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2.
Nano Lett ; 21(18): 7448-7456, 2021 Sep 22.
Artigo em Inglês | MEDLINE | ID: mdl-34498884

RESUMO

A concept of spin plasmon, a collective mode of spin-density, in strongly correlated electron systems has been proposed since the 1930s. It is expected to bridge between spintronics and plasmonics by strongly confining the photon energy in the subwavelength scale within single magnetic-domain to enable further miniaturizing devices. However, spin plasmon in strongly correlated electron systems is yet to be realized. Herein, we present a new spin correlated-plasmon at room temperature in novel Mott-like insulating highly oriented single-crystalline gold quantum-dots (HOSG-QDs). Interestingly, the spin correlated-plasmon is tunable from the infrared to visible, accompanied by spectral weight transfer yielding a large quantum absorption midgap state, disappearance of low-energy Drude response, and transparency. Supported with theoretical calculations, it occurs due to an interplay of surprisingly strong electron-electron correlations, s-p hybridization and quantum confinement in the s band. The first demonstration of the high sensitivity of spin correlated-plasmon in surface-enhanced Raman spectroscopy is also presented.

3.
J Phys Condens Matter ; 34(6)2021 Nov 23.
Artigo em Inglês | MEDLINE | ID: mdl-34340220

RESUMO

A new phenomenon of correlated plasmons was first observed in the insulating phase of the Sr1-xNb1-yO3+δfamily (Asamaraet al2017Nat. Commun.815271). The correlated plasmons are tunable, have multiple plasmonic frequencies, and exhibit low loss-making them desirable in numerous plasmonic applications. However, their fundamental mechanism is yet to be explored. While conventional plasmons can be understood solely by considering long-range interactions, unconventional correlated plasmons arise in correlated electron systems and require consideration of the short-range interactions. Here, we report how the interplay of short-range and long-range interactions determines the correlated plasmon phenomena through a coupled harmonic oscillator model of both 1D and quasi-1D systems. In each system, the impact of various physical parameters like the number of oscillators, energy scale, free electron scattering parameter, quasi-particle concentration, charges, effective masses, and Coulomb interaction strengths are explored to gain an understanding of their impact on the complex dielectric function and loss function. We study both cases where the parameters are the same for all quasi-particles and where effective mass, Coulomb interaction strength, and charge are varied for individual quasi-particles. In an extended model of the quasi-1D system, we study both cases where the rung symmetry of all parameters is conserved and where it is broken. When rung symmetry is conserved, the overall trends in optical and plasmonic peaks are the same as the 1D model, though the peaks tend to shift to higher energies and amplitudes. When rung symmetry is broken, the quasi-1D behavior deviates significantly from the 1D model, including an increase in the maximum possible number of optical and plasmonic peaks. Overall, our results demonstrate the significance of the interplay of short-range and long-range interactions in determining the correlated plasmons and identifying how various parameters can be used to tune the resulting plasmons.

4.
Biochem Mol Biol Educ ; 49(2): 216-227, 2021 03.
Artigo em Inglês | MEDLINE | ID: mdl-32897655

RESUMO

The fundamental mechanism of biochemistry lies on the reaction kinetics, which is determined by the reaction pathways. Interestingly, the reaction pathway is a challenging concept for undergraduate students. Experimentally, it is difficult to observe, and theoretically, it requires some degree of physics knowledge, namely statistical and quantum mechanics. However, students can utilize computational methods to study the reaction kinetics without paying too much attention but not wholly neglecting the comprehension of physics. We hereby provided an approach to study the reaction kinetics based on density-functional calculations. We particularized the study of the isomerization case involving five molecules at three different temperatures and emphasized the importance of the transition state in the study of reaction kinetics. The results we presented were in good agreement with the experiments and provided useful insights to assist students in the application of their knowledge into their research.


Assuntos
Bioquímica/educação , Modelos Químicos , Termodinâmica , Humanos , Isomerismo , Cinética
5.
Small ; 16(50): e2004683, 2020 Dec.
Artigo em Inglês | MEDLINE | ID: mdl-33191619

RESUMO

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.

