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Dynamic terahertz devices are vital for the next generation of wireless communication, sensing, and non-destructive imaging technologies. Metasurfaces have emerged as a paradigm-shifting platform, offering varied functionalities, miniaturization, and simplified fabrication compared to their 3D counterparts. However, the presence of in-plane mirror symmetry and reduced degree of freedom impose fundamental limitations on achieving advanced chiral response, beamforming, and reconfiguration capabilities. In this work, a platform composed of electrically actuated resonators that can be colossally reconfigured between planar and 3D geometries is demonstrated. To illustrate the platform, metadevices with 3D Split Ring Resonators are fabricated, wherein two counteracting driving forces are combined: i) folding induced by stress mismatch, which enables non-volatile state design and ii) unfolding triggered by the strain associated with insulator-to-metal transition in VO2, which facilitates volatile structural reconfiguration. This large structural reconfiguration space allows for resonance mode switching, widely tunable magnetic and electric polarizabilities, and increased frequency agility. Moreover, the unique properties of VO2, such as the hysteretic nature of its phase transition is harnessed to demonstrate a multi-state memory. Therefore, these VO2 integrated metadevices are highly attractive for the realization of 6G communication devices such as reconfigurable intelligent surfaces, holographic beam formers, and spatial light modulators.
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The defect emission from h-BN at 1.55 eV is interesting as it enables optical readout of spins. It is necessary to identify the nature of the relevant point defects for its controlled introduction. However, it is challenging to engineer point defects in h-BN without changing the local atomic structure. Here, we controllably introduce boron vacancies in h-BN using an ultrahigh spatial resolution and low-energy He+ ion beam. By optimizing the He+ ion irradiation conditions, we control the quantity and location of defects spatially and along the depth of h-BN to achieve a robust photoluminescence emission at 1.55 eV from 10 K to room temperature. We show that as-generated defects activate an additional Raman mode at 1295 cm-1. Electron energy loss spectroscopy confirms introduction of boron vacancies without modification of the local h-BN crystal structure. Our results provide a deterministic strategy to create scalable boron vacancy emitters in h-BN for quantum photonics.
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This clinical study presents a comprehensive investigation into the utility of breath analysis as a non-invasive method for the early detection of lung cancer. The study enrolled 14 lung cancer patients, 14 non-lung cancer controls with diverse medical conditions, and 3 tuberculosis (TB) patients for biomarker discovery. Matching criteria including age, gender, smoking history, and comorbidities were strictly followed to ensure reliable comparisons. A systematic breath sampling protocol utilizing a BIO-VOC sampler was employed, followed by VOC analysis using Thermal Desorption-Gas Chromatography-Mass Spectrometry (TD-GC/MS). The resulting VOC profiles were subjected to stringent statistical analysis, including Orthogonal Projections to Latent Structures-Discriminant Analysis (OPLS-DA), Kruskal-Wallis test, and Receiver Operating Characteristic (ROC) analysis. Notably, 13 VOCs exhibited statistically significant differences between lung cancer patients and controls. The combination of eight VOCs (hexanal, heptanal, octanal, benzaldehyde, undecane, phenylacetaldehyde, decanal, and benzoic acid) demonstrated substantial discriminatory power with an area under the curve (AUC) of 0.85, a sensitivity of 82%, and a specificity of 76% in the discovery set. Validation in an independent cohort yielded an AUC of 0.78, a sensitivity of 78%, and a specificity of 64%. Further analysis revealed that elevated aldehyde levels in lung cancer patients' breath could be attributed to overactivated Alcohol Dehydrogenase (ADH) pathways in cancerous tissues. Addressing methodological challenges, this study employed a matching of physiological and pathological confounders, controlled room air samples, and standardized breath sampling techniques. Despite the limitations, this study's findings emphasize the potential of breath analysis as a diagnostic tool for lung cancer and suggest its utility in differentiating tuberculosis from lung cancer. However, further research and validation are warranted for the translation of these findings into clinical practice.
