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"Cheng Liu"
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Experimental realization of two-dimensional Dirac nodal line fermions in monolayer Cu2Si
Topological nodal line semimetals, a novel quantum state of materials, possess topologically nontrivial valence and conduction bands that touch at a line near the Fermi level. The exotic band structure can lead to various novel properties, such as long-range Coulomb interaction and flat Landau levels. Recently, topological nodal lines have been observed in several bulk materials, such as PtSn
4
, ZrSiS, TlTaSe
2
and PbTaSe
2
. However, in two-dimensional materials, experimental research on nodal line fermions is still lacking. Here, we report the discovery of two-dimensional Dirac nodal line fermions in monolayer Cu
2
Si based on combined theoretical calculations and angle-resolved photoemission spectroscopy measurements. The Dirac nodal lines in Cu
2
Si form two concentric loops centred around the Γ point and are protected by mirror reflection symmetry. Our results establish Cu
2
Si as a platform to study the novel physical properties in two-dimensional Dirac materials and provide opportunities to realize high-speed low-dissipation devices.
Nodal line semimetals have been observed in three-dimensional materials but are missing in two-dimensional counterparts. Here, Feng et al. report two-dimensional Dirac nodal line fermions protected by mirror reflection symmetry in monolayer Cu
2
Si.
Journal Article
Selective photoelectrochemical oxidation of glycerol to high value-added dihydroxyacetone
It is highly profitable to transform glycerol – the main by-product from biodiesel production to high value-added chemicals. In this work, we develop a photoelectrochemical system based on nanoporous BiVO
4
for selective oxidation of glycerol to 1,3-dihydroxyacetone – one of the most valuable derivatives of glycerol. Under AM 1.5G front illumination (100 mW cm
−2
) in an acidic medium (pH = 2) without adscititious oxidant, the nanoporous BiVO
4
photoanode achieves a glycerol oxidation photocurrent density of 3.7 mA cm
−2
at a potential of 1.2 V versus RHE with 51% 1,3-dihydroxyacetone selectivity, equivalent to a production rate of 200 mmol of 1,3-dihydroxyacetone per m
2
of illumination area in one hour.
The selective conversion of inexpensive precursors to high-value chemicals presents valuable academic and industrial consequences. Here, the authors show bismuth vanadate photoanodes to utilize light and photoelectrochemically oxidize glycerol selectively to valuable industrial products.
Journal Article
Epitaxial growth of single-domain graphene on hexagonal boron nitride
The epitaxial growth of large-area single-domain graphene on hexagonal boron nitride by plasma-assisted deposition is now reported. New sets of Dirac points are produced as a result of a trigonal superlattice potential, while Dirac fermion physics near the original Dirac point remain unperturbed. This growth approach could enable band engineering in graphene through epitaxy on different substrates.
Hexagonal boron nitride (h-BN) has recently emerged as an excellent substrate for graphene nanodevices, owing to its atomically flat surface and its potential to engineer graphene’s electronic structure
1
,
2
. Thus far, graphene/h-BN heterostructures have been obtained only through a transfer process
1
, which introduces structural uncertainties due to the random stacking between graphene and h-BN substrate
2
,
3
. Here we report the epitaxial growth of single-domain graphene on h-BN by a plasma-assisted deposition method. Large-area graphene single crystals were successfully grown for the first time on h-BN with a fixed stacking orientation. A two-dimensional (2D) superlattice of trigonal moiré pattern was observed on graphene by atomic force microscopy. Extra sets of Dirac points are produced as a result of the trigonal superlattice potential and the quantum Hall effect is observed with the 2D-superlattice-related feature developed in the fan diagram of longitudinal and Hall resistance, and the Dirac fermion physics near the original Dirac point is unperturbed. The macroscopic epitaxial graphene is in principle limited only by the size of the h-BN substrate and our synthesis method is potentially applicable on other flat surfaces. Our growth approach could thus open new ways of graphene band engineering through epitaxy on different substrates.
