemission. This crosscheck constitutes a reference on the correlation between the electronic π* states in the conduction band and the Dirac plasmon evolution upon in situ electron doping of fully free-standing graphene.

•En pacientes pediátricos o adultos con patología psiquiátrica o demencia, que presentan rinorrea unilateral, obstrucción nasal y/o dolor, debemos pensar en la posibilidad de que presenten un cuerpo extraño intranasal.•Las localizaciones más frecuentes de los cuerpos extraños intranasales son el vestíbulo nasal y el meato medio.•La técnica usada para la extracción del cuerpo extraño nasal dependerá del tipo, el material y la localización del objeto nasal, del grado de obstrucción y de la colaboración del paciente.•Antes de la extracción es aconsejable el uso de anestésicos tópicos y, a veces, sedación anestésica. Una vez finalizada la extracción, se debe valorar si la extracción ha sido traumática o ha podido provocar algún desgarro en la mucosa nasal.•En el caso de que el cuerpo extraño sea una pila de botón o no pueda ser extraído se debe valorar la derivación a ORL

Nanowire heterostructures of the oxide (shell)–semiconducting (core) type are of interest for various applications in energy harvesting, such as electrodes for photocatalysis and in sensors. Their complete synthesis often requires the deposition of the shell and the core in two separate reactors, with the risk of exposing the core to oxidation from atmospheric conditions during transfer. Here, we study the desorption mechanisms and protection efficiency of an arsenic shell, which was purposely deposited on the GaAs core for protection against undesirable oxidation. Using in situheating in transmission electron microscopy and synchrotron radiation scanning photoelectron microscopy, we explore the morphology, structure, and surface chemistry of GaAs nanowires capped with an arsenic shell, from room temperature to 500 °C. A phase transformation from amorphous to polycrystalline arsenic is evidenced at a temperature of about 300 °C, alongside the disappearance of the surface oxidation observed at room temperature. At higher temperatures, the arsenic shell desorbs with an activation energy of 2.32 eV, leading to clean facets. These results are helpful to determine pathways toward improving the efficiency of oxidation-protective layers on III–V semiconducting nanostructures.

Our experimental results indicate the formation of extended ordered S–Ti–Se layers (Janus layers) in the Ti(Se1–xSx)2system. The presence of these layers is observed as a folding of the typical Fermi surface of TiS2and TiSe2. High-resolution transmission electron microscopy (HRTEM) allows us to observe these layers by a typical rotation of the moiré fringe images. Analysis of the dependence of the electromotive force of the electrochemical cell on the S:Se ratio, angle-resolved photoelectron spectroscopy, resonant photoelectron spectroscopy, Fermi surface mapping, and HRTEM data allows us to conclude that the structure of the solid solution consists of S–Ti–Se and TiCh2(Ch = S or Se) Janus layers.

Spatially controlling the Fermi level of topological insulators and keeping their electronic states stable are indispensable processes to put this material into practical use for semiconductor spintronics devices. So far, however, such a method has not been established yet. Here we show a novel method for doping a hole into n-type topological insulators Bi2X3(X= Se, Te) that overcomes the shortcomings of the previous reported methods. The key of this doping is to adsorb H2O on Bi2X3decorated with a small amount of carbon, and its trigger is the irradiation of a photon with sufficient energy to excite the core electrons of the outermost layer atoms. This method allows controlling the doping amount by the irradiation time and acts as photolithography. Such a tunable doping makes it possible to design the electronic states at the nanometer scale and, thus, paves a promising avenue toward the realization of novel spintronics devices based on topological insulators.