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Electro-optic modulators are among the most important building blocks in optical communication networks. Lithium niobate, for example, has traditionally been widely used to fabricate high-speed optical modulators due to its large Pockels effect. Another material, barium titanate, nominally has a 50 times stronger r-parameter and would ordinarily be a more attractive material choice for such modulators or other applications. In practice, barium titanate thin films for optical waveguide devices are usually grown on magnesium oxide due to its low refractive index, allowing vertical mode confinement. However, the crystal quality is normally degraded. Here, a group of scandate-based substrates with small lattice mismatch and low refractive index compared to that of barium titanate is identified, thus concurrently satisfying high crystal quality and vertical optical mode confinement. This work provides a platform for nonlinear on-chip optoelectronics and can be promising for waveguide-based optical devices such as Mach-Zehnder modulators, wavelength division multiplexing, and quantum optics-on-chip.
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While direct bandgap monolayer 2D transition metal dichalcogenides (TMDs) have emerged as an important optoelectronic material due to strong light-matter interactions, their multilayer counterparts exhibit an indirect bandgap resulting in poor photon emission quantum yield. We report strong direct bandgap-like photoluminescence at â¼1.9 eV from multilayer MoS2 grown on SrTiO3, whose intensity is significantly higher than that observed in multilayer MoS2/SiO2. Using high-resolution electron microscopy we observe interlayer twist and >8% increase in the van der Waals gap, which leads to weaker interlayer coupling. This affects the evolution of the band structure in multilayer MoS2 as probed by transient absorption spectroscopy, causing higher photo carrier recombination at the direct gap. Our results provide a platform that could enable multilayer TMDs for robust optical device applications.
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Exploring exotic interface magnetism due to charge transfer and strong spin-orbit coupling has profound application in the future development of spintronic memory. Here, the emergence and tuning of topological Hall effect (THE) from a CaMnO3 /CaIrO3 /CaMnO3 trilayer structure are studied in detail, which suggests the presence of magnetic Skyrmion-like bubbles. First, by tilting the magnetic field direction, the evolution of the Hall signal suggests a transformation of Skyrmions into topologically-trivial stripe domains, consistent with behaviors predicted by micromagnetic simulations. Second, by varying the thickness of CaMnO3 , the optimal thicknesses for the THE signal emergence are found, which allow identification of the source of Dzyaloshinskii-Moriya interaction (DMI) and its competition with antiferromagnetic superexchange. Employing high-resolution transmission electron microscopy, randomly distributed stacking faults are identified only at the bottom interface and may avoid mutual cancellation of DMI. Last, a spin-transfer torque experiment also reveals a low threshold current density of ≈109 A m-2 for initiating the bubbles' motion. This discovery sheds light on a possible strategy for integrating Skyrmions with antiferromagnetic spintronics.
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One common challenge highlighted in almost every review article on organic resistive memory is the lack of areal switching uniformity. This, in fact, is a puzzle because a molecular switching mechanism should ideally be isotropic and produce homogeneous current switching free from electroforming. Such a demonstration, however, remains elusive to date. The reports attempting to characterize a nanoscopic picture of switching in molecular films show random current spikes, just opposite to the expectation. Here, this longstanding conundrum is resolved by demonstrating 100% spatially homogeneous current switching (driven by molecular redox) in memristors based on Ru-complexes of azo-aromatic ligands. Through a concurrent nanoscopic spatial mapping using conductive atomic force microscopy and in operando tip-enhanced Raman spectroscopy (both with resolution <7 nm), it is shown that molecular switching in the films is uniform from hundreds of micrometers down to the nanoscale and that conductance value exactly correlates with spectroscopically determined molecular redox states. This provides a deterministic molecular route to obtain spatially homogeneous, forming-free switching that can conceivably overcome the chronic problems of robustness, consistency, reproducibility, and scalability in organic memristors.
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Electrical control of material properties based on ionic liquids (IL) has seen great development and emerging applications in the field of functional oxides, mainly understood by the electrostatic and electrochemical gating mechanisms. Compared to the fast, flexible, and reproducible electrostatic gating, electrochemical gating is less controllable owing to the complex behaviors of ion migration. Here, the interface-dependent oxygen migration by electrochemical gating is resolved at the atomic scale in the LaAlO3-SrTiO3 system through ex situ IL gating experiments and on-site atomic-resolution characterization. The difference between interface structures leads to the controllable electrochemical oxygen migration by filling oxygen vacancies. The findings not only provide an atomic-scale insight into the origin of interface-dependent electrochemical gating but also demonstrate an effective way of engineering interface structure to control the electrochemical gating.
