Jiuxiang Dai

This study explores the synthesis of boron nitride (BN) interphases using Fluidized Bed Chemical Vapor Deposition (FB-CVD) with triethylamine borane (TEAB). It highlights optimizing CVD parameters to limit carbon contamination, with thermodynamic calculations and FTIR confirming the impact of TEAB dilution. Characterizations reveal dense, uniform, low-carbon BN coatings with minimal impurities, demonstrating the benefits of non-chlorinated precursors.

Abstract

This study examines the optimization and characterization of stoichiometric and carbon-free boron nitride interphase coatings using triethylamine borane complex as a precursor in the Fluidized Bed Chemical Vapor Deposition process. It highlights the importance of optimizing chemical vapor deposition parameters to control coating formation, limit carbon contamination, and assess the feasibility of stoichiometric boron nitride from triethylamine borane complex coatings. The study investigates the thermal decomposition of triethylamine borane complex and its effect on carbon contamination through theoretical thermodynamic calculations, corroborated by Fourier-transform infrared spectroscopy. Analysis shows a consistent, uniform microstructure. Auger electron spectroscopy and X-ray photoelectron spectroscopy confirm the presence of boron, nitrogen, carbon, and oxygen, with negligible carbon inclusions. Transmission electron microscopy and electron energy loss spectroscopy reveal a low-crystalline, isotropic structure. Carbon-rich areas in boron nitride coatings indicate intricate chemical interactions during deposition, while disordered structures highlight the need to understand the effects of structural variations. Despite using a high-carbon precursor, boron nitride coatings are remarkably stoichiometric with low carbon and oxygen contamination, demonstrating the benefits of non-chlorinated precursors.

npj 2D Materials and Applications, Published online: 12 August 2024; doi:10.1038/s41699-024-00492-7

Giant exchange splitting in the electronic structure of A-type 2D antiferromagnet CrSBr

In 2D optoelectronic devices with the electrodes of 2D ferromagnet Fe₃GaTe₂ and channel of WSe₂, the photoresponse is effectively controlled by magnetic fields at room temperature. This room-temperature magneto-photoresponse, achieved by the 2D magneto-band structure, lays the groundwork for multidimensional responsive optoelectronic devices. It holds promise for the development of robust in-sensor machine vision systems with gate-free architectures.

Abstract

Interplay between magnetism and photoelectric properties introduces the effective control of photoresponse in optoelectronic devices via magnetic field, termed as magneto-photoresponse. It enriches the application scenarios and shows potential to construct in-sensor vision systems for artificial intelligence with gate-free architecture. However, achieving a simultaneous existence of room-temperature magnetism and notable photoelectric properties in semiconductors is a great challenge. Here, the room-temperature magneto-photoresponse is accomplished in all-2D optoelectronic devices, employing 2D ferromagnet Fe₃GaTe₂ as the source and drain, with WSe₂ forming the channel. The interplay between room-temperature magnetism and photoelectric properties is realized by introducing the unique magneto-band structure effect from 2D interface, resulting in magneto-tunable charge transfer between Fe₃GaTe₂ and WSe₂. The photocurrent in this 2D optoelectronic device exhibits robust response to both the direction and amplitude of external magnetic fields. Utilizing constructed 2D optoelectronic devices with magneto-photoresponse, traditional gate-controlled phototransistors are replaced and a prototype in-sensor vision system with visual adaptation, significantly improving the recognition accuracy to over four times in low-contrast environments is established. These findings pave a way for achieving high-temperature magneto-photoresponse, thereby guiding the construction of robust in-sensor vision systems toward high performance and broad applications.

Nature Materials, Published online: 12 August 2024; doi:10.1038/s41563-024-01968-z

The synthesis of wafer-scale ultraflat single-crystal hexagonal boron nitride film is realized by strong coupling to a Cu0.8Ni0.2(111)/sapphire wafer, providing a potential method for industry-compatible high-κ dielectric integration in two-dimensional electronics.

Adding graphene to copper introduces interface scatterings that decrease the copper's electrical conductivity. However, compressive strain can increase the conductivity.

Abstract

There is great interest in developing advanced electrical conductors with higher conductivity, lighter weight, and higher mechanical strength than copper (Cu). One promising candidate is copper-graphene (Cu-Gr) composite, which is hypothesized to have a higher electrical conductivity than Cu. In this work, it is shown that this is not true, supported by state-of-the-art first-principles calculations of electron transport. Particularly, contrary to the belief that graphene in the composite is more conductive than pristine Cu, it is less conductive due to increased scattering despite increased carrier concentration. On the other hand, it is found that compressive strain along the (111) plane increases the conductivity, which is confirmed experimentally, while tensile strain has little effect. The work offers new insights into understanding and developing advanced conductors.

