Publications by authors named "Chenqiang Hua"

7 Publications

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Manifold dynamic non-covalent interactions for steering molecular assembly and cyclization.

Chem Sci 2021 Sep 5;12(35):11659-11667. Epub 2021 Aug 5.

Department of Chemistry, National University of Singapore 3 Science Drive 3 Singapore 117543

Deciphering rich non-covalent interactions that govern many chemical and biological processes is crucial for the design of drugs and controlling molecular assemblies and their chemical transformations. However, real-space characterization of these weak interactions in complex molecular architectures at the single bond level has been a longstanding challenge. Here, we employed bond-resolved scanning probe microscopy combined with an exhaustive structural search algorithm and quantum chemistry calculations to elucidate multiple non-covalent interactions that control the cohesive molecular clustering of well-designed precursor molecules and their chemical reactions. The presence of two flexible bromo-triphenyl moieties in the precursor leads to the assembly of distinct non-planar dimer and trimer clusters by manifold non-covalent interactions, including hydrogen bonding, halogen bonding, C-H⋯π and lone pair⋯π interactions. The dynamic nature of weak interactions allows for transforming dimers into energetically more favourable trimers as molecular density increases. The formation of trimers also facilitates thermally-triggered intermolecular Ullmann coupling reactions, while the disassembly of dimers favours intramolecular cyclization, as evidenced by bond-resolved imaging of metalorganic intermediates and final products. The richness of manifold non-covalent interactions offers unprecedented opportunities for controlling the assembly of complex molecular architectures and steering on-surface synthesis of quantum nanostructures.
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http://dx.doi.org/10.1039/d1sc03733aDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8442717PMC
September 2021

Rashba valleys and quantum Hall states in few-layer black arsenic.

Nature 2021 05 5;593(7857):56-60. Epub 2021 May 5.

Zhejiang Province Key Laboratory of Quantum Technology and Device, Department of Physics, Zhejiang University, Hangzhou, People's Republic of China.

Exciting phenomena may emerge in non-centrosymmetric two-dimensional electronic systems when spin-orbit coupling (SOC) interplays dynamically with Coulomb interactions, band topology and external modulating forces. Here we report synergetic effects between SOC and the Stark effect in centrosymmetric few-layer black arsenic, which manifest as particle-hole asymmetric Rashba valley formation and exotic quantum Hall states that are reversibly controlled by electrostatic gating. The unusual findings are rooted in the puckering square lattice of black arsenic, in which heavy 4p orbitals form a Brillouin zone-centred Γ valley with p symmetry, coexisting with doubly degenerate D valleys of p origin near the time-reversal-invariant momenta of the X points. When a perpendicular electric field breaks the structure inversion symmetry, strong Rashba SOC is activated for the p bands, which produces spin-valley-flavoured D valleys paired by time-reversal symmetry, whereas Rashba splitting of the Γ valley is constrained by the p symmetry. Intriguingly, the giant Stark effect shows the same p-orbital selectiveness, collectively shifting the valence band maximum of the D Rashba valleys to exceed the Γ Rashba top. Such an orchestrating effect allows us to realize gate-tunable Rashba valley manipulations for two-dimensional hole gases, hallmarked by unconventional even-to-odd transitions in quantum Hall states due to the formation of a flavour-dependent Landau level spectrum. For two-dimensional electron gases, the quantization of the Γ Rashba valley is characterized by peculiar density-dependent transitions in the band topology from trivial parabolic pockets to helical Dirac fermions.
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http://dx.doi.org/10.1038/s41586-021-03449-8DOI Listing
May 2021

Coexistence of Ferroelectricity and Ferromagnetism in One-Dimensional SbN and BiN Nanowires.

ACS Appl Mater Interfaces 2021 Mar 9;13(11):13517-13523. Epub 2021 Mar 9.

School of Materials Science and Engineering, Zhejiang University, Hangzhou 310027, China.

Ferroelectricity exists in a variety of three- and two-dimensional materials and is of great significance for the development of electronic devices. However, the presence of ferroelectricity in one-dimensional materials is extremely rare. Here, we predict ferroelectricity in one-dimensional SbN and BiN nanowires. Their polarization strengths are 1 order of magnitude higher than ever reported values in one-dimensional structures. Moreover, we find that spontaneous spin polarization can be generated in SbN and BiN nanowires by moderate hole doping. This is the first time the coexistence of both ferroelectricity and ferromagnetism in a one-dimensional system has been reported. Our finding not only broadens the family of one-dimensional ferroelectric materials but also offers a promising platform for novel electronic and spintronic applications.
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http://dx.doi.org/10.1021/acsami.0c20570DOI Listing
March 2021

Tunable Topological Energy Bands in 2D Dialkali-Metal Monoxides.

Adv Sci (Weinh) 2020 Feb 7;7(4):1901939. Epub 2020 Jan 7.

Zhejiang Province Key Laboratory of Quantum Technology and Device and Department of Physics in Zhejiang University State Key Lab of Silicon Materials School of Materials Science and Engineering in Zhejiang University Hangzhou 310027 P. R. China.

