Jiuxiang Dai

Building Airy castles: An alternative method to achieve highly controlled micropatterning for photosculpting metallic structures, called Airy castles, by means of pulsed laser radiation and silver nanorods (AgNRs) is presented. Optical trapping and optical binding forces followed by photooxidation, melting, and ripening drive building up luminescent Airy castles, which remain stable for potential sensing applications.

Abstract

Controlling the nano- and micropatterning of metal structures is an important requirement for various technological applications in photonics and biosensing. This work presents a method for controllably creating silver micropatterns by laser-induced photosculpting. Photosculpting is driven by plasmonic interactions between pulsed laser radiation and silver nanorods (AgNRs) in aqueous suspension; this process leads to optical binding forces transporting the AgNRs in the surroundings, while electronic thermalization results in photooxidation, melting, and ripening of the AgNRs into well-defined 3D structures. This work call these structures Airy castles due to their structural similarity with a diffraction-limited Airy disk. The photosculpted Airy castles contain emissive Ag nanoclusters, allowing for the visualization and examination of the aggregation process using luminescence microscopy. This work comprehensively examines the factors that define the photosculpting process, namely, the concentration and shape of the AgNRs, as well as the energy, power, and repetition rate of the laser. Finally, this work investigates the potential applications by measuring the metal-enhanced luminescence of a europium-based luminophore using Airy castles.

A synaptic device with violet phosphorusheterostructure, a new stable 2D phosphorus is demonstrated, which shows a remarkable light-to-dark ratio of over 10⁶, 128 conductance states, and excellent synaptic behaviors.The effect of large dynamic ranges and multi-states on recognition tasks of varying complexity is further validated, providing guidance for advancingneuromorphic computing applications.

Abstract

Neuromorphic computing can efficiently handle data-intensive tasks and address the redundant interaction required by von Neumann architectures. Synaptic devices are essential components for neuromorphic computation. 2D phosphorene, such as violet phosphorene, show great potential in optoelectronics due to their strong light-matter interactions, while current research is mainly focused on synthesis and characterization, its application in photoelectric devices is vacant. Here, the authors combined violet phosphorene and molybdenum disulfide to demonstrate an optoelectronic synapse with a light-to-dark ratio of 10⁶, benefiting from a significant threshold shift due to charge transfer and trapping in the heterostructure. Remarkable synaptic properties are demonstrated, including a dynamic range (DR) of > 60 dB, 128 (7-bit) distinguishable conductance states, electro-optical dependent plasticity, short-term paired-pulse facilitation, and long-term potentiation/depression. Thanks to the excellent DR and multi-states, high-precision image classification with accuracies of 95.23% and 79.65% is achieved for the MNIST and complex Fashion-MNIST datasets, which is close to the ideal device (95.47%, 79.95%). This work opens the way for the use of emerging phosphorene in optoelectronics and provides a new strategy for building synaptic devices for high-precision neuromorphic computing.

Nature Materials, Published online: 25 May 2023; doi:10.1038/s41563-023-01564-7

Author(s): Xiaohan Wan, Siddhartha Sarkar, Shi-Zeng Lin, and Kai Sun

We study flat bands and their topology in 2D materials with quadratic band crossing points under periodic strain. In contrast to Dirac points in graphene, where strain acts as a vector potential, strain for quadratic band crossing points serves as a director potential with angular momentum ℓ=2. We p…

[Phys. Rev. Lett. 130, 216401] Published Thu May 25, 2023

Author(s): Ying Liu, Ranming Niu, Andrzej Majchrowski, Krystian Roleder, Kumara Cordero-Edwards, Julie M. Cairney, Jordi Arbiol, and Gustau Catalan

In the archetypal antiferroelectric PbZrO3, antiparallel electric dipoles cancel each other, resulting in zero spontaneous polarization at the macroscopic level. Yet in actual hysteresis loops, the cancellation is rarely perfect and some remnant polarization is often observed, suggesting the metasta…

[Phys. Rev. Lett. 130, 216801] Published Thu May 25, 2023

The hot carriers generated in BiFeO₃ are capable of coupling with phonons and undergo quasi-ballistic transport over a distance of 340 nm in the first picosecond. Even after undergoing cooling processes, the carrier diffusion coefficient mediated by electron-phonon coupling remains significantly higher than that of bulk. These findings introduce novel perspectives for the development of efficient electronic devices based on BiFeO₃.

