Jiuxiang Dai

An additive approach for spatially defined and controllable assembly of colloidal quantum dots is reported. The approach is based on pH tunable assembly of quantum dots over printed polymer features. Hierarchically structured encoding of information through stochastic and deterministic pathways is demonstrated.

Abstract

Patterning of quantum dots (QDs) is essential for many, especially high-tech, applications. Here, pH tunable assembly of QDs over functional patterns prepared by electrohydrodynamic jet printing of poly(2-vinylpyridine) is presented. The selective adsorption of QDs from water dispersions is mediated by the electrostatic interaction between the ligand composed of 3-mercaptopropionic acid and patterned poly(2-vinylpyridine). The pH of the dispersion provides tunability at two levels. First, the adsorption density of QDs and fluorescence from the patterns can be modulated for pH > ≈4. Second, patterned features show unique type of disintegration resulting in randomly positioned features within areas defined by the printing for pH ≤ ≈4. The first capability is useful for deterministic patterning of QDs, whereas the second one enables hierarchically structured encoding of information by generating stochastic features of QDs within areas defined by the printing. This second capability is exploited for generating addressable security labels based on unclonable features. Through image analysis and feature matching algorithms, it is demonstrated that such patterns are unclonable in nature and provide a suitable platform for anti-counterfeiting applications. Collectively, the presented approach not only enables effective patterning of QDs, but also establishes key guidelines for addressable assembly of colloidal nanomaterials.

Nature Communications, Published online: 02 September 2023; doi:10.1038/s41467-023-40997-1

By using a magnetostrictive/ferroelectric laminated structure, magnetic field-induced biaxial strain could be efficiently transferred to piezotronic devices. The charge carrier transport and corresponding drain current of the piezotronic devices can be directly modulated by either the applied magnetic field or external strain. The device exhibits high sensitivity with on/off ratio of 1700% and a gauge factor as high as 2.3 × 10⁴.

Abstract

Piezotronics is the coupling effect of the piezoelectric and semiconductor properties; however, the piezoelectric constant of the piezoelectric semiconductor is relatively small while the ferroelectric materials with large piezoelectric constant typically possess weak semiconductor properties, thus limiting the effective coupling coefficient of the piezotronic materials and devices. Here, a piezotronics and magnetic dual-gated ferroelectric semiconductor transistor (PM-FEST) is fabricated by Terfenol-D, aluminum oxide (Al₂O₃), and ferroelectric semiconductor α-In₂Se₃, which has a large piezoelectric coefficient, room-temperature ferroelectricity, and dipole locking. The charge carrier transport and corresponding drain current of the PM-FEST can be directly modulated by either the applied magnetic field or external strain. At a low magnetic field (<200 mT), the maximum current on/off ratio of α-In₂Se₃ based PM-FEST is as high as 1700%. Compared with traditional piezotronic devices, the PM-FEST demonstrates a higher gauge factor (2.3 × 10⁴) than that of the piezoelectric semiconductors. This work provides a possibility of realizing magnetism-modulated electronics in semiconductors by exploiting the coupling of piezotronics and magnetostriction.

A strong second harmonic generation up to 0.28% is obtained from a photonic crystal vertical cavity embedded with lithium niobate thin film. This is a significant improvement compared with previous ones with a similar framework, which provides a promising platform to develop ultracompact efficient nonlinear light sources.

Abstract

This study presents photonic vertical cavities consisting of nonlinear materials embedded in photonic crystals (PhCs) for resonantly enhancing second harmonic generation (SHG). Previous attempts at SHG in such structures have been limited to efficiencies of 10⁻⁷ to 10⁻⁵, but a high SHG efficiency of 0.28% by constructing a vertical cavity with a lithium niobate membrane placed between two PhCs is demonstrated, which exhibits high-quality resonances. The results open up new possibilities for compact laser frequency converters that can have a revolutionary impact on the fields of nonlinear optics and photonics.

A security label capable of dual information encoding for reflection and fluorescence states is established based on polymer-stabilized blue phase, which is achieved by photonic band gap tuning of patterned polymerization and emission transition of fluorescent molecules during UV irradiation, respectively.

Abstract

Anticounterfeit labels with multiple information-carrying functions serve a critical role in boosting security and minimizing counterfeit-related losses, whose development remains challenging. Here, a security label with the ability to encode information in reflective and fluorescent sates is fabricated from light-emitting polymer-stabilized blue phase (LE-PSBP) liquid crystals (LCs). The LE-PSBP with temperature-dependent reflective color can be encoded with information by UV irradiation through photomasks. On the other hand, introduction of a fluorescent molecule, which can be easily photocyclized upon UV irradiation, enables the convenient encoding of fluorescent information without impacting the reflective information. As an illustration, a security label with distinct information in reflective and fluorescent states is demonstrated. Such innovative security labels have tremendous potential to provide a platform for multi-information encoding to enhance the protection level in anticounterfeiting technology.

