Energy

/Tag: Energy

Promoted Glycerol Oxidation Reaction in an Interface‐Confined Hierarchically Structured Catalyst

2018-11-18T00:34:15+00:00November 17th, 2018|Categories: Publications|Tags: , |

The confinement of Pt nanosheets is realized in a vertically erected graphene array with hierarchically porous architecture to address the mass‐diffusion limitation in interface‐confined catalysis. Such a confined 3D catalyst exhibits a much stronger oxidation and CC bond cleaving ability for the glycerol oxidation reaction, leading to a superior mass activity and selectivity toward C1 products than commercial Pt/C catalysts. Abstract Confined catalysis in a 2D system is of particular interest owing to the facet control of the catalysts and the anisotropic kinetics of reactants, which suppress side reactions and improve selectivity. Here, a 2D‐confined system consisting of intercalated Pt nanosheets within few‐layered graphene is demonstrated. The strong metal–substrate interaction between the Pt nanosheets and the graphene leads to the quasi‐2D growth of Pt with a unique (100)/(111)/(100) faceted structure, thus providing excellent catalytic activity and selectivity toward one‐carbon (C1) products for the glycerol oxidation reaction. A hierarchically porous graphene architecture, grown on carbon cloth, is used to fabricate the confined catalyst bed in order to enhance the mass‐diffusion limitation in interface‐confined reactions. Owing to its unique 3D porous structure, this graphene‐confined Pt catalyst exhibits an extraordinary mass activity of 2910 mA mgPt−1 together with a formate selectivity of 79% at 60 °C. This paves the way toward rational designs of heterogeneous catalysts for energy‐related applications.

Published in: "Advanced Materials".

Deactivating Defects in Graphenes with Al2O3 Nanoclusters to Produce Long‐Life and High‐Rate Sodium‐Ion Batteries

2018-11-18T00:32:36+00:00November 17th, 2018|Categories: Publications|Tags: , |

The defects in graphene are deactivated by the coverage of Al2O3 nanoclusters, which suppress the irreversible decomposition of the sodium conductive salt in sodium‐ion battery electrolytes. An ion‐conducting, thin and homogenous solid electrolyte interphase is formed, resulting in high initial Coulombic efficiency, good rate capability, and cyclic stability for sodium‐ion storage. Abstract Carbon materials are the most promising anodes for sodium‐ion batteries (SIBs), but low initial Coulombic efficiency (ICE) and poor cyclic stability hinder their practical use. It is shown herein, that an effective but simple remedy for these problems can be achieved by deactivating defects in the carbon with Al2O3 nanocluster coverage. A 3D porous graphene monolith (PGM) is used as the model material and Al2O3 nanoclusters around 1 nm are grown on the defects of graphene. It is shown that these Al2O3 nanoclusters suppress the decomposition of conductive sodium salt in the electrolyte, resulting in the formation of a thin and homogenous solid electrolyte interphase (SEI). In addition, Al2O3 nanoclusters appear to reduce the detrimental etching of the SEI by hydrogen fluoride (HF) and improve its stability. Therefore, after the introduction of Al2O3 nanoclusters, the ICE, cyclic stability, and rate capability of the PGM are greatly improved. A higher ICE (70.2%) and capacity retention (82.9% after 500 cycles at 0.5 A g−1) than those of normally reported for large surface area carbons are achieved. This work indicates a new way to deactivate defects and modify the SEI of carbon materials, and hopefully accelerate the commercialization of carbon

Published in: "Advanced Energy Materials".

