Science Advances

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Propane oxidative dehydrogenation over highly selective hexagonal boron nitride catalysts: The role of oxidative coupling of methyl

2019-03-16T02:37:08+00:00March 16th, 2019|Categories: Publications|Tags: |

Hexagonal boron nitride (h-BN) catalyst has recently been reported to be highly selective in oxidative dehydrogenation of propane (ODHP) for olefin production. In addition to propene, ethylene also forms with much higher overall selectivities to C2-products than to C1-products. In this work, we report that the reaction pathways over the

Published in: "Science Advances".

Detection of thermodynamic “valley noise” in monolayer semiconductors: Access to intrinsic valley relaxation time scales

2019-03-01T22:36:37+00:00March 1st, 2019|Categories: Publications|

Together with charge and spin, many novel two-dimensional materials also permit information to be encoded in an electron’s valley degree of freedom—that is, in particular momentum states in the material’s Brillouin zone. With a view toward valley-based (opto)electronic technologies, the intrinsic time scales of valley scattering are therefore of fundamental

Published in: "Science Advances".

Ultrafast electron calorimetry uncovers a new long-lived metastable state in 1T-TaSe2 mediated by mode-selective electron-phonon coupling

2019-03-01T22:36:33+00:00March 1st, 2019|Categories: Publications|Tags: , |

Quantum materials represent one of the most promising frontiers in the quest for faster, lightweight, energy-efficient technologies. However, their inherent complexity and rich phase landscape make them challenging to understand or manipulate. Here, we present a new ultrafast electron calorimetry technique that can systematically uncover new phases of quantum matter.

Published in: "Science Advances".

Manipulating surface magnetic order in iron telluride

2019-03-01T22:36:30+00:00March 1st, 2019|Categories: Publications|

Control of emergent magnetic orders in correlated electron materials promises new opportunities for applications in spintronics. For their technological exploitation, it is important to understand the role of surfaces and interfaces to other materials and their impact on the emergent magnetic orders. Here, we demonstrate for iron telluride, the nonsuperconducting

Published in: "Science Advances".

Extraordinary tensile strength and ductility of scalable nanoporous graphene

2019-02-16T04:47:11+00:00February 16th, 2019|Categories: Publications|Tags: |

While the compressive strength-density scaling relationship of ultralight cellular graphene materials has been extensively investigated, high tensile strength and ductility have not been realized in the theoretically strongest carbon materials because of high flaw sensitivity under tension and weak van der Waals interplanar bonding between graphene sheets. In this study,

Published in: "Science Advances".

Imaging quantum spin Hall edges in monolayer WTe2

2019-02-09T12:36:27+00:00February 9th, 2019|Categories: Publications|Tags: |

A two-dimensional (2D) topological insulator exhibits the quantum spin Hall (QSH) effect, in which topologically protected conducting channels exist at the sample edges. Experimental signatures of the QSH effect have recently been reported in an atomically thin material, monolayer WTe2. Here, we directly image the local conductivity of monolayer WTe2

Published in: "Science Advances".

Transient exciton-polariton dynamics in WSe2 by ultrafast near-field imaging

2019-02-02T00:37:41+00:00February 1st, 2019|Categories: Publications|Tags: |

Van der Waals (vdW) materials offer an exciting platform for strong light-matter interaction enabled by their polaritonic modes and the associated deep subwavelength light confinement. Semiconductor vdW materials such as WSe2 are of particular interest for photonic and quantum integrated technologies because they sustain visible–near-infrared (VIS-NIR) exciton-polariton (EP) modes at

Published in: "Science Advances".

Imaging of local structures affecting electrical transport properties of large graphene sheets by lock-in thermography

2019-02-02T00:37:38+00:00February 1st, 2019|Categories: Publications|Tags: |

The distribution of defects and dislocations in graphene layers has become a very important concern with regard to the electrical and electronic transport properties of device applications. Although several experiments have shown the influence of defects on the electrical properties of graphene, these studies were limited to measuring microscopic areas

Published in: "Science Advances".

Etching gas-sieving nanopores in single-layer graphene with an angstrom precision for high-performance gas mixture separation

2019-01-25T22:36:53+00:00January 25th, 2019|Categories: Publications|Tags: |

One of the bottlenecks in realizing the potential of atom-thick graphene membrane for gas sieving is the difficulty in incorporating nanopores in an otherwise impermeable graphene lattice, with an angstrom precision at a high-enough pore density. We realize this design by developing a synergistic, partially decoupled defect nucleation and pore

Published in: "Science Advances".

Polymorphism of bulk boron nitride

2019-01-19T06:36:32+00:00January 19th, 2019|Categories: Publications|Tags: |

Boron nitride (BN) is a material with outstanding technological promise due to its exceptional thermochemical stability, structural, electronic, and thermal conductivity properties, and extreme hardness. Yet, the relative thermodynamic stability of its most common polymorphs (diamond-like cubic and graphite-like hexagonal) has not been resolved satisfactorily because of the crucial role

Published in: "Science Advances".

Gate tuning from exciton superfluid to quantum anomalous Hall in van der Waals heterobilayer

2019-01-18T20:43:13+00:00January 18th, 2019|Categories: Publications|Tags: |

Van der Waals heterostructures of two-dimensional (2D) materials provide a powerful approach toward engineering various quantum phases of matter. Examples include topological matter such as quantum spin Hall (QSH) insulator and correlated matter such as exciton superfluid. It can be of great interest to realize these vastly different quantum phases

Published in: "Science Advances".

Laser-writable high-k dielectric for van der Waals nanoelectronics

2019-01-18T20:43:03+00:00January 18th, 2019|Categories: Publications|Tags: |

Similar to silicon-based semiconductor devices, van der Waals heterostructures require integration with high-k oxides. Here, we demonstrate a method to embed and pattern a multifunctional few-nanometer-thick high-k oxide within various van der Waals devices without degrading the properties of the neighboring two-dimensional materials. This transformation allows for the creation of

Published in: "Science Advances".

Synthetic WSe2 monolayers with high photoluminescence quantum yield

2019-01-03T00:36:50+00:00January 2nd, 2019|Categories: Publications|Tags: |

In recent years, there have been tremendous advancements in the growth of monolayer transition metal dichalcogenides (TMDCs) by chemical vapor deposition (CVD). However, obtaining high photoluminescence quantum yield (PL QY), which is the key figure of merit for optoelectronics, is still challenging in the grown monolayers. Specifically, the as-grown monolayers

Published in: "Science Advances".

A single-stranded coordination copolymer affords heterostructure observation and photoluminescence intensification

2019-01-03T00:36:49+00:00January 2nd, 2019|Categories: Publications|Tags: |

Few artificial systems can be exfoliated into, and observed as, single wires with lengths of more than several micrometers, and no previous example features a copolymer structure; this is in contrast with biopolymers such as single-strand DNAs. Here, we create a set of one-dimensional coordination copolymers featuring bis(dipyrrinato)zinc complex motifs

Published in: "Science Advances".

Anomalous interfacial stress generation during sodium intercalation/extraction in MoS2 thin-film anodes

2019-01-03T00:36:45+00:00January 2nd, 2019|Categories: Publications|Tags: |

Although the generation of mechanical stress in the anode material is suggested as a possible reason for electrode degradation and fading of storage capacity in batteries, only limited knowledge of the electrode stress and its evolution is available at present. Here, we show real-time monitoring of the interfacial stress of

Published in: "Science Advances".

Discovering the forbidden Raman modes at the edges of layered materials

2018-12-14T20:36:54+00:00December 14th, 2018|Categories: Publications|Tags: , , , , |

The edges of layered materials have unique properties that substantially differ from the body regions. In this work, we perform a systematic Raman study of the edges of various layered materials (MoS2, WS2, WSe2, PtS2, and black phosphorus). The Raman spectra of the edges feature newly observed forbidden Raman modes,

Published in: "Science Advances".

Graphene catalyzes the reversible formation of a C-C bond between two molecules

2018-12-14T20:36:50+00:00December 14th, 2018|Categories: Publications|Tags: |

Carbon deposits are well-known inhibitors of transition metal catalysts. In contrast to this undesirable behavior, here we show that epitaxial graphene grown on Ru(0001) promotes the reversible formation of a C–C bond between –CH2CN and 7,7,8,8-tetracyano-p-quinodimethane (TCNQ). The catalytic role of graphene is multifaceted: First, it allows for an efficient

Published in: "Science Advances".

Multifunctional wafer-scale graphene membranes for fast ultrafiltration and high permeation gas separation

2018-11-24T00:36:28+00:00November 23rd, 2018|Categories: Publications|Tags: |

Reliable and large-scale manufacturing routes for perforated graphene membranes in separation and filtration remain challenging. We introduce two manufacturing pathways for the fabrication of highly porous, perforated graphene membranes with sub–100-nm pores, suitable for ultrafiltration and as a two-dimensional (2D) scaffold for synthesizing ultrathin, gas-selective polymers. The two complementary processes—bottom

Published in: "Science Advances".

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".

Extremely flat band in bilayer graphene

2018-11-09T20:36:28+00:00November 9th, 2018|Categories: Publications|Tags: |

We propose a novel mechanism of flat band formation based on the relative biasing of only one sublattice against other sublattices in a honeycomb lattice bilayer. The mechanism allows modification of the band dispersion from parabolic to “Mexican hat”–like through the formation of a flattened band. The mechanism is well

Published in: "Science Advances".

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