Jiuxiang Dai

Nature, Published online: 12 July 2023; doi:10.1038/d41586-023-02028-3

Synthesis of 2D Janus  and  nanoscrolls is achieved by strain anisotropy and reaction engineering of the top chalcogen layer. High-resolution electron microscopy shows a preferential scrolling orientation and the formation of moiré patterns. Experimental results supported by ab-initio molecular dynamics (AIMD) simulations clearly show the free-standing nature of the 2D Janus monolayers for the very first time.

Abstract

2D Janus transition metal dichalcogenides (TMDs) have attracted attention due to their emergent properties arising from broken mirror symmetry and self-driven polarization fields. While it has been proposed that their vdW superlattices hold the key to achieving superior properties in piezoelectricity and photovoltaic, available synthesis has ultimately limited their realization. Here, the first packed vdW nanoscrolls made from Janus TMDs through a simple one-drop solution technique are reported. The results, including ab initio simulations, show that the Bohr radius difference between the top sulfur and the bottom selenium atoms within Janus MSeS${\rm{M}}_{{\rm{Se}}}^{\rm{S}}$ (M = Mo, W) results in a permanent compressive surface strain that acts as a nanoscroll formation catalyst after small liquid interaction. Unlike classical 2D layers, the surface strain in Janus TMDs can be engineered from compressive to tensile by placing larger Bohr radius atoms on top (MSSe)${\rm{M}}_{\rm{S}}^{{\rm{Se}}})\ $to yield inverted C scrolls. Detailed microscopy studies offer the first insights into their morphology and readily formed Moiré lattices. In contrast, spectroscopy and FETs studies establish their excitonic and device properties and highlight significant differences compared to 2D flat Janus TMDs. These results introduce the first polar Janus TMD nanoscrolls and introduce inherent strain-driven scrolling dynamics as a catalyst to create superlattices.

An anchored crystal-seed epitaxial growth method is developed to effectively suppress the multiple nucleation behavior of the molecules and enhance the 2D growth of organic crystals. In consequence, wafer-scale few-layer organic single crystals are successfully fabricated on the viscous liquid substrate. Organic field-effect transistors based on the crystal exhibit high device performance with excellent uniformity.

Abstract

The success of state-of-the-art electronics and optoelectronics relies heavily on the capability to fabricate semiconductor single-crystal wafers. However, the conventional epitaxial growth strategy for inorganic wafers is invalid for growing organic semiconductor single crystals due to the lack of lattice-matched epitaxial substrates and intricate nucleation behaviors, severely impeding the advancement of organic single-crystal electronics. Here, an anchored crystal-seed epitaxial growth method for wafer-scale growth of 2D organic semiconductor single crystals is developed for the first time. The crystal seed is firmly anchored on the viscous liquid surface, ensuring the steady epitaxial growth of organic single crystals from the crystal seed. The atomically flat liquid surface effectively eliminates the disturbance from substrate defects and greatly enhances the 2D growth of organic crystals. Using this approach, a wafer-scale few-layer bis(triethylsilythynyl)-anthradithphene (Dif-TES-ADT) single crystal is formed, yielding a breakthrough for organic field-effect transistors with a high reliable mobility up to 8.6 cm² V⁻¹ s⁻¹ and an ultralow mobility variable coefficient of 8.9%. This work opens a new avenue to fabricate organic single-crystal wafers for high-performance organic electronics.

Author(s): Yang-Zhi Chou and Sankar Das Sarma

We systematically study emergent Kondo lattice models from magic-angle twisted bilayer graphene using the topological heavy fermion representation. At the commensurate fillings, we demonstrate a series of symmetric strongly correlated metallic states driven by the hybridization between a triangular …

[Phys. Rev. Lett. 131, 026501] Published Tue Jul 11, 2023

Nature Communications, Published online: 11 July 2023; doi:10.1038/s41467-023-39809-3

Publication date: July–August 2023

Source: Materials Today, Volume 67

Author(s): Quanyan Man, Yongling An, Hengtao Shen, Chuanliang Wei, Shenglin Xiong, Jinkui Feng

A multidrug delivery microrobot inspired by the fish structure with three components: skeleton, head, and body, is fabricated. The skeleton is made by poly(ethylene glycol) diacrylate (PEGDA) photoresist embedding with Fe₃O₄ nanoparticles and can respond to magnetic fields for microrobot actuation and drug-targeted delivery. The drug storage structures, head, and body, made by biodegradable GelMA exhibit enzyme-responsive drug release.