Abstract

The electron-phonon interaction is known as one of the major mechanisms determining electrical and thermal properties. In particular, it alters the carrier transport behaviors and sets fundamental limits to carrier mobility. Establishing how electrons interact with phonons and the resulting impact on the carrier transport property is significant for the development of high-efficiency electronic devices. Here, carrier transport behavior mediated by the electron-phonon coupling in BiFeO₃ epitaxial thin films is directly observed. Acoustic phonons are generated by the inverse piezoelectric effect and coupled with photocarriers. Via the electron-phonon coupling, doughnut shape carrier distribution has been observed due to the coupling between hot carriers and phonons. The hot carrier quasi-ballistic transport length can reach 340 nm within 1 ps. The results suggest an effective approach to investigating the effects of electron-phonon interactions with temporal and spatial resolutions, which is of great importance for designing and improving electronic devices.

Nature Reviews Materials, Published online: 24 May 2023; doi:10.1038/s41578-023-00569-7

Nature Reviews Materials, Published online: 24 May 2023; doi:10.1038/s41578-023-00570-0

Substrate-imposed deviatoric strain in epitaxial BiVO₄ films distorts the lattice and the BiO₈ dodecahedra. By using a combination of high-resolution X-ray diffraction methods and optical spectroscopies, the degree of structural distortion can be correlated to the shifts in the bandgaps and the polaronic photoluminescence emission peaks. This strategy can be used to modulate the optoelectronic properties of oxide photoabsorbers.

Abstract

Transition metal oxide (TMO) photoabsorbers are expected to play an important role in the development of renewable solar-to-fuel devices. Modest efficiencies have been demonstrated with devices based on TMO photoabsorbers, and further progress will likely rely on material property control beyond conventional bulk chemistry or nanostructuring strategies. To this end, model TMO photoabsorbers such as single crystalline monoclinic bismuth vanadate (BiVO₄) are beneficial to advance the understanding of structure-functionality relationships with minimal convoluted effects inherent in polycrystalline systems. Here, the authors reveal for the first time the effects of strain modulation strategies on the optoelectronic properties of epitaxial BiVO₄ films synthesized by alternate-target layer-by-layer pulsed laser deposition. Through a combination of high-resolution X-ray diffraction methods and optical and photoluminescence spectroscopies, the correlation between anisotropic, uniaxial strain-driven bandgap widening and deviatoric strains associated with volume-preserving lattice distortions is established. Broad polaronic photoluminescence signals are detected in epitaxial BiVO₄, and its redshift is attributed to the structural distortion in BiO₈ dodecahedra. Overall, the relationship between the structural and optoelectronic properties revealed in this study suggests that strain modulation and engineering of local distortion in complex transition metal oxides may be exploited as a viable strategy for the development of efficient photoabsorbers.

A series of metal phosphides are selectively fabricated via a general and convenient “in situ etch-adsorption-phosphatization” strategy. Among them, the obtained FeP/Fe₂P/Cu₃P-N, P codoped carbon (FeP/Cu₃P-NPC) not only exhibits superior performances as a cathode for the flexible zinc–air batteries (ZABs) but also displays an excellent stable performance even under bending circumstances.

Abstract

Benefiting from the admirable energy density (1086 Wh kg⁻¹), overwhelming security, and low environmental impact, rechargeable zinc–air batteries (ZABs) are deemed to be attractive candidates for lithium-ion batteries. The exploration of novel oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) bifunctional catalysts is the key to promoting the development of zinc–air batteries. Transitional metal phosphides (TMPs) especially Fe-based TMPs are deemed to be a rational type of catalyst, however, their catalytic performance still needs to be further improved. Considering Fe (heme) and Cu (copper terminal oxidases) are nature's options for ORR catalysis in many forms of life from bacteria to humans. Herein, a general “in situ etch-adsorption-phosphatization” strategy is designed for the fabrication of hollow FeP/Fe₂P/Cu₃P-N, P codoped carbon (FeP/Cu₃P-NPC) catalyst as the cathode of liquid and flexible ZABs. The liquid ZABs manifest a high peak power density of 158.5 mW cm⁻² and outstanding long-term cycling performance (≈1100 cycles at 2 mA cm⁻²). Similarly, the flexible ZABs deliver superior cycling stability of 81 h at 2 mA cm⁻² without bending and 26 h with different bending angles.

