Catálogo de publicaciones - revistas

<jats:title>Abstract</jats:title> <jats:p>The discovery of superconductivity and its modulation are long-standing cutting-edge research topics in condensed matter physics. As a powerful tool, the high-pressure technique can be used to achieve novel superconductors and tune their physical properties. One typical example is binary germanium phosphides with different stoichiometries, which exhibit abundant physical properties with layered lattice structures similar to blue phosphorus. The detailed phase diagrams of the Ge–P systems are important for understanding the influence of stoichiometry on pressure-driven superconductivity, but it remains unexplored. Here, we measured and compared the detailed superconducting phase diagrams of the Ge–P systems of layered isostructural germanium phosphides GeP3 and GeP5 under pressure. Even though these two binary phosphides exhibit obviously different atomic occupations in the crystal structure due to their distinct stoichiometric ratios, the onset superconducting transition temperatures Tc of GeP3 and GeP5 both show dramatic enhancements from ~2.5 K at 12.0 GPa to the maximum values of ~9.0 K at 28.0 GPa, which are higher than those of other binary metal phosphides. Such pressure-enhanced superconductivity therein is accompanied by significant pressure-induced phonon mode softening, which is confirmed via in situ high-pressure Raman measurements. Our observations deepen the physical understanding of pressure-driven superconductivity in phosphorous-rich layered compounds and pave the way for potential applications in microsuperconducting devices. &amp;#xD;</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The low-frequency interlayer vibration modes in bilayer-MoS2/monolayer-WSe2 heterostructures were investigated to study the modification of interlayer interactions due to the moiré periodicity. The interplay of the interlayer interaction within bilayer MoS2 and the interfacial interaction between the two materials results in rich features in the phonon spectra. Several shear and breathing modes are observed for samples with small twist angles (&lt;10°), whereas only one shear and two breathing modes are observed for larger twist angles. For larger twist angles, the interfacial interaction between the two materials amounts to ~75% of the intrinsic interlayer interaction between the MoS2 layers. The phonon spectrum evolves non-monotonically as the twist angle increases, which is explained with the help of atomistic calculations.&amp;#xD;</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Area-selection reactions have been extensively investigated to control or change physicochemical properties of substances with micro- or nanoscale precision. Several polymeric materials called photoresists have been used to mask and pattern the specific region, which can block chemical reactions or deposition. However, they are not suitable for certain chemical reaction since they are vulnerable to high temperature. Here, we report the graphene mask to achieve area-selective chalcogenization, which is performed at high temperature by chemical vapor deposition method. Due to its physicochemical properties, graphene does not allow chalcogen precursor gases to penetrate into metal films. Several characterizations is performed to prove the successful sulfurization and selenization of molybdenum and tungsten films. As an application, WS2 field-effect transistors with graphene mask are fabricated, and they show the typical characteristics of transistors successfully. Therefore, we expect that graphene-assisted area-selective reaction can be utilized for various fields such as semiconductors, sensors, and etc.&amp;#xD;</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The hybrid-induced photogating effect is considered as an effective way for photoconductance modulating in low-dimensional photodetectors. Besides, through constructing the local photogate vertical heterostructures on 2D SnS2 surface can significantly increase its photoconductive gain. However, the potential of this photogain mechanism for SnS2 films has not yet been revealed in practical photodetection devices. To investigate its special advantages on promoting the optical-sensing activity, the high-quality SnS2 films with discrete, micro-area, and uniform rubrene-nanodots modification have been prepared. Benefit from the local interfacial photogating effect induced by hole trap states by rubrene-nanodots, the light-absorption and carrier-excitation efficiencies were significantly enhanced. Afterwards, the high-performance photodetector was designed based on the photogate vertical heterostructures of rubrene-nanodots/SnS2, which demonstrated an enhanced photoelectric response to 1064 nm light. Note that the maximum photocurrent density, photoresponsivity, and photodetectivity can reach up to 0.389 mA·cm-2, 388.71 mA·W-1, and 1.13×1010 Jones, respectively. Importantly, the optimal band-structure offsets accelerated the localized hole transfer from SnS2 film to rubrene-nanodots. The trapped holes in rubrene-nanodots induced an enhanced interface gating effect, which may help to modulate the number and lifetime of excess electrons under light illuminations. These superior features make the newly-developed photodetector be suitable for future multifunctional photodetection applications.&amp;#xD;</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Interlayer excitons in transition-metal dichalcogenide (TMD) bilayers, alongside their interplay with direct excitonic species, are supposed to offer a pathway towards robust nonlinearity, enabling the exploration of many-body quantum effects. We present a theoretical investigation of interaction among various exciton species within these structures where Coulomb attraction and repulsion are subject to reduced screening. For a homobilayer MoS<jats:sub>2</jats:sub>, we examine both direct, spatially-indirect, and hybridised excitons, considering the effects of direct and exchange interaction of electrons and holes distributed across one or different layers. Similar physics arises in perfectly aligned twisted TMD heterobilayers which support the direct-to-indirect exciton hybridisation. Deriving the exciton-exciton interaction matrix elements, we unveil a distinct non-monotonic dependence of the interaction on transferred momentum, changing sign from repulsive to attractive even for ground-state excitons, and compare our results with existing calculations for monolayers. Our findings demonstrate that for large momenta involved in high-density effects (strongly correlated phases), the interaction is chiefly governed by the prevailing attractive exchange component. At the same time, at small momenta that are more relevant for rarefied systems, we find that the enhancement of the interaction constant for dipolar species compared to intralayer non-dipolar excitons may be hindered by the surrounding medium. We draw comparisons with existing experiments and discuss the implications of our findings on the collective effects in TMD-based systems of excitons and exciton-polaritons.