Phosphorus‐Mediated MoS2 Nanowires as a High‐Performance Electrode Material for Quasi‐Solid‐State Sodium‐Ion Intercalation Supercapacitors

2018-11-17T22:34:20+00:00November 17th, 2018|Categories: Publications|Tags: , |

We propose an efficient P‐anion doping strategy to enhance the electrochemical performance of the MoS2 nanowires by increasing the number of electrochemically active sites, improving the electrical conductivity, and decreasing the energy barrier of Na+ ion diffusion. The P‐doped MoS2 delivers remarkable specific capacitance and rate capability. This study highlights the dominating role of P dopants in electrode materials for supercapacitors. Abstract Molybdenum disulfide (MoS2) is a promising electrode material for electrochemical energy storage owing to its high theoretical specific capacity and fascinating 2D layered structure. However, its sluggish kinetics for ionic diffusion and charge transfer limits its practical applications. Here, a promising strategy is reported for enhancing the Na+‐ion charge storage kinetics of MoS2 for supercapacitors. In this strategy, electrical conductivity is enhanced and the diffusion barrier of Na+ ion is lowered by a facile phosphorus‐doping treatment. Density functional theory results reveal that the lowest energy barrier of dilute Na‐vacancy diffusion on P‐doped MoS2 (0.11 eV) is considerably lower than that on pure MoS2 (0.19 eV), thereby signifying a prominent rate performance at high Na intercalation stages upon P‐doping. Moreover, the Na‐vacancy diffusion coefficient of the P‐doped MoS2 at room temperatures can be enhanced substantially by approximately two orders of magnitude (10−6–10−4 cm2 s−1) compared with pure MoS2. Finally, the quasi‐solid‐state asymmetrical supercapacitor assembled with P‐doped MoS2 and MnO2, as the positive and negative electrode materials, respectively, exhibits an ultrahigh energy density of 67.4 W h kg−1 at 850 W kg−1 and excellent cycling stability with 93.4% capacitance

Published in: "Small".

Dipole Formation at the MoO3/Conjugated Polymer Interface

2018-11-17T22:32:20+00:00November 17th, 2018|Categories: Publications|Tags: |

MoO3 forms a strong dipole at the interface to P3HT/PC61BM. The dipole increases with increasing thickness of the MoO3 layer and saturates at 2.2 eV at a thickness around 3 nm of MoO3. The formation of the strong dipole is of high importance for the charge transport over the MoO3/polymer interface. Abstract MoO3 is known as high work function (WF) transparent metal oxides. It is used as anode buffer layer in organic based solar cells because of its capability to extract electrons and inject holes from the active layer due to its high WF. Here a broad range of techniques is used to determine the energy levels of the bulk heterojunction (BHJ) and MoO3 to determine that the minimum deposition thickness to achieve a closed layer is 1 nm due to penetration of the evaporated MoO3 into the BHJ. The investigation shows that upon evaporation of the MoO3, a strong dipole is formed at the extended interface between the active layer and the MoO3 and that the strength of the dipole increases with increasing thickness of the MoO3 layer and saturates at 2.2 eV at a thickness around 3 nm.

Published in: "Advanced Functional Materials".

Exfoliated Layered Manganese Trichalcogenide Phosphite (MnPX3, X = S, Se) as Electrocatalytic van der Waals Materials for Hydrogen Evolution

2018-11-17T22:32:00+00:00November 17th, 2018|Categories: Publications|Tags: |

Metal phosphorus chalcogenides (MPX 3) have reclaim ample interest as 2D layered materials, due to favorable performances in energy storage and conversion. Herein, MnPX 3 (X = S, Se) are synthetized and submitted to shear force exfoliation. Exfoliated MnPSe3 has the lowest onset potential and best stability for hydrogen evolution. Such materials show a great promise for future in a hydrogen‐based economy. Abstract Layered metal trichalcogen phosphites, also entitled as metal phosphorus chalcogenides (MPX 3), have regained abundant interest, not only due to their magnetic properties, but also due to promising performances in energy storage and conversion. Herein, two different layered manganese trichalcogen phosphites, MnPX3 (X = S, Se), are synthetized and submitted to shear force exfoliation. Structural and morphological characterization point to the fact that exfoliated MPX 3 (exf‐MnPX 3) undergo mainly a downsizing process, alongside with delamination. Layered exf‐MnPSe3 has the lowest onset potential for hydrogen evolution reaction (HER) in both media. In acidic media, a comparative improvement of 350 mV is observed for exf‐MnPSe3 relative to the bulk MnPSe3. The materials stability as electrocatalysts is also tested for HER in a wide pH range, in which exf‐MnPSe3 has a good stability after 100 cycles. The improved performance of exf‐MnPSe3 can be correlated with the lower relative abundance of Mn and P oxides detected in the Mn 2p and P 2p core levels. Such materials show a great promise for future in a hydrogen‐based economy.