LiNi0.5Mn1.5O4(LNMO) is a promising 5V-class electrode for Li-ion batteries but suffers from manganese dissolution and electrolyte decomposition owing to the high working potential. An attractive solution to stabilize the surface chemistry consists in mastering the interface between the LNMO electrode and the liquid electrolyte with a surface protective layer made from the powerful surface deposition method. Here, we show that a 7400 nm thick sputtered LNMO film coated with a nanometer-thick lithium-ion-conductive Li3PO4layer was deposited by the atomic layer deposition method. We demonstrate that this “material model system” can deliver a remarkable surface capacity (∼0.4 mAh cm–2at 1C) and exhibits improved cycling lifetime (×650%) compared to the nonprotected electrode. Nevertheless, we observe that mechanical failure occurs within the LNMO and Li3PO4films when long-term cycling is performed. This in-depth study gives new insights regarding the mechanical degradation of LNMO electrodes upon charge/discharge cycling and reveals for the first time that the surface protective layer made from the ALD method is not sufficient for long-term stability applications.

Multilayer graphene and its stacking order provide both fundamentally intriguing properties and technological engineering applications. Several approaches to control the stacking order have been demonstrated, but a method of precisely controlling the number of layers with desired stacking sequences is still lacking. Here, we propose an approach for controlling the layer thickness and crystallographic stacking sequence of multilayer graphene films at the wafer scale via Cu–Si alloy formation using direct chemical vapour deposition. C atoms are introduced by tuning the ultra-low-limit CH4concentration to form a SiC layer, reaching one to four graphene layers at the wafer scale after Si sublimation. The crystallographic structure of single-crystalline or uniformly oriented bilayer (AB), trilayer (ABA) and tetralayer (ABCA) graphene are determined via nano-angle-resolved photoemission spectroscopy, which agrees with theoretical calculations, Raman spectroscopy and transport measurements. The present study takes a step towards the layer-controlled growth of graphite and other two-dimensional materials.

The doping mechanism of fully suspended nanoporous graphene with alkali metals unveils the charge redistribution between the donors and graphene. The evolution of the electronic charge induced in the graphene upper Dirac cone has been correlated with the electron–phonon interaction by employing complementary electronic and vibrational spectroscopic techniques in ultra high vacuum ambient. K and Cs doping induces a significant rigid band shift and Dirac cone filling correlated with the neat formation of a π*-plasmon mode and a clear signature of electron–phonon interaction in the Raman spectra, while Na doping slightly influences the graphene electronic and vibrational response, fostered by adatom Na clustering.

For quasi-freestanding 2H-TaS2in monolayer thickness grown by in situmolecular beam epitaxy on graphene on Ir(111), we find unambiguous evidence for a charge density wave close to a 3 × 3 periodicity. Using scanning tunneling spectroscopy, we determine the magnitude of the partial charge density wave gap. Angle-resolved photoemission spectroscopy, complemented by scanning tunneling spectroscopy for the unoccupied states, makes a tight-binding fit for the band structure of the TaS2monolayer possible. As hybridization with substrate bands is absent, the fit yields a precise value for the doping of the TaS2layer. Additional Li doping shifts the charge density wave to a 2 × 2 periodicity. Unexpectedly, the bilayer of TaS2also displays a disordered 2 × 2 charge density wave. Calculations of the phonon dispersions based on a combination of density-functional theory, density-functional perturbation theory, and many-body perturbation theory enable us to provide phase diagrams for the TaS2charge density wave as functions of doping, hybridization, and interlayer potentials, and offer insight into how they affect lattice dynamics and stability. Our theoretical considerations are consistent with the experimental work presented and shed light on previous experimental and theoretical investigations of related systems.

