Huiqiang Liu

Wafer-Size and Single-Crystal MoSe2 Atomically Thin Films Grown on GaN Substrate for Light Emission and Harvesting.

Two-dimensional (2D) atomic-layered semiconductors are important for next-generation electronics and optoelectronics. Here, we designed the growth of an MoSe2 atomic layer on a lattice-matched GaN semiconductor substrate. The results demonstrated that the MoSe2 films were less than three atomic layers thick and were single crystalline of MoSe2 over the entire GaN substrate. The ultrathin MoSe2/GaN heterojunction diode demonstrated ∼850 nm light emission and could also be used in photovoltaic applications.

Terahertz photodetector arrays based on a large scale MoSe2 monolayer

Large domains of monolayered transition-metal dichalcogenides (TMDCs) have emerged as exciting materials because of their potential to provide a platform for ultrathin circuits and optoelectronics systems. Herein, we report ambient pressure chemical vapor deposition (CVD) growth of large scale MoSe2 film for terahertz (THz) applications. Arrays of 100 × 60 μm MoSe2 rectangle layers were etched out and field effect transistors (FETs) were fabricated on these arrays. The device exhibits current on/off ratio of ∼104. The THz photoresponse of the devices was studied and a THz responsivity of ∼38 mV W−1 was demonstrated, suggesting that TMDCs can be promising materials for long wavelength optoelectronic applications.

Terahertz detectors arrays based on orderly aligned InN nanowires.

Nanostructured terahertz detectors employing a single semiconducting nanowire or graphene sheet have recently generated considerable interest as an alternative to existing THz technologies, for their merit on the ease of fabrication and above-room-temperature operation. However, the lack of alignment in nanostructure device hindered their potential toward practical applications. The present work reports ordered terahertz detectors arrays based on neatly aligned InN nanowires. The InN nanostructures (nanowires and nano-necklaces) were achieved by chemical vapor deposition growth, and then InN nanowires were successfully transferred and aligned into micrometer-sized groups by a “transfer-printing” method. Field effect transistors on aligned nanowires were fabricated and tested for terahertz detection purpose. The detector showed good photoresponse as well as low noise level. Besides, dense arrays of such detectors were also fabricated, which rendered a peak responsivity of 1.1 V/W from 7 detectors connected in series.

Large-area snow-like MoSe2 monolayers: synthesis, growth mechanism, and efficient electrocatalyst application

This study explores the large-area synthesis of controllable morphology, uniform, and high-quality monolayer. MoSe2 is essential for its potential application in optoelectronics, photocatalysis, and renewable energy sources. In this study, we successfully synthesized snow-like MoSe2 monolayers using a simple chemical vapor deposition method. Results reveal that snow-like MoSe2 is a single crystal with a hexagonal structure, a thickness of ∼0.9 nm, and a lateral dimension of up to 20 μm. The peak position of the photoluminescence spectra is ∼1.52 eV corresponding to MoSe2 monolayer. The growth mechanism of the snow-like MoSe2 monolayer was investigated and comprised a four-step process during growth. Finally, we demonstrate that the snow-like MoSe2 monolayers are ideal electrocatalysts for hydrogen evolution reactions (HERs), reflected by a low Tafel slope of ∼68 mV/decade. Compared with the triangular-shaped MoSe2 monolayer, the hexangular snow-like shape with plentiful edges is superior for perfect electrocatalysts for HERs or transmission devices of optoelectronic signals.

Synthesis, microstructure, growth mechanism and photoluminescence of high quality [0001]-oriented InN nanowires and nanonecklaces

Novel indium nitride (InN) based nanomaterials are important for high speed electronics and infrared optoelectronics. In this paper, high quality indium nitride (InN) nanostructures, including nanowires and nanonecklaces, have been grown on one substrate by chemical vapor deposition. The morphologies and microstructures of the InN nanowires and nanonecklaces were characterized, which confirmed their chemical composition as well as single crystallinity. The InN nanonecklaces consist of multiple beads composed of two equilateral truncated hexagonal cones faceted with {10} and {101} planes. The growth mechanism of the InN nanonecklace was studied and a three-step process was suggested for the growth. Finally, the room temperature photoluminescence spectra of the two nanostructures showed near band edge emissions of around 0.73 eV, where the emission from the nanonecklace was found to be stronger, indicating promise for near-infrared optoelectronics applications.