Published in: "Advanced Functional Materials".

Exfoliated Layered Manganese Trichalcogenide Phosphite (MnPX3, X = S, Se) as Electrocatalytic van der Waals Materials for Hydrogen Evolution

2018-11-17T02:32:30+00:00November 17th, 2018|Categories: Publications|Tags: |

Metal phosphorus chalcogenides (MPX 3) have reclaim ample interest as 2D layered materials, due to favorable performances in energy storage and conversion. Herein, MnPX 3 (X = S, Se) are synthetized and submitted to shear force exfoliation. Exfoliated MnPSe3 has the lowest onset potential and best stability for hydrogen evolution. Such materials show a great promise for future in a hydrogen‐based economy. Abstract Layered metal trichalcogen phosphites, also entitled as metal phosphorus chalcogenides (MPX 3), have regained abundant interest, not only due to their magnetic properties, but also due to promising performances in energy storage and conversion. Herein, two different layered manganese trichalcogen phosphites, MnPX3 (X = S, Se), are synthetized and submitted to shear force exfoliation. Structural and morphological characterization point to the fact that exfoliated MPX 3 (exf‐MnPX 3) undergo mainly a downsizing process, alongside with delamination. Layered exf‐MnPSe3 has the lowest onset potential for hydrogen evolution reaction (HER) in both media. In acidic media, a comparative improvement of 350 mV is observed for exf‐MnPSe3 relative to the bulk MnPSe3. The materials stability as electrocatalysts is also tested for HER in a wide pH range, in which exf‐MnPSe3 has a good stability after 100 cycles. The improved performance of exf‐MnPSe3 can be correlated with the lower relative abundance of Mn and P oxides detected in the Mn 2p and P 2p core levels. Such materials show a great promise for future in a hydrogen‐based economy.

Published in: "Advanced Functional Materials".

Realization of flat band with possible nontrivial topology in electronic Kagome lattice

2018-11-16T22:36:24+00:00November 16th, 2018|Categories: Publications|Tags: |

The energy dispersion of fermions or bosons vanishes in momentum space if destructive quantum interference occurs in a frustrated Kagome lattice with only nearest-neighbor hopping. A discrete flat band (FB) without any dispersion is consequently formed, promising the emergence of fractional quantum Hall states at high temperatures. Here, we report

Published in: "Science Advances".

Ultrafine MnO2 nanowires grown on RGO-coated carbon cloth as a binder-free and flexible supercapacitor electrode with high performance

2018-11-16T12:33:28+00:00November 16th, 2018|Categories: Publications|Tags: , , |

RSC Adv., 2018, 8,38631-38640DOI: 10.1039/C8RA05890C, Paper Open Access &nbsp This article is licensed under a Creative Commons Attribution-NonCommercial 3.0 Unported Licence.Zhihui Xu, Shishuai Sun, Wen Cui, Dan Yu, Jiachun DengReduced graphene oxide coated carbon cloth has been used as a substrate for the

Published in: "RSC Advances".

