Catálogo de publicaciones - revistas

<jats:title>Abstract</jats:title> <jats:p>Triangular lattice is one most generic structure in two-dimensional (2D) limit with many exotic properties manifested, such as the magnetic frustration and quantum spin liquid. Here, we investigate the electronic properties of multi-orbital (px, py, pz) triangular lattice, focusing on the role of rotation and mirror symmetry breaking in regulating the topological phase diagram. Through tight-binding modeling, we reveal that rotation symmetry (C2z) breaking splits the Dirac point while the nodal-loop is preserved, and further inclusion of broken horizontal mirror symmetry (Mh) destroys the nodal-loop. Consequently, with spin-orbit coupling (SOC), (px, py, pz)-orbital triangular lattice is topologically non-trivial with only C2z or Mh symmetry breaking, and with both symmetries breaking, it becomes trivial, except when SOC is large enough to initiate band-inversion. For real materials, we propose that the recently grown AgSe/AgTe monolayer in a binary-honeycomb structure, is an ideal system to realize the multi-orbital triangular lattice. By first-principles calculations, we demonstrate that free-standing AgSe and AgTe are Z2 non-trivial; on Ag(111) substrate, AgSe becomes trivial due to the breaking of both C2z and Mh symmetries, while AgTe remains non-trivial thanks to the strong SOC of Te. Our work not only provides physical insights into the experimentally synthesized 2D binary-honeycomb structures, but also sheds light on manipulating the electronic and topological properties through symmetry/orbital physics, valuable for designing new quantum materials and devices.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Layered transition metal carbides or nitrides (MXenes), as a novel two-dimensional material, are widely used in the field of electromagnetic (EM) functions and devices due to their unique EM properties. However, the excessive conductivity of MXenes nanosheets often causes impedance mismatch, resulting in a single EM function. Moreover, original MXenes nanosheets are too small in size and needed to be dispersed in the matrix during application, resulting in inconvenience and unstable performance. Architecture strategy is an effective way to handle these problems. Assembling MXenes nanosheets into hierarchical structures, on the one hand, can effectively tailor conductivity, optimize impedance, and tune the EM response of MXenes, achieving multiple EM functions, on the other hand, can obtain directly usable macro assemblies. Herein, we systematically summarize various methods for fabricating MXenes hierarchical architectures, gaining deep insight into the EM response mechanism. Subsequently, the multiple EM functions including electromagnetic absorption (EMA) and electromagnetic interference (EMI) shielding were concluded. More importantly, rich progress has been made in EM functional devices based on MXene, but there is no review in this regard. We have provided a comprehensive summary of relevant excellent work in this review. Ultimately, we have provided insightful commentary on the challenges in this area and predicted the future direction.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Ballistic graphene p-n junctions are uniquely suited to develop electrical counterparts of optical circuits as the large transparency enables a better carrier modulation in their interfaces than the diffusive junctions. Here we demonstrate a low-cost and scalable method for the fabrication of ballistic planar graphene p-n junctions based on the deposition of physisorbed Zn adatoms. A detailed study of spatially resolved Raman spectroscopy through a quartz transparent substrate enables the accurate mapping of the charge doping and strain across the graphene/Zn interface and underneath the metal layer. At the same time, the electrical measurements of transistor structures with varying channel length, i.e. transfer length electrical measurements, and their modelling reveal the ballistic nature of the charge transport up to room temperature.&amp;#xD;</jats:p>

