Search

We report experimental characterization of DC electro-optic coefficients r13, r23 and r33 in thin film single crystalline BaTiO3 on DyScO3. The epitaxial BaTiO3 thin film is sandwiched between a SrRuO3 bottom electrode and an indium tin oxide (ITO) top electrode. We characterize the DC electro-optic coefficients r13, r23, and r33 by the prism coupling method at 636.6 nm for the BaTiO3 thin film. The results show the DC coefficients r13 = 4.2 pm/V, r23 = 4.6 pm/V and r33 = 9.0 pm/V.

Craters have been observed upon irradiation by single ion impacts of Ar monomer and Ar dimer ions with 35 keV/atom in monolayer graphene on copper at a fluence of 1 × 1012 atoms/cm2. The observed craters at the ion impacts are in the underlying copper substrate, which pull down the graphene layer conformally towards them, introducing disorder into graphene. The number density of craters per atom produced by Ar-monomers is higher than that of Ar-dimer ions. In the ion impact region, disorder is high, and graphene is metallic in both Ar-monomer and dimer irradiation. In the ion impact region of dimer irradiated graphene, local density of states is higher and there is a shift in Dirac point position by +0.07 eV and a bandgap opening of 0.25 eV in the ordered region ∼15 nm away from the ion impact. Microscopic ripples in graphene are not observed in the case of monomer irradiation while they are present in the case of dimer irradiation with a reduced wavelength. Isotropic compressive strain is introduced by the ion impacts and it is larger for Ar-dimer irradiation. The combined effects of compressive strain along with breaking the equivalence between A and B sublattice of graphene is attributed to the opening of the band gap in graphene.

Profuse dendritic-synaptic interconnections among neurons in the neocortex embed intricate logic structures enabling sophisticated decision-making that vastly outperforms any artificial electronic analogues1–3. The physical complexity is far beyond existing circuit fabrication technologies: moreover, the network in a brain is dynamically reconfigurable, which provides flexibility and adaptability to changing environments4–6. In contrast, state-of-the-art semiconductor logic circuits are based on threshold switches that are hard-wired to perform predefined logic functions. To advance the performance of logic circuits, we are re-imagining fundamental electronic circuit elements by expressing complex logic in nanometre-scale material properties. Here we use voltage-driven conditional logic interconnectivity among five distinct molecular redox states of a metal–organic complex to embed a ‘thicket’ of decision trees (composed of multiple if-then-else conditional statements) having 71 nodes within a single memristor. The resultant current–voltage characteristic of this molecular memristor (a 'memory resistor', a globally passive resistive-switch circuit element that axiomatically complements the set of capacitor, inductor and resistor) exhibits eight recurrent and history-dependent non-volatile switching transitions between two conductance levels in a single sweep cycle. The identity of each molecular redox state was determined with in situ Raman spectroscopy and confirmed by quantum chemical calculations, revealing the electron transport mechanism. Using simple circuits of only these elements, we experimentally demonstrate dynamically reconfigurable, commutative and non-commutative stateful logic in multivariable decision trees that execute in a single time step and can, for example, be applied as local intelligence in edge computing7–9. Multiple redox transitions in a molecular memristor can be harnessed as ‘decision trees’ to undertake complex and reconfigurable logic operations in a single time step.

The quantum eraser is a variation of the celebrated Young's interference experiment that can be used to demonstrate the elusive complementarity principle in quantum physics. Here we show the construction of its classical analogue for deployment in classrooms in a simple, cost-effective yet robust manner by employing a laser pointer, double-slits, and polarizers., 4 pages, 3 figures, 4 supplementary information pages

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...