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Charge localization is critical to the control of charge dynamics in systems such as perovskite solar cells, organic-, and nanostructure-based photovoltaics. However, the precise control of charge localization via electronic transport or defect engineering is challenging due to the complexity in reaction pathways and environmental factors. Here, charge localization in optimal-doped La1.85 Sr0.15 CuO4 thin-film on SrTiO3 substrate (LSCO/STO) is investigated, and also a high-energy plasmon is observed. Charge localization manifests as a near-infrared mid-gap state in LSCO/STO. This is ascribed to the interfacial hybridization between the Ti3d-orbitals of the substrate and O2p-orbitals of the film. The interfacial effect leads to significant changes in the many-body correlations and local-field effect. The local-field effect results in an inhomogeneous charge distribution, and due to perturbation by an external field, the high polarizability of this nonuniform charge system eventually generates the high-energy plasmon. Transformation of the electronic correlations in LSCO/STO is further demonstrated via temperature-dependent spectral-weight transfer. This study of charge localization in cuprates and interfacial hybridization provides important clues to their electronic structures and superconductive properties.
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Grain boundaries could exhibit exceptional electronic structure and exotic properties, which are determined by a local atomic configuration and stoichiometry that differs from the bulk. However, optical and plasmonic properties at the grain boundaries in metallic oxides have rarely been discussed before. Here, we show that non-stoichiometric grain boundaries in the newly discovered metallic SrNbO3 photocatalyst show exotic electronic, optical and plasmonic phenomena in comparison to bulk. Aberration-corrected scanning transmission electron microscopy and first-principles calculations reveal that a Nb-rich grain boundary exhibits an increased carrier concentration with quasi-1D metallic conductivity, and newly induced electronic states contributing to the broad energy range of optical absorption. More importantly, dielectric function calculations reveal extended and enhanced plasmonic excitations compared with bulk SrNbO3. Our results show that non-stoichiometric grain boundaries might be utilized to control the electronic and plasmonic properties in oxide photocatalysis.
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Using interlayer interaction to control functional heterostructures with atomic-scale designs has become one of the most effective interface-engineering strategies nowadays. Here, we demonstrate the effect of a crystalline LaFeO3 buffer layer on amorphous and crystalline LaAlO3/SrTiO3 heterostructures. The LaFeO3 buffer layer acts as an energetically favored electron acceptor in both LaAlO3/SrTiO3 systems, resulting in modulation of interfacial carrier density and hence metal-to-insulator transition. For amorphous and crystalline LaAlO3/SrTiO3 heterostructures, the metal-to-insulator transition is found when the LaFeO3 layer thickness crosses 3 and 6 unit cells, respectively. Such different critical LaFeO3 thicknesses are explained in terms of distinct characteristic lengths of the redox-reaction-mediated and polar-catastrophe-dominated charge transfer, controlled by the interfacial atomic contact and Thomas-Fermi screening effect, respectively. Our results not only shed light on the complex interlayer charge transfer across oxide heterostructures but also provide a new route to precisely tailor the charge-transfer process at a functional interface.
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Reduced graphene oxide (rGO) has attracted significant interest in an array of applications ranging from flexible optoelectronics, energy storage, sensing, and very recently as membranes for water purification. Many of these applications require a reproducible, scalable process for the growth of large-area films of high optical and electronic quality. In this work, we report a one-step scalable method for the growth of reduced-graphene-oxide-like (rGO-like) thin films via pulsed laser deposition (PLD) of sp2 carbon in an oxidizing environment. By deploying an appropriate laser beam scanning technique, we are able to deposit wafer-scale uniform rGO-like thin films with ultrasmooth surfaces (roughness <1 nm). Further, in situ control of the growth environment during the PLD process allows us to tailor its hybrid sp2-sp3 electronic structure. This enables us to control its intrinsic optoelectronic properties and helps us achieve some of the lowest extinction coefficients and refractive index values (0.358 and 1.715, respectively, at 2.236 eV) as compared to chemically grown rGO films. Additionally, the transparency and conductivity metrics of our PLD grown thin films are superior to other p-type rGO films and conducting oxides. Unlike chemical methods, our growth technique is devoid of catalysts and is carried out at lower process temperatures. This would enable the integration of these thin films with a wide range of material heterostructures via direct growth.