6.
Nat Commun ; 11(1): 5483, 2020 Oct 30.
Artigo em Inglês | MEDLINE | ID: mdl-33127900

RESUMO

Quasi-two-dimensional perovskites have emerged as a new material platform for optoelectronics on account of its intrinsic stability. A major bottleneck to device performance is the high charge injection barrier caused by organic molecular layers on its basal plane, thus the best performing device currently relies on edge contact. Herein, by leveraging on van der Waals coupling and energy level matching between two-dimensional Ruddlesden-Popper perovskite and graphene, we show that the plane-contacted perovskite and graphene interface presents a lower barrier than gold for charge injection. Electron tunneling across the interface occurs via a gate-tunable, direct tunneling-to-field emission mechanism with increasing bias, and photoinduced charge transfer occurs at femtosecond timescale (~50 fs). Field effect transistors fabricated on molecularly thin Ruddlesden-Popper perovskite using graphene contact exhibit electron mobilities ranging from 0.1 to 0.018 cm2V-1s-1 between 1.7 to 200 K. Scanning tunneling spectroscopy studies reveal layer-dependent tunneling barrier and domain size on few-layered Ruddlesden-Popper perovskite.

7.
Science ; 369(6501): 292-297, 2020 07 17.
Artigo em Inglês | MEDLINE | ID: mdl-32675370

RESUMO

High-performance piezoelectric materials are critical components for electromechanical sensors and actuators. For more than 60 years, the main strategy for obtaining large piezoelectric response has been to construct multiphase boundaries, where nanoscale domains with local structural and polar heterogeneity are formed, by tuning complex chemical compositions. We used a different strategy to emulate such local heterogeneity by forming nanopillar regions in perovskite oxide thin films. We obtained a giant effective piezoelectric coefficient [Formula: see text] of ~1098 picometers per volt with a high Curie temperature of ~450°C. Our lead-free composition of sodium-deficient sodium niobate contains only three elements (Na, Nb, and O). The formation of local heterogeneity with nanopillars in the perovskite structure could be the basis for a general approach to designing and optimizing various functional materials.

8.
Adv Mater ; 32(34): e2000153, 2020 Aug.
Artigo em Inglês | MEDLINE | ID: mdl-32643185

RESUMO

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.

9.
Phys Chem Chem Phys ; 22(28): 16431, 2020 Jul 22.
Artigo em Inglês | MEDLINE | ID: mdl-32639488

RESUMO

Correction for 'The effect of crystallinity on the surface modification and optical properties of ZnO thin films' by Muhammad Abiyyu Kenichi Purbayanto et al., Phys. Chem. Chem. Phys., 2020, 22, 2010-2018, DOI: 10.1039/C9CP05464B.

10.
Adv Sci (Weinh) ; 7(10): 1902726, 2020 May.
Artigo em Inglês | MEDLINE | ID: mdl-32440469

RESUMO

The quasimetallic 1T' phase 2D transition-metal dichalcogenides (TMDs) consist of 1D zigzag metal chains stacked periodically along a single axis. This gives rise to its prominent physical properties which promises the onset of novel physical phenomena and applications. Here, the in-plane electronic correlations are explored, and new mid-infrared plasmon excitations in 1T' phase monolayer WSe2 and MoS2 are observed using optical spectroscopies. Based on an extensive first-principles study which analyzes the charge dynamics across multiple axes of the atomic-layered systems, the collective charge excitations are found to disperse only along the direction perpendicular to the chains. Further analysis reveals that the interchain long-range coupling is responsible for the coherent 1D charge dynamics and the spin-orbit coupling affects the plasmon frequency. Detailed investigation of these charge collective modes in 2D-chained systems offers opportunities for novel device applications and has implications for the underlying mechanism that governs superconductivity in 2D TMD systems.

11.
Opt Express ; 28(9): 12922-12935, 2020 Apr 27.
Artigo em Inglês | MEDLINE | ID: mdl-32403778

RESUMO

Undesired mask-induced effects caused by thick absorber layers in EUV photomasks reduce the quality of the projected patterns at the wafer stage in EUV photolithography scanners. New materials with better absorption properties than the state-of-the-art absorbers, TaN and TaBN, are required to mitigate these effects. In this work, we investigated the optical properties (δ and k) of Te and TeO films in the 13-14 nm range, and the absorption properties of these two materials at 13.5 nm. δ and k are obtained through fitting experimental values of reflectivity versus angle of incidence in the EUV range. We follow a methodology which combines different characterization techniques (X-ray reflectivity, EUV reflectivity, and X-ray photoemission spectroscopy) to reduce the number of free parameters in models and hence, increase the reliability of the optical constants obtained. At 13.5 nm, we obtain δ=0.03120, k = 0.07338 for Te, and δ=0.04099, k = 0.06555 for TeO. To experimentally verify the absorption properties of these materials, different thicknesses of Te and TeO films are cast on top of a state-of-the-art mask-quality EUV multilayer with 66.7% reflectivity at 13.5 nm. We found that a reflectivity of ∼0.7% can be attained with either 32.4 nm of Te, or 34.7 nm of TeO, greatly surpassing the absorption properties of TaN and TaBN. The morphology and surface roughness of the Te and TeO films deposited on the multilayer are also investigated.