A CMOS-compatible plasmonic waveguide with a metal or metal-like strip sandwiched in-between dielectrics has been proposed for intra-chip communication in the more-than-Moore era. A sequence of numerical models has been presented to evaluate the plasmonic waveguide performance. For device-level consideration, we demonstrated through simulations that Cu (1450 nm pitch) and PLD-TiN (900 nm pitch) plasmonic waveguides symmetrically sandwiched by SiO₂ with much smaller and hence denser interconnects,are promising candidates for use in global wires for the asynchronous communication. This design of plasmonic waveguide can bridge the CMOS circuitry and high-speed communication at optical frequencies within chip. For a system-level assessment, both of them have the same bandwidth throughput of∼19.8 Gbps. The other performance parameters of Cu and PLD-TiN plasmonic waveguides are respectively, signal latency of ∼0.18 ps and 0.19 ps,energy dissipation per computing bit of ∼2.5×10⁻³ fJ/bit and 3.8×10⁻³ fJ/bit, and 25% crosstalk coupling length of 155μm and 125μm. These findings suggest that plasmonic waveguide for intra-chip communication surpass those of existing electronic interconnects for all the categories of performance parameters. National Research Foundation (NRF) Published version This research was supported by National Research Foundation Singapore project of Integration of Electrically Driven Plasmonic Components in High Speed (NRF2016_CRP001_111).

Two-dimensional (2D) materials1–5 offer a unique platform from which to explore the physics of topology and many-body phenomena. New properties can be generated by filling the van der Waals gap of 2D materials with intercalants6,7; however, post-growth intercalation has usually been limited to alkali metals8–10. Here we show that the self-intercalation of native atoms11,12 into bilayer transition metal dichalcogenides during growth generates a class of ultrathin, covalently bonded materials, which we name ic-2D. The stoichiometry of these materials is defined by periodic occupancy patterns of the octahedral vacancy sites in the van der Waals gap, and their properties can be tuned by varying the coverage and the spatial arrangement of the filled sites7,13. By performing growth under high metal chemical potential14,15 we can access a range of tantalum-intercalated TaS(Se)y, including 25% Ta-intercalated Ta9S16, 33.3% Ta-intercalated Ta7S12, 50% Ta-intercalated Ta10S16, 66.7% Ta-intercalated Ta8Se12 (which forms a Kagome lattice) and 100% Ta-intercalated Ta9Se12. Ferromagnetic order was detected in some of these intercalated phases. We also demonstrate that self-intercalated V11S16, In11Se16 and FexTey can be grown under metal-rich conditions. Our work establishes self-intercalation as an approach through which to grow a new class of 2D materials with stoichiometry- or composition-dependent properties.

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.

Plasmons, collective excitations of charge density, have attracted much interest in fundamental science and applications. While plasmons have been observed in metal-like phase of high-Tc supercondu...

Integrating multiple properties in a single system is crucial for the continuous developments in electronic devices. However, some physical properties are mutually exclusive in nature. Here, we report the coexistence of two seemingly mutually exclusive properties-polarity and two-dimensional conductivity-in ferroelectric Ba$_{0.2}$Sr$_{0.8}$TiO$_3$ thin films at the LaAlO$_3$/Ba$_{0.2}$Sr$_{0.8}$TiO$_3$ interface at room temperature. The polarity of a ~3.2 nm Ba$_{0.2}$Sr$_{0.8}$TiO$_3$ thin film is preserved with a two-dimensional mobile carrier density of ~0.05 electron per unit cell. We show that the electronic reconstruction resulting from the competition between the built-in electric field of LaAlO$_3$ and the polarization of Ba$_{0.2}$Sr$_{0.8}$TiO$_3$ is responsible for this unusual two-dimensional conducting polar phase. The general concept of exploiting mutually exclusive properties at oxide interfaces via electronic reconstruction may be applicable to other strongly-correlated oxide interfaces, thus opening windows to new functional nanoscale materials for applications in novel nanoelectronics., Comment: Main text: 25 pages, 4 figures Supplementary note: 19 pages, 11 figures

International audience; 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.

The effects of atomic-scale disorder and charge (de)localization hold significant importance, and they provide essential insights to unravel the role that strong and weak correlations play in condensed matter systems. In the case of perovskite oxide heterostructures, while disorders introduced via various external stimuli have strong influences over the (de)localization of interfacial two-dimensional (2D) electrons, these factors alone could not fully account for the system's charge dynamics where interfacial hybridization holds very strong influence. Here, we determine that the displaced 2D free electrons have been localized in the specific hybridized states of the LaAlO3/SrTiO3 interface. This experimental study combines both transport measurements and temperature-dependent x-ray absorption spectroscopy and suggests that the localization of 2D electrons can be induced via temperature reduction or ionic liquid gating. Furthermore, this localization effect is found to be applicable to both amorphous and crystalline interfacial systems. In particular, we demonstrate that interfacial hybridization plays a pivotal role in regulating the 2D electron localization effects. Our study resolves the location where the 2D electrons are localized not only does it highlight the importance of interfacial hybridization but it also opens a new avenue for device fabrication in amorphous film systems where charge localization can be done at much great ease as compared to epitaxial crystalline heterostructures.