<jats:title>Abstract</jats:title> <jats:p>A potential application of two-dimensional (2D) MXenes, such as Ti<jats:sub>2</jats:sub>CT<jats:sub>x</jats:sub> and Ti<jats:sub>3</jats:sub>C<jats:sub>2</jats:sub>T<jats:sub>x</jats:sub>, is energy storage devices, such as supercapacitors, batteries, and hydride electrochemical cells, where intercalation of ions between the 2D layers is considered as a charge carrier. Electrochemical cycling investigations in combination with Ti <jats:italic>1s</jats:italic> X-ray absorption spectroscopy (XAS) have therefore been performed with the objective to study oxidation state changes during potential variations. In some of these studies Ti<jats:sub>3</jats:sub>C<jats:sub>2</jats:sub>T<jats:sub>x</jats:sub> has shown main edge shifts in the Ti <jats:italic>1s</jats:italic> X-ray absorption near-edge structure (XANES). Here we show that these main edge shifts originate from the Ti <jats:italic>4p</jats:italic> orbital involvement in the bonding between the surface Ti and the termination species at the fcc-sites. The study further shows that the <jats:italic>t<jats:sub>2g</jats:sub>-e<jats:sub>g</jats:sub> </jats:italic> crystal field splitting (10Dq) observed in the pre-edge absorption region indicate weaker Ti-C bonds in Ti<jats:sub>2</jats:sub>CT<jats:sub>x</jats:sub> and Ti<jats:sub>3</jats:sub>C<jats:sub>2</jats:sub>T<jats:sub>x</jats:sub> compared to TiC and the corresponding MAX phases. The results from this study provide information necessary for improved electronic modeling and subsequently a better description of the materials properties of the MXenes. In general, potential applications, where surface interactions with intercalation elements are important processes, will benefit from the new knowledge presented.&amp;#xD;</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Recent advancements in the field of two-dimensional (2D) materials have led to the discovery of a wide range of 2D materials with intriguing properties. Atomistic-scale simulation methods have played a key role in these discoveries. In this review, we provide an overview of the recent progress in ReaxFF force field developments and applications in modeling of the following layered and nonlayered 2D materials: graphene, transition metal dichalcogenides, MXenes, hexagonal boron nitrides, groups III-, IV- and V-elemental materials, as well as the mixed dimensional van der Waals heterostructures. We discuss knowledge gaps and challenges associated with the synthesis and characterization of 2D materials. We close this review with an outlook addressing the challenges as well as plans regarding ReaxFF development and possible large-scale simulations, which should be helpful to guide experimental studies in a discovery of new materials and devices.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Ultrafast charge separation after photoexcitation is a common phenomenon in various van-der-Waals (vdW) heterostructures with great relevance for future applications in light harvesting and detection. Theoretical understanding of this phenomenon converges towards a coherent mechanism through charge transfer states accompanied by energy dissipation into strongly coupled phonons. The detailed microscopic pathways are material specific as they sensitively depend on the band structures of the individual layers, the relative band alignment in the heterostructure, the twist angle between the layers, and interlayer interactions resulting in hybridization. We used time- and angle-resolved photoemission spectroscopy combined with tight binding and density functional theory electronic structure calculations to investigate ultrafast charge separation and recombination in WS2-graphene vdW heterostructures. We identify several avoided crossings in the band structure and discuss their relevance for ultrafast charge transfer. We relate our own observations to existing theoretical models and propose a unified picture for ultrafast charge transfer in vdW heterostructures where band alignment and twist angle emerge as the most important control parameters.&amp;#xD;</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The moire superlattice has emerged as a powerful way to tune excitonic properties in two-dimensional van der Waals structures. However, the current understanding of the influence of the twist angle for interlayer excitons in heterostructures is mainly limited to momentum-direct K-K transitions. In this work, we use a judicious combination of spectroscopy and many-particle theory to investigate the influence of the twist angle on momentum-indirect interlayer excitons of a MoSe<jats:sub>2</jats:sub>/MoS<jats:sub>2</jats:sub> heterostructure. Here, the energetically lowest state is a dark and strongly hybridized ΓK exciton. We show that increasing the twist angle from an aligned structure (0<jats:sup>○</jats:sup> or 60<jats:sup>○</jats:sup>) gives rise to a large blue shift of the interlayer exciton, which is a manifestation of the strong dehybridization of this state. Moreover, for small twist angle heterostructures, our photoluminescence measurements reveal contributions from two interlayer exciton states, which our modelling attributes to transitions from different moire minibands. Our finding contributes to a better fundamental understanding of the influence of the moire pattern on the hybridization of dark interlayer exciton states, which may be important for applications in moiretronics including novel quantum technologies.