Phosphorus‐Mediated MoS2 Nanowires as a High‐Performance Electrode Material for Quasi‐Solid‐State Sodium‐Ion Intercalation Supercapacitors

2018-11-16T04:38:32+00:00November 16th, 2018|Categories: Publications|Tags: , |

We propose an efficient P‐anion doping strategy to enhance the electrochemical performance of the MoS2 nanowires by increasing the number of electrochemically active sites, improving the electrical conductivity, and decreasing the energy barrier of Na+ ion diffusion. The P‐doped MoS2 delivers remarkable specific capacitance and rate capability. This study highlights the dominating role of P dopants in electrode materials for supercapacitors. Abstract Molybdenum disulfide (MoS2) is a promising electrode material for electrochemical energy storage owing to its high theoretical specific capacity and fascinating 2D layered structure. However, its sluggish kinetics for ionic diffusion and charge transfer limits its practical applications. Here, a promising strategy is reported for enhancing the Na+‐ion charge storage kinetics of MoS2 for supercapacitors. In this strategy, electrical conductivity is enhanced and the diffusion barrier of Na+ ion is lowered by a facile phosphorus‐doping treatment. Density functional theory results reveal that the lowest energy barrier of dilute Na‐vacancy diffusion on P‐doped MoS2 (0.11 eV) is considerably lower than that on pure MoS2 (0.19 eV), thereby signifying a prominent rate performance at high Na intercalation stages upon P‐doping. Moreover, the Na‐vacancy diffusion coefficient of the P‐doped MoS2 at room temperatures can be enhanced substantially by approximately two orders of magnitude (10−6–10−4 cm2 s−1) compared with pure MoS2. Finally, the quasi‐solid‐state asymmetrical supercapacitor assembled with P‐doped MoS2 and MnO2, as the positive and negative electrode materials, respectively, exhibits an ultrahigh energy density of 67.4 W h kg−1 at 850 W kg−1 and excellent cycling stability with 93.4% capacitance

Published in: "Small".

Deactivating Defects in Graphenes with Al2O3 Nanoclusters to Produce Long‐Life and High‐Rate Sodium‐Ion Batteries

2018-11-16T04:36:45+00:00November 16th, 2018|Categories: Publications|Tags: , |

The defects in graphene are deactivated by the coverage of Al2O3 nanoclusters, which suppress the irreversible decomposition of the sodium conductive salt in sodium‐ion battery electrolytes. An ion‐conducting, thin and homogenous solid electrolyte interphase is formed, resulting in high initial Coulombic efficiency, good rate capability, and cyclic stability for sodium‐ion storage. Abstract Carbon materials are the most promising anodes for sodium‐ion batteries (SIBs), but low initial Coulombic efficiency (ICE) and poor cyclic stability hinder their practical use. It is shown herein, that an effective but simple remedy for these problems can be achieved by deactivating defects in the carbon with Al2O3 nanocluster coverage. A 3D porous graphene monolith (PGM) is used as the model material and Al2O3 nanoclusters around 1 nm are grown on the defects of graphene. It is shown that these Al2O3 nanoclusters suppress the decomposition of conductive sodium salt in the electrolyte, resulting in the formation of a thin and homogenous solid electrolyte interphase (SEI). In addition, Al2O3 nanoclusters appear to reduce the detrimental etching of the SEI by hydrogen fluoride (HF) and improve its stability. Therefore, after the introduction of Al2O3 nanoclusters, the ICE, cyclic stability, and rate capability of the PGM are greatly improved. A higher ICE (70.2%) and capacity retention (82.9% after 500 cycles at 0.5 A g−1) than those of normally reported for large surface area carbons are achieved. This work indicates a new way to deactivate defects and modify the SEI of carbon materials, and hopefully accelerate the commercialization of carbon

Published in: "Advanced Energy Materials".

Effect of Magnetic Field on Goos-H”anchen Shifts in Gaped Graphene Triangular Barrier. (arXiv:1811.06513v1 [cond-mat.mes-hall])

2018-11-16T04:30:21+00:00November 16th, 2018|Categories: Publications|Tags: , |

We study the effect of a magnetic field on Goos-H”anchen shifts in gaped graphene subjected to a double triangular barrier. Solving the wave equation separately in each region composing our system and using the required boundary conditions, we then compute explicitly the transmission probability for scattered fermions. These wavefunctions are then used to derive with the Goos-H”anchen shifts in terms of different physical parameters such as energy, electrostatic potential strength and magnetic field. Our numerical results show that the Goos-H”anchen shifts are affected by the presence of the magnetic field and depend on the geometrical structure of the triangular barrier.

