Jianwei Chai

Bio: Jianwei Chai is an academic researcher from Agency for Science, Technology and Research. The author has contributed to research in topics: X-ray photoelectron spectroscopy & Band gap. The author has an hindex of 30, co-authored 101 publications receiving 2832 citations. Previous affiliations of Jianwei Chai include National University of Singapore.

Growth of wafer-scale MoS2 monolayer by magnetron sputtering

Abstract: The two-dimensional layer of molybdenum disulfide (MoS2) exhibits promising prospects in the applications of optoelectronics and valleytronics. Herein, we report a successful new process for synthesizing wafer-scale MoS2 atomic layers on diverse substrates via magnetron sputtering. Spectroscopic and microscopic results reveal that these synthesized MoS2 layers are highly homogeneous and crystallized; moreover, uniform monolayers at wafer scale can be achieved. Raman and photoluminescence spectroscopy indicate comparable optical qualities of these as-grown MoS2 with other methods. The transistors composed of the MoS2 film exhibit p-type performance with an on/off current ratio of ∼10(3) and hole mobility of up to ∼12.2 cm(2) V(-1) s(-1). The strategy reported herein paves new ways towards the large scale growth of various two-dimensional semiconductors with the feasibility of controllable doping to realize desired p- or n-type devices.

Facile Synthesis of Vanadium-Doped Ni3S2 Nanowire Arrays as Active Electrocatalyst for Hydrogen Evolution Reaction.

Abstract: Ni3S2 nanowire arrays doped with vanadium(V) are directly grown on nickel foam by a facile one-step hydrothermal method. It is found that the doping can promote the formation of Ni3S2 nanowires at a low temperature. The doped nanowires show excellent electrocatalytic performance toward hydrogen evolution reaction (HER), and outperform pure Ni3S2 and other Ni3S2-based compounds. The stability test shows that the performance of V-doped Ni3S2 nanowires is improved and stabilized after thousands of linear sweep voltammetry test. The onset potential of V-doped Ni3S2 nanowire can be as low as 39 mV, which is comparable to platinum. The nanowire has an overpotential of 68 mV at 10 mA cm–2, a relatively low Tafel slope of 112 mV dec–1, good stability and high Faradaic efficiency. First-principles calculations show that the V-doping in Ni3S2 extremely enhances the free carrier density near the Fermi level, resulting in much improved catalytic activities. We expect that the doping can be an effective way to enhance...

Synergistic effect of 2D Ti2C and g-C3N4 for efficient photocatalytic hydrogen production

Abstract: Photocatalytic water splitting is an environmentally friendly technique for hydrogen production. In this work, we report a novel photocatalyst consisting of two-dimensional (2D) titanium carbide (Ti2C) and graphitic carbon nitride (g-C3N4). We observe substantially enhanced water splitting activities due to the efficient synergistic interaction between Ti2C and g-C3N4. Optimal properties are achieved in the g-C3N4 with a loading of 0.4 wt% Ti2C with a hydrogen production rate of 47.5 μmol h−1, which is 14.4 times as much as that in the case using pure g-C3N4, and it even outperforms Pt-loaded g-C3N4. We further show that the Ti2C/g-C3N4 has high stability and good reproducibility. We expect that the Ti2C/g-C3N4 can be a photocatalyst for large scale applications because both Ti2C and g-C3N4 are low-cost, abundant, and nontoxic.

A Robust Hybrid Zn-Battery with Ultralong Cycle Life

Abstract: Advanced batteries with long cycle life and capable of harnessing more energies from multiple electrochemical reactions are both fundamentally interesting and practically attractive. Herein, we report a robust hybrid zinc-battery that makes use of transition-metal-based redox reaction (M–O–OH → M–O, M = Ni and Co) and oxygen reduction reaction (ORR) to deliver more electrochemical energies of comparably higher voltage with much longer cycle life. The hybrid battery was constructed using an integrated electrode of NiCo2O4 nanowire arrays grown on carbon-coated nickel foam, coupled with a zinc plate anode in alkaline electrolyte. Benefitted from the M–O/M–O–OH redox reactions and rich ORR active sites in NiCo2O4, the battery has concurrently exhibited high working voltage (by M–O–OH → M–O) and high energy density (by ORR). The good oxygen evolution reaction (OER) activity of the electrode and the reversible M–O ↔ M–O–OH reactions also enabled smooth recharging of the batteries, leading to excellent cycling ...