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Engineering the doping level in graphene is essential to realizing functional electronic and optoelectronic devices. While achieving strong p-doping is relatively straightforward, electrostatic or chemical approaches to negatively dope graphene have yielded electron densities (n<jats:sub>s</jats:sub>) of -9.5 × 10<jats:sup>12</jats:sup> cm<jats:sup>-2</jats:sup> or below. In this work, we demonstrate very high ns (-10<jats:sup>13</jats:sup> to -10<jats:sup>14</jats:sup> cm<jats:sup>-2</jats:sup>) in graphene, on an ion-exchanged (IOX) glass substrate, which is widely used in touch screen displays (e.g. smart phones). Moreover, the proposed method, which is easy to implement and scalable, leads to relatively stable graphene doping, with about a 40% increase in sheet resistance over 5 months at ambient conditions.&amp;#xD;</jats:p>

<jats:title>Abstract</jats:title> <jats:p>As a promising energy conversion system, zinc air battery (ZABs) usually suffers from short cycle life and poor reversibility due to the slow kinetics of the redox reaction on the air cathode, making it a big-barriers in practical applications. Herein, three-dimensional (3D) porous Co<jats:sub>3</jats:sub>O<jats:sub>4</jats:sub>/graphdiyne oxide (GDYO) hybrid nanomaterials with sea urchin-like structures have been prepared by in-situ epitaxial growth. The 3D porous Co<jats:sub>3</jats:sub>O<jats:sub>4</jats:sub>/GDYO hybrid nanomaterials with sea urchin-like structures expand the larger contact area between the electrolyte and the electrode, which provide abundant channels for ion diffusion and electron transport with enhanced charge transfer kinetics and structural stability. The 3D porous Co<jats:sub>3</jats:sub>O<jats:sub>4</jats:sub>/GDYO hybrid nanomaterials with sea urchin-like structures shows excellent bifunctional electrocatalytic activity for both OER (onset potential of 1.38 V, overpotential of 335 mV at 10 mA cm<jats:sup>-2</jats:sup>) and ORR (onset potential of 0.84 V, half-wave potential of 0.6 V). ZABs fabricated with 3D porous Co<jats:sub>3</jats:sub>O<jats:sub>4</jats:sub>/GDYO hybrid nanomaterials as cathode display a high power density of 96 m W cm<jats:sup>-2</jats:sup>, an open circuit voltage of 1.53 V, as well as a specific capacity of 799.5 mA h g<jats:sup>-1</jats:sup> (at 10 mA cm<jats:sup>-2</jats:sup>) and a corresponding energy density of 965 W h kg<jats:sup>-1</jats:sup>. Further, its charge and discharge voltages remain stable for over 400 hours at a constant current charge-discharge cycling of 3 mA cm<jats:sup>-2</jats:sup>. This work offers novel insights on developing excellent bifunctional electrocatalysts for both OER and ORR, which expands a new application of graphdiyne oxide on ZABs.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Moiré systems provide a highly tunable platform for engineering band structures and exotic correlated phases. Here, we theoretically study a model for a single layer of graphene subject to a smooth moiré electrostatic potential, induced by an insulating substrate layer. For sufficiently large moiré unit cells, we find that ultra-flat bands coexist with a triangular network of chiral one-dimensional (1D) channels. These channels mediate an effective interaction between localized modes with spin-, orbital- and valley degrees of freedom emerging from the flat bands. The form of the interaction reflects the chiralilty and 1D nature of the network. We study this interacting model within an SU(4) mean-field theory, semi-classical Monte-Carlo simulations, and an SU(4) spin-wave theory, focusing on commensurate order stabilized by local two-site and chiral three-site interactions. By tuning a gate voltage, one can trigger a non-coplanar phase characterized by a peculiar coexistence of three different types of order: ferromagnetic spin order in one valley, non-coplanar chiral spin order in the other valley, and 120° order in the remaining spin and valley-mixed degrees of freedom. Quantum and classical fluctuations have qualitatively different effects on the observed phases and can, for example, create a finite spin-chirality&amp;#xD;purely via fluctuation effects.</jats:p>