• Fundamental issues of nanostructure formation & device fabrication
- High quality nanostructureal materials,
- Mobility and contacts in atomically thin TMDC FET devices
• Physical properties of low dimensional nanostructures
- 1D: Carbon nanotubes, semiconductor nanowires
- 2D: Graphene and transition metal dichalcogenide device and quantum transport
- Disorders, quantum transport and quantum capacitance
• Energy related nanomaterails (1D, 2D and hierarchical structures)
- Dye-sensitized solar cells (DSCs); - CZTS Nano-crystals & thin-film solar cells.
• Electron microscopy and nano lithography
- In-situ structure and property characterization
- Gen Long received E-MRS Best Presentation Award 2015 in recognition of his outstanding research on graphene.
- Yingying Wu received the Departmental Research Award 2016 for her outstanding research on black phosphorus quantum transport.
• Type-controlled black phosphorusdevices for quantum transport (2D Materails 3(2016)031001). ...click here for more information: http://dx.doi.org/10.1088/2053-1583/3/3/031001
• Probing the electronic states and impurity effects in black phosphorus heterostructures: (2D Materials 3(2016)015012)...Clikc here for more information, https://arxiv.org/abs/1604.00420
• Resonant impurities - Negative compressibility - "e-e" Interaction ... click here for more information.
• Negative compressibility in graphene-terminated black phosphorus heterostructures..... click here for more information.
Job & opportunity
- Post-Doctoral Positions: No position available for 2015/16.
- Postgraduate Positions: available in quantum phenomena in graphene and transition metal dichalcogenides.
- We thank you very much for being interested in our reserach
•• Intrinsic Valley Hall Transport in Atomically Thin MoS2 (NEW)
We report the first observation of intrinsic valley Hall transport without any extrinsic symmetry breaking in the non-centrosymmetric monolayer and trilayer MoS2... Such a hallmark survives even at room temperature. Our work elucidates the topological origin of valley Hall effects and marks a significant step towards the purely electrical control of valley degree of freedom in topological valleytronics. See Nature Comm. 10(2019)611.
• • Determine Interaction Enhanced Valley Susceptibility in Spin-Valley-Locked MoS2 (NEW)
We discovered many-body interaction effects in the conductance band of MoS2 and established afertile ground for exploring strongly correlated phenomena of massive Direc electrons.
• Odd-integer Quantum Hall States and Giant Spin Sussceptibility in p-type Few-layer WSe2
Recently, we fabricate hihg-mobility p-type few-layer WSe2 FETs and surprisingly observe a serious of quantum Hall states following an unconventional sequence predominated by odd-integer states. We observe a very large Zeeman energy that is almost three times as large as the cyclotron energy. Details can be found at linek: Phys. Rev. Lett. 118(2017)067702.(Editor's Suggestion paper).
• Achieving Ultrahigh Carrier Mobility in Two-Dimensional Hole Gas of Black Phosphorus
We demonstrate ultrahigh mobility FET devices made from few-layer black phosphorus (BP).
The carrier mobility has been increased to 45,000cm^2/V s in our newly fabricated BP samples. Our high-mobility BP devices show clear quantum Hall effect in laboratory magnetic field. The Landau level crossing has been studied using the standard coincidence technique. A spin-selective quantum scattering mechanism is proposed to interpret the quantum oscillation. See details in Nano Lett, Dec. 2016.
• Even-Odd Layer-dependent Magnetotransport of High Mobility Q-Valley Electrons in Few-layer Transition Metal Disulfids
We demonstrate that at moderate magnetic fields of 2.5–4 T and relatively low carrier density quantum
oscillations are dominated by the Q valleys, exhibiting a universal even–odd layer dependence. Above 4 T, we observe spin Zeeman effects in even-layer devices and valley Zeeman effects in odd-layerdevices. We also observe the onset of quantum Hall plateaus in the 3L device. The high-quality atomically thin BN-TMDC-BN-based FE transistors fabricated in this work pave the way for understanding the multi-valley band structures of FL TMDCs and for exploring their spin-valley entangled unconventional QHEs. Nature Comm. 7 (2016)12955.
• Universal Low-temperature Ohmic Contacts for Quantum Transport in Transition Metal Dichalcogenides
Low carrier mobility and high electrical contact resistance are two major obstacles prohibiting explorations of quantum transport in TMDCs. We have developed an effective method to achieve low-temperature ohmic contacts in BN encapsulted TMDC devices based on selective etching and conventional e-beam evaporation of metal electrodes. Our TMDC devices show excellent performance with remarkably improved field-effect mobilities up to 16000cm^2/V s and interesting quantum oscillations. (2D materials 3 (2016)021007).
• High-quality Sandwiched Black Phosphorus Hetero-structure and Its Quantum Oscillations
We report that sandwiched BN/black-phosphorus/BN heterostructures show high mobility and quantum oscillations at low magnetic fields. Importqantly, these heterostructuires ensure that the quality of black phosphorus remains high under ambient conditions. See details in Nature Comm. 6 (2015) 7315. doi:10.1038/ncomms8315.
• Probing the Electron States in Atomically Thin MoS2 by Capacitance Measurements
We show that the vertical heterostructures built from atomically thin MoS2 are ideal capacitors for probing the electron states. This structure offers the added advantage of eliminating the influence of large impedance at the band tails and allows the observation of fully excited electron states .……See details in Nature Comm. 6 (2015) 6088 ; doi:10.1038/ncomms7088.
• van der Waals Epitaxial Growth of Atomically Thin Bi2Se3 and Thickness-Dependent Topological Phase Transition
We report the van der Waals epitaxial growth of high-quality atomically thin Bi2Se3 on h-BN. Our quantum capacitance measurements for h-BN/Bi2Se3/h-BN sandwiched structures showed a compelling phenomenon of thickness-dependent topological phase transition….See details in Nano Lett. 15 (2015) 2645; DOI: 10.1021/ acs.nanolett.5b00247.
• Negative Quantum Capacitance Induced by Midgap States in Single-layer Graphene
Single-layer graphene decorated with a higih density of Ag adatoms displays negative quantum capacitance. Ag atoms act as resonant impurities and generate negative electronic compressibility ....See details in Scientific Report 3 (2013) 2041; Phys. Rev. B89 (2014)75410.