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We report the control of the interplane magnetic exchange coupling in CaIrO3 perovskite thin films and superlattices with SrTiO3. By analyzing the anisotropic magneto-transport data, we demonstrate that a semimetallic paramagnetic CaIrO3 turns into a canted antiferromagnetic Mott insulator at reduced dimensions. The emergence of a biaxial magneto-crystalline anisotropy indicates the canted moment responding to the cubic symmetry. Extending to superlattices and probing oxygen octahedral rotation by half-integer X-ray Braggs diffraction, a more complete picture about the canted moment evolution with interplane coupling can be understood. Remarkably, a rotation of the canted moments' easy axes by 45° is also observed by a sign reversal of the in-plane strain. These results demonstrate the robustness of anisotropic magnetoresistance in revealing quasi two-dimensional canted antiferromagnets, as well as valuable insights about quadrupolar magnetoelastic coupling, relevant for designing future antiferromagnetic spintronic devices.
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Topologically protected magnetic states have a variety of potential applications in future spintronics owing to their nanoscale size (<100 nm) and unique dynamics. These fascinating states, however, usually are located at the interfaces or surfaces of ultrathin systems due to the short interaction range of the Dzyaloshinskii-Moriya interaction (DMI). Here, magnetic topological states in a 40-unit cells (16 nm) SrRuO3 layer are successfully created via an interlayer exchange coupling mechanism and the interfacial DMI. By controlling the thickness of an antiferromagnetic and ferromagnetic layer, interfacial ionic polarization, as well as the transformation between ferromagnetic and magnetic topological states, can be modulated. Using micromagnetic simulations, the formation and stability of robust magnetic skyrmions in SrRuO3 /BiFeO3 heterostructures are elucidated. Magnetic skyrmions in thick multiferroic heterostructures are promising for the development of topological electronics as well as rendering a practical approach to extend the interfacial topological phenomena to bulk via antiferromagnetic order.
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The reduced electrical screening in 2D materials provides an ideal platform for realization of exotic quasiparticles, that are robust and whose functionalities can be exploited for future electronic, optoelectronic, and valleytronic applications. Recent examples include an interlayer exciton, where an electron from one layer binds with a hole from another, and a Holstein polaron, formed by an electron dressed by a sea of phonons. Here, a new quasiparticle is reported, "polaronic trion" in a heterostructure of MoS2 /SrTiO3 (STO). This emerges as the Fröhlich bound state of the trion in the atomically thin monolayer of MoS2 and the very unique low energy soft phonon mode (≤7 meV, which is temperature and field tunable) in the quantum paraelectric substrate STO, arising below its structural antiferrodistortive (AFD) phase transition temperature. This dressing of the trion with soft phonons manifests in an anomalous temperature dependence of photoluminescence emission leading to a huge enhancement of the trion binding energy (≈70 meV). The soft phonons in STO are sensitive to electric field, which enables field control of the interfacial trion-phonon coupling and resultant polaronic trion binding energy. Polaronic trions could provide a platform to realize quasiparticle-based tunable optoelectronic applications driven by many body effects.
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Transition metal oxides exhibit strong structure-property correlations, which has been extensively investigated and utilized for achieving efficient oxygen electrocatalysts. However, high-performance oxide-based electrocatalysts for hydrogen evolution are quite limited, and the mechanism still remains elusive. Here we demonstrate the strong correlations between the electronic structure and hydrogen electrocatalytic activity within a single oxide system Ti2O3. Taking advantage of the epitaxial stabilization, the polymorphism of Ti2O3 is extended by stabilizing bulk-absent polymorphs in the film-form. Electronic reconstructions are realized in the bulk-absent Ti2O3 polymorphs, which are further correlated to their electrocatalytic activity. We identify that smaller charge-transfer energy leads to a substantial enhancement in the electrocatalytic efficiency with stronger hybridization of Ti 3d and O 2p orbitals. Our study highlights the importance of the electronic structures on the hydrogen evolution activity of oxide electrocatalysts, and also provides a strategy to achieve efficient oxide-based hydrogen electrocatalysts by epitaxial stabilization of bulk-absent polymorphs.