Published : "arXiv Mesoscale and Nanoscale Physics".

Interlayer excitons in bilayer MoS2 with strong oscillator strength up to room temperature. (arXiv:1811.06469v1 [cond-mat.mtrl-sci])

2018-11-16T02:29:23+00:00November 16th, 2018|Categories: Publications|Tags: , |

Coulomb bound electron-hole pairs, excitons, govern the optical properties of semi-conducting transition metal dichalcogenides like MoS$_2$ and WSe$_2$. We study optical transitions at the K-point for 2H homobilayer MoS$_2$ in Density Functional Theory (DFT) including excitonic effects and compare with reflectivity measurements in high quality samples encapsulated in hexagonal BN. In both calculated and measured spectra we find a strong interlayer exciton transition in energy between A and B intralayer excitons, observable for T$=4 -300$ K, whereas no such transition is observed for the monolayer in the same structure in this energy range. The interlayer excitons consist of an electron localized in one layer and a hole state delocalized over the bilayer, which results in the unusual combination of high oscillator strength and a static dipole moment. We also find signatures of interlayer excitons involving the second highest valence band (B) and compare absorption calculations for different bilayer stackings. For homotrilayer MoS$_2$ we also observe interlayer excitons and an energy splitting between different intralayer A-excitons originating from the middle and outer layers, respectively.

Published in: "arXiv Material Science".

Computational insights and the observation of SiC nanograin assembly: towards 2D silicon carbide. (arXiv:1701.07387v2 [cond-mat.mtrl-sci] UPDATED)

2018-11-16T02:29:21+00:00November 16th, 2018|Categories: Publications|Tags: , , , , |

While an increasing number of two-dimensional (2D) materials, including graphene and silicene, have already been realized, others have only been predicted. An interesting example is the two-dimensional form of silicon carbide (2D-SiC). Here, we present an observation of atomically thin and hexagonally bonded nanosized grains of SiC assembling temporarily in graphene oxide pores during an atomic resolution scanning transmission electron microscopy experiment. Even though these small grains do not fully represent the bulk crystal, simulations indicate that their electronic structure already approaches that of 2D-SiC. This is predicted to be flat, but some doubts have remained regarding the preference of Si for sp$^{3}$ hybridization. Exploring a number of corrugated morphologies, we find completely flat 2D-SiC to have the lowest energy. We further compute its phonon dispersion, with a Raman-active transverse optical mode, and estimate the core level binding energies. Finally, we study the chemical reactivity of 2D-SiC, suggesting it is like silicene unstable against molecular absorption or interlayer linking. Nonetheless, it can form stable van der Waals-bonded bilayers with either graphene or hexagonal boron nitride, promising to further enrich the family of two-dimensional materials once bulk synthesis is achieved.

Published in: "arXiv Material Science".

Toward the Identification of Atomic Defects in Hexagonal Boron Nitride: X-Ray Photoelectron Spectroscopy and First-Principles Calculations. (arXiv:1811.05924v1 [cond-mat.mtrl-sci])

2018-11-15T02:29:15+00:00November 15th, 2018|Categories: Publications|Tags: , |

Defects in hexagonal boron nitride (hBN) exhibit single-photon emission (SPE) and are thus attracting broad interest as platforms for quantum information and spintronic applications. However, the atomic structure and the specific impact of the local environment on the defect physical properties remain elusive. Here we articulate X-ray photoelectron spectroscopy (XPS) and first-principles calculations to discern the experimentally-observed point defects responsible for the quantum emission observed in hBN. XPS measurements show a broad band, which was deconvolved and then assigned to $N_{B}V_{N}$, $V_{N}$, $C_{B}$, $C_{B}V_{N}$, and $O_{2B}V_{N}$ defect structures using Density Functional Theory (DFT) core-level binding energy (BE) calculations.