Abstract

Multidrug combination therapy provides an effective strategy for malignant tumor treatment. This paper presents the development of a biodegradable microrobot for on-demand multidrug delivery. By combining magnetic targeting transportation with tumor therapy, it is hypothesized that loading multiple drugs on different regions of a single magnetic microrobot can enhance a synergistic effect for cancer treatment. The synergistic effect of using two drugs together is greater than that of using each drug separately. Here, a 3D-printed microrobot inspired by the fish structure with three hydrogel components: skeleton, head, and body structures is demonstrated. Made of iron oxide (Fe₃O₄) nanoparticles embedded in poly(ethylene glycol) diacrylate (PEGDA), the skeleton can respond to magnetic fields for microrobot actuation and drug-targeted delivery. The drug storage structures, head, and body, made by biodegradable gelatin methacryloyl (GelMA) exhibit enzyme-responsive cargo release. The multidrug delivery microrobots carrying acetylsalicylic acid (ASA) and doxorubicin (DOX) in drug storage structures, respectively, exhibit the excellent synergistic effects of ASA and DOX by accelerating HeLa cell apoptosis and inhibiting HeLa cell metastasis. In vivo studies indicate that the microrobots improve the efficiency of tumor inhibition and induce a response to anti-angiogenesis. The versatile multidrug delivery microrobot conceptualized here provides a way for developing effective combination therapy for cancer.

Here, for the first time, a highly effective graphdiyne/molybdenum (GDY/MoS₂) type-II heterojunction in a charge separation is reported toward a high-performance photodetector. The device exhibits broadband detection (453–1064 nm) with a maximum responsivity of 78.5 A W⁻¹ and a high speed of 50 µs.

Abstract

Graphdiyne (GDY), a new 2D material, has recently proven excellent performance in photodetector applications due to its direct bandgap and high mobility. Different from the zero-gap of graphene, these preeminent properties made GDY emerge as a rising star for solving the bottleneck of graphene-based inefficient heterojunction. Herein, a highly effective graphdiyne/molybdenum (GDY/MoS₂) type-II heterojunction in a charge separation is reported toward a high-performance photodetector. Characterized by robust electron repulsion of alkyne-rich skeleton, the GDY based junction facilitates the effective electron–hole pairs separation and transfer. This results in significant suppression of Auger recombination up to six times at the GDY/MoS₂ interface compared with the pristine materials owing to an ultrafast hot hole transfer from MoS₂ to GDY. GDY/MoS₂ device demonstrates notable photovoltaic behavior with a short-circuit current of −1.3 × 10⁻⁵ A and a large open-circuit voltage of 0.23 V under visible irradiation. As a positive-charge-attracting magnet, under illumination, alkyne-rich framework induces positive photogating effect on the neighboring MoS₂, further enhancing photocurrent. Consequently, the device exhibits broadband detection (453–1064 nm) with a maximum responsivity of 78.5 A W⁻¹ and a high speed of 50 µs. Results open up a new promising strategy using GDY toward effective junction for future optoelectronic applications.

npj 2D Materials and Applications, Published online: 10 July 2023; doi:10.1038/s41699-023-00403-2

Nature Physics, Published online: 10 July 2023; doi:10.1038/s41567-023-02104-5

Recent work in atom-by-atom fabrication techniques using electron beams has suggested that a combination of bottom-up synthesis and top-down fabrication approaches can enable greater control over atomic patterning and precision manufacturing. To enable this approach, advances in in situ atomized material delivery is required. In this work, the design and testing of a prototype evaporative material delivery platform are presented.