This review reports recent advances in Sb₂Se₃ photodetectors (PDs), focusing on fundamental characteristics, nanostructure tuning, applications in heart rate monitoring, and monolithic integrated matrix imaging. The challenges, including the broadening of the detection range, the reduction of dark current, and the potential applications of flexible devices are highlighted, which provide a valuable reference for Sb₂Se₃ PDs and expand application areas.

Abstract

Photodetectors (PDs) rapidly capture optical signals and convert them into electrical signals, making them indispensable in a variety of applications including imaging, optical communication, remote sensing, and biological detection. Recently, antimony selenide (Sb₂Se₃) has achieved remarkable progress due to its earth-abundant, low toxicity, low price, suitable bandgap width, high absorption coefficient, and unique structural characteristics. Sb₂Se₃ has been extensively studied in solar cells, but there's a lack of timely updates in the field of PDs. A literature review based on Sb₂Se₃ PDs is urgently warranted. This review aims to provide a concise understanding of the latest progress in Sb₂Se₃ PDs, with a focus on the basic characteristics and the performance optimization for Sb₂Se₃ photoconductive-type and photodiode-type detectors, including nanostructure regulation, process optimization, and stability improvement of flexible devices. Furthermore, the application progresses of Sb₂Se₃ PDs in heart rate monitoring, and monolithic-integrated matrix images are introduced. Finally, this review presents various strategies with potential and feasibility to address challenges for the rapid development and commercial application of Sb₂Se₃ PDs.

Strongly coupled NbSe₂ nanosheets/graphene (NbSe2 NSs/G) heterostructure with expanded interlayer spacings and high electron conductivity is applied as anode for boosting potassium storage performance. The intercalation-based storage mechanism and heterostructure feature alleviate the severe volume change during potassiation/depotassiation, thereby significantly improving structural stability and ensuring long-term cycle stability. Notably, the assembled PTCDA//NbSe2 NSs/G full-cells achieve both high energy density and power density.

Abstract

Layered transition metal dichalcogenides are of intensive interest for potassium-ion batteries (PIBs) due to their high theoretical capacity, relatively low working potential, and layered structures. However, the limited interlayer spacing poses challenges in accommodating large-radius potassium ions, significantly affecting their rate and cycling performances, particularly for selenide counterparts. Herein, a class of the strongly coupled NbSe₂ nanosheets (NSs)/graphene (G) heterostructure with expanded interlayer spacings and high electron conductivity for boosting the performance of potassium storage is reported. NbSe₂ NSs/G delivers a reversible capacity of 348.4 mAh g⁻¹ at 0.05 A g⁻¹, exceptional rate performance (117.5 mAh g⁻¹ at an ultrahigh current density of 10.0 A g⁻¹), and excellent cycle stability (capacity retention of 167.8 mAh g⁻¹ after 2350 cycles under 2.0 A g⁻¹), placing it among the top performers in reported TMD-based PIB anodes. In situ XRD and Raman measurements reveal the intercalation-based mechanism in NbSe₂ NSs/G and the introduction of graphene can alleviate the severe volume change, making it possess superior rate performance and cycle stability Prominently, full-cell PIBs employing NbSe₂ NSs/G anodes demonstrate remarkable rate capability, and achieve a high energy density of 103.0 Wh kg⁻¹ and a high power density of 1140.6 W kg⁻¹.

Non-destructive in situ scanning transmission electron microscopy reveals a novel atomic fracture behavior in suspended monolayer MoS₂ and MoSe₂, featured by single chalcogen atoms (S or Se) on both crack edges. The out-of-plane deformation, arising from the ultrathin nature of these suspended monolayer films, plays a central role in this fracture process.

Abstract

A comprehensive understanding of atomic fracture mechanisms in 2D materials is essential for their practical applications, yet this knowledge is currently limited. To address this gap, an aberration-corrected scanning transmission electron microscope (STEM) to induce new cracks in suspended monolayer transition metal dichalcogenides (TMDs) using broad electron beam illumination, is employed. During characterization, a low-dose electron beam to avoid irradiation damage, allowing to observe the atomic fracture behavior in these materials, is utilized. The STEM experiments reveal a novel atomic fracture pattern along the zigzag direction, resulting in a distribution where half of the chalcogen atoms (S or Se) adhered to the molybdenum-terminated (Mo-T) edge and the other half to the chalcogen-terminated (S-T or Se-T) edge. Density functional theory (DFT) calculations suggest that this fracture mode produces a pair of edges with the lowest formation energy. Additionally, molecular dynamics (MD) simulations support the observed fracture behavior under a mixed mechanical loading mode of “I+III” with both in-plane and out-of-plane stress, originating from the ultrathin nature and nonplanar deformation in suspended 2D materials. This research offers new insights for the development of 2D fracture mechanics and is pivotal for designing devices incorporating 2D materials.