Ferromagnetic ordering of monolayer vanadium dichalcogenides (VSe2and VS2) has been predicted by density functional theory (DFT), and suggestive experimental evidence for magnetic ordering in VSe2monolayers has been reported. However, such ferromagnetic ordering would be in stark contradiction to the known paramagnetic nature of the bulk VSe2. Herein, we investigate the electronic structure of VSe2monolayers by angle-resolved photoemission spectroscopy (ARPES) and first-principles DFT. The ARPES measurements demonstrate the absence of spin-polarized bands for monolayers in close correspondence to nonmagnetic nature of the bulk VSe2. We demonstrate that the stabilization of the nonmagnetic state occurs due to the appearance of a charge density wave (CDW) state in VSe2monolayers. In contrast to well-established 4 × 4 × 3 periodicity of the CDW in bulk VSe2, we identify a √3 × √7 unit cell for VSe2monolayers from both scanning tunneling microscopy imaging and first-principles calculations. Moreover, DFT predicts that the √3 × √7 charge order state is energetically competitive with a ferromagnetic 1 × 1 state. This suggests that the experimentally observed CDW state is the nonmagnetic ground state of a perfectVSe2monolayer, consistent with the absence of spin-polarized bands in ARPES measurements. Therefore, monolayer VSe2is not an itinerant magnet.

We explore the electrical characteristics of TiS3nanowire field-effect transistor (FETs), over the wide temperature range from 3 to 350 K. These nanomaterials have a quasi-one-dimensional (1D) crystal structure and exhibit a gate-controlled metal–insulator transition (MIT) in their transfer curves. Their room-temperature mobility is ∼20–30 cm2/(V s), 2 orders of magnitude smaller than predicted previously, a result that we explain quantitatively in terms of the influence of polar-optical phonon scattering in these materials. In the insulating state (<∼220 K), the transfer curves exhibit unusual mesoscopic fluctuations and a current suppression near zero bias that is common to charge-density wave (CDW) systems. The fluctuations have a nonmonotonic temperature dependence and wash out at a temperature close to that of the bulk MIT, suggesting they may be a feature of quantum interference in the CDW state. Overall, our results demonstrate that quasi-1D TiS3nanostructures represent a viable candidate for FET realization and that their functionality is influenced by complex phenomena.

A Correction to this paper has been published: https://doi.org/10.1038/s41565-020-00821-z.

All-inorganic halide perovskite nanowires (NWs) exhibit improved thermal and hydrolysis stability and could thus play a vital role in nanoscale optoelectronics. Among them, blue-light-based devices are extremely limited because of the lack of a facile method to obtain high-purity CsPbCl3NWs. Herein, we report a direct and facile method for the synthesis of CsPbCl3NWs assisted by inorganic ions that served both as a morphology controlling agent for the anisotropic growth of nanomaterials and a surface passivation species modulating the surface of nanomaterials. This new approach allows us to obtain high-purity and size-uniform NWs as long as 500 nm in length and 20 nm in diameter with high reproducibility. X-ray photoelectron spectroscopy and ultrafast spectroscopic measurements confirmed that a reduced band gap caused by the surface species of NWs relative to nanocubes (NCs) was achieved at the photon energy of 160 eV because of the hybrid surface passivation contributed by adsorbed inorganic ions. The resulting NWs demonstrate significantly enhanced photoelectrochemical performances, 3.5-fold increase in the photocurrent generation, and notably improved stability compared to their NC counterparts. Our results suggest that the newly designed NWs could be a promising material for the development of nanoscale optoelectronic devices.

Transition-metal dichalcogenides exhibit strong quantum confinement effects, and their electronic structure is strongly dependent on the number of layers. Resolving the thickness-dependent electronic structure is important. While the electronic structure of atomically thin 2H-MoSe2or 2H-MoS2have been explored, information on the experimental electronic structure of 2H-MoTe2is still missing. Here, by using nanospot angle-resolved photoemission spectroscopy (nanoARPES), we reveal the experimental electronic structure of exfoliated 2H-MoTe2thin flakes with different thickness (three, five, and seven monolayers). Well-separated quantum-well states are clearly observed in thin 2H-MoTe2flakes at deep valence bands at energies between −3 to −5 eV, while those at the top of the valence band between −1 and −2 eV are much more closely spaced compared with those from 2H-MoSe2and 2H-MoS2. First-principles calculation shows that the main difference is attributed to the weaker hybridization and smaller energy difference between Mo 4dz2and Te 5pzorbitals as compared with Se 4pzand S 3pzorbitals. Our work demonstrates the power of nanoARPES in resolving the electronic structure of atomically thin exfoliated flakes.