Efficient photocatalysis is important for sustainable energy. Recently, an unconventional photocatalyst based on intrinsic plasmon, called intrinsic plasmonic photocatalyst (IPP), seems promising for higher efficiency in hydrogen evolution. This catalyst seems to benefit from the advantages of visible light absorption, plasmon-assisted hot carrier generation, and good catalytic stability over conventional semiconductor photocatalysts. In this work, we report the relative hydrogen evolution efficiency under visible light irradiation of a family of IPP based on alkaline earth niobates (MNbO3, where M = Ca, Sr, or Ba), with efficiency of CaNbO3 > SrNbO3 > BaNbO3. The contributions of electron–phonon coupling time constant and solar energy absorption to the hydrogen evolution efficiency are identified as key based on our comprehensive study and characterization of carrier density (1022 cm–3), plasmon absorption, carrier dynamics, and surface area. This study demonstrates a generic approach to create a family of IPPs and further validates the role of solar energy absorption by intrinsic plasmon resonance in the enhancement of photocatalytic efficiency. Ministry of Education (MOE) National Research Foundation (NRF) Accepted version The NUS researchers acknowledge Singapore National Research Foundation under its Competitive Research Funding ’Oxide Electronics on silicon beyond Moore’ (NRF-CRP15-2015-01). X.R.W. acknowledges the support from the Nanyang Assistant Professorship grant from Nanyang Technological University, Academic Research Fund Tier 1 (RG108/17 and RG177/18) from Singapore Ministry of Education. P.Y. is supported by SSLS via NUS Core Support (C-380-003-003-001). The authors thank the Singapore Synchrotron Light Source (SSLS) for providing the facility necessary for conducting the research. The laboratory is a National Research Infrastructure under the National Research Foundation (NRF) Singapore. The authors also thank for the support from Dr. Zhongxin Chen for the photocatalytic reaction measurements. The computational work for this article was partially performed on resources of the National Supercomputing Centre, Singapore (https://www.nscc.sg).

Large polarons have been of significant recent technological interest as they screen and protect electrons from point-scattering centers. Anatase TiO2 is a model system for studying large polarons as they can be studied systematically over a wide range of temperature and carrier density. The electronic and magneto transport properties of reduced anatase TiO2 epitaxial thin films are analyzed considering various polaronic effects. Unexpectedly, with increasing carrier concentration, the mobility increases, which rarely happens in common metallic systems. We find that the screening of the electron–phonon (e–ph) coupling by excess carriers is necessary to explain this unusual dependence. We also find that the magnetoresistance could be decomposed into a linear and a quadratic component, separately characterizing the carrier transport and trapping as a function of temperature, respectively. The various transport behaviors could be organized into a single phase diagram, which clarifies the evolution of large p...

Boron-doped diamond granular thin films are known to exhibit superconductivity with an optimal critical temperature of T c = 7.2 K. Here, we report the measured in-plane complex surface impedance of boron-doped diamond films in the microwave frequency range using a resonant technique. Experimentally measured inductance values are in good agreement with estimates obtained from the normal state sheet resistance of the material. The magnetic penetration depth temperature dependence is consistent with that of a fully gapped s-wave superconductor. Boron-doped diamond films should find application where high kinetic inductance is needed, such as microwave kinetic inductance detectors and quantum impedance devices.