2D materials with nontrivial energy bands are highly desirable for exploring various topological phases of matter, as low dimensionality opens unprecedented opportunities for manipulating the quantum states. Here, it is reported that monolayer (ML) dialkali-metal monoxides, in the well-known 2H-MoS type lattice, host multiple symmetry-protected topological phases with emergent fermions, which can be effectively tuned by strain engineering. Based on first-principles calculations, it is found that in the equilibrium state, ML NaO is a 2D double Weyl semimetal, while ML KO is a 2D pseudospin-1 metal. These exotic topological states exhibit a range of fascinating effects, including universal optical absorbance, super Klein tunneling, and super collimation effect. By introducing biaxial or uniaxial strain, a series of quantum phase transitions between 2D double Weyl semimetal, 2D Dirac semimetal, 2D pseudospin-1 metal, and semiconductor phases can be realized. The results suggest monolayer dialkali-metal monoxides as a promising platform to explore fascinating physical phenomena associated with novel 2D emergent fermions.
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http://dx.doi.org/10.1002/advs.201901939DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7029633PMC
February 2020

Electronic structures of ultra-thin tellurium nanoribbons.

Nanoscale 2019 Aug;11(30):14134-14140

Department of Physics, Zhejiang University, Hangzhou, 310027, P. R. China.

The structural stability and electronic properties of monolayer and bilayer tellurium nanoribbons (TNRs) with different edge structures have been systematically investigated by means of first-principles calculations, revealing that the stability of both monolayer and bilayer TNRs largely rely on their width. Regardless of width, tip TNRs are metallic, while notch TNRs are p-type-like conductors. Interestingly, both mono- and bi-layer chain TNRs exhibit a semiconductor-to-metal transition as the width increases. The electronic structures of tip and notch TNRs are mainly determined by atomic reconstruction and the unsaturated electronic states on the edges. For chain TNRs, the origin of the semiconductor-to-metal transition can be attributed to the spontaneous in-plane electronic polarization across the ribbon. Our work reveals diverse electronic properties of one-dimensional elemental tellurium nanostructures, which considerably extend the potential applications of tellurene-based materials in nanodevices.
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http://dx.doi.org/10.1039/c9nr04112eDOI Listing
August 2019

Dialkali-Metal Monochalcogenide Semiconductors with High Mobility and Tunable Magnetism.

J Phys Chem Lett 2018 Dec 12;9(23):6695-6701. Epub 2018 Nov 12.

Zhejiang Province Key Laboratory of Quantum Technology and Device, Department of Physics , Zhejiang University , Hangzhou 310027 , P. R. China.

The discovery of archetypal two-dimensional (2D) materials provides enormous opportunities in both fundamental breakthroughs and device applications, as evident by the research booming in graphene, transition-metal chalcogenides, and black phosphorus. Here, we report a new, large family of semiconducting dialkali-metal monochalcogenides (DMMCs) with an inherent AX monolayer (ML) structure, in which two alkali sub-MLs form hexagonal close packing and sandwich the triangular chalcogen atomic plane. Such a unique lattice leads to extraordinary physical properties, such as good dynamical and thermal stability, visible to near-infrared energy gap, and high electron mobility. Most strikingly, DMMC MLs host extended van Hove singularities near the valence band (VB) edge, readily accessible by moderate hole doping within 1.0 × 10 cm. Upon critical doping, DMMC MLs undergo spontaneous ferromagnetic transition when the top VBs become fully spin-polarized by strong exchange interactions. Such 2D gate tunable magnetism are promising for exploring novel device concepts in spintronics, electronics and optoelectronics.
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http://dx.doi.org/10.1021/acs.jpclett.8b02859DOI Listing
December 2018

Defects controlled hole doping and multivalley transport in SnSe single crystals.

Nat Commun 2018 01 3;9(1):47. Epub 2018 Jan 3.

Department of Physics, Zhejiang University, Hangzhou, 310027, China.

SnSe is a promising thermoelectric material with record-breaking figure of merit. However, to date a comprehensive understanding of the electronic structure and most critically, the self-hole-doping mechanism in SnSe is still absent. Here we report the highly anisotropic electronic structure of SnSe investigated by angle-resolved photoemission spectroscopy, in which a unique pudding-mould-shaped valence band with quasi-linear energy dispersion is revealed. We prove that p-type doping in SnSe is extrinsically controlled by local phase segregation of SnSe microdomains via interfacial charge transferring. The multivalley nature of the pudding-mould band is manifested in quantum transport by crystallographic axis-dependent weak localisation and exotic non-saturating negative magnetoresistance. Strikingly, quantum oscillations also reveal 3D Fermi surface with unusual interlayer coupling strength in p-SnSe, in which individual monolayers are interwoven by peculiar point dislocation defects. Our results suggest that defect engineering may provide versatile routes in improving the thermoelectric performance of the SnSe family.
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http://dx.doi.org/10.1038/s41467-017-02566-1DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5752673PMC
January 2018
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