Published in: "arXiv Material Science".

Homogeneous Large-area Quasi-freestanding Monolayer and Bilayer Graphene on SiC. (arXiv:1811.04998v1 [cond-mat.mtrl-sci])

2018-11-14T04:30:27+00:00November 14th, 2018|Categories: Publications|Tags: , |

In this study, we first show that the argon flow during epitaxial graphene growth is an important parameter to control the quality of the buffer and the graphene layer. Atomic force microscopy (AFM) and low-energy electron diffraction (LEED) measurements reveal that the decomposition of the SiC substrate strongly depends on the Ar mass flow rate while pressure and temperature are kept constant. Our data are interpreted by a model based on the competition of the SiC decomposition rate, controlled by the Ar flow, with a uniform graphene buffer layer formation under the equilibrium process at the SiC surface. The proper choice of a set of growth parameters allows the growth of defect-free, ultra-smooth and coherent graphene-free buffer layer and bilayer-free monolayer graphene sheets which can be transformed into large-area high-quality quasi-freestanding monolayer and bilayer graphene (QFMLG and QFBLG) by hydrogen intercalation. AFM, scanning tunneling microscopy (STM), Raman spectroscopy and electronic transport measurements underline the excellent homogeneity of the resulting quasi-freestanding layers. Electronic transport measurements in four-point probe configuration reveal a homogeneous low resistance anisotropy on both {mu}m- and mm scales.

Published : "arXiv Mesoscale and Nanoscale Physics".

Spin transport in a graphene normal-superconductor junction in the quantum Hall regime

2018-11-13T16:33:57+00:00November 13th, 2018|Categories: Publications|Tags: , , |

Author(s): Tibor Sekera, Christoph Bruder, and Rakesh P. TiwariIn graphene-superconductor heterostructures, superconductivity and the quantum Hall effect may coexist for an experimentally accessible range of magnetic fields. When the graphene edge states are coupled to a superconductor in the presence of a Zeeman field, the charge carriers with one spin projection get transmitted while the ones with the opposite spin projection get reflected within a certain energy region. This spin-filtering effect is a consequence of the interplay between specular Andreev reflections and Andreev retro-reflections. While the edge termination of graphene and the geometrical details do matter for the charge conductance, they have little effect on the spin polarization of the charge carriers.[Phys. Rev. B 98, 195418] Published Tue Nov 13, 2018

Published in: "Physical Review B".

Photogalvanic currents in dynamically gapped Dirac materials. (arXiv:1811.04564v1 [cond-mat.mes-hall])

2018-11-13T04:30:36+00:00November 13th, 2018|Categories: Publications|Tags: |

We develop a microscopic theory of an unconventional photogalvanic effect in two-dimensional materials with the Dirac energy spectrum of the carriers of charge under strong driving. As a test bed, we consider a layer of a transition metal dichalcogenide, exposed to two different electromagnetic fields. The first pumping field is circularly-polarized, and its frequency exceeds the material bandgap. It creates an extremely nonequilibrium distribution of electrons and holes in one valley (K) and opens dynamical gaps, whereas the other valley (K’) remains empty due to the valley-dependent interband selection rules. The second probe field has the frequency much smaller than the material bandgap. It generates intraband perturbations of the nonequilibrium carriers density, resulting in the photogalvanic current due to the trigonal asymmetry of the dispersions. This current shows threshold-like behavior due to the dynamical gap opening and renormalizations of the density of states and velocity of quasiparticles.

Published : "arXiv Mesoscale and Nanoscale Physics".

Magnetic superconfinement of Dirac fermions zero-energy modes in bilayer graphene quantum dots. (arXiv:1811.04550v1 [cond-mat.mes-hall])

2018-11-13T04:30:35+00:00November 13th, 2018|Categories: Publications|Tags: , |

We show that in bilayer graphene it is possible to achieve a very restrictive confinement of the massless Dirac fermions zero-modes by using inhomogeneous magnetic fields. Specifically, we show that, using a suitable nonuniform magnetic fields, the wave function may be restricted to a specific region of the space, being forbidden all transmission probability to the contiguous regions. This allows to construct mesoscopic structures in bilayer graphene by magnetic fields configurations.