Abstract

The escalating electromagnetic (EM) pollution issues and the demand to elevate military stealth technology make it imperative to develop cost-effective and high-performance electromagnetic wave (EMW) absorbing materials. In this paper, the flower-like CuS/γ-Fe₂O₃ van der Waals (vdW) heterostructures have been synthesized via a facile two-step solvothermal approach. The flower-like CuS skeleton increases the attenuation path of EMW while reducing the material density. Different contents of γ-Fe₂O₃ nanoparticles anchor between the flower-like CuS nanosheets to constitute a heterogeneous structure, which enables dielectric and magnetic loss synergistically to optimize impedance matching and remarkably improve the EMW absorption performance. The minimum reflection loss (RL_min) is −49.36 dB with a thickness of only 1.6 mm and the effective absorption bandwidth (EAB) reaches 4.64 GHz (13.36–18 GHz). By adjusting the thickness of the absorber, the EAB can cover 96% of the GHz band. Notably, the superior absorption of −61.53 dB at middle frequency band can be obtained by adjusting the amount of Fe₂O₃ addition. In this study, the adjustment of EM parameters and the optimization of impedance matching have been achieved by constructing a novel vdW heterogeneous structure, which provides fresh ideas and references for the design of high-performance EMW absorbing materials.

Here, a flexible artificial vision system integrated with perception, computation, and learning functionalities is constructed using ambipolar SnO optoelectronic synaptic transistor. By introducing HfO₂ passivation layer, the SnO transistors exhibit gate-tunable bidirectional photoresponse, and the proposed learning circuit achieves fast recognition at a 16% Gaussian noise level and high recognition accuracy up to 95.2% for pattern letters.

Abstract

Metal oxide semiconductors (MOSs) are considered as potential candidates for the low-cost, large-area fabrication of flexible optoelectronic devices. However, the current optoelectronic devices based on MOSs are limited to unidirectional photoresponse, which constrains the performance of MOSs-based vision sensors for artificial vision systems. Herein, for the first time, a flexible artificial vision system integrated with optical perception, computation, and learning functionalities is demonstrated using SnO optoelectronic synaptic transistor-based event-driven vision sensors to enable dynamic image perception, noise reduction, detection, and recognition. Specifically, an ambipolar SnO transistor is demonstrated by introducing HfO₂ passivation layer, which facilitates the movement of O atoms around Sn-vacancy sites to the HfO₂ layer to achieve the transformation from p-type to ambipolar transport behaviors. More importantly, the HfO₂-passivated SnO transistors exhibit gate-tunable bidirectional photoresponse behavior, which is essential to simulate the neurobiological functionalities of bipolar cells. This way, the multilayer neural network learning circuit built from SnO transistors achieves fast recognition at a 16% Gaussian noise level and high recognition accuracy up to 95.2% for pattern letters. Under the bending states, recognition accuracies are still retained at 91.2%. These properties are well retained even under the influence of 100% offset of the synaptic programming value.

The fusion of inkjet printing and soft lithography techniques is employed to obtain differently shaped light emitting motifs made out of phosphor inks. The potential of this approach is depicted by processing a self-standing photoluminescent quick response code whose emission is both polarized and directionally beamed.

Abstract

Herein a versatile and scalable method to prepare periodically corrugated nanophosphor surface patterns displaying strongly polarized and directional visible light emission is demonstrated. A combination of inkjet printing and soft lithography techniques is employed to obtain arbitrarily shaped light emitting motifs. Such predesigned luminescent drawings, in which the polarization and angular properties of the emitted light are determined and finely tuned through the surface relief, can be used as anti-counterfeiting labels, as these two specific optical features provide additional means to identify any unauthorized or forged copy of the protected item. The potential of this approach is exemplified by processing a self-standing photoluminescent quick response code whose emission is both polarized and directionally beamed. Physical insight of the mechanism behind the directional out-coupled photoluminescence observed is provided by finite-difference time-domain calculations.

Excellent plasticity is demonstrated in wide-gap AgCl and AgBr bulks at room temperature under tension, bending, compression, and rolling. The metal-like plasticity is attributed to the ionic feature of the Ag-Cl/Br interactions with appreciable anionic polarization. This work will advance the development of wide-gap plastically deformable inorganic materials for complex-structured high-power electronics, optoelectronics, and dielectrics.

Abstract

In general, inorganic non-metallic materials exhibit brittleness, and achieving plasticity in wide-gap semiconductors or dielectrics poses an even greater challenge. Historically, silver halides have been suggested to be ductile; however, their deformability under different load modes has not been well demonstrated, and the underlying mechanisms are not fully understood. In this study, the authors demonstrate the excellent plasticity of AgCl and AgBr polycrystals at room temperature under tension, bending, compression, and roller pressing. In particular, the rolling reduction rate of AgCl/AgBr exceeds 97%, corresponding to the plastic extensibility from 3600% to 4200%. The metal-like plasticity and multiple slip systems are attributed to the ionic features, specifically the Coulombic nature of the Ag-Cl/Br interactions, and the appreciable polarization of the anions. Such less localized diffuse bonding can be readily switched upon atomic gliding, thus ensuring slip without cleavage. This study contributes to the advancement of the understanding and development of wide-gap plastically deformable inorganic materials for applications in flexible, shape-conformable high-power electronics and dielectrics.