The LaAlO₃/SrTiO₃ interface hosts a plethora of gate-tunable electronic phases. Here, quasi-1D ballistic electron waveguides are sketched at the LaAlO₃/SrTiO₃ interface as a probe to understand how gate tunability varies as a function of spatial separation. Gate tunability measurements reveal a non-Coulombic coupling at the interface in contrast to traditional semiconductor systems.

Abstract

The LaAlO₃/SrTiO₃ interface hosts a plethora of gate-tunable electronic phases. Gating of LaAlO₃/SrTiO₃ interfaces is usually assumed to occur electrostatically. However, increasing evidence suggests that non-local interactions can influence and, in some cases, dominate the coupling between applied gate voltages and electronic properties. Here, quasi-1D ballistic electron waveguides are sketched at the LaAlO₃/SrTiO₃ interface as a probe to understand how gate tunability varies as a function of spatial separation. Gate tunability measurements reveal the scaling law to be at odds with the pure electrostatic coupling observed in traditional semiconductor systems. The non-Coulombic gating at the interface is attributed to a long-range nanoelectromechanical coupling between the gate and electron waveguide, possibly mediated by the ferroelastic domains in SrTiO₃. The long-range interactions at the LaAlO₃/SrTiO₃ interface add unexpected richness and complexity to this correlated electron system.

Nature Photonics, Published online: 14 August 2024; doi:10.1038/s41566-024-01504-0

Using electrostatic doping, the real and imaginary parts of the refractive index along the extraordinary axis of semiconducting, highly aligned, single-walled carbon nanotubes over 4″ wafers can be tuned by up to 5.9% and 14.3% in the infrared at 2,200 nm and 1,660 nm, respectively.

The first time nanoribbons of sodium niobate from a porous nanostructure supported on a metallic substrate is investigated. To fundamentally understand these nanoribbons, advanced electron microscopy with computer simulations are combined to identify their phase, specific atomic displacements, and unprecedented surface structure and composition. This work enhances their potential applications in electronics and photocatalysis.

Abstract

Ferroelectric materials exhibit switchable spontaneous polarization below Curie's temperature, driven by octahedral distortions and rotations, as well as ionic displacements. The ability to manipulate polarization coupled with persistent remanence, drives diverse applications, including piezoelectric devices. In the last two decades, nanoscale exploration has unveiled unique material properties influenced by morphology, including the capability to manipulate polarization, patterns, and domains. This paper focuses on the characterization of nanometric sodium niobate (SN) synthesized from metallic niobium through alkali hydrothermal treatment, utilizing electron microscopy techniques, including high-resolution differential phase contrast (DPC) in scanning transmission electron microscopy (STEM). The material exhibits a nanoribbon structure forming a tree root-like network. The study identifies crystallographic phase, atomic columns displacement directions, and surface features, such as exposed planes and the absence of particular atomic columns. The high sensitivity of integrated DPC images proves crucial in overcoming observational challenges in other STEM modes. These observations are essential for potential applications in electronic, photocatalytic, and chemical reaction contexts.

Nanoribbons exfoliated from bulk van der Waals crystals exhibit exciting new properties based on their edge configuration, width, and strain. A new exfoliation method can be applied to obtain monolayer, parallel aligned, and single crystalline nanoribbons from a wide variety of layered materials. The technique allows for thorough experimental characterization of their optical, electronic, and magnetic properties, informing future practical applications.

Abstract

Confinement of monolayers into quasi-1D atomically thin nanoribbons could lead to novel quantum phenomena beyond those achieved in their bulk and monolayer counterparts. However, current experimental availability of nanoribbon species beyond graphene is limited to bottom-up synthesis or lithographic patterning. In this study, a versatile and direct approach is introduced to exfoliate bulk van der Waals crystals as nanoribbons. Akin to the Scotch tape exfoliation method for producing monolayers, this technique provides convenient access to a wide range of nanoribbons derived from their corresponding bulk crystals, including MoS₂, WS₂, MoSe₂, WSe₂, MoTe₂, WTe₂, ReS₂, and hBN. The nanoribbons are predominantly monolayer, single-crystalline, parallel-aligned, flat, and exhibit high aspect ratios. The role of confinement, strain, and edge configuration of these nanoribbons is observed in their electrical, magnetic, and optical properties. This versatile exfoliation technique provides a universal route for producing a variety of nanoribbon materials and supports the study of their fundamental properties and potential applications.

