Jiuxiang Dai

Journal of Applied Physics, Volume 133, Issue 13, April 2023.
To realize fully integrated silicon photonics (Si photonics), reliable III–V light sources that can be efficiently coupled with Si/SiN waveguides are essential. Here, based on a monolithic InP/silicon-on-insulator (SOI) platform, we developed a selective regrowth scheme and constructed a regrowth platform for on-chip lasers that can be efficiently coupled with Si/SiN waveguides. InP and InGaAs/InP multi-quantum wells (MQWs) were regrown on the regrowth template on SOI as well as patterned commercial InP wafers in the same growth run for comparison. A flat (001) top surface after regrowth with a low roughness of 0.38 nm was obtained on SOI. Benefitting from the high quality of MQWs regrowth, strong photoluminescence emission at telecom band can be obtained on both growth templates. Also, multi-wavelength emission on the same chip can be potentially achieved by designing various regrowth openings. Furthermore, the large material volume with vertical stacking structure and intimate placement of MQWs and the Si layer of SOI allow for the potential demonstration of electrically pumped lasers and efficient light coupling between them and Si/SiN waveguides. Therefore, the demonstrated regrowth method provides a promising solution for the monolithic integration of III–V on-chip lasers on Si.

Through careful control of total diffusion-limited regime, it is possible to purify carbon black at the expense of far more stable graphite. This shows that targeted exploitation of total diffusion may be used to bypass the classical chemical reactivity. This represents a new technique for materials purification or synthesis not allowed by other methods.

Abstract

External diffusion may be exploited as a tool to purify materials in a way thought to be inaccessible from a chemical reactivity point of view. A mixture of two carbonaceous materials, graphite and carbon black, are thermally oxidized in either i) outside total diffusion-limited regime or ii) total diffusion-limited regime. Depending on the treatment applied it is possible to purify either graphite, a trivial task, or carbon black, a task thought impossible. Introducing geometrical selectivity, controlled total diffusion-limited chemistry exceeds by far the field of carbon materials and can be used as an engineering tool for many materials purification, original synthesis, or to introduce asymmetry in a system. Several examples for direct applications of the findings are mentioned.

1.9 kilograms of Eu³⁺-doped CaMoO₄ nanocrystals with a photoluminescence quantum yield of up to 85% and a particle size of 3.4 nm have been successfully synthesized in ethanol and water-mixed solvent by a facile ligand-assisted coprecipitation method at room temperature. This reaction can be finished in 1 min under ambient conditions.

Abstract

Rare earth-doped metal oxide nanocrystals have a high potential in display, lighting, and bio-imaging, owing to their excellent emission efficiency, superior chemical, and thermal stability. However, the photoluminescence quantum yields (PLQYs) of rare earth-doped metal oxide nanocrystals have been reported to be much lower than those of the corresponding bulk phosphors, group II-VI, and halide-based perovskite quantum dots because of their poor crystallinity and high-concentration surface defects. Here, an ultrafast and room-temperature strategy for the kilogram-scale synthesis of sub-5 nm Eu³⁺-doped CaMoO₄ nanocrystals is presented, and this reaction can be finished in 1 min under ambient conditions. The absolute PLQYs for sub-5 nm Eu³⁺-doped CaMoO₄ nanocrystals can reach over 85%, which are comparable to those of the corresponding bulk phosphors prepared by the high-temperature solid state reaction. Moreover, the as-produced nanocrystals exhibit a superior thermal stability and their emission intensity unexpectedly increases after sintering at 600 °C for 2 h in air. 1.9 kg of Eu³⁺-doped CaMoO₄ nanocrystals with a PLQY of 85.1% can be obtained in single reaction.

The manuscript combines experimental data, first-principles calculations, atomistic simulations, and transfer learning to show that irradiation-induced defects can induce a rotation-dependent moiré pattern in vertically stacked homobilayers of MoS₂. Extended defects formed during ion irradiation induce thermoelastic stresses and strains, which deform MoS₂ and excite surface acoustic waves, thus providing an avenue for controlling twist angle in 2D materials.