Abstract

The engineering of quantum materials requires the development of tools able to address various synthesis and characterization challenges. These include the establishment and refinement of growth methods, material manipulation, and defect engineering. Atomic-scale modification will be a key enabling factor for engineering quantum materials where desired phenomena are critically determined by atomic structures. Successful use of scanning transmission electron microscopes (STEMs) for atomic scale material manipulation has opened the door for a transformed view of what can be accomplished using electron-beam-based strategies. However, serious obstacles exist on the pathway from possibility to practical reality. One such obstacle is the in situ delivery of atomized material in the STEM to the region of interest for further fabrication processes. Here, progress on this front is presented with a view toward performing synthesis (deposition and growth) processes in a scanning transmission electron microscope in combination with top-down control over the reaction region. An in situ thermal deposition platform is presented, tested, and deposition and growth processes are demonstrated. In particular, it is shown that isolated Sn atoms can be evaporated from a filament and caught on the nearby sample, demonstrating atomized material delivery. This platform is envisioned to facilitate real-time atomic resolution imaging of growth processes and open new pathways toward atomic fabrication.

Author(s): Héctor Sainz-Cruz, Pierre A. Pantaleón, Võ Tiến Phong, Alejandro Jimeno-Pozo, and Francisco Guinea

Junctions provide a wealth of information on the symmetry of the order parameter of superconductors. We analyze junctions between a scanning tunneling microscope (STM) tip and superconducting twisted bilayer graphene (TBG) and TBG Josephson junctions (JJs). We compare superconducting phases that are…

[Phys. Rev. Lett. 131, 016003] Published Fri Jul 07, 2023

Light: Science & Applications, Published online: 07 July 2023; doi:10.1038/s41377-023-01211-5

Crystallographic shear plane is a special plane defect, which is composed of blocks comprising edge-sharing octahedrons and 3D open tunnels. Herein, the experiments and theoretical calculations prove that edge step defects can provide nucleation sites for crystallographic shear planes. Moreover, artificial defects can also induce its growth and regulate direction.

Abstract

As representative extended planar defects, crystallographic shear (CS) planes, namely Wadsley defects, play an important role in modifying the physical and chemical properties of metal oxides. Although these special structures have been intensively investigated for high-rate anode materials and catalysts, it is still experimentally unclear how the CS planes form and propagate at the atomic scale. Here, the CS plane evolution in monoclinic WO₃ is directly imaged via in situ scanning transmission electron microscope. It is found that the CS planes nucleate preferentially at the edge step defects and proceed by the cooperative migration of WO₆ octahedrons along particular crystallographic orientations, passing through a series of intermediate states. The local reconstruction of atomic columns tends to form (102) CS planes featured with four edge-sharing octahedrons in preference to the (103) planes, which matches well with the theoretical calculations. Associated with the structure evolution, the sample undergoes a semiconductor-to-metal transition. In addition, the controlled growth of CS planes and V-shaped CS structures can be achieved by artificial defects for the first time. These findings enable an atomic-scale understanding of CS structure evolution dynamics.

This article systematically presents a generalized theoretical frame termed as “Liquid Metal Combinatorics” (LMC), and summarized promising candidate technical routes toward new generation liquid metals-derived functional material discovery. Here, the connotation of L_iM_jCks$C_k^s$ represents the interaction of liquid metal raw material L_i with other materials M_j to generate all possible combinations (Cks$C_k^s$), thus deriving abundant, diverse combination opportunities.

Abstract

Liquid metals and their derivatives provide several opportunities for fundamental and practical exploration worldwide. However, the increasing number of studies and shortage of desirable materials to fulfill different needs also pose serious challenges. Herein, to address this issue, a generalized theoretical frame that is termed as “Liquid Metal Combinatorics” (LMC) is systematically presented, and summarizes promising candidate technical routes toward new generation material discovery. The major categories of LMC are defined, and eight representative methods for manufacturing advanced materials are outlined. It is illustrated that abundant targeted materials can be efficiently designed and fabricated via LMC through deep physical combinations, chemical reactions, or both among the main bodies of liquid metals, surface chemicals, precipitated ions, and other materials. This represents a large class of powerful, reliable, and modular methods for innovating general materials. The achieved combinatorial materials not only maintained the typical characteristics of liquid metals but also displayed distinct tenability. Furthermore, the fabrication strategies, wide extensibility, and pivotal applications of LMC are classified. Finally, by interpreting the developmental trends in the area, a perspective on the LMC is provided, which warrants its promising future for society.

npj 2D Materials and Applications, Published online: 08 July 2023; doi:10.1038/s41699-023-00412-1

Monolithic integration of III-V quantum dot (QD) lasers on Si photonic wafers in narrow pockets in a butt-coupled configuration via direct epitaxy is the ultimate solution for achieving on-chip light sources. The pocket orientation dependence of QD quality and the pocket geometry dependence of stress and defect configuration have been investigated experimentally and theoretically. This study offers guidance to obtain integration templates that will facilitate high yield and high performance epitaxial on-chip lasers at large scale.