Phase change materials provide unique reconfigurable properties for photonic applications that mainly arise from their exotic characteristic to reversibly switch between the amorphous and crystalline nonvolatile phases. Optical pulse based reversible switching of nonvolatile phases is exploited in various nanophotonic devices. However, large area reversible switching is extremely challenging and has hindered its translation into a technologically significant terahertz spectral domain. Here, this limitation is circumvented by exploiting the semiconducting nature of germanium antimony telluride (GST) to achieve dynamic terahertz control at picosecond timescales. It is also shown that the ultrafast response can be actively altered by changing the crystallographic phase of GST. The ease of fabrication of phase change materials allows for the realization of a variable ultrafast terahertz modulator on a flexible platform. The rich properties of phase change materials combined with the diverse functionalities of metamaterials and all-optical ultrafast control enables an ideal platform for design of efficient terahertz communication devices, terahertz neuromorphic photonics, and smart sensor systems. Agency for Science, Technology and Research (A*STAR) Ministry of Education (MOE) National Research Foundation (NRF) The authors acknowledge research funding support from the Ministry of Education, Singapore (AcRF Tier 1, Grant RG191/17, MOE2017-T2-1-110, MOE2019-T2-1-058, and MOE2016-T3-1-006(S)), Advanced Manufacturing and Engineering (AME) Programmatic grant (A18A5b0056) from Agency for Science, Technology and Research (A*STAR) and NRF CRP on Oxide Electronics on silicon Beyond Moore (NRF-CRP15-2015-01).

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 ∼1.9 eV from multilayer MoS

Photoinduced phase transitions in matters have gained tremendous attention over the past few years. However, their ultrashort lifetime makes their study and possible control very challenging. Here, we report on highly anisotropic d-d excitonic excitations yielding photoinduced metal-insulator transitions (MITs) in quasi-one-dimensional metals Sr1-yNbOx using Mueller-Matrix spectroscopic ellipsometry, transient ultraviolet Raman spectroscopy, transient mid-infrared reflectivity and angular-resolved photoemission spectroscopy supported with density functional theory. Interestingly, the MITs are driven by photo-pumping of d-d excitons, causing the metallic a-axis to become insulating while the insulating b- and c-axis concomitantly become a correlated metal. We assign these effects to an interplay between the melting of charge and lattice orderings along the different anisotropic optical axes and Bose-Einstein-like condensation of the photoinduced excitons. The long lifetime in the order of several seconds of the metastable MITs gives greater flexibility to study and manipulate the transient excitonic state for potential applications in exciton-based optoelectronic devices., Communications Physics, 3 (1)

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.

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

In the quest for post-CMOS technologies, ferromagnetic skyrmions and their anti-particles have shown great promise as topologically protected solitonic information carriers in memory-in-logic or neuromorphic devices. However, the presence of dipolar fields in ferromagnets, restricting the formation of ultra-small topological textures, and the deleterious skyrmion Hall effect when driven by spin torques have thus far inhibited their practical implementations. Antiferromagnetic analogues, which are predicted to demonstrate relativistic dynamics, fast deflection-free motion and size scaling have recently come into intense focus, but their experimental realizations in natural antiferromagnetic systems are yet to emerge. Here, we demonstrate a family of topological antiferromagnetic spin-textures in $\alpha$-Fe$_2$O$_3$ - an earth-abundant oxide insulator - capped with a Pt over-layer. By exploiting a first-order analogue of the Kibble-Zurek mechanism, we stabilize exotic merons-antimerons (half-skyrmions), and bimerons, which can be erased by magnetic fields and re-generated by temperature cycling. These structures have characteristic sizes of the order ~100 nm that can be chemically controlled via precise tuning of the exchange and anisotropy, with pathways to further scaling. Driven by current-based spin torques from the heavy-metal over-layer, some of these AFM textures could emerge as prime candidates for low-energy antiferromagnetic spintronics at room temperature., Comment: 18 pages, 4 figures

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 provides a new route to precisely tailor the charge-transfer process at a functional interface., 40 Pages, 14 Figures, 1 Table

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 SrNbO

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., The interface‐dependent oxygen migration by electrochemical gating is resolved at the atomic scale in the LaAlO3–SrTiO3 system through ex situ ionic liquid gating experiments and on‐site atomic‐resolution characterization. The difference between interface structures leads to the controllable electrochemical oxygen migration by filling oxygen vacancies.

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...