Abstract

Ultrathin MoS₂ has shown remarkable characteristics at the atomic scale with an immutable disorder to weak external stimuli. Ion beam modification unlocks the potential to selectively tune the size, concentration, and morphology of defects produced at the site of impact in 2D materials. Combining experiments, first-principles calculations, atomistic simulations, and transfer learning, it is shown that irradiation-induced defects can induce a rotation-dependent moiré pattern in vertically stacked homobilayers of MoS₂ by deforming the atomically thin material and exciting surface acoustic waves (SAWs). Additionally, the direct correlation between stress and lattice disorder by probing the intrinsic defects and atomic environments are demonstrated. The method introduced in this paper sheds light on how engineering defects in the lattice can be used to tailor the angular mismatch in van der Waals (vdW) solids.

This article reports the phenomenon of liquid metal droplet spin on ice induced by a spontaneous dual-fluid solid-liquid phase transition. The droplet motion is lubricated by a thin water film and driven by the escaping bubbles as the ice melts. Such spin effect is found to be universal for different objects including liquid metal droplets and solid balls.

Abstract

The non-contact and non-wetting droplet motion isolated from the solid surface has a high degree of freedom and thus can exhibit many peculiar interfacial phenomena. Here, an experimental phenomenon of spinning liquid metal droplets on an ice block is discovered, which adopts the dual solid-liquid phase transition of the liquid metal and the ice. The whole system is somewhat a variant of the classic Leidenfrost effect, which directly uses the latent heat released by the spontaneous solidification of the liquid metal droplet as a heat source to melt the ice and create an intervening lubricant water film. Interestingly, it is found that the droplets on ice become very mobile and undergo rapid spin as the solidification process proceeds. A series of comparative experiments clarify that the circumferential driving force comes from the escaping bubbles as the ice melts. Furthermore, by comparing the motion characteristics of different kinds of liquid metal droplets and solid balls on ice and investigating their physical properties and heat transfer, it is disclosed that the spin effect can be universal for objects of different materials, as long as the two necessary elements of rapid liquid film establishment and gas bubble release can be satisfied simultaneously.

As proof-of-principle, the preparation of various metal sulfides in a flame process using single-droplet combustion and enclosed flame spray pyrolysis in O₂-lean condition is demonstrated. Using a large-tube reactor MnS, CoS, Cu₂S, ZnS, Ag₂S, In₂S₃, SnS, and Bi₂S₃ are formed at a rate of 5 g h⁻¹. The flame aerosol process is a key toward scalable synthesis of binary/ternary metal sulfides for next-generation functional materials.

Abstract

The development of a novel reactive spray technology based on the well-known gas-phase metal oxide synthesis route provides innumerable opportunities for the production of non-oxide nanoparticles. Among these materials, metal sulfides are expected to have a high impact, especially in the development of electrochemical and photochemical high-surface-area materials. As a proof-of-principle, MnS, CoS, Cu₂S, ZnS, Ag₂S, In₂S₃, SnS, and Bi₂S₃ are synthesized in an O₂-lean and sulfur-rich environment. In addition, the formation of Cu₂S in a single-droplet combustion experiment is reported. The multiscale approach combining flame sprays with single-droplet combustion is expected to pave the way toward a fundamental understanding of the gas-phase formation of metal sulfides in the future. The knowledge acquired can open the possibility for the development of a next-generation gas-phase technology facilitating the scalable synthesis of functional binary/ternary metal sulfides.

Through the engineering of interfacial forces during the transfer process, the crack-free and clean transfer of 4-inch-sized graphene wafers onto silicon wafers within only 15 min is realized, which is compatible with batch production of graphene wafers on target substrates.

Abstract

Recently, scalable production of large-area graphene films on metal foils with promising qualities is successfully achieved by eliminating grain boundaries, wrinkles, and adlayers. The transfer of graphene from growth metal substrates onto functional substrates remains one inescapable obstacle on the road to the real commercial applications of chemical vaport deposition (CVD) graphene films. Current transfer methods still require time-consuming chemical reactions, which hinders its mass production, and produces cracks and contamination that strongly impede performance reproducibility. Therefore, graphene transfer techniques with fine intactness and cleanness of transferred graphene, and improved production efficiency would be ideal for the mass production of graphene films on destination substrates. Herein, through the engineering of interfacial forces enabled by sophisticated design of transfer medium, the crack-free and clean transfer of 4-inch-sized graphene wafers onto silicon wafers within only 15 min is realized. The reported transfer method is an important leap over the long-lasting obstacle of the batch-scale graphene transfer without degrading the quality of graphene, bringing the graphene products close to the real applications.