A surfactant-free liquid-phase synthetic route for high-quality 2D tellurium based on ultrasonication-assisted exfoliation of metastable 1T'-MoTe₂ is reported. The as-grown 2D tellurium nanosheets exhibit excellent single crystallinity and clean surface. 2D tellurium-based field-effect transistors show ultrahigh hole mobility exceeding 1000 cm² V^-1 s^-1 at room temperature and exceptional chemical and operational stability in both solid- and liquid-state gating devices.

Abstract

Elemental 2D materials (E2DMs) have been attracting considerable attention owing to their chemical simplicity and excellent/exotic properties. However, the lack of robust chemical synthetic methods seriously limits their potential. Here, a surfactant-free liquid-phase synthesis of high-quality 2D tellurium is reported based on ultrasonication-assisted exfoliation of metastable 1T'-MoTe₂. The as-grown 2D tellurium nanosheets exhibit excellent single crystallinity, ideal 2D morphology, surfactant-free surface, and negligible 1D by-products. Furthermore, a unique growth mechanism based on the atomic escape of Te atoms from metastable transition metal dichalcogenides and guided 2D growth in the liquid phase is proposed and verified. 2D tellurium-based field-effect transistors show ultrahigh hole mobility exceeding 1000 cm² V⁻¹ s⁻¹ at room temperature attributing to the high crystallinity and surfactant-free surface, and exceptional chemical and operational stability using both solid-state dielectric and liquid-state electrical double layer. The facile ultrasonication-assisted synthesis of high-quality 2D tellurium paves the way for further exploration of E2DMs and expands the scope of liquid-phase exfoliation (LPE) methodology toward the controlled wet-chemical synthesis of functional nanomaterials.

chemical beam vapor deposition in a combinatorial configuration allows a fine tuning of Li/Nb flow ratio from ≈0.25 to ≈2.45 on a single wafer. This approach produces high quality LiNbO₃ thin film on sapphire (001) substrate with light propagation behaviour promising for photonic applications.

Abstract

Lithium niobate is a material of special interest for its challenging functional properties, which can suit various applications. However, high quality 200-mm Li_xNb_1-xO₃ thin film grown on sapphire substrate have never been reported so far which limits these potential applications. This paper reports the efficient optimization of high quality LiNbO₃ thin film deposition on sapphire (001) substrate through chemical beam vapor deposition in a combinatorial configuration. With this technique, flow ratio of Li/Nb can be tuned from ≈0.25 to ≈2.45 on a single wafer. Various complementary characterizations (by means of diffraction, microscopy and spectroscopy techniques) have been performed at different areas of the film (different cationic ratios) in order to investigate the impact of the cationic stoichiometry deviation on the film properties. Close to cationic stoichiometry (LiNbO₃), the epitaxial films are of high quality (single phase in spite of two in-plane domains, low mosaicity of 0.04°, low surface roughness, refractive index and band gap close to bulk values). Deviating from the stoichiometry conditions, secondary phases are detected (LiNb₃O₈ for Nb-rich flow ratios, and Li₃NbO₄ with partial amorphization for Li-rich flow ratios). LiNbO₃ films are of high interest for various key applications in data communications among others.

Nature Electronics, Published online: 31 August 2023; doi:10.1038/s41928-023-01021-y

Nature Electronics, Published online: 31 August 2023; doi:10.1038/s41928-023-01018-7

Light: Science & Applications, Published online: 31 August 2023; doi:10.1038/s41377-023-01259-3

Gate-last MoS₂-thin-film transistors, along with active-matrix display driving circuits, are successfully realized with MoS₂-buffer/Al₂O₃ stack. Endowing with the transfer-free process, the display driving circuits exhibits high yield, excellent uniformity, and good driving capability. The implementation of the two transistor-one capacitor configuration enhances the operating effectiveness and addresses cross-talk issues, demonstrating the potential for using 2D material for the ever-demanding display technology.

Abstract

Advancements in display technology have primarily focused on discovering new materials to develop thin-film transistors (TFTs) that complement mainstream technologies. The emerging 2D semiconductors are one of the most promising candidates due to their ultra-thin thickness, exceptional electrical qualities, and large-scale availability. However, these atomically thin materials are delicate and typically prepared through standard gate-first fabrication processes, necessitating their transfer onto specific substrates. In this study, a demonstration of an in situ gate-last process for 2D semiconductor-based TFTs technology is presented. This approach bypasses the yield-limiting transfer process, enabling large-scale display applications. The as-fabricated MoS₂ TFTs retains their intrinsic properties with a current density reaching ≈≈10 µA µm⁻¹. Additionally, it is successfully showcased that the two transistor-one capacitor active-matrix display driving circuits with a high pixel yield. The patterned matrix exhibits no crosstalk and can be driven by either the pulse amplitude modulation or pulse width modulation scheme, offering flexible applications.

Publication date: September 2023

Source: Materials Today, Volume 68

Author(s): Cordelia Sealy

Nature, Published online: 30 August 2023; doi:10.1038/s41586-023-06281-4