Publication date: October 2024

Source: Materials Today, Volume 79

Author(s): Katarzyna Z. Donato, Gavin K.W. Koon, Sarah J. Lee, Alexandra Carvalho, Hui Li Tan, Mariana C.F. Costa, Jakub Tolasz, Petra Ecorchard, Paweł P. Michałowski, Ricardo K. Donato, A.H. Castro Neto

Air sensitivity remains a substantial barrier to the commercialization of sodium (Na)–layered oxides (NLOs). This problem has puzzled the community for decades because of the complexity of interactions between air components and their impact on both bulk ...

Metal oxide films are essential in most electronic devices, yet they are typically deposited at elevated temperatures by using slow, vacuum-based processes. We printed native oxide films over large areas at ambient conditions by moving a molten metal ...

Inspired by water striders, an electricity-driven multifunctional swimming Marangoni robot is proposed, which is fabricated by super-aligned carbon nanotube and polyimide composites. The robot swims on the water surface based on the thermal Marangoni effect and can grasp objects using air-ambient actuators. The functions of swimming through tunnels, being charged on the water surface, and being driven by light are also demonstrated.

Abstract

Marangoni actuators that are propelled by surface tension gradients hold significant potential in small-scale swimming robots. Nevertheless, the release of “fuel” for conventional chemical Marangoni actuators is not easily controllable, and the single swimming function also limits application areas. Constructing controllable Marangoni robots with multifunctions is still a huge challenge. Herein, inspired by water striders, electricity-driven strategies are proposed for a multifunctional swimming Marangoni robot (MSMR), which is fabricated by super-aligned carbon nanotube (SACNT) and polyimide (PI) composite. The MSMR consists of a Marangoni actuator and air-ambient actuators. Owing to the temperature gradient generated by the electrical stimulation on the water surface, the Marangoni actuators can swim controllably with linear, turning, and rotary motions, mimicking the walking motion of water striders. In addition, the Marangoni actuators can also be driven by light. Importantly, the air-ambient actuators fabricated by SACNT/PI bilayer structures demonstrate the function of grasping objects on the water surface when electrically Joule-heated, mimicking the predation behavior of water striders. With the synergistic effect of the Marangoni actuator and air-ambient actuators, the MSMR can navigate mazes with tunnels and grasp objects. This research will provide a new inspiration for smart actuators and swimming robots.

By employing a nitrate-assisted oxidation strategy, amorphous mesoporous IrO_x nanomeshes (a-m IrO_x NMs) and various amorphous metal oxide nanomeshes are fabricated. As an anode electrocatalyst in proton exchange membrane water electrolyzer, the a-m IrO_x NMs exhibit a cell voltage of 1.67 V at 1 A cm⁻² with low loading (0.4 mg_catalyst cm⁻²), maintained for 120 h without apparent attenuation.

Abstract

Constructing the pore structures in amorphous metal oxide nanosheets can enhance their electrocatalytic performance by efficiently increasing specific surface areas and facilitating mass transport in electrocatalysis. However, the accurate synthesis for porous amorphous metal oxide nanosheets remains a challenge. Herein, a facile nitrate-assisted oxidation strategy is reported for synthesizing amorphous mesoporous iridium oxide nanomeshes (a-m IrO_x NMs) with a pore size of ∼4 nm. X-ray absorption characterizations indicate that a-m IrO_x NMs possess stretched Ir─O bonds and weaker Ir–O interaction compared with commercial IrO₂. Combining thermogravimetric-fourier transform infrared spectroscopy with differential scanning calorimetry measurements, it is demonstrated that sodium nitrate, acting as an oxidizing agent, is conducive to the formation of amorphous nanosheets, while the NO₂ produced by the in situ decomposition of nitrates facilitates the generation of pores within the nanomeshes. As an anode electrocatalyst in proton exchange membrane water electrolyzer, a-m IrO_x NMs exhibit superior performance, maintaining a cell voltage of 1.67 V at 1 A cm⁻² for 120 h without obvious decay with a low loading (0.4 mg_catalyst cm⁻²). Furthermore, the nitrate-assisted method is demonstrated to be a general approach to prepare various amorphous metal oxide nanomeshes, including amorphous RhO_x, TiO_x, ZrO_x, AlO_x, and HfO_x nanomeshes.