Journal of Applied Physics, Volume 133, Issue 13, April 2023.
To realize fully integrated silicon photonics (Si photonics), reliable III–V light sources that can be efficiently coupled with Si/SiN waveguides are essential. Here, based on a monolithic InP/silicon-on-insulator (SOI) platform, we developed a selective regrowth scheme and constructed a regrowth platform for on-chip lasers that can be efficiently coupled with Si/SiN waveguides. InP and InGaAs/InP multi-quantum wells (MQWs) were regrown on the regrowth template on SOI as well as patterned commercial InP wafers in the same growth run for comparison. A flat (001) top surface after regrowth with a low roughness of 0.38 nm was obtained on SOI. Benefitting from the high quality of MQWs regrowth, strong photoluminescence emission at telecom band can be obtained on both growth templates. Also, multi-wavelength emission on the same chip can be potentially achieved by designing various regrowth openings. Furthermore, the large material volume with vertical stacking structure and intimate placement of MQWs and the Si layer of SOI allow for the potential demonstration of electrically pumped lasers and efficient light coupling between them and Si/SiN waveguides. Therefore, the demonstrated regrowth method provides a promising solution for the monolithic integration of III–V on-chip lasers on Si.

Applied Physics Letters, Volume 122, Issue 14, April 2023.
We report deterministic control over a moiré superlattice interference pattern in twisted bilayer graphene by implementing designable device-level heterostrain with process-induced strain engineering, a widely used technique in industrial silicon nanofabrication processes. By depositing stressed thin films onto our twisted bilayer graphene samples, heterostrain magnitude and strain directionality can be controlled by stressor film force (film stress × film thickness) and patterned stressor geometry, respectively. We examine strain and moiré interference with Raman spectroscopy through in-plane and moiré-activated phonon mode shifts. Results support systematic C3 rotational symmetry breaking and tunable periodicity in moiré superlattices under the application of uniaxial or biaxial heterostrain. Experimental results are validated by molecular statics simulations and density functional theory based first principles calculations. This provides a method not only to tune moiré interference without additional twisting but also to allow for a systematic pathway to explore different van der Waals based moiré superlattice symmetries by deterministic design.

This work presents the hydrothermal synthesis of La doped MoS₂ nanosheets exhibiting the significant catalytic degrdation of methylene blue dye and antimicrobial activity against E. coli bacteria. 2% La doped MoS₂ nanosheets used as an ideal catalyst and 4% La doped MoS₂ used as a best potential inhibitor.

Abstract

The development of efficient catalysts with a large number of active sites, tunable bandgap, and large surface area has been very challenging. In addition, a significant bottleneck in the application of catalysts for water treatment is their dissolution under extreme conditions, such as highly acidic or highly alkaline conditions that lead to poor application of the reported materials in real-world applications. In this study, the lanthanum (La)-doped molybdenum disulfide (MoS₂) nanosheets are reported for efficient breakdown of toxic pollutants from wastewater under a wide pH range from strongly alkaline to strongly acidic solutions. The La-MoS₂ nanosheets (NSs) are prepared by a facile hydrothermal approach using a two-step methodology. A redshift is observed upon La doping, indicating that the bandgap is lowered after La doping in MoS₂. The changes in bandgap and electronic structure are further investigated using the density functional theory (DFT), which reveal that doping of La introduces new states within the bandgap region, allowing for further induced energy transitions. The La-MoS₂, having a doping concentration of 2%, exhibits the highest catalytic activity against methylene blue (MB) in neutral, acidic, and alkaline solutions, as well as substantial inhibitory activity for bacterial strains such as Escherichia coli (E. coli). In summary, the modified catalyst provides a pathway to design highly efficient catalysts for all pH range water treatment as well as good activity against microbes.

A strategy of graphene-enhanced integration for realizing strong van der Waals contacts between a variety of 2D semiconductors and metals with atomically flat and ultra-clean interface for high-performance 2D electronics.

