Catálogo de publicaciones - revistas

<jats:title>Abstract</jats:title> <jats:p>Energy transfer between quantum emitters is a key process for many scientific domains and technological applications, and can be influenced by strategic placement of appropriate materials in the vicinity. However, all explored conventional isotropic materials lacks directional control over this process. Here, we show that multilayered Black Phosphorus (bP), a novel anisotropic two-dimensional material, can simultaneously dramatically boost and directionally control energy transfer rates in the near-field regime. We find that bP exhibits a critical thickness above which the energy transfer rates increase by several orders of magnitude compared to vacuum. Moreover, we demonstrate that bP can manipulate the energy transfer in specific in-plane directions due to its strong in-plane anisotropy. Our results build the framework and provide fundamental insights into the mechanisms of energy transfer near anisotropic materials, and open up new possibilities for designing and optimizing energy transfer-based devices, systems and applications.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Two-dimensional material-based field-effect transistors (2DM-FETs) exhibit both ambipolar and unipolar carrier transports. To physically and compactly cover both cases, a quasi-Fermilevel phase space (QFLPS) approach was proposed, but it still involves complicated integration operations. This article aims at improving the numerical efficiency of the QFLPS model by several orders of magnitude so that it can readily be implemented in a standard circuit simulator. We first rigorously derive the integral-free formula for the drain-source current to achieve this goal. Besides computationally benign, it explicitly gives the correlation terms between the electron and hole components. Secondly, to work out the boundary values required by the new expressions, we develop an algorithm for the channel electrostatic potential based on the zerotemperature limit property of the 2DM-FET system. By calibrating the model with the realistic device data of black phosphorus and monolayer molybdenum disulfide FETs, the algorithm is tested against practical cases. Two orders of magnitude improvement in time consumption can be achieved compared with the integral-form QFLPS approach, and it is even four orders of magnitude faster than the traditional continuity-equation based approach.&amp;#xD;</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Poor quality interfaces between metal and graphene cause non-linearity and impair the carrier mobility in graphene devices. Here, we use aberration corrected scanning transmission electron microscopy to observe hexagonally close-packed Ti nano-islands grown on atomically clean graphene, and establish a 30◦ epitaxial relationship between the lattices. Due to the strong binding of Ti on graphene, at the limit of a monolayer, the Ti lattice constant is mediated by the graphene epitaxy, and compared to bulk Ti, is strained by ca. 3.7% to a value of 0.306(3) nm. The resulting interfacial strain is slightly greater than what has been predicted by density functional theory calculations.&amp;#xD;Our early growth stage investigations also reveal that, in contrast to widespread assumptions, Ti does not fully wet graphene but grows initially in islands with a thickness of 1-2 layers. Raman spectroscopy implies charge transfer between the Ti islands and graphene substrate.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Epitaxial growth has become a promising route to achieve highly crystalline continuous two-dimensional layers. However, high-quality layer production with expected electrical properties is still challenging due to the defects induced by the coalescence between imperfectly aligned domains. In order to control their intrinsic properties at the device scale, the synthesized materials should be described as a patchwork of coalesced domains. Here, we report multi-scale and multi-structural analysis on highly oriented epitaxial WS<jats:sub>2</jats:sub> and WSe<jats:sub>2</jats:sub> monolayers using scanning transmission electron microscopy (STEM) techniques. Characteristic domain junctions are first identified and classified based on the detailed atomic structure analysis using aberration corrected STEM imaging. Mapping orientation, polar direction and phase at the micrometer scale using four-dimensional STEM enabled to access the density and the distribution of the specific domain junctions. Our results validate a readily applicable process for the study of highly oriented epitaxial transition metal dichalcogenides, providing an overview of synthesized materials from large scale down to atomic scale with multiple structural information.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The investigation of photon response in the superconducting state of interfacial superconductors holds both fundamental and practical significance, yet it remains largely unexplored. Here, we report an energy-sensitive photodetector utilizing a microstrip patterned on an interfacial superconductor (LaAlO3/KTaO3), achieving photon response spanning from visible to near-infrared wavelengths. Remarkably, the photon response pulse amplitude at the same wavelength is linearly related to the incident light power, showing a unique detection capability that is different from the conventional superconducting single-photon detectors. Our results suggest that the energy-sensitive characteristic arises from the Kondo effect observed in the two-dimensional electron gases of the interfacial superconductor, wherein incident photons alter the normal resistance. This study broadens the potential applications of interface superconductors and presents a versatile approach for the advancement of energy-sensitive photodetection technologies.