This study reports an inhomogeneous friction behavior in nanoscale spontaneous phase separated Cu_0.2In_1.26P₂S₆. The friction is highest in paraelectric In_4/3P₂S₆ (IPS), followed by ferroelectric CuInP₂S₆ (CIPS), and low-friction phase boundaries (PB). Different lattice strains are suggested to be the main contribution of this phenomenon, which influence surface deformation and thus friction during AFM tip slide.

Abstract

Mechanical friction leads to wear and energy dissipation, and its control is of high importance in new-generation miniature electromechanical devices. 2D materials such as graphene are considered to be excellent solid lubricants due to their ultralow friction and have attracted considerable research interest. Unique friction properties are discovered in various other 2D materials. However, the friction of functional van der Waals materials which have potential applications in novel nanoelectronics, like ferroelectric copper indium thiophosphate, has barely been studied. Herein, the study reports on the observation of inhomogeneous friction behavior existing in copper-deficient CuInP₂S₆ (Cu_0.2In_1.26P₂S₆), which exhibits a nanoscale phase separation of polar and non-polar crystalline phases. The paraelectric In_4/3P₂S₆ phase exhibits higher friction than the ferroelectric CuInP₂S₆ phase, while phase boundaries between the two phases, interestingly, display the lowest friction. The origin of this phenomenon is attributed to different lattice strains of phases together with the presence of large strains at the nanoscale phase boundaries, which also manifests in the nonuniform tip-sample adhesion force. The findings provide new insights into nanoscale device design and wear behavior of a phase-separated van der Waals ferroelectric, which may help to reduce the power consumption of friction-exhibiting devices and extend their service life.

Nature Reviews Methods Primers, Published online: 25 May 2023; doi:10.1038/s43586-023-00225-y

Second harmonic generation (SHG) in few-layer ReS₂ can be controlled by stacking order and layer number. In the SHG-active AB_y-stacked even-layers, the SHG intensities can be greatly enhanced when the photon energy matches with the exciton level, and bulk SHG susceptibility χ(2)${\chi}^{(2)}$ always shows the largest value for the bilayer.

Abstract

The second harmonic generation (SHG) is systematically investigated in mechanically exfoliated, few-layer ReS₂ samples. The stacking orders are identified as (AA)_nA and (AB_y)_nA for (2n+1)-layer samples and (AA)_n and (AB_y)_n for 2n-layer samples. The layer structure A stands for that of a monolayer, and the layer structure B_y is mirror to A followed by a one-tenth unit cell translation along the mirror axis, that is, the b -axis of the crystal. Only the even-layer samples with (AB_y)_n stacking order are SHG active. After carefully extracting the effective bulk susceptibility for SHG, it is found that the spectra are greatly enhanced as the fundamental photon energy matches exciton levels. The polarization dependence is strongly anisotropic, and each susceptibility component shows very different wavelength dependence. The results demonstrate that few-layer ReS₂, with its unique SHG, can be considered as an ideal platform for fundamental research in anisotropic nonlinear optics.

The synthesis of InP nanocrystals with different phosphorus sources is briefly summarized. The research progress in the optical properties of InP/ZnE and InP/ZnE/ZnE nanocrystals, including absorption, fluorescence, carrier dynamics, and nonlinear optics, are summarized. In addition, the relevant applications based on InP/ZnE and InP/ZnE/ZnE nanocrystals are also presented, ranging from light emitting diodes, bioimaging, and solar cells to photocatalytic hydrogen production.

Abstract

As the most promising candidate for luminescent semiconductor materials in the future environmentally friendly society, InP nanocrystals (NCs) have attracted strong attention in the past decade. Tremendous efforts have been devoted to address the unstable and poor optical properties of InP NCs for practical applications. An extensive and in-depth summary of existing literatures can not only provide an important reference for further optimizing of the optical properties of InP NCs, but also lay a foundation for subsequent related applications. In this review, the methods for the synthesis with different P sources and different ZnE (E = Se, S) shells are briefly summarized. The research progress in the optical properties investigation of InP/ZnE and InP/ZnE/ZnE NCs, including absorption, fluorescence, carrier dynamics, and nonlinear optics, are summarized. The relevant applications based on InP/ZnE and InP/ZnE/ZnE NCs are also presented, ranging from light emitting diodes, bioimaging, and solar cells to photocatalytic hydrogen production.

Nature Nanotechnology, Published online: 22 May 2023; doi:10.1038/s41565-023-01399-y