Tailoring spin-orbit interactions and Coulomb repulsion are the key features to observe exotic physical phenomena such as magnetic anisotropy and topological spin texture at oxide interfaces. Our study proposes a novel platform for engineering the magnetism and spin-orbit coupling at LaMnO3/SrIrO3 (3d-5d oxide) interfaces by tuning the LaMnO3 growth conditions which controls the lattice displacement and spin-correlated interfacial coupling through charge transfer. We report on a tunable and enhanced interface-induced Rashba spin-orbit coupling and Elliot-Yafet spin relaxation mechanism in LaMnO3/SrIrO3 bilayer with change in the underlying magnetic order of LaMnO3. We also observed enhanced spin-orbit coupling strength in LaMnO3/SrIrO3 compared to previously reported SrIrO3 layers. The X-Ray spectroscopy measurement reveals the quantitative valence of Mn and their impact on charge transfer. Further, we performed angle-dependent magnetoresistance measurements, which show signatures of magnetic proximity effect in SrIrO3 while reflecting the magnetic order of LaMnO3. Our work thus demonstrates a new route to engineer the interface induced Rashba spin-orbit coupling and magnetic proximity effect in 3d-5d oxide interfaces which makes SrIrO3 an ideal candidate for spintronics applications., Comment: 10 Pages, 4 Figures

Spatiotemporal manipulation of electromagnetic waves has recently enabled a plethora of exotic optical functionalities, such as non-reciprocity, dynamic wavefront control, unidirectional transmission, linear frequency conversion, and electromagnetic Doppler cloak. Here, an additional dimension is introduced for advanced manipulation of terahertz waves in the space-time, and frequency domains through integration of spatially reconfigurable microelectromechanical systems and photoresponsive material into metamaterials. A large and continuous frequency agility is achieved through movable microcantilevers. The ultrafast resonance modulation occurs upon photoexcitation of ion-irradiated silicon substrate that hosts the microcantilever metamaterial. The fabricated metamaterial switches in 400 ps and provides large spectral tunability of 250 GHz with 100% resonance modulation at each frequency. The integration of perfectly complementing technologies of microelectromechanical systems, femtosecond optical control and ion-irradiated silicon provides unprecedented concurrent control over space, time, and frequency response of metamaterial for designing frequency-agile spatiotemporal modulators, active beamforming, and low-power frequency converters for the next generation terahertz wireless communications. National Research Foundation (NRF) The authors acknowledge the research funding support from National Research Foundation (NRF) Singapore and Agence Nationale de la Recherche (ANR), France- NRF2016- ANR004 (M4197003), NRF CRP on Oxide Electronics on silicon Beyond Moore (NRF-CRP15-2015-01) and Advanced Manufacturing and Engineering (AME) Programmatic grant (A18A5b0056) from Agency for Science, Technology and Research (A*STAR).

The chemical asymmetry at the hetero-structure interface offers an effective opportunity to design desirable electronic structures by controlling charge transfer and orbital hybridization across the interface. However, controlling the hetero-interface remains a daunting task. Here, we report the modulation of interfacial coupling of (La0.67Sr0.33MnO3)n/(SrTiO3)n superlattices by manipulating the periodic thickness with n unit cells of SrTiO3 and n unit cells of La0.67Sr0.33MnO3 with a fixed thickness of ~120 unit cells. The easy axis of magnetic anisotropy rotates ~45° towards the out-of-plane direction from n = 10 to n = 2 at reduced temperature TRe = T/TS = 0.87, where TS is the temperature at the onset of magnetization. Transmission electron microscopy reveals an enlarged tetragonal ratio >1 with breaking of volume conservation around the (La0.67Sr0.33MnO3)n/(SrTiO3)n interface and electronic charge transfer from Mn to Ti 3d orbitals across the interface. Orbital hybridization accompanying the charge transfer results in preferred occupancy of $${3d}_{3z^2-r^2}$$ orbitals at the interface and induces a stronger electronic hopping integral and interfacial magnetic anisotropy along the out-of-plane direction, which contributes to the rotation towards the out-of-plane direction of an effective magnetic easy axis for n = 2. We demonstrate that interfacial orbital hybridization with charge transfer in the superlattice of strongly correlated oxides may be a promising approach to tailor electronic and magnetic properties in device applications. A composite material with tuneable magnetic properties which could add novel functionality to electronic devices has been developed by scientists from Singapore and the USA. The interface between two crystalline materials can exhibit properties differing from those of either substance separately. These interface properties can be extended to three dimensions by stacking alternating thin layers of the two materials, creating a so-called superlattice. Bangmin Zhang from the National University of Singapore and co-workers used this concept to alter the magnetic response of a superlattice consisting of lanthanum strontium manganite and strontium titanate. They showed that they could rotate the direction along which the smallest magnetic field is required to magnetize the material by changing the thickness of the layers. This could be useful in devices that are controlled by interaction between electric and magnetic fields. The modulation of interfacial coupling of (La0.67Sr0.33MnO3)n/(SrTiO3)n superlattices with n unit cells of SrTiO3 and n unit cells La0.67Sr0.33MnO3, offers an effective opportunity to control charge transfer and orbital hybridization. The easy axis of magnetic anisotropy rotates ~45° towards the out-of-plane direction from n = 10 to n = 2 at reduced temperature TRe = T/TS = 0.87 (TS is onset of magnetization). Orbital hybridization accompanying the charge transfer results in preferred occupancy of $$3d_{3z_{2} - r_{2}}$$ orbital at the interface, and induces stronger electronic hopping integral and interfacial magnetic anisotropy along perpendicular direction, useful to tailor properties in device applications.