Self-Organized Growth of Two-Dimensional GaTe Nanosheet on ZnO Nanowires for Heterojunctional Water Splitting Applications

Epitaxial two-dimensional GaTe nanosheets on ZnO nanowires were routinely prepared via a two-step chemical vapor deposition procedure. The epitaxial relationship and growth mechanism of the GaTe/ZnO core/shell structures were explored and attributed to a layer-overlayer model. The hybrid structures increased the surface area and the favorable p-n heterojunction enhanced the charge separation for photoelectrochemical performance in water splitting. The above synergistic effects boosted the photocurrent density from -0.3 mA cm-2 for the pristine ZnO nanowires to -2.5 mA cm-2 for the core/shell GaTe/ZnO nanowires at -0.39 V vs RHE under the visible light irradiation. This highlights the promise for utilization of GaTe nanosheet/ZnO nanowires as efficient photoelectrocatalyst for water splitting.

Controllable Synthesis of [11−2−2] Faceted InN Nanopyramids on ZnO for Photoelectrochemical Water Splitting

Indium nitride (InN) is one of the promising narrow band gap semiconductors for utilizing solar energy in photoelectrochemical (PEC) water splitting. However, its widespread application is still hindered by the difficulties in growing high-quality InN samples. Here, high-quality InN nanopyramid arrays are synthesized via epitaxial growth on ZnO single-crystals. The as-prepared InN nanopyramids have well-defined exposed facets of [0001], [11-2-2], [1-212], and [-2112], which provide a possible routine for understanding water oxidation processes on the different facets of nanostructures in nanoscale. First-principles density functional calculations reveal that the nonpolar [11-2-2] face has the highest catalytic activity for water oxidation. PEC investigations demonstrate that the band positions of the InN nanopyramids are strongly altered by the ZnO substrate and a heterogeneous n-n junction is naturally formed at the InN/ZnO interface. The formation of the n-n junction and the built-in electric field is ascribed to the efficient separation of the photogenerated electron-hole pairs and the good PEC performance of the InN/ZnO. The InN/ZnO shows good photostability and the hydrogen evolution is about 0.56 µmol cm-2 h-1 , which is about 30 times higher than that of the ZnO substrate. This study demonstrates the potential application of the InN/ZnO photoanodes for PEC water splitting.

Liquid metal nano/micro-channels as thermal interface materials for efficient energy saving

Thermal interface material (TIMs) pads/sheets with both high elasticity and low thermal resistance are indispensable components for thermal management. In this paper, we propose a facile strategy for the fabrication of highly thermal conductive liquid metal (LM) nano/micro-channels embedded in an elastomeric matrix (polydimethylsiloxane, PDMS). The isolated LM micro-droplets were reshaped and became thermally connected upon applying stress to form conductive LM nano-channels, while improving the thermal conductivity (κ) up to 8.3 W m−1 K−1, which is greater than that of most commercial thermal silicone pads (<6 W m−1 K−1). In addition, a series of experiments on a commercial smartphone were performed to evaluate the heat dissipation performance. The results proved that LM thermal pads could not only reduce the temperature of the CPU and the back cover, but could also save energy and enhance the battery running time by as much as 31%.

Controllable synthesis of flower-like MoSe2 3D microspheres for highly efficient visible-light photocatalytic degradation of nitro-aromatic explosives

Nitro-aromatic explosives existing on the surface of the Earth are difficult to degrade, and they greatly harm the ecological environment and human security. Herein, we successfully conducted the large-scale synthesis of novel flower-like MoSe2 3D microspheres and nanospheres by a simple hydrothermal method. The two types of MoSe2 3D spheres had a high crystal quality with abundant nanosheets, and their diameters were approximately 1.5 μm and 300–400 nm, respectively. The Brunauer–Emmett–Teller (BET) and UV-vis diffuse reflectance spectra (UV-vis DRS) analyses revealed that the specific surface area and the band gap of MoSe2 microspheres and nanospheres were 33.3 m2 g−1 and 1.68 eV and those of the nanostructures were 13.6 m2 g−1 and 1.52 eV, respectively. Moreover, two different morphologies of MoSe2 were used for the degradation of nitrobenzene (NB), p-nitrophenol (PNP) and 2,4-dinitrophenol (2,4-DNP) through a photocatalytic process. The results demonstrated that the three nitro-aromatic explosive solutions NB, PNP and 2,4-DNP (40 mg L−1) could be completely degraded by MoSe2 3D microspheres under visible-light irradiation in 3.5 h, 1.5 h and 2.5 h, and the degradation time for MoSe2 nanospheres was 4.5 h, 2.5 h and 4 h, respectively. The mechanism of the photocatalytic reaction was also investigated in detail, and the photocatalytic degradation process was found to follow the pseudo-first-order kinetics. Our study demonstrated the potential application of MoSe2 microspheres as a photocatalyst for the degradation of nitro-aromatic explosives and other organic contaminants.