Synergistic effect of 2D Ti₂C and g-C₃N₄ for efficient photocatalytic hydrogen production

Abstract: Photocatalytic water splitting is an environmentally friendly technique for hydrogen production. In this work, we report a novel photocatalyst consisting of two-dimensional (2D) titanium carbide (Ti₂C) and graphitic carbon nitride (g-C₃N₄). We observe substantially enhanced water splitting activities due to the efficient synergistic interaction between Ti₂C and g-C₃N₄. Optimal properties are achieved in the g-C₃N₄ with a loading of 0.4 wt% Ti₂C with a hydrogen production rate of 47.5 μmol h⁻¹, which is 14.4 times as much as that in the case using pure g-C₃N₄, and it even outperforms Pt-loaded g-C₃N₄. We further show that the Ti₂C/g-C₃N₄ has high stability and good reproducibility. We expect that the Ti₂C/g-C₃N₄ can be a photocatalyst for large scale applications because both Ti₂C and g-C₃N₄ are low-cost, abundant, and nontoxic.

High-κ gate dielectrics: Current status and materials properties considerations

Abstract: Many materials systems are currently under consideration as potential replacements for SiO2 as the gate dielectric material for sub-0.1 μm complementary metal–oxide–semiconductor (CMOS) technology. A systematic consideration of the required properties of gate dielectrics indicates that the key guidelines for selecting an alternative gate dielectric are (a) permittivity, band gap, and band alignment to silicon, (b) thermodynamic stability, (c) film morphology, (d) interface quality, (e) compatibility with the current or expected materials to be used in processing for CMOS devices, (f) process compatibility, and (g) reliability. Many dielectrics appear favorable in some of these areas, but very few materials are promising with respect to all of these guidelines. A review of current work and literature in the area of alternate gate dielectrics is given. Based on reported results and fundamental considerations, the pseudobinary materials systems offer large flexibility and show the most promise toward success...

Diamond-like amorphous carbon

Abstract: Diamond-like carbon (DLC) is a metastable form of amorphous carbon with significant sp3 bonding. DLC is a semiconductor with a high mechanical hardness, chemical inertness, and optical transparency. This review will describe the deposition methods, deposition mechanisms, characterisation methods, electronic structure, gap states, defects, doping, luminescence, field emission, mechanical properties and some applications of DLCs. The films have widespread applications as protective coatings in areas, such as magnetic storage disks, optical windows and micro-electromechanical devices (MEMs).

High dielectric constant gate oxides for metal oxide Si transistors

Abstract: The scaling of complementary metal oxide semiconductor transistors has led to the silicon dioxide layer, used as a gate dielectric, being so thin (14?nm) that its leakage current is too large It is necessary to replace the SiO2 with a physically thicker layer of oxides of higher dielectric constant (?) or 'high K' gate oxides such as hafnium oxide and hafnium silicate These oxides had not been extensively studied like SiO2, and they were found to have inferior properties compared with SiO2, such as a tendency to crystallize and a high density of electronic defects Intensive research was needed to develop these oxides as high quality electronic materials This review covers both scientific and technological issues?the choice of oxides, their deposition, their structural and metallurgical behaviour, atomic diffusion, interface structure and reactions, their electronic structure, bonding, band offsets, electronic defects, charge trapping and conduction mechanisms, mobility degradation and flat band voltage shifts The oxygen vacancy is the dominant electron trap It is turning out that the oxides must be implemented in conjunction with metal gate electrodes, the development of which is further behind Issues about work function control in metal gate electrodes are discussed

High dielectric constant oxides

Abstract: The scaling of complementary metal oxide semiconductor (CMOS) transistors has led to the silicon dioxide layer used as a gate dielectric becoming so thin (1.4 nm) that its leakage current is too large. It is necessary to replace the SiO2 with a physically thicker layer of oxides of higher dielectric constant (κ) or 'high K' gate oxides such as hafnium oxide and hafnium silicate. Little was known about such oxides, and it was soon found that in many respects they have inferior electronic properties to SiO2 ,s uch as a tendency to crystallise and a high concentration of electronic defects. Intensive research is underway to develop these oxides into new high quality electronic materials. This review covers the choice of oxides, their structural and metallurgical behaviour, atomic diffusion, their deposition, interface structure and reactions, their electronic structure, bonding, band offsets, mobility degradation, flat band voltage shifts and electronic defects. The use of high K oxides in capacitors of dynamic random access memories is also covered.

Cocatalysts for Selective Photoreduction of CO2 into Solar Fuels.

Abstract: Photoreduction of CO2 into sustainable and green solar fuels is generally believed to be an appealing solution to simultaneously overcome both environmental problems and energy crisis. The low selectivity of challenging multi-electron CO2 photoreduction reactions makes it one of the holy grails in heterogeneous photocatalysis. This Review highlights the important roles of cocatalysts in selective photocatalytic CO2 reduction into solar fuels using semiconductor catalysts. A special emphasis in this review is placed on the key role, design considerations and modification strategies of cocatalysts for CO2 photoreduction. Various cocatalysts, such as the biomimetic, metal-based, metal-free, and multifunctional ones, and their selectivity for CO2 photoreduction are summarized and discussed, along with the recent advances in this area. This Review provides useful information for the design of highly selective cocatalysts for photo(electro)reduction and electroreduction of CO2 and complements the existing reviews on various semiconductor photocatalysts.