Abstract

Integrating quantum dot (QD) gain elements onto Si photonic platforms via direct epitaxial growth is the ultimate solution for realizing on-chip light sources. Tremendous improvements in device performance and reliability have been demonstrated in devices grown on planar Si substrates in the last few years. Recently, electrically pumped QD lasers deposited in narrow oxide pockets in a butt-coupled configuration and on-chip coupling have been realized on patterned Si photonic wafers. However, the device yield and reliability, which ultimately determines the scalability of such technology, are limited by material uniformity. Here, detailed analysis is performed, both experimentally and theoretically, on the material asymmetry induced by the pocket geometry and provides unambiguous evidence suggesting that all pockets should be aligned to the [1 1¯0$\bar{1}\ 0$] direction of the III-V crystal for high yield, high performance, and scalable on-chip light sources at 300 mm scale.

The high thermoelectric performance in low-temperature α-Cu₂Se is speculated to arise from the complex and specific structure, including the fluctuating Cu sublattice and rigid Se sublattice, which can provide pathway for electrons in a long-range crystalline framework and maintains good electrical transport propertities, while phonons may be frequently scattered by the boundaries and low lattice thermal conductivity is achieved.

Abstract

The atomic-scale structure of cuprous selenide room temperature phase (α-Cu₂Se), which plays an important role in understanding the mechanism of its high thermoelectric performance, is still not fully determined. Here, direct observation with atomic-scale resolution is realized to reveal the fine structure of α-Cu₂Se via spherical-aberration-corrected scanning transmission electron microscopy. It is observed to be an interesting self-independent binary-sublattice construction for Cu and Se in α-Cu₂Se, respectively, which shows a variety of ordered copper fluctuation structures are embedded in a rigid pseudo-cubic Se sublattice. Ordering of Cu uses a variety of configurations with little energy difference, forming considerable amounts of “boundaries,” which may lead to ultrastrong phonon scattering. Furthermore, density functional theory calculations indicate that the electronic structures are mainly determined by the rigid Se face-centered cubic sublattice and not sensitive to the various copper fluctuations, which may guarantee the electron transfers with large carrier mobility. The self-independent binary-sublattice construction is speculated to enhance phonon scattering while still maintaining good electrical transport property. This study provides new critical information for further understanding the possible correlation between the specific structure and thermoelectric performance of α-Cu₂Se, as well as designing new thermoelectric materials.

The short-channel tunneling transistor comprising all 2D components is developed, exhibiting high switching performance due to the energy band modulation of vertical heterojunction through the dual-gates. Leveraging the unique short-channel and tunneling mechanism, it can circumvent the general issues of voltage spikes and long reverse recovery time, realizing an access to high-frequency integrated circuits (IC) interface.

Abstract

With continuous size scaling, the surface dangling bonds and short-channel effects will degrade silicon based transistor performance. Thus, it is of great importance to seek new channel materials and transistor architectures to further continue Moore's law. Herein, a new ultra-thin short-channel tunneling transistor is developed comprising all 2D- components. Distinct from usual 2D planar transistor, this device is configured with vertical MoS₂/WSe₂ junction and in-plane WSe₂ channel, the switch states are realized by the gate-regulated barrier height of heterojunction, enabling the transition of transport mechanism between thermionic-emission and tunneling. Under dual-gate configuration, the transistor exhibits high performance with drive current of 4.58 µA, on/off ratio of 4 × 10⁷, subthreshold swing (SS) of 97 mV decade⁻¹ and drain-induced barrier lowering (DIBL) of 12 mV V⁻¹, that can meet the requirement of logical applications in integrated circuits (IC). Taking advantage of the high-speed tunneling current and unique short-channel architecture, the device overcomes the issues of voltage spikes and long reverse recovery time that exist in usual electric components, and thus gains an access to the IC interface. This work provides a proof-of-concept transistor architecture relying on dual-gate modulation, opening up a promising perspective for next generation low-power, high-density, and large-scale IC technologies.