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Interface-driven magnetic effects and phenomena associated with spin-orbit coupling and intrinsic symmetry breaking are of importance for fundamental physics and device applications. How interfaces affect the interplay between charge, spin, orbital, and lattice degrees of freedom is the key to boosting device performance. In LaMnO3 /SrTiO3 (LMO/STO) polar-nonpolar heterostructures, electronic reconstruction leads to an antiferromagnetic to ferromagnetic transition, making them viable for spin filter applications. The interfacial electronic structure plays a critical role in the understanding of the microscopic origins of the observed magnetic phase transition, from antiferromagnetic at 5 unit cells (ucs) of LMO or below to ferromagnetic at 6 ucs or above, yet such a study is missing. Here, an atomic scale understanding of LMO/STO ambipolar ferromagnetism is offered by quantifying the interface charge distribution and performing first-principles density functional theory (DFT) calculations across this abrupt magnetic transition. It is found that the electronic reconstruction is confined within the first 3 ucs of LMO from the interface, and more importantly, it is robust against oxygen nonstoichiometry. When restoring stoichiometry, an enhanced ferromagnetic insulating state in LMO films with a thickness as thin as 2 nm (5 uc) is achieved, making LMO readily applicable as barriers in spin filters.
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Breath analysis is a promising technique for lung cancer screening. Despite the rapid development of breathomics in the last four decades, no consistent, robust, and validated volatile organic compound (VOC) signature for lung cancer has been identified. This review summarizes the identified VOC biomarkers from both exhaled breath analysis and in vitro cultured lung cell lines. Both clinical and in vitro studies have produced inconsistent, and even contradictory, results. Methodological issues that lead to these inconsistencies are reviewed and discussed in detail. Recommendations on addressing specific issues for more accurate biomarker studies have also been made.
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The strikingly contrasting optical properties of various phases of chalcogenide phase change materials (PCM) has recently led to the development of novel photonic devices such as all-optical non-von Neumann memory, nanopixel displays, color rendering, and reconfigurable nanoplasmonics. However, the exploration of chalcogenide photonics is currently limited to optical and infrared frequencies. Here, a phase change material integrated terahertz metamaterial for multilevel nonvolatile resonance switching with spatial and temporal selectivity is demonstrated. By controlling the crystalline proportion of the PCM film, multilevel, non-volatile, terahertz resonance switching states with long retention time at zero hold power are realized. Spatially selective reconfiguration at sub-metamaterial scale is shown by delivering electrical stimulus locally through designer interconnect architecture. The PCM metamaterial also features ultrafast optical modulation of terahertz resonances with tunable switching speed based on the crystalline order of the PCM film. The multilevel nonvolatile, spatially selective, and temporally tunable PCM metamaterial will provide a pathway toward development of novel and disruptive terahertz technologies including spatio-temporal terahertz modulators for high speed wireless communication, neuromorphic photonics, and machine-learning metamaterials.
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Defects in crystalline materials have a tremendous impact on their functional behavior. Controlling and tuning of these imperfections can lead to marked improvements in their physical, electrical, magnetic, and optical properties. Thanks to the development of aberration-corrected (scanning) transmission electron microscopy (STEM/TEM), direct visualization of defects at multiple length scales has now become possible, including those critically important defects at the atomic scale. Thorough understanding of the nature and dynamics of these defects is the key to unraveling the fundamental origins of structure-property relationships. Such insight can therefore allow the creation of new materials with desired properties through appropriate defect engineering. Herein, several examples of new insights obtained from representative functional materials are shown, including piezoelectrics/ferroelectrics, oxide interfaces, thermoelectrics, electrocatalysts, and 2D materials.