12.
Nano Lett ; 20(4): 2493-2499, 2020 Apr 08.
Artigo em Inglês | MEDLINE | ID: mdl-32134679

RESUMO

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.

13.
ACS Nano ; 14(3): 3290-3298, 2020 Mar 24.
Artigo em Inglês | MEDLINE | ID: mdl-32101687

RESUMO

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.

14.
Nano Lett ; 20(3): 1890-1895, 2020 Mar 11.
Artigo em Inglês | MEDLINE | ID: mdl-32004008

RESUMO

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.

15.
Phys Chem Chem Phys ; 22(4): 2010-2018, 2020 Jan 28.
Artigo em Inglês | MEDLINE | ID: mdl-31903459

RESUMO

We have studied the effects of crystallinity on the emergence of porous morphology and strong green emission in ZnO thin films after H2 annealing treatment. The unique multiple-stacked porous structure is observed after performing H2 annealing treatment on the film with low crystallinity. However, the annealed high-crystallinity film exhibits surface morphology with a shallow porous structure, as revealed by SEM images. To study the effects of these unique porous structures on the optical properties, photoluminescence (PL) spectroscopy, Raman spectroscopy, spectroscopic ellipsometry, and X-ray photoelectron spectroscopy (XPS) are conducted. The multiple-stacked porous structure produces strong green emission as compared to the shallow porous structure centered at 2.5 eV, as detected by PL. Here, the green emission originates from the electronic transition related to the oxygen vacancy (VO). XPS spectra show that the high density of VO located on the multiple-stacked porous surface is much higher as compared to that for the shallow porous structure due to a high surface-to-volume ratio. The results show that the multiple-stacked porous structure has the potential to enhance the functionality of ZnO for applications in light-emitting.

16.
Nano Lett ; 20(2): 1101-1109, 2020 Feb 12.
Artigo em Inglês | MEDLINE | ID: mdl-31944125

RESUMO

Oxide heterostructures have attracted a lot of interest because of their rich exotic phenomena and potential applications. Recently, a greatly enhanced tunneling electroresistance (TER) of ferroelectric tunnel junctions (FTJs) has been realized in such heterostructures. However, our understanding on the electronic structure of resistance response with polarization reversal and the origin of huge TER is still lacking. Here, we report on electronic structures, particularly at the interface and surface, and the control of the spontaneous polarization of BaTiO3 films by changing the termination of a SrTiO3 substrate. Interestingly, unusual electron and hole midgap states are concurrently formed and accompanied by orbital reconstructions, which determine the ferroelectric polarization orientation in the BaTiO3/SrTiO3. Such unusual midgap states, which yield a strong electronic screening effect, reduce the ferroelectric barrier width and height, and pin the ferroelectric polarization, lead to a dramatic enhancement of the TER effect. The midgap states are also observed in BaTiO3 films on electron-doped Nb/SrTiO3 revealing its universality. Our result provides new insight into the origin of the huge TER effect and opens a new route for designing ferroelectric tunnel junction-based devices with huge TER through interface engineering.

17.
ACS Appl Mater Interfaces ; 12(3): 4114-4122, 2020 Jan 22.
Artigo em Inglês | MEDLINE | ID: mdl-31927903

RESUMO

A controllable electronic manipulation in a frustrated magnetic system such as solution-based two-dimensional (2D) all-inorganic perovskites offers a possible route for their integrations with electronic and magnetic devices for their advanced applications. Here, we perform element-specific investigations of an emergent class of quasi-2D all-inorganic perovskites Cs2CuCl4-xBrx with (0 ≤ x ≤ 4) using a combination of synchrotron-radiation photoelectron techniques. Surface- and element-sensitive X-ray absorption spectroscopy spectra of Cu L2,3 edges indicate strong electronic transition that is largely influenced by their halogen content at room temperature. This implies that site-selective occupation largely dominates the electronic transition across the unoccupied states of these series since chlorine atoms possess a stronger electronegative character than bromine atoms. Moreover, the implication of halogen site is reflected in the valence band of Cl-rich copper perovskite in which the valence band edge is closer to Fermi energy (EF) than that of the Br-rich compound. Furthermore, X-ray magnetic circular dichroism spectra of mixed ratio and Br-rich compounds exhibit antiferromagnetism at room temperature. These site-specific magnetic-spectroscopic results are corroborated by density functional theory calculations. The strong electronic modulation and the local magnetic spectroscopy results in these solution-based and low-temperature-growth materials will pave the way toward energy- and cost-efficient perovskite devices.