We investigate the electronic and vibrational properties of bottom-up synthesized aligned armchair graphene nanoribbons of N= 7 carbon atoms width periodically doped by substitutional boron atoms (B-7AGNRs). Using angle-resolved photoemission spectroscopy and density functional theory calculations, we find that the dopant-derived valence and conduction band states are notably hybridized with electronic states of Au substrate and spread in energy. The interaction with the substrate leaves the bands with pure carbon character rather unperturbed. This results in an identical effective mass of ≈0.2 m0for the next-highest valence band compared with pristine 7AGNRs. We probe the phonons of B-7AGNRs by ultrahigh-vacuum (UHV) Raman spectroscopy and reveal the existence of characteristic splitting and red shifts in Raman modes due to the presence of substitutional boron atoms. Comparing the Raman spectra for three visible lasers (red, green, and blue), we find that interaction with gold suppresses the Raman signal from B-7AGNRs and the energy of the green laser (2.33 eV) is closer to the resonant E22transition. The hybridized electronic structure of the B-7AGNR–Au interface is expected to improve electrical characteristics of contacts between graphene nanoribbon and Au. The Raman fingerprint allows the easy identification of B-7AGNRs, which is particularly useful for device fabrication.

Variations of the lattice parameter can significantly change the properties of a material, and, in particular, its electronic behaviour. In the case of graphene, however, variations of the lattice constant with respect to graphite have been limited to less than 2.5% due to its well-established high in-plane stiffness. Here, through systematic electronic and lattice structure studies, we report regions where the lattice constant of graphene monolayers grown on copper by chemical vapour deposition increases up to ~7.5% of its relaxed value. Density functional theory calculations confirm that this expanded phase is energetically metastable and driven by the enhanced interaction between the substrate and the graphene adlayer. We also prove that this phase possesses distinctive chemical and electronic properties. The inherent phase complexity of graphene grown on copper foils revealed in this study may inspire the investigation of possible metastable phases in other seemingly simple heterostructure systems.

HgTe, thanks to its unique spectral tunability in the infrared, is the only material able to cover near-, short-, and mid-wave infrared. Current best devices rely on electrodes made from transparent conductive oxides and gold, but so far, none of these completely fit for the intended purpose. Gold is not compatible with Si foundries, and transparent conductive oxides are highly lossy in this spectral range, limiting electrode transparency. Metal-based electrodes appear as good alternative candidates but require further investigations. While obvious constraints of work function get raised, chemical stability appears equally important. Here, we screen the use of Au, Al, Ag, and Zn as possible metals and reveal that in the case of Ag, dramatic transformations of Ag and HgTe are observed. Especially, a cation exchange procedure can occur over a solid-state film without intentional heating of the sample. This process has then been studied by combining both structural and electronic probes. This work points out the importance of the careful choice of surrounding electrodes in the case of HgTe since the observed mechanism is likely not limited to Ag. On the other hand, both Au and Al appear stable toward this transformation.

Exfoliated magnetic 2D materials enable versatile tuning of magnetization, e.g., by gating or providing proximity-induced exchange interaction. However, their electronic band structure after exfoliation has not been probed, presumably due to their photochemical sensitivity. Here, we provide micrometer-scale angle-resolved photoelectron spectroscopy of the exfoliated intralayer antiferromagnet MnPS3above and below the Néel temperature down to one monolayer. Favorable comparison with density functional theory calculations enables identifying the orbital character of the observed bands. Consistently, we find pronounced changes across the Néel temperature for bands consisting of Mn 3d and 3p levels of adjacent S atoms. The deduced orbital mixture indicates that the superexchange is relevant for the magnetic interaction. There are only minor changes between monolayer and thicker films, demonstrating the predominant 2D character of MnPS3. The novel access is transferable to other MPX3materials (M: transition metal, P: phosphorus, X: chalcogenide), providing several antiferromagnetic arrangements.