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Atomic layer deposition (ALD), a layer-by-layer controlled method to synthesize ultrathin materials, provides various merits over other techniques such as precise thickness control, large area scalability and excellent conformality. Here we demonstrate the possibility of using ALD growth on top of suspended 2D materials to fabricate nanomechanical resonators. We fabricate ALD nanomechanical resonators consisting of a graphene/MoS2 heterostructure. Using AFM indentation and optothermal drive, we measure their mechanical properties including Young’s modulus, resonance frequency and quality factor, showing a lower energy dissipation compared to their exfoliated counterparts. We also demonstrate the fabrication of nanomechanical resonators by exfoliating an ALD grown NbS2 layer. This study exemplifies the potential of ALD techniques to produce high-quality suspended nanomechanical membranes, providing a promising route towards high-volume fabrication of future multilayer nanodevices and nanoelectromechanical systems.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The rich nature of van der Waals interactions between artificially-stacked atomic layers has been demonstrated by various quantum states and resonant tunneling transport in low-dimensional materials. However, the role of topological fluctuations in quantum transport through artificially-stacked junctions of 2D superconducting materials, and the resulting energy dissipation, remain elusive. In this research, unique phase-slip centers are designed in artificially-stacked junction areas, where nonequilibrium quasiparticles are formed and relaxed with energy dissipation. The phase slips are observed as voltage steps (peaks or valleys) in transport measurements across a junction between two exfoliated NbSe2 flakes, and at a distance of 4 μm from the junction using local and nonlocal chemical potential probes. Accordingly, two types of energy dissipation modes are newly identified in the artificially-stacked NbSe2 when subjected to an in-plane magnetic field, which implies distinct vortex formation and current flow in the superconducting junction under magnetic fields.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Moiré interference effects influence profoundly the optoelectronic properties of vertical van der Waals structures. Here we systematically establish secondary electron imaging in a scanning electron microscope as a powerful technique for visualizing reconstruction of moiré lattices into registry-contrasting domains in vertical homobilayers and heteorbilayers of transition metal dichalcogenides with parallel and antiparallel alignment. With optimal parameters for contrast-maximizing imaging of high-symmetry registries, we identify distinct crystal realizations of WSe2 homobilayers and MoSe2-WSe2 heterostructures synthesized by chemical vapor deposition. In particular, we find evidence for a mutually exclusive competition between RhX and RhM registries, manifesting in complete reconstruction of bilayer crystals into one distinct registry or alternating large-area domains in RhX and RhM stacking. Our results have immediate implications for the optical properties of registry-specific excitons in layered stacks of transition metal dichalcogenides, and demonstrate the general potential of secondary electron imaging for van der Waals twistronics.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Controlling the electronic structure of two-dimensional materials using the combination of twist angle and electrostatic doping is an effective means to induce emergent phenomena. In bilayer graphene with an interlayer twist angle near the magic angle, the electronic dispersion is strongly modified by a manifold of hybridizing moiré Dirac cones leading to flat band segments with strong electronic correlations. Numerous technical challenges arising from spatial inhomogeneity of interlayer interactions, twist angle and device functionality have so far limited momentum-resolved electronic structure measurements of these systems to static conditions. Here, we present a detailed characterization of the electronic structure exhibiting miniband dispersions for twisted bilayer graphene, near the magic angle, integrated in a functional device architecture using micro-focused angle-resolved photoemission spectroscopy. The optimum conditions for visualizing the miniband dispersion are determined by exploiting the spatial resolution and photon energy tunability of the light source and applied to extract a hybridization gap size of (0.14 ± 0.03) eV and flat band segments extending across a moiré mini Brillouin zone. In situ electrostatic gating of the sample enables significant electron-doping, causing the conduction band states to shift below the Fermi energy. Our work emphasizes key challenges in probing the electronic structure of magic angle bilayer graphene devices and outlines conditions for exploring the doping-dependent evolution of the dispersion that underpins the ability to control many-body interactions in the material.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>This work demonstrates the band-type engineering and the detailed charge transport mechanism upon visible light illumination for various configurations of vertically stacked monolayers of MoS2-ReS2 grown by a two-step Chemical Vapour Deposition (CVD) method. In order to understand the stacking order of both materials has a direct impact on the band alignment arrangements, we investigate the optical properties of both ReS2-MoS2 stacking configurations using micro-photoluminescence and interestingly observed the change in the band alignment upon changing the stacking order (ReS2-MoS2 and MoS2-ReS2). The formation of the vertically stacked heterostructure is further validated by observing its morphology by HR-TEM. The MoS2 on top of ReS2 yielded Type II and ReS2 on top of MoS2 yielded type I band alignment. The fabricated photodetector exhibits responsivities of 152 A/W for pristine ReS2, 72 A/W for MoS2 on top, and 400 A/W for ReS2 on top respectively for visible light illumination of 554 nm suggesting that the stacking configuration of the monolayer TMDs play a vital role in the performance of the optoelectronic properties. The detailed study of such configurations of vertically stacked 2D heterostructure is essential to better understand the optimal configuration for the development of highly responsive photodetectors.</jats:p>