18.
ACS Nano ; 13(12): 14529-14539, 2019 Dec 24.
Artigo em Inglês | MEDLINE | ID: mdl-31702890

RESUMO

The intricate features of many-body interactions and spin-orbit coupling play a significant role in numerous physical phenomena. Particularly in two-dimensional transition metal dichalcogenides (2D-TMDs), excitonic dynamics are a key phenomenon that promises opportunities for diverse range of device applications. Here, we report the direct observation of a visible-range three-dimensional resonant exciton and its associated charged exciton in monolayer tungsten diselenide, as compared to monolayer molybdenum disulfide. A comprehensive experimental study that includes high-resolution TEM, Raman, high-resolution spectroscopic ellipsometry over a wide temperature range down to 4 K, high-energy temperature, and excitation power-dependent photoluminescence spectroscopy has been conducted. It is supported by first-principles calculations to unravel the influence of spin-orbit coupling in the formation of the resonant exciton and to identify its in-plane and out-of-plane features. Furthermore, we study the impact of temperature and thickness on the spin-orbit coupling strength in 2D-TMDs. This work is crucial in creating a platform in the fundamental understanding of high-energy resonant exciton in layered two-dimensional systems and that such high-energy optoelectronic features make them an increasingly attractive candidate for novel electronic and optoelectronic applications particularly in the aspects of solar cells and light-emitting diodes via the manipulation of excitonic states.

19.
ACS Appl Mater Interfaces ; 11(46): 43781-43788, 2019 Nov 20.
Artigo em Inglês | MEDLINE | ID: mdl-31660716

RESUMO

High magnetization materials are in great demand for the fabrication of advanced multifunctional magnetic devices. Notwithstanding this demand, the development of new materials with these attributes has been relatively slow. In this work, we propose a new strategy to achieve high magnetic moments above room temperature. Our material engineering approach invoked the embedding of magnetic nanoclusters in an oxide matrix. By precisely controlling pulsed laser deposition parameters, Co nanoclusters are formed in a 5 at % Co-TiO2 film. The presence of these nanoclusters was confirmed using transmission electron microscopy, energy-dispersive X-ray spectroscopy, and X-ray absorption fine structure. The film exhibits a very high saturation magnetization of 99 emu/cm3. Detailed studies using X-ray magnetic circular dichroism confirm that Co has an enhanced magnetic moment of 3.5 µB/atom, while the Ti and O also contribute to the magnetic moments. First-principles calculations supported our hypothesis that the metallic Co nanoclusters surrounded by a TiO2 matrix can exhibit both large spin and orbital moments. Moreover, a quantum confinement effect results in a high Curie temperature for the embedded Co nanoclusters. These findings reveal that 1-2 nm nanoclusters that are quantum confined can exhibit very large magnetic moments above room temperature, representing a promising advance for the design of new high magnetization materials.

20.
Nano Lett ; 19(11): 8040-8048, 2019 11 13.
Artigo em Inglês | MEDLINE | ID: mdl-31560545

RESUMO

Although Si acts as an electrical semiconductor, it has properties of an optical dielectric. Here, we revisit the behavior of Si as a plasmonic metal. This behavior was previously shown to arise from strong interband transitions that lead to negative permittivity of Si across the ultraviolet spectral range. However, few have studied the plasmonic characteristics of Si, particularly in its nanostructures. In this paper, we report localized plasmon resonances of Si nanostructures and the observation of plasmon hybridization in the UV (∼250 nm wavelength). In addition, simulation results show that Si nanodisk dimers can achieve a local intensity enhancement greater than ∼500-fold in a 1 nm gap. Lastly, we investigate hybrid Si-Al nanostructures to achieve sharp resonances in the UV, due to the coupling between plasmon resonances supported by Si and Al nanostructures. These results will have potential applications in the UV range, such as nanostructured devices for spectral filtering, plasmon-enhanced Si photodetectors, interrogation of molecular chirality, and catalysis. It could have significant impact on UV photolithography on patterned Si structures.

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