Currently, serial manipulators are the boom in the industry. Most companies are looking for solutions that improve production processes and that are human collaborative. They seek to simulate the skills that humans perform. Nowadays there is a constant question of comparison between a redundant robot of 7-DOF and one that meets the necessary joints to perform complex jobs useful in the industry as is the 6-DOF. In this paper we design a mathematical model that describes the forwards kinematics of the 7-DOF manipulator using the famous D-H convention and determine if the kinematic chain of the manipulators interferes in the performance of their work and thus reach a comparison with its predecessor of 6-DOF in the industry by means of a simulation in CoppeliaSim. As the main results the 6-DOF is more useful for repetitive production assignments and the 7-DOF for human collaboration.

Conversion of free-standing graphene into pure graphane─where each C atom is sp3bound to a hydrogen atom─has not been achieved so far, in spite of numerous experimental attempts. Here, we obtain an unprecedented level of hydrogenation (≈90% of sp3bonds) by exposing fully free-standing nanoporous samples─constituted by a single to a few veils of smoothly rippled graphene─to atomic hydrogen in ultrahigh vacuum. Such a controlled hydrogenation of high-quality and high-specific-area samples converts the original conductive graphene into a wide gap semiconductor, with the valence band maximum (VBM) ∼ 3.5 eV below the Fermi level, as monitored by photoemission spectromicroscopy and confirmed by theoretical predictions. In fact, the calculated band structure unequivocally identifies the achievement of a stable, double-sided fully hydrogenated configuration, with gap opening and no trace of π states, in excellent agreement with the experimental results.

In this paper, an experimental review of the isotherms of the metallotetraphenylporphyrin (M-TPP) molecules has been carried out in the air-water interface. The isotherms are a function of the M-TPP concentration in the organic solvent used (chloroform) before spreading on the aqueous subphase. For very low M-TPP concentrations (10-5M) in this solvent, isotherms whose extrapolated areas to π = 0 mN/m are on the order of 100-110 Å2per molecule are obtained. This value is intermediate between those expected for a flat orientation of the molecules (160 Å2) and a perpendicular one (70 Å2). When a constant pressure is applied, such monolayers are initially not stable. However, after waiting sufficient time, one can observe a sudden condensation of this monolayer (decrease of the area at a constant pressure) which leads to the formation of a stable monolayer, with an area per molecule on the order of 67 Å2for H2-TPP, 69 Å2for Mg-TPP, and 86 Å2for Zn-TPP (π = 7 mN/m). Monolayers were characterized by visible spectroscopy following transfer to glass slides. In this paper, a possible explanation for this phenomenon in relation to the molecular structure of the M-TPP is reached.

We measured serum levels of anti-Gal(α1 → 3)Gal and anti-Gal(α1 → 2)Gal antibodies in 89 and 91 women, respectively, by using ELISA. These patients had cervical intraepithelial neoplasia (CIN) grades 1 to 3 and early invasive cervical carcinoma (ICC). Our objective was to compare anti-α-galactosyl antibody levels among them and with those of normal controls. High levels of anti-Gal(α1 → 2)Gal antibodies were detected in 22% of patients (P= 0.006). The mean level was 1.6 times greater than that of controls, without difference among subgroups. Thirty percent of patients had abnormally high anti-Gal levels (P= 0.001). Mean levels were twofold greater than the mean control value. Subsets with human papillomavirus/CIN 1 and CIN 2–3 had high immunoreactivity (P= 0.004). Both antibodies showed a significant correlation (r= 0.53,P< 0.00001). We conclude that 22 to 30% of patients with CIN 1–3 showed significantly high levels of anti-α-galactosyl antibodies. This seroreactivity might be related to the abnormal expression of α-galactosyl residues at some point of the natural history of human papillomavirus infection of the uterine cervix, suggesting an active immune response by natural antibodies against this virus. Further studies are needed to determine whether anti-α-galactosyl antibodies confer protection in human papillomavirus infection.