Abstract

2D semiconductors have shown great potentials for ultra-short channel field-effect transistors (FETs) in next-generation electronics. However, because of intractable surface states and interface barriers, it is challenging to realize high-quality contacts with low contact resistances for both p- and n- 2D FETs. Here, a graphene-enhanced van der Waals (vdWs) integration approach is demonstrated, which is a multi-scale (nanometer to centimeter scale) and reliable (≈100% yield) metal transfer strategy applicable to various metals and 2D semiconductors. Scanning transmission electron microscopy imaging shows that 2D/2D/3D semiconductor/graphene/metal interfaces are atomically flat, ultraclean, and defect-free. First principles calculations indicate that the sandwiched graphene monolayer can eliminate gap states induced by 3D metals in 2D semiconductors. Through this approach, Schottky barrier-free contacts are realized on both p- and n-type 2D FETs, achieving p-type MoTe₂, p-type black phosphorus and n-type MoS₂ FETs with on-state current densities of 404, 1520, and 761 µA µm⁻¹, respectively, which are among the highest values reported in literature.

Applied Physics Letters, Volume 122, Issue 15, April 2023.
We report a vertical β-Ga2O3 Schottky barrier diode (SBD) with BaTiO3 as field plate oxide on a low doped thick epitaxial layer exhibiting 2.1 kV breakdown voltage. A thick drift layer of 11 μm with a low effective doping concentration of 8 × 1015 cm–3 is used to achieve high breakdown voltage. Using the high-k dielectric with a dielectric constant of 248, the breakdown voltage increases from 816 V for the non-field-plated SBD to 2152 V (>2× improvement) for the field-plated SBD without compromising the on-state performance. The diode dimensions are varied to analyze the effect of edge high-field related leakage with reverse bias and also the effect of current spreading during forward operation. Very uniform distribution of breakdown voltages of 2152 ± 20 V are observed for the diode diameters from 50 to 300 μm for the field-plated SBDs. The on and off state power losses are also analyzed and compared with the non-field-plated devices and the switching losses are estimated analytically.

This work reports a high-reproducible, high-efficient epitaxial growth method of wafer-scale (over two inches) monolayer MoS₂ single crystals on the industry-compatible sapphire substrates, by designing a “face-to-face” metal-foil-based precursor supply route, carbon-cloth-filter based precursor concentration decay strategy, and the precise optimization of the chalcogenides and metal precursor ratio.

Abstract

2D semiconducting transition-metal dichalcogenides (TMDs) have attracted considerable attention as channel materials for next-generation transistors. To meet the industry needs, large-scale production of single-crystal monolayer TMDs in highly reproducible and energy-efficient manner is critically significant. Herein, it is reported that the high-reproducible, high-efficient epitaxial growth of wafer-scale monolayer MoS₂ single crystals on the industry-compatible sapphire substrates, by virtue of a deliberately designed “face-to-face” metal-foil-based precursor supply route, carbon-cloth-filter based precursor concentration decay strategy, and the precise optimization of the chalcogenides and metal precursor ratio (i.e., S/Mo ratio). This unique growth design can concurrently guarantee the uniform release, short-distance transport, and moderate deposition of metal precursor on a wafer-scale substrate, affording high-efficient and high-reproducible growth of wafer-scale single crystals (over two inches, six times faster than usual). Moreover, the S/Mo precursor ratio is found as a key factor for the epitaxial growth of MoS₂ single crystals with rather high crystal quality, as convinced by the relatively high electronic performances of related devices. This work demonstrates a reliable route for the batch production of wafer-scale single-crystal 2D materials, thus propelling their practical applications in highly integrated high-performance nanoelectronics and optoelectronics.

2D Materials

It highlights the remarkable technological advances achieved in this work, that ice can be used to transfer 2D materials, yielding ultraclean and ultra-uniform products. Compared to the traditional poly(methyl methacrylate) (PMMA) method for 2D materials transfer, which leads to contamination and rippling defects, the ice-transfer method achieved by Jiong Zhao, Qingming Deng, Thuc Hue Ly, and co-workers in article number 2210503 paves a new way for 2D materials science and technology.

Nature Nanotechnology, Published online: 06 April 2023; doi:10.1038/s41565-023-01363-w

This study uncovers the role of aromatic clusters in the receptor extracellular loop of sialic-acid-binding immunoglobulin-like lectins that recognize carbon nanotubes and suggests inhibiting Syk signalling as a therapeutic intervention against inflammation.

Nature Physics, Published online: 06 April 2023; doi:10.1038/s41567-023-01991-y

Levitated nanoparticles can now be cooled to the motional ground state in two dimensions. This advance could enable a new generation of macroscopic quantum experiments.