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Among the allotropes of phosphorus, black phosphorus (BP) is one of the most thermodynamically stable structures. Due to its unique physical and chemical properties, BP has shown considerable potential in many applications, such as field-effect transistors, energy storage and conversion, and photocatalysis. However, low-dimensional BP is easily corroded by oxygen and water owing to the large specific surface area and unbonded lone pair electrons on the surface, which reduces its chemical stability in the environment. As a result, different passivation approaches, relying on noncovalent bonding, covalent functionalization, and surface coordination, are employed to enhance the stability and performance of BP. In this review, the degradation mechanisms of BP are first analyzed for the material in both its ground state and excited state. Subsequently, the promising strategies for improving stability are overviewed. A comprehensive and in-depth understanding of the oxidation mechanisms and protection strategies of BP will provide guidance for the large-scale applications of BP and its derivatives.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Intervalley scattering mechanisms strongly affect the dynamics of excitonic complexes in transition metal dichalcogenide monolayers. Here, we investigate the excitation energy dependence of the valley polarization of excitons in a WSe<jats:sub>2</jats:sub> monolayer. We observe that the valley polarization drastically decreases when the excitation is resonant with the B<jats:sub>1s</jats:sub> resonance. This behaviour can be explained by a Dexter-like coupling in the momentum space between exciton states residing in opposite valleys but with the same spin configuration. This induces a net transfer of the exciton population from the optically driven valley towards the opposite, undriven valley. We observe the long-term fingerprints of this population transfer, as a vanishing valley polarization for the neutral exciton, and a negative valley polarization for biexcitonic complexes, in qualitative agreement with theoretical predictions based on a fully microscopic many-particle approach. This, together with a decrease of the PL energy when the excitation is resonant with the B<jats:sub>1s</jats:sub> state, points to the prominent role of the Dexter-like coupling in the exciton dynamics of atomically thin semiconductors.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Introducing magnetism to the surface state of topological insulators, such as Bi<jats:sub>2</jats:sub>Te<jats:sub>3</jats:sub>, can lead to a variety of interesting phenomena such as magnetoelectric effects, Weyl semimetal phases, and the quantum anomalous Hall effect. We use scanning tunneling microscopy (STM) to study a single quintuple layer (QL) of the van der Waals magnet Fe<jats:sub>3</jats:sub>GeTe<jats:sub>2</jats:sub> (FGT) that is grown on Bi<jats:sub>2</jats:sub>Te<jats:sub>3</jats:sub> via molecular beam epitaxy. STM topographic images show that the FGT grows as free-standing islands on Bi<jats:sub>2</jats:sub>Te<jats:sub>3</jats:sub> and outwards from Bi<jats:sub>2</jats:sub>Te<jats:sub>3</jats:sub> steps. Atomic resolution imaging shows atomic lattices of 390 ± 10 pm for FGT and 430 ± 10 pm for Bi<jats:sub>2</jats:sub>Te<jats:sub>3</jats:sub>, consistent with the respective bulk crystals. A moiré pattern is observed on FGT regions with a periodicity of 4.3 ± 0.4 nm that can be attributed solely to this lattice mismatch and thus indicates zero rotational misalignment. While most of the surface is covered by a single QL of the FGT, there are small double QL regions, as well as regions with distinct chemical terminations due to an incomplete QL. The most common partial QL surface termination is the FeGe layer, in which the top two atomic layers are missing. This termination has a distinctive electronic structure and a √3 x √3R30° reconstruction overlaid on the moiré pattern in STM images.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Due to high tissue penetration depth and low autofluorescence backgrounds, near-infrared (NIR) fluorescence imaging has recently become an advantageous diagnostic technique used in a variety of fields. However, most of the NIR fluorophores do not have therapeutic delivery capabilities, exhibit low photostabilities, and raise toxicity concerns. To address these issues, we developed and tested five types of biocompatible graphene quantum dots (GQDs) exhibiting spectrally-separated fluorescence in the NIR range of 928 – 1053 nm with NIR excitation. Their optical properties in the NIR are attributed to either rare-earth metal dopants (Ho-NGQDs, Yb-NGQDs, Nd-NGQDs) or defect-states (NGQDs, RGQDs) as verified by Hartree-Fock calculations. Moderate up to 1.34 % quantum yields of these GQDs are well-compensated by their remarkable &gt;4-hour photostability. At the biocompatible concentrations of up to 0.5 – 2 mg/mL GQDs successfully internalize into HEK-293 cells and enable in vitro imaging in the visible and NIR. Tested all together in HEK-293 cells five GQD types enable simultaneous multiplex imaging in the NIR-I and NIR-II shown for the first time in this work for GQD platforms. Substantial photostability, spectrally-separated NIR emission, and high biocompatibility of five GQD types developed here suggest their promising potential in multianalyte testing and multiwavelength bioimaging of combination therapies.&amp;#xD;</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Interplay between defects like mirror twin boundaries (MTBs) and dopants may provide additional opportunities for furthering the research on two-dimensional monolayer (ML) transition metal dichalcogenides (TMDs). In this work, we successfully dope rhenium (Re) into molecular beam epitaxy grown ML MoSe<jats:sub>2</jats:sub> and confirm the formation of a new type of MTBs, named 4|4E-M (M represents metal, Mo/Re) according to the configuration. Data from statistic atomic resolution scanning transmission electron microscopy (STEM) also reveals a preferable MTB enrichment of Re dopants, rather than intra-domain. In conjunction with density functional theory calculation results, we propose the possible routes for Re doping induced formation of 4|4E-M MTBs. Electronic structures of Re doped MTBs in ML MoSe<jats:sub>2</jats:sub> are also predicted theoretically and then preliminarily tested by scanning tunnelling microscopy and spectroscopy.</jats:p>