Published : "arXiv Mesoscale and Nanoscale Physics".

Manifestation of kinetic-inductance in spectrally-narrow terahertz plasmon resonances in thin-film Cd3As2. (arXiv:1811.04306v1 [physics.optics])

2018-11-13T04:30:31+00:00November 13th, 2018|Categories: Publications|Tags: , |

Three-dimensional (3D) semimetals have been predicted and demonstrated to have a wide variety of interesting properties associated with its linear energy dispersion. In analogy to two-dimensional (2D) Dirac semimetals, such as graphene, Cd3As2, a 3D semimetal, has shown ultra-high mobility, large Fermi velocity, and has been hypothesized to support plasmons at terahertz frequencies. In this work, we demonstrate synthesis of high-quality large-area Cd3As2 thin-films through thermal evaporation as well as the experimental realization of plasmonic structures consisting of periodic arrays of Cd3As2 stripes. These arrays exhibit sharp resonances at terahertz frequencies with associated quality-factors (Q) as high as ~ 3.7. Such spectrally-narrow resonances can be understood on the basis of a large kinetic-inductance, resulting from a long momentum scattering time, which in our films can approach ~1 ps at room-temperature. Moreover, we demonstrate an ultrafast tunable response through excitation of photo-induced carriers in optical pump / terahertz probe experiments. Our results evidence that the intrinsic 3D nature of Cd3As2 provides for a very robust platform for terahertz plasmonic applications. Overall, our observations pave a way for the development of myriad terahertz (opto) electronic devices based on Cd3As2 and other 3D Dirac semimetals, benefiting from strong coupling of terahertz radiation, ultrafast transient response, magneto-plasmon properties, etc. Moreover, the long momentum scattering time, thus large kinetic inductance in Cd3As2, also holds enormous potential for the re-design of passive elements such as inductors and hence can have a profound impact in the field of RF integrated circuits.

Published : "arXiv Mesoscale and Nanoscale Physics".

Ultrafast photocarrier recombination dynamics in black phosphorus-molybdenum disulfide (BP/MoS2) heterostructure. (arXiv:1811.04706v1 [cond-mat.mes-hall])

2018-11-13T04:30:17+00:00November 13th, 2018|Categories: Publications|Tags: , , , |

Van der Waals (vdW) heterostructures constructed with two-dimensional (2D) materials have attracted great interests, due to their fascinating properties and potential for novel applications. While earlier efforts have advanced the understanding of the ultrafast cross-layer charge transfer process in 2D heterostructures, mechanisms for the interfacial photocarrier recombination remain, to a large extent, unclear. Here, we investigate a heterostructure comprised of black phosphorus (BP) and molybdenum disulfide (MoS2), with a type-II band alignment. Interestingly, it is found that the photo-generated electrons in MoS2 (transferred from BP) exhibit an ultrafast lifetime of about 5 ps, significantly shorter than those of the constituent materials. By corroborating with the relaxation of photo-excited holes in BP, it is revealed that the ultrafast time constant is as a result of efficient Langevin recombination, where the high hole mobility of BP facilitates a large recombination coefficient (approximately 2×10^-10 m^2/s). In addition, broadband transient absorption spectroscopy confirms that the hot electrons transferred to MoS2 distribute over a broad energy range following an ultrafast thermalization. The rate of the interlayer Langevin recombination is found to exhibit no energy level dependence. Our findings provide essential insights into the fundamental photo-physics in type-II 2D heterostructures, and also provide useful guidelines for customizing photocarrier lifetimes of BP for high-speed photo-sensitive devices.

Published : "arXiv Mesoscale and Nanoscale Physics".

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