Understanding the interaction of CO2 with perovskite metal oxide surfaces is crucial for the design of various perovskite (electro)chemical functionalities, such as solid oxide fuel cells, catalyti...

Out-of-plane ferroelectricity with a high transition temperature in nanometer-scale films is required to miniaturize electronic devices. Direct visualization of stable ferroelectric polarization and its switching behavior in atomically thick films is critical for achieving this goal. Here, ferroelectric order at room temperature in the two-dimensional limit is demonstrated in tetragonal BiFeO3 ultrathin films. Using aberration-corrected scanning transmission electron microscopy, we directly observed robust out-of-plane spontaneous polarization in one-unit-cell-thick BiFeO3 films. High-resolution piezoresponse force microscopy measurements show that the polarization is stable and switchable, whereas a tunneling electroresistance effect of up to 370% is achieved in BiFeO3 films. Based on first-principles calculations and Kelvin probe force microscopy measurements, we explain the mechanism of polarization stabilization by the ionic displacements in oxide electrode and the surface charges. Our results indicate that critical thickness for ferroelectricity in the BiFeO3 film is virtually absent, making it a promising candidate for high-density nonvolatile memories., High temperature perpendicular ferroelectricity in nano thin films is crucial for miniaturization of electronic devices. Here the authors show the presence of stable and switchable out-of-plane ferroelectricity in tetragonal BiFeO3 thin films at the two-dimensional limit and 370% tunneling electroresistance in ferroelectric tunnel junctions.

Electrons commonly couple through Fr\"ohlich interactions with longitudinal optical phonons to form polarons. However, trions possess a finite angular momentum and should therefore couple instead to rotational optical phonons. This creates a polaronic trion whose binding energy is determined by the crystallographic orientation of the lattice. Here, we demonstrate theoretically within the Fr\"ohlich approach and experimentally by photoluminescence emission that the bare trion binding energy (20 meV) is significantly enhanced by the phonons at the interface between the two-dimensional semiconductor MoS$_2$ and the bulk transition metal oxide SrTiO$_3$. The low-temperature {binding energy} changes from 60 meV in [001]-oriented substrates to 90 meV for [111] orientation, as a result of the counter-intuitive interplay between the rotational axis of the MoS$_2$ trion and that of the SrTiO$_3$ phonon mode., Comment: 5+ pages (4 figures) + Suppl. Materials (7 figures), to appear in Phys. Rev. Lett. (August 2020)

In contrast to Ti4+-containing titanium dioxide (TiO2), which has a wide bandgap (∼3.0 eV) and has been widely explored for catalysis and energy applications, titanium sesquioxide (Ti2O3) with an intermediate valence state (Ti3+) possesses an ultranarrow bandgap (∼0.1 eV) and has been much less investigated. Although the importance of Ti3+ to the applications of TiO2 is widely recognized, the connection between TiO2 and Ti2O3 and the transformation pathway remain unknown. Herein, we investigate the oxidation-induced structural, phase, and property evolution of Ti2O3 using a complementary suite of microscopic and spectroscopic tools. Interestingly, transformation pathways to both rutile and anatase TiO2 are identified, which sensitively depend on oxidation conditions. Unique Ti2O3/TiO2 core–shell structures with annealing-controlled surface nanostructure formation are observed for the first time. The compositional and structural evolution of Ti2O3/TiO2 particles is accompanied by continuously tuned optical...

In recent years, there has been an extensive search for a non-invasive screening technique for early detection of lung cancer. Volatile organic compound (VOC) analysis in exhaled breath is one such promising technique. This approach is based on the fact that tumor growth is accompanied by unique oncogenesis, leading to detectable changes in VOC emitting profile. Here, we conducted a comprehensive profiling of VOCs and metabolites from six different lung cancer cell lines and one normal lung cell line using mass spectrometry. The concomitant VOCs and metabolite profiling allowed significant discrimination between lung cancer and normal cell, nonsmall cell lung cancer (NSCLC) and small cell lung cancer (SCLC), as well as between different subtypes of NSCLC. It was found that a combination of benzaldehyde, 2-ethylhexanol, and 2,4-decadien-1-ol could serve as potential volatile biomarkers for lung cancer. A detailed correlation between nonvolatile metabolites and VOCs can demonstrate possible biochemical pathways for VOC production by the cancer cells, thus enabling further optimization of VOCs as biomarkers. These findings could eventually lead to noninvasive early detection of lung cancer and differential diagnosis of lung cancer subtypes, thus revolutionizing lung cancer treatment.

Polymorph engineering of 2H-MoS2, which can be achieved by alkali metal intercalation to obtain either the mixed 2H/1T′ phases or a homogeneous 1T′ phase, has received wide interest recently, since this serves as an effective route to tune the electrical and catalytic properties of MoS2. As opposed to an idealized single crystal-to-single crystal phase conversion, the 2H to 1T′ phase conversion results in crystal domain size reduction as well as strained lattices, although how these develop with composition is not well understood. Herein, the evolution of the phonon modes in Li-intercalated 1T′-MoS2 (LixMoS2) are investigated as a function of different 1T′-2H compositions. We observed that the strain evolution in the mixed phases is revealed by the softening of four Raman modes, Bg (J1), Ag (J3), E12g, and A1g, with increasing 1T′ phase composition. Additionally, the first-order temperature coefficients of the 1T′ phonon mode vary linearly with increasing 1T′ composition, which is explained by increased e...

Brain-inspired computing is an emerging field, which intends to extend the capabilities of information technology beyond digital logic. The progress of the field relies on artificial synaptic devices as the building block for brainlike computing systems. Here, we report an electronic synapse based on a ferroelectric tunnel memristor, where its synaptic plasticity learning property can be controlled by nanoscale interface engineering. The effect of the interface engineering on the device performance was studied. Different memristor interfaces lead to an opposite virgin resistance state of the devices. More importantly, nanoscale interface engineering could tune the intrinsic band alignment of the ferroelectric/metal-semiconductor heterostructure over a large range of 1.28 eV, which eventually results in different memristive and spike-timing-dependent plasticity (STDP) properties of the devices. Bidirectional and unidirectional gradual resistance modulation of the devices could therefore be controlled by tuning the band alignment. This study gives useful insights on tuning device functionalities through nanoscale interface engineering. The diverse STDP forms of the memristors with different interfaces may play different specific roles in various spike neural networks.

Herein, we report a systematic study of water contact angle (WCA) of rare-earth oxide thin-films. These ultra-smooth and epitaxial thin-films were grown using pulsed laser deposition and then characterized using X-Ray diffraction (XRD), Rutherford backscattering spectroscopy (RBS), and atomic force microscopy (AFM). Through both the traditional sessile drop and the novel f–d method, we found that the films were intrinsically hydrophilic (WCA < 10°) just after being removed from the growth chamber, but their WCAs evolved with an exposure to the atmosphere with time to reach their eventual saturation values near 90° (but always stay ‘technically’ hydrophilic). X-Ray photoelectron spectroscopy analysis was used to further investigate qualitatively the nature of hydrocarbon contamination on the freshly prepared as well as the environmentally exposed REO thin-film samples as a function of the exposure time after they were removed from the deposition chamber. A clear correlation between the carbon coverage of the surface and the increase in WCA was observed for all of the rare-earth films, indicating the extrinsic nature of the surface wetting properties of these films and having no relation to the electronic configuration of the rare-earth atoms as proposed by Azimi et al.