Journal Article
Matching visibility and performance : a standing challenge for world-class universities
World-class universities (WCU) are regarded as cornerstone institutions of any academic system and imperative to develop a nation?s competitiveness in the global knowledge economy. Visibility and performance are among the most watched concepts in relation to develop WCUs, but remain complicated in nature and with no agreed upon definitions. Existing literature have focused on how to raise universities? prestige, status, impact and rankings in the global and regional arena on the one hand, and how to enhance universities? quality, efficiency, effectiveness and academic output on the other. However, whether visibility is a legitimate indicator of performance, or vice versa, is yet to be answered. This book provides insights of developing academic excellence from global, national and institutional perspectives, and intends to stimulate discussion on how universities can be?globally visible and locally engaged? and how visibility and performance can be integrated and balanced in practice.
Book
Heterogeneous Fe3 single-cluster catalyst for ammonia synthesis via an associative mechanism
The current industrial ammonia synthesis relies on Haber–Bosch process that is initiated by the dissociative mechanism, in which the adsorbed N
2
dissociates directly, and thus is limited by Brønsted–Evans–Polanyi (BEP) relation. Here we propose a new strategy that an anchored Fe
3
cluster on the θ-Al
2
O
3
(010) surface as a heterogeneous catalyst for ammonia synthesis from first-principles theoretical study and microkinetic analysis. We have studied the whole catalytic mechanism for conversion of N
2
to NH
3
on Fe
3
/θ-Al
2
O
3
(010), and find that an associative mechanism, in which the adsorbed N
2
is first hydrogenated to NNH, dominates over the dissociative mechanism, which we attribute to the large spin polarization, low oxidation state of iron, and multi-step redox capability of Fe
3
cluster. The associative mechanism liberates the turnover frequency (TOF) for ammonia production from the limitation due to the BEP relation, and the calculated TOF on Fe
3
/θ-Al
2
O
3
(010) is comparable to Ru B5 site.
The current industrial ammonia synthesis relies on the Haber-Bosch process that is limited by the Brønsted–Evans–Polanyi relation. Here, the authors propose a new strategy that an anchored Fe
3
on θ-Al
2
O
3
(010) surface serves as a heterogeneous single cluster catalyst for ammonia synthesis from first-principles calculations and microkinetic analysis.
Journal Article
How world-class universities affect global higher education : influences and responses
World-class universities, commonly recognized as global research universities or flagship universities, are cornerstone institutions embedded in any academic system and play an important role in developing a nation?s competitiveness in the global knowledge economy. The development of world-class universities is high on the policy agenda of various stakeholders across the globe. In the past few years, an increasing number of nations, regions and higher education institutions in both developed and developing countries have joined the same race for academic excellence and have adopted a range of development strategies and implemented various reforms. From a comparative perspective, How World-Class Universities Affect Global Higher Education intends to provide an in-depth picture of excellence initiatives and relevant policies adopted in various nations and regions, and to reflect opportunities and challenges of developing excellence.
Book
Non defect-stabilized thermally stable single-atom catalyst
Surface-supported isolated atoms in single-atom catalysts (SACs) are usually stabilized by diverse defects. The fabrication of high-metal-loading and thermally stable SACs remains a formidable challenge due to the difficulty of creating high densities of underpinning stable defects. Here we report that isolated Pt atoms can be stabilized through a strong covalent metal-support interaction (CMSI) that is not associated with support defects, yielding a high-loading and thermally stable SAC by trapping either the already deposited Pt atoms or the PtO
2
units vaporized from nanoparticles during high-temperature calcination. Experimental and computational modeling studies reveal that iron oxide reducibility is crucial to anchor isolated Pt atoms. The resulting high concentrations of single atoms enable specific activities far exceeding those of conventional nanoparticle catalysts. This non defect-stabilization strategy can be extended to non-reducible supports by simply doping with iron oxide, thus paving a new way for constructing high-loading SACs for diverse industrially important catalytic reactions.
Developing stable single-atom catalysts (SACs) with a high metal loading remains a challenge due to the difficulty of creating high densities of defects on support materials. Here the authors prepare Pt SACs with high Pt loadings by virtue of strong covalent metal